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External shading is an important energy-saving method in architecture which can isolate sunlight as well as alter indoor thermal environment. Therefore, this study is to investigate the effects of building facilities for horizontal exterior shading on indoor thermal environment, comfort, dissatisfaction, and energy saving.
The investigated sites of this study were classrooms of the campus buildings B with south-facing window at Chia Nan University of Pharmacy and Science, on the third floor (Class B305) and the fourth floor (Class B406). There are two stages in the surveys, during the first stage (Oct., 2014 to Feb., 2015), class B305 was equipped with external shading (depth ratio at 0.8), while the class B406 was not. The study purpose of this stage is to investigate the effect of horizontal exterior shading on room temperature. During the second stage (March, 2015 - May, 2015), class B406 was also applied external shading, but in depth ratio at 0.9, in order to discuss the effect of different depth ratio on horizontal external shading. This study measured three-dimensional space of indoor temperature, in order to analyze the profile of the indoor temperature. Three periods has been experimented, morning session (8:00~9:00), at noon time (11:00~12:00), and afternoon session (14:00~15:00), to observe changes in room temperature in different periods. Besides, the indoor humidity, the comfort of the indoor environment (Predicted Mean Vote, PMV) and dissatisfaction Predicted of Percentage Dissatisfied), PPD) index have as well as been experimented.
During the first stage, 22 monitoring days have been conducted, results showed that the average temperature of the central cross section in class B305 was less than B406, especially at noon time. The average temperature of the central longitudinal section of the class B305 was 1.5~1.6 ℃ lower than B406. The average cross-sectional temperature in class B305 is about 1.6℃ lower than class B406. At noon time, horizontal section at the height of 200 cm in class B305 can be lower than the outdoor temperature of 2.8 ℃. The average temperature difference between the window side and the aisle side showed 0.1 ~ 0.5℃in class B305, which was significantly lower than 0.3 ~ 1.0℃in class B406. These results illustrated the effect of horizontal insulation of external shading. PMV in class B305 was 0.14 better than 0.37 in class B406, while the index of PPD was 10% in class B305 lower than 14% in class B406. A total of 11 monitoring days was experimented in the second stage. After class B406 being equipped with horizontal external shading, the temperature converted to be close to the temperature in B305. At noon, the figure of central longitudinal sectional and central cross section in class B305 were 0.1 ℃ ~ 0.2 ℃ lower than class B406. At noon, at the 200 cm height, class B406 compared to outdoor temperature difference was 2.7 ℃, while class B305 compared to outdoor temperature difference was 2.5 ℃. Results of temperature difference between window side and aisle side, 0.1 ~ 0.4 ℃ in class B305, 0.1 ~ 0.3 ℃ in B406. Both PMV in class B305 and class B406 were 0.80, while dissatisfaction (PPD) in class B305 was 28%, 27% in B406.
In this study, measured-temperature was brought into heat transfer equation to estimate the flux of heat transfer from indoor to outdoor. Results showed that class with external shading can save 156 kw-hr/yr of electricity, which was 343 NT dollars per year and can reduce 225.83 kg C/yr of carbon dioxide.
Horizontal external shading was in the simulation experiment, and not the long time monitoring. Through this study, better understandings were offered to the thermal changes of applying external shading for future standard to enhance efficiency of horizontal external shading.
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