Heat gains through the building fabrics

ISSN 114-1284 100 200 300 400 500 600 700 no_N 75 ls _N 75 gb _N 75 pc _N 75 no_E 75 ls _E 75 gb _ E7 5 pc _E 75 no_S 75 ls _S 75 gb_S 75 pc _S 75 no_W 75 ls _W 75 gb_W 75 pc _W 75 average illuminance lux illuminance distribution Figure 7: Average illuminance and illuminance distribution of windows for 75 students classroom the second experiment. Figure 8: Daylight Factor in a classroom for 25 students with lightshelf facing to East the first experiment Figure 8 and figure 9 show that high daylight factors 7 or illuminance level 600 lux are located on the area near the windows, because large amount sunlight passed through view windows directly. Two alternatives to improve daylight distribution without reducing window area in order to maintain comfortable view angles: - Enlarge the shading device. This alternative seems to be unrealistic, as the recent shading devices are large enough. - Change glass of view window with low visible transmittance glass, such as: tinted glass. Figure 9: Illuminance level in a classroom for 25 students with lightshelf facing to East the second experiment

3.2 Heat gains through the building fabrics

Simulation results of hourly heat flowing through the building fabrics figure 10 show similar conclusion. Window with projected clerestory is the most energy-efficient. Windows with glass block-clerestory perform better in heat gains comparing to windows with lightshelf. This is opposite to results produced by simulations of thermal transfer value through exposed wall surfaces. Interesting results were shown by comparing results of classroom for 50 students to those of classroom for 25 students. Three window models have the same pattern. Heat energy flowing through classroom models for 25 students has higher rate than those for 50 students if window models applied are glass block clerestory, lightshelf and without shading. These make sense, because classrooms for 25 students have bigger WWR, window to floor area ratio, window to wall height ratio, clerestory height to room width ratio, and smaller room width to window height ratio. Classrooms with projected clerestory show opposite results. Higher value of classroom for 50 students than its classroom for 25 students may be related to the ratio of the room width to the room length. The ratio of classroom for 25 students is 0.73 0.02 higher than the ratio of classroom for 50 students. Relative narrow space allows higher penetration of solar radiation. Ratio of room width to room height seems to work in a room with projected clerestory. A classroom having 10 Wm 2 heat loads through the building fabrics with adequate daylight level can be considered as energy-efficient if it is compared with 15 Wm 2 for energy standard of lighting for classroom [5]. Page 571 ISSN 114-1284 0.00 20.00 without shading lightshelf projected clerestory glass block clerestory without shading lightshelf projected clerestory glass block clerestory without shading lightshelf projected clerestory glass block clerestory without shading lightshelf projected clerestory glass block clerestory N o rt h S o u th w e st E a st W m2 classroom for 50 students classroom for 25 students Figure 10: Hourly heat flows through the building fabrics the first experiment 100 200 300 400 500 600 700 800 900 1000 no _ 2 5 E no _ 4 E no _ 6 E no _ 7 5 E ls _2 5E ls _4 0E ls _6 0E ls _7 5E g b _25 E g b _40 E g b _60 E g b _75 E pc _25 E pc _40 E pc _60 E pc _75 E conductive heat transfer sol-air direct solar heat transfer Fi gure 11: Heat Transfer Through The Building Skins of Classrooms Facing to East in Watt 100 200 300 400 500 600 700 800 900 1000 no_25N no_40N no_60N no_75N ls _25N ls _40N ls _60N ls _75N g b_25N g b_40N g b_60N g b_75N pc _25N pc _40N pc _60N pc _75N conductive heat transfer solar air direct solar gain Figure 12: Heat Transfer Through The Building Skins of Classrooms Facing to North in Watt 100 200 300 400 500 600 700 800 900 1000 no_ 25 S no_ 40 S no_ 60 S no_ 75 S ls _25 S ls _40 S ls _60 S ls _75 S gb _2 5S gb _4 0S gb _6 0S gb _7 5S pc _2 5S pc _4 0S pc _6 0S pc _7 5S conductive heat transfer solar air direct solar gain Figure 13: Heat Transfer Through The Building Skins of Classrooms Facing to South in Watt Results of the second experiment show the effect of shading device on the heat transfer. The present of shading device reduces direct solar gain of the classrooms. Window with glass-block clerestory reduces the greatest direct solar gain. Lightshelf can decrease the direct solar gain. Window facing to south admits the lowest direct solar gain, but the greatest effect occurs on windows facing to east. Projected clerestory gives unreasonable results again. Its energy performance is worse than without shading device. 0.00 5.00 10.00 15.00 20.00 25.00 30.00 no_25S no_40S no_60S no_75S ls_25S ls_40S ls_60S ls_75S gb_25S gb_40S gb_60S gb_75S pc_25S pc_40S pc_60S pc_75S cooling loads heat gain through the building skins F igure 14: Energy profile of classrooms facing to South Wm2 Calculations of classrooms cooling load in the the second experiment show similar pattern. Window with glass-block clerestory or lightshelf has the best energy performance. Page 572 ISSN 114-1284 Glass-block clerestory can reduce solar heat gain until below 10 Wm 2 for the window facing to south. Relative high energy performance of classroom can be reached by applying lightshelf on its windows. Lightshelf can reduce cooling load a little bit lower than glass-block clerestory. However, it can distribute daylight more evenly, especially in classrooms with big capacity. Application of glass block on clerestory has an advantage in construction cost. Lightshelf and more even projected clerestory are still much more expensive. However, the internal shading device which presents on lightshelf and projected clerestory can prevent annoying glare that may appear on its clerestory. 0.00 5.00 10.00 15.00 20.00 25.00 30.00 no_25E no_40E no_60E no_75E ls_25E ls_40E ls_60E ls_75E gb_25E gb_40E gb_60E gb_75E pc_25E pc_40E pc_60E pc_75E cooling load per area heat gain through the building skins Figure 15: Energy profile of classrooms facing to East Wm2

3.3 Window glazing