Book - School of Science and Technology

Solar heat gains 75Table 3.1 Selected notional temperatures (t s C) for a typical hot July day in south-east England, takingaccount of solar radiation and time-lag effects (British Summer Time)ItemBSTtaken forOrientationloads f Horizontal N NE E SE S SW W NW1 1.0 1100 38.0 26.5 33.0 43.0 43.5 35.0 27.5 27.5 27.01300 47.0 31.5 32.0 38.5 45.5 45.0 36.5 32.5 32.01500 48.5 33.0 33.5 34.0 38.5 46.5 47.0 40.0 39.01700 44.0 32.5 33.0 33.5 33.5 40.5 49.0 48.5 39.04±6 0.47±0.53 1100 23.0 23.5 26.5 27.0 25.0 23.5 24.0 23.5 22.51300 28.0 23.5 31.0 34.0 31.5 25.0 25.5 25.5 24.51500 33.5 26.0 30.0 36.0 36.5 31.5 28.5 28.0 27.01700 38.0 28.5 29.5 33.5 37.5 36.5 33.0 30.5 29.55±7 0.42±0.48 1100 22.5 21.5 22.5 23.5 23.5 23.0 23.5 23.5 22.51300 22.5 24.5 29.5 31.0 28.5 24.5 25.0 25.0 24.01500 30.5 24.5 30.5 34.5 33.5 28.0 26.5 27.0 26.01700 35.5 27.0 29.5 34.0 36.0 33.5 29.5 29.0 28.06±8 0.37±0.43 1100 23.5 22.0 23.0 24.0 24.0 23.5 24.0 24.0 23.01300 24.0 23.5 26.5 27.5 26.0 24.0 25.0 24.5 23.51500 28.0 24.0 30.0 33.0 31.0 25.5 26.0 26.0 25.01700 32.5 25.5 29.5 34.5 35.0 31.0 28.0 28.0 27.07±9 0.32±0.38 1100 24.5 22.5 24.0 25.0 25.0 24.5 25.0 25.0 24.01300 24.0 22.0 23.5 24.5 25.0 24.0 25.0 24.5 23.51500 26.5 24.5 29.0 31.0 28.5 25.5 26.0 25.5 24.51700 30.0 24.5 29.5 33.0 32.5 28.0 27.5 27.5 26.58±11 0.22±0.33 1100 26.0 23.5 25.0 26.0 26.5 26.0 26.5 26.0 25.01300 25.5 23.0 25.0 26.0 26.5 25.5 26.5 26.0 25.01500 25.5 24.0 26.5 27.5 26.5 25.5 26.0 25.5 24.51700 28.0 24.5 29.0 32.0 30.5 26.0 27.0 26.5 25.5NoteBased upon t ao ˆ 28 C at 16.00 hours with a 10 K diurnal range.From Table 2.2 and interpolating from Table 3.2:U value ˆ 1:9 W/m 2 KTime lag ˆ 7 hoursDecrement ˆ 0:46Thence, interpolating from Table 3.1:t s ˆ (33:5 ‡ 36:0)/2 ˆ 34:8 CandHeat gain at 16:00 hours ˆ 1:9 (34:8 21) ˆ 26 W/m 2It is appropriate to note that, when considered in relation to the customary internal designtemperature range 21±23 C for summer, the data listed in Table 3.1 illustrate the pointmade earlier and show that there are numerous occasions when the heat gain from opaquesurfaces may be negative. It is common practice to ignore any such small `credits' incalculations for plant capacity, in the same way that small adventitious heat gains areignored in winter calculations.