Daylighting Analysis of Vernacular Architecture in Guizhou Province, China

Transcription

1 Daylighting Analysis of Vernacular Architecture in Guizhou Province, China Huang Xuan, PhD Chun Wu, Director Wei Su, [Shanghai Jiaotong University, China] [Urban and Rural Planning Bureau, [Shanghai Jiaotong University, Miao and Dong Autonomous Prefecture China] of Guizhou Province] ABSTRACT China has 55 minorities, most of whom have their own unique architecture. Due to urbanization these traditions are in danger and traditional dwellings are replaced with modern houses in the hope of better living conditions. By understanding and finding solutions to the problems emerging in these traditional dwellings and by using their features in a more sustainable and more adaptive way to local climate, living conditions could be improved without losing this unique culture. Due to its substantial minority population and varied terrain, Guizhou province in China has a rich source of different types of traditional dwellings. Dwellings representing the typical architecture of three different ethnic groups Han, Miao, and Dong were selected to conduct daylighting analysis. Measurements made during a field work helped to explore how the different building ways, folk customs, topography and other factors impact on architectural daylighting. With the help of the results, suggestions are made on how to reform existing dwellings under the corresponding architectural language and lifestyle, and what modifications should be made to meet the modern daylighting needs of occupants. Different scenarios are simulated using ECOTECT 2011 software (Ecotectt, 2011) to show the positive results of the changes suggested. INTRODUCTION China is a multi-ethnic country with a long history and a vast territory, during the thousands of years of its history a vast amount of varied residential building types have evolved. Different regions have different natural conditions and cultural background, which is reflected by vernacular dwellings all over the country. Over the recent decades, due to the acceleration of urbanization, modern architecture became more widespread. Modern architecture promises to accomplish a better living environment, but it contributes to the destruction of traditional vernacular dwellings. Traditional vernacular dwellings represent a valuable heritage and help to preserve the habits and folk-custom of ancient people. More importantly the ecological thinking and technical solutions of vernacular buildings are a significant knowledge source for the sustainable development of new settlements and an indispensable reference on terrain adaptation, climate adaptation and construction of passive energy-saving measures. To renew the vitality of a traditional vernacular dwelling, its adaptability to modern life and comfort must be improved. Daylighting is an important measure of building comfort. Because of limited building and technical resources available at the time they were constructed, traditional houses typically take advantage of natural light. However with changes in living habits and the improvement of living standards, original daylighting conditions are not able to meet the demands of the present. Improvements of vernacular dwellings should also focus on enhancing daylighting condition, an area which needs to be researched in more detail. Few studies already have been conducted on architectural daylighting of Chinese traditional vernacular dwellings (Wang, Zhuo and Dac y 2008, Duan, Lau and Ford, 2012, Lin, Li, and Chen, 2013), but it is a generally a neglected area of research to which this paper tries to contribute. There are many types of dwellings in different regions that have not been researched yet, from which this study is focusing on three typical types of dwelling characteristic of three ethnicities, a special group of the Han, the Dong and the Miao, all of which are characteristic to Guizhou Province, 1

2 which due to its less developed infrastructure and economy was especially neglected. The principle aim of this research is to investigate the daylighting performance of three traditional vernacular dwellings and the factors influencing it, by means of on the spot data collection, analysis, software simulation, in order to suggest viable modifications of the original dwellings, to meet the occupants lighting needs better. After introducing the characteristics of the locations of the field research, research methodology is explained. Results and analysis will then be presented, together with simulation, finally conclusions are made and suggestions for future improvements are given. ETHNIC ARCHITECTURE AND LOCAL CLIMATE The vernacular dwellings selected for the research are located in Guizhou province, in the village of Jiangchang, SanBao and Xijiang (Figure 1). The dwelling in Jianchang is a typical example of Han Chinese vernacular architecture and the tunpu culture retained locally. The dwelling in Xijiang reflects the local architecture of Miao minority and is part of the world s largest Miao settlement while the dwelling in SanBao is typical of the Dong minority. All of the three ethnic groups have a history of hundreds of years and rich cultural traditions, which are reflected in architecture, clothes, food, folk beliefs and entertainment. Guizhou has a typical subtropical monsoon climate, where summer is hot, humid, and sunny and winters are relatively warm. Figure 1: Location of Jiangchang, SanBao Dong and Xijiang Miao in Guizhou province, China Each of the three dwellings chosen carry the main characteristics of the local traditional architecture. The main structure of the dwellings in Jiangchang consist of a wood structure and the building envelope is made of stone blocks. This is coupled with the most distinctive feature of these buildings, the thin slab stone roof, stacked layer upon layer. (Figure 2 (a)) The Dong minority s dwellings in SanBao Dong are almost solely constructed from wood, from the load bearing structure, through the inner envelope and wooden stairs. Only the kitchen is made of brick, which is usually attached to the main building. (Figure 2 (b)) Both the Han and Dong dwellings usually consist of two storeys, with living areas located on the ground floor and storage places on the first floor. In the Xijiang Miao village local houses are typical mountain buildings, wooden houses on stilts located mainly on a hillside, built row upon row. A unique feature of these dwellings is the semi opened balcony located outside of the living room with railings locally called as beauty s leaning. Buildings usually consist of two to three storeys. The ground level is used for storage or for livestock, accommodation and main living spaces are on the first floor while upstairs is used for storage. (Figure 2 (c)) (a) (b) (c) Figure 2: Traditional Dwelling in Jiangchang (a), SanBao Dong (b) and Xijiang Miao (c) 2

3 FIELD SURVEY METHODOLOGY The field research was conducted during the summer, data collection took place from 4 th and 9 th July 2013, over two days in each location. Daylighting data were collected through spot measurements using Digital LUX METER (TES 1330A) illuminometers. Data collection focused on the floor where main living spaces were located, in the Jiangchang and Sanbao Dong on the whole ground floor, while for the dwelling in Xijiang on the first floor, as for places used for storage or livestock daylighting is not of crucial interest and thus was omitted in this research. In the collection of illuminance values, the researcher took account of individual rooms and functions to determine the number of measuring points. A grid was drawn on the floor plan of each room, with intersection points not further apart than 1 meter, illuminance values were collected at each intersection at 800 mm above floor level, according to the reference working surface level suggested by the Standard for daylighting design of buildings (China, 2013). Inside and outside illuminance data were collected simultaneously by a pair of field researchers. To reduce error and to ensure the accuracy of the data, three complete sets of illuminance measurements were taken in each room under overcast conditions. No additional artificial lighting was used during measurement times. Outdoor illuminance values have drastic fluctuations, even under overcast conditions, resulting in change of indoor illuminance, but for the same test points, the ratio between the indoor and outdoor illumination value should remain stable. Ratio of outdoor and indoor illumination is called the daylight factor (DF), and it will be used as a basis for research daylighting performance in this research. DATA ANALYSIS Indoor daylighting condition is influenced by various factors, such as the proportion of the space (depth and width), presence of shading device or outside structures providing shading, the area ratio of windows to floor, the presence of grilles or wooden decoration on the windows and the reflectivity of the walls. The analysis of data focused on these factors. The first step was to obtain the plan of the dwellings through measurements taken with Leica Disto TM D2 laser ruler and tape measures, layouts and section plans were drawn. Details of the size, position and form of the daylight openings in the house and the presence of shading devices were also recorded. The vernacular dwelling in Jiangchang village has a simple rectangular layout (Figure 3 (a)). The dwelling is surrounded by a stone wall forming a courtyard. Building layout is simple, only consisting of three rooms arranged next to each other in a linear fashion, with the living room located in the middle facing south. The shape of the bedrooms is long and narrow, the depth reaching 7.5 meters, and the rooms have windows on both of their south and north wall. A bungalow was later built on the southeast corner of the main building. The windows are all the same size of 1300mm (w) *1000mm (h) decorated with grid patterns and with window sills height at about 1.1 meters. The layout of the dwelling in SanBao Dong is also symmetrical with the total of three bays, the main living area is located in the middle with the main entrance facing south. (Figure 3 (b)) The living room is surrounded by two-two bedrooms on both sides. Each bedroom has only one window the size of 850mm (width) * 900mm (height) and are equipped with safety grilles. Windowsill is relatively high, reaching 1.4 meters. The dwelling selected in Xijiang is a three floor pillar supported building, the back side of the building is connected to the mountain, while the front of it is facing south. The whole design embraces the mountain terrain specifications. The plan is long with an axis from east to west and symmetrical layout. (Figure 3 (c)) In the middle is the main living room area opened on the south side with the beauty s leaning, which is connected to the rooms on its sides through a corridor. The kitchen is located on the west side. Window sizes vary on the first floor, with a width between 650 to 750mm and heights between 600 to 900mm. Window sills are at the height at 1 meter. The three layouts are different and represent the local culture and adaptation to terrain, however there are some features which are present in all the three dwellings. The local subtropical climate of 3

4 Guizhou is quite wet, annual rainfall is around 1360 mm. In these wet conditions wood structures need to be protected, thus the presence of a roof overhang was observed at all the dwellings. In Jiangchang the building has a double pitch roof with 1.4-metres overhang on both south and north sides. In Sanbao Dong the south side of the building also has a 1.1 meter roof overhang while the overhang on the north side reaches the kitchens outer wall. In Xijinag it reaches 1.3 meter on both south and north sides. Inside separation walls are made of wood, with a quite dark colour due to the aging of the material. The size and shape of the windows vary but, in each case the glass has a decorative wooden pattern. In Jiangchang this has decorative function, while in the other two dwellings it is a simple pattern and is more part of the traditional way of window construction than a decorative function. Next the area ratio of windows to floor (AW/AR) was calculated, by dividing the total area of the windows (AW) present in a room by the area of the room (AR). As the national standard minimum requirement are given in fractions, results in decimals were rounded to fractions. (Table 1) Illuminance data collected was processed first by getting the ratio between the indoor and outdoor illumination value of every test point, and then by taking the average of the three measurements as the measuring points on the daylight factor (DF) values. Based on the data obtained in this way daylighting contours for all the rooms tested were generated using the software package Surfer 8 (2004) and daylighting situation in all the three dwellings was analysed based on the DF isolux contours obtained with Surfer. Results are shown on Figure 3. (a) (b) (c) Figure 3: Floor plans and DF isloux contours of rooms tested in Jiangchang dwelling ground floor (a), SanBao Dong dwelling ground floor (b) and Xijiang Miao dwelling first floor (c) 4

5 Table 1. Area Ratio of Windows to Floor Place Room area (m 2 ) A W /A R A W /A R in Fractions Jiangchang Living room /6 East Bedroom /7 West bedroom /7 Kitchen /3 Bungalow /3 Sanbao Dong Living room /12 East Bedroom /16 West bedroom /11 Kitchen /14 Xijiang Miao Living room /3 East Bedroom /12 West bedroom /16 FINDINGS The analysis showed that daylighting of these dwellings has the following problem: The minimum daylight factor (DFmin) cannot meet the residential building standard The architectural lighting design standards for residential buildings (China, 2013) sets the minimum value of daylight factor at DFmin=1%. From the data analysis, it can be seen that, the minimum value of daylight factor of the three dwellings do not meet the specification above in none of the rooms, with DFmin values ranging from 0.01% to 0.26%. Living rooms in all the three dwellings have a better daylighting performance than bedrooms, where daylighting conditions are not favourable. Concluding from the analysis of the data, the following factors have negative effects on daylighting in the three traditional dwellings: 1) The size and proportions of the rooms. The face width of the rooms can be considered normal according to modern building standards, however great depth, reaching even 7.5 meters in Jiangchang, results in not good daylighting condition and areas with almost no light. Great depth is especially characteristic and thus problematic for the living rooms, which are the main living area and such should have the best daylighting performance. 2) The colour of the interior wall. Internal partition walls are made of wood, which darkened after prolonged use. The dark colour of the partition walls makes the reflection of natural light more difficult, while also contributing to a feeling of darkness. 3) The size and construction of the daylight openings. According to the National standard minimum requirement of the area ratio of window to floor (GB , 2011) needs to reach 1/7 in general. Normal values for bedrooms are considered to be between 1/6-1/8, and 1/4-1/6 for living rooms. Looking only at this value the situation in Jiangchang dwelling is quite favourable, with all rooms meeting national minimum requirements, however the great depth of the rooms disturbs the daylighting effect. The values are a lot below the standards, ranging from 1/11-1/16, only in one case is the value in the acceptable range, for the living room in Xijiang Miao dwelling. Besides the size, the presence of a wood pattern on windows, reduces the daylight effect even further, by reducing the area of the window. COMPUTER SIMULATION Simulation description To show the effect of the identified problems and to find the best solutions for improving daylighting conditions in the dwellings, simulations were carried out using ECOTECT 2011 software 5

6 (Ecotectt, 2011). During simulation, factors identified before to cause problems were impoved compared to original measurements and the positive effect of these changes were evaluated. Three factors were selected to be variable in the experiment, the depth of the room, the colour of the interior wall and the presence of the grid on the window. (Table 3) The layout and original filed measurements of the Jiangchang dwelling were used as the control group for the simulation, as many of the factors causing daylighting problems were prominent. However simulation was only carried out on this one dwelling, findings should also reflect the other two dwellings, due to the similarity of the emerging problems, the similarity of outside conditions and the same orientation. All the simulations were done under the conditions summarized in Table 2. Table 2. Simulation Conditions Name Location Daylight Climate zone Critical illuminance value Illumination sky model Value degrees north, latitude degrees east IV Daylight Climate zone 4500lux CIE cloudy sky Table 3. Simulatin options descriptions Simulation Variable changed Change compared to original situation Control group None Variables are the same as in original conditions: bedroom depth 7.5m, living room depth 5.1m, walls are dark stone with dark wood, reflectivity rate is 0.16, grid is present on the window shown by transmission rate of 0.5, doors open A Room depth Bedrooms depth is reduced to 6 m, livingroom s depth is reduced to 3.6m B Indoor wall color Indoor walls are set as painted a light wood color, the light reflectivity increases to 0.4 C Window grid No grid on the windows, transmittance rate increases to 0.7 D All the above All the above variables are present at the same time Simulation results and analysis Analysis of the different models resulted in five situations showing the impact of each variable on the indoor daylighting condition. Compared to Figure 3 (a), the indoor distribution curve of daylight factor of the control group has a similar distribution trend of the original dwelling (Figure 4 (a)). Although there are still some deviations in the data, the pattern of DF in the simulation experiments can be considered consistent with the existing situation. To show the effect of the different variables on the daylighting condition, average DF and the percentage of all values between DF 0-1% (under standard), DF 1-2% (gloomy but acceptable conditions) and DF 2% (reasonably good) were calculated and compared. When a higher percentage of the values are in the higher DF range the effect of the change of the variable can be considered stronger. (Table 4) Table 4. Change in Daylighting condition for different simulation described by the percentage of values in different DF ranges Simulation Average DF DF between 0-1% DF between 1-2% DF above 2% Control group 1.77% 47.79% 24.64% 27.56% A 2.26% 23.05% 39.78% 37.16% B 2.00% 33.03% 36.04% 30.93% C 2.27% 31.59% 32.33% 36.08% D 3.67% 6.3% 32.76% 60.94% 6

7 (a) (b) Figure 4: Dayligt factor simulation results, control group (a) and simulation D, all variables changed (b) The impact of room depth on daylighting: The change of the room depth affected the distance between the north window and the south window, and thus the area ratios of window to floor. From all the variables changing the room depth has the most positive effect on daylighting. The percentage of DF values between 0-1%, values, under the accepted standard, reduced to 23% while the percentage in the range of above 2% increased to 37.16%. Reducing the depth allows the same amount of light to be able to meet the needs of indoor better. Lighting distance on both sides also reflects the advantages of twosided lighting. The impact of interior wall surface reflectivity on daylighting: After the colour of the interior walls is changed to a light colour, their reflectivity increases from 0.16 to 0.4 resulting in the increase of the area with a value of DF in the range of 1% to 2%, however it s a smaller increase than in the case of the other two factors. The increase of the interior walls reflectivity allows better diffuse reflection of the light entering through the windows and the doors. The impact of grids on the window on daylighting: The grid on the window reduces the area of the window, but since its area is difficult to calculate, it was simulated by altering the transmittance rate for testing purposes. Simulation results showed that when there is no grid present, DF values near the windows increased and only 31.59% of DF values are under the standard compared to the original 47.79%. Removing the grid can increase the injection of indoor natural light and thus can positively affect daylighting condition. Figure 4 (b) shows the cumulated effect of all changes. It can be seen that daylighting situation improved significantly. When applying all the changes together only 6.3% of DF values are under the standard and more than 60% of the DF values are reasonably good range. Considering the above results suggestions are given for future improvements. Suggestions for improvement By analysing the results, it can be concluded that both the large depth and dark interior wall of the traditional dwellings in the three villages have a negative effect on daylighting conditions of the residential living areas. Also, the traditional carved wood decoration and safety grills on the windows increase the self-shading of these houses and decrease the amount of light penetrating the rooms even in the case of an appropriate window area ratio in Jiangchang village. Not to mention in the other two cases, where the ratio of window to floor is much lower than suggested by modern building standards. These dwellings cannot guarantee even the basic lighting requirements of daily life. Based on the data analysis and the results of the simulation future refurbishment or new build projects should be carried out including measures to increase the amount of sunlight and to improve the natural daylighting condition. To increase the comfort of occupants the following measures can be taken: The amount of sunlight is most influenced by the area ratio of window to floor. The easiest measure would be to increase the window size. In the case of rebuilding traditional houses, this can be done to an extent when the appearance of the traditional dwellings doesn t loose its originality. However when old dwellings are refurbished this could be problematic. 7

8 Another solution can be to replace the original glass of the window with high transmission glass and to replace the fixed carved wooden grilles with ones that can be opened at times, thus daylighting in the rooms can be improved without changes that influence local building style. Under modern living conditions too large depth of the rooms is not useful anymore for the occupants of these dwellings. It was observed that due to shortage of daylighting the opposite end of the room is usually used as storage only and is not part of the active living space. The most hands on solution would be to reduce the depth of the room, as this is the factor having the biggest positive influence on daylighting condition, but it is a very difficult and complicated job to carry out as part of the refurbishment. Therefore, this modification is generally possible in case of new built dwellings following the traditional design style, but there it should be the primary consideration. The change in the surface of indoor wall is a more feasible suggestion during refurbishment. In terms of traditional wood building material and stone, plastering on all walls seems too simple and rude, and it would destroy the native beauty of these residential dwellings. Despite painting the walls white would have a stronger positive effect on daylighting, taking in consideration the consistency of the traditional style, the solution suggested here is to clean the wooden walls and repaint them with wood protective paint. Such a change may not only improve the indoor lighting, but also protect the building components. CONCLUSION This research consisted of two parts. In the first part lighting data of the traditional dwellings in Jiang Chang Village, SanBao Dong and Xijiang Miao was collected during a field research. Based on the data collected features and influential factors of lighting were studied in detail. The other part was to study the lighting variables of the vernacular dwellings. A simulation experiment was carried out using ECOTECT software, which verified futures assumptions of influencing factors of daylighting. Renovation suggestions, such as cleaning and treatment of wood walls, movable grilles and replacement of the window glass, were given, which measures will improve daylighting situation. In case of new built dwellings using the traditional style, primary focus should be on reducing room depth. All these measures will have a positive effect on occupant comfort and thus contribute to the protection and preservation of these traditional dwellings, and could also be on dwellings in other parts of China. However, further reserach is needed in this area, to understand daylighting conditions in different dwellings and to explore more possible solutions to improve it. ACKNOWLEDGEMENTS The works was supported by National Natural Science Foundation of China(Grant No ). REFERENCES CHINA, Ministry of Housing and Urban Rural Develeopment of the Peoples Republic of China, Standard for daylighting design of buildings, 建筑采光设计标准 [In Chinese]. ECOTECT 2011, Autodesk Inc., USA GB , Design Code for Residential Building, 住宅设计规范, Beijing: China Architecture & Building Press. [In Chinese]. DUAN, Z., LAU, B. FORD, B., The Daylighting Performance of Vernacular Sky-well Dwellings in South-eastern China. PLEA th Conference, Opportunities, Limits & Needs Towards an environmentally responsible architecture Lima, Peru 7-9 November 2012 LIN, Z., LI, H., CHEN, S Research on simulation of natural lighting of traditional dwellings in Yingtan Village.Huazhong Architecture.3, p SURFER 8, Golden Software Inc., USA WANG, A., LI Z., DAC Y, A Sustainable Daylighting Strategy of a Chinese Traditional Building: FaLun Palace of Yonghe Tibet Temple. PLEA th Conerence on Passive and Low energy Architecture, Dublin 22nd to 24th October