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How Heating and Ventilation Loads are Assessed

written by: Chief Engineer Mohit Sanguri • edited by: Lamar Stonecypher • updated: 12/27/2013

Before selecting the appropriate HVAC system, builders first need to determine the heating and ventilating loads. Loads are determined by some environmental factors and design calculations. Learn more about why its so important.

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    The most important element in the design and selection of a heating and ventilating system is the determination of the heating and ventilation loads in the building where the system is to be installed. Accurate assessment of these loads will facilitate the correct selection of the system for the required building. A perfect system will function constantly with variable productivity, which is commensurate with the heat load of the building as the climate changes. Such a system can be attained with accurate design analysis of the heating load of the building and the selection of a proper heating system.

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    Factors of Heating and Ventilating Loads

    The following factors should be taken into consideration while determining the heating and ventilating loads of a structure:

    • Amount of heat distributed through the area exposed to locations which are not heated.
    • Amount of heat necessary for the air to become hot, which penetrates from the cracks adjacent to the windows and doors, and also from the entrance, when persons come in or go out of the building.
    • Heat which is necessary to make the air that has come mechanically into the building as ventilation air hot.
    • A variety of other loads.
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    Design Calculations

    The basis for determining the heating load are the constant average temperature for winter nights and any continuous supply of heat present at all times. The quantity of heat accumulated by the building must be taken into consideration as well as the energy of any cooling equipment.

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    Method for Estimating Heating Load

    The normal process for estimation of heat load is as follows:

    • Carry out an assessment of the weather conditions prevailing outside the building, including humidity, temperature, path of wind and speed.
    • Determine the desirable inside air temperature to be maintained.
    • Assess the temperature in adjoining locations which are not heated.
    • Choose the coefficient of heat transmission.
    • Establish the outside areas by which heat is dissipated.
    • Estimate the losses by heat transference from glass, bricks, and base in the building.
    • Calculate the heat loss from the underground area.
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    Structure Of Building

    Design calculations, and the selection of heating system, are largely based on the structure of the building and its use, including the exposure of building to wind, the direction of the sun, periods of occupancy and part of day when the building will be used, and the expected financial impact of the equipment and fuel. All these factors should be considered while assessing the heating and ventilating loads of a building.


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