Healthy uildings 2017 Europe July 2-5, 2017, Lublin, Poland Paper ID 0270 ISN: 978-83-7947-232-1 Research on indoor thermal environment of stilted buildings in Chongqing, China Ya nan Xu 1, Zhenjing Yang 1, *, Mingxi Peng 1 1 Chongqing University (CQU), Chongqing, China * Corresponding email: 1440829179@qq.com SUMMARY Indoor thermal environment is one of the most important factors that affecting human comfortableness directly in a healthy building. In order to study the indoor thermal environment, acquire some experiences and technologies about vernacular ecological architecture and provide a useful reference for modern architectural design, a typical stilted building (Diaojiaolou in Chinese) which is one representative of Chongqing vernacular dwellings was investigated through field measurements in summer and the indoor airflow were conducted on the building model using the simulation program PHOENICS. The field data combined with simulation results, local climate, architectural characteristics and living habits of residents was analysed, and the comfort was assessed using the adaptive predicted mean vote (APMV). The results show that without mechanical cooling facilities, indoor thermal comfort at night is significantly well but less well in the daytime due to light-weight envelops, stilted construction form and natural ventilation. Therefore, it is necessary to treat the vernacular dwellings dialectically. KEYWORDS Vernacular dwellings; Thermal comfort; Filed measurement; Natural ventilation 1 INTRODUCTION As one of the most important factors of health building, indoor thermal environment directly affects human comfort. Nowadays more people prefer to use mechanical equipment to improve indoor thermal environment, and large energy consumption and air condition disease come with it. Conversely, vernacular buildings create a better indoor thermal environment with many excellent ecological experiences. There are a variety of vernacular dwellings in Southwest China because of varied terrain and complex climate, and one of the most widespread is stilted buildings. Most of stilted buildings are built by mountains and rivers and in accordance with contour lines and formed a patchwork pattern, and the plot partly on ground and partly supported by pillars. This distinctive form is a perfect combination of mountain terrain and buildings. Moreover, most stilted dwellings distribute in rural areas with occupants on low incomes, and even in hot summer indoor cooling equipment is also less to be used. Therefore, it is of great significance to study the indoor thermal environment of the stilted dwellings and analyse their ecological experiences and existing defect. The research can help to improve the indoor environmental quality of these houses and provide a useful reference to modern architecture.
In this paper, a typical stilted dwelling was chosen as the research object and investigated through field measurements in summer. Through the analysis of the field data, its indoor thermal environment was evaluated, and its ecological experiences and imperfection was summarized. 2 MATERIALS/METHODS Regional overview The object is located in Songji village, Chongqing, backed by mountains and fronting the Yangtze River. ecause of rugged terrains, the layout of the village is compact and orderly, and the main streets are narrow and paralleled with the river roughly. Almost all buildings in the town have large eaves to shade the building from the sun and rain, and its pitched roof with Chinese-style tile was strewn at random. Most layouts of the buildings have a small width and a deep depth. All of these give the impression of modest and local flavour (Figure 1. (a)). The air quality and the environment of the village is good, the average annual temperature is 17.9, average annual rainfall is 1030mm and average annual sunshine is 1273h. ecause the area belongs to warm wet climate and mainly performed as hightemperature, high humidity, much rain and fog and relatively mild in winter, the most intractable problem for the daily life of the local residents is ventilation, cooling and dehumidification. Almost all walls of the dwellings in the village are bamboo wall circled by clay and the thickness is about 40mm and its surface is bright and smooth. Its construction is similar to frame structure, wood columns and horizontal members are load-bearing elements (Figure 1. (b)). A Figure 1. Features of Songji village. a) Street, b) bamboo wall circled by clay. Research object The object is an intermediate house, towards south by east 30. The south of the house is a street 3.5m wide, and the north is a greening slope, further is the Yangtze River. Figure 2 (a) shows the plot of the building and figure 2 (b) shows the section. Living room and kitchen are built on ground and the floor material is concrete. edroom 1 and bedroom 2 are built on stilts, and the floor material is solid wood boards. The building walls is bamboo wall circled by clay and the roof is pitched with Chinese-style tile. In addition to the living room has a fan, the other rooms are naturally conditioned.
A Temperature Relative humidity Figure 2. The plan and section of the dwelling. a) Plan, b) Section Testing program The effective measurement time is July 27 to August 18, 2016. The test contents include outdoor and indoor air temperature, surface temperature of floor and relative humidity. Figure 2 shows the specific test point and Table 1 shows the test items and major equipment. Table 1. Measurement contents and major equipment Measurement contents Major equipment Equipment parameters Air temperature and floor UX100-014M, range:-20-70, HOO thermometer surface temperature Accuracy:±0.7 UX100-003,range:-20-70, 15-95%rH, Relative humidity HOO hygrometer Accuracy:±0.7 ±7.5% 3 RESULTS Outdoor climate During the measurement period, the average solar radiation in the town was 172W/ m2, which is about 750W/ m2 on a sunny day and 100W/ m2 on a cloudy day, indicating that the local radiation resources were abundant in summer. The average outdoor temperature is 29.7, the highest is 39.5 and the lowest is 23.8 and the greatest diurnal temperature range is 11, reflecting that the temperature of the village is high in summer. As the main problem of the local construction is heat insulation, August 14th with a high outdoor temperature was chosen to be a typical day to be analysed. Indoor temperature and humidity Figure 3 (a) shows the indoor and outdoor temperature of the dwelling on typical day. The day the heat lag time of each room is almost 0 and outdoor average temperature is 31.4 and the maximum and minimum temperature is 37.1 and 27.3 respectively. The temperature of bedroom 1 and bedroom 2 is almost the same, the maximum temperature is 33.9 and 4.1 less than the outdoor maximum temperature and the average is 30.3 and the daily range is 6.6. esides, the temperature of living room is lower than bedrooms in the daytime and higher than the bedrooms at night, and the daily range is 4.8, 1.8 less than bedrooms, indicating that the heat insulation of the dwelling is not ideal, and the bedrooms is more susceptible to outdoor environment.
As the living room and bedrooms floor is different, the surface temperature of concrete floor and wood floor was measured, and the result was shown in Figure 3 (b). Comparing the surface temperature, it can be found that the fluctuation range of the wood floor is significantly larger than the concrete. The average surface temperature of the wood floor is 29.4 and the daily range is 3.2 and the average surface temperature of the concrete floor is 27.7 and the daily range is only 0.8. Figure 3(c) shows the indoor and outdoor relative humidity on typical day. The average outdoor relative humidity of typical day is 76%, the highest is 93%, and the lowest is 54%. The indoor average humidity is 78% and stays above 60% all day long for each room, reflecting that the village has a high humidity in summer. A C Figure 3. Temperatures and humidity on typical day. a) Air temperatures, b) Surface temperatures, c) Relative humidity Figure 4 presents the difference of heat transfer between two bedrooms and the living room simply. Two bedrooms are built on stilts, and outside surface of the floors is contact with outdoor air directly. Moreover, the material of floors are wood board with a low thermal resistance and small thermal inertia, its thermal performance is poor. Therefore, the bedrooms are susceptible to outdoor environment. Contrary to the bedrooms, the living room built on the ground with a concrete floor has a bigger thermal inertia than wood and it is less prone to the environment. During the daytime (figure 4(a)), outdoor temperature rises, a lot of heat conducts across walls and roofs to the rooms, the indoor temperature rises closely behind. In the meantime, the floor of the living room has lower temperature which can help to cool the living room. As for bedrooms, the heat of outdoor air can also conduct across floors to the indoor space. This explains why living room s temperature is lower than bedrooms during the daytime. At night (figure 4(b)), outdoor temperature dropped rapidly, the indoor heat that gets during the day can be released can be released not only through walls and roofs but also through stilted wood floor. As to living room, the indoor heat can only be released through walls and roofs. It explains why bedrooms has a lower temperature than living room at night and opposite in the daytime. A
Figure 4. Heat transfer analysis between living room and bedrooms. a) Daytime, b) Night time, Simulation of indoor air flow ecause the north of the dwelling is Yangtze River, when the doors and windows opened, river-land-breeze formed by the temperature difference between the land and river would blow from the river to the dwelling as figure 5(a) shows. In the daytime the wind brings outdoor hot air into the room but at night the wind brings cool air into the room, which contribute to night cooling. esides, a moderate and uniform airflow is comfortable. To analyse the indoor air flow visually, the air flow condition was conducted on the building model using simulation program PHOENICS. The model was established based on field measurement and its boundary conditions are openings. Initial wind direction is northwest and airflow rate is 2m/s, which is calculated from weather date of Typical Meteorological Year. The grid cell is about 0.2m*0.2m. When the computation is converged, contour plot of wind speed above the ground 1.2m is got as Figure 5(b) shows. The figure shows that the wind speed at the opening is the largest and bedrooms have a better natural ventilation than living room. The average wind speed of the bedroom 1 is 0.13m/s, the bedroom 2 is 0.16m/s, the living room is 0.1m/s and the distribution of wind speed is more uniform in living room. A Figure 5. Analysis of natural ventilation. a) Natural ventilation, b) Contour plot of wind speed 4 DISCUSSION Evaluation of indoor thermal environment Since the dwelling is natural conditioned and conforms to the requirements of Evaluation standard for indoor thermal environment in civil building, the thermal environment could evaluate by adaptive predicted mean vote (APMV), which takes into account the psychological, physical and behavioral adaptability and other factors in the natural environment and is implementing in China. APMV calculated by APMV = PMV 1 + λ PMV (1) Where PMV is the predicted mean vote; λ is the adaptive coefficient and for residential in summer is 0.21. To calculate the PMV, the clothing insulation is 0.3clo, the metabolic rate is 0.8, and the airflow rate is the average value of the simulation. The air temperature and humidity is from field data. The results is shown in figure 6.
Figure 6. Value of APMV When APMV value is between ±1, it means the thermal environment is comfortable. Figure 6 shows that indoor thermal environment is comfortable during 20:00-10:00. It s appropriate for bedrooms relative to living room. ecause bedrooms is occupied at night and living room is occupied in the daytime. The time when APMV value of living room is between ±1 is 21:00-11:00 and beyond ±1 for the whole afternoon, which means that the indoor thermal environment of the living room is not ideal on the daytime. Evaluation of the building envelops The results show that the indoor temperature is high and indoor thermal environment is unsatisfactory in the daytime but pleasing at night. To analyse reasons, the envelopes was studied. First, walls of the dwelling are 40mm thick bamboo wall circled by clay and its thermal resistance is 0.22( m2 k)/w, while the thermal resistance of 240mm brick wall is 0.44( m2 k) /w. The thermal resistance of bamboo-clay wall is only 1/2 of the brick wall. Second, the roof of the dwelling is only two layers of 10mm thick tile and 2-3mm thick air layer. The thermal resistance of the roof is about 0.15( m2 k)/w, only 1/2 of the concrete roof. And thermal inertia of the roof is 0.28, only 1/6 of the concrete roof. Therefore, heat insulation and thermal stability of building envelopes are poor. ut it is conducive to heat dissipation at night. 5 CONCLUSIONS y the analysis of thermal environment in stilted dwelling, the following conclusions are reached: 1. The envelopes of stilted buildings have a poor thermal insulation properties. Lots of outdoor air heat conducts across envelopes to the rooms and indoor temperature rises closely behind in the daytime, but the indoor heat gets in the day could be dissipate rapidly at night. It provide a suitable temperature at night for occupants. 2. edrooms are more susceptible to the outdoor environment because of stilted floor. And that is the reason why indoor temperature of the bedrooms is higher than living room in the daytime and lower than living room at night. The stilted floors also play an important role in improving indoor thermal environment at night. 3. Model simulations illustrate that the average airflow rate above the ground 1.2m of each rooms are 0.1m/s and above except the kitchen, and the distribution of wind speed is more uniform in living room. The wind play a positive role at night but a negative role in the daytime. 4. The technologies about stilted buildings are a positive response to the characteristics of mountainous terrain and complex climate in Chongqing, but its indoor thermal environment in the daytime still need some improvement. 6 ACKNOWLEDGEMENT This work was supported by a grant from Chongqing Construction Science & Technology Program (No.2007075). Many thanks for my teachers and the residents from Songji village.
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