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What is HVAC Heat Load Calculations? Part 2: Various Sources of Heat

written by: Haresh Khemani • edited by: Lamar Stonecypher • updated: 11/26/2008

The heat load calculations is very important part of the HVAC designer or HVAC consultant. This article describes the various sources of heat inside the room that has to be considered by the HVAC designer.

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    Various Sources of Heat

    In the previous article of this series we saw the major source of heat inside the rooms, which is sun. Let us see more sources of heat inside the rooms.

    2) Heat from the human beings: Another major source of heat inside the rooms is the heat generated by the human beings. Human beings consume lots of calories in the form of food, which generate heat inside the body. This heat is thrown away by the body into the surroundings of the room leading to increase in heat inside the room. The heat from human body is also released due to perspiration.

    The more the number of people inside the room, more is the heat generated inside the room from human beings. In applications where large spaces are to be air-conditioned like halls, auditoriums, theaters, cinema halls, air-ports, etc the heat generated from the human beings becomes major source of heat.

    3) Outdoor air heat: The air outside the air conditioned room is called as outdoor air or atmospheric air. The outdoor air is at temperature higher than the air-conditioned room. When this air enters the air-conditioned room, it adds the heat inside the room and it tends to increase the room temperature. The outdoor air enters air-conditioned room by the leakages in doors and windows and also by their opening and closing.

    4) Heat from the electrical and electronic appliances: In most of the rooms there are number of electrical and electronic appliances like tube lights, television, coffee maker, glass water heater, etc. These appliances consume electricity and release some heat inside the air-conditioned space thus heating the room. The ordinary tube light generates more heat while the CFL lights generate lesser heat. The devices like coffee-maker and the water heated also add heat due to evaporation of water.

    During heat load calculations the total amount of heat generated inside the room by all sources is calculated by carrying out the survey of the different rooms of the building, hall, air-port or whatever the application.

    Based on the heat load calculations, the HVAC designer recommends the type of the air-conditioning system suitable for the application and total size of the system. This helps in avoiding installing the over sized system that can lead to high initial and running costs and also avoids under sized system that could lead to under-cooling of the rooms of the building.