Book - School of Science and Technology

Solar heat gains 85`brochure level' guidance, as exemplified by that given under the next heading, can beoffered in the abstract.Building orientationFor the particular case of the tall rectangular slab block, modelled to match a packet ofbreakfast cereal, and having a width/depth ratio of 3:1 as Figure 3.11, a simple calculationmay be made to compare heat gains at two seasons for two different orientations. Usingthe 24 hour mean values for solar radiation from Figure 3.5:Case 1, in JuneCase 2, in JuneS and N faces 245 3 ˆ 735 S and N faces 245 1 ˆ 245E and W faces 390 1 ˆ 390 E and W faces 390 3 ˆ 11701125 1415Case 1, in SeptemberCase 2, in SeptemberS and N faces 241 3 ˆ 723 S and N faces 241 1 ˆ 241E and W faces 236 1 ˆ 236 E and W faces 236 3 ˆ 708959 949It is evident that, in mid-summer, the orientation of case 1 produces a lower heat gain thanthat of case 2 but that in spring and autumn the difference will be much less. In reality, witha slab block of this plan, the narrow ends would very probably be solid and windowless: inthat situation, when due allowance is made for the substitution, case 1 shows up to evengreater advantage. This rudimentary example serves to confirm the rule of preference foran east±west axis, now well established, and Figure 3.12 shows solutions for other orientationsand for the three periods which represent the six warmer months.ConductionThis subject has been explored in detail in Chapter 2 and the mechanism of heat transferhere is similar, being a function of the thermal transmittance coefficient (U ) and thetemperature difference, inside to outside. A factor may be applied in this instance to allowfor the effect of the radiant component of heat transfer which arises from the adoption ofCase 1 Case 2Figure 3.11 Plan of tall slab building