Applied Mechanics and Materials Vols. 193-194 (2012) pp 1165-1173 © (2012) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMM.193-194.1165
Lighting Environment Study on Rural Residential Buildings in Weihe Plain of China Xi LIAO1, a , Jing LUO1,b , Yuan JIANG 1, c, Yiping ZHU 1, d and Wenbo WU1, e 1
School of Architecture, Xi’an University of Architecture and Technology, Xi’an, China,710055 a
yinweiai527lx@hotmail.com, bkaka930@126.com, jiangyuan8921@gmail.comc, zhuyiping114@gmail.com d，413477743@qq.come
Key words: Weihe Plain, Rural Residential Building, Lighting Environment, Energy Saving
Abstract: As an important index reflecting residential quality, the lighting environment level of residential buildings exerts tremendous influence on both physical and psychological health of residents. Taking a typical rural house in Weihe Plain as example, with indoor lighting environment test, lighting habits of the resident and Ecotect software, the paper studies indoor lighting environment quality of rural residential buildings in Weihe Plain and analyzes the influence of residential buildings' design on lighting environment. The result shows that rural residents in Weihe Plain usually don’t attach due importance to the lighting environment quality of living space, and the design of indoor space goes against effective utilization of natural light. Thus, the paper eventually brings forward a method to consummate the lighting environment of rural residential buildings and explores the buildings’ potential of saving energy by making use of natural light. 1. Introduction At present, urban and rural construction area of China has exceeded 40 billion m2, and annual energy consumption of buildings amounts to 376 million tce, accounting for 27.60% of total energy consumption of the whole society. Rural residential buildings constitutes above 60% of total residential area, i.e. about 25 billion m2, and annual power consumption of rural residential buildings is more than 100 billion kW•h[1]. Hence, energy saving of rural residential buildings is of vital importance to create an economized society. According to regulations of daylighting coefficient standard value of residential buildings in Standard for Daylighting Design of Buildings[annotate], daylighting standards of residential buildings should comply with the minimum daylighting coefficient in Table 3.2.1 and the area ratio of window to floor in Table 5.0.1 (Ac/Ad）, i.e. the minimum side daylighting coefficient of bed rooms, dining rooms and kitchens is 1%, the area ratio of window to floor （Ac/Ad）is 1/7, which will be used in following comparison and analysis. Pursuant to the standards, the daylighting coefficient standard value of residential buildings and the area ratio of window to floor are shown in Table 1 and Table 2.
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Table 1 Daylighting Coefficient Standard Value of Residential Buildings Side daylighting Minimum Critical Daylighting Name of room daylighting illuminance of Level coefficient indoor natural light Cmin(%) (lx) living room, bed IV room, study room, 1 50 kitchen Toilet, corridor, V staircase, dining 0.5 25 room Table 2 Area Ratio of Window to Floor Side Daylighting Daylighting Level
I II III IV V
Side Window Civilian building 1/2.5 1/3.5 1/5 1/7 1/12
Industrial building 1/2.5 1/3 1/4 1/6 1/10
Top daylighting Rectangular skylight Civilian Industrial building building 1/3 1/3 1/4 1/3.5 1/6 1/4.5 1/10 1/8 1/14 1/11
Dentate skylight Civilian Industrial building building 1/4 1/4 1/6 1/5 1/8 1/7 1/12 1/10 1/19 1/15
Flat skylight Civilian Industrial building building 1/6 1/6 1/8.5 1/8 1/11 1/10 1/18 1/13 1/27 1/23
Note: Calculating condition: Civilian building: levels I~IV are for clean rooms, pj=0.5; level V is for generally polluted rooms, pj=0.3. Industrial building: Level I is for clean rooms, pj=0.5; levels II and III are for clean rooms, pj=0.5; level IV is for generally polluted rooms, pj=0.4; level V is for generally polluted rooms, pj=0.3. Area ratio of window to floor in Non-III type lighting climate regions should be mulitified with the lighting climate coefficient K.
However, the result of on-the-spot investigation shows that although these standards were promulgated long time ago, they aren’t applicable to rural residential buildings, because they are designed for urban residential buildings; in addition, the residential environment in rural areas of China is usually very poor； the farmers usually don’t attach adequate importance to indoor daylighting due to traditional farming habits, which leads to undesirable lighting environment quality of rural residential buildings. After the Reform and Open to Outside World, the electric power industry of China has developed quickly, and the electric power utilizing rate in rural areas is increasing ceaselessly. By now, most rural areas of China have been able to use electric light. However, the following problems still exist in rural illumination that cannot be ignored. 1.1 The price of illuminating electric power in rural areas is higher than that in cities, which leads to poor illuminating quality. The illuminating lights in rural families are usually limited to filament lights and thick fluorescent lights. In order to reduce the expenditure of electric fee, most farmers use low-power lights, and 25W or 4 0W fluorescent lights with low power and low illuminating effect take a large proportion, which reduces the illuminating quality in rural areas and affects the living quality of farmers.
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1.2 Electric power used for illumination cannot be guaranteed. With the development of China’s electric power industry, the demand and supply contradiction is alleviated to some extent. However, in rush season of electric power consumption, the demand and supply contradiction of electric power is still serious and power supply in rural areas is often cut off. 1.3 Consumption of electric power for illumination increases greatly. The ratio of electric power for illumination is closely related to the development degree of rural economy. Most families in rural areas of China use few household electrical appliances, and the ratio of electric power for illumination accounts for more than 80% of total electric power consumption of rural families. The amount of electric power consumption goes up year by year with the development of rural living condition. Solar light is a kind of safe and clean energy. Rural areas are ideal to use solar energy due to high transparency of the atmosphere. The most important task of improving the lighting environment of rural residential buildings is to make full use of natural light, because the consummation of lighting environment can effectively reduce the consumption of electric power for illumination of rural residential buildings. The demand of different regional climate and exterior environment on energy saving design of buildings varies greatly. Aiming at the lighting environment characteristics in Liquan county, Shaanxi province, the paper tests and simulates the lighting environment of existing local rural residential buildings, and analyzes the core reasons leading to existing problems. 2. Surveying and mapping of typical courtyard 2.1 Testing object The testing object is a typical rural residential building in a village named Baicun in Weihe Plain of Shaanxi province, and heating method wasn’t adopted when the test is carried out. Plane graph of the testing object is shown in Fig. 10. This is a single-layer building, with the layer height of 3.8m. In the graph, rooms A and B are bedrooms with the windows face the south, and the size of the bedrooms are 4500mm×3300mm; room C is a living room, with windows in the east and west and the size of 3500mm×6600mm; room D is a bedroom, with the size of 4500mm×3300mm; room E is the kitchen, with the size of 4500mm×3300mm.Width of all exterior walls of the rooms is 240mm, formed with thick solid adobes. South-facing windows of rooms A and B consist of aluminum alloy frames and single-layer glass, with the size of 1670mm×2000mm; north-facing windows of rooms E and F also consist of aluminum alloy frames and single-layer glass, with the size of 1670mm×2000mm; other windows are made of wooden frame and single-layer glass. Fig. 1 is the plane graph of the courtyard and the distribution graph of testing spots.
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Fig.1 Plane Graph of a Typical Courtyard and the Distribution Graph of Testing Spots
Fig. 2 Vertical Plan of the Entrance
Fig.3 South Vertical plan of the Court yard
Fig.4 North Vertical Plan (Unit: MM)
Fig. 2～4 are the testing object’s vertical plan of the entrance, south vertical plan and north vertical plan of the courtyard, and their area ratios of window to floor are 0.219，0.224 and 0.219 respectively, which is lower than national standard. In order to further judge the quality of indoor daylighting, we measured the luminance of indoor natural daylighting. 3. Indoor lighting environment test of residential building 3.1 Testing method According to Standard for Daylighting Design of Buildings （GBT 50033-2001）, daylighting coefficient C is taken as the quantity index of daylighting design. Thus the daylighting coefficient of a spot in the building can be calculated with expression 1: C=（En/Ew）×100%
（Expression 1）
Where: En——under the condition of overcast diffusion light, the illumination（lx）produced by sky diffusion light on a given spot in the building. Ew — — under the condition of overcast diffusion light, the outdoor illumination（ lx ） produced by diffusion light on an uncovered outdoor surface at the same time and same spot with an given indoor spot.
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According to above definitions, indoor and outdoor illuminations should be measured simultaneously while measuring daylighting coefficient. Hence, two thermometers are needed, one is used to measure indoor illumination, and the other is used to measure outdoor illumination. Indoor illumination changes with the change of outdoor illumination. Testing apparatus used during the measurement, their performance parameters & sampling modes are shown in Table 3. Table 3 Performance Parameters & Sampling Modes of Testing Apparatus Testing item Indoor and outdoor daylighting coefficient
Testing apparatus Luminometer
Precision of apparatus ±0.1℃
Mode Manual
Sampling Interval （min） 60
Distribution of the testing spots is shown in Fig. 1, the photocell used to measure outdoor illumination should be placed flatwise on an uncovered open place or rooftop without daily influence; the distance L between the photocell and the shelter should be at least 6 times of the height of the shelter. Choose several indoor measuring spots, the daylighting testing spots should be chosen on the joint line of the typical section of the building and the 0.8m flat working face. Generally, the interval should be 2～4 m; for small rooms, the interval can be 0.5～1.0 m. 3.2 Testing result analysis
Fig.5 Sky Average Illumination Fig.5 is the sky illumination changing diagram from 10:00 am to 4:00 pm. It can be found from the figure that sky illumination reduces from the vertex 5800lx to the rock bottom 3180lx. And the average sky illumination is 4539lx.
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Fig.6 Daylighting Coefficient of Bedroom A Fig.6 is the sky illumination changing diagram of bedroom A from 10:00 am to 4:00 pm calculated according to expression. It can be found from the figure that daylighting coefficient of the room reduces with the increase of the distance between the testing spot and the window. daylighting coefficient goes up from 10:00 to 12:00. At 12:00, average value 1 of testing spot reaches its peak value 15. Then, the spot near the window reduces gradually and the spot far to the window reduces quickly. At approximately 14:30, average value 3 of the testing spot reaches its lowest value 5. Daylighting of the room is higher than standard daylighting value and isn’t utilized during testing period, because the room doesn’t adopt artificial lighting.
Fig.7 Daylighting Coefficient of Bedroom C Fig.7 is the sky illumination changing diagram of bedroom C from 10:00 am to 4:00 pm. It can be found from the figure that average value 1 and average value 2 of the testing spot fluctuate between 0.004 and 0.008 during the testing period. Average value 3 of the testing spot less than 0.002 is much lower than average value 1 and average value 2. In addition, all average values of the testing spot are lower than standard daylighting value. During the testing period, artificial lighting is only adopted during dining time, i.e. between 12:00 and 12:30.
Fig. 8 Daylighting Coefficient of Kitchen E
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Fig.8 is the sky illumination changing diagram of Kitchen E from 10:00 am to 4:00 pm. It can be found from the figure that average value 1 of the testing spot gradually climbs to 0.07 from 0.04. Average value 2 of the testing spot fluctuates between 0.01 and 0.03 during the testing period. And average value 3 of the testing is always slightly lower than that of average value 2 of the testing spot. In addition, all average values of the testing spot are higher than standard daylighting value. During the testing period, artificial lighting isn’t adopted at all.
Fig.9 Daylighting Coefficient of Bedroom D Fig.9 is the sky illumination changing diagram of bedroom D from 10:00 am to 4:00 pm. It can be found from the figure that daylighting coefficient of the room reduces with the increase of the distance between the testing spot and the window. Daylighting coefficient goes up from 10:00 to 12:00. At 12:00, average value 1 of testing spot reaches its peak value 0.07. Then, the average value of testing spot maintain between 0.016 and 0.04. Daylighting of the room is higher than standard daylighting value and isn’t utilized during testing period, because the room doesn’t adopt artificial lighting. 4. Residential building indoor lighting environment simulation According to the constructing materials and structure of the typical courtyard, we choose corresponding materials and parameters in ecotect to carry out lighting environment simulation and testing. Table 4 shows the constructing structures and relevant coefficients used in the simulation. Sky illumination adopts the average value tested in the day of the experiment: 4500lx. Table 4 All kinds of Internal and External Surface Materials and Parameters Building component Walls Roof
Material 240mm brick wall， 10mm cement mortar Pitch water proof layer Concrete layer 100mm thick concrete board floor
Reflectivity of internal surface R：0.569 R：0.753
Reflectivity of Light external surface Transmission R：0.647 R：0.337
R：0.592
R：0.592
Courtyard soil General soil surface 1500mm deep
R：0.251
R：0.251
Wooden single-layer glass window
T：0.737
T：0.737
Floor Window
Refraction coefficient
0.737
1.74
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Fig.10 Natural Daylighting Illumination Analysis Diagram
Fig.11 Daylighting Coefficient Analysis Diagram
Fig.10 and Fig.11 are daylighting coefficient and natural daylighting illumination analyzing diagrams. It can be found that the result basically conforms to the testing data of that day. The daylighting coefficient and natural daylighting illumination of the kitchen and the bedrooms meet the standards, while the daylighting coefficient and natural daylighting illumination of the living room are lower than national standards. 5. Conclusions After studying the space modes of rural residential buildings in Weihe Plain, carrying out indoor lighting environment testing and indoor software simulation and analyzing the result, the following conclusions can be reached: The lighting environment of the living space is poor, and the daylighting coefficient is always lower than national standards during the testing period. The lighting environment of the bedrooms is desirable, and the daylighting coefficient is always higher than national standards during the testing period, so artificial lighting isn’t needed. The kitchen and storehouses have desirable daylighting, and the daylighting coefficient is always higher than national standards during the testing period, so artificial lighting isn’t needed. The toilet hasn’t natural lighting, so artificial lighting must be adopted. Thus, it can be concluded that the lighting environment of the bedrooms and auxiliary rooms is great, while that of the living space is poor. After studying the architectural design and living habits of this region, we found that the architectural design and living habits influences the indoor daylighting and the quality of lighting in the following ways. 5.1. Base layout. The bases of rural residential buildings in Guanzhong region usually are long in north-south direction and narrow in east-west direction. Since there are walls without daylighting in east-west direction and the daylighting in north-south direction is limited, poor-daylighting rooms are likely to appear in rural residential buildings. 5.2. Layout and size of architectural plane. There is unreasonable phenomenon in plane layout of buildings: bedrooms not requiring good daylighting condition with low utilization rate occupy favorable natural lighting source, while living space doesn’t have direct daylighting. It can be found from room sizes that the size of auxiliary space in rural residential buildings is much larger than that in cities, which is due to the demand of rural labor. While living space is small, which shows again that local people doesn’t attach great importance to indoor communicating space.
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5.3. Conformation of buildings. The buildings adopt wooden-framed single layer glass windows. Since local craftwork level of glass is limited, and the quality is poor, so the transparency of the glass is low. Indoor floors usually are deep grey concrete board without superficial decoration, so the refractive index is low. However, the walls and ceilings of the buildings are white with high refractive index, which, to some extent, enhances the indoor lighting environment. 5.4. Lighting habits. The residents usually turn on their lights when the lighting condition is under 80lux, which is lower than national luminance standard of living space and shows that the demand of the rural residents on lighting environment is lower than that of urban residents. 5.5. Living habits. The residents in Weihe Plain attach great importance to the lighting environment of bedrooms and the kitchen, and they usually ignore the lighting environment of the living space, which is caused by the living habits with courtyards as the core of family life and varies greatly with the living habits of urban residents. Pursuant to the lighting environment quality problems existed in rural residential buildings in Weihe Plain and the living habits of current permanent residents, in the aspect of consummating natural lighting, we should reform the space of local residents, so as to make the living space with high utilizing rate occupy favorable natural lighting condition, e.g. living room should be arranged in the direction and location with favorable daylight resource, and the daylighting of bedrooms should be considered secondly. In the next place, for side windows as the main daylighting access, high side windows have better illumination evenness than lower ones, so high side widows can be adopted. In order to control energy consumption of rural residential buildings, first of all, we should make full use of natural light; second, we can adopt the method of converting solar energy into electricity. Acknowledgement This study project is financially supported by National Undergraduates Innovating Experimentation Project. Meanwhile, the authors would like to extend their heart-felt thanks to the villagers in Baicun village, Yanxia county for their active cooperation and assistance during data testing and questionnaire survey. References [1] Residential building design specification GB 50096-1999。 [2] Huang Haijing. Daylighting and energy saving design subarea study（C）, Green buildings and architectural physics——Memoir of the 9th national architectural physics academic conference. Beiing: Chinese construction industry publishing house, 2004. [3] Sheng Tianxing, Yuan Lei. Technology of introducing daylight into ground floor of north-facing buildings CJ3. Architectural journal, 2004,（4）：78—79。 [4] Tu Fengxiang, Wang Meijun. Chinese climate and energy saving of buildings [J] . Heating, ventilating and air conditioning, 1996（4）. [5] Zhang Shaogang. On-spot testing, investigation and study on natural illumination of residential buildings. China housing facilities,2004（06）.