Cooling Load Estimator: engineer's guide
For concept and tender stages the cooling load is estimated by W/m² rules of thumb applied to zone area, then refined during design with detailed load software.
Open the Cooling Load Estimator →
What this calculator does
The calculator sums envelope, internal, occupant, and ventilation loads using per-m² and per-person planning values, and returns total TR and per-zone breakdown.
Formulas used
- Total sensible:
Qs = qenvelope + qlights + qequip + qpeople,s + qvent,s - Latent:
Ql = qpeople,l + qvent,l - Total:
Qtotal = Qs + Ql
Variables
- qenvelope = solar + conduction through walls/roof/glass
- qpeople = sensible + latent per occupant
- qvent = fresh-air load, enthalpy-based
Worked example
Scenario: 500 m² open office, 50 people, 12 W/m² equipment, 10 W/m² lighting, hot climate.
- Envelope: 60 W/m² × 500 = 30 kW
- Lights + equipment: 22 × 500 = 11 kW
- People: 50 × 120 W = 6 kW
- Ventilation: 500 L/s at 12 kJ/kg Δh ≈ 7.2 kW
- Total ≈ 54 kW ≈ 15.4 TR. Add 15% margin → 18 TR.
Common mistakes to avoid
- Missing ventilation load (often 20 to 30% of total in hot climates)
- Using indoor W/m² benchmark without envelope correction
- Ignoring solar gain through glazing
- Same block value for office and retail (retail is 30% higher)
Frequently asked questions
Typical W/m²?
Office 100 to 130, retail 130 to 180, restaurant 200 to 250, data centre 400+.
When to run full load software?
Anything beyond schematic design. HAP, TRACE, and IES are standard.
Standards and references
ASHRAE Fundamentals Ch. 18, CIBSE Guide A
Related tools on this site
Open the calculator that pairs with this guide: Cooling Load Estimator.
Verification note
This guide is planning support only. Final design must be verified against the applicable project specification, authority requirements, manufacturer data, and the standards cited above. Consult a licensed engineer for construction-issue calculations.