The composition of heat gains
Heat gains are either sensible, tending to cause a rise in air temperature, or latent, causing an increase in moisture content. In comfort air conditioning sensible gains originate from the following sources:
(i) Solar radiation through windows, walls and roofs.
(ii) Transmission through the building envelope and by the natural infiltration of warmer air from outside.
(iv) Electric lighting.
(v) Business machines and the like.
Latent heat gains are due to the presence of the occupants and the natural infiltration of more humid air from outside.
In the case of industrial air conditioning there may be additional sensible and latent heat gains from the processes carried out.
All the above sources of heat gain are well researched but a measure of uncertainty is introduced by the random nature of some, such as the varying presence of people and the way in which electric lights are switched. The thermal inertia of the building structure also introduces a problem when calculating the sensible heat gain arising from solar radiation. It follows that a precise determination of heat gains is impossible. Nevertheless, it is vital that the design engineer should be able to calculate the heat gains with some assurance and this can be done when generally accepted methods of calculation are followed, supported by sound common sense. The following text discusses and describes such methods.
Posted in Engineering Fifth Edition