A cooling load calculation determines total sensible cooling load due to heat gain: through structural components (walls, floors, and ceilings); through windows; caused by infiltration and ventilation; due to occupancy and appliances.     The latent portion of the cooling load is evaluated separately. While the entire structure may be considered a single zone, equipment selection and system design should be based on a room-by-room calculation. For proper design of the distribution system, the amount of conditioned air required by each room must be known.

Peak load computation

To select a properly sized cooling unit, the peak or maximum load (block load) for each zone must be computed. Because this procedure may vary considerably for different types of buildings, each building type has to be considered; the block load for a single family detached house with one central system in the sum of all the room loads. If the house has a separate system for each zone, each zone block load (i.e., the sum of the loads for all rooms in each zone) is required. When a house is zoned with one central cooling system, the block load must be computed for the complete house as if it were one zone. In multifamily structures, each living unit has a zone load that equals the sum of the room loads. For apartments with separate systems, the block load for each unit establishes the system size. Apartment buildings with a central cooling system (i.e., a hydronic system with fan-coils in each apartment) require a block load calculation for the complete structure to size the central system; each unit load establishes the size of the fan-coil and air distribution system for each apartment.