Draft rules for energy efficiency in buildings

PROMOTING ENERGY EFFICIENCY IN BUILDINGS IN EAST AFRICA

DRAFT RULES FOR ENERGY EFFICIENCY IN BUILDINGS

PROPOSALS FOR THE UNITED REPUBLIC OF TANZANIA

Claude-Alain Roulet Building Physics PO box 108 1143 Apples Switzerland

18/07/2013


This report is one of the outcomes of a mandate of the United Nations Human Settlement Programme of Nairobi, asking to review existing building codes of East African countries, and propose resources efficiency measures. The review of Tanzanian documents is presented in another report. In this report, we propose recommendations for including energy efficiency in building codes. These recommendations take account of the various climatic conditions found in Tanzania and aim to encourage the design of healthy and comfortable buildings that require a minimum amount of non-renewable energy. These recommendations include appropriate criteria for indoor environment quality, recommendations for building design, including building location and orientation, building envelope, solar protection, natural ventilation, passive solar heating and passive cooling, and day lighting. They also address building systems, including cooling, space and hot water heating, mechanical ventilation, electrical heating, kitchen equipment and other electrical appliances. Additional recommendations address the appropriate choice of building materials, moisture control, renewable energy, water and waste management. The main proposals can be summarised as follows:

Summary

The buildings shall be designed and built so as to ensure a good indoor environment quality with a minimum use of non-renewable energy. In particular: • The thermal comfort should be provided as far as possible without artificial cooling or heating. • Indoor air quality shall be ensured first by the quality of construction materials and source control; and second by ventilation. Ventilation should use natural means (wind and stack effect) as far as possible. Mechanical ventilation should be used only where and when necessary. • Day lighting should be used as far as possible, and buildings should be designed to promote day lighting. • All appliances using non-renewable energy should present among the best energy efficiency. Most of these recommendations are supported by arguments that are exposed in the third part of this document. This part not only presents the reasons for proposing some recommendations, but also some ways to apply them. Improving the thermal comfort in buildings and reducing the non-renewable energy use require that building design is adapted to climate. Therefore, to show the various designs, simulations of the thermal behaviour of various designs were performed, for four climates presented in part four.

DRAFT RULES FOR ENERGY EFFICIENCY IN BUILDINGS PROPOSALS FOR THE UNITED REPUBLIC OF TANZANIA

Table of contents 1

INTRODUCTION ..................................................................................................3 1.1 Mandate ...............................................................................................................3 1.2 Brief History ........................................................................................................3 1.3 performance and prescriptive requirements ..........................................................4

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PROPOSED DRAFT REGULATION TEXTS .....................................................5 2.1 Definitions ...........................................................................................................5 2.2 Applicable buildings ............................................................................................8 2.3 Climate zones ......................................................................................................8 2.4 Criteria for indoor environment quality ................................................................8 2.5 Primary requirements ......................................................................................... 11 2.6 Checking the compliance to requirements .......................................................... 11 2.7 Design prescriptions related to energy efficiency ............................................... 15 2.8 Prescriptions for building systems ...................................................................... 19 2.9 Renewable energy .............................................................................................. 23 2.10 Moisture control .............................................................................................. 23 2.11 Use of water .................................................................................................... 24 2.12 Waste management in buildings. ...................................................................... 24

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COMMENTS AND COMPLEMENTS ............................................................... 25 3.1 Indoor environment quality criteria .................................................................... 25 3.2 Energy efficient building design......................................................................... 38 3.3 Building Envelope ............................................................................................. 43 3.4 Avoiding the use of energy for heating ............................................................... 45 3.5 Reducing the cooling energy use ........................................................................ 49 3.6 Solar hot water heater ........................................................................................ 59 3.7 Ensuring indoor air quality ................................................................................. 62 3.8 Lighting ............................................................................................................. 67 3.9 Acoustics ........................................................................................................... 68

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CLIMATES IN TANZANIA ................................................................................ 70 4.1 Collecting, comparing and selecting significant climates .................................... 73 4.2 Arusha ............................................................................................................... 76 4.3 Dodoma ............................................................................................................. 78 4.4 Mwanza ............................................................................................................. 81 4.5 Dar es Salaam .................................................................................................... 85 4.6 Solar radiation.................................................................................................... 87

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BIBLIOGRAPHY................................................................................................. 90

INDEX ......................................................................................................................... 94

1

INTRODUCTION

1.1 M AND AT E The United Nations Human Settlements Programme gave a mandate to two experts to undertake, among others, the following tasks: • Review of existing building codes, related documents and standards in five East African countries. This review should target resources efficiency gaps. • Propose simplified and easy understanding standard resources efficiency measures to be included in the building codes. The author of this document is in charge of Burundi and Tanzania, while Dr. Adel Mourtada addresses Kenya, Uganda and Rwanda.

1.2 B RIEF H IST ORY A first report addressing both tasks mentioned above for Tanzania was delivered in April 2013, and was presented at the Kigali Workshop organised by UN Habitat. This report included the review of the Building Control Act, the National Energy Policy, and the Land Use Planning Act. It was discussed with the Tanzanian delegation, which asked to examine some additional official papers. The review of all these documents is presented in another report. Both experts also presented their recommendations for resource efficiency measures. Indeed these recommendations were complementary, since M. Mourtada mainly addressed energy efficiency in conditioned buildings, while the undersigned presented mostly building design measures that, by adapting the design to the local climate, allows improving the indoor environment quality at lower - or even at no - energy cost. The delegation of Tanzania asked the experts to provide a ready-to-use building energy efficiency code combining both approaches. The development of such a document requires additional research work for - among others - developing simplified calculation methods and prescriptive rules adapted to all climatic zones, and therefore cannot be completed within the frame of this limited mandate. However, this document already combines both approaches, and outlines, wherever necessary, the methodology to be used for making it complete. A similar report was prepared, in French, for the Republic of Burundi. It proposes a set of rules that have the ambition to constitute a prototype, prototype that should be adapted and modified if necessary, by the institutions and competent authorities of the United Republic of Tanzania. These rules are based on recent knowledge in building physics, on texts from international standards and from nations submitted to a tropical or moderated climate. Our experience in drafting standards or codes related to energy efficiency of buildings have shown that every new text must be tested for a certain period of time and be readapted thereafter to be fully satisfactory. Moreover, the standards or codes must be accepted by the concerned people, and therefore must be adapted to the users. This document should therefore be regarded as a proposal which still requires modifications and adaptations according to the local needs. These adaptations could be brought by Tanzanian research institutions such as the Building Research Unit, the University College of Lands and Architectural Studies, and the Institute of Human Settlements and Building Research (IHSBR). Texts that anyway require a local adaptation are marked in grey. Parts to be fully developed locally are marked in yellow. 3


1.3 P ERFORMANCE

AND PRESCRIPT IVE REQ UIREMENT S

Each regulatory text has one or more aims. This text has as fundamental objective that the future buildings - as well as the renovated buildings - ensure a comfort acceptable for the occupants, while requiring a minimum amount of energy for their construction, their operation and their deconstruction, and in which renewable energy has the largest share. These objectives should however not be achieved to the detriment of the health of the occupants. According to the National Human Settlements Development Policy that proposes to "revise building and construction standards so that they become functional and performance based rather than prescriptive", this draft basically proposes performance based rules. Such requirements are both necessary and sufficient to achieve the objectives, allow great design freedom, which goes hand in hand with a certain responsibility for the architect. However, it may happen that the architect does not know how to design the building to satisfy these performance requirements or does not have access to tools such as building performance simulation programs to check that his project meets the basic requirements. Therefore, these basic requirements should be supplemented by simple and clear prescriptive requirements that guarantee, if they are met, that the targeted performance will be achieved. For this, the prescriptive requirements must be stricter than the performance requirements and therefore leave less design freedom. In fact, the application of all prescriptive rules should ensure that performance requirements are met.

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2

PROPOSED DRAFT REGULATION TEXTS

2.1 D EFINIT IONS 2.1.1 Energy 2.1.1.1 Energy: (from the greek : ενεργεια, energeia, force in action) is the ability of a system to change a state, to produce a work, light or heat. It is a physical quantity which characterizes the state of a system and which is generally conserved during conversions. In the international system of units, the energy is expressed in joules (J). In everyday life, the kilowatt-hour (kWh) is preferred. 1 kWh = 3'600 ' 000 J. 2.1.1.2 Power: Power is the ability to do a given work in a given time, or to quickly heat a given mass. It is expressed in Watt (abbreviated W). A watt is therefore the possibility of transforming energy of one Joule in one second. The kW is 1000 Watt. This kW acting during one hour gives1 kilowatt hour of energy. 2.1.1.3 Energy carrier: agent carrying energy. There are non-renewable agents, whose human consumption rate exceeds the rate at which the nature products it (oil, coal, uranium, natural gas) and renewable agents, the source of which will not be exhausted by human views. The original source of these is primarily solar radiation, which should last for a few billion years and which is at the origin of biomass, waterfalls, and wind. Geothermal energy uses the internal heat of the Earth, which is theoretically finite, but allows an important use without significantly accelerating the cooling of the Earth. 2.1.1.4 Useful energy: amount of energy required for the service requested. For example heat to warm up a litre of water, energy in the light that illuminates a work place, work to lift a person one floor, etc. 2.1.1.5 Final energy: energy delivered to the user (building, vehicle) to make services, for example electricity delivered, energy content of wood, gas, oil or fuel. The final energy consumption includes the useful energy produced and all transformation losses of the user. 2.1.1.6 Primary energy: total energy needed to deliver the final energy. It includes the final energy and all the energy needed for the extraction, refining, processing and transportation of the final energy. 2.1.1.7 Primary energy factor: ratio of the primary to the final energy. There are total primary energy factor, which includes all energy agents, and non-renewable primary energy factor which includes only non-renewable agents. 2.1.1.8 Primary energy factors depend on the chain from the source of primary energy to the final energy use, and these chains vary from one region to another, and also over time. Table 1 gives standard values. 2.1.2 Table 1: Standard primary energy factors according to ISO 16346 [1].

Fossil fuels Electricity Wood Biogas

Total primary energy factors 1,2 3,0 1,1 1,5 5

Non-renewable primary energy factors 1,2 2,5 0,1 0,5


2.1.2.1 Energy efficiency of a service: ratio of the useful energy to the primary energy used to provide this service. 2.1.2.2 Specific primary energy use: Total primary energy use of a building during one full year, divided by its gross conditioned floor area (including walls. It is a measure of the building energy efficiency. In SI units, it is expressed in kWh/m² or MJ/m² 2.1.2.3 Climate 2.1.2.4 Air temperature θa: the dry-bulb temperature of the air surrounding the occupant. 2.1.2.5 Dew point θd: the temperature at which moist air becomes saturated (100% relative humidity) when cooled at constant pressure. 2.1.2.6 Climate zone: in what concerns building physics, territory in which the evolution of outdoor temperature, air humidity, solar radiation and wind over the seasons and during the day is similar. The architectural climate adaptation rules are the same in a given climate zone. 2.1.3 Comfort 2.1.3.1 PMV: Predicted Mean Vote is a thermal index derived from the heat-balance model of thermal comfort developed by Fanger [2]. The scale runs from -3 (cold) to +3 (hot), 0 expressing neutral sensation or comfort (see 3.1.1). 2.1.3.2 Free-running building: is the building that does not make any use of mechanical cooling or heating. They are naturally ventilated with operable windows and other devices such as ceiling or table fans allowing the occupants to adapt their climatic environment. [3]. 2.1.3.3 Free-running temperature: is temperature which represents indoor temperature of building in thermal balance with outdoor environment when neither heating nor cooling is used [4]. 2.1.3.4 Adaptive comfort model: a model that relates indoor design temperatures or acceptable temperature ranges to outdoor meteorological or climatological parameters[3]. 2.1.3.5 Adaptive opportunity: device (such as mobile solar protections, operable window, fans) or provision (e.g. free clothing code, availability of cold drinks) allowing the occupants to adjust the internal environment and themselves to achieve thermal comfort [5]. 2.1.3.6 Mean radiant temperature θr: the uniform surface temperature of an imaginary black enclosure in which an occupant would exchange the same amount of radiant heat as in the actual non uniform space [2]. An approximation is the average of the temperatures of the surrounding surfaces weighted by the areas of these surfaces. 2.1.3.7 Operative temperature θo: the uniform temperature of an imaginary black enclosure in which an occupant would exchange the same amount of heat by radiation plus convection as in the actual non uniform environment. Operative temperature is numerically the average of the air temperature Ta and mean radiant temperature Tr, weighted by their respective heat transfer coefficients (see 3.1.1). 2.1.3.8 Running mean temperature θrm: Average of all the temperatures measured during the last 48 hours. To get accurate results, the measurement interval should not exceed 1 hour.

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2.1.3.9 Indoor environment quality: (IEQ) refers to the overall comfort of a building’s interior and the well-being and health of its occupants. Factors contributing to indoor environmental quality include thermal comfort, humidity, lighting, acoustics and indoor air quality (IAQ), itself related to indoor sources of air contaminants and ventilation. 2.1.3.10 Indoor air quality (IAQ) : refers to the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants. IAQ can be affected by toxic gases, particulates or microbial contaminants that can induce adverse health conditions. 2.1.3.11 Illuminance: is the total luminous flux incident on a surface, per unit area. It is a measure of how much the incident light illuminates the surface, wavelength-weighted by the luminosity function to correlate with human brightness perception. In SI units these are measured in lux (lx) or lumens per square metre (cd·sr/m2). 2.1.3.12 Sound level: logarithmic measure of the effective sound pressure of a sound relative to a reference value. It is measured in decibels (dB) above a standard reference level. The standard reference sound pressure in air or other gases is 20 µPa, which is usually considered the threshold of human hearing (at 1 kHz). 2.1.3.13 Noise level: In this document, it is the sound level of unwanted noises. 2.1.3.14 Reverberation time: measure of the acoustic properties of a room, equal to the time taken for a sound after stopping the sound emission to fall in intensity by 60 decibels. 2.1.4 Envelope characteristics 2.1.4.1 Envelope Air permeability of the envelope: Measure of the airtightness of the building envelope. It is the airflow rate necessary to maintain a pressure difference of 50 Pa between the interior and the exterior of the building, reported to the total inner surface of the enclosure. It is expressed in m³/(h·m²). The measurement procedure is defined in ISO 9972[6]. 2.1.4.2 Heat transfer coefficient: Ratio of the heat flow rate through a 1 square meter building envelope component to the temperature difference between both sides This coefficient is calculated according to ISO 6946 [7] for opaque elements, to ISO 12631 [8] for curtain walls and ISO 10077 [9, 10] for doors and windows. 2.1.4.3 Dynamic thermal transmittance: Measure of the permeability of a building envelope elements to the variation of the outdoor temperature. It is calculated according to ISO 13786[11] 2.1.4.4 Equivalent windows-to-walls ratio: It is the ratio of the total amount of solar radiation entering the building to the total solar radiation reaching the fenestration areas over an entire year. This ratio is used to determine the impact of the solar load on the cooling energy usage of a building. This ratio depends on the following factors: ratio of windows to gross wall areas, ratio of skylight to roof area, global solar energy transmission coefficient of the glazing and architectural shading factor. 2.1.4.5 Global solar energy transmission coefficient: For a glazing, it is the ratio of the total power transmitted to the inside (light and heat) to the power of the solar radiation incident on the glazing. It is calculated according to ISO 15099[12]. 2.1.5 Appliances 2.1.5.1 Coefficient of performance (COP) of cooling machine is the ratio of the heat evacuated by the machine to its energy use under nominal conditions. The annual coeffi7


cient of performance of cooling facilities, is the ratio of the annual heat evacuated by the facility to the annual energy use of the whole facility, including accessories and controls.

2.2 A PPLIC ABLE

BUIL DIN GS

2.2.1

The texts below apply to all spaces intended for housing, administration, hospitality and hospitalization, education, meetings, restaurants or similar, that are operated under natural ventilation without heating or cooling, or that are heated, cooled or have mechanical ventilation.

2.2.2

They also apply as far as possible to industrial premises, premises for the exercise of sports and other premises occupied by persons, as well as to any premise equipped with mechanical ventilation or whose climate is conditioned by mechanical installations.

2.2.3

They do not apply to unoccupied premises that are neither conditioned nor ventilated by mechanical installations.

2.2.4

Where this standard is found to conflict with safety, health, or environmental codes, the safety, health, or environmental codes shall take precedence.

2.3 C LIM AT E

ZONES

2.3.1

The building design shall be adapted to the climate zone, in order to fulfil the performances required in 2.4.

2.3.2

The four climate zones are defined as follows 1:

1 Semi temperate highland areas

1265

Extreme temperatures (°C) 15-31°C

2 High lake regions

1137

16-30 °C

68%

3 Central plateau

1120

17- 32°C

66%

4 Coastal hinterland

50-400

18-32 °C

72%

5 Coastal area

0-200

20-33 °C

72%

Altitude (meters)

Climate zone

2.4 C RIT ERIA

Average relative humidity 66%

FOR INDOOR EN VIRONMENT Q UALIT Y

Comfort requirement should be adapted to the users, their activity and clothing, as well as to user's habits. Too strict requirements may strongly increase the energy use without improving the satisfaction of the occupants. The proposals below are funded on the most recent knowledge, which is presented in 3.1.1. 2.4.1 Thermal comfort Complements in 3.1.1. 2.4.1.1 In residential, administrative, educational and similar buildings, the temperature inside premises with natural ventilation, in which people can adapt their clothing, is considered as comfortable if it is within the comfort zone of Figure 1.

1

These zones are based on available information from various sources. They should be refined by local authorities, taking into account the parameters influencing comfort and energy in buildings, i.e. outdoor air temperature and temperature variations, outdoor air humidity, direct solar radiation coming directly from the sun, and diffuse solar radiation coming from the whole sky. A map should clearly define these areas.

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Figure 1: Comfort zone in premises with natural ventilation, when they are neither heated nor cooled. 2.4.1.2 The ISO 7730 standard is applicable in premises when the temperature is controlled by mechanical cooling or heating. In residential, administrative, educational and similar buildings, this corresponds to the comfort zone illustrated in Figure 2.

Figure 2: Comfort zone in premises with controlled temperature. 2.4.1.3 The relative humidity is considered as comfortable when between 30% and 75%, as long as the operative temperature is within the limits mentioned in articles 2.4.1.1 and 2.4.1.2. 2.4.2 Indoor air quality Complements in 3.1.4 2.4.2.1 The indoor air quality in occupied premises shall neither cause discomfort nor any health hazard for the occupants, and shall not damage the building.

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2.4.2.2 In particular, the concentration of toxic gases should be as low as reasonably possible. They shall not exceed the limit values in these spaces. Limit values may be given as average values over a period of time or as a dose accumulated over a period. If several limits are given, none of them should be exceeded. 2.4.3 Visual comfort Complements in 3.1.5 2.4.3.1 The illuminance (in Lux) shall be adapted to the occupations at each location of the premises. Table 2: Recommended illuminance. Activity and premise Corridors, theatres, concert halls Workshops, assembly halls, shops Schools, offices, reading, writing, screen work, etc. Delicate work, drawing, technical work, etc. Precision work, fine mechanics, colours control, visual quality control, etc.

Recommended illuminance levels (lux) Min. Average Max. 20 70 150 120 150 200 250 300 375 500 750 1000 1000

to

5000

2.4.3.2 At the working places, the variation of luminance of the surfaces and sources of light in the visual field should be limited to a factor 3 in the ergorama (60° aperture field around the centre of attention) and a factor 10 in the panorama, 120 ° aperture field. 2.4.4 Acoustical comfort Complements in 3.1.6 2.4.4.1 The outdoor noise produced by human activities shall not exceed the levels of Table 3, when measured at 10 m from the source. Table 3: Maximum noise levels outdoor (dB A, 10 seconds average) Main land use Activities that require a low noise level (hospitals, quiet areas) Residential areas, hotels, schools Agriculture, mixed residential and industrial areas Industry

Day 55 60 65 70

Night 45 50 55 60

2.4.4.2 The background noise level in the occupied premises shall not exceed the levels of Table 4. It shall in no case exceed 85 dB (on 10 seconds average). Table 4: Maximum background noise levels in premises (dB A) Sleeping rooms For the intellectual work For manual work Noise from ventilation systems

30 - 40 50 - 70 80 30

2.4.4.3 The acoustic insulation of the building envelope shall be adapted to external noise, so that the levels mentioned in Table 4 are not exceeded. 2.4.4.4 The reverberation time in the premises shall be adapted to occupants' activities. For good speech intelligibility, it should be between 0.5 and 1 second. 10


2.5 P RIM AR Y

REQ UIREME NT S

Complements in 3.2. 2.5.1

The buildings shall be designed and built so as to ensure a good indoor environment quality with a minimum use of non-renewable energy. In particular:

a) The thermal comfort (see 2.4.1) shall be provided without artificial cooling or heating. Exceptions are hot humid area as defined in 2.8.1 and premises where the internal thermal load cumulated over 24 h is larger than120 Wh/m² net floor area. b) Indoor air quality shall be ensured by the quality of construction materials (2.7.2), contaminant source control (2.4.2) and natural ventilation (2.7.5). Mechanical ventilation may be authorized in some cases (2.8.1). c) For each building project, a ventilation principle is established. Possible ventilation modes are as follows: • natural ventilation with automatic or manual control; • mechanical extraction with air supply through on purpose openings; • double flow mechanical ventilation with heat recovery if the air is conditioned; and their combinations. d) The description of the ventilation principle includes the localization of air inlets and outlets, and airflow rates at all possible regimes. e) The ventilation principle should allow users to get the necessary airflow by an appropriate use of the mechanical ventilation or ventilation openings. f) The location, shape and size of lighting openings shall allow adequate natural lighting of the premises during the day (2.4.2). g) Acoustic comfort (2.4.4) is ensured by appropriate acoustic protection against the noise the outside and, especially for large premises, by a suitable internal acoustics.

2.6 C HECKING

T HE COMPLI ANCE T O REQUI REMENT S

2.6.1 Three compliance checking paths For each building project or major conversion of building, and for each type of performance, the compliance to requirements listed in 2.5 is verified by one of the three following paths: a) By similarity, demonstrating that the project is similar to an existing building that meets the performance requirements. b) By simulation: Using authorized computer software to simulate the behaviour of the building or of its parts. c) By compliance with all the requirements corresponding to the type of proposed building and to the climate zone where the proposed building is located. These requirements are listed in section 2.7

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2.6.2 Compliance checking by similarity 2 The project shall have the same characteristics as an existing reference building, which has shown in practice that it meets the performance requirements. The similarity must include the following characteristics: • Same climate zone. • Same architecture. • Same uses (habitat, offices, shops, etc.) in same proportions. • The thermal masses (inertia) of facades, roof and building at least equal to those of the reference building. • Thermal insulation (U-values of envelope elements) equal or smaller than those of the reference building. • Same equivalent window to wall ratio with a 10% margin (see 2.7.5.). • Same solar protections or better. • All appliances and installations have an energy performance at least equal to those of the reference building. 2.6.3 Checking the hygro-thermal performances by computer simulation 3 2.6.3.1 To check the compliance with thermal requirements, any dynamic simulation method calculating the evolution of the operative temperature in buildings is authorized, provided that it meets the following criteria: • It is validated according to ISO 13791[13], ISO 13792[14] or EN 15265[15]. • all heat exchanges such as: • internal and external heat inputs • heat exchanges between the indoor air and the building fabric (thermal storage) • heat losses and gains by natural or mechanical ventilation are taken into account; • The calculation shall be done room by room. If the room that are clearly the most exposed to cold, respectively to heat, meet the performance requirements, it is not necessary to do the calculation for the other rooms that have the same characteristics according to 2.6.2. The boundary conditions for these simulations are defined in Table 5 • Any deviation must be justified and all other simulation assumptions shall be plausible. • The evaluation of the thermal discomfort is given by the number of hours of occupation during which the temperature is outside the comfort zone shown in Figure 1 for free-running premises, and in Figure 2 for conditioned premises. The room meets the performance requirements if this number is zero 4. • In rooms with natural ventilation, the air humidity for every hour is obtained by dividing the water vapor pressure of the outside air by the saturated vapor pressure at room temperature. The relative humidity should be between 30% and 70% most of the time. It may exceed the upper limit (over 70%) for a few hours if these periods are separated by drier periods of at least a day.

2

This path is a simplifies the checking process for similar buildings, and allows taking account of local experience, in particular of the knowledge cumulated in vernacular architecture.. 3 This path allows a direct checking of the performances. It is the only one leaving some design freedom. 4 There is no tolerance on the number of discomfort hours during occupancy, since the tolerance is already included in the comfort model.

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• If the relative humidity exceeds 70% for more than five consecutive days 5, air drying (or air conditioning) should be considered. Table 5: Boundary conditions for the evaluation of thermal conditions Checking that the operative temperature and air humidity are within the comfort domain for the planned use of a room. Operative temperature within the occupied space. Determining physical quanIf there are no significant radiant sources (e.g. hot wall or cold ceiling), the air temperatity ture at the middle of the room can be used instead of the operative temperature. Time step The calculation time step is one hour or less. Weather data for the climatic zone where the building is located. A correction of altitude Climatic data on the outdoor temperature of - 0.5 ° C per 100 m must be made. Convective part of the external thermal loads 20%, radiative part 80%. Time period The year xxxx 6, that also determine working days and holidays. Characteristics and existing or planned control strategy of mobile solar protections. If no such information is available, solar protections are deployed when the solar irradiance outside the window is larger than 200 W/m² and the indoor temperature above the Solar protections lower comfort limit. If an automatic storm lifting system is provided, the wind resistance should be taken into account, assuming that the wind speed near the sunscreen is the wind speed 1 m above the roof, in a free field. Internal heat and moisture Use the agreed conditions of use. If no such conditions exist, use standard operating loads conditions for the type d "use provided (to be developed locally). Occupation schedule and density and internal heat loads according to the standard operating conditions for the type of use in the room (to be developed locally). - Persons Convective part of the heat loads 50%, radiative part 50%. Only the sensible heat emitted by the persons is taken into account. Illumination and internal heat loads from appliances according to the standard operating conditions (to be developed locally). - Lighting The actual control mode according to daylight and the use of sunscreens is taken into account. Possible simplification: no artificial lighting within 5 m of the windows as long as there is daylight. Convective part 30%, radiative part 70%. Use of appliances and internal heat loads according to to the standard operating condi- Appliances tions (to be developed locally). Convective part 80%, radiative part 20%. Calculation model for natu- A dynamic model for determining the airflow rate should be used as long as the natural ral ventilation ventilation is possible. The influence of the wind can be neglected except in windy areas. Use the airflow rates calculated with the dynamic model as long as the ambient temperature is above 22 ° C and the outdoor temperature. Otherwise, apply the hygienically Airflow rates from natural required external airflow rate for the occupants during the periods of occupancy and ventilation constant outdoor airflow rate of 0.3 m³/h·per m² floor area, outside the periods of occupancy. Airflow rate from mechan- Apply the hygienically required external airflow rate for occupants. If the temperature ical ventilation during exceeds 25 ° C or below 15 ° C, apply a reduction up to 50% (minimum flow 15 m³/h occupancy and person). Apply a constant external airflow rate of 0.3 m³/h·per m² floor area. If the indoor air Airflow rate from mechantemperature is above 24 ° C and exceeds by 4 K or more the outdoor air temperature, ical ventilation outside apply the nominal airflow rate or higher, if this is technically possible but not more occupancy periods than twice the nominal airflow rate. Mechanical ventilation Installation starts morning 1 hour before the occupation and stopped one hour after the schedule end of the occupation of the premises. It remains switched on during the lunch break. Objective

2.6.3.2 Verification on a conditioned building (cooled or heated) shall include the calculation of the annual energy use of the building for conditioning, taking into account, as appropriate the energy use for: • The cooling of premises 5

The actual limit should be determined by local experts. Criteria are discomfort and mould growth.-. To be defined locally 6 The competent authorities should define a reference year for which hourly values of the climatic data exist and represent a typical year.

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• • • •

The dehumidification of the air The energy performance of the conditioning system; The energy use of fans, pumps and other accessories such as the control system The heating of premises, including the efficiency of the system.

If several energy agents are used, the calculation shall provide the use of each of them separately. This calculation is performed according to ISO 13790[16] and ISO 16346[17] 2.6.3.3 The uses of each energy agent, expressed in kWh are multiplied by their total primary energy factor. If the information corresponding to the agents consumed in Tanzania is not available, the values given in ISO 16346, reproduced in the Table 6 can be used. Table 6: Conventional primary energy factors from ISO 16346 Total 1,2 3,0 1,1 1,5

All fossile fuels Electricity Wood Liquid biomass and biogasz

Non-renewable 1,2 2,5 0,1 0,5

2.6.3.4 The total primary energy use of the building, divided by its gross conditioned floor area (including walls), shall not exceed the limits of Table 7. Table 7: Upper limit for annual specific primary energy use 1 2 3 4 5

Building type : Semi temperate highland High lake regions Central plateau Coastal hinterland Coastal area

Dwellings

7

Offices

Hotels

Schools

2.6.4 Checking the lighting performances by computer simulation 8 2.6.4.1 To check compliance of lighting conditions, any simulation method for calculating the illumination of premises is authorized provided that it meets the following criteria: • The external, local horizon is taken into account, • The shape of the room (rectangular, trapezoidal, horizontal or sloped ceiling, etc.) is simulated, • Internal objects (obstacles, pillars, walls, balconies) can be simulated, • Fixed and mobile solar protections are simulated. • The autonomy in natural lighting, i.e. the part of the occupied time during which artificial lighting is not necessary is calculated. 2.6.4.2 Natural lighting is sufficient when the lighting openings bring the minimum illuminance values given in 2.4.3.1 between 07:00 and 17:00 h.

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These limits can only be defined by local experience or many simulations. To be defined locally. Checking compliance to requirements related to acoustics and air quality by computer simulations is complex and not reliable. Therefore, this path is not of common use for these criteria.

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2.7 D ESIGN

PRESCRIPT IONS RELAT ED T O ENERG Y EFFICIENC Y

2.7.1 Building orientation Complements in 3.2.4 2.7.1.1 The orientation of the building and of its lighting and ventilation openings shall contribute to improve thermal comfort, ventilation and daylight. 2.7.1.2 In particular, less occupied spaces (corridors, service rooms) should be adjacent to the façade that is most exposed to nuisance, and frequently occupied spaces should be adjacent to the facades best protected against nuisances and most exposed to sight. 2.7.1.3 The facades with the largest windows area should be oriented towards the North or the South, with ± 20° tolerance. 2.7.2 Building materials Building materials are, as far as possible, selected from materials extracted or manufactured locally. Building materials must not be harmful to health and shall not release gases or aerosols in quantities that can be harmful to health. 2.7.3 Building envelope Complements in 3.3 2.7.3.1 The building envelope includes all walls, roofs and floors separating the occupied spaces from outdoor space. 2.7.3.2 This envelope shall protect the occupants from external nuisance, including rain, noise, and wind. It shall contribute to thermal comfort. 2.7.3.3 The heat transfer coefficient of the facades must be less than the values given in Table 8. Table 8: Maximum heat transfer coefficient of the façade components 9 UMax in W/m²K Doors and Opaque walls windows 1 3 1 3 2 6 1 3 1 3

Climate zone 1 2 3 4 5

Semi temperate highland High lake regions Central plateau Coastal hinterland Coastal area

2.7.3.4 Ventilated roofs have a space between the roof and the ceiling, the smallest thickness of which is larger than a hundredth of the distance between the cornice and the ridge. Ventilation openings with an area exceeding one hundredth of the area of the roof must be practised at the cornice and the ridge. 2.7.3.5 The reflection coefficient for solar radiation of roofs must be as large as possible, preferably greater than 70%. 9

Important: These figures are not validated. It should be checked that the buildings designed and built according to these criteria comply to performance requirements for all climate zones..

15


2.7.3.6 The dynamic thermal transmittance of not ventilated roofs, calculated according to ISO 13786[11] shall not exceed 0.20 W/(m² K). (Roofs which thermal transmission coefficient U equal to or less than 0.20 W/(m²K) meet this requirement.) 2.7.3.7 Where the climate is adequate, unventilated roofs can also be covered with vegetation (green roofs). In this case, the article 2.7.3.6.does not apply. 2.7.3.8 The envelope of buildings with mechanical ventilation or air conditioning shall be as airtight as reasonably possible when the doors, windows and other openings are closed. The measurement must be done according to ISO 9972with all the ventilation openings and mechanical ventilation openings sealed. Air flow under a pressure difference of 50 Pa must not exceed 25% of the supply airflow rate of the ventilation system 10. 2.7.4 Movable solar protections Complements in 0 2.7.4.1 Wind-resistant, external movable solar protections are installed on every window of occupied spaces. The overall solar energy transmission factor of the window (glazing and solar protection) shall not exceed 0.1511. 2.7.4.2 Transparent or translucent roof lights are equipped with mobile solar protection and have an area of less than 5% of the net floor area of the lighted premises. 2.7.4.3 The requirements on mobile sunscreens may be reduced in the presence of fixed solar protection, as long as the external heat load on a sunny day does not exceed the external heat load with an overall energy transmission factor of the window equals to 0.10. Verification shall be performed for each room. The compliance can also be checked for the building according to 2.7.5. 2.7.4.4 Solar protections shall allow natural lighting suitable to the activities of the occupants. Moveable solar protections that can be adjusted to user's needs comply to this requirement. 2.7.5 Fixed solar protections and equivalent window to wall ratio 12 2.7.5.1 The equivalent window to wall ratio of buildings not equipped with mobile solar protections according to 2.7.4 shall not exceed the limits given in Table 9. Table 9: Upper limits for the equivalent window to wall ratio 13 Climate zone 1 2 3 4 5

WWRmax

Semi temperate highland areas High lake regions Central plateau Coastal hinterland Coastal area

10

0.30 0.25 0.30 0.25 0.20

Since naturally occurring pressure differences are much lower than 50 Pa, the actual air leakage through the envelope will then not exceed 5% of the supply airflow rate. 11 This implies that the external solar protection is ventilated enough to avoid overheating. 12 This section is strongly inspired from 18. Mourtada, A., Resources Efficiency and Conservation Measures for Buildings - “RECM- Standard”, 2013, United Nations Human Settlements Programme: Nairobi. p. 86. 13 Important: These figures are not validated for Tanzania. These should be checked wit local experience and computer simulations..

16


2.7.5.2 The equivalent window to wall ratio WWR is calculated as follows: 1 2 𝑅𝑆𝑉 = � 𝑔𝑗 𝐹𝑗 𝐴𝑓,𝑗 + � 𝑔𝑘 𝐴𝑓,𝑘 𝐴𝑣 𝐴𝑡 𝑗

𝑘

where: Av Area of all vertical surfaces (opaque walls + windows) At Area of all roof surfaces (roofs + skylights) Af Area of the individual window gj Global solar energy transmission coefficient of the individual glazing of window j Fj Architectural shading factor of the individual window for fixed solar protections The sum is over all windows in facades, j, and all skylights, k.

2.7.5.3 The architectural shading factor Fj for fixed solar protections (overhangs, fins, claustra) is determined as follows 14: The projection factor Fp is the ratio of the Horizontal extension of the overhang from the vertical wall plane that contains the fenestration to the Distance between the bottom edge of the fenestration and the bottom edge of the overhang It is the ratio A/B on Figure 3. A A

B

B A

Overhang

Fins

B

Claustra

Figure 3 : Fixed solar protections. Architectural shading factors Fj for various types of fixed shadings are given in the following Tables. These are valid under the Equator ±10° de latitude. Table 10: Architectural shading factors fort windows protected only by an overhang, as a function of the projection factor Fp and for the four main orientations. Fp ≤ 0.15 0.15 < Fp ≤ 0.40 0.40 < Fp ≤ 0.65 0.65 < Fp ≤ 0.90 Fp >0.90

NE,N, NW 1 0.88 0.80 0.75 0.72

EN, E, ES 1 0.80 0.65 0.55 0.50

WN,W WS 1 0.80 0.65 0.55 0.50

SE,S,SW 1 0.78 0.63 0.52 0.43

Table 11: Architectural shading factors fort windows protected only by fins, as a function of the projection factor Fp and for the four main orientations.

14

La méthode est tirée du projeet de "RECM Standard" d'Adel Mourtada, préparé dans le cadre du même mandat de UH habitat.

17


Fp ≤ 0.15 0.15 < Fp ≤ 0.40 0.40 < Fp ≤ 0.65 0.65 < Fp ≤ 0.90 Fp >0.90

NE,N, NW 1 0.74 0.67 0.58 0.52

EN, E, ES 1 0.80 0.72 0.65 0.60

WN,W WS 1 0.80 0.72 0.65 0.60

SE,S,SW 1 0.79 0.69 0.60 0.66

Table 12: Architectural shading factors fort windows protected only by a claustra, as a function of the projection factor Fp and for the four main orientations. Fp ≤ 0.15 0.15 < Fp ≤ 0.40 0.40 < Fp ≤ 0.65 0.65 < Fp ≤ 0.90 Fp >0.90

NE,N, NW 1 0.64 0.51 0.44 0.37

EN, E, ES 1 0.60 0.49 0.42 0.35

WN,W WS 1 0.60 0.49 0.42 0.35

SE,S,SW 1 0.60 0.46 0.35 0.30

2.7.6 Natural ventilation Complements in 3.7.3 2.7.6.1 In every occupied space, openings for natural ventilation shall be provided. In rooms without mechanical ventilation, two openings shall be provided, one of it being as close as possible to the ceiling. 2.7.6.2 In each residential room, the ventilation openings have an area equal at least to 5% of the net floor area. This ratio is 15% in schools, offices, meeting rooms, restaurants and other spaces with high occupancy. These openings must be opened and closed at will. 2.7.6.3 New or renovated premises with natural ventilation are equipped with a ceiling fan from or an electrical socket for such a fan for every 20 m² of floor. 2.7.7 Thermal inertia 2.7.7.1 In occupied spaces, the thermal capacity per unit net floor area, CR/Anetf, shall be at least 180 kJ/m2K or 45 Wh/(m2·K). 2.7.7.2 The calculation of the thermal capacity of the elements is performed according to EN 13786[19], for a period of 24 hours, taking into account the surface thermal resistances. For the calculation of heat capacity CR, the false ceilings should be regarded as completely closed and taken into account as an additional thermal resistance. 2.7.7.3 A ground floor, a concrete slab with(or without) tiles, or adobe, concrete or solid masonry walls that are apparent on an area corresponding to at least 80% of the floor area of the room meet these requirements. 2.7.8 Passive cooling Complements in 3.5 2.7.8.1 In climate zones 1, 2 and 3, the passive ventilation cooling strategy shall be applied in residential buildings and, as far as possible in other buildings. This strategy consists in evacuating during the night, by natural ventilation, the heat accumulated in the mass of the building during the day. The building design elements to apply this strategy are as follows: 18


• The outdoor dew point must be lower by 6 ° C to the upper comfort temperature limit.15 • The thermal capacity shall comply with 2.7.7 • Large openings that can remain open overnight shall be provided at suitable places to secure strong aeration of premises even in the absence of wind. Facade and roof windows can be used for this purpose. A large opening must be located as high as possible in the considered volume, to evacuate all hot air. • The total area of these openings shall be at least 5% of the floor area. Single sided ventilation is suitable for the premises of less than 3 m deep. In the other premises, openings shall be provided on two opposite walls. 2.7.9 Passive solar heating Complements in 3.4 2.7.9.1 In climate zones where the daily mean temperature may fall below the comfort range, every new or renovated building is designed to allow using the passive solar heating strategy. This consists in heating the building by allowing solar radiation to enter, in most cases through the windows. The building is then heated during the day; and thermal insulation and inertia are sufficient to maintain a comfortable temperature overnight. The building design elements to apply this strategy are as follows: • Premises to be heated in the morning are oriented to the East, and to the West for heating in the afternoon. • The thermal insulation of the building envelope suffices to reduce the heating energy demand to less than 10 kWh/m² floor area. • The thermal capacity shall comply with 2.7.7. • The windows of the premises to be heated have a transparent area between20% and 30% of the net floor area. These windows are equipped with clear glass and mobile sunscreens according to 2.7.3.8. 2.7.10 Daylight Complements in 3.8.1 2.7.10.1 In every occupied room, daylight openings shall be provided. 2.7.10.2 The effective area of daylight openings, i.e. their transparent area multiplied by their light transmission coefficient without mobile solar protections shall be between 20% and 30% of the net floor area of the room. 2.7.10.3 The distance between the work or stay places and these openings shall not exceed 3 times the height of the openings above the working place.

2.8 P RESCRIPT IONS

FOR BUILD ING S YST EMS

2.8.1 Mechanical ventilation Complements in 3.7.4 and 3.7.5 2.8.1.1 Mechanical ventilation facilities are subject to authorization. This authorization may be granted only if it is impossible to properly ventilate the premises by natural ventilation, especially if the outside air is too polluted, if the external environment is too noisy, or if the premises are too large. 15 It is likely the case in call climate zones except the coast and on the shores of the big lakes. To be checked locally

19


2.8.1.2 The airtightnessof the envelope of a building equipped with mechanical ventilation (ventilation openings being closed) complies with Erreur ! Source du renvoi introuvable.. 2.8.1.3 The ductwork shall be airtight and sized so that the discharge air velocity 16 does not exceed 2 m/s. 2.8.1.4 The specific energy use of every fan, namely the ratio of the used electrical power to the nominal airflow rate, shall not exceed 0.1 Wh/m³. 2.8.1.5 Air flow adjustment is performed with a frequency inverter powering the fan, and not with registers. In offices, theatres, schools and similar premises, as well as in indoor car parks, the airflow rate is adapted according to occupancy using a CO2 sensor or any other occupancy-sensitive sensor. Mechanical ventilation of the toilet is activated according to their use. 2.8.1.6 Subject to article 2.8.1.7, mechanical ventilation is switched off when the premises are not occupied, but shall be restarted early enough to purge the space before the arrival of the occupants 17. 2.8.1.7 If the mechanical ventilation facility should be used for night cooling of the building, the specific airflow rate should be at least 3 volumes per hour or at least 9 m3/(h·m2) net floor area. This airflow rate is increased to 4 volumes per hour or 12 m3/(h·m2) net floor area if the glazing-to façade area ratio exceeds 30%. 2.8.1.8 Mechanical ventilation facilities of heated or cooled premises have supply and return ducts with enthalpy recovery; unless it is proven that the energy recovery is not profitable. 2.8.1.9 Every new ventilation system shall be commissioned after installation. The effective airflow rates, pressure differentials and energy efficiency of fans shall be measured and compared to the design values. 2.8.2 Artificial cooling Complements in 3.5 and 3.7.5 2.8.2.1 Mechanical cooling facilities are subject to authorization. This authorization may be granted only in hot-humid areas or if the internal heat loads accumulated over 24 hours exceed 160 Wh/m² net floor area. Mechanical cooling cannot be justified by thermal loads due to solar radiation or insufficient thermal insulation. 2.8.2.2 Hot humid areas in Tanzania are18: • The Zanzibar and Mafia Islands, • The areas below 1000 m in the regions of Tanga, Pwani, Lindi, Mtwara, Morogoro and Rukwa. 2.8.2.3 The sizing of mechanical cooling system is based on the following conditions : • Airflow rate per person : between 10 and 30 m³/h, as fixed in the ventilation principle according to 2.5.1 letters c) to d) • Internal operative temperature 25 °C • Indoor relative humidity 70% • Climatic condition according to Table 13 16

This is the airflow rate in the duct (in m³/s) divided by the section of the duct (in m²). 17 i.e a time interval equal to the ventilated volume in m³ divided by the outdoor air flow rate in m³/h. 18 These areas should be better defined with input from the Tanzania Meteorological Agency, and be one or more of the climate zones defined in 3.2.

20


Table 13: Design temperatures for air conditioning and other mechanical cooling systems19 Outdoor temperatures Climate zone 1 2 3 4 5

Semi temperate highland areas High lake regions Central plateau Coastal hinterland Coastal area

Dry bulb °C 29 28 30 30 31

Wet bulb °C 17 20 18 23 25

2.8.2.4 The overall annual coefficient of performance (COP) of cooling facilities shall exceed 3.8 20. This requirement does not apply to mechanical cooling facilities using solar energy. 2.8.2.5 Ground-cooled heat pumps should be installed wherever it is possible instead of aircooled heat pumps for cooling buildings. 2.8.2.6 According to 2.8.1.8, air conditioning systems have supply and return ducts with an enthalpy recovery. A droplet catcher shall be installed downwind the cooling coil. 2.8.2.7 The design indoor operative temperature for cooling system is 25 °C. The cooling temperature set point shall not be below 25°C. 2.8.3 Space heating Complements in 3.4 and 3.4.2 21

2.8.3.1 Except for altitudes over 2000 m , heating premises with non-renewable energy is not allowed in Tanzania. Where heating is allowed, the building is designed to take the best of passive solar heating according to 2.7.9 and to reduce the energy need for heating to a minimum. 2.8.3.2 The heating design power is such that 20°C operative temperature can be obtained in premises when the outdoor air temperature is at the lowest 72 hours average. 2.8.3.3 Solid, liquid and gaseous fuel stoves shall have a closed combustion room with adjustable air inlet. Flue gas must be evacuated by a flue gas duct outside the occupied space. 2.8.4 Hot water heating Complements in 0 2.8.4.1 Only solar energy or waste heat recovery can be used for tap hot water heating in new or renovated buildings 22. 2.8.4.2 For safety and energy efficiency reasons, a thermostatic mixing valve limiting the temperature of the distributed hot water at 55 ° C maximum is installed on the boiler. 19

Important: These figures are rather arbitrary and should be locally determined. This figure could be discussed. Japan requires 4,9, USA, China, and the European Community requires between 3,2 and 3,8. 21 This figure should be adjusted according to local experience. A well designed, occupied building does not need heating if the daily average external temperature is above10°C. 22 It is possible to have no hot water heating in a building. The objective is to avoid the use of fossil or electrical energy to provide hot water. 20

21


2.8.4.3 If a hot water circulation system is provided, it must be equipped with a clock interrupting the circulation when hot water is not necessary. Supply and return pipes shall be insulated with at least 4 cm thick of insulating material, which thermal conductivity is not larger than 0.04 W/(m·K). 2.8.5 Electrical lighting Complements in 3.8.2 2.8.5.1 Electric lighting sources sold in Tanzania have a light emitting efficiency of 60 lm/W or better. Note: This eliminates the incandescent lamps (including quartz iodine lamps) and the worse compact fluorescent lamps. Candles and gas lamps, much less effective, are not prohibited by this article which refers only to the electric lamps. 2.8.5.2 All sources of electrical lighting or set of sources close to each other shall be equipped with a switch. Fixtures illuminating the corridors, stairs or occasional passing places are equipped with a sensor, in such a way that the artificial lighting is switched off in absence of users or when natural lighting is sufficient. 2.8.5.3 The electrical lighting of offices, meeting rooms, teaching rooms, hotel rooms, etc. is equipped with a system switching off the lighting in absence of occupants. 2.8.5.4 In spaces of more than 60 m²floor area, the lights far of the windows and those close to the windows shall have separate switches. 2.8.6 Kitchen equipment 2.8.6.1 Cooking wood stoves shall have a closed combustion room with adjustable air inlet. Flue gas shall be directly evacuated outside the occupied space with a duct. 2.8.6.2 Hoods evacuating gases and aerosols shall be installed above every fuel stove. 2.8.6.3 The evacuation of the gases can be natural (stack effect) or mechanical. In the latter case, the requirements of article 2.8.1 apply to the installation. 2.8.7 Lifts and escalators 2.8.7.1 The installation of lifts and escalators is subject to authorization. This authorization will be granted if this equipment is necessary (e.g. in high rise buildings with disabled persons), if the safety of the equipment is sufficient and if its maintenance is guaranteed. 2.8.7.2 Escalators are equipped with a sensor, in such a way that the escalator runs only in the presence of users. 2.8.7.3 The lifts are equipped with an energy recovery system. 2.8.7.4 The standby energy use of such equipment shall be negligible. 2.8.8 Other electrical appliances All electrical appliances made in Tanzania or imported shall have an energy label according to (choose between US or European standard, or create a national one). The import or sale of devices below class B (or 5 stars) is prohibited.

22


2.9 R ENEWABLE

EN ERG Y

Renewable energy sources should obviously be used as much as possible. In residential buildings, the solar water heater (2.8.3.3) is certainly profitable. However, the initial investment is often very high, even if it is profitable at term. The government may take various measures to solve this problem, for example: • remove taxes on renewable energy equipment; • finance and build renewable energy-producing facilities and sell the produced energy, • buy the energy produced by private owners of renewable energy-producing facilities at actual cost and not at the market price (Feed-in tariff), • allocate loans for the construction of facilities, these loans being reimbursed on the basis of the energy produced. Depending on political decisions, the government can then make mandatory certain types of renewable energy production facilities.

2.10 M OIST URE

CONT ROL

2.10.1 General requirements 2.10.1.1 Accumulation of water in cracks, pores and voids of building components in quantities that may cause damage or promote mould growth is not allowed. 2.10.1.2 The thermal resistance of a construction element must not decrease under the influence of moisture. A minor and reversible variation is nevertheless tolerated. 2.10.1.3 Irreversible changes caused by humidity shall be excluded. 2.10.2 Removing moisture 2.10.2.1 Spaces with important sources of humidity (kitchens, bathrooms, laundries, etc.) shall be sufficiently ventilated (naturally or mechanically), so as to quickly evacuate the water vapour produced. 2.10.2.2 Air drying is necessary if the water vapour content of outdoor air exceeds that corresponding to 75% RH indoors. 2.10.3 Condensation or mould growth risk 2.10.3.1 The building shall be designed and built so that, in occupied spaces: a) There is nowhere surface condensation of water vapour b) There is no risk of mould growth. 2.10.3.2 The momentary appearance of surface condensation is tolerated if it causes no damage. 2.10.3.3 To avoid the mould growth risk, the relative humidity of the air near the surface layer shall not exceed 80% for a period of more than two consecutive weeks. 2.10.3.4 Special operating measures (stopping ventilation, reducing airing, dehumidification or heating depending of the use of the space) must be taken in the premises with locations whose surface temperature is kept permanently at or below the dew point of the outdoor air.

23


2.10.4 Moisture in building components 2.10.4.1 No harmful build-up of moisture should appear in building components. 2.10.4.2 The risk assessment must take into account the transport of moisture by: • convective air flows, • capillarity, • the diffusion of water vapour. 2.10.4.3 Calculations according to the standard ISO 13788[20] allow assessing the transport of moisture by vapour diffusion. Specific assessments may be necessary to take into account the above three modes of transport.

2.11 U SE

OF WAT ER

2.11.1 Each building separately collects its clear water (rain) and its wastewater. These two collection systems are connected separately to the respective urban networks. 2.11.2 In new buildings, rain water is accumulated in a tank. This water is used for non-food uses (toilets, watering, cleaning). The tank capacity is large enough to collect at least half the annual rain water.

2.12 W AST E

MAN AGEME NT IN BUILD INGS .

2.12.1 Each building is equipped with containers for selective harvesting of the following waste: glass

• • • •

paper and paperboard, plastics metals organic waste.

2.12.2 The capacity of these containers shall be sufficient to store waste between two pickups.

Alternative (depending on the waste collection system): 2.12.3 The following wastes:

• • • •

paper and paperboard, plastics metals organic waste.

is not mixed with garbage but taken separately to the local dump.

24


3

COMMENTS AND COMPLEMENTS

Note: Large parts of this chapter are inspired from [21]

3.1 I NDO OR

EN VIRONME NT QUAL IT Y CRIT ERIA

3.1.1 Thermal comfort criteria Essentially, comfort is expressed by the satisfaction of a building’s occupants. Therefore, the most appropriate way to measure comfort is to ask occupants if they feel comfortable. The ISO 7730 [22] standard scale is most frequently used to determine this (see Table 14). When there are several people in a room, the mean vote is calculated. Table 14 ISO thermal comfort scale –3

Cold

–2

Cool ‘Cold’ dissatisfied

–1

Slightly cool

0

Comfortable Satisfied

1

Slightly warm

2

Warm ‘Hot’ dissatisfied

3

Hot

Our body exchanges heat by convection and conduction with the air, evaporation to the air, as well as by radiation to and from surrounding surfaces. Therefore, the thermal comfort depends on the air temperature as well as on the temperatures of surrounding surfaces. To make things simpler, a combination of these temperatures, the operative temperature, was defined. At a given location, it is, by definition, the temperature of an isothermal room in which a person has the same total heat loss as in the actual location. An approximation is:

θop= a θa+ (1 - a) θr

1

where a is a factor depending upon the air velocity v relative to the subject: a = 0.5 + 0.25v

2

This approximation can be used for air velocities up to 1 metre per second (m/s). In closed spaces, where the air velocity is low, the operative temperature is the arithmetical average of air- and mean radiant temperatures. Thermal comfort criteria should be adapted to the activities, clothing and uses of the occupants. The Fanger's criteria[2] are of wide use and standardised [22]. They are however developed on the basis of experiences at steady state in climatic chambers. For this reason, they are valid only in spaces where the temperature is controlled by mechanical means (heated or cooled spaces). In naturally ventilated premises where occupants can adapt their clothing and have enough control on their environment, the criteria are not the same. Therefore, it is important to apply different criteria to premises that are conditioned and to those that are running free.

25


3.1.2 Thermal comfort criteria in conditioned premises 3.1.2.1 Ideal operative temperature Since they are based on experiments performed in climatic chambers with imposed clothing and activity, the following rules apply in premises where the temperature is controlled by mechanical means, i.e in premises that are either cooled or heated. Other rules apply to naturally ventilated spaces when they are neither cooled nor heated (see 3.1.3). Fanger [2] proposed a method for calculating the mean vote of a group of people from air parameters (temperature, humidity and air velocity), clothing and activity. He called this the ‘predicted mean vote’ (PMV). This comfort model is adopted in most standards, and it is described in very details in ISO 7730 [22]. It should be noted that, according to this model, it is impossible to satisfy everybody: the minimum number of dissatisfied people is approximately 5 per cent. Figure 4 shows the ideal operative temperature (plain lines) as a function of clothing and activity at which there will be only 5 per cent dissatisfied individuals. This figure is valid for low air velocities and acceptable relative humidity. Shaded and white areas are tolerance domains, in which the percentage of dissatisfied individuals will be less than 10 per cent.

Activity [met]

Activity [W/m²]

Clothing thermal resistance [m²K/W]

Clothing [clo]

Figure 4: Optimal operative temperatures for various clothing and activities [22] For example, a sitting person wearing a lounge suit would prefer, on average, an operative temperature of 22°C ± 2°C. If this person is more active – for example, when giving a lecture, a temperature of 18°C ± 3°C is preferred. This is why a temperature of about 20°C is preferred in schools and offices. A sitting person wearing shorts and a light shirt will prefer 26°C ± 1.5°C, while an average person naked and at rest is comfortable, on average, at 28°C ± 1°C. 26


The Fanger equation is valid within the following domain: • only in premises that are heated or cooled • metabolism from 46 to 232 watt per square meter body area.[W/m2] (0.8 to 4 [met]); • clothing from 0 to 2 [clo] (or clothing thermal resistance from 0 to 0.310 [m2K/W]); • air temperature between 10 and 30°C; • mean radiant temperature from 10 to 40°C; • relative air velocity less than 1 m/s; • water vapour partial pressure between 0 and 2700 [Pa]. The practical consequence for administrative buildings and dwellings, where the activity is close to 1.1 met, is that acceptable operative temperature in cold climates, where people are fully dressed (about 1 clo) is between 20.5 and 24.5°C, while in warm climates, with lighter clothing, the acceptable operative temperature is between 22 and 27°C. These consequences are reported in Figure 2. 3.1.2.2 Effects of thermal gradients The operative temperature is an average. Even if it is optimal, temperature gradients may induce discomfort [23]. Radiant temperature asymmetry is the difference in mean radiant temperature between the two sides of a small, plane surface, each face seeing one half of the surrounding space. Note that the warm ceiling is clearly less appealing than the cold one and that warm walls are more comfortable than cold ones (Figure 5).

Figure 5: Effect of radiant temperature asymmetry at optimal operative temperature. (adapted from [24, 25]) Even at optimal operative temperature, a temperature difference of 4K between head and ankles is uncomfortable for 10 per cent of office workers (Figure 6). This is of particular importance when applying displacement ventilation for cooling, where the cold air falls down in a cold air layer close to the ground.

27


Figure 6: Effect of a temperature difference between head and ankle. (adapted from [23]) 3.1.2.3 Draught risk The percentage of people complaining of draughts depends upon the air temperature, air velocity and turbulence intensity. Because of turbulence, air velocity at a given place varies with time. If vi are several successive measurements of the air velocity, the mean velocity and its standard deviation are: N

v=

∑ vi i =1

N

σ=

and

N

∑ (v i =1

− v)

2

i

3

N −1

The turbulence intensity is the ratio σ/v. The percentage of dissatisfied persons, PD, can be calculated from the empirical relationship published by [23]:

 0   PD=max − 0 . 05 v  

0, 6223

(3.143 + 36.96 ⋅ σ ) ⋅ (34 − θ a )

4

where θa is the air temperature. From this, one can deduce the minimum temperature needed to limit the percentage of dissatisfied persons:

θ a ,min =34 −

PD  0   max  v − 0,05 

0, 6223

5

(3,143 + 36,96 ⋅ σ ) ⋅

This relationship is illustrated in Figure 7, calculated for 10 per cent of dissatisfied individuals. Note that turbulence intensity in most rooms is around 0,5. At comfortable temperatures, air velocity should therefore not exceed 0.15 metres per second. Most mechanical ventilation systems are designed to fulfil this condition. In naturally ventilated buildings, the occupants generally monitor the openings in order to avoid uncomfortable draughts. In warm environments, however, it is recommended that the air velocity is increased by using fans or large openings.

28


Figure 7: Air velocities at which 10 per cent of people complain of draughts for various temperatures and turbulence intensities. Turbulence intensity is most often at about 0,5. 3.1.3 Thermal comfort criteria in naturally ventilated and not conditioned premises 3.1.3.1 Experiments The comfort model standardised in ISO 7730 is based on measurements in conditioned climatic chambers, and in a steady state, regarding occupants as passively reacting to thermal stimuli. Everyday experience, however, shows that the ideal temperature is not a constant. It depends upon the activity and clothing of the occupants and should therefore vary according to these parameters. Occupants change the indoor climate to suit their preferences and vice versa, and adapt themselves to the ambient temperature by changing their clothing or adapting their activity. For example, at high temperatures, draughts reduce the perceived temperature, by increasing the evaporation and the convective heat transfer from the skin to the air. Figure 8 shows the relationship between the reduction of perceived temperature and air velocity for various differences between radiant and air temperatures. Note that, except when surfaces are especially heated or cooled, the mean radiant temperature in a room is close to the air temperature.

Figure 8: Air velocities required to offset increased temperature. The various curves correspond to various differences between radiant and air temperatures. Source [22] In addition, occupants accept larger temperature variation in some environments than in others. Within the frame of the ASHRAE research project 884, comfort data from 160 buildings 29


all over the world were compiled. De Dear and Brager [5] have split these buildings into two types: naturally ventilated and air-conditioned buildings. In air-conditioned buildings, perceived comfort temperature fits rather well with the PMV calculated according to ISO 7730 if the clothing is adapted to outdoor temperature [2] (Figure 9: a). Air conditionned

Natural ventilation 27

Observed Predicted Adjusted

26 25

Indoor temperature [°C] .

Indoor temperature [°C] .

27

24 23 22 21 20

Observed Predicted Adjusted

26 25 24 23 22 21 20

-5

0

5 10 15 20 25 30 35 Outdoor temperature [°C]

-5

0

(a)

5 10 15 20 25 30 35 Outdoor temperature [°C]

(b)

Figure 9: (a) Observed and predicted indoor comfort temperatures from ASHRAE RP-884 database for air-conditioned buildings (b) Observed and predicted indoor comfort temperatures from RP-884 database for naturally ventilated buildings[5]. 3.1.3.2 Adaptative comfort models Taking account that clothing is lighter when outdoor air is warm; the ISO 7730 model gives an optimal operative temperature that can be summarised by the following equation: θc = 0.12 θo,m + 21.6

6

where θo,m is the monthly mean outdoor air temperature. This equation is illustrated by the red line in (Figure 9: b). In naturally ventilated buildings however, ISO 7730 does not predict the comfort temperature correctly. Indeed occupants adapt themselves using means - such as fans (see Figure 8), adapting clothing and activity, cold drinks, etc. - not taken into account in the EN-ISO 7730 model (Figure 9: b). De Dear and Brager [5] proposed the following model for the ideal comfort temperature θc in free running buildings: θc = 0.310 θo,m + 17.8

7

McCartney and Nichol [26] arrive at similar conclusions from experiments in European buildings. For hot-humid climates, they proposed the following models for the ideal comfort temperature Tc: For free running buildings: For air-.conditioned buildings:

θc = 0.534 θo,m + 12.9[27]

8

θc=0.16 θo,m + 18.6 [28]

9

30


Figure 10: Ideal operative indoor temperature versus mean outdoor temperature according to various models proposed in the literature for hot humid climates. Note that the mean outdoor temperature is not the same for all models: monthly mean for the Nicol models, daily mean for the ISO 7730 model and running mean for the EN 15215 model. These adaptive comfort models were developed, discussed and finalised in the European standard EN 15251[29, 30]: 𝜃𝑜𝑝 = 18.8 + 0.33 𝜃𝑟𝑚

10

𝜃𝑟𝑚 (𝑑 ) = 𝑎 ∙ 𝜃𝑟𝑚 (𝑑 − 1) + (1 − 𝑎)𝜃𝑑

11

where θop is the internal operative temperature and θrm is the outdoor running mean temperature. This temperature is calculated, for a given day d, from the daily mean temperature θd of the preceding days as follows: The reason of this running mean is that the perceived temperature is influenced by those of the former days. The interval is ±2 K for 90 per cent acceptance and ±3 K for 85 per cent. 3.1.3.3 Proposed comfort models If the calculation of the running mean temperature according to EN 15215 is found too complex, a good approximation is the running mean θ48 over 2 days or 48 hours. If this running mean temperature is taken, the model should be slightly modified: 𝜃𝑜𝑝 = 18.1 + 0.32 𝜃48 12 It is this model, with modified lower limit adapted to very low and very high temperatures, which is used in the Swiss standard and proposed in Figure 1. Note that in his study[3], M. Baruti proposes to use the Nicol models, i.e. equations 7 and 8. However, these models require lower temperatures than the EN 15215 modified (equation 11) and ISO 7730 (adapted for clothing, equation) models. Therefore, in order to save energy in hot climate, we propose to use these latter models. The adaptive comfort model not only provides design rules for better comfort in naturally ventilated buildings, but also allows substantial energy savings, especially in hot climates.

31


3.1.4 Air quality criteria We spend a large part of our life indoors, and most of the air we breathe is indoor air. Therefore, this air should not contain unhealthy substances, or if there are some, their concentration should remain harmless. According to Olesen et al. [31], "A value judgement of indoor air quality can be given in several ways. One can make a classification (for example yes/no), as used in ASHRAE 62-1989 [32](whether the air is acceptable or not), resulting in a percentage of dissatisfied, or one can use a list of descriptors to describe a chemical substance". Looking at toxic substances, the acceptable concentration depends on their effect on health. The effects of some substances, for example carbon monoxide or dioxide, are recovered by the metabolism up to a given threshold, and not above this threshold. For these substances, it is therefore straightforward to take the recovery threshold as limit concentration. For other contaminants, for example radon, the health risk is growing with the concentration and is zero only at zero concentration, a concentration that nowhere occurs. For these substances, giving an acceptable limit concentration means that some risk is accepted. These limit concentration should therefore be determined by local authorities, taking account of acceptable health risks. Indoor air guide values for individual substances are developed by several authorities, and various values could be found in the literature. Since most building host not only healthy adults but also children and elderly people that are more sensitive to toxic substance, we present here low or precautionary values. These can also be considered as target values during rehabilitation efforts. These precautionary guide values represent the concentration of a substance in indoor air for which, when considered individually, there is currently no evidence that even life-long exposure is expected to cause any adverse health impacts. Higher concentrations are deemed to constitute an exposure that is higher than normal and therefore undesirable. The guide values apply to individual substances and provide no indication of any possible combined effects with different substances. Table 15: Precautionary guide values for some compounds

Contaminant

OFSP 23

Radon 400 Nitrogen dioxyde Sulfur dioxyde (24 h) Formaldehyde 125 Carbon monoxyde (8 h) Ozone Bacteria Thermoactinomycetes Mould Asbestos 1000 PM 2.5 (particulate matter < 2,5 μ) PM 10 (particulate matter < 10 μ) 1,2,4-Triméthylbenzol

Recommended guide concentration VDI WHO WHO 24 200703 2000 [33] 2011 [34] 100 40 40 20 100 60 7000 100 190 0 120

UWB DE 25 60

1500

10 20 100

23

OFSP: Swiss federal office of public health World Health Organisation 25 http://www.umweltbundesamt.de/gesundheit/innenraumhygiene/richtwerte-irluft.htm 26 CFU: Colony forming unit 27 BAF : breathable asbestos fibres 24

32

Unit Bq/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ CFU 26/m³ CFU/m³ CFU/m³ BAF 27/m³ μg/m³ μg/m³ μg/m³


Contaminant 1,5-Pentanedial 1-Butanol 1-Methoxy-2-propanol 2-(1-Methoxy)-propylacetate 2-(2-Butoxyethoxy)-ethanol 2-Butanone 2-Butanone oxime 2-Butoxyethanol 2-Ethyl-1-hexanol 2-Furaldehyde 2-Phenoxyethanol 3-/4-Ethyltoluol 3-Carene 3-Methyl-butanal Acetaldehyde Aldehydes, C4 to C11 Alkanes / Isoalkanes, C9 to C14 Alkylbenzols, C9-C15 Benzaldehyde Benzene Benzylalcool Polychlorated Biphenyle PCB Butanal Butenal Cresols Dichloromethane Dimethylsiloxanes cyclic D3-D6 Esters Ether Ethylacetate Ethylbenzol Glycols and derivates Hexanal Hydrocarbons, aliphatic Hydrocarbons, aromatic Hydrocarbons, chlorated Mercury (vapour in air) Methylisobutylketone Monoterpenes monocyclic Naphthaline n-Butylacetate n-Decane n-Dodecane n-Undecane o-Xylol Pentachlorphenol (PCP) Pentanal Phenol Propanal Propenal Siloxane Styrol Terpenes

OFSP 23

Recommended guide concentration VDI WHO 24 WHO UWB 200703 2000 [33] 2011 DE 25 [34] 20 200 200 200 200 200 100 200 200 10 150 300 50 20 200 100 200 100 50 20 0 5 400

2 10 5 5 200 400 300 300 200 300 300 60 500 500 10 200 10

5 200 200 200 200 300

200

0.035 100 1000 2

0.1 20 20 20 5 500 300

33

30 200

Unit μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³


Contaminant

OFSP 23

Tetrachlorethylene Toluol Trichlorethylene Tris(2-chlorethyl)phosphate (TCEP) Xylol α-Pinene

Recommended guide concentration VDI WHO 24 WHO UWB 200703 2000 [33] 2011 DE 25 [34] 0 5 300 250 5 300 200

Unit μg/m³ μg/m³ μg/m³ μg/m³ μg/m³ μg/m³

3.1.5 2.7Visual comfort criteria Light is necessary for human activities and well-being. It not only allows vision but controls the internal biological clock as well as several essential body functions. To ensure a good vision, the illuminance level should be adapted to each task [35]. Further, the colours in the environment, of objects and of the human skin, are rendered naturally, correctly and in a way that makes people look attractive and healthy. The colour temperature should be adapted to the illuminance and to the room colours, e.g. strong illuminance asks for high colour temperatures and low illuminance for low colour temperatures. Finally, the luminance contrasts should not be too large in the field of view. These requirements can be achieved by either daylight or artificial light. More information is given below. 3.1.5.1 Photometric units All measurement related to lighting are based on the spectral sensitivity of the human eye, which is illustrated on this diagram for daylight (photopic luminosity function, both cones and rod cells in retina are active) and at low illuminance (scotopic luminousity function), when only rods are active.

Figure 11: Sensitivity of the human eye for various wavelength. 1 nm (nanometer) = 10-9 m The luminous flux or luminous power is the measure of the perceived power of light. It is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light. The SI unit of luminous flux is the lumen (lm). One lumen is defined as the luminous flux of light produced by a light source that emits one candela of luminous intensity over a solid angle of one steradian. In other systems of units, luminous flux may have units of power. 34


The total emitted power, without wavelength weighting, is the radiant flux in Watt. The ratio of the total luminous flux to the radiant flux is the luminous efficacy. For example, a tungsten filament light bulb using 100 W of electric energy emits 1200 lm of light, but radiates close to 100 W of light and infrared radiation. A fluorescent tube using only 36 Watt emits 2400 lm, that is twice as much. It is then much more efficient. Illuminance is the total luminous flux incident on a surface, per unit area. It is measured in lux (lx) in the SI units system. The human eye is capable of seeing within a 2 trillion-fold range: The presence of white objects is somewhat discernible under starlight, at 10−4 lux, and clearly visible at moonlight (0,3 lx), while at the bright end, it is possible to read large text at 108 lux, or about 1,000 times that of direct sunlight, although this can be very uncomfortable and cause long-lasting afterimages. The luminous intensity is the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle. The SI unit of luminous intensity is the candela (cd). By definition, a light source that emits monochromatic green light with a frequency of 540 THz (555 nm wavelength), and that has a radiant intensity of 1/683 watts per steradian in a given direction emits one candela in the specified direction The luminance is the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square metre (cd/m2) or nit. Luminous intensity is obtained by dividing the luminous flux per the solid angle in a given direction. Illuminance is obtained by dividing the luminous flux per the illuminated area Luminance is the luminous intensity emitted by a unit area.

Per unit area

Φ [lm]

Illuminance E [lx]

Per solid angle

Intensity I [cd] Per unit area

Flux

In short:

Luminance L [cd/m²]

3.1.5.2 Visual comfort conditions Visual comfort requires •An illuminance adapted to the activity •Limited luminance contrasts in the visual field •Correct colour rendering Illuminance should be adapted to activity. While a low level is easily accepted in passageways, very high levels could be required for delicate work such as surgery or fine mechanics. These illuminance levels are generally recommended in the literature. Requirements

Lux

Examples

Low

20-70

Staircase, passageway

Moderate

120-185

Lobby, restaurants

Average

250-375

Common activities

High

500-1000

Reading, writing

Very high

> 1000

Fine work, surgery

35


3.1.5.3 Colour rendering The light received by the eye from an illuminated object is, for each wavelength or colour, the part of the light coming from the illuminating source reflected by the object. If the light source has a single colour (or a very narrow spectrum), this colour will be reflected by the object only if that object has the same colour on it. A red object illuminated by a sodium lamp (yellow light) will look black or slightly yellow. The eye is chromatic, it does not focalise blue and red light at the same depth. If the spectrum is continuous (like the spectrum of the sun or of a tungsten light bulb) the brain gives orders to focus on an average image. It the light has two colours only, like the one shown on the figure, or the poor quality fluorescent tubes, the eye focuses alternatively on both blue and red images and get quickly tired. Therefore, the light sources should include, preferably at the same intensity, all wavelength of the visible spectrum, from 340 to 750 nm. 3.1.5.4 Colour temperature A black body is a surface absorbing all the electromagnetic radiation that falls onto it. This body will also emit all the electromagnetic radiation corresponding to its temperature, or to the random movement of its atoms. A good physical model of such a body is a hole in a piece of isothermal matter. Planck has modelled such a body and given its theoretical spectrum illustrated on Figure 12. The maximum is emitted at a wavelength that is inversely proportional to the absolute temperature (Wien’s law), and the significant part of the spectrum is between ¼ and 4 times this wavelength. If the temperature is high enough to emit visible light, the colour will be reddish at relatively low temperature, then white (all wavelength having a similar intensity) and finally bluish at high temperatures. Colour temperature is the absolute temperature of an ideal black body at which the colour of the light source and the black body are identical.

Figure 12: Black body spectrum for various temperatures Reddish and yellowish colours (“warm” colours) have therefore a low temperature, less that 2000 K, while bluish sources (“cold” light) has a high colour temperature.

36


For optimal comfort, the colour temperature of the source should be adapted to the illuminance level as illustrated in Figure 13. The highest the illuminance level, the highest the colour temperature should be.

Figure 13: Adaptation of colour temperature to illuminance 3.1.5.5 Contrasts and glare Glare should of course be avoided. More precisely, the contrasts in the field of view should be limited. The luminance ratio between the brightest and darkest areas should not exceed 3 in the ergorama and 10 in the panorama. Note that the areas to be considered should have a significant area. The ergorama is a field of ±30° around the centre (the object looked at) and the panorama is a field of ±60° around the centre. When contrasts are too large in the visual field, glare occurs (Figure 14).

Glare

3

10

© Claude-A. Roulet, Apples, 2009

91

© Claude-A. Roulet, Apples, 2009

92

Figure 14: Panorama and ergorama. Left is an acceptable distribution of luminance, while an example of glare is given at right. 3.1.6 Acoustic comfort criteria In order to make possible a good acoustical comfort, important noise sources and, at the opposite, activities that require quietness, should be grouped in separate areas. The Swiss law on noise protection[36] defines four types of zones: 37


I.

areas which require greater protection against noise, especially in the areas of relaxation.

II.

areas where no noisy industry is allowed, especially in residential areas as well as in those dedicated to public buildings and facilities.

III.

areas where moderately noisy activities are allowed, especially in residential areas mixed with small-scale companies; as well as in agricultural areas;

IV.

areas where highly troublesome activities, particularly in industrial areas are allowed.

It is therefore recommended to fix the noise protection level in each zone delimited in the land use planning. Then the builders or owners of buildings in which the activity is too noisy for the zone where they are shall take noise control measure to respect the noise protection level. The acoustic comfort in a room is determined by the noise level in the room and by the room acoustics or acoustic ambience. The maximum acceptable noise level in the building depends on the activity: In rooms in dwellings (living rooms, bedrooms, kitchens): 30 to 40 dB(A) 28 Small offices and meeting rooms: 30 to 40 dB(A) Large offices to open, busy offices: 40 to 60 dB(A) Hand work (e.g. in factory buildings): 80 dB(A) Permanent damage to the hearing system occurs above 85 dB(A). These limits can be respected first by reducing the intensity of the noise sources, and second by acoustic insulation. A measure of the room acoustics is the reverberation time, i.e. the time required for the sound level to be reduced by 60 dB after having switched off the noise source. The optimal reverberation time depends on the size of the room and its use: Table 16: Optimal reverberation times for various spaces. Reverberation times are for empty rooms. Values of 0,5 second are for furnished rooms. In rooms in dwellings (living rooms, bedrooms, kitchens) Offices Large offices to open, busy offices Meeting rooms Hand work (e.g. in factory buildings up to 50 m2) Large rooms (more than 50 m2) for hand work

3.2 E NERG Y

0,5 second 0,6 to 0,8 second 0,5 to 0,7 second 0,7 to 0,9 second 0,5 to 0,8 second 1,0 to 1,5 seconds

EFFICIE NT BUILD ING DESIG N

3.2.1 Energy needs in buildings In buildings, energy is required, among others, for purposes given in Table 17. This table also proposes known ways to save energy, and presents some effects of these energy saving measures on comfort or indoor environment quality. It can readily be seen that there are many cases where energy conservation opportunities (ECO's), when well planned and executed, improve the indoor environment quality. Table 17: Functions of the building requiring energy, together with some ways to save energy and effects of these energy saving measures on comfort.

28

Lower levels for night time activities and sources, such as concert halls and cinemas.

38


Energy required for Compensation of transmission heat losses or gains Compensation of convective (ventilation) heat loss and gains Heating in cold climates

Elimination of excessive heat gains (cooling) Internal temperature control De-humidification Lighting

Cooking

Ways to save energy Better, thicker insulation, low emissivity-coated multiple glazing. Limit the ventilation rate to the required level Use heat recovery on exhaust air.

Impact on indoor environment Improves thermal comfort Improves health by preventing mould growth. Less drafts, less noise, good IAQ

Generally improves IAQ in winter. Improve solar gains with large, Over-heating if poor solar protecwell oriented, good windows. tions. Improve the use of gains by better If well planned: good visual coninsulation and good thermal iner- tact outdoors, excellent summer tia. and winter comfort. Use passive cooling Very comfortable in appropriate climates and buildings. Use efficient, well commissioned Better IAQ and comfort and maintained systems Higher internal temperature Should be within comfort limits. Comfortable set-point temperaAvoids over- and under-heating ture, improved control Use only when needed No effect in many cases. Use daylighting Comfortable light, with limited heat gains when well controlled. Use efficient artificial lighting. Comfort depends on the quality of light. Limited heat gains. Use solar cookers Cooking outdoors, sunny hours only! Use efficient combustion stoves Improves indoor air quality Use induction electric cookers Reduces heat load

3.2.2 Design principles for comfortable and energy efficient buildings. The building is (or at least should be) designed and constructed first to bring a good indoor environment to its occupants. There could be other objectives, such as: prestige, image, low cost, energy saving, real estate business, speculation; but indoor environment should have the highest priority. Indeed, sustainable development requires that high quality buildings should be designed, built and maintained taking account of environmental, economical, and social stakes. Healthy, comfortable and energy efficient buildings are the result of a conscious design keeping constantly these three objectives in mind. Basic recommendation that could be given to reach these objectives are: • Wherever possible, prefer passive methods to active ones • Think about the user comfort, needs and behaviour • Adapt the building to its environment

39


3.2.3 Passive and active means to get high quality (HQ) buildings Passive means are architectural and constructive measures that naturally provide a better indoor environment quality at very low, or even no energy cost. Examples are: • improving winter thermal comfort with thermal insulation, passive solar gains (see 3.3.1), thermal inertia, and controlled natural ventilation (see 3.7.2); • improving summer thermal comfort with thermal insulation, solar protections, thermal inertia, and appropriate natural ventilation (see 3.5); • ensuring indoor air quality by using low-emitting materials and controlled natural ventilation (see 3.1.2); • providing controlled day-lighting (see 3.8.1); • protecting from outdoor noise with acoustical insulation, adjusting the reverberation time for a comfortable indoor acoustics (see 3.9). Passive means are often cheap, use very few or no energy29, and are much less susceptible to break down than active means. However, they often depend on meteorological conditions and therefore cannot always fulfil the objectives. They should be adapted to the location and therefore need creativity and additional studies, in particular an interdisciplinary planning early in the project. Also a design error may have dramatic consequences. Active (or technological) means allow reaching the objectives by mechanical actions, using energy. Examples are: heating boilers and radiators for winter comfort; artificial cooling by air conditioning or radiant panels for summer comfort; mechanical ventilation, and artificial lighting. Active means, when appropriately designed, built and maintained, are perfectly adapted to the needs. These are designed and applied by specialized engineers according to well-known technology. Flexible and relatively independent on meteorological conditions, they allow correcting architectural errors. However, the required technology is often expensive, uses much energy and may break down. Furthermore active means require a higher maintenance input. The fact that they allow correcting architectural ‘errors’ can also be considered as a disadvantage…. Table 18 summarizes the pros and cons of both ways. It clearly shows that passive and active ways are complementary: the disadvantages of one are compensated by the advantages of the other and vice-versa. Passive ways are however preferred because of their low cost and good energy performance, but cannot always fulfil the comfort objectives. Therefore, the appropriate strategy is to use them as much as reasonably possible and to compensate for their insufficiencies with active systems, which will then be smaller and cheaper. Table 18: Advantages and disadvantages of passive and active ways to ensure a good indoor environment. Passive ways Cheap No energy Don’t break down Need careful design Difficult to control

Active ways Expensive Use energy May break down Easy to design Easy to control

29

Here, energy is the energy bought from the market. Passive means indeed use free energy, such as solar radiation for heating and heat of the air or the ground for cooling. The energy that is used during the manufacturing process (grey energy) is not in the focus here.

40


3.2.4 Adaptation to the Environment The outdoor environmental characteristics (temperature, solar radiation, wind, dust, pollution, noise, etc.) change with the location of the building and with time. Therefore, a design that is well adapted in a place may be completely unsuitable to another one: Bedouin tents, igloos, tropical huts, all well adapted to their environment, cannot be used elsewhere. This is also valid for contemporary building design: it is of course possible to compensate for environmental changes using active techniques, but this often decreases the indoor environment quality and increases the energy use. Adaptation of the building to the environment includes the following: • Adaptation to climate using appropriate thermal insulation, thermal inertia, solar protections and openings for light and ventilation. An appropriate building design should ensure that the building be at least as comfortable as the external environment, without any heating or cooling (i.e. free-running). In many cases, it is easy to do better by passive means. • Adaptation to noise: Improve acoustical insulation in noisy areas, for example by using a double skin or sound-proof windows, and installing mechanical ventilation with sound barriers. • Adaptation to pollution: Locate air intake as far as possible from pollution sources, install mechanical ventilation with appropriate filters and ensure appropriate maintenance. Nevertheless, it should be mentioned that clothing is the most natural first step for temperature control. During the HOPE survey[37], a building management has justified air conditioning because full casual dress was mandatory in the company. This should no more be the case, since allowing clothing adaptation in buildings certainly improves comfort and saves much energy! 3.2.5 Building orientation 3.2.5.1 Orientation with respect to winds The main facades should be oriented taking account of the sun path, the prevailing winds, the slope of the ground and external obstacles. If the winds are strong, the building and its occupied surroundings should be protected. If they are weak, placing the ventilation openings upwind and downwind improves the natural ventilation. The wind can be very disturbing when it is strong, and in this case the buildings are oriented so as to provide sheltered spaces. Although it is currently possible to overcome this constraint by building sufficiently airtight facades and windows and by using controlled ventilation openings, it remains recommended to shelter facades with many windows, or to reduce the number of openings on the facades very exposed to strong winds. The impact of wind on a facade can be reduced by plantations (trees, hedges) or embankments, or adapting the shape of the building (Figure 15).

Figure 15 : Protection against wind for an isolated building.

41


The arrangement of neighboring buildings also has its importance. These can protect each other or instead create corridors in which wind accelerates (Figure 16). The siting of buildings should not create an uncomfortable environment for pedestrians, in terms of wind speed.

Figure 16 : Effets possibles de l'implantation des bâtiments sur le vent local. Some orientations are exposed to driving rain, blown by the wind. These facades must be particularly well protected; the walls with a thick plaster or cladding; and openings by overhangs and an appropriate tin ware. 3.2.5.2 Orientation with respect to the sun. In cold and temperate climate, the living and working rooms are exposed as much as possible to the Sun, which contributes to their heating and lighting. In hot climates, these should be protected against solar radiation canopies, awnings, or plantations providing shade. In the tropics, the South and North facades are almost not exposed to the Sun and the solar protection of these facades is much easier and more efficient than for the East or West facades that are hit by the direct sun in the morning or afternoon.

Figure 17: Direct and diffuse radiation. Radiation coming directly from the Sun is partly diffused in the atmosphere by the molecules of the air - which gives the blue sky when it is clear - and by ice crystals or water droplets of the clouds. The solar radiation can be schematically divided into direct radiation, coming in straight line from the Sun, and diffuse radiation coming from all other directions. The intensi42


ty of the global solar radiation is the sum of these two components. The energy contained in the diffuse radiation is important, especially when the sky is hazy, for both solar energy systems and protection against overheating. In the tropics, diffuse radiation is, on average, as important as direct radiation. Thus, a obstacle covering the totality of solar radiation will protect better against solar radiation than one that only obscures the solar disk. 3.2.6 Taking account of the user The occupant of a building expects that the building provides an acceptable indoor environment, according to his wishes. The occupant likes to have a control on this environment and even needs such a control to adapt it to his needs. The HOPE survey has shown that the control an occupant has over his environment not only improves his perceived comfort, but is also linked in some way with his well being [38, 39]. Therefore, the building design as well as the system must take into account the user's needs and wishes, and allow the user to adapt its environmental conditions to his needs as much as possible. Where the environment cannot be modified by accessible means, the occupant finds another way: bringing in heaters, opening the window in winter instead of putting the (nonexistent) thermostat down, using tape or paper to close draughty ventilation openings, etc.

3.3 B UILD ING E N VEL OPE 3.3.1 Thermal insulation A good thermal insulation not only reduces heating and cooling energy use, but also improves comfort by reducing the unpleasant effects of cold or warm surfaces and allowing a better control on the indoor temperature. In temperate and hot climates, where buildings require essentially cooling, a good thermal insulation reduces the heat gains from outdoor air and solar radiation. It should be combined, wherever possible, with passive cooling to evacuate internal heat gains. The thermal insulation of a building is characterised by its transmission heat loss coefficient HT, which is the power needed to compensate the heat losses by transmission through the building envelope and maintain 1 Kelvin temperature difference between indoor and outdoor environment. This parameter can be calculated from the detailed drawings according to the ISO 13789 standard [40]. Any building has some thermal insulation that protects the occupants from the outdoor environment. One measure to improve energy efficiency is to reduce the global heat transmission coefficient. For this, all building envelope components should be improved. One or more layers of thermal insulating materials are added to walls, roof, and doors; and windows are equipped with insulating glazing and frames. Note that some material used in vernacular architecture, like adobe and straw have remarkable thermal properties and contribute to the thermal insulation of buildings. The parameter that characterises the thermal insulation of a building envelope component is its thermal transmittance U, also named U-value. It is the density of heat flow rate, in W/m², that flows through one square meter of the element when the temperature difference between both sides is 1 Kelvin. For opaque elements, this parameter can be calculated from the dimensions and materials used in the component according to the ISO 6946 standard [41]. For windows, doors and shutters, the calculation method is described in ISO 10077 [9]. The U-value characterises the building envelope component in steady state, i.e. under a constant temperature difference. However, the outdoor temperature and over all the solar radiation changes with time, the main period being the daily variations. In particular, the roof is well exposed the solar radiation and its surface temperature may rise over 70°C. 43


To protect the occupants of under-roof spaces, it is important that these variations are not reflected in temperature variations inside. The parameter characterising this phenomenon is the periodic thermal transmittance for a period of 24 hours, which can be calculated using the method described in the ISO 13786 standard [11]. This figure gives the temperature variations inside resulting from a variation of heat flow rate outside. Note that the periodic thermal transmittance is always smaller (i.e. better) than the U-value. Some software for personal computers10 allows computing these parameters. Some examples of appropriate roofs are given in Table 19. As a general rule, a light roof requires more isolation (e.g. 20 cm of typical insulation material) while 5 cm is enough on a heavy roof Table 19: Examples of roof structures that protect the occupants from excessive temperature variations resulting from solar radiation on the roof. Thermal transmittance W/m²K Static Dynamic Concrete deck, external thermal insulation 5cm thick or more Steel sheet roof, thermal insulation 20cm thick or more Roof of tiles or metal sheet, 6 cm thick insulation between rafters, panelled or plastered ceiling

< 0.92

< 0.19

< 0.30

< 0.18

< 0.54

< 0.20

3.3.2 Solar Protections Passive solar gains can be useful to improve comfort at low cost in cold climates, but may be uncomfortable when poorly controlled, especially in mid- or hot climates. I was observed through surveys that buildings with solar protections have a better perceived thermal comfort and temperature stability than those without solar protections[39].

Inside protection: radiation absorbed by the protection heats the internal environment

Outside protection: the radiation absorbed by the protection is evacuated into the air and is not transmitted to the internal environment.

Figure 18: Sunscreens must be outdoors to protect from heat.

44


Good solar protections are external, since only these can significantly reduce the gains to avoid overheating. Indeed, a large part of the solar radiation is absorbed in the protection and increases its temperature. If this protection is outdoors, this heat is released to outdoor air and does not enter the building. If the solar protection is inside, this heat is delivered to indoor air, thus heating the building. Internal solar shading shadings are however preferred in winter, since they avoid glare but allow solar heat gains. In the tropics, overhangs may be used on North and South facades to protect the windows against direct solar rays. For this, their length should be about half the height from the bottom of the window. There are no fixed solar protections for East and West, where direct rays are more or less perpendicular to the windows during a part of the day. In fact, fixed solar protections and sun reflective glazing are not ideal, since they don't allow any control: they either are not sufficient on some sunny days, or reduce daylight on overcast days. Note that the sun is the most efficient light source: only 1 W/m² heating load for 100 lux. There is no artificial light source on the market having a lower heat load for the same illuminance than the sun 30 and that can be used in buildings. Daylight changes naturally as well as solar radiation, and these are sometime very useful (passive solar gains, day-lighting) and sometime uncomfortable (glare, too hot). Therefore, solar protections shall be moveable to control the solar radiation entering the building. An automatic control with possibility for individual override is preferred. Use wind proof external solar protection.

3.4 A VOID ING

T HE USE OF ENERGY FOR HE AT ING

3.4.1 Principle Except at very high altitudes, the outdoor temperature is not cold enough to need heating in the premises, provided that the building is designed and built to protect its occupants from cold nights. Therefore, the building code could require that the buildings are designed and built in such a way that heating is not necessary. Such a requirement is very easy for most climates in Tanzania, but may be more difficult in parts of the country that have a colder climate, for example in the mountains. In these cold conditions, a minimum of thermal insulation and the use of passive solar heating allow to avoid heating while ensuring a comfortable indoor temperature. 3.4.2 Passive Solar Heating Solar energy enters freely in the building, mainly through the windows, thus contributing to heat the building. The following conditions should be met to take the best profit of these gains during the cold season without being overheated (Figure 20): 1. The spaces used during the day should be located on the sunny side of the building. Buffer zones (corridor, staircase, garage, etc.) may be on the shaded side of the building. 2. The heated zone must be well insulated, to avoid excessive heat losses. 3. It should have large collecting areas on the sunny side of the building (from south-east to south-west in Northern hemisphere). Collecting areas are mostly windows, but can also be sunspaces or walls with transparent insulation. 4. These windows and other collecting areas must be equipped with mobile, solar protections, in order to control the gains.

30

Some light emitting diodes reach that performance.

45


5. A large thermal mass (heavy construction) allows to store heat, thus avoiding overheating during sunny day and maintaining a mild indoor climate during the night. A massive building fabric, in direct contact with the internal environment, provides at best this thermal mass. 6. The heating control should switch of the heating system as soon as solar gains suffice to keep a comfortable internal temperature, and switch it on as soon as necessary.

6 2

4 1 5

3

Figure 19: Design for passive solar heating: 1) spaces used the day on sunny side; 2) Efficient thermal insulation; 3) Large windows or sunspaces on sunny side, 4) with efficient, mobile and external solar protections; 5) massive structure bringing a large thermal mass and 6) adapted heating system with efficient control. 3.4.3 Example For example, we simulated a room 5 m wide, 4 m depth and 3 m high, without heating, oriented to the South, located between identical premises on the other sides. The South façade is equipped with two large single-glazed windows, totalising 6 m². A room with two exposed facades, South and West, both with windows, was also simulated (Figure 21). The construction is made in masonry with concrete slabs. Three levels of thermal insulation were simulated: 1) No specific thermal insulation, single pane windows. 2) 5 cm thick external thermal insulation and double pane glazing 3) 10 cm thick external thermal insulation, high performance insulating glazing The outdoor climate used for this simulation is the coldest we found, i.e. Arusha.

Figure 20: 3-D views of the simulated rooms. Left with south façade only, right with South and West facades. 46


The computations were performed with the Dial+ software, which uses the building model algorithms described in the ISO 13790 standard, annex C [16]. For the simulations, solar protections were used when the solar irradiance on the window is larger than 90 W/m², except when the indoor temperature is below 22 °C. Windows are open during occupancy when the indoor temperature is too hot. Internal solar heat gains (persons, appliances) totalize daily 160 Wh/m² floor area. Airflow rate is 51 m³/h when occupied and 6 m³/h when unoccupied. Results for the room with south façade only are illustrated in Figure 23 and Figure 23; and all results are summarized in Table 20.

Figure 21: Operative temperature inside a local with south windows only, versus 48 h running mean outdoor temperature, in Arusha. The comfort zone is in grey. Left: outdoor hourly temperature. Right: Building without thermal insulation, single pane windows. While outdoor air is often too cold, the number of uncomfortable hours is already strongly reduced in the room with no specific thermal insulation and single pane glazing.

Figure 22: Operative temperature inside a local with south windows only, versus 48 h running mean outdoor temperature, in Arusha. The comfort zone is in grey. Left: 5 cm outside 47


thermal insulation, double pane windows. Right: 10 cm outside thermal insulation, high quality insulating glazing. With a slightly improved design, including 5 cm thick outside thermal insulation and double pane glazing, the operative temperature is only 170 hours per year below the comfort zone, and never below 20 °C. Heating is obviously not necessary in Arusha, hence neither in warmer areas. Improving the thermal insulation (i.e. reducing the heat loss coefficient by a factor 2) does not bring much for south-(or north) oriented rooms. Table 20: Number of uncomfortable hours (i.e. outside the comfort domain shown on Figure 1), Number of hours when the relative humidity inside exceeds 75%, as well as maximum and minimum operative temperatures of outdoor air and for three difference designs of the south façade.

Outdoor air Only south win- 1) No insulation dows, with solar 2) Insulated facades protections 3) Well insulated facades 1) No insulation South and west windows, no solar 2) Insulated facades protections 3) Well insulated facades 1) No insulation South and west windows, with 2) Insulated facades solar protections 3) Well insulated facades

Number of hours Too hot Too cold >75% 49 6687 5755 0 784 496 0 0 169 0 1 118 1046 115 18 2126 0 1 3147 0 4 0 465 370 0 0 119 2 0 31

Operative temperature Max Min 29.6 6.2 26.6 17.7 26.6 20.1 26.9 20.0 30.9 18.7 31.7 22.2 32.2 22.4 26.3 18.3 27.0 20.4 28.2 21.5

Higher temperatures (or less cold hours) could be obtained with windows oriented East or West, but these shall be protected with moveable solar protection to control the solar heat gains, otherwise the premises are too often overheated. Such solar protections does not seem necessary on the South (and likely also North) facades. The best results are obtained with the room having also a west (or east) window (increasing the solar heat gains), with solar protection and an improved thermal insulation (last line in Table 20). For this room, the number of uncomfortable hours is negligible. Note that the room without thermal insulation has much more hours with too humid indoor air than the insulated versions. These occur mainly in May and June. The few too humid hours in insulated buildings will not increase too much the risk of mould growth. Both operative temperature and humidity of each hour are represented in Figure 24, together with the comfort limits proposed by Givoni. Each dot represents one hour, and all of them are within the comfort zone for naturally ventilated buildings. The well-insulated building is dryer than the one with minimum insulation.

48


Figure 23: Comfort diagram according to Givoni [42]. Left: room with south windows only and minimum thermal insulation. Right: South and west windows, solar protection and improved thermal insulation.

3.5 R ED UCING

T HE COOLIN G ENERG Y USE

3.5.1 Principle The building may be at risk of being too hot for various reasons: • • • •

Located in a warm climate Large glazed area without solar protection Neither passive nor active cooling Too large internal heat load

Expected comfort problems are transpiration, reduced performance and productivity, increase of human errors. The risk of reduced air quality (smells, humidity) also exists. A high perceived temperature decreases the perceived productivity [39]. Buildings that become hot because of poor design increase the cooling load or encourage mechanical cooling. It is now acknowledged that occupants of buildings without mechanical cooling are more tolerant than those in fully conditioned buildings. This means that both comfort and energy efficiency are improved if the building design avoids overheating where the climate allows it. 3.5.2 Passive cooling Passive cooling by night-time ventilation is a comfortable, cheap, and energy-efficient way to keep the indoor environment within a comfortable temperature range in most temperate climates. In well adapted buildings, it can ensure a comfortable indoor climate in summer without artificial cooling, provided that internal heat load is not too large.

49


Temperature (°C)

Day Ventilation

Night Ventilation

Ext. temp.. Date in August Figure 24: Temperatures in two identical office rooms. One is aired as usual, only during the day and shows large, often uncomfortable temperature swings. The other one is aired mainly at night and stays comfortable during office hours. Thin green line is outdoor temperature.

Figure 25 shows the evolution of internal and external temperatures in two identical office spaces (40 m3) of the LESO building 31, which are ventilated following two different strategies: a) the common strategy in office buildings, airing during the day but not at night; b) the passive cooling strategy with natural ventilation at night. It is easily seen that overheating is experienced nearly every day in case a) and never in case b). The office spaces have considerable thermal inertia and external solar blinds. The night ventilation rate corresponds to about 10 building air volumes per hour. One person occupies the office during 8 hours per day, often with a personal computer running. This experiment, along with many others, shows that summer comfort can be greatly improved at low cost using passive cooling. Principles of passive cooling are compatible with those of passive solar heating. As shown on Figure 26, they are: 1) Adequate climate: the daily average outdoor temperature should be within comfort limits, and the temperature swing between night and day should be large enough, at least 5 K. The air should not require drying to ensure comfort. In particular, passive cooling cannot be used in areas where the water vapour content of outdoor air exceeds that corresponding to 75% RH indoors for more than a week. 2) Good thermal insulation to avoid heat gains through the building envelope. 3) Large openings to ensure at least 5 (better 10) air changes par hour, one at the top of space to evacuate hot air. These openings should be safe enough to remain open at night. 4) Efficient solar protections to avoid solar gains (see 0) 5) High thermal mass to store the heat gains during the day with a reduced increase of the temperature. For this, the heavy building structure should be in direct contact with the indoor environment. These gains are evacuated with the air during the night 6) Reduced internal gains: install high energy efficient appliances, use day lighting and switch off any unused apparatus (see also 3.5.3).

31

The LESO building is a passive solar office building at the EPFL, the Swiss Federal Institute of Technology, Lausanne.

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7) Airing at night, not during the day! Cool the building structure with a large ventilation rate when the external temperature is lower than the internal temperature. Large ventilation rates are easily obtained by natural ventilation through windows and doors. 3

1

4 6 3

2 5

Figure 25: Requirements for an efficient passive cooling: 1) Adequate climate; 2) good thermal insulation; 3) large openings, one at the top of space; 4) efficient solar protections; 5) large thermal mass; 6) reduced internal gains; 7) airing night, not during the day! If passive cooling is not possible, mechanically driven night ventilation is an alternative that should be considered [43]. 3.5.3 Heat load Heat loads from solar radiation shall and can be reduced to the minimum compatible with day-lighting; that is to less that 5 W/m² during the day. Internal heat loads should be reduced to a minimum by using high energy efficient appliance and switching then off when not in use. Some heat loads however cannot be avoided: the occupants and used appliances generate heat. Each watt-hour electricity used in a room ends in heat. This heat is accumulated in the air and in the building mass, and increases their temperature. This temperature increase is smaller if the building mass is higher. When cooling (for example by passive cooling) the heat is evacuated outdoors through large air change and the building mass is cooled down, and will be ready to accumulated heat load the next day. Therefore, the important parameter is not the peak heating power, but the total heat load accumulated for 24 hours. For example, in a 20 m² office: Minimum solar load, 4 W/m² for 8 hours

640 Wh

2 persons i.e. 140 W sensible heat during 8 working hours 960 Wh 2 computers with screen, 200 W for 8 hours 1600 Wh Total 3200 Wh or 160 Wh/m² 3.5.4 Examples Simulations were performed for the mild and warm climates, with the same room with one facade than that described in section 3.4.3. The room is 5 m wide, 4 m depth and 3 m high, without heating, located between identical premises on the other sides. The façade is equipped with two large windows 2 m broad and 1,5 m high, totalising 6 m² (Figure 21 left) The construction is made in masonry with concrete slabs. 51


Five types of facades were simulated: 1) Not insulated: Hollow concrete blocks walls without specific thermal insulation, single pane windows. 2) Insulated: Same wall, with 5 cm thick added external thermal insulation and double pane clear glazing (U value 3 W/m²K) 3) Well insulated: Same wall, with 10 cm thick added external thermal insulation, high performance insulating clear glazing (U value 1.1 W/m²K) 4) Lightweight: Sandwich panel with 5 cm thick insulation inside, and double pane glazing. 5) Insulated lightweight: Same sandwich panel with 10 cm thick insulation, high performance insulating glazing. The windows are equipped with venetian blinds. When closed, only 15% of the solar energy enters in the room. In the simulations, these solar protections were either always open (no solar protection) or used adequately, i.e. closed when the solar irradiance on the window is larger than 90 W/m², except when the internal temperature is below 22 °C. The façade was oriented to south and west. Two simulations were performed with east orientation, which showed that east and west orientations are similar for thermal comfort and energy use, east being slightly better. Two natural ventilation strategies were simulated: a) As usual: Manual opening the windows during office hours, when the indoor temperature is higher than the outdoor temperature b) Passive cooling strategy: solar protections used adequately, together with day and night automatic opening of the windows when indoor temperature is above a comfortable temperature and higher than the outdoor temperature. When air conditioning is used, the installed power is 500 W, with 70% heat recovery. In some cases this power was not large enough, and we increased it to 1, or even 4 kW. 3.5.4.1 Dodoma Results are summarised in Table 21. These show that, if solar protections are used in a massive enough building, neither heating nor cooling are necessary in this climate, except in buildings where the internal heat load is too large.

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Strategy

Number of hours Façade type Too hot Too cold >75% Outdoor air 51 1903 2322 No insulation 1434 0 0 No solar Insulated facades 2377 0 0 prot. Well insulated facades 2106 0 0 With No insulation 0 0 19 solar Insulated facades 0 0 12 prot. Well insulated facades 0 0 269 No insulation 0 0 269 Insulated facades 0 0 312 Well insulated facades 0 0 270 No insulation 0 0 344 Insulated facades 0 0 392 Well insulated facades 0 0 361 Lightweight, passive cooling 2 0 0 Lightweight, airing the day only 637 63 0

Solar protections, passive coolng

West

South

Orientation

Table 21: Results for a free running room in Dodoma: Number of uncomfortable hours (i.e. outside the comfort domain shown on Figure 1), number of hours when the relative humidity inside exceeds 75%, as well as maximum and minimum operative temperatures of outdoor air and for three difference designs of the façades. Operative temperature Max Min 31.2 13 33.4 22.8 34.2 23.6 33.6 23.8 30.3 21.4 30.2 22.7 29.3 21.1 29.3 21.1 28.6 21.5 28.8 21.1 28.7 21.3 28.2 21.6 28.3 21.5 326 29.6 13 31.1

Figure 26: Thermal comfort diagram in Dodoma. The comfort zone is in grey. Left: outdoor hourly temperature. Right: without solar protection. In Dodoma, the outdoor temperature is often below the comfort limit and seldom above. However, solar protection is absolutely needed to avoid overheating, even for the south orientation. Heating is clearly not needed. The passive cooling strategy gives good results to completely avoid overheating, and the relative humidity exceeds 70% less than 9% of the time. Therefore, mechanical cooling is not needed in this climate, as long as the internal heat load is not too high. Adding thermal insulation in this climate does not help.

53


Figure 27: Thermal comfort diagrams in Dodoma. Left: With solar protection, airing the day only. Right: With the passive cooling strategy. The Figure 29 clearly shows the effects of various cooling strategies. Because of the passive solar heating, the room is never too cold, but often too warm when the solar protections are not used. The passive cooling strategy allows to completely avoiding the few remaining overheating hours when the solar protections are adequately used. 3.5.4.2 Mwanza Since the necessity to use solar protections is clearly established, all simulations were performed with solar protections. Results are summarised in Table 22, and illustrated in Figure 30 and Figure 31.

Figure 28: Thermal comfort diagrams in Mwanza. Left: Outdoor air. Right: With solar protection, airing the day only.

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Figure 29: Thermal comfort diagrams in room oriented West in Mwanza, applying the passive cooling strategy. Left: Heavy facade, not insulated. Right: Lightweight facade slightly insulated. The number of hot hours is much larger with a lightweight façade and increases with the thermal insulation of the façade.

With solar protections, day window openings

Orientation

With solar protection and night passive Strategy cooling

Table 22: Results for a free running room in Mwanza: Number of uncomfortable hours (i.e. outside the comfort domain shown on Figure 1), number of hours when the relative humidity inside exceeds 75%, as well as maximum and minimum operative temperatures of outdoor air and for three difference designs of the façades.

South

West

South

West

East

Façade type Outdoor air No insulation Insulated facades Well insulated facades No insulation Insulated facades Well insulated facades Lightweight facade No insulation Insulated facades Well insulated facades No insulation Insulated facades Well insulated facades Lightweight Lightweight insulated No insulation

Number of hours Too hot Too cold >75% 923 3258 2630 0 4 635 0 10 748 0 8 669 0 5 618 0 9 705 0 12 685 409 322 795 223 0 131 558 0 69 745 0 51 336 0 127 611 0 62 748 0 60 1359 0 139 1562 0 67 411 0 108

Operative temperature Max Min 34.8 13.8 29.1 21.4 28.0 21.0 28.4 20.7 29.3 21.3 28.4 21.1 28.4 20.7 30.9 19.0 30.8 23.4 30.8 22.6 31.0 22.9 30.9 23.3 31.2 22.5 31.2 22.8 32.8 22.6 31.9 22.8 31.2 23.6

If the solar protections are used, the orientation of the main façade has not much influence on the indoor temperature. 55


Opening windows during the day only, results in many hours that are uncomfortably hot, with a humidity that remains acceptable most of the time. The passive cooling strategy, with nighttime ventilation results in a temperature that is always comfortable, except with a lightweight facade. The relative humidity however overpasses 75% about 9% of the time. This arises from mid-October to the end of May. Air conditioning should be used during the humid season to avoid this discomfort and avoid mould growth risk. Therefore we performed a few simulations with air conditioning, using the room oriented West. The results are summarised in Table 23 and illustrated in Figure 32. Table 23: Results of simulations performed with the west-oriented room with air conditioning. Operative Energy Number of hours temperature use* Solar protections Façade type and power Too hot Too cold Max Min kWh/m² 8 0 26.9 Not insulated facade 23.2 62 0 0 26.0 Insulated facade 22.5 56 With 0 0 25.9 Well insulated facade 22.8 63 173 0 27.3 Lightweight insulated facade 22.8 68.3 1715 0 30.4 Insulated 500 W 23.3 138 372 0 Without 28.1 23.3 Insulated, 1kW 145 327 0 27.0 23.3 Insulated, 4kW 145 * This is the energy use for cooling only. This figure does not include the energy for drying the air. For more information, see the simulations for Dar Es Salaam below.

Figure 30: Thermal comfort diagrams in room oriented West, with air conditioning in Mwanza. Left: Heavy facade slightly insulated. Right: Lightweight facade slightly insulated. 500 W cooling power suffice to control the temperature when the solar protections are used adequately, except for the lightweight façade. The lowest energy use is with the insulated façade. Over-insulating the façade increases slightly the cooling energy. Without solar protection, 500 W does not suffice to ensure comfort, and it is not possible to reduce the number of hot hours even with 4 kW power. The energy use is more than doubled when compared to rooms with solar protections.

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3.5.4.3 Dar Es Salaam Results for Dar Es Salaam are summarised in Table 24, and some results are illustrated in Figure 33.

Figure 31: Thermal comfort diagrams in Dar Es Salaam. Left: Outdoor air. Right: The best result with passive cooling, i.e. with insulated, south-oriented facade.

With solar protections, day window openings

Orientation

With solar protection and night passive Strategy cooling

Table 24: Results of simulations for the free running room in Dar Es Salaam: Number of uncomfortable hours (i.e. outside the comfort domain shown on Figure 1), number of hours when the relative humidity inside exceeds 75%, as well as maximum and minimum operative temperatures of outdoor air and for three difference designs of the façades.

South

West

South

West

East

Façade type Outdoor air No insulation Insulated facade Well insulated facade No insulation Insulated facade Well insulated facade Lightweight facade No insulation Insulated facade Well insulated facade No insulation Insulated facade Well insulated facade Lightweight Lightweight insulated No insulation

Number of uncomfortable hours Too hot Too cold >75% 336 1451 5891 1 17 3860 0 14 4219 0 10 3865 9 11 3689 0 11 4060 0 10 3851 111 37 3641 88 34 3626 156 0 1598 230 0 1095 574 0 860 189 0 1475 313 0 997 0 10 3851 536 0 1395 264 0 1536

Operative temperature Max Min 34.7 16.6 32.3 22.0 31.6 21.9 31.9 21.8 32.6 21.9 31.8 22.0 31.9 21.9 33.5 21.6 33.2 21.5 33.5 24.6 33.3 23.8 33.6 24.3 33.7 24.9 33.6 23.8 31.9 21.9 34.5 24.7 33.8 24.7

Passive cooling can obviously not be applied in Dar Es Salaam, since the air is too humid. Passive cooling indeed cools down the premises, which also cools down the indoor air, whose relative humidity increases above acceptable limits nearly all the time. With day airing only 57


(no night cooling) the number of hot hours increases strongly, but the air remains too humid most of the time. Therefore, we performed simulations with air conditioning, which not only cools the air but also dries it, avoiding all humidity problems. The set point is 25 °C. Results of these simulations are summarised in Table 25. If the mobile solar protections are used adequately, 500 W cooling power is enough to keep the temperature in this 20 m² room, except for the lightweight façade. The energy use is slightly reduced by some thermal insulation. Without solar protections however, 500 W cooling power is not sufficient, and 4 kW should be installed instead if the facade has no insulation. The energy use is doubled. Solar protections are therefore absolutely needed. Note that M. Baruti, in his master thesis[44] studied four buildings in Dar Es Salaam and simulated 12 different configurations, varying the building materials, glazing type, orientation, internal load and internal thermal mass. He got similar, but more detailed conclusions: •

Mechanical cooling is necessary to ensure comfort in Dar Es Salaam

•

Energy use for cooling is strongly reduced by the use of efficient shading system (or reducing window areas).

•

The mass and low thermal transmittance of the façade also reduces the energy demand.

These conclusions can be generalised in all areas with a similar hot-humid climate. Table 25: Results for an air-conditioned room in Dar Es Salaam: Number of uncomfortable hours (i.e. outside the comfort domain shown on Figure 2), as well as maximum and minimum operative temperatures of outdoor air and energy use, for various configurations. Number of hours Too hot Too cold 45 0 0 0 0 0 131 0 1315 0 3699 0 511 0 144 0 0 0

Configuration

Facade No insulation With solar protec- Insulated facades tions, 500 W coolWell insulated facades ing power Lightweight Insulated facade, 500 W No insulation, 500 W No solar No insulation, 1 kW protections No insulation, 3 kW No insulation, 4 kW

Operative Energy temperature use* Max Min kWh/m² 24.0 123 28.1 25.6 23.8 92 26.5 24.3 100 28.2 23.7 110 30.5 24.5 166 33.4 24.4 186 30.0 24.3 223 27.6 24.3 226 25.0 23.9 226

* This is the energy use for cooling only. This figure does not include the energy for drying the air. To dry the air, water vapour in excess must be condensed on a surface - the cooling coil which temperature is at or below the required dew point of the indoor air (e.g. at less than 16°C to finally get a relative humidity of 60% at 25 °C). The condensation latent heat (about 0,7 Wh for each gram of condensed vapour), must be evacuated by the cooling machine. This amount of energy depends on the temperature and humidity of outdoor and indoor air. In a given hot, humid climate, the energy use will be larger if the setpoints for indoor air are at low temperature and humidity. Therefore, as shown on Figure 34, the annual energy to be evacuated by the cooling machine for air conditioning may strongly vary depending on the temperature and humidity setpoints. For each cubic meter per hour, the annual energy use for 58


conditioning can be as low as 41 kWh to get 60% RH at 26 °C and as high as 77 kWh for 50% RH at 21°C. Note that the cooling machine needs only a fraction of this amount as electric energy. To get the final energy use, these figures should be divided by the coefficient of performance (COP) of the machine.

Figure 32: Annual energy use for cooling and drying 1 m³/h outdoor air in Dar Es Salaam at given temperatures and humidity's.

Figure 33: Thermal comfort diagrams in air-conditioned rooms in Dar Es Salaam, both with 500 W cooling power. Left: Heavy, insulated façade, right: Lightweight, insulated façade.

3.6 S OL AR

HOT WAT ER HEAT ER

Given the regular sunshine enjoyed by Tanzania, the solar water heater should be THE way to provide hot water. 3.6.1 Solar water heater elements A solar water heater, as illustrated in Figure 36 includes the following components:

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Purge Solar collectors

Thermostatic control valve anti-syphon check valve Expansion tank

Pump

Control

Safety valve

Hot water Auxiliary heater

Safety valve

Filling valves

Cold water

Y

Figure 34: Diagram of a solar water heater. •

•

•

•

• •

•

•

The solar collectors that converts solar radiation into heat. In the tropics, these collectors can have any orientation with a low slope allowing the evacuation of rain, which also cleans the collector from the dust accumulated between two showers. A hot water tank that plays a role of buffer to adapt the solar energy input to the hot water use. It may be equipped with an auxiliary heater if the hot water supply must absolutely be guaranteed at all times. Heat transfer circuit: two main lines connect the collector to the water tank. A pump circulates the heat transfer fluid, most often water. Antifreeze may be added in cold climates to avoid freeze damages. A check valve prevents that the heat transfer fluid circulates by thermosiphon when the pump is stopped (e.g. at night), which would have the effect to heat the collectors with the heat from the water tank. This circuit also includes a valve system facilitating the filling and maintenance. The transfer of heat from the heat transfer fluid to the water to be heated is through a heat exchanger, for example a helical coil located at the bottom of the water tank. It is not advised to circulate the tap water, which could be corrosive, in the solar collectors. The electronic control module switches the circulation pump when the solar collectors are at higher temperature than the water in the bottom of the water tank. As an option, an auxiliary heater (electrical resistance, heat exchanger coupled to a boiler), is often installed in the upper part of the water tank allows guaranteeing the hot water supply for any weather. This booster can also be separated, powered by the water pre-heated by the solar water heater. A safety valve avoids that the pressure exceeds the safety pressure of the weaker components (often the collectors themselves), by discharging the heat transfer fluid in a tank; and a pressure gauge to measure pressure, particularly when filling the system. As the heat transfer fluid expands when heated, and expansion tank absorbs the excess volume. It is recommended that this device be able to absorb the entire content of the 60


collectors, where the liquid could boil in the event of pump failure by strong sun. This avoids that the safety valve opens to evacuate the excess volume, so avoiding having to refill the installation. When the water tank can be placed above the upper level of the collectors, it is possible to dispense with the pump and control, provided that the length of the pipes does not exceed a few metres (Figure 37).

Figure 35: Thermo-siphon solar water heater. The minimum distance between the top of the solar collector and the bottom of the storage tank is between 30 and 80 cm. When the sun shines, the heat transfer fluid begins to circulate under the effect of the density difference between the hot part of the circuit (the collector) and the coldest part. It is the thermo-siphon effect. This completely autonomous system uses only solar energy. It is common in countries without freeze and is perfectly adapted to tropical countries. 3.6.2 Sizing the components of the solar water heater For solar water heaters, the sizing to be applied per person (or 50 litres hot water at about 45 °C per day) is: • • • •

2

1 m glazed solar collector or 2 m2 unglazed solar collector. 60 to 80 litres per person in the storage tank, of which 50 litres is above the auxiliary heating if installed. The pump of the solar circuit (if needed) should provide 30 to 60 litres per hour (0,5 to 1 litre/minute) for each square meter of solar collector. An expansion tank which capacity equals that of the collectors

The surface area of the collectors could be reduced in very sunny climates and, conversely, increased if it is expected to use much hot water. It is recommended to size large plants more

61


accurately taking into account the local climate, the position of the sensors and equipment available. There are pieces of software for this type of calculations 32.

3.7 E NS URIN G

INDO OR AIR Q UALIT Y

3.7.1 Principles Indoor air quality is improved by three complementary ways: • Reducing the indoor sources or air pollution • Extracting indoor pollutants as close as possible from their sources • Replacing contaminated air by fresher outdoor air In one hour, a person breathes about 1 m³ of air, but contaminates with its body odour, humidity and carbon dioxide, more than 10 m³. Indeed, the main reason for airing is to evacuate contaminants, and the consequence of this is that new, outdoor air is brought indoors to replace the evacuated one. 3.7.2 Sources of air pollution 3.7.2.1 External Sources of Pollution There is a risk of pollution from external sources such as car parking, attached garage, busy road, power plant, industry, cooling towers, landfill site, or agriculture. Potential problems are infiltration of toxic gases such as benzene, CO, NOx, etc., dust and bad smells. The best way to reduce problems coming from outdoor contaminant sources is to avoid their immission into the indoor environment. Wherever possible, locate occupied buildings far from busy roads, power plants, industrial area, and landfill sites. Build garage in a separate building or install a ventilated lock or an airtight door and ensure a positive pressure difference between living space and garage. Specific measures shall be taken in area with large radon emission, e.g. by insulating the occupied space from the ground by a ventilated space or by draining the radon out of the ground under the building. Balanced mechanical ventilation, with air inlet as far as possible from pollution sources and equipped with efficient filters (F7/EU7) can stop particles. Additional active charcoal filters strongly reduce odours and other volatile organic compounds 3.7.2.2 Internal Sources of Pollution Since the buildings should be designed and built for occupants, the occupants and their activities should be the only internal source of pollution. As it was shown in several studies [45, 46], this is by far not the case. The building itself and its ventilation system are often the main source of pollution. It is however possible to reduce the number and the strength of the internal pollution sources by applying the following recommendations [47]: • Do not smoke in buildings (prohibited in office buildings in most countries). It was often noticed that smoking in buildings designed as no smoking lead to problems. The ventilation and zoning are not designed for the heavy pollution load brought by smokers. Even when smoking is allowed only is restricted zones, odours spread and lead to complaints. • Choose materials, paints and furniture that do not emit pollutants or that have low source strength. information on the emission and odour of building products is found 32

E.g. Polysun (www.polysun.ch)

62


• • • •

• • • •

through the labels such as M1 (Finland), DICLE (Denmark) or Blue Engel (Germany) but also in the SOPHIE database [48] . Avoid polluting activities indoors, or ventilate strongly the areas where these activities are performed. Use cleaning agents that do not contain toxic solvents or components. Follow the AIRLESS recommendations (see 3.7.2) in mechanically ventilated buildings. Install proper flue gas pipes or chimneys for combustion appliances (heater, boiler, gas stoves). Close open fireplaces e.g. by installing an insert. Heating with coal or wood in ordinary furnaces, not equipped to burn them properly, produces toxic fumes that could enter in the building. Install the central heat plant or local heater outside the building or separate the room containing the plant from the occupied premises by airtight walls and doors. Use a kitchen hood evacuating the cooking fumes and gases outside. Provide enough space, at least 10 m² per occupant in office rooms. Avoid sources of moisture: tumble driers or other such sources should vent outside.

3.7.3 Natural ventilation Natural ventilation is the passive way to evacuate indoor contaminants. Wind and air density differences, resulting mainly from temperature differences, induce pressure differences that blow air through ventilation opening or natural ventilation ducts. Other openings such as doors and windows are also used for natural ventilation when large air flows are needed. Natural ventilation has the advantages of the other passive means. It is moreover generally well accepted by the occupants, who understand and control it easily, and allows very large airflow rates (more than 10 volumes per hour), in particular for passive cooling. However some drawbacks, which are: • It cannot be used in noisy or polluted areas. • It is efficient only in rooms with a depth-to-height ratio smaller than 3 or having openings on both sides. • Heat recovery is nearly impossible. • The airflow rate varies with the meteorological conditions, and an adequate control is needed to ensure the ventilation requirements. An alternative solution is using selfregulated (pressure-controlled) ventilation grills. Forces for natural ventilation are winds and stack effect, and control systems are the ventilation openings, including doors and windows.

Figure 36 : Wind induced pressure on a building 63


The wind creates an overpressure on the façade exposed to wind and under-pressures on the roof and the facades downwind (Figure 38). The air flows from high to low pressure through ventilation openings When the indoor and outdoor air temperatures differ - which is the case most of the time – the temperature difference induces a density difference. Therefore, a warmer column of air is lighter than a colder one, and a pressure difference, depending on the height in the building, results (Figure 39). When the indoor air is warmer than outdoor air, this stack effect pushes the air in the building through openings at the bottom of the spaces and out of the building at the top of the spaces. It is the contrary when indoors is colder than outdoors.

Figure 37: The stack effect for the case when the indoor air is warmer than the outdoor air. Since these forces vary with time, the airflow rate should be controlled with variable openings. These could be ad-hoc ventilation openings and ducts, but windows and doors can also be used as natural ventilation openings. 3.7.4 Mechanical ventilation and air conditioning Mechanical ventilation is often used where natural ventilation cannot fulfil the requirements, either because of poor outdoor conditions (noise, pollution, climate) or in locations that cannot be naturally ventilated. It has the following advantages: • Allows ventilating deep spaces with low ceilings and rooms that are not accessible to natural air flow. • Where well designed and built in an airtight building, it ensures a total and continuous control of air flows and also allows a better control of the indoor climate. • It can protect from outdoor noise and pollution. • Air conditioning can be combined with mechanical ventilation • Heat recovery from exhaust air is relatively easy. Its drawbacks are however: • Mechanical ventilation is often not well accepted by the occupants, who lack control on it (see 3.2.6) • The system, especially air ducts, uses a large part (up to 25%) of the building volume. • The installation and exploitation costs are high. • It uses energy not only to condition the air but also to move it. • It can be noisy, especially at low frequencies.

64


• • •

The quality of delivered air may be poor if special caution is not brought to it when building and maintaining the system (see 3.7.2). It may break down or function in an improper way. In poorly designed buildings, air-conditioning may be a cause of discomfort because of cold draughts and may reduce indoor air quality because of recirculation.

HOPE audits have shown that the well-being of occupants is not as good in buildings with mechanical ventilation than in those with hybrid and natural ventilation, and in buildings with sealed windows than in buildings with operable windows [39]. There are no significant differences for the perceived air quality and comfort, and for energy use. It should however be emphasized that there were, in the audited sample, buildings equipped with mechanical ventilation or air conditioning that are healthy and comfortable. It is those that fulfil the AIRLESS recommendations (see 3.7.5 below) and in which the design was appropriate. 3.7.5 AIRLESS Recommendations The EU project AIRLESS [49] proposed several recommendations for improving the indoor air quality and energy performance of mechanical ventilation [50]. These are remembered below, together with HOPE complements. Avoid recirculation In mechanical ventilation systems with recirculation, only the hygienic airflow rate is taken outdoors, while heat is given or taken to a mixed air flow circulating in the building. This spreads pollutants from one place into the whole building, thus decreasing indoor air quality, and does not save energy at constant air quality. Recirculation may be needed in air-cooled buildings, because the air is a poor heat transfer fluid, and large airflow rates may be needed to evacuate the heat. In order to improve energy efficiency and air quality, it is nevertheless recommended to condition (i.e. dry and cool) only the hygienic airflow rate and avoid recirculation. If indoor air is dry enough (dew point below 18°C), additional cooling can then be done efficiently with other means, such as cold ceilings or fan-coil units. Use a heat recovery system in a building that is not leaky In a mechanical ventilation system, heat recovery is an efficient way of saving energy while ensuring a good indoor air quality. Heat recovery is however efficient where and only where the building envelope, the ventilation unit and the ducts are reasonably airtight, to ensure that the air passes through the heat recovery system. In systems well-installed in airtight buildings, the actual heat recovery efficiency can be as high as 85% of the efficiency of the heat recovery system itself, so about 75% in the best cases. At the contrary, the actual efficiency may be zero if the system is not well designed, and installed in a leaky building. This reduction was indeed observed in practice [51]. In a few cases, the actual heat recovery is reduced to nothing, and in several cases the recovered heat was not worth the invested money. Use a rotating heat exchanger only if odors or COV are not a problem Rotating heat exchangers have in principle a better heat recovery than other types of heat exchangers, and this is the reason why they are used instead of other models (heat pipes, plate exchangers, etc.). However, they do transfer a part of the pollutants from the exhaust air into the supply air [52-54]. Therefore, heat pipes or plate exchangers should be installed instead of rotating heat exchangers where some recirculation of odours cannot be accepted. Supply and

65


exhaust fans should be located and sized so that a positive pressure difference of about 200 Pa is achieved between supply and exhaust ducts at the wheel level. The use of a purging sector only decreases the heat recovery efficiency by 3%, but decreases by half or more the amount of transferred contaminants. Avoid humidification whenever possible This recommendation applies to cold countries. Of course, no humidification is necessary in tropical countries. Shut the ventilation system down when no air is required. A reduction in operation hours will consequently result in a reduction of energy use for ventilation. However, the system should be restarted early enough before occupants arrive, in order to purge the building from contaminants accumulated during off time. Use a filtering system that “cleans” the air and has a resistance as low as possible Filtering of the air is necessary to clean the air from particles to protect the HVAC-system. Common filter techniques (bag filters) are such that filtering leads to an increasing film of dust collected on the filter. The fact that fresh outdoor air is transported through dirt accumulated on the filter is asking for problems. Therefore, filters should be changed or cleaned often enough to prevent that the filter becomes a source of pollution. Dirty filters have a larger pressure drop than clean ones and therefore use more power to move the air. They have a higher filter efficiency for dust but emit gaseous pollutants [55]. Use ductwork that is smooth, as large as possible and with a minimum number of curves The use of energy by ducts during the operation of an HVAC-system is related to the air velocity in ducts, the length of the ducts, the amount of curves, and the smoothness of the interior surface. Simulations showed that the pressure difference over the system of 1600 Pa instead of 1000 Pa leads to an increase in electric power use of 60%. Reducing air velocity in ducts from 5 m/s down to 2 m/s theoretically divides energy use to move air in ducts by a factor 6. This requires ducts 60% larger in diameter to keep the airflow rate at its original value. If cooling is applied, use a cooling coil with a droplet catcher A droplet catcher behind a cooling coil results in a negligible effect for the energy demand, but increases air quality by avoiding droplets humidifying the filters or sound absorbers that are located downstream. Humid filters increase the risk of microbial growth. Increase/decrease the set point for cooling/heating as much as possible (with respect to comfort conditions of occupants) An increment of the set point for cooling resulted in decrease of cooling demand by a factor 3 to 8, for the simulations performed [56]. In several cooled buildings, occupants found the temperature too low [57]. These buildings are indeed overcooled and use more energy to decrease the comfort! Commissioning the air handling system after installation is essential. The effective airflow rates and pressure differentials should be measured and compared to the design values when commissioning the ventilation system. It is also advised to check the energy efficiency of all systems. From investigations in many buildings in several countries, it was confirmed that the functioning of a building and its systems is seldom checked. It was also found that ventilation systems for which a commissioning report was available has airflow rates closer to the design values than the others [58]. 66


Keep clean the parts exposed to supply air (filters, heat exchangers, sound dampers, ducts) Source control should also be emphasized for ducts: start with clean ducts (free of oil residuals and dust), and then avoid dirt to get in by efficient filtering. Quality management on the construction site should be focused on this.

3.8 L IG HT ING 3.8.1 Dayligting Daylight is, when and where available, the best source of light for living beings. It is not only essential to life, it also has an ideal, continuous, white spectrum with perfect colour rendering. The reason is that our eyes are, since a very long time, used and adapted to daylight. Therefore, it is not surprising that we prefer daylight over artificial light. Its spectrum is ideal for biological stimulation and it is delivered for free. In addition, the sun is the light source that has the smallest heat load per lux (1 W for 100 lux). Therefore, daylight should be used wherever and as far into the room as possible. It was also shown in many experiments that productivity is improved with daylight. There are several possibilities for light openings: • Vertical windows are suitable to provide light at distances up to twice the window height. Properly selected daylight systems can increase this distance. • Roof lights can bring daylight in deep rooms which are located under the roof. Roof lights should be oriented north or they should be placed so that they are not in the ergorama. • Daylight guiding systems, such as lumiducts, may bring some light in locations that don't have direct access to outside. For best daylight supply, the following guidelines should be applied: • Use clear glazing and avoid fixed solar protections such as overhangs, at least in climates where there is not too much sun the whole year long. Permanent solar protections reduce daylight even when it is most needed. • Install daylight control systems such as Venetian blinds or shutters, since daylight is sometimes too strong. • Use clear colours (preferably white) inside for ceiling, walls and even floor and furniture. • Design high windows. For the same area, a narrow and high window brings more light into the room than a broad and low window. The top of the window brings more light into the back of the room than the bottom. • Avoid glare by placing the work places perpendicular to the openings or vice versa. Openings should be out of the central field of view. • Special devices such as lightshelfs, anidolic mirrors or holographic glazing cannot solve all problems and may even be worse that simple glazing. If planned, ensure by (full) scale experiments or simulations that they will bring the expected advantages, without causing discomfort. 3.8.2 Artificial Lighting Systems Artificial lightingshould be designed as an addition to the available daylight and to replace daylight in case of insufficient supply. Various electric lamps found on the market use several ways of producing light, and their efficiency and colour rendering strongly vary with type (Table 26). 67


Table 26: Light emitting efficiency in lumen per Watt of various light sources. Grey shaded sources have a long switch-on time and are not commonly used in premises. Lamp type Incandescent Quartz halogen Mercury LED, white Metal halide Fluorescent, T8 Sodium, HPS Sodium, LPS

lm/W 13 - 20 20 - 35 50 - 55 30 - 100 65 - 115 80 - 100 85 - 150 100 - 200

Minimum power W n/a n/a 100 n/a 150 n/a 500 35

Color yellow-white white blue-white white white white white yellow

It is of course recommended to install high efficiency light sources having an adapted spectrum. Sodium discharge lamps are very efficient but a poor colour rendering. They are adapted to street lighting. Best fluorescent tubes, equipped with electronic control avoiding flickering are very efficient and provide a good light spectrum. Light emitting diodes (LED) now appearing on the market, are very efficient and promising. An additional daylight responsive control system can decrease the light output of the lamps in case daylight supply is sufficient and thus save energy. Further, efficient lamps and welldesigned luminaries that reflect or diffuse most of the light emitted by the light source to the place needing light should be applied. Well-designed lighting may be more comfortable at 250 lux than poorly designed lighting at 500 lux.

3.9 A CO UST ICS 3.9.1 Sources of Noise There are several sources of noise around buildings, some of them, such as road traffic or parking being linked to the activities in the building. These sources may disturb the occupants of buildings. Within the HOPE office building sample, occupants of buildings close to a potential noise source such as a busy road, an airport or a car park are significantly more disturbed by outdoor noise than those located in a more silent area. When such sources are present, the building - in particular its acoustic protection - should be designed so that the indoor sound level remains within acceptable limits. Internal sources of noise are mainly the activities of occupants, but could also be the building systems. Within the HOPE office building sample, occupants of buildings with natural ventilation are significantly less disturbed by noise from building systems than those in mechanically ventilated buildings. 3.9.2 Acoustic Protection Noise produced outside or at some place in a building is transmitted to other places in the building by the air itself and by the building structure. There are mainly three ways for improving the acoustic protection: • Reducing the intensity of the noise sources: silent appliances, reduced air velocity in ventilation and water systems, vibrating appliances installed on silent blocs, etc. • Installing sound barriers between the noise source and the occupant: massive, airtight walls and decks, multilayer structure alternating stiff and soft materials. Important is that these barriers have no weaknesses at all, especially if the best possible sound insu68


•

lation is required: a small sound bridge such as a rigid connection between two panels or a small hole (e.g. a keyhole) in a wall may completely destroy the efficiency of the sound barrier. Efficient barriers against impact noise are soft layers that damp the impact. Such layers, such as a carpet, could be at the source or within the structure such as a floating floor Increasing the sound absorption in the occupied room (see below).

3.9.3 Acoustic Ambience Sound waves present in a room are reflected by the walls, floor, ceiling and the furniture. Reflected waves are added to the original ones and increase the sound level. Reducing the reflection by placing absorbing materials on walls, floor, ceiling and furniture therefore reduce the sound level in rooms and the reverberation time. Sound absorbing devices are oscillating panels closing off cavities, which are generally good for absorbing sound at low frequencies, resonators, i.e. open cavities whose dimensions can be adjusted to absorb any specific frequency, and porous materials which give better absorption of sound in the mid and high frequency range (Figure 40.).

Oscillating panels

Resonators

Porous panels

Figure 38: Sound absorbing devices. There is an optimal absorption area and arrangement of absorbing and reflecting materials, which provides the most convenient acoustic ambience. When the reverberation time is too long in rooms where occupants have discussions, they speak louder trying to cover the echo, which therefore increases and so forth. The ambience then becomes quickly very noisy. Adding absorbing material is however not very efficient to reduce the sound level in rooms with strong noise sources: The absorbing area should be multiplied by ten to reduce the sound level by 10 dB. It is often more efficient to reduce the source itself.

69


4

CLIMATES IN TANZANIA

Adaptation of building design to climate is among the best way to improve both comfort and energy efficiency of buildings. Therefore design rules and requirements strongly depend on climate, and climate zones adapted to building physics should be defined. In this chapter, information from several sources related to climate is analysed, with the aim to define such climate zones. Climate characteristics for building physics applications are related to human comfort. Main parameters are therefore: outdoor air temperature and temperature variations, outdoor air humidity, direct solar radiation coming directly from the sun, and diffuse solar radiation coming from the whole sky. Winds and breezes have an effect on natural ventilation, while rainfall frequency and strength influence the building construction. Af: equatorial climate Am: monsoon climate Aw: tropical savanna climate BWh: warm desert climate Bsh: warm semi-arid climate Cwa: humid subtropical climate Cwb: humid subtropical climate/subtropical oceanic highland climate Cfb: temperate oceanic climate

Figure 39 Climatic zones of Tanzania and neighbouring countries according to Peel, M. C. and Finlayson, B. L. and McMahon, T. A. (2007). "Updated world map of the Köppen-Geiger climate classification". Hydrol. Earth Syst. Sci. 11: 1633-1644. ISSN 1027-5606 According to Wikipedia, the Köppen–Geiger climate classification system is based on the concept that native vegetation is the best expression of climate. Thus, climate zone boundaries have been selected with vegetation distribution in mind. It combines average annual and monthly temperatures and precipitation, and the seasonality of precipitation. Indeed the map of Figure 41 presents some similarity with that of Figure 42 that represents precipitations, but the large differences in temperatures of Figure 43 are not reflected in Figure 41. Therefore, the Köppen–Geiger climate classification is by essence not well adapted for building physics.

70


Figure 40: Precipitations (www.WorldTradePress.com)

According the Encyclopaedia of the Nations (http://www.nationsencyclopedia.com), there are four main climatic zones: (1) the coastal area and immediate hinterland, where conditions are tropical, with temperatures averaging about 27° C (81° F ), rainfall varying from 100 to 193 cm (40 to 76 in), and high humidity; (2) the central plateau, which is hot and dry, with rainfall from 50 to 76 cm (20 to 30 in), although with considerable daily and seasonal temperature variations; (3) the semi temperate highland areas, where the climate is healthy and bracing; and (4) the high, moist lake regions.

71


Figure 41: Annual mean temperature (www.WorldTradePress.com) The Wikitravel.org website gives the map shown on Figure 44. The intenti0nis not to provide climatic zones, but this map approximately illustrate the text of the Encyclopedia of the Nations. Taking the climate zones defined in 2.3.2, the correspondences could be as follows: Table 27: Correspondence of climate zones according to three sources. 1 2

Climate zone according to 2.3.2 Semi temperate highland areas High lake regions

Encyclopaedia of the Nations Semi temperate highland areas High, moist lake regions

3

Central plateau

Central plateau

4

Coastal hinterland

The coastal area and immediate hinterland

5 Coastal area

72

Fitzgerald (Figure 44) Northeast Tanzania Northwest Tanzania Central Tanzania and Southern Highlands Pembwe and the Southeast, Zanzibar


Central Tanzania a plateau with grasslands Northeast Tanzania the mountainous location of Kilimanjaro Northwest Tanzania Africa's "great lakes" and the Serengeti Pembwe and the Southeast the hot, humid shoreline Southern Highlands

Zanzibar

Figure 42: Regions of Tanzania according to Peter Fitzgerald, and Fanny Schertzer, (http://wikitravel.org/)

4.1 C OLLECT ING ,

COMPARIN G AND SELECT ING SIGN IFIC ANT CLIMAT ES

In order to test design rules adapted to the various climates, we collected available climatic data using the METEONORM software33. It is a climatological database for solar energy and building physics applications, containing comprehensive climatological data at every location of the globe. It includes a computer program for climatological calculations; a standardization tool permitting developers and users of engineering design programs access to a comprehensive, uniform data basis. METEONORM's allows interpolating using appropriate algorithms, between meteorological stations for locations where some meteorological data are not available. In the considered area, data are available for locations shown in Figure 45.

33

www.meteonorm.ch

73


Figure 43: Locations where meteorological data are available from METEONORM. Stations with measured solar radiation are in blue, stations with interpolated solar radiation in green, and some cities are in red. Annual and monthly values of various meteorological parameters for 13 locations in Tanzania are given in Table 28. These data do not have all the same accuracy. Data for Mbeya and Tanga (shaded red) are all interpolated from other stations. Only air temperature and rain are measured in Mtwara. In Table 28 measured data are written in bold font, while interpolated data are in italics. Important parameters to be considered for adapting the building design to improve thermal comfort are not only outdoor temperature but also air humidity and solar radiation. Since all locations present an important solar energy potential, they can be considered as similar from this point of view. Unfortunately, we have only few measured data on wind. METEONORM provides calculated data that do not correspond to the reality for the locations where measured data are available and cannot be used for building design purposes. However, we found on www.windfinder.com, measured wind data for Dar Es Salaam and Mwanza. These data are illustrated in Figure 58 and Figure 63. Table 28: Annual and monthly values of various meteorological parameters for 12 locations in Tanzania. Figures are given for the year, and for the months when the value are lowest and highest. Color scales indicate the rank in each line. Locations are ranked from the coldest at left to the warmest at right. The numbers linked to the names of places are WMO 34 station numbers. Measured data are in bold font while interpolated data are in italics.

34

World Meteorological Organisation

74

Dodoma 638620

Tabora 638320

Mwanza 637560

Kigoma 638940

Kilimanjaro 637910

Morogoro 639710

Mtwara

700

426

119

181

139

882

891

526

113

Population

1665

3662

1737

2112

2349

2942

1814

1665

V, 3 °C

V, 2

V, 3

V, 3

V, 3

V, 2

V, 2

Yearly avg.

17.9 18.7

19.3

22.8

23.2

23.5

Min. month

15.2 16.8

17.4

19.8

21.5

Max. month 19.8 20.8 Dew point °C

21.2

25.1

11.7

6.4

Max month Relative humidity

Zanzibar Is. 638700

Iringa 638940

1387

Tanga TZ

Mbeya TZ

Altitude

Site

Dar Es Salaam 638940

Arusha 637890


55

15

15

2115

3566 3118

1967

1274

V, 3

V, 4

V, 3 V, 2 V, 2

V, 2

23.6

23.6

24.4 25.3 26.1 26.7

27.1

22.6

22.9

20.7

21.2 23.6 23.9 24.6

25.1

25.6

24.3

24.8

25.6

26.5 26.7 28.3 28.6

29

15.1

14.3

16.2

18.2

16.4

18.8 20.1 22.1 22.7

22.9

8.1

11.8

10.4

13.1

15.3

14.3

15.9 17.4 19.4 20.8

21.1

16.8 14.2 %

15.5

17.7

17.9

18.3

19.8

19.3

21.8 22.4 24.4 24.5

25.1

Yearly avg.

77.9 60.6

61.9

61.9

58.2

63.9

72.3

64.4

71.4 73.0 78.8 78.9

78.3

Min. month.

68.0 45.6

46.1

53.8

42.1

54.4

60.4

57.2

63.7 67.3 75.9 75.0

74.0

Max month 92.4 75.8 Solar radiation W/m²

76.0

70.2

72.2

72.0

80.1

76.9

82.1 79.4 85.0 82.9

84.0

Climate Temperatures

Yearly avg. Min. month.

13.9 10.8 11.9

Yearly avg.

241

239

261

236

233

227

182

239

179

213

202

213

206

Min. month.

182

214

233

214

206

196

155

176

147

187

164

184

182

Max month % diffuse

289

270

303

265

253

240

208

282

208

241

240

233

225

Yearly avg.

39% 38%

31%

41%

39%

43%

54%

40%

56% 45% 51% 50%

51%

Min. month.

46% 27%

18%

35%

34%

38%

56%

51%

58% 40% 53% 52%

47%

Max. month

35% 49% mm

36%

43%

42%

49%

52%

36%

63% 49% 52% 51%

52%

Annual total 1237 1228

742

796

Rain

879 1083

928 1030

889 1118 1042 1214 1409

Min. month.

14

0

0

4

0

14

3

15

10

8

21

43

28

Max. month

369

248

175

173

170

175

150

351

206

212

264

254

320

Looking at Table 28 for outdoor temperature and air humidity, we have retained 4 typical climatic locations (marked in green in Table 28): 1. Arusha, fresh and humid, similar to Mbeya and Iringa, which are however slightly warmer and significantly dryer. This station is however not representative of the whole regions of Arusha and Iringa, where temperatures strongly depend on the altitude. 2. Dodoma, temperate and dry, similar to Tabora 3. Mwanza, a bit warmer, similar to Kigoma (more humid) and Kilimanjaro 4. Dar Es Salaam, warm and humid coastal climate, similar to Tanga and Zanzibar, and also to Mtwara, which is however slightly dryer. Table 29: Correspondence of climate zones and chosen stations.

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1 2 3 4

Climate zone according to 2.3.2 Semi temperate highland areas High lake regions Central plateau Coastal hinterland

5 Coastal area

Meteorological station Arusha Mwanza Dodoma Dar es Salaam

We are conscious that this choice may not the best one. It mainly results from available data, in order to simulate the examples given in this document. Let us look at these 4 climates more in detail in the next sections.

4.2 A R USH A Table 3 shows the monthly and annual averages of the most important climatic data for building physics, as collected from the METEONORM database. Table 30 : Monthly mean climatic data for Arusha. Based on data from 1972 to1991.

Month Jan. Feb. March April May June July Août Sept. Oct. Nov. Dec. Year

Air temperature °C 19.6 19.8 19.6 19.6 16.8 15.2 15.2 15.7 16.5 18.7 19.0 18.7 17.9

Dew point °C 14.4 14.1 15.6 16.8 15.6 13.4 12.4 12.2 11.9 12.7 13.4 14.4 13.9

Solar radiation on horizontal plane Diffuse Global W/m² W/m² 98.6 254 96.9 260 98.6 259 93.7 233 89.4 212 95.3 193 93.8 182 94.7 229 102.0 259 83.9 289 94.9 264 99.3 257 95.1 240.9

Relative humidity % 71.8 69.6 77.7 83.9 92.4 89.2 83.2 79.6 74.1 68.0 69.7 76.1 77.9

Rain mm 58 83 178 369 212 33 14 20 20 36 112 102 1237

Rainy days 4 4 8 14 13 6 4 5 5 7 13 9 92

The daily mean air temperature is close to the comfort range from November to April (Figure 47), but slightly too cold the other months. The frequency distribution (Figure 46) shows that these are within the comfort range about 15% of the time, and too cold the rest of the year. However, the solar radiation remains significant, and buildings designed to use passive solar heating (2.7.9, 3.4.2) will be comfortable without specific heating. In addition, the daily temperature variations with about 10 °C amplitude (Figure 47) will help in maintaining a comfortable internal temperature by airing at appropriate times.

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100%

8%

80%

6%

60%

4%

40%

2%

20%

Frequency

10%

0%

0% 10

11.5

13 14.5 16 17.5 19 20.5 Daily average outdoor temperature

22

23.5

25

Figure 44: Frequency distribution of the daily mean outdoor air temperatures. The relative humidity is at its highest during the cold months (Figure 48). If buildings are heated (e.g. by passive solar heating) during these months, the humidity inside will be lower, thus reducing the risk of mould growth. 35 Outdoor air température °C

Daily mean

Minima

Maxima

30 25 20 15 10 5 01

02

03

04

05

06

07

08

09

10

11

12

Figure 45: Daily mean, highest and lowest outdoor air temperatures along the year. Daily avg. relative humidity

100% 90% 80% 70% 60% 50% 01

02

03

04

05

06

07

Figure 46: Daily mean relative humidity, along the year.

77

08

09

10

11

12


Dots in Figure 49 each represent a day, located at its daily average temperature and humidity (represented by the water vapour partial pressure). Most of the days are outside the comfort area proposed by Givoni [42].

Figure 47: Daily average temperatures and vapour pressure, placed in a Carrier diagram. Polygons indicate comfort areas according to Givoni. H: for heated rooms; C: for cooled rooms; and V: comfort zone acceptable in not conditioned premises with natural ventilation.

4.3 D ODOM A Table 31 shows the monthly and annual averages of the most important climatic data for building physics, as collected from the METEONORM database. Table 31 : Monthly mean climatic data for Dodoma. based on data from 1972 to1991.

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Air temperature °C 24 23.2 23.4 22.9 22.1 21.5 19.8 20.7 22.3 24 25.1 24.8 22.8

Dew point °C 17.4 17.1 17.7 16.8 14.7 13.5 11.8 12.2 12.9 14.1 15.6 17.4 15.1


Relative humidity % 66.5 68.5 70.2 68.4 63 60.3 59.8 58 55.4 53.8 55.4 63.4 61.9

Rain mm 149 116 173 128 43 10 5 4 8 12 43 105 796

Rainy days 3 1 5 10 14 10 10 8 9 9 8 7 94

The frequency distribution (Figure 50) shows that the daily mean air temperature is within the comfort range for naturally ventilated buildings for most of the time.

Figure 48: Frequency distribution of the daily mean outdoor air temperatures. The lowest temperatures are below comfort range, but the thermal inertia of buildings stabilises the internal temperature, and the daily temperature variations with about 10 °C amplitude (Figure 51) helps in maintaining a comfortable internal temperature by airing at appropriate times.

79


Figure 49: Daily mean, highest and lowest outdoor air temperatures along the year. The relative humidity is within the comfort range (Figure 52).

Figure 50: Daily mean relative humidity, along the year. Dots in Figure 57 each represent a day, located at its daily average temperature and humidity (represented by the water vapour partial pressure). Nearly all the days are inside the comfort area proposed by Givoni for naturally ventilated premises [42]. During the few cold days, it will be easy to use passive solar heating for getting comfortable temperatures inside.

80



4.4 M WANZ A Table 32 shows the monthly and annual averages of the most important climatic data for building physics, as collected from the METEONORM database. Table 32 : Monthly mean climatic data for Mwanza. Based on data from 1972 to1991.

81



Air temperature °C 23.7 23.2 23.7 23.4 23.4 23.2 22.6 23.2 23.7 24.3 24 23.4 23.5

Solar radiation on horizontal plane Diffuse Global W/m² W/m² 103.6 219 102.2 226 104.9 240 96.1 225 91 222 78.2 233 74.7 235 88.5 240 102.2 231 103.4 234 111.4 219 117 196 97.7 226.7

Dew Relative point humidity °C % 17.7 69.2 17.7 71.1 18.3 72 17.8 70.9 17.3 68.5 15.1 60.4 13.1 55 13.5 54.4 14.3 55.4 15.1 56.3 16.9 64.5 17.5 69.4 16.2 63.9

Rain mm 98 113 151 175 92 17 14 20 32 87 136 148 1083

Rainy days 4 4 8 15 13 5 3 4 4 7 14 9 90

The frequency distribution (Figure 54) shows that the daily mean air temperature is always within the comfort range for naturally ventilated buildings.

Figure 52: Frequency distribution of the daily mean outdoor air temperatures. In addition, the daily temperature variations with about 10 °C amplitude (Figure 55) helps in maintaining a comfortable internal temperature by airing at appropriate times, in particular to evacuate internal heat loads.

82


Figure 53: Daily mean, highest and lowest outdoor air temperatures along the year. The relative humidity (Figure 56) is within the comfort range from June to December, but a bit high from January to May.

Figure 54: Daily mean relative humidity, along the year. Dots in Figure 57 each represent a day, located at its daily average temperature and humidity (represented by the water vapour partial pressure). Only four days are outside the comfort area proposed by Givoni for naturally ventilated premises [42].

83



Figure 56: Annual wind rose at Mwanza Airport . © windfinder.com

84


4.5 D AR

ES

S AL AAM

Table 33 shows the monthly and annual averages of the most important climatic data for building physics, as collected from the METEONORM database. Table 33 : Monthly mean climatic data for Dar es Salaam. Based on data from 1972 to1991.


Air temperature °C 27.8 28.3 27.8 26.7 25.6 24.4 23.9 23.9 24.4 25.6 26.7 27.8 26.1


Dew Relative point humidity °C % 23.9 79.3 23.7 76.2 24.4 82 24 85 22.3 82 20.3 78.1 19.4 76 19.4 75.9 20 76.4 21.3 77 22.5 77.9 24.1 80.1 22.1 78.8

Rain

Rainy days

mm 58 68 128 264 219 33 21 24 28 48 68 83 1042

3 1 5 10 14 10 10 8 9 9 8 7 94

The frequency distribution (Figure 59) shows that the daily mean air temperature is outside the comfort range (too warm) for naturally ventilated buildings a large part of the time. This occurs mainly between December and March ((Figure 60).

Figure 57: Frequency distribution of the daily mean outdoor air temperatures. Note that the thermal inertia of buildings stabilise the internal temperature and the daily temperature variations with about 8 °C amplitude (Figure 60) can be used to reduce overheating by airing at appropriate times (passive cooling).

85


Figure 58: Daily mean, highest and lowest outdoor air temperatures along the year. The relative humidity (Figure 61) is rather high throughout the year, and is uncomfortable when linked to a high temperature.

Figure 59: Daily mean relative humidity, along the year. Dots in Figure 62 each represent a day, located at its daily average temperature and humidity (represented by the water vapour partial pressure). Nearly all the days are inside the comfort area proposed by Givoni for naturally ventilated premises [42]. There are however too many hot and wet days outside this comfort area.

86


Figure 60: Daily average temperatures and vapour pressure, placed in a Carrier diagram. Polygons indicate comfort. The blue line marks the areas acceptable in not conditioned premises with natural ventilation, according to Givoni.

Figure 61: wind rose at Dar Es Salaam White Sands. © windfinder.com

4.6 S OL AR

R ADI AT IO N

The solar radiation remains important throughout the year at all locations, nevertheless with important daily variations (Figure 64). 87


Figure 62: Daily total solar irradiance on a horizontal plane, along the year, in Dar Es Salaam. Figure 65 shows the percentage of the days for which the daily irradiance is larger than the value given in abscissa, at the four selected locations. The four curves are very similar, with Dar Es Salaam receiving however a little bit less solar radiation than the other locations. There is nevertheless no day receiving less than 1 kWh/m², and half of the days receive more than 5 to 6 kWh/m². This allows covering practically all the energy for domestic water heating with solar collectors. The yearly total solar radiation is more than 2000 kWh/m² which is very high when compared to other countries in the world, and guarantees a good production for solar plants such as photovoltaic systems.

Figure 63: Cumulated frequency of the daily total solar irradiance on a horizontal plane at the four selected locations. The stereographic projection of the sun path (Figure 66) helps in assessing the effects of shadings.

88


North

o

Latitude: -6

Figure 64: Stereographic projection of sun path (red lines) for the 21st of each month at -6° latitude

89


5

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93


INDEX acoustical comfort 10, 37, 68 active means ................ 40 adaptation to the environment............. 41 adaptative comfort ....... 30 adaptive comfort model . 6 air conditioning 13, 16, 64 air ducts ....................... 66 air permeability ....... 7, 16 air quality . 7, 9, 11, 32, 62 airtightness .................. 20 applicable buildings ....... 8 Ardhi Institute ............... 3 Arusha climate ..................... 76 simulations .............. 46 building design ................ 11, 15 envelope ............ 15, 43 free-running ~ ............ 6 materials .................. 15 orientation ......... 15, 41 standards ................... 4 Building Research Unit.. 3 buildings applicable ~ ............... 8 carrier, energy ~............. 5 ceiling fan.................... 18 climate..................... 6, 70 in Arusha ................. 76 in Dar Es Salaam ..... 85 in Dodoma ............... 78 in Mwanza ............... 81 zone ........................... 8 climate zone .6, 11, 12, 70 coefficient of performance......... 7, 21 colour .......................... 36 comfort .......................... 8 acoustical∼......... 10, 68 acoustical~............... 37 adaptative∼ .............. 30 adaptive ..................... 6 thermal∼ .................. 25 thermal∼ .............. 8, 11 visual∼ ............... 34, 35 visual∼ ..................... 10 commissioning ............ 66

compliance checking ~ 11 control on the environment ............ 43 cooking ....................... 22 cooling ...................49, 66 mechanical∼ ............ 20 passive ...............18, 50 Dar Es Salaam climate .................... 85 simulations .............. 57 daylight ..................19, 67 design principles................. 39 temperatures ............ 21 dew point ...................... 6 Dodoma climate .................... 78 simulations .............. 53 draughts ...................... 28 ducts, air∼ ................... 66 dynamic thermal transmittance ....... 7, 16 electric appliances ............... 22 lighting ...............22, 67 energy ........................... 5 carrier ........................ 5 efficiency .................. 6 final ~ ........................ 5 in buildings ............. 38 label ........................ 22 primary ~ ................... 5 renewable ................ 23 efficiency ...................... 6 envelope of building ... 15, 43 environment adaptation to the ...... 41 control ..................... 43 environmental codes...... 8 equivalent window to wall ratio ............. 7, 16 escalators .................... 22 filter ............................ 66 final energy ................... 5 fireplaces ..................... 21 free-running building ..................... 6 temperature ............... 6 94

glare.............................37 global solar energy transmission coefficient7, 17 green roofs ...................16 ground-cooled heat pumps ......................21 healthcodes ....................8 heat loads ........................51 recovery ...................65 transfer coefficient7, 15 heating ................... 21, 45 hot water ............ 21, 59 passive solar∼..... 19, 46 hot water ................ 21, 59 humidity .................. 9, 12 IHSBR ...........................3 illuminance ........ 7, 10, 35 indoor air quality ......... 7, 9, 11 environment quality ..7, 8, 25 inertia, thermal~ ...........18 ISO 7730 standard .........9 kitchen equipment ........ 22 lifts ..............................22 light efficiency ............. 67 lighting ........................14 electric∼ ............. 22, 67 luminance ....................35 materials, building∼ .....15 mean radiant temperature ..................................6 mechanical cooling .....................20 ventilation 8, 16, 19, 64 moisture .......................23 mould ..........................23 Mwanza climate .....................81 simulations ...............54 natural ventilation .. 18, 63 night cooling ................20 noise ............................68 level ..................... 7, 10 occupant ......................43 operative temperature.....6 orientation of building . 15, 41


overheating .................. 49 passive means ...................... 40 solar heating ...... 19, 46 ventilation cooling .. 18, 50 performance based rules 4 pollution ...................... 62 power ............................ 5 predicted mean vote....... 6 prescriptive requirements .................................. 4 primary energy .............. 5 primary energy factors . 14 principles, design ∼ ...... 39 protections, solar∼ . 16, 44 recirculation ................ 65 renewable energy......... 23 requirements performance based~ ... 4 prescriptive~ .............. 4 reverberation time.... 7, 10 roofs ............................ 15 rotating heat exchanger 65

running mean temperature .............................. 6, 9 safety codes ................... 8 simulations Arusha ..................... 46 Dar Es Salaam ......... 57 Dodoma .................. 53 Mwanza .................. 54 solar protections .... 16, 44, 46 radiation .................. 87 water heating ........... 59 solar energy transmission coefficient ........... 7, 17 sound level .................... 7 specific primary energy use............................. 6 sun path....................... 88 temperature mean radiant ~ ........... 6 operative ~................. 6 running mean ~...... 6, 9 thermal capacity ................... 18

95

comfort .......... 8, 11, 25 gradients ..................27 insulation .................43 transmittance, dynamic ~ ...................... 7, 16 transmission heat loss coefficient ................ 43 energy ............................5 useful energy .................5 user ..............................43 ventilated roofs ............ 15 ventilation mechanical ......... 19, 64 natural......................18 natural......................63 openings ..................18 principle ...................11 visual comfort .. 10, 34, 35 waste management .......24 water............................24 window to wall ratio 7, 16 WWR ...................... 7, 16