sustainable wooden envelope for subtropical regions

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REGIONS – THE REALIZATION AND VALIDATION IN JAPAN. Yutaka Goto1, York ... Energy efficient housing therefore seems to be a valid way to proceed with.
SUSTAINABLE WOODEN ENVELOPE FOR SUBTROPICAL REGIONS – THE REALIZATION AND VALIDATION IN JAPAN Yutaka Goto1, York Ostermeyer2, Karim Ghazi Wakili3, Andrea Frangi4, Naoto Ando5, Holger Wallbaum6. ABSTRACT: A vapor-open wooden building envelope for subtropical regions and its design optimization method, which considers environmental, economic and thermo-hygric aspects, were developed by the authors. As a case study, a test house (a detached residential building) has been constructed in Ohmihachiman (central Japan) and a number of temperature/humidity sensors were installed inside the walls as well as in the rooms. It was found that close communications among the designers, the constructors and the client is essential in order to realize a building with new features as it is designed. The hygrothermal model of the building envelope was successfully validated. KEYWORDS: Sustainability, Vapor-open envelope, whole building hygrothermal model, test house, Japan

1 INTRODUCTION 123 With regard to the resource depletion and the global climate change, it is widely recognized that the construction industry is playing a key role in potentially mitigating these issues [1]. In order to improve the energy efficiency of buildings, several design protocols for building envelope and equipment have been proposed and implemented in cold/mild climate regions. The MINERGIE® Building Association [2] of Switzerland has developed the energy certification method such as MINERGIE® and MINERGIE-P®. Due to promotion schemes driven by subsidies from local governments in Switzerland, more than 10,000 housings have been certified by this energy label [3]. The Passivhaus Institute [4] from Germany developed one of the first energy labeling method for nearly zero energy buildings. Recent studies have shown that the actual energy performance of certified Passivhaus buildings match the calculated energy 1

Yutaka Goto, Chalmers University of Technology, SE-412 96 Gothenburg, Gothenburg, Sweden. Email: [email protected] 2 York Ostermeyer, Chalmers University of Technology, SE-412 96 Gothenburg, Gothenburg, Sweden 3 Karim Ghazi Wakili, Empa. Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, Duebendorf, Switzerland 4 Andrea Frangi, ETH Zurich, Wolfgang-Pauli-Strasse 15, Zurich, Switzerland 5 Naoto Ando, The University of Tokyo, 1-1-1 Yayoi, Tokyo, Japan 6 Holger Wallbaum, Chalmers University of Technology, SE-412 96 Gothenburg, Gothenburg, Sweden

demand [4]. Energy efficient housing therefore seems to be a valid way to proceed with. In order to achieve the desired performance of a building with advanced technologies, it is always important to consider the local frame conditions when a technology is deployed in a certain place for the first time. Especially the climatic and behavioral difference may result in differences in the performance of a technology and as a result in a serious damage in building components and/or inhabitants’ health. When the air-tightness was introduced in order to achieve higher energy efficiency of buildings, cases of collapse of building frame [5] and users’ health problem [6] due to moisture accumulation and mold growth were reported. The reason for this was that the moisture load from outside/inside was not properly considered when changing the building concept in accordance with the local climatic conditions. Furthermore, when applying a new technology, there should be a sound investigation not only before applying but also during the construction and the operational phase in order to validate whether or not the technology is performing as desired. Within a research projects, the authors have developed an innovative vapor-open wooden building envelope system for subtropical regions, which can provide highly energy efficient buildings with high level of indoor comfort. In June 2013, a test house was realized in central Japan. This paper reports the designing and construction processes of this test house and the preliminary results of the measurement and analyses of the indoor climate and the temperature and humidity inside the envelope.

2 SUSTAINABLE BUILDING ENVELOPE FOR SUBTROPICAL REGIONS The interest of energy efficiency is growing in subtropical regions because of the high growth rate in the urbanizing areas in these regions. From the view point of building physics, such a climatic condition is very challenging because of both heating and cooling demands. Figure 1 shows such regions according to Köppen-Geiger Climate classification [7].

these methods, Life Cycle Assessment (LCA) and Life Cycle Cost Assessment (LCCA), the authors proposed the optimization method for the thickness of the insulation layer [10]. The optimal insulation thickness taking into account the heating/cooling cost, the environmental impact based on multiple indicators and the minimum requirement concerning the moisture accumulation over the lifetime of the insulation layer was calculated based on a certain design setting of a house. Finally it was shown that the envelope system is economically, environmentally and hygrothermally feasible in Japan (especially in the ventral part) which has a wide range of climatic diversity. (The climate division of Japan according to Japan’s energy conservation law is shown in Figure 3.)

Figure 1: Subtropical regions according to Köppen-Geiger climate classification

Considering this issue, a new building envelope system was developed within the research team led by the authors. This envelope system mainly consists of major layers with natural materials, namely the external insulation layer with wood fiber board, the structural layer with cross laminated wooden panel and the interior finishing layer with the composite of wood and clay. The illustration of the envelope system and the materials for each layer is shown in Figure 2. The basic design philosophy of this system is that the envelope consists of hygroscopic materials with moderate vapor permeability. This system allows the moisture flux to move through the wall in both directions. By defining the appropriate thickness to each layer, it is possible to avoid moisture related problems inside the wall by humidity buffering. The hygrothermal property of the envelope has already been studied and it was shown that the heat and moisture transfer across the wall under laboratory condition is predictable with a commercial simulation tool and that the envelope system is applicable while avoiding excessive moisture accumulation in exterior walls under the actual climate in central Japan [8]. Based on this modelling and moisture accumulation evaluation, the whole building heat and moisture balance simulation method for buildings with this system was also developed [9]. It was made possible to predict the indoor temperature-humidity and heating/cooling demand of a building with this envelope system. It was also shown that it is possible to realize a highly energy efficient house (as good as the MINERGIE P® standard [2]) with a realistic design set-up of the envelope and housing services. Furthermore, combining

Figure 2: Layered structure of the vapor-open envelope system for subtropical regions

3 DESIGN OF THE TEST HOUSE It was decided that a building with the envelope system would be realized in Ohmihachiman (central Japan, in zone 4 which has a typical subtropical climate with hothumid summer and cold-dry winter). The geographical location of Ohmihachiman (35.1° N, 136.0° E) is shown in Figure 3. The annual AMeDAS (Automated Meteorological Data Acquisition System [11]) climate data (temperature and absolute humidity) from the weather station in Hikone ,which is the closest one to Ohmihachiman, is shown in Figure 4.

Figure 3: Climate division of Japan and the location of the test house

(a) Temperature

(a) Plan of GF

(b) Absolute humidity Figure 4: Annual climatic condition of Hikone ((a) temperature and (b) absolute humidity)

The general design of the building was done by local architects and the technical supervision was done by the research team. The building is a detached residential building where two to four persons (two adults and up to two children) were supposed to reside. Based on the LCA, LCCA and thermo-hygric analysis considering the specific design conditions, the optimal thickness of wood fiber insulation was given at 10-17 cm based on the estimated material price [12]. The economic optimal insulation thickness was recalculated upon the final decision of the insulation material based on its retail price. This calculation modified the optimal thickness to 10-20 cm. There was also the consideration of acquiring the energy certificate of MINERGIE P®. Then the insulation thickness was decided to be 18 cm finally. As for HVAC system, radiators for heating and cooling-dehumidification and a mechanical ventilation with heat exchanger were employed. The façade consists of cladding with venting layer of 18 mm. The surface of the insulation was designed to be covered with vapor-open and water-tight membrane. Air-tight membrane is employed between the insulation and the structural panel in order to avoid the air stream across the wall due to pressure difference. The plan and the elevation of the test house is shown in Figure 5.

(b) Plan of 1F

(c) Elevation of south facade Figure 5: Plan of ground floor (GF) (a) and the first floor (1F) (b), elevation of south façade and the position of sensor nodes

The challenge of the design process was to achieve the same level of understanding when integrating the existing local technologies and the innovation from another context as well as the local legal framework and socio-cultural aspect such as the difference of preference on housing service. Throughout the designing processes, it was experienced that a close communication among all the international players (client, architect, construction manager, master carpenter, technical supervisor, material provider) through a communication hub (project coordinator) was essential in order to avoid misunderstandings, to promote the consensus and to eventually realize the intended performance of the building. Especially the active involvement of the client and establishing a solid pipeline between the client and the technical supervisor (which is not often the case with other projects) was the key in order to enhance the common understanding among all the project members.

Figure 6: Foundation of the test house

4 CONSTRUCTION OF THE TEST HOUSE 4.1 PREPARATORY WORKS The concrete foundation was designed to have a flat surface so that the control of heat and moisture transfer through it becomes the least intricate. The top of the foundation was covered with asphalt sheet in order to create a water and vapor proof layer. The gaps that could possibly let termites go through were closed with metal mesh. The foundation itself is shown in Figure 6.

Figure 7: Pre-cut and pre-assemble process in the factory

The structural panels were carried in a factory near the construction site and pre-cut and pre-assembled so that the work at the building site could be minimized. The work is shown in Figure 7. 4.2 THE ERECTION OF THE BUILDING FRAME The assembled panels were carried into the building site on the 5th March 2013, and the building frame (floors, walls and roof) was constructed in three days. Figure 8 shows on of the processes of this. Subsequently windows were installed. Upon the completion of these processes, the whole building frame was wrapped with air-tight membrane. In order to ensure the air-tightness performance, blowing door test was carried out. The air leakage rate at the pressure difference of 50 Pa between interior and exterior was measured at 351 m3/h. By dividing this value with the actual air volume of the house (589.4 m3), the air-tightness n50 was given at 0.596 1/m3. This met the requirement of the air-tightness for those advanced standards (such as Passivhaus and MINERGIE P®), therefore it was decided to continue with the construction of other building parts. Figure 9 shows the north façade before the installation of the air-tight membrane. Figure 10 shows the east façade after the installation of air-tight membrane. Figure 11 shows the blower door test operation.

Figure 8: The construction of the building frame

Figure 9: North façade after installing the windows

screwed to the wall, the joints of the boards were filled with clay plaster and the whole surface of the clay boards was finished with fine clay plaster and clay paint. Figure 14 shows the installation of the clay boards.

Figure 10: East façade after installing the air-tight membrane

Figure 12: Installation of wall insulation

Figure 11: Blower door test operation

4.3 CONSTRUCTION OF THE INSULATION LAYER AND THE INTERIOR FINISH After confirming the sufficient air-tightness of the building frame, the insulation layer was added. The insulation layer for the walls consisted of two layers. Each layer was 90 mm thick. Firstly wooden slats (45 mm x 90 mm) were screwed vertically to the structural panel 437.5 mm apart according to the width of the wood fiber insulation product. After filling the gaps of those wooden slats with the wood fiber insulation, wooden slats with the same dimension was screwed horizontally to those of the first layer with the same pitch. The gaps were likewise filled with wood fiber insulation. In the case of the roof, the first layer had the thickness of 100 mm (wooden slats were orthogonal to the roof slope) and the second layer had the thickness of 120 mm (wooden slats were parallel to the roof slope). The surface of both wall and roof insulation were covered with vapor-open and water-tight membrane. The wall was finished with wooden cladding by giving an air venting layer with 18mm thick. The roof was finished with rafters (45 mm x 90 mm), plywood (12 mm thick), water-tight asphalt sheet and roofing (Aluminum-Zinc alloy coated sheet steel). Figure 12 shows the installation of the wall insulation. Figure 13 show the installation of the water-tight membrane. The interior surface of the building frame was covered with 14 mm thick clay board. The product was a dried board which was produced in factory. The boards were

Figure 13: Installation of water-tight membrane

Figure 14: Installation of clay board

4.4 OTHER ELEMENTS AND THE COMPLETION OF THE CONSTRUCTION In parallel with the works above, plumbing, electric cables, housing service etc. were installed. Additionally, 21 temperature and humidity sensors were installed in order to measure the indoor climate and the conditions inside the external walls and roof. The points of the measurements are; the northern wall on the ground floor (Node 1, five sensors), the western wall in the master bedroom on the first floor (Node 2, five sensors), the northern wall of bathroom on the first floor (Node 3, five sensors), the roof

of the bed room on the first floor (Node 4, four sensors) and the kitchen & living room (Node 5, two sensors). The measuring points are shown in Figure 5. Figure 15 shows one of the sensors (one sensor of Node 2 between the airtight membrane and the first layer of the insulation). The construction was completed on the 26th June 2013. Figure 16 shows the completed house. The construction processes were carefully supervised by the research team so that no faulty works were to be done until the insulation and the water-tight membrane was completed. In fact, because of the lack of experience with this construction system, several significant faults were observed and modified. For example, it was observed that the joint between the structural panel and the insulation layer at the bottom of the wall was not sufficiently sealed. This would result in insufficient air-tightness. This would let the ambient air flow into the gap between the structural panel and the insulation layer which is most sensitive part in terms of moisture condensation. The reason for this was that the construction manager and the carpenters did not have sound understanding of the mechanism of the heat and moisture transfer. Needless to say, it is absolutely necessary both to promote a better understanding of the craftsmen and to provide better documentations of joint details when introducing a new and unfamiliar system in any case. In addition to this, it is highly necessary that the construction processes are closely supervised by the technical staff in order assure the quality of the construction of an innovative building and its performance in the use phase.

Figure 15: A temperature and humidity sensor inserted between air-tight membrane and insulation layer

(b) Living room Figure 16: Completed house ((a): west side façade, (b): living room on the ground floor)

5 MEASUREMENT 5.1 MEASUREMENT SET-UP As mentioned in 4.4, temperature and humidity sensors were installed in the respective parts of the building. The measurement system consists of three types of component, namely base station, sensor node and sensor cable. Each sensor cable is capable of monitoring the temperature and humidity of ambient air. Sensor cables are connected to sensor node. Sensor node is a standalone unit with battery. The data collected by the sensor node and sensor cables are transmitted to the base station wirelessly and the gathered data is uploaded to the online monitoring platform by the base station. This system enables the remote simultaneous monitoring. Figure 17 shows the base station and sensor node with sensor cables. The time step of the measuring was set at ten minutes. Sensor cables were either put in the air next to building components or inserted in between layers of building components. In the case of Node 1-4, the sensors were in the air venting layer (as exterior climate), in between the two insulation layers, between the first layer or the insulation and air-tight membrane, between structural element and clay board (except Node 4) and in the room (as indoor climate). In the case of Node 5, the sensors were put in the air of the kitchen and the living room on the ground floor. The sensors were put in a straight line across the wall. The monitoring started on the 28th Sep 2013. (a)

Figure 16(a) west side façade

(b)

Figure 17: Sensor device ((a): base station, (b): sensor node (Node 5) and sensor cables)

5.2 PRELIMINARY RESULT Figure 18 and Figure 19 show the measurement results of temperature and relative humidity of each sensor node from the 10th to the 31st Jan 2014 respectively. It was generally observed that the temperature gradient across the wall and roof confirmed the proper construction of the envelope. The clay board as interior finish significantly contributes to stabilize the humidity swing in the wall. The exterior air at node 1 shows a rather significant swing of both temperature and humidity. This is due to the influence of the exhaust air from a gas-based water boiler which is located not far from the sensor in the exterior air. (c) Node 3

(a) Node 1 (d) Node 4

(b) Node 2 (e) Node 5

Figure 18: Measured temperature at each sensor node

(a) Node 1

(b) Node 2

(d) Node 4

(e) Node 5 Figure 19: Measured relative humidity at each sensor node

5.3 ANALYSIS OF THE MEASUREMENT

(C) Node 3

In order to verify the hygrothermal performance of the envelope, the simulation of the temperature and humidity across the wall was carried out. A two dimensional transient heat and moisture transfer model was composed using a commercial software (WUFI® 2D-3) ([13] and [14]). The model was given to have 180 mm thick wood fiber insulation, 90 mm thick solid structural element, 14mm thick clay board and 3 mm thick clay plaster. The height of each element was set at 250 mm. The air-tight membrane between the insulation and the structural element was neglected as it has little impact on heat and moisture transfer. The water-tight membrane on the surface of the insulation layer was translated into the surface resistance factor, namely heat resistance was set at 0 m2K/W as it is only a very thin membrane and Sd-value (vapor diffusion resistance equivalent to the thickness of stagnant air) was set at 0.01 m according to the material property provided by the manufacturer [15]. Figure 20 shows the geometry of the finite element model.

(a) In between insulation layers Figure 20: Geometry of finite element model for the heat and moisture transfer simulation

The interior and exterior condition measured with Node 2 (from the 1st Oct 2013 to the 28th Feb 2014) was applied to this model as the boundary condition. As the façade is consisted of wooden cladding and air venting layer, the influence of sunshine and rain water on the exterior surface was excluded in the simulation. The hygrothermal properties of wooden structural panel and clay board were taken from past measurements [8]. Those of wood fiber insulation and clay plaster were taken from the respective manufacturers’ website ([16] and [17]). The time step for the calculation was set at ten minutes. The measurement was interrupted twice due to technical reasons (from the 20th to the 23rd Nov 2013 and from the 29th Dec 2013 to the 8th Jan 2014). Thus the simulation was divided into three periods. The initial condition of each period was given according to the condition and ambient air of each sensor. Figure 21 shows the comparison between the measurement and the simulation of the Node 2. It is observed that the temperature and humidity across the wall can be predicted with a good accuracy in general. Although the fluctuation in the measurement is not predicted exactly in the simulation (ex. see the humidity curve in Figure 21 (a)), the mean value of these fluctuations is calculated with a good accuracy. This means that the construction of the building envelope was done properly and it is working as it was designed. Figure 21 (b) shows the temperature and the humidity of the most sensitive point in terms of interstitial moisture condensation, namely between the first layer of insulation and the air-tight membrane. It shows there is no moisture accumulation within the investigated period. Figure 22 (c) shows that the measured relative humidity between the structural panel and the clay board is rather higher than the calculated values. It is assumed that the drying process of the interior finish (clay plaster) still has a certain impact on the moisture accumulation in the envelope.

(b) Between insulation layer and air-tight membrane

(c) Between structural panel and clay board Figure 21: Comparison of measurement and simulation at Node 2

6 CONCLUSIONS The authors have developed an innovative vapor-open wooden building envelope system for subtropical regions. A test house was planned to be realized in Ohmihachiman (central Japan) in cooperation with practitioners and the client in Japan and technical supervisors (the research team). The insulation thickness of the test house was optimized (18mm) by the method taking into account life time economic, environmental cost and the longevity of the insulation layer. The construction was completed on the 26th June 2013. Throughout the designing and construction processes, it was experienced that a close communication among all the project members (client, architect, construction manager, master carpenter, technical supervisor, material provider) was essential in order to avoid misunderstandings, to promote the consensus and to eventually realize the intended performance of the building especially in such a case as a technology transfer is done as a light house project. The active involvement of the client may be a key to ensure the desired performance of the building. Going from single lighthouse prototypes to an up-scaling approach, where this might not be possible anymore, will be a massive challenge. Furthermore, it is highly necessary that the construction processes are closely supervised by the technical stuff in order assure the quality of the construction of an innovative building and its performance in the use phase. In later up-scaling scenarios schooled craftsmen and skills on the building site will be critical for success. The measurement of the temperature and humidity in the rooms and inside the exterior walls/roof was compared to the calculated values. It was shown that the temperature and humidity across the wall can be predicted with a good accuracy in general. It is concluded that the construction of the building envelope was done properly and the simulation model is valid to predict the behavior of the wall in the real life. The hygrothermal behavior needs to be observed for a longer period for the investigation under hot-humid conditions. The heating and cooling demand should also be investigated in depth for the verification of the whole building heat and moisture balance model in the future.

7 ACKNOWLEDGEMENT The innovation promotion agency CTI of the Swiss Confederation is acknowledged for financial support (grant 9755.1 PFIW-IW). The authors express their sincere gratitude to R. Paul of Swiss Building Components, Y. Hirayama of PS company, Iida-family, K. Matsuo, T. Takamiya, T. Kishimoto for their cooperation for the realization of the test house.

REFERENCES

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