Cooling demand is usually determined by HVAC designers for the design condition. It consists of the following main factors:

• heat load caused by high external temperatures,

• heat load caused by solar radiation (this has the greatest effect through the windows),

• ventilation (air must be cooled and heated to adjust the temperature and humidity of the inlet air),

• internal heat generation of people,

• internal heat generation of lighting,

• heat loss from electronic devices, computers, printers, servers, hot surfaces (eg during production), etc. internal heat generation.

 

A value is set for the design state, this is the cooling demand (100%). (when sizing, the cooling equipment is usually oversized to the 110 ÷ 130% demand)

Due to different external temperatures and different uses (fewer people, machines, lighting, etc.), the actual, instantaneous cooling demand differs from the design value, in which case the refrigerator operates in a part-load condition. For most of the year, the design state is not reached (usually never reached), so the refrigerator typically operates at partial load.

 

With the help of cooling profiles, the daily, weekly, monthly and annual change can be described.

Example of a summer day profile for an office building:

Demand is low at night because there are typically no people inside and the external temperature is lower. As the external temperature starts to rise between 7 and 8 in the morning, people arrive and start using their heat-generating electronic devices, and the demand for cooling increases. The peak occurs between 12 and 2 p.m., then decreases as the external temperature decreases and fewer and fewer people are in the building.