The total quantity of heat which is required to be pumped out from the air conditioned space to be maintained at desired temperature level by the refrigerating equipment is known as cooling load. The amount of cooling load determines the capacity of the refrigeration plant to be installed.

The cooling load comprises of two components, viz. sensible heat gain and latent heat gain.

FACTORS WHICH ARE RESPONSIBLE FOR SENSIBLE HEAT GAIN:

A gain of sensible heat is said to occur when there is a direct addition of heat to the enclosed space by any one or all of the modes of heat transfer i.e., conduction, convection and radiation. 

Sensible heat gain includes the following:

1. Heat transmitted by conduction through structures such as walls, floors and ceilings, due to temperature differential between their two sides. 

2. Heat transferred into enclosed space by solar radiation through window panes, doors and ventilators. 

3. Heat brought in by leaking (infiltrating) outside air entering the conditioned space through door openings, or cracks around windows, doors etc. 

4. Heat liberated by occupants. 

5. Heat given off by the products brought in at higher temperature than the conditioned space temperature. 

6. Heat given off by lights, fans, computers, motors, cooking and other appliances, installed in the conditioned space.

FACTORS WHICH ARE RESPONSIBLE FOR LATENT HEAT GAIN:

A gain of latent heat is said to occur when there is an addition of water vapour to the air of the conditioned space. 

Latent heat gain includes the following:

1. Moisture entering the conditioned space through permeable walls where vapour pressure is higher. 

2. Heat gain due to condensation of moisture from occupants. 

3. Heat gain due to condensation of moisture from food or other products placed in the conditioned space. 

4. Heat gain due to condensation of moisture from other internal sources such as wet surfaces, appliances, apparatus etc.

FACTORS WHICH ARE RESPONSIBLE FOR COMBINATION OF SENSIBLE HEAT AND LATENT HEAT GAIN:

Such heat gains are caused due to the introduction of outside air for ventilation purposes. 

These gains are: 

1. Sensible heat gain due to the temperature difference between fresh air and the air in conditioned space and 

2. Latent heat gain due to difference of humidity.