Cooling load estimation or Heat load calculation is the most important & primary step in any HVAC system design. In this article we will discuss important components that has to be taken into account while calculating Heat load for any space.
The total heat required to be removed from the space in order to bring it to the desired temperature by the air conditioning is known as cooling load.
The purpose of load estimation is to determine the size of air-conditioning equipment that is required to maintain inside design condition during periods of extreme outside conditions.
The two main components of cooling load imposed on any air conditioning plant are as below
- Sensible Heat Gain
- Latent Heat Gain
1.Sensible Heat Gain
The Heat added or removed without change in moisture content is called Sensible Heat. When there is direct addition of such heat to the enclosed space, a gain in sensible heat is said to occur. This sensible heat has to be removed during the process of summer air-conditioning.
Sensible heat gain may occur due to any one or all of the below sources of heat transfer:
(1.1) Conduction heat transfer through structure: Conduction heat transfer into the building or space through the walls, roofs , ceilings, doors, & windows due to temperature difference between inside & outside of the structure.
(1.2) Radiation heat transfer: Heat gain from solar radiation consists of;
- Solar Heat transmitted directly through the glass windows or glass façade.
- Solar Heat absorbed by exposed walls & roofs later transferred to room by conduction.
(1.3) Heat gain from non conditioned areas: Conduction Heat transfer from non conditioned areas/rooms of building through internal partitions & walls.
(1.4) Heat gain from Lighting & appliances: Heat dissipated from light fittings & equipment load from other appliances like Computers, motor or any other mechanical or electrical devices which aids to heat load.
(1.5) Heat gain from the occupants: Amount of Sensible heat released from the human body depends on the type of activity they are involved in.
(1.6) Heat gain due to to infiltration: Infiltration of outside air through cracks & gaps in windows, doors etc carries additional heat which should be calculated for load estimation.
(1.7) Heat gain due to ventilation: Heat added from fresh outside air introduced in the room & other fan work.
(1.8) Heat gain from Ductwork: Heat gain by the supply & return ducts passing from non conditioned areas of the building.
2.Latent Heat Gain
The heat added or removed with change in moisture content of air is termed as latent heat. Addition of water vapour or moisture leads to latent heat gain which needs to be calculated & removed from space to provide comfort inside condition during summer air conditioning.
Latent heat gain may occur due to any one or all of the below sources of heat transfer:
(2.1) Heat gain from outside air: Heat gain due to moisture in the outside air entering the space through infiltration & ventilation.
(2.2) Latent Heat gain from Occupants: Heat dissipated from human body in form of respiration & precipitation.
(2.3) Latent heat gain form appliance or process: Addition of Moisture due to any process such as cooking of food in conditioned area or any running appliance which generates moisture.
(2.4) Latent Heat gain through moisture added directly from adjoining area where water vapour pressure is high.
Total heat load to be removed by any air-conditioning equipment shall be sum of Sensible & Latent heat load.
Same components are considered during calculation of heating load.
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