Experimental study on thermal characteristicsof a double skin fa?ade building

Wang Fang Zhang Xiaosong Tan Junjie Li Xiuwei

(1School of Power and Energy Engineering, Nanjing University of Science and Technology, Nanjing 210094, China)(2School of Energy and Environment, Southeast University, Nanjing 210096, China)

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Experimental study on thermal characteristicsof a double skin fa?ade building

Wang Fang1Zhang Xiaosong2Tan Junjie1Li Xiuwei1

(1School of Power and Energy Engineering, Nanjing University of Science and Technology, Nanjing 210094, China)(2School of Energy and Environment, Southeast University, Nanjing 210096, China)

An experimental study of the thermal characteristics of an existing office building with double skin fa?ade (DSF) were conducted in hot summer daytime in Nanjing, China. The temperature distributions of the DSF and indoor environment were measured at different control modes of DSF. The results show that the energy consumption of the air conditioning system in room B with opened exterior vents, a closed interior fa?ade, and an air cavity with shading was 21.0% less than that in room A with closed exterior vents, a closed interior fa?ade, and air cavity without shading in 9.5 h. The temperature distributions of the DSF and indoor environment in both horizontal and vertical directions were decisively influenced by shading conditions. The usage of shading devices strengthens the stack effect on the air cavity. Compared to room A, the temperature distribution in room B is more uniform with smaller fluctuations. Meanwhile, the problem of overheating in the air cavity of the DSF is still present in all tested conditions.

double skin fa?ade; thermal characteristics; temperature distribution; energy consumption

The thermal characteristics of a double skin fa?ade (DSF) varies in different locations and climate conditions. Model tests and numerical simulation are effective methods to explore the correlation between thermal properties and different climate and usage conditions. Field experiments are the important basis for optimizing operation strategies, modifying model tests and numerical simulation[1]. Hashemi et al.[2]monitored the DSF building in the hot and dry climate zone in Iran for two weeks during the winter and summer seasons. Mingotti et al.[3-4]experimented on the energy consumption potential of DSF.

DSF buildings are challenged by the conflicts in the hot summer and cold winter zones in China. Wang et al.[5]pointed out that most of the existing buildings in hot summer and cold winter zones were overwhelmed by the conditions of poor heat insulation performance in hot summer and poor cold resistance performance in cold winter. The discrepancy between existing DSF buildings and weather was due to the lack of field test data of thermal performance regarding existing DSF buildings[5]. Shameri et al.[6-7]pointed out the energy saving potential of DSF buildings with proper control strategies.

This study focuses on the field experiments of energy consumption and thermal performance of an in-use office building with DSF in summer conditions in Nanjing. Nanjing is a typical city of a hot summer and cold winter zone, which is located at longitude east of 118°48′ and the northern latitude of 32°00′. Experiments were conducted in order to investigate the following: the temperature distributions of DSF and the indoor environment in horizontal and vertical directions under different operating strategies of DSF on a hot sunny summer day and the energy saving potential for DSF with a proper operation strategy.

1 Methodologies

The surveyed building was put into use in 2007 in Nanjing, China. It has 19 floors above ground and is oriented 34° northeast. The fa?ade from the fifth floor to the eighteenth floor is a double skin glazed fa?ade of box-window type with an air cavity of 530 mm. Shading devices of the DSF are electric aluminum alloy blinds in the air cavity and are close to the exterior fa?ade. The exterior fa?ade of DSF is fixed and composed of single ferrules of 10 mm thickness while the interior fa?ade is composed of insulating glass 6+12A+6 with a low-e coating outside. Ventilation can be achieved by the opening of the interior fa?ade and vents in the exterior fa?ade. Each floor is conditioned by two individual VRV systems and one fresh air conditioning system powered by electricity. Two offices A and B with DSF on adjacent floors facing southwest of the same size and function were chosen for conducting the experiments on the longest sunning duration of southwest orientation in summer.

The temperature measuring points are shown in Fig.1. Each measuring point is named asXY, whereXmeans the vertical direction (cmeans the height of 0.3 m to the ground;bmeans the height of 1.1 m to the ground;ameans the height of 2.5 m to the ground) andYmeans the horizontal direction (1 means the inside surface of the exterior fa?ade; 2 means the middle of the air cavity; 3 means the outside surface of the interior fa?ade; 4 means the inside surface of the interior fa?ade; 5 means the place with a 0.5 m distance to the inside surface of the interior fa?ade; 6 means the place with a 1 m distance to the inside surface of the interior fa?ade; 7 means the place with a 2 m distance to the inside surface of the interior fa?ade; 8 means the place with a 4 m distance to the inside surface of the interior fa?ade; o means the outside environment). Each temperature was recorded by two thermocouples of T-typed (φ0.254 mm) at an interval of 10 s. Meteorological data was taken from the weather station Vantage Pro2 Plus. The temperature of each layer of DSF was named ast1,t2,t3,t4. For example,t1is the average temperature ofta1,tb1andtc1.tiis the typical temperature of the indoor environment, which is the average temperature ofta7,tb7andtc7.

Fig.1 Distribution of temperature measuring points (unit: mm)

Preliminary experiments indicated that the best condition in hot summer sunny daytime for DSF in Nanjing was with opened exterior vents, a closed interior fa?ade and an air cavity with shading while the worst condition was with closed exterior vents, a closed interior fa?ade and air cavity without shading. So in this paper, one contrast experiment was provided to evaluate the energy saving effect and thermal characteristics of the DSF under the best condition and the worst condition. Tab.1 presents the schedule of measurements. The experiment was performed from 8:00 to 17:30 on 25th July. The opened exterior windows meant that all the vents of the exterior fa?ade were opened fully. The closed interior fa?ade means that all the windows of the interior fa?ade were completely enclosed. Air conditioning systems were in operation during the experiments and the indoor environment temperature was set to be 26 ℃. 95% of the testing error was within 7.6%[8].

Tab.1 Schedule of measurements

2 Results and Discussion

The temperature distribution of DSF in horizontal direction from outside to inside varies under different conditions (see Fig.2). The temperature distribution of DSF in room A ist2(38.9 ℃)>t3(38.0 ℃)>t1(37.3 ℃)>t4(30.6 ℃)>ti(26.3 ℃) while the temperature distribution of room B ist1(37.4 ℃)>t2(34.4 ℃)>t3(33.5 ℃)>t4(28.3 ℃)>ti(25.9 ℃) (The data in brackets is the average temperature from 8:00 to 17:30). With closed interior windows and the usage of blinds in room B, the highest temperature decrease of the air cavity and outside surface of the interior fa?ade reaches 4.5 ℃.The average temperature difference between the indoor air temperaturetiand inside surface of the interior fa?adet4of room B is 2.4 ℃ while that of room A is 4.3 ℃. With the decrease in temperature difference betweentiandt4, indoor environmental comfort can be improved.

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(b)

It can be seen that shading is the decisive factor in the temperature distribution of DSF in a horizontal direction (see Fig.2). With shading, the instantaneous temperature of the inside surface of exterior fa?ade is the highest. Without shading, the instantaneous temperature of the outside surface of the interior fa?ade is the highest. Shading can decrease the instantaneous temperatures of the air cavity, the outside surface of the interior fa?ade, the inside surface of the interior fa?ade and indoor air; but it is ineffective at affecting the temperature decrease of the inside surface temperature of the exterior fa?ade. That is because shading rejects solar radiation effectively.

Figs.3 and 4 supply the temperature distributions of DSF in a vertical direction of both room A and room B. From Figs.3(a) to (d), the temperature of the inside surface of the interior fa?ade and outside surface of the interior fa?ade of room A decreases with the increasing distance from the ground. The vertical temperature difference of each layer of DSF of room B can be seen in Figs.4(a) to (d). The temperature of each layer of DSF in room B increases with the increasing distance from the ground. The instantaneous vertical temperature difference of the air cavity of room B reaches the highest temperature of 2.5 ℃. The stack effect can be clearly found in the air cavity of room B.

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(b)

(c)

(d)

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(d)

Figs.5 and 6 supply the temperature distributions of the indoor environment in horizontal and vertical directions, respectively. The horizontal temperature distributions of room A change dramatically (see Fig.5). The average indoor temperature of room A with a distance of 0.5 m to the inside surface of the interior fa?ade is 27.7 ℃, while the temperature with distances of 1, 2, and 4 m to the inside surface of the interior fa?ade approximates 25.7 ℃. Comparatively, the temperature distributions of room B with the increasing distance to DSF are basically uniform (see Fig.6). This illustrates that the working conditions of room B is helpful for increasing the uniformity of the indoor temperature distribution in a horizontal direction. Vertical temperature differences are found in the indoor air of both room A and room B at the distance of 2 m to DSF (see Figs.6(a) and (b). The maximum instantaneous vertical temperature difference of room A is 1.4 ℃ higher than that of room B (0.8 ℃).

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(b)

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(b)

Shading influences the vertical temperature difference significantly. Although the ventilation mode with opened exterior vents and a closed interior fa?ade is helpful for decreasing the temperature of the inside surface of the exterior fa?ade, the air cavity and the outside surface of the interior fa?ade, especially for the air cavity; it is powerless in the temperature decrease of indoor air and the inside surface of the interior fa?ade.

Form 8:00 to 17:30, the cumulative power consumption of the air conditioning system in room A is 54.6 kW·h while that in room B is 43.2 kW·h. The cumulative air conditioning system energy consumption of room B is 21.0% less than that of room A in 9.5 h. When the indoor air temperature is set to be 26 ℃ in the air conditioning system, the accurate average indoor air temperature of room A is 26.3 ℃ while that of room B is 25.9 ℃. The overheating problem of the air cavity in both room A and room B still exists, regardless of the working condition of DSF. The average temperature of the air cavity in both tested rooms is higher than the average temperature of the whole DSF, the average temperature of the indoor environment and the average temperature of the outdoor environment during testing time.

3 Conclusions

With the field experiments on an existing DSF building on a hot sunny summer day in Nanjing, the key findings are as follows:

1) Shading is the decisive factor in the temperature distribution of DSF and the indoor environment in both horizontal and vertical directions. The stack effect on the air cavity is significant when shading devices are used in DSF.

2) For the working conditions of DSF with open exterior vents, closed interior fa?ade, and an air cavity with shading, the indoor temperature distribution is more uniform with smaller fluctuations in both horizontal and vertical directions compared to that for working conditions with opened vents on the exterior fa?ade and a closed interior fa?ade and without shading.

3) In hot summer and cold winter zones in China, DSF with opened exterior vents, a closed interior fa?ade, and an air cavity with shading is the optimal open condition which saves 21.0% energy consumption of the air conditioning system in 9.5 h compared to a DSF with closed exterior vents, a closed interior fa?ade, and an air cavity without shading in hot sunny daytime.

4) The overheating problem of the air cavity still persists even with the combination of shading and ventilation.

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雙層玻璃幕墻建筑夏季熱特性試驗研究

王 芳1張小松2譚俊杰1李秀偉1

(1南京理工大學能源與動力工程學院, 南京 210094)(2東南大學能源與環境工程學院, 南京 210096)

通過對南京地區某雙層玻璃幕墻建筑在夏季白天不同運行模式下的表皮各層和室內溫度分布對比實測,分析該建筑的熱特性.結果表明:在9.5 h內,房間B在外層通風口打開、內層表皮緊閉、中間遮陽完全啟用的情形下,空調系統能耗比房間A在內外層表皮均完全緊閉、無遮陽設施情形下減少21.0%.玻璃幕墻各層表皮和室內各狀態點的溫度沿水平和垂直方向的分布規律均受到遮陽狀態的顯著影響.中間遮陽設施的啟用有助于強化熱通道的煙囪效應.相較于房間A,房間B的溫度分布更加均勻.但在所有的測試工況下,雙層玻璃幕墻熱通道的過熱問題始終存在.

雙層玻璃幕墻;熱特性;溫度分布;能耗

TU111

Received 2014-06-20.

Biographies：Wang Fang(1979—), female, doctor; Zhang Xiaosong (corresponding author), male, doctor, professor, rachpe@seu.edu.cn.

s：The National Natural Science Foundation of China (No.51308295, 51206080), China Postdoctoral Science Foundation (No.2013M531368).

：Wang Fang, Zhang Xiaosong, Tan Junjie, et al. Experimental study on thermal characteristics of a double skin fa?ade building[J].Journal of Southeast University (English Edition),2014,30(4):462-466.

10.3969/j.issn.1003-7985.2014.04.011

10.3969/j.issn.1003-7985.2014.04.011