building energy savings and indoor air quality

ÉCOLE POLYTECHNIQUE FÉDÉRALE DE LAUSANNE

INSTITUT DE TECHNIQUE DU BATIMENT, LESO-.PB, EPFL, CH 1015 LAUSANNE

SEMINAR ON

ENERGY LABELLING FOR SOUTHERN EUROPE COUNTRIES SEVILLA, 7-8 SEPTEMBER 1995

BUILDING ENERGY SAVINGS AND INDOOR AIR QUALITY

Claude-Alain Roulet

BUILDING ENERGY SAVINGS AND INDOOR AIR QUALITY

Claude-Alain Roulet, PhD Institut de Technique du Bâtiment, LESO-.PB, EPFL, CH 1015 Lausanne

INTRODUCTION The main purpose of buildings is to provide a comfortable living environment for occupants. This includes, among others, thermal, visual and acoustical comfort as well as indoor air quality. Except during the fifties and sixties, buildings were also built and managed to avoid an excess use of energy, sometimes by lowering the comfort level. Energy saving is however not the main purpose of the building. Indeed, if it were really so, large energy savings could be obtained by not erecting the building. Some energy is required to control the indoor climate and indoor air quality. Therefore, it is often suspected that energy savings result in poorer indoor environment quality, or, at the contrary, that high comfort level is a result of high technology and high energy consumption. This is not true, and it is now generally admitted among building scientists that high quality energy services do not necessarily incur a high energy use, and that good environment quality can be obtained with a reasonable amount of energy and power. This paper intends to bring some evidence to support this assertion.

ENERGY USE IN BUILDINGS Most energy surveys in buildings have shown a huge dispersion of the energy consumption, whatever this consumption is related to: building volume, heated floor area, envelope area, degree-days, etc. There are many reasons for this, most of them being known: level of thermal insulation, heating and cooling system efficiency, passive solar gains, inhabitant behaviour, building management, and, last but not least, ventilation rate. It is generally admitted that, in temperature-controlled buildings (this means either heated of cooled), the part of energy required for ventilation is between 10 and 50%, depending on the ventilation rate, on the ventilation system and on the energy required for other purposes. The energy saving potential related to ventilation is hence very large.

INTERACTION BETWEEN VENTILATION ENERGY SAVINGS AND INDOOR AIR QUALITY It is often claimed, and sometimes with reason, that problems and health hazards are encountered when applying energy conservation opportunities (ECO's) related to ventilation. We intend to demonstrate below that these problems can be easily avoided, often with an increase in indoor environment quality.

Lower ventilation rate and poor indoor air quality Indoor air quality depends on both contaminant source strength and pure air flow rate. At steady state, a contaminant concentration, C, is the ratio of contaminant source strength, S, and air flow rate, V :

C

S V

S V  C

hence

The outdoor air flow rate, which may require heating or cooling energy, can then be lowered either by increasing the acceptable contaminant concentration or by decreasing the contaminant source strength. The first way cannot be recommended, unless the real concentration is far below the maximum limit. The second way, however, improves indoor air quality without increasing (even decreasing) the energy requirement. Within the frame of the "European Audit Project to Optimise Indoor Air Quality and Energy Consumption in Office Buildings", part of the JOULE Programme (CEC-DG XII) [1], fiftysix office buildings, selected throughout Europe for being as far as possible representative of the building stock, were audited between December 1993 and March 1994. These audits were performed according to a commonly agreed procedure. Among the audited buildings, there was a majority of:  mechanically ventilated buildings, mostly with automatic control and mixing principle,  buildings equipped with cooling,  mechanical ventilation without recirculation. None of the audited buildings exhibited sick building syndrome The indoor air quality was found acceptable by a majority of occupants in 70% of buildings. In this respect the audited buildings, including their ventilation systems, can be considered as being typical of the current situation in European buildings. Results from this audit will be shown as examples. Figure 1 shows the outdoor air flow rate and total air supply per working place in audited rooms. The average value for outdoor air is about 25 l/(s·person) and the median at 21 l/(s·person). 100% 80% 60% 40% Outdoor air 20%

Supply

0% 0

20 40 60 80 Air flow rate/person [l/(s·pers.)]

100

Figure 1: Cumulated frequencies of total and supply air flow rate per working place

No clear relationship was found between outdoor air flow rate and indicators of indoor air quality such as perceived IAQ (decipol), TVOC, CO2, CO or dust concentrations. This results from the fact that, in most buildings, the main contaminant source was the building itself. Moreover, contaminant source strengths have shown wide variations among buildings.

Figure 3: Theoretical energy saving on ventilation heat loss, in relation to specific outdoor air flow rate. A, B and C indicate the limits recommended by prENV 1752.

Ventilation energy saving [%

On the average, buildings were found over-ventilated with respect to today's standards. In fact, if all audited buildings would comply to recommendation of prENV 1752 [2] class C (that is 0.8 [l/(s m²)], 57% energy savings on ventilation heat loss could theoretically be achieved (Figure 3). Note that this draft pre-standard assumes that the building is clean, what was not the case, on the average, in the audited buildings.

60% 40% 20% 0% C

B

A

-20% 0.5

1.0 1.5 2.0 Outdoor air flow rate [l/(s·m²)]

In reality, no relation was found between energy index (ratio of the total yearly energy consumption to gross heated floor area) and measured outdoor air change rate (Figure 2). Figure 2: Energy index related to outdoor air change rate in audited buildings. Each dot represents a building. Legends on top of the figure indicate design air change rates (volumes per hour).

Energy Index [MJ/m²]

0.5 to 1

1 to 3

>3

2500 2000 1500 1000 500 0 0

1 2 3 4 5 Measured air change rate [/h]

6

This lack of correlation has two reasons: 1. Energy is used for in buildings for many purposes other than ventilation, and is typically only 30 - 50% of the energy used for space heating. There is a large range in energy consumption, resulting from the wide variety of buildings and uses. The differences in energy consumption caused by ventilation cannot be seen amongst the variations of energy consumption resulting from other causes. 2. Buildings may use a range of energy in providing a given ventilation rate. For example, some of the buildings are equipped with heat recovery systems, and others have heating and cooling ensured by other means than air (e.g. water radiators, cooling building structure, etc.). This absence of correlation also indicates that it is possible to make low energy buildings with any rteasonable air change rate.

High humidity and mould growth In dwellings, and especially in social dwellings, an increase in mould growth was often observed after energy retrofitting measures were undertaken. It can indeed be expected that air humidity will be increased when:  Single pane glazing are replaced by double pane glazing.  Old, untight windows and doors are replaced by new, airtight ones.  Ventilation openings are closed to avoid drafts.  Internal temperature is decreased in winter. A necessary condition for mould growth is humid surfaces. This happens when internal surface temperature is close to the dew point of indoor air, that is either when the surface temperature is too low (poor thermal insulation) or when the indoor air is too humid. In winter, single pane windows dry the internal air by condensation on the glass. The water freezes or drops on the shelf below the windows, the housewife wipes it form time to time, and the risk of mould growth is relatively low. Moreover, old single pane windows are often not very tight, and the ventilation rate remains high enough to avoid surface condensation on poorly insulated walls. If the glazing is changed to more airtight and double pane windows, two phenomena occur at the same time: the ventilation rate may decrease, and condensation no more takes place on the glazing. Indoor air humidity is increased and surface moisture rises on cold surfaces - that is on poorly insulated walls - and mould grows. If such a health hazard is to be feared of, the building envelope should be better insulated before or together with changing the glazing. From our experience, poor thermal insulation is the primary cause of mould growth in Swiss dwellings, and probably also in many other countries. Buildings of the late sixties were poorly insulated and not airtight: this results in acceptable indoor environment if much energy is used to maintain a comfortable indoor temperature. But as soon as the indoor air dew point is increased or the ventilation rate is decreased, mould grow. For such buildings, energy retrofit shall necessarily include a better thermal insulation, and then (or at the same time), an improved air tightness. Today's thermal insulation standards would result, in most European countries, in an internal surface temperature higher than 2 K below internal temperature. This would allow for a relative indoor air humidity as high as 90% without surface condensation or 70% without mould growth. Such high indoor air humidity cannot be reached in dwellings with usual activity and minimum ventilation. In other words, if a dwelling is thermally insulated according to today's standards, lack of ventilation would result in unbearable odour and carbon dioxide concentration far before mould growth is made possible. Airtight envelope is a prerequisite for controlled ventilation and should also be included in energy retrofit planning. Ventilation must be ensured by other means than infiltration: by either ventilation openings, stack effect ducts or mechanical ventilation. Mould growth after energy retrofit measures is the result of a poor planning of these measures, not the result of the measures themselves.

Energy, ventilation and sick building syndrome Basically, office buildings should be planned, built and managed to offer an environment in which workers feel well. It can be expected than people showing symptoms of poor health related to their work environment will be less productive. Since a lost working hour costs as much as the heat required over one year for two to seven square meters of office space, we

might expect that greater emphasis is given by management to occupants satisfaction than to energy use in office buildings. Managers are hence ready to install costly HVAC installations to ensure a good indoor climate. However, Figure 5 shows that greater energy consumption does not result in better occupant health. At 95% probability, there is a significant and positive correlation between BSI and energy index observed within the European IAQ Audit. In fact, the higher the energy consumption is, the larger is the BSI. The link between these two variable could be common causes such as:  poor control on indoor climate is energy wasteful and not acceptable to occupants,  air conditioning often uses significantly more energy, yet is often not well liked,  well-designed and well-managed buildings provide a very good indoor environment quality (hence a low BSI) together with a rational use of energy. Energy 2500 Index 2000 [MJ/m²] 1500 1000 500 0 0

1

2

3

4

5

6

BSI

Figure 3: Energy index related to Building Symptom Index (BSI). The BSI used here is the average number of building related symptoms declared by the occupants, out of a list of 12.

It is now clear that, if poor ventilation may result in sick building syndrome, the reciprocal is not always true: sick building syndrome may be (and often is) the result of poor indoor environment not related to ventilation.

Higher radon concentration The fear of higher radon internal concentration is often feared in relation to energy savings by reduced ventilation rate. In fact, this is completely wrong, for several reasons. First, when radon concentration becomes unacceptable, it is one or more orders of magnitude too high. For example, in Switzerland, 10% of investigated buildings present a radon activity higher than 200 Bq/m³, even up to 5000 Bq/m³ [3], while outdoor air has an activity below 20 Bq/m³. This means that indoor radon cannot be diluted by increased ventilation, since this would result in unacceptable draughts. The only way to avoid excessive radon activity is to keep it out of the building (airtight floor), or to blow it out before it enters the living areas (ventilated crawl space or cellar). If radon concentration is acceptable, decreasing ventilation rate by as much as a factor of two would theoretically increase the radon concentration by the same factor, but this concentration would still be accepted in many cases. However, there is experimental evidence that energy retrofit, including envelope air-tightness improvement, does not result in increased internal radon activity, but even decreases it slightly within the living area (Figure 4). Radon activity was measured in twenty-five Swiss multifamily dwellings and seven single-family homes, before and after energy retrofitting,

under very similar meteorological conditions [4]. On the average, radon concentration increased slightly in the cellars, decreased in the lowest floors and remained about the same in higher floors. The explanation is that radon enters in the building through the cellar. If the envelope is more airtight, infiltration decreases as well as exfiltration. Controlled ventilation replaces uncontrolled infiltration, the part of outdoor air increases while the infiltration from the cellar decreases.

250 Radon [Bq/m³]

Radon [Bq/m³]

80 60 40 20

200 150 100 50 0

0

-1 0 1 2 2 3 4 5 6 Floor Floor Nr. Figure 4: Geometric average ± 95% confidence interval of radon concentration in 25 multifamily dwellings (left) and 7 single family homes in Switzerland; before (full line) and after (dotted line) energy retrofit [4].

-1

0

1

IMPROVING BOTH INDOOR AIR QUALITY AND ENERGY EFFICIENCY. Some ways to solve the mentioned problems and to ensure good indoor air quality together with sustainable energy use were already mentioned above. There are some more ways, not related to possible problems which will be presented below.

Source control The strategy consisting in  avoiding any unnecessary contaminant sources indoors,  separating areas with contaminant sources from other living areas,  extracting unavoidable contaminants as close as possible from their sources, was already mentioned, as well in this contribution as in innumerable and valuable papers in the literature. Since this basic strategy is still not universally applied, it should be repeated. Such a strategy allows for the reduction of ventilation rates to minimum levels without decreasing the indoor air quality, but reduces considerably the energy required for ventilation.

Efficient ventilation system It is well known that ventilation efficiency can be improved in many buildings. This would result in a better indoor air quality in occupied areas wit lower air flow rates. Moreover, the energy efficiency of ventilation systems is often very poor, especially in small systems. For example, efficiencies as low as 5% were measured for ventilation fans [5].

Table 1 shows several statistics of energy index for various groupings of buildings audited within the European IAQ Audit, according to their design air change rate, their ventilation system, the presence of cooling, and the type of heat recovery. There is no relation between energy index and design air change rate. One more reason for lack of correlation is that design air change rate is not much related to real air change rate. Among the audited buildings, the seven buildings with natural ventilation present, on the average, the lowest energy index. In this group is also the smallest energy consumer. However, two buildings of this group have an energy index larger than 1200 MJ/m². The other buildings, having mechanical ventilation, present similar average energy consumption and include the largest consumers. There are anyway buildings with relatively low energy index in each group. Table 1: Statistics of energy index [MJ/m²] for various groups related to ventilation system.

Number Design air change rate 0.5 to 1 8 1 to 3 22 >3 13 Ventilation system Natural 7 Supply 3 VAV 5 Dual duct 10 Induction 10 Other 16 Cooling No 14 Yes 38 Heat recovery None 17 Wheel 14 Plate 4 Other 11

Mean Stdev Max. 1 183 499 1 850 1 087 413 1 872 1 172 486 2 045 879 306 1 267 1 036 234 1 220 1 340 412 1 789 1 046 522 1 835 1 375 579 2 476 1 041 411 1 872 1 007 360 1 664 1 168 498 2 476 1 087 449 1 872 1 047 406 1 850 1 239 355 1 730 1 365 610 2 476

Min 525 526 400 372 772 813 400 720 525 372 400 400 525 881 536

The presence of cooling or heat recovery does not seem to have a large influence on the average energy index, except that the largest consumers are also cooled buildings. Here again, there are low energy buildings in all groups. Note that "other" heat recovery systems is often recirculation. The conclusion of this is that it is possible to make low- or high-energy buildings with any ventilation system.

Coordination and planning Unfortunately, it is still necessary to repeat that good coordination and planning are paramount for good quality buildings at reasonable cost. Good quality includes ventilation, indoor environment quality and energy savings. In addition, it should be said that planning includes a careful commissioning of the building and its installations. This is the only way to ensure that they actually function as planned.

Maintenance Once well planned, built and commissioned, any building should be maintained. The best ventilation or energy system becomes dirty and may present failures after some time. Only a proper maintenance can ensure continuous performance over years. At the contrary, it was shown by experience that dangerous health hazards and large energy wastes may result from insufficient maintenance.

CONCLUSIONS In buildings, energy is required, among others, for purposes given in Table 2. This table also propose 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 2: Functions of the building requiring energy, together with some ways to save energy and effects of these energy saving measures on comfort. Energy required for Compensation of transmission heat loss in winter Compensation of ventilation heat loss in winter

Ways to save energy Better, thicker insulation, low emmissivity multiple glazing. Lower ventilation rate

Impact on comfort Improvement through higher internal surface temperature of envelope elements. May result in low IAQ in "dirty" buildings Limit the ventilation rate to Less drafts, less noise, good IAQ the required level Use heat exchangers Limits the use of natural ventilation to mild seasons. Winter heating in general Improve solar gains with If windows are poor: cold surfaces. larger, well placed Over-heating if poor solar windows. protections. Improve the use of gains by If well planned: nice visual contact better insulation and good with outdoor environment, very good thermal inertia. summer- and winter comfort. Elimination of heat gains Use passive cooling Very comfortable in appropriate during warm season climates and buildings. Use efficient, well Better IAQ and comfort commissioned and maintained systems Higher internal temperature Should be kept within comfort zone. Internal temperature Comfortable set-point Avoid over- and under-heating control temperature, good control Air humidity control Switch it off No effect in many cases, but not applicable in hot and moist climates. Lighting Use daylighting Comfortable light, with limited heat gains when well controlled. Use efficient artificial Comfort depends on the quality of lighting. light. Limited heat gains.

Of course, some ECO's may also destroy the indoor environment. The EC Directive 89/106 [6] considers as well good "hygiene, health and environment" as "energy economy and heat retention" as essential:requirements. Measures such as low internal temperature or too low ventilation rate should therefore either be avoided, or taken only in case of emergency. Some other ECO's should be only used in conjunction with others. A typical example is retrofitting windows in poorly insulated dwellings. The following conclusions related to energy can then be deduced from experience and surveys:  Energy consumption varies strongly from building to building. In practice, it depends more on planning, construction, and management than on climate, building type or HVAC systems.  It is hence possible to make low-energy buildings with good indoor air quality, pleasant architectures and various HVAC systems.  If planning, construction, and management are performed by energy conscious persons, the result will be a low energy consumption together with a good indoor environment quality.  On the contrary, one single weak step (e.g. poor management or poor planning) may destroy the qualities of a building or the effects of a conscious management. There are then some arguments showing that healthy buildings do not require necessarily much energy. Smart managers, architects and engineers make and operate buildings in a way that both good indoor environment and low energy consumption can be achieved. At the contrary, some expensive ways aiming to improve indoor environment are sometimes counter productive. Even when recommendations on physical parameters (temperature, air flow rates, etc.) are met, occupants do not feel well. Energy labelling should also consider the building performance in indoor environment quality. Energy should not be saved on the cost of indoor environment: this would result in a bad perception, and may generate unexpected wastes.

ACKNOWLEDGEMENTS A part of this work was integrated in the "European Audit Project to Optimise Indoor Air Quality and Energy Consumption in Office Buildings", part of the JOULE Programme (CECDG XII), under the management of Dr. G. Deschamps (CEC), and the coordination of Dr. Philomena Bluyssen (TNO) and Prof. E. De Oliveira Fernandes (U. Of Porto), with the participation of the following institutions: TNO-Building and Construction Research, Department of Indoor Environment, Building physics and Systems, The Netherlands; Technical University of Denmark, Laboratory of Heating and Air Conditioning, Denmark; Danish Building Research Institute (SBI), Denmark; Building Research Establishment (BRE), United Kingdom; EA Technology, United Kingdom; University of Athens, Department of Applied Physics, Greece; CSTB, France; Belgium Building Research Institute (CSTCWCTB), Belgium; Swiss Federal Institute of Technology Lausanne (EPFL), Solar energy and building physics laboratory, Switzerland; Technical Research Centre of Finland, Finland; Norwegian Building Research Institute (Byggforsk), Norway; University of Berlin, Germany.

REFERENCES [1]

Bluyssen, Ph.: de Oliveira Fernandes, E., Fanger, P.O., Groes, L.; Clausen, G.; Roulet, C.-A.; Bernhard, C.-A.; Valbjorn, O.: European Audit Project to Optimise Indoor Air Quality and Energy Consumption in Office Buildings, Final report. TNO, Delft, 1995.

[2]

prENV 1752. Ventilation for buildings - Design criteria for the indoor environment. Draft from CEN/TC 156, 1994.

[3]

Völkle, H.; Sturny, B.; Steffes, F.; Tercier, P.-A.; Truffer, R.; Schnyder, M. und Johner, Ch.: Radon-messungen in schweizer Wohnhäusern. In Radonprogram Schweitz "RAPROS", Bericht üher die ergebnisse der Jahre 1987-1991. OFSP (Swiss office for public health), March 1992.

[4]

Crameri, R.; Furrer, D.; und Burkhardt, W.: Radon und Dichtigkeit der Gebäudehülle. In Radonprogram Schweitz "RAPROS", Bericht üher die ergebnisse der Jahre 19871991. OFSP (Swiss office for public health), March 1992.

[5]

Spoehrle, G.; Siegnthaler Usrsu, E.: Extraction d’air des bains, WC, Cuisines. Publications RAVEL, OFQC, Bern, 1993. OCFIM Nr: 724.397.11.51

[6]

Directive 89/106/EEC on the approximation of laws, regulation and administrative rovisions of the member states relating to construciton products.