A conservative approach to the building energy analysis is to calculate the maximum load assuming all the heat-producing equipment is on, e.g., the lights and equipment; plus the occupancy is at its maximum. These data are used to determine two critical parameters: (1) the airflow required to each zone and (2) the peak building load. These values, in turn, are used to balance the air-distribution system and to size the central HVAC equipment, respectively.
This is a conservative way to calculate the necessary airflow to a zone to offset heat-producing loads, while some diversity may be possible for the peak building load calculation. Every building has a typical load profile for each hour of the day, versus the three major loads.
As an example, consider a facility for which a preliminary load analysis was run, outputting the peak loads as occurring at 6 p.m. Typically, the peaks for the loads at this time are 80 percent for lights, 30 percent for receptacles, and 10 percent for occupancy. If the chiller and air handlers are sized assuming 100 percent of loading at this time, then it will be oversized to the actual building profile.
Another computer run inputting the above values would give the actual peak load.
If the two calculations differ significantly, it may because to study the building in greater detail, perhaps downsizing the equipment so that it will be more fully loaded at peakâthus operating most efficiently. This will also reduce the installation costs for the project.
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Excerpt from Energy Conservation Projects.