|Natural Energy and Vernacular Architecture: Principles and Examples with Reference to Hot Arid Climates (UNU, 1986, 172 pages)|
|Part 1. Man, natural environment, and architecture|
|2. Architectural thermodynamics and human comfort in hot climates|
The difference between diurnal and nocturnal heat losses in a building when not considering artificial cooling devices, is not marked as in the case of heat gain. Heat is lost by conduction through the walls, by exactly the same process that it is gained from the direct solar radiation once it has been absorbed by the surface, or through the roof by a combination of convection and conduction.
Ventilation is also another mode of heat loss which occurs when hot air escapes through an opening in the roof or a wall to be replaced by cooler air from outside. Nocturnal heat losses can be retarded by closing vents.
Evaporation from the surface of the building or from objects within the interior can produce a cooling effect on the building which acts as a source of heat loss. In hot arid climates, this can be a particularly effective cooling mechanism since the rate of evaporation in dry air is very high.
Figure 4 also shows the modes of heat loss.