How is total heat load calculated for a commercial building?

Total heat load for a commercial building is calculated by considering all sources of heat that affect the indoor environment. This includes both internal and external gains. Internal gains refer to heat produced within the building from sources such as occupants, equipment, lighting, and any other activities generating heat. External gains come from factors outside the building, like solar radiation through windows, heat conduction through walls and roofs, and infiltration of outside air.

When summing these two components, internal and external gains, you get a complete picture of the heat load that needs to be managed by the HVAC system. The total heat load calculation is crucial for sizing equipment appropriately to ensure comfort and efficiency in the building.

The other choices focus on either only internal or external gains, or suggest averaging the two, which doesn’t accurately reflect the total heat load that an HVAC system must address. Therefore, the comprehensive approach that sums both internal and external heat gains provides the accurate basis necessary for effective HVAC design.