an experimental and theoretical study on the indoor ... · 4th international conference on building...

4th International Conference On Building Energy, Environment

An Experimental and Theoretical Study on the Indoor Thermal Environment of a New Cave Dwelling in the Northwest of China

X. Fan, B. Chen, T. Zhao

Lab. of Building Environment and New Energy Resources

Dalian University of Technology (DUT), Dalian 116024，China

SUMMARY The cave dwelling was widely used in Northwest of China because that it could keep warm in winter and cool in summer. However, traditional cave dwelling could only be built on the hillside, which restricted the widespread use of cave dwellings. This paper introduced a new cave dwelling without building on mountain. The paper investigated three types of local building indoor thermal performance including new and traditional cave dwelling. We found the thermal performance of new cave dwelling was almost as same as traditional cave dwelling. Finally, this paper analysed the relationship among various building dimensions.

INTRODUCTION The building forms of cave dwelling contained green, energy saving ideas, which was widely used in the Loess Plateau of China, as shown in Figure 1a. It was estimated that 40 million people lived in cave dwelling in northern China. However, the traditional cave dwelling could only be built by mountain, which was restricted the widespread use. When there was no mountains, local people selected the courtyard (Siheyuan) to live, as shown in Figure 1b. The courtyard was

formed by four directions building. The courtyard indoor thermal performance was not very good. In order to solve the traditional courtyard indoor thermal environment, many people began to think how to make the cave dwelling built on flatlands. When we did some experiments in northwest of China, we found a new cave dwelling which could build in flatlands. The new cave dwelling created by local people and retained shape of traditional cave dwelling, as shown in Figure 2. In order to know this new cave dwelling indoor thermal performance, we measured the indoor temperature and humidity in winter and summer. The three types of building was selected to analysis including traditional cave dwelling, new cave dwelling, and the courtyard. At the same time, we did questionnaire.

METHODS The traditional cave dwelling, cave dwelling, courtyard was tested on July 4 - 14, 2014 in summer and February 11 - 26, 2015 in winter. The indoor temperature and humidity test equipment were selected TR72U which was produced by Japan. The equipment accuracy was ± 0.1°C / ± 5%. The test point was located in the centre of the room 1.5 m. The

a) Cave dwelling b) Courtyard

Figure 1. Cave dwelling and Courtyard of distribution and history development

ISBN: 978-0-646-98213-7 COBEE2018-Paper347 page 964


Figure 2 The difference between traditional cave dwelling and new cave dwelling

Figure 3 Typical Chinese kang and building combined types

tested place was located in the northwest of the Loess Plateau, Gansu province. The tested buildings took Chinese kang heating system in winter. The Chinese kang was the most ancient heating system which is widely used in rural residences in cold regions of China, especially in Northeast China. Even though the outdoor air temperature was very low, the surface temperature of Chinese kang could still remain above 30 °C (Chen Bin et al. 2007). Chinese kang has five basic types, as shown in Figure 3. This research investigation building with Chinese kang was type B. The three building take natural ventilation in summer. A total 53 questionnaire was collected from different architectural forms and ages. The questionnaire mainly used for comparison of prediction evaluation index PMV and heat Sensation Vote value TSV.

Figure 4 Prediction evaluation index PMV and heat Sensation Vote value TSV



It can be observed that traditional Cave dwelling and new cave dwelling was regarded as comfortable, as shown in Figure 4. As we can seen, the calculated value of prediction evaluation index PMV was generally higher than heat Sensation Vote value TSV through measuring. It turned out that the local people have high heat tolerance.

INDOOR THERMAL ENVIROMENT STABILITY Generally, many researches used indoor thermal environment stability to evaluate architectural performance (Kalamees T et al. 2009). Because Cumulative distribution functions (CDF) could describe the data dispersion and cumulative probabilities, so it’s an important way to describe building thermal stability. Therefore, this research used MATLAB CDF function to analysis three types building temperature distribution in summer and winter, as shown in Figure 5.

a) Winter

b) SummerFigure 5 Three tested houses CDF temperature in winter and summer

Different countries had different indoor design requirements, as shown in Figure 6. China lower indoor design temperature range was 18 - 24 °C in winter and 27 -28 °C in summer based on China standard “Design code for heating ventilation and air conditioning of civil buildings” GB50736-2012. However, the whole indoor temperature of new cave dwelling, traditional cave dwelling and courtyard was 12 - 16 °C, 14 ~ 16 °C and 6 - 17 °C in winter, respectively. We found that 60% of thecourtyard room temperature below 12 °C. It was difficult tomeet the winter indoor temperature design temperature (i.e.18 °C). Winter CDF temperature distribution showed that newcave dwelling and traditional cave dwelling indoor thermalperformance have 82% and 90% time period better thancourtyard respectively. In summer, the new cave dwelling andtraditional cave dwelling had better indoor thermal stability,while the courtyard house temperature range was larger. Thewhole indoor temperature of new cave dwelling, traditionalcave dwelling and courtyard was 22 - 26.5 °C, 19.8 - 24 °C,20 - 30 °C in summer, respectively. It could be observed thatoutdoor and indoor temperature lines were crossed in summer.It showed that the indoor temperature in summer have twodifferent conditions which were higher or lower than outdoorenvironment. Summer indoor temperature lower than outdoor

temperature begins: traditional cave dwelling was about 21 °C accounting for 45% of the time periods, new cave dwelling was about 24.3 °C accounting for 35% of the time periods, courtyard was about 29 °C accounting for 10% of the time periods. Trough CDF analyses in winter and summer it showed that the indoor thermal stability is traditional cave dwelling better than new cave dwelling and courtyard.

a) Temperature

b) HumidityFigure 6 Different countries indoor design temperature and humidity in winter and summer

INDOOR ENVIRONMENT THERMAL COMFORT The preceding analysis was a statistical analysis of indoor thermal stability. However, it was difficult to describe indoor thermal comfort and human environment perception. Generally, many standard use thermal comfort to evaluate indoor thermal comfort. This paper was based on ISO 7730, ASHRAE handbook, Chinese building energy saving standard,

winter / summer thermal comfort limit Ⅱ selected as 18 ± 2 °C

and 24 ± 2 °C. The analyses result were showed in Figure 6. We must describe that thermal comfort index (PMV) need six important parameters to take into account: human metabolic rate, indoor temperature, pressure, average radiation temperature, velocity, human activity and type of clothes. However, it was difficult to record all the above mentioned parameters inside three residential houses under normal living conditions. Finally, we had made an approximation thermal comfort zone to describe indoor thermal comfort. The Figure 7 showed that new cave dwelling which had a perfect environment was similar to traditional cave dwelling. However, traditional cave dwelling have little cold in summer and warm in winter. We found that new cave dwelling could replace traditional cave dwelling to the extent. Through experimental investigation, we found different towards building of courtyard has different indoor environment, as showed in Figure 8. From the winter point of view, towards south building of courtyard



has a better indoor environment because it could get more solar radiation from window in winter. However, towards north / south / east building of courtyard indoor thermal condition was almost same in summer.

a) Winter

b) Summer

Figure 7 The relationship between indoor - outdoor temperature difference and outdoor temperature in winter and summer among three different building The indoor comfort zones are shaded in grey color.

a) Winter

b) Summer

Figure 8 The relationship between indoor - outdoor temperature difference and outdoor temperature in winter and summer in courtyard. The indoor comfort zones are shaded in grey color.

From the above analysis, we found that new cave dwelling was a new architectural form which could be satisfied with basic thermal comfort. New cave dwelling was a representation in Chinese culture. Through rural investigation, we found it also have many questions needed to solve. In addition to the above description, we found that the use of the building habits, life behavior can affect the building indoor environment. This paper only analyzed indoor temperature distribution and thermal comfort. The indoor natural ventilation and public health required future research.

STRUCTURAL PERFORMANCE ANALYSIS OF THE NEW CAVE DWELLING How to design the new cave dwelling? It was generally believed that the state of the wall without bending was the best design. As can be seen from the above, the arch axis which was designed according to the pressure curve was a reasonable axis. This study assumed that the top of the new cave dwelling was evenly filled with soil / gravel with a bulk density of γ. The distribution load of all new cave dwelling was qc+γf. According to the force analysis, we could get the stress equation and boundary condition of the new cave dwelling, as shown in Equation 1.

a) Basic information of new cave dwelling



b) The structural performance of cave dwelling

Figure 9 Force analysis of new cave dwelling

2 2 0

2 2

1

c 1: 0, 0;

c 2: 0, 0;

:H

d y d M

dx F dx

Boundary ondition x y

dyBoundary onditio

Reasonab

n x

le arch ax

dx

is

(1)

Where FH (N/m2) was Horizontal thrust, 0 ( )2

qM x l x (kN•

m) was the moment equation of simply supported beam. By

solving the equation, the reasonable axis equation of the cave

can be obtained, as shown in Equation 2.

( 1)c

H

qy ch x

F

(2)

However, the different filling materials and the mixing ratio would affect the new cave dwelling axis equation. Finally, the equation should be adjusted appropriately. This equation could provide basic design principles of new cave dwelling.

DISCUSSION In this investigation, we studied indoor thermal environment of three typical building forms including traditional cave dwelling, new cave dwelling and courtyard with the same tested period. This paper use PMV/TSV, indoor thermal environment stability, indoor thermal comfort to analysis indoor thermal environment of the new cave dwelling compared with traditional cave dwelling and courtyard. We found that PMV higher than TSV which showed that the people with high heat tolerance. These results were consistent with some research about indoor thermal comfort in China (Zhang Nan et al. 2017). At present, many researches have showed that people of different culture background have different indoor expectations. It had deviations between TSV and PMV exist for different regions, indicating that the PMV model fails to accurately predict actual thermal sensation. The heat comfort perception was not only related to culture, but also heat history (Luo Maohui et al. 2015). It means that the comfortable thermal experience will lift occupants' thermal expectation. That is to say, the new cave dwelling could influence occupants' thermal expectation.

The results from the indoor thermal environment stability showed the new cave dwelling almost same as cave dwelling, which is better than courtyard building. In the future, this new

cave dwelling may be used for energy-saving. From what we

tested, the fluctuation range was 12 - 16℃ in winter and 22 -

26 ℃ in summer. If the new cave dwelling took more passive

heating systems, it could build better indoor environment. This new cave dwelling retain the basic cave dwelling shape to meet culture need. This best benefit of these building forms best benefit was that it could build in flatlands and provide good indoor thermal environment. The new cave dwelling could improve indoor thermal comfort compared courtyard.

In order to make this new cave dwelling be used to more and more places, this paper analysed the cave dwelling structural performance. We found the relationship between height and width, which could be used as basic building structural design principles.

CONCLUSIONS Through the investigation and research on traditional cave dwellings, the following conclusions were obtained:

1) New cave dwelling indoor thermal stability which is similar

to traditional cave dwelling. The fluctuation range was 12 - 16℃

in winter and 22 - 26℃ in summer. Building towards and

human behaviour could influence indoor thermal environment.

2) New cave dwelling could not only just build aroundmountain but also in any other places. It’s a good choice forpeople building new cave dwelling.

3) The basic design principles of the new cave dwelling wasput forward.

ACKNOWLEDGEMENT The authors would like to thank the research funding from the National Natural Science Foundation of China (NSFC, No. 51178073, No. 51578103), Key Projects in the National “Twelfth Five-Year” Science and Technology Support Program (No.2012BAJ02B05) of China.

REFERENCES Chen, B., et al. 2007. Field survey on indoor thermal

environment of rural residences with coupled Chinese kang and passive solar collecting wall heating in Northeast China. Solar Energy, 781-790.

Luo M, et al. 2015. The Dynamics of Thermal Comfort Expectations. Building & Environment.

Kalamees T, et al. 2009. The effects of ventilation systems and building fabric on the stability of indoor temperature and humidity in Finnish detached houses. Building and Environment. 44(8): 1643-1650.

Zhang, Nan, et al. 2017. A comparison of winter indoor thermal environment and thermal comfort between regions in Europe, North America, and Asia. Building & Environment, 208-217.


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