Proceedings of Clima 2007 WellBeing Indoors

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1 Improving building design and indoor conditions in the mid-highlands of the French tropical island of La Réunion. Application to a green building high school Le Tampon Trois Mares. François Garde 1, Alain Bastide 1, Franck Lucas 1, Lauren Christie 2 1 Laboratory of Building Physics and Systems, University of La Reunion, La Reunion, France 2 Centre for Building Performance Research, Victoria University of Wellington, New Zealand Corresponding garde@univ-reunion.fr SUMMARY This paper deals with the use of passive solutions to reach thermal comfort conditions in an educational building under specific tropical climatic conditions. A case study of a green high school building located in the French tropical island of La Reunion at an altitude of 600m was used. The building designers initially planned for mechanical air conditioning in the classrooms and in the administrative section however dynamic simulations pointed out that with an optimisation of passive solutions such as solar protection, insulation, natural and mechanical ventilation; active air conditioning systems could be avoided. Condensation risks during the winter season were analysed also. The high school has been in service since September This research was the first scientific study conducted in the highlands of a tropical island. This paper presents the methodology used and describes the results and passive solutions recommended which are now widely used by building owners to design new building projects located in the same range of altitude. INTRODUCTION The methodology and results presented in this paper were developed within the framework of a research project funded by the Regional council of La Reunion and SEMADER, which is the company responsible for the construction of the high school. The island of La Reunion is a small French tropical island located in the Indian Ocean (21 of latitude south and 55,5 of longitude east). The island is only 70km long and 50 km wide (see Fig.1) and has a growing population. It is estimated that in the next 15 years, the population will have reached the billion marks with 25% of them being less than 20 years old. Ten more high schools are needed to account for this growing population, highlighting the importance of influencing green construction for new educational buildings in every sector elementary schools, primary schools, colleges, high schools and university buildings. The urban areas mainly affected have so far been located along the coastline (see figure 1), but the recent regional urban planning act focuses now on developing the mid-highlands of the island rather than extending new urban areas along the coastline. This is mainly because most of the land is dedicated for the sugar cane industry. Electricity output in these highland areas is restricted and the area is mainly oil-powered (60%) and it is predicted that the energy supply will encounter difficulties with the 7% per year growing energy demand. The Regional Council is aware of the energy problem that is facing the island of La Reunion and has decided to launch a wide program of demand side management and development of the use of renewable energy [1]. The final aim of this programme is to have the island energy autonomous by A part of this program is dedicated to the construction of green buildings, which is the subject of this paper.

2 METHODOLOGY The project consisted of the following steps: 1. Elaboration of typical hourly climatic data representative of the summer season and of the winter season; 2. Choice and Modeling of the typical buildings (that is, classroom, office and computing room); 3. Determination of the outputs and the simulations tools; 4. Simulation and analysis of the results; 5. Synthesis of the results and conclusions. Climate in La Reunion and typical hourly data. As shown in Figure 1, the climate in the island of La Reunion can be divided into four main zones [2]. The first two zones correspond to standard coastal tropical climates. They are both located below 400 metres and differ mainly by the average wind speed. The downwind coast, named zone 1, is the driest, the sunniest and the warmest. This part of the island is protected from trade winds by the mountains. The upwind coast (that is, zone 2) is wet because of its wind exposure. The mean global solar radiation is the same as in zone 1 (5000 kwh/m²/year). The highlands, named zone 4, are situated above 800 metres. The temperature is cool in summer and cold in winter with a minimum that can go down to minus 1 C. The period of sunshine remains good and the humidity is very high. Inhabitants Zone % Zone % Zone % Zone % Total Location of the High school Le Tampon 640 m Zone km Scale Trade winds Figure 1 : Urban areas and climatic zoning of the island of La Reunion The high school is located in zone 3 in the suburbs of a town called Le Tampon. For this reason, we will focus on this specific zone. The main climatic features are given in Table 1. Zone 3 is a mid-highlands zone located between 400 and 800 metres above sea level. The average yearly temperature is 18.2 C. The mean solar radiation and the humidity are high all year round. The climate in this zone does not correspond to an existing classification mainly because of the altitude. Comparison with a standard tropical climate highlights the main differences to be summer conditions which can be hot and humid with temperature and humidity values that can go up to 30 C/78% and winters that can be cold for a tropical climate with temperature and humidity values that can go below 12 C/70%. Due to this, the existing refer-

3 ences on recommendations for building in tropical climates can not be applied to this zone [3]. The recent publications concerning the thermal comfort in classrooms deal with the thermal conception of buildings in tropical climates in Singapore or Hawaii [4] [5] and mainly focus on the comparison between the thermal sensation of the occupants and the ASHRAE Standard [6]. Even the recent work of Kwok in Japanese schools deals with a field survey and a comparison of the occupants preferred thermal state to the ASHRAE comfort standard [7]. While the climate there is close to zone 3, with hot and humid summers and mild winters, wider discrepancies exist between the mean temperatures in summer and winter. These are 27 C and 4 C respectively instead of 22.8 C and 17 C for zone 3. Other research concerning the energy performance of school buildings has been conducted in Israel by Becker [8] for hot and dry conditions in summer and moderate conditions in winter. The climate which seems to be the closest to that of zone 3 can be found in the work of Lam where passive design principles have been defined for different climatic zones in China by using a bioclimatic approach. In the southern part of China, the average annual temperature is around 21 C with hot and humid summers and mild winters. Lam recommends using natural ventilation for passive cooling in summer and assesses that passive solar design is sufficient enough to ensure the comfort is maintained during winter. Table 1: Main features for Zone 3 (mid-highlands) annual, summer season, winter season Air temperature ( C) and associated Relative humidity (%) Typical day T mean RH T max RH T min RH Diurnal temperature range T T max - T min Mean global solar radiation (kwh/m²/day) Annual 18,2 76% 25,1 64% 16 73% 9,1 C ,5 Mean summer 22,8 79% 28,3 68% 18,9 80% 9,4 C ,4 Extreme summer 23,5 75% 30,1 62% 19 78% 11,1 C ,5 Mean Winter 17 73% 21,9 62% 13,2 74% 8,7 C ,7 Extreme winter 14,8 75% 18 67% 12 70% 6 C ,5 Mean wind speed (m/s) With reference to school building design, it can be seen that the existing material for school design recommendations is not suitable for the climate in question. That is, in zone 3, the building design has to provide for both tropical climates in summer (use of cross ventilation and solar shadings) and temperate climates in winter (passive solar heating and condensation risk). A main charactistic of the mid-highlands climate of La Reunion is that neither airconditioning nor heating are necessary if some basic passive design principles are applied. This was the purpose of this study to demonstrate this assessment through the use typical meteorogical data file and dynamic thermal simulations. The recommandations through this research could then be applied to new building projects in the area and on a wider scale through setting local thermal standards [2]. The generation of hourly typical meteorological days for zone 3 has been performed by calculation methods developed by David [10], [11]. These methods are based on algorithms of classifications applied to several years of data. An eleven year period from 1993 to 2004 has been considered to generate the typical sequences which can be read as a TMY format file by our simulation code. The climatic data include outdoor air temperature, relative humidity, global and diffuse radiation, wind speed and wind direction.

4 Main features of the high school The high school consists of a three storey building with a capacity of 720 college students (which can be expanded to 900). The total floor space is 8352 m². Typical to most schools, it is composed of different sections comprising the administration part and different use classrooms (for tutorials, practical work and computer activities). A specific building on the east side is dedicated to sport activities. All the walls are 16 cm thick concrete walls with no insulation. The roofs are double skin consisting of a terrace concrete roof with 6 cm of external insulation and a 10% slope corrugated iron roof above this. At the design stage of the project, all the buildings were already cross ventilated with sun shading devices, louvres and overhangs. Most windows are louvres but some windows have slide-windows with an additional louvre on the side. Heating and cooling air conditioning systems were supposed to be installed in the administrative building, staff room, and in the on-site row houses of the administrative staff. Computer rooms and classroom are naturally cross-ventilated. No mechanical ventilation or air conditioning was planned for these rooms. The high school has a rain water storage tank that collects water for the toilet and watering use only. 391m² of PV panels are installed on the northern roof, which represents an installed power of 51 kwp. The annual production is estimated to be 66,300 kwh. Figure 2 : The three storeys main building with sun shading devices, external corridors facing north and louver windows (right). All the classrooms are cross ventilated with sliding windows, louvers and air fans (left). 7.2 m N Figure 3 : Plan view of the administrative offices (left), of a typical classroom (middle) and cross section of a typical building with the double skin roof (right). The typical rooms used for the simulations are spot marked.

5 This study mainly focused on three typical rooms as they represented 80% of the floor space. These were one administrative office, one classroom, and one computing room. The size of the two classrooms is the same. Only the internal loads due to the computers differ. For each typical room, different scenarios of building components (insulation) and air renewal have been tested. As previously stated, the main problem of thermal design in this area comes from the humidity during winter time [11]. The lack of insulation coupled with no mechanical ventilation is the main cause of such problems. At the same time however, the summers can be hot and uncomfortable. Due to low temperature at night during summer, night cooling is a possible solution to consider. This passive cooling technique (used mostly in European countries) has not been tested as yet in La Reunion [12]. Outputs and simulation tools A thermal and air flow simulation program was used, which in conjunction with a model of large openings under pressure, showed the impact of natural ventilation on thermal comfort. (See reference [13] for a detailed description of Roldan s mass transfer model. The model takes into account one air volume per room neglecting stratification. The comfort indices chosen for summer time were Givoni s comfort diagram [14] and the resultant temperature T res. The comfort zones allow us to find the percentage of points within each comfort zone (0 m.s -1, 0.5 m.s -1 and 1 m.s -1 ) as well as the number of hours of discomfort. T res is a weight equation between the air temperature T a and the average wall temperature T rm for a naturally ventilated room In summer T res = 2/3.T a + 1/3 T rm. During winter time, the Predicted Mean Vote (PMV) [15], the resultant temperature and the condensation risk were used as outputs. In winter T res = 0,45.Ta+ 0,55.T rm which is the usual equation used for low-level indoor air velocities. RESULTS AND DISCUSSION As a large number of simulations and data have been carried out and analysed, the results presented in this section will focus on a typical office only. The most important conclusions for the other rooms studied will be presented however. The whole research report is available by request to the corresponding author or by downloading it at The office room has 13m² floor space with a window facing west which has a solar factor of 0.3 (one meter deep solar shading device with clear glass). The internal loads consist of one person (occupancy from 0800 to 1700hrs), artificial lighting from 1400h to 1700h (13 W/m²) and one computer from 0800h to 1700h. The main objectives are to check the possibility of removing air-conditioning devices while ensuring a good level of comfort is maintained all year round and avoiding problems due to condensation. Comfort conditions during summer typical office room Different scenarios of mechanical air renewal listed in Table 2 have been considered. - Case 1 : one ACH (ie18 m 3 /h) 24 hours a day; - Case 2 : one ACH from 8h to 19h then 20 ACH from 20h to 7h, window remains closed ; - Case 3 : one ACH from 8h to 19h then 20 ACH from 20h to 7h, windows is opened from 14h to 17h. One can notice that the mechanical night cooling lower the morning resultant temperature by 4 C. It remains below 26 C until 13h. With opened window, the mean maximum temperature never goes above 27 C during the whole summer. The effect of opening the window during the afternoon (case 3) lowers the temperature by 1 C compared to case 2.

6 Figure 4 shows the impact of mechanical night cooling in terms of thermal comfort. Case 3, which is definitely the best scenario, (grey tint in Table 2) allows to have 100% of the time inside the 0,5 m/s comfort zone (see Table3). That means that air-conditioning is not necessary. The speed of 0,5 m/s can be obtained by using cross ventilation and/or coupled with the use of one air fan. Even if for acoustic reasons the window remain closed (case 2), the use of air-fan is sufficient enough to ensure the comfort conditions 100% of the time. Table 2 : Impact of the different scenarii of mechanical air renewal on the resultant temperature T res 8h-12h T res noon T res 13h-17h Mean T res,max Abs T res, max Case 1 : 1 ACH 24h/day Case 2 : 1 ACH /20 ACH (20h-7h) Case 3 :1 ACH 20 ACH (20h-7h) windows opened in the afternoon Outdoor temp Figure 4 : Impact of the air change rate and mechanical night cooling on thermal comfort : case 1 (left), case 2 (middle), case 3 (right). Table 3 : Percentage of dots within the comfort zones and number of hours of discomfort Office Case 3 Classroom Cross ventilated Computing room Cross ventilated Computing room Single side windows Comfort zone - 0 m.s -1 69% 32% 22% 14% Comfort zone m.s -1 31% 60% 60% 30% Comfort zone - 1 m.s -1 0% 4% 13% 49% % outside the comfort zones 0% 4% 5% 7% Hours of discomfort none 36 h 54 h 70 h Table 3 synthesises the results in terms of thermal comfort for the all the typical rooms. It is shown that thermal comfort conditions are reached most of the time. The worst configuration is for single sided computing rooms where 70 hours of discomfort were calculated. As for the impact of the different cooling solutions on the installed power and on energy consumption, several simulations have been carried out with different scenarios that are listed in Table 4. A Coefficient of Performance (COP) of 2 has been considered to determine the electric power of HVAC systems. Case 1 and case 2 represent the initial project with and without artificial lighting. Case 3 and 4 are an intermediate solution where air conditioning is only used in the afternoon thanks to the effect of night cooling. Case 5 and 6 only use mechanical night cooling and ceiling fans. It is noticeable when comparing case 1 with case 2, that the use of artificial lighting increases both the power and the energy use by 30%. The use of night cooling allows a reduction in electric power by 10% and the energy consumption by 40% (see case 3 and case 4). The best solution was found to be the use of air fans that reduce both the power and the energy consumption by a factor of 12 and achieving good levels of thermal comfort.

7 Table 4 : Impact of the different cooling solutions on the installed power and on the daily electric comsumption Electric Installed Cooling P max el consum. Energy Index power load (kw) kwh (W e /m²) kwh e /da (kwh e /day/m 2 ) cool y 1. Air cond. all day /natural lighting/1 ACH Air cond. all day/artificial lighting/1 ACH Afternoon air cond. / natural lighting ACH at night/1 ACH during daytime 4. Afternoon air cond. / artificial lighting ACH at night/1 ACH during daytime 5. 1 hour use of ceiling fan /natural lighting ACH at night/1 ACH during daytime 6. 3 hours use of ceiling fan /artificial lighting 20 ACH at night/1 ACH during daytime Comfort conditions during winter typical office room As for the study of comfort during winter, two solutions have been evaluated: case 1, one ACH 24 hours a day, and case 2, one ACH only during the day (8h-19h). Preliminary simulations conducted without mechanical equipment have pointed out that condensation occurred most of the time on the internal surface of windows and even on the walls if they are not insulated. Table 5 shows that when the mechanical air renewal is off at night, the temperature is slightly better (0.7 C) but condensation occurs almost every time on the window. On the contrary, if it is used for 24 hours, the condensation risk is totally avoided. The comfort conditions remains good with only a few hours outside the comfort zone for 0 m/s (see Figure 5). The low-level risk of condensation is confirmed. Most of the humidity/temperature pairs are far away from the saturation curve. The simulated PMV is only 12h below -0,5 throughout the entire winter period. Table 5 : Impact of the mechanical air renewal on the resultant temperature in winter T res T res T res Mean Abs. 8h-12h noon 13h-17h T res,min T res,min Condensation risk 1 ACH 24h/day none 1 ACH 12h/day Yes. 90% of the time on the indoor window surface. Outdoor temp Figure 5 : Impact of the mechanical air renewal on thermal comfort and on condensation risk 1 ACH 12h during daytime (left), 1 ACH 24 hours a day (right).

8 SYNTHESIS AND CONCLUSION The keys findings of this study are as follows. The mid-highlands climate in tropical islands must be considered apart because one must cope with the duality of the design principles for tropical climates in summer (use of cross ventilation and solar shadings) and temperate climates in winter (passive solar heating and risk of condensation). Nevertheless, this study has demonstrated that neither air-conditioning nor heating are necessary if some basic passive design principles are applied. With respect to the building envelope, a minimum of 10% of openings for cross ventilation and a minimum solar factor for windows is required. The values of solar factor function of the window orientation are given in [2]. Air treatment in the administrative offices is needed with a 20 ACH of mechanical night cooling coupled with ceiling fans proving to be an interesting alternative to air conditioning during summer time. During winter time, one ACH of mechanical air renewal is mandatory to avoid condensation problems. The comfort conditions are almost reached all year round with only 12 hours of PMV <-0,5. This proposed solution is the first of its kind in La Reunion. It has since been applied to other building projects, either office or educational buildings. In the others typical rooms studied (that is, classroom and computing rooms), natural ventilation and use of airfans is sufficient enough in summer to ensure good comfort conditions. During winter, louvers must remain slighlty open to avoid condensation. The PMV for this scenario is below -1 only one hour per day. REFERENCES 1. ICE Consulting, INSET PRERURE final report. Regional Plan for Demand Side Management and Renewable Energies in Reunion Island. Report downloadable at 2. Garde, F., David, M., Adelard, L., et al Elaboration of thermal standards for french tropical islands. Presentation of the PERENE Project. In Proceedings of Clima2005, Lausanne, Switzerland. 3. De Waal,.B New recommendations for buildings in tropical climates. Building and Environment. Vol. 28 (3) pp Wong, N.H, Khoo S.S Thermal comfort in classrooms in the tropics. Energy and Buildings. 35, pp Kwok, A.G Thermal comfort in tropical schools. ASHRAE Transactions. 104 (pt.1), pp Also published in ASHRAE Technical Data Bulletin, 14 (no. 1) pp ASHRAE, ASHRAE Standard 55 : Thermal Environmental Conditions for Human Occupancy, American Society of Heating, Refrigerating and Air-Conditioning Engineers. 7. Kwok, A.G., Chun, C Thermal comfort in Japanese schools. Solar Energy 74 pp Becker, R., Goldberger, I., Paciuk, M. Improving energy performance of school building while ensuring indoor air quality ventilation Building and Environnement. doi: /j.buildenv (article in press). 9. Lam, C.L., Yang L., Liu, J Development of passive design zones in China using bioclimatic approach. Energy Conversion and Management Vol. 47 pp David, M., Adelard, L., Garde, F., et al Weather data analysis based on typical weather sequences. Application to energy building simulation. In Proceedings of IBPSA World Congress, Montreal, Lucas, F., Adelard, L., Garde, F., Boyer, H Study of moisture in buildings for hot humid climates. Energy and Buildings. Vol 34 (4), pp Breesch, H., Bossaer, A., Janssens, A Passive cooling in a low-energy office building. Solar Energy. Vol. 79 pp Boyer,,H., Garde, F., Gatina, J.C., et al A multi model approach of thermal building simulation for design and research purposes. Energy and Buildings 28 (1) pp Givoni, B; Man, climate and architecture London : Applied Science Publishers limited. 15. Fanger, P.O Thermal comfort : analysis and applications in environmental engineering. New York : McGraw-Hill.