How to split sensible and latent cooling loads
Cooling load divides into sensible heat, which changes air temperature, and latent heat, which removes moisture. The ratio between them, the sensible heat ratio, decides the supply air temperature the coil has to deliver and whether reheat is needed. Sizing equipment from a total BTU/hr figure alone is how rooms end up cold and clammy at the same time, so this calculator reports occupants, lighting and equipment, and outdoor air as separate sensible and latent streams.
Occupant heat gains come straight from the ASHRAE Fundamentals table of activity levels: 245 BTU/hr sensible and 205 latent per person for seated office work, rising to 580 sensible and 920 latent for heavy factory work, where the latent share dominates. Outdoor air load uses the standard US shortcut constants, Qs = 1.08 × CFM × ΔT and Ql = 0.68 × CFM × ΔW in grains per pound. Both constants assume standard air at 0.075 lb/ft³: 1.08 comes from 60 × 0.075 × 0.24, and 0.68 from 60 × 0.075 × 1,061 ÷ 7,000.
Lighting and plug loads are entered in watts and converted at 3.412 BTU/hr per watt, and all of it is treated as sensible gain. Required capacity is expressed in US refrigeration tons at 12,000 BTU/hr per ton. Envelope conduction and solar gain through glass are not included here, so add a separate envelope calculation to the sensible total and have a mechanical engineer review the result before equipment is selected.
Frequently asked questions
It means dehumidification dominates. Below about 0.70 you generally need a colder coil leaving-air temperature, reheat, or dedicated dehumidification to hold the space humidity setpoint.
This tool covers internal gains and ventilation air. Envelope loads need orientation, glazing performance and shading coefficients, so calculate them separately and add the result to the sensible total.