Study on the Thermal Performance of the Vernacular Dwellings in Wei-he Plain of Shaanxi Province

Advanced Materials Research Vols. 476-478 (2012) pp 1589-1595 Online available since 2012/Feb/27 at www.scientific.net © (2012) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.476-478.1589

Study on the Thermal Performance of the Vernacular Dwellings in Wei-he Plain of Shaanxi Province Yiping ZHU1, a, Xi LIAO1, b, Shuyun WU1, c, Jing LUO1, d, Yuan JIANG1, e and Wenbo WU1, f 1

School of Architecture, Xi’an University of Architecture and Technology, Xi’an, China, 71005 a

b

c

zhuyiping114@gmail.com, yinweiai527lx@hotmail.com, wu_shu_yun@163.com, d e f kaka930@126.com, 415894084@qq.com, 413477743@qq.com

Keywords: vernacular dwelling, maintenance structure, thermal performance, indoor thermal environment

Abstract: Based on indoor thermal environment test and questionnaire surveys, the paper studies on thermal insulation capacity and indoor thermal environment of the vernacular dwellings in Wei-he Plain of Shaanxi Province, China, and analyses their heating methods and application status. Besides, the popularity of sustainable techniques in local area has been evaluated and summarized. Moreover, the paper discusses the present problems in local indoor thermal environment and energy-saving status.

Introduction Currently, the building area of urban and rural architecture in China has exceeded 40 billion m2, which consumes 376 million tons of standard coal tce, accounting for 27% of terminal energy consumption of the entire society. More than 60% of the total building area is covered by vernacular dwellings (around 23 billion m2), consuming energy of over 100 billion kW•h. Therefore, saving energy in vernacular dwellings is of great importance to a sustainable society in China.

With the promulgation of “construction of new socialist countryside” policy, the winter indoor thermal condition of vernacular dwellings has been improved, but it is still much inferior in quality to that in cities. Most areas in northwestern China are in cold climates; in winter, it is dry, cold, windy and dusty, and the winter indoor thermal condition is relatively poor. So, it is of great importance to research the winter thermal performance of vernacular residence in northwestern China and subsequently to improve its living quality.

In recent years, many scholars have been focusing on the energy saving issues of vernacular dwellings. However, by fieldwork in Wei-he Plain of Shaanxi Province, China, it is found that the research findings and energy-saving technologies regarding this field are rarely applied in building construction, and the local indoor thermal environment still falls short of the thermal comfort target.

Therefore, through subjective evaluation of indoor thermal environment survey and indoor thermal environment test, the author demonstrated the local indoor thermal condition and importance of applying energy-saving renovations.

Indoor Thermal Condition Subjective Evaluation Survey Overview. Bai village, the subject of the investigation, is located in Yanxia Town, Liquan County, Xianyang City, Shannxi Province, China; the survey was done in December. Liquan County is located in the southwest of Central Shannxi Plain where Wei-he Valley and Loess Plateau intersect. It covers an area of 1018 km2, containing 11 towns and 4 villages, with a population of 450 thousand. By interviews and questionnaire survey, the local residents’ subjective evaluation of indoor thermal condition has been recorded and summarized. Meanwhile, by researching on residents’ satisfaction and acceptance degree of energy-saving technologies, the questionnaire searched the relationship between subjective evaluation of residents and the efficiency of energy-saving renovation. Ultimately, the paper proposed solutions to the problems and obstacles facing energy-saving renovation based on the results of the survey.

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Results Analysis. By investigation, the condition of population composition, building structure, materials and thermal insulation structures of external walls, structure of windows and doors, solar technologies, other eco-technologies and residents' subjective evaluation of indoor thermal environment in winter are reflected.

Fig.1 illustrates the population age structure of the village. Senior citizens over the age of 60 take up over 40% of the population. With the process of urbanization, about 30% families are empty nest households now.

Fig.1 Bai village population age structure

Fig.2 Residential structure

Fig.2 shows that the mainstream dwellings in Bai village are load-bearing wall structure. Wall materials and insulation situation can be seen clearly from Fig.3 and Fig.4: 82.5% of exterior walls are built by solid clay bricks while hollow clay brick walls and rammed earth walls only account for 9.7% and 6.3% respectively. Most of the walls do not have heat preservation structure.

Fig.3 Exterior wall materials

Fig.4 Wall insulation status

From Fig.5, it can be seen that 77.5% of houses use wood-framed single-glazed windows. Houses using steel-framed single-glazed windows hold 12.3% of the total amount. Other types of windows, including double glazed windows, have not been popularized.

Fig.5 The types of residential windows

Fig.6 Residential heating methods

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As can be seen from Fig. 6, 40.1% of households use fire heating bed (kang) as the only heating equipment in winter. The main fuel of kang is straw, and hot kitchen smoke is utilized as second heat source. Mixed uses of coal stoves and fire heating beds (kang) are adopted by 43.2% of households.

And the remaining 16.7% are heated by coal stoves alone. The survey also found that the proportion of families that use kang is gradually reducing.

Fig.7 Solar energy utilization

Fig.8 Other energy-saving technologies applied

Fig. 7 shows that 12.0% of the Bai village dwellings are equipped with active solar installations, and the only active solar energy technology adopted is solar water heater. 16.5% of households use passive solar energy technology, and the main mode of application is sun room. Among those who have not applied sun room, 40% expressed their willingness to accept it, and the main obstacles that they face are the existing spatial distribution and building structure of their houses. The rest stated that they could not accept such technologies due to economic reasons.

Fig.8 shows that the metabolic wastes of each household go into the public biogas digester of the village, and the residues are distributed back to the households as fertilizer. All dwellings use double-skin roof for natural ventilation, which proves to be effective. However, other energy-saving technologies have not yet been applied.

Fig.9 Subjective evaluation of indoor thermal environment

Fig.9 reveals residents subjective evaluation of indoor thermal environment: regarding indoor thermal environment in winter, most residents feel the indoor temperature is lower than the outdoor one.

Winter Indoor Thermal Environment Test.

Test Object. The test object is a typical dwelling in Bai Village, Wei-he Plain, Shannxi Province, which is free from heating measures on the test day. The house is single-storey, 3.8m high. Room A and B are bedrooms that face south, measuring 4500mm by 3300mm; room C is a living room with no direct light, measuring 3500mm by 6600mm; room D is a bedroom, facing north and measuring 4500mm by 3300mm; room E is a kitchen, measuring 4500mm by 3300mm. The external walls are solid clay bricks, 240mm thick; room A and B use steel-framed single-glazed windows that face south, measuring 16700mm by 2000mm; room E and F use steel-framed single-glazed windows, facing

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north and measuring 16700mm by 2000mm; the rest of the windows are wood-framed and single glassed. Room B is the only one that applies heating equipments, and it is heated by a fire heating bed (kang).

Test methods. Test instruments and their performance parameters as well as sampling methods are listed by table 1.

Table 1 Performance parameters of test instruments and sampling methods Test items

Test instruments

Precision

Indoor and outdoor air temperature

Humidity thermometer

±0.1˚C

Indoor and outdoor air wet bulb temperature Envelope inside and outside surface temperature

Humidity thermometer

±0.1˚C

IR thermometer

±0.01˚C

Methods Manual acquisition Manual acquisition Auto acquisition

sampling time interval(min) 60 60 60

The layout of measuring points is shown in Fig. 10; to minimize the external interference, the thermometers rise above 1.2m from the ground when measuring indoor and outdoor air temperatures; while testing the wall temperatures with thermocouple thermometers, the thermal probe is drawn against the wall in case that there is a air layer remained.

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Fig. 10 Floor plan of a typical local dwelling and the layout of measuring points

Test results analysis. Fig. 11 describes the changes of the dry bulb temperature from 10:00 to 16:00 of each measuring point. It can be seen that the indoor and outdoor temperature difference is large.

During the test, the maximum indoor temperature is 7.5℃ in 16:00. Although the indoor temperature fluctuated slightly, it is always lower than the comfortable temperature, and even lower than 10˚C. So the winter indoor thermal environment is very poor. Besides, the rooms that face south have higher temperatures than those facing north; the temperatures in room D, kitchen E and Parlor C are about 2℃ lower than those of room A and B. And the maximum temperature difference reaches 2.7˚C.

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Fig. 11 Dry bulb temperature of the local house

Fig. 12 Relative humidity of the local house

Fig. 12 is composed of indoor relative humidity curves of each measuring point form 10:00 to 16:00. As can be seem form the data in the figure, the temperature of the courtyard F is directly influenced by the changes of outdoor temperature, whose relative humidity declines as the rise of outdoor temperature and falls to the lowest point in 14:00, around 10%. Hence, it is very dry outdoor.

And then its relative humidity rebounds with the decrease of temperature. The relative humidity in the kitchen is relatively high, and there are significant fluctuations accompanied by cooking activities.

The other rooms maintain a stable relative humidity between 40% and 70%, within the comfortable range.

Fig. 13 shows the wall interior surface temperature curves of each room. As the wall temperature rises form solar radiation heat gain, the average temperature difference between south and north rooms is 2℃, and the maximum one reaches 4.9℃.

It’s calculated that the mean radiant temperature is 4.3 ℃ lower than the average indoor temperature, and it is basically consistent to the fluctuation of indoor temperature as well as research conclusions drawn by other scholars.

Fig. 13 Window interior surface temperature of different walls

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Conclusion Based on indoor thermal environment test, subjective evaluation of indoor thermal environment survey and results analysis, there are five main conclusions: 1. Fundamental changes have taken place in rural household composition, and the empty nest families take a large proportion of all households.

2. The small percentage of thermal insulation walls, materials and windows is the main reason leading to poor indoor thermal environment and energy efficiency.

3. Coal and straws are the main burning material for winter heating, and the mainstream heating methods are coal stoves and fire heating beds (kang), which are backward and inefficient, affecting indoor air quality. Despite these inferiorities, heating kang with kitchen waste heat is in line with the concept of energy recycling, and this method should be retained and optimized. Meanwhile, the living space should be scientifically arranged in order to make better use of kitchen waste heat and subsequently improve the indoor thermal environment.

4. The indoor thermal environment is better in rooms that face south than those facing north. So, passive solar techniques such as additional sun rooms should be promoted.

5. The efficiency of biogas utilization is low; however, since biogas is accepted by most residents, it has great potential in future development. And the present biogas system provides possibilities for gas burning kangs in the next step.

Acknowledgements The research is financially supported by the national undergraduate innovative experiment program of China. The authors would like to express their thanks for their kind help with the field measurement and questionnaire surveys of the residents at Bai village in Liquan County, Shaanxi Province.

References [1]Yuping Wu, Taojian Hu, Wei Ge: Optimize Building Energy Conservation Policy, Promote Energy Saving Techniques in China, China Construction Dynamics, (May, 2007) [2]Ling Li, Junge Li, Gaochao Du: Study on Energy Conservation Design for Building Envelope of Typical Vernacular Dwellings in Central Shannxi Area, Building Science, (Aug., 2009) [3]Zhengmin Li, Xiaojuan Han, Study on Energy Conservation Design for Typical Vernacular Dwellings in Central Shannxi Area, Journal of Xi'an Eurasia University, (Apr., 2009)

New Materials and Processes 10.4028/www.scientific.net/AMR.476-478

Study on the Thermal Performance of the Vernacular Dwellings in Wei-He Plain of Shaanxi Province 10.4028/www.scientific.net/AMR.476-478.1589