🌡️ HVAC

HVAC Cooling Load Calculator (Heat Load)

Calculate HVAC cooling load (heat load) for buildings. Includes solar, occupancy, lighting, equipment and ventilation loads. ASHRAE compliant.

📐 Standard: ASHRAE / NBC Part 8
✅ Free to use
📄 PDF export
📱 Mobile friendly

ℹ️ About This Calculator

The cooling load (or heat load) is the rate at which heat must be removed from a space to maintain the desired indoor temperature and humidity. It drives every HVAC system design decision — the chiller or AC unit capacity, the AHU airflow, the duct sizes, and the pump and pipe sizes. Oversizing adds unnecessary capital cost; undersizing means the building never reaches comfort conditions.

ASHRAE Handbook of Fundamentals provides detailed CLTD (Cooling Load Temperature Difference), CLF (Cooling Load Factor), and SHGF (Solar Heat Gain Factor) tables for precise calculations. NBC 2016 Part 8 provides outdoor design conditions for major Indian cities. For residential buildings, a rule-of-thumb of 100–150 W/m² (or 350–500 BTU/hr per m²) can be used for preliminary sizing — but always verify with a full load calculation before finalizing equipment.

📐 Cooling Load Components (ASHRAE)

ASHRAE / NBC Part 8

Total Cooling Load = Q_sensible + Q_latent

Sensible components:
  Q_solar   = A_glass × SC × SHGF × CLF        [solar through glass]
  Q_wall    = U × A × CLTD                      [conduction through walls]
  Q_people  = N × sensible_heat_per_person       [occupancy]
  Q_lights  = W_lights × CLF                    [lighting]
  Q_equip   = Equipment load × usage factor

Latent components:
  Q_lat_occ = N × latent_heat_per_person
  Q_lat_vent = fresh air × ΔW × 2501

Total system capacity = (Q_sensible + Q_latent) × 1.1 safety factor

❓ Frequently Asked Questions

What is the thumb rule for AC capacity in India? +
A common rule of thumb for Indian conditions is 1 TR (3.517 kW) per 15–20 m² of floor area for residential buildings with moderate insulation. For commercial offices with high lighting and IT loads: 1 TR per 10–12 m². These are starting estimates only — always do a full heat load calculation for equipment selection.
What is the difference between sensible and latent cooling load? +
Sensible cooling load is the heat that changes air temperature — from walls, windows, people, lighting, and equipment. Latent cooling load is the energy needed to remove moisture from the air — from occupants breathing and sweating, fresh air infiltration, and kitchen/bathroom exhaust. Both must be handled by the HVAC system. In humid Indian climates, latent load can be 30–40% of total load.
What outdoor design temperature should I use for Chennai? +
NBC 2016 Part 8 and ISHRAE data give Chennai outdoor design conditions of 38°C DB / 27°C WB (dry bulb / wet bulb) for cooling design. For other cities: Delhi 42°C DB / 26°C WB, Mumbai 33°C DB / 28°C WB, Bangalore 32°C DB / 21°C WB, Hyderabad 38°C DB / 24°C WB.
How many watts of heat does a person generate? +
ASHRAE gives: seated at rest — 75W sensible + 55W latent = 130W total. Office work — 75W sensible + 55W latent. Light work — 80W sensible + 145W latent. Walking — 110W sensible + 185W latent. Use the appropriate activity level for accurate occupancy load calculation.
Should I add a safety factor to the calculated cooling load? +
Yes. Standard practice is to add a 10% safety factor to the total calculated load before selecting equipment. This accounts for uncertainties in occupancy patterns, solar orientation, future load growth, and calculation assumptions. Some conservative engineers use 15–20% for critical applications like server rooms or hospitals.

🔗 Related Calculators

❄️
Chiller Tonnage Calculator
💨
AHU Sizing Calculator
💨
Duct Size Calculator

🧮 99 Free MEP Calculators

Browse all HVAC, Electrical, Plumbing, Fire, Gas and Mechanical calculators — IS/NBC/ASHRAE compliant, free PDF export.

Browse All Calculators →

⚠️ Disclaimer: For preliminary engineering design only. Verify all results with a licensed engineer before use. Full disclaimer →

🌡️ HVAC Heat Load Calculator
Reference: ASHRAE / NBC Part 8