The thermal system of a building is
described in Figure 1. The main heat flow quantities are listed as follows:
Qi = Internal heat gain from electric
lights, people, power equipment and appliances.
Qs = Solar heat gain through fenestration
areas and, conduction heat gain through roofs and external walls by using the sol-air
Qc = Conduction heat gain or heat loss
through the enclosing elements, caused by a temperature difference between outside and
Qv = Ventilation heat gain or heat loss due
to natural or mechanical ventilation and infiltration.
Qm = Mechanical heating or cooling produced
by some energy-based installation.
Qe = Latent heat gain or loss from moisture
transfer through permeable building materials.
If Eqn. (1) = 0, a thermal balance exists.
If Eqn. (1) > 0, the indoor temperature increases. If Eqn. (1) < 0, the indoor
temperature decreases. Except Qm which is quite small, net value of all heat flow
quantities in Eqn. (1) determines the requirement of SPACE HEATING AND COOLING.