Commercial HVAC Load Calculator
Estimates commercial building heating and cooling loads based on ASHRAE simplified load calculation methods. Calculates sensible heat gain/loss through walls, roof, windows, infiltration, and internal loads.
Building Envelope
Climate & Occupancy
Formulas Used
Conduction (Walls, Roof, Windows):
Qcond = U × A × ΔT [BTU/hr]
where U = U-value [BTU/hr·ft²·°F], A = area [ft²], ΔT = design temperature difference [°F]
Solar Heat Gain:
Qsolar = SHGC × Awindow × Ipeak × forient
where SHGC = Solar Heat Gain Coefficient, Ipeak = 200 BTU/hr·ft² (ASHRAE peak vertical surface),
forient = 0.5 (orientation diversity factor)
Infiltration & Ventilation (Sensible):
Q = 1.1 × CFM × ΔT [BTU/hr]
CFMinfil = ACH × Volume / 60 | CFMvent = Occupants × CFM/person
Internal Gains:
Occupants: 250 BTU/hr·person (sensible) + 200 BTU/hr·person (latent)
Lighting: W/ft² × Area × 3.412 BTU/W
Equipment: W/ft² × Area × 3.412 × 0.75 (sensible) / 0.25 (latent)
Unit Conversions:
1 Ton = 12,000 BTU/hr | 1 kW = 3,412 BTU/hr