ABSTRACT
Building heating and cooling load calculations can only be undertaken if the heat transfer mechanisms between the building walls and the internal and surrounding environment are identified. Heat transfer through building walls is caused by a difference in temperature between the exterior and interior surfaces of the wall. During the day, solar radiation strikes the exterior wall surface. A small portion of this energy is reflected while the remainder is absorbed, thereby increasing the wall surface temperature. Because of the higher outer surface temperature of the wall, convection also takes place between the wall and the outdoor air. Heat received at the exterior wall surface is then transferred by conduction through the various material layers in the wall to the interior surface. It should be noted that the nature of this process is strongly affected by the number of wall materials involved, the thickness of each layer and the properties of each material, namely thermal conductivity, density, thickness and heat capacity.
