Load calculation guide
Cooling Load Calculation Explained
Cooling load is more than outdoor temperature: it includes sensible heat and moisture from the building, people, equipment, and outdoor air.
Separate sensible and latent load
Sensible load changes dry-bulb temperature. Latent load is associated with moisture removal. A space can have a modest sensible total but still need meaningful dehumidification capacity because of people or humid outdoor air.
Where cooling gains come from
| Gain | What changes it | Check |
|---|---|---|
| Envelope | U-values, area, outdoor conditions | Construction and design temperature |
| Solar through glass | Orientation, SHGC, shade, time | Glazing data and exposure |
| Internal | People, lights, equipment, schedule | Actual watts and occupancy |
| Outdoor air | Ventilation, infiltration, humidity | Airflow and psychrometric conditions |
Useful calculation checks
Electrical input can be converted at 1 W = 3.412141633 BTU/h. For a preliminary sensible outdoor-air check in U.S. customary units, 1.08 × CFM × dry-bulb temperature difference estimates the sensible rate. Neither shortcut captures latent load or the hourly solar-storage behavior used in detailed methods.
Example
A 300 W lighting load contributes about 1,024 BTU/h before schedule and heat-to-space assumptions. If 100 CFM of outdoor air is 20°F warmer than indoors, the preliminary sensible outdoor-air term is 2,160 BTU/h. Both values must be combined with the relevant building and moisture inputs.
Decision rule
Use a detailed calculation when selecting equipment, when humidity matters, when solar exposure is significant, or when rooms have different exposures. A square-foot rate is only a comparison value.