A significant part of the HVAC load is attributable to electronic equipment located in the space. Some of the equipment used, such as refrigerators, water heaters, or freezers, runs all the time. So their use factor will be 100 percent or 1.0. Other items will require a fractional use factor, according to the use of the item during the peak demand hour—typically mid-afternoon in July or August for the cooling season.
As an example, take an office that has various equipment located in a large area of partitioned workspaces: To find the total wattage contributed to the HVAC load, each item is listed with its nameplate wattage multiplied by its use range and the number of items. These are extended to arrive at the actual wattage in use each hour. These calculations apply only when the item is located within the conditioned space. To calculate the sensible heat gain from the appliances,
Heat gain = wattage * 3.4 Btu/Watt-hour
This type of analysis does not apply to motors or lights, which will be studied in separate sections. In assuming all the electric energy becomes heat, the above results are conservative, since a portion of the electricity use becomes the work or output of the device. The larger energy users—lights and motors—are evaluated more carefully since taking a conservative approach as this might lead to greatly oversizing the cooling tonnage and under sizing the heating equipment.
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Excerpt from Energy Conservation Projects.