Book - School of Science and Technology

Heat losses 27Temperature °C1.813.4–0.5–0.21.413.916.917.919.019.0–1.0 –1.0(a)(b)Figure 2.2 Surface and interface temperaturesbeing illustrated in part (a). In this case, the overall resistance would be made up asfollows:Outside surface, R so ˆ 0:06Brickwork (1/0:84) (210/1000) ˆ 0:25Inside surface, R si ˆ 0:12R ˆ 0:43 m 2 K/WThe temperature gradient, including the components at the surfaces, will be pro rata tothe resistances and, for inside and outside air temperatures of 21 C and 1 C, respectively,would be:Outside air to outside surface ˆ 22 (0:06/0:43) ˆ 3:1 CAcross the brickwork ˆ 22 (0:25/0:43) ˆ 12:8 CInside surface to inside air ˆ 22 (0:12/0:43) ˆ 6:1 CThe surface temperature of the brickwork inside the enclosure would thus be21 6:1 ˆ 14:9 C.The more complexcase of the curtain wall construction in the previous example is dealtwith in the same way, the surface and the interface temperatures being as shown in part(b) of Figure 2.2.ApplicationHaving established the transmittance coefficients for the various structural elementsenclosing a space, it is then possible to evaluate the conduction component of the heatrequirement. This process is best illustrated by an example.