Book - School of Science and Technology

88 The building in summerConduction gain due to temperature difference:Area:Total ˆ 88 m 2From Table 2.6:U valueˆ 4:5 W/m 2 KTemperatures:Outsideˆ 28 CInsideˆ 21 CThus, gain ˆ (88 4:5 7) ˆ 2772 W ˆ 2:77 kWWallsCombined solar and conduction gainArea, wall less glazing:SW exposure (30 10) 44 ˆ 256 m 2NE exposure (30 10) 44 ˆ 256 m 2From Table 3.2:U value ˆ 0:47 W/m 2 KTime lag ˆ 8:4 hoursDecrement ˆ 0:44From Table 3.1, interpolating for t s at 15.30 BST, temperatures approximate to:SW exposure ˆ 26 CNE exposure ˆ 29 CThus, combined gain:SW exposure ˆ (256 0:47) (26 21) ˆ 602 WNE exposure ˆ (256 0:47) (29 21) ˆ 963 W ˆ 1:57 kWRoofCombined solar and conduction gain:Area:(30 20) ˆ 600 m 2From Table 3.2:U value ˆ 0:51 W/m 2 KTime lag ˆ 10 hoursDecrement ˆ 0:17From Table 3.1, extrapolating for t s at 15.30 BST, temperature approximates to:Horizontal ˆ 25 CThus, combined gain:Horizontal ˆ (600 0:51)(26 21) ˆ 1530 W ˆ 1:53 kWThe total heat gain, carried forward to p. 519=23.87 kW