SUSTAINABLE LOW COST BUILDING ENVELOPES IN TROPICAL COUNTRIES AND INTEGRATED DESIGN PROCESS: A CASE STUDY IN CAMBODIA F. Garde1; A. Scognamiglio2; M. Basile3; J. Gorgone3; D. Mathieu1; M. L. Palumbo3; 1: Faculty of Engineering ESIROI, University of Reunion, France 2: ENEA (Italian National Institute for New Technologies, Energy and Sustainable Economic Development), Photovoltaic Technologies Area, Portici Research Centre, largo E. Fermi 1, Portici, Italy 3: InArch, Italian National Institute of Architecture, via Gorizia 42, Rome, Italy
ABSTRACT
This paper deals with the integrated design approach that was used by an international team to design a low-cost and sustainable house for Cambodia’s future. The main issue was to design houses that promote health, and to allow local people to live in at affordable and attractive conditions. The aim was to find sustainable solutions that take into account the local architectural tradition, the use of renewable materials (clay, bamboo and palm leaves), the local climate conditions, and the use of the solar energy as well. One important feature of the project is the replicability of the prototype to a wide number of sites and conditions common to Cambodia. The first step was a climate assessment of the country in terms of possible and optimum conditions that could be reached with passive means and to collect information about the traditional Khmer houses in terms of architectural, social and cultural aspects. A design charette was then organised to taken into account all the aspects (Ecological footprint, optimised solar shading systems, use of cross natural ventilation etc.). The paper presents the evolution of the project until the final stage. It will include the architectural concept, dynamic thermal simulations and the use of the Givoni comfort zones. A comparison was made between the project and a traditional Cambodian Khmer house to assess the improvements in terms of thermal comfort. The final project gets an indoor air temperature which is 4°C lower compare to a traditional house. Keywords: Design, Sustainable, Low-cost Housing, Tropical Countries INTRODUCTION
The occasion for the research experience presented with this paper was an international competition for low cost housing in Cambodia, launched by Building Trust International. This is an organisation that works with existing charities and communities in need, and that regularly holds design competitions to raise funds and get the best solution to a global issue. One of the most recent competitions was Cambodia Sustainable Housing. The object of the competition was designs that could propose a sustainable future for housing in the South-east Asian country. Any proposal had to keep below a budget of $2000 and deal with the yearly flooding that effects most residential areas. The winning designs could influence the way they build housing in the region, being a kind of reference models for future developments. We entered the competition by forming an interdisciplinary international working group (architects and engineers experienced in sustainable design, modelling, use of renewables), having the appropriate expertise for facing the challenge of the competition.
Despite the brief didn’t ask for specific energy / ecological requirements, we focused on the design of a house-system that could be self-sufficient from the ecological and energy point of view. We took into account the available lot assigned by the competition brief, and, within the border of this lot, we tried to design a productive house, so that it could work as an organism able to produce the energy that the users need (food-energy for metabolism + energy for the building operation), and to collect and re-use the rain water so to that food could be grown all the year long. To do this, we gave a form to what we call “productive footprint” of the building that is necessary area for placing energy generating systems, so to get a Zero Energy Balance of the building. [1] METHODOLOGY
A design methodology was set-up by the multidisciplinary team composed as we said before by people from different countries and from different backgrounds (architects and engineers/building physicists). We follow an integrated design process based on several steps: 1. Knowledge of the climate and of the traditional Khmer houses, bibliography about the materials used in Cambodia and in close countries; 2. Design charette to take into account all the design aspects (Ecological footprint, optimised solar shading systems, use of cross natural ventilation, material etc.); 3. Multiple exchanges between all the team participants to improve the components of the envelope; 4. Design of the final project; 5. Building thermal simulations, CFD modelling; 6. Preparation of the final poster to be submitted. KNOWLEDGE OF THE TRADITIONAL HOUSES/CULTURE
We started from the study of the traditional Khmer house, in order to understand how the living and the working space can be organized [2]. In a few words, the traditional Khmer house is a wooden two-floor house, organized in a ground level that is generally opened on its sides, and an upper level that is a kind of closed box, often covered by a sloped roof (see Fig. 1a). The kitchen space is in between this two floor, close to the wooden stairs (so to protect food from animals). The structure is made out of wood, and the light walls are made out of palm leaves. The foundation of the building, especially if very close to rivers, is made out of poles.
Figures 1a and 1b : Traditional rural Khmer houses with wooden poles. The building serves as a shelter. During the day the house functions as a large umbrella. Work and life go on at ground level, where the most effective shade is provided. At night, people sleep upstairs
From the analysis, we understood that a very important part of the organization of the traditional Cambodian house is the ground floor, and the contact with the ground itself. On the ground the food is produced, on the ground animals are bred, very often people are seated directly on the ground. Nevertheless this ground often is flooded, due to the presence of rivers that flood in the rain season (see Fig. 1b). As a consequence people who are in river areas use light wooden platform, to create a kind of artificial level, slightly detached from the ground, which protect them and their goods from the water in case of flood. This wooden artificial level is the main living and working space of the Cambodian house, also because it is the most comfortable part of the house, being ventilated and being shadowed by the upper part of the house. In addition to this, the ground floor is also very important in terms of social connections, since it is a relation space that allows people to share the daily life among the community. In terms of thermal comfort, Ono has carried some interesting measurements in different type of houses in Cambodia. He shows that the indoor temperature of the traditional house can reach 38°C, which is a 4°C higher than the outdoor temperature. This is mainly due to the radiant heat from the structure, especially the roof [3]. CLIMATE ASSESSMENT
The latitude of Cambodia ranges from 10° North to 14° North. This country experiences a tropical climate with two seasons: the monsoon between April and September and a dry season the rest of the year. The hottest month is March at the end of the dry season with maximum temperatures that can reach 40°C in the interior of the country. The climate is weakly different between the southwest coast (Kampot) and the interior (Steung-Treng). The differences between the dry and wet season are more pronounced in the interior. In our case, the simulations and design solutions were achieved with weather data from Phnom-Penh (figures below). The climate of the Cambodia’s capital is intermediate with a mean monthly dry bulb temperature that range from 25°C to 30°C. The maximum temperature never exceeds 35°C but also never drops below 20°C (see Fig. 2). At this latitude, the sun path is relatively high in the sky all the year. Consequently, the main surfaces exposed to the sunrays are the roof, the east and west walls. The wind rose of this town shows that most of the time blows a wind from the north or from the south. With only a weak part of the time without wind (6.5%), the potential of natural ventilation of buildings is real (see Fig. 3). Even if the weather is hot and wet the major part of the year, the Givoni’s chart [4]. Figure 2 shows that the comfort conditions can be reach 71% of the time with a air velocity of 1m/s.
Figure 2 : Temperature and humidity couples for the capital city Phnom-Penh
Figure 3 : Wind rose of Phnom-Penh
The Final project Obviously the main design aim, due to the geographical area where the project is located, was to face the summer challenge. The climate analysis and the understanding of the design of the traditional Khmer house helped us to understand how the thermal behaviour of this kind of house could be improved. So our challenge was in one hand to develop a functional spatial scheme that could reproduce the one of the traditional Khmer house (very effective also in terms of social relationships), and on the other hand to improve its quality and its energy performance by passive strategies. Figure 4 explains in details all our strategies in terms of sustainability and thermal comfort. Basically, the enveloped has been designed to have large solar shadings and big openings to avoid overheating of the roof and the walls and to have an efficient cross natural ventilation, which are the two main passive strategies in a tropical climate [5], [6]. Local materials such as vetiver and bamboo have been used in priority [7].
Figure 4 : Description of the passive design and sustainable features of the project. Local materials are mostly used, such as bamboo, vetiver, local timber, palm leaves, with a double skin roof and efficient solar shadings that prevent the light walls from overheating We designed a two-floor house, characterized by a compact volume on the Northern side, and by a open space on the South side; a sun-shading system protects the East side from overheating, and the openings on the West side walls enhance the natural ventilation. The
roof, made out of bamboo, allows the rain water collection, and the water is stored in tanks, placed on the North side of the building, so to improve the thermal performance of the service block (kitchen + toilettes). The ground floor is characterized by a productive garden where food can be grown for the family’s needs, and this, together with the artificial wooden platform, constitutes the main living and working area of the house. At the upper level there are the bedrooms, which face the double height corresponding to the productive garden. We considered that in case on further needs for space, this bedrooms space can be extended over the productive garden. MODEL AND SIMULATION
Two models of houses have been developed under the Google Sketchup/Open studio environment: the traditional Khmer house and the improved project. The thermal and physical properties of the materials used are detailed in Table 1. The simulations have been run under a whole year at an hourly time step. The outputs were the operative temperature and the Givoni’s comfort zones. Table 1 : Thermal and physical properties of the materials used Material
Thermal conductivity
2 0.075
(W/m.K) 0,14 0,07 1,5 0.6 0,19 45
Specific Heat (J/kg.K) 2000 2000 2085 4185 2390 500
4
2
1000
Thickness (cm)
Nipa palm (Walls) Vetiver (straw) Clay Water (Tank) Teck wood (floor) Corrugated iron (Trad) Concrete (water storage)
2 20 20
Density
Absorptivity
0.5 0,5 1.5 1 0.7 78
0,7 0,6 0,6 0.78 0.6
2.4
0.6
RESULTS AND DISCUSSION
Figures 4 shows the comparison between the project and a traditional Cambodian Khmer house in terms of operative temperature. The final project gets an indoor air temperature which is 4°C lower compare to a traditional house.
Figure 5 : Comparison of the operative temperature during the hottest days in a traditional Khmer house and in the final project. The difference is approximately 4°C below.
Figure 6: Thermal comfort conditions Project (Roof: Bamboo and Vetiver straw; Walls: Nipa palm; Floors: wood)
Figure 7: Thermal comfort conditions Traditional rural house: (Roof: Corrugated iron + Nipa Palm; Walls: Nipa palm; Floors: wood)
In terms of thermal comfort, the final project (Figure 6) behaves better than the traditional house (Figure 7). The resultant temperature and humidity couples are closer to the comfort zone. The indoor temperature never reaches 36°C for the project model whereas it reaches 40°C for the traditional house. These results are close to Ono’s measurements [3]. CONCLUSION
The IDP approach that was used by the multidisciplinary team to design a low-cost and sustainable house for Cambodia has lead to an efficient house that respond to all of the constraints of the site. The constant interaction between architects and engineers from the early sketch of the project has lead to a final design that behaves well in terms of thermal comfort with a gain in temperature of 4°C and in the same time that responds to the social and living needs of the occupants. The traditional spatial model of the house can be improved by considering the need to contain the ecological footprint within the building’s footprint (rain water collection, phyto-depuration system, productive garden, and photovoltaic modules on the roof, together with the use of sustainable materials). REFERENCES
1. Palumbo, M. L., Scognamiglio, A. Designing material and energy flows for an urban ecosystem. Proceedings of the CISBAT 2011- International Scientific Conference Renewables in a changing climate. From Nano to Urban Scale, Lausanne, Switzerland, 14-16 September 2011, pp. 671-677, ISBN 9782839909068. 2. Rural Khmer house on Wikipedia. http://en.wikipedia.org/wiki/Rural_Khmer_house, October 2012. 3. Ono, K. et al. Investigation of Residential Energy Consumption and Indoor Thermal Environment of Housing in Cambodia. In Proceedings of SUDAC 2010, International Conference on Sustainable Urban Design in Asia City. October 2010. 4. Givoni, B. Comfort, Climate Analysis and Building Design Guidelines. Energy and Buildings, v.18, n.1, p. 11-23, 1992 5. Tantasavasdi C., Srebic, J. Chen, Q. Natural ventilation design for houses in Thailand. Energy and Buildings, 33(8), 815-824. 2001. 6. Garde, F., Boyer, H., Celaire, R., Bringing simulation to implementation : Presentation of a global approach in the design of passive solar buildings under humid tropical climates., Solar Energy, Vol.71, 2001, p.109-120. 7. Hengsadeekul, T. Construction of Paddy Storage Silo Using Vetiver Grass and Clay. Australian Journal of Technology. 7(3): 120-128 (Jan. 2004)
