Thermal Control
Home Up Thermal Control Design Conditions Heating Load Calculation Cooling Load Calculation


1 Thermal Control

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 temperature.

Qc = Conduction heat gain or heat loss through the enclosing elements, caused by a temperature difference between outside and inside.

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.

Figure 1 Thermal System of Building Figure 2 Outdoor Dry-bulb and Wet-bulb

                                                                Temperature Curves for A Typically Hot

                                                                Summer Day in Hong Kong