Inputs
Formula used
- Volume = L × W × H, Floor area = L × W
- Wall area = 2(L + W)H − Window area, Roof area = Floor area
- Conduction: Q = U × A × ΔT
- Solar gain: Q = Awin × SHGC × I × shading × orientation
- Outdoor air sensible: Q = ρ × cp × V̇ × ΔT
- Outdoor air latent: Q = ṁ × (wout − win) × hfg
- Total = sensible + latent, then apply safety margin
How to use this calculator
- Select input units, then enter the room dimensions.
- Enter window area, SHGC, shading, and a representative irradiance.
- Set outdoor and indoor design temperature and humidity targets.
- Add occupants, activity level, lighting density, and equipment watts.
- Specify ventilation per person and estimated infiltration in ACH.
- Press Calculate to view results above the form.
- Use the CSV or PDF buttons to export the last result.
Example data table
| Scenario | Room (m) | Outdoor / Indoor | People | Vent (L/s·person) | Adjusted Capacity |
|---|---|---|---|---|---|
| Small office | 6 × 5 × 3 | 38°C 55% / 24°C 50% | 4 seated | 10 | ~ 2.0–3.5 TR |
| Retail room | 10 × 8 × 3.5 | 40°C 60% / 24°C 50% | 12 light work | 8 | 3.5–6.0 TR |
| Server corner | 5 × 4 × 3 | 35°C 50% / 22°C 45% | 2 seated | 5 | 2.5–4.5 TR |
Load estimation for early design
This calculator supports early-stage sizing by translating project inputs into sensible, latent, and total cooling load. Room dimensions set floor and wall areas, while the outdoor–indoor temperature difference drives envelope conduction. Results are presented in kW, BTU/h, and tons of refrigeration, helping estimators compare options quickly during tender, budgeting, and concept design. Document key assumptions for future revisions.
Envelope conduction and glazing gains
Wall, roof, and window transmission are modeled with Q = U × A × ΔT. Use U-values that match the intended assembly and workmanship level, because insulation gaps and thermal bridges raise effective U. Window area, SHGC, shading factor, orientation, and solar irradiance estimate peak solar gain. When shading devices or reflective films are planned, reduce the shading factor to reflect their performance.
Outdoor air and infiltration impacts
Ventilation and infiltration often dominate humid climates. The tool converts ventilation per person and air changes per hour into an outdoor-air flow rate, then calculates sensible load with air density and specific heat. Latent load is calculated from the humidity ratio difference between outdoor and indoor air and the latent heat of vaporization. Tightening doors, sealing joints, and balancing exhaust can significantly reduce both components.
People, lighting, and equipment diversity
Internal gains represent what the space actually does. Occupant sensible and latent rates vary with activity level; meeting rooms and retail floors typically need higher values than offices. Lighting is based on power density and a use factor, which approximates dimming, switching, or occupancy sensors. Equipment watts are adjusted by a diversity factor to avoid oversizing for intermittent loads.
Selecting capacity and safety margin
After summing all contributors, the calculator applies a safety margin to account for uncertainty, future heat sources, and short-term peaks. Use a lower margin when you have verified inputs, and a higher margin when envelope data or schedules are uncertain. Compare the adjusted total to available unit capacities, then confirm coil selection and dehumidification performance with manufacturer data before final procurement.
FAQs
Which inputs influence the load the most?
Outdoor air, window solar gain, and equipment often dominate. Start by validating ventilation, window area, SHGC, and equipment watts, then refine U-values and shading once envelope details are confirmed.
Why does humidity change the required capacity?
Moist outdoor air adds latent load. The calculator estimates moisture removal using humidity ratio difference and latent heat, so higher outdoor RH or lower indoor RH targets increase capacity and may require better dehumidification control.
How should I choose solar irradiance?
Use a representative peak value for the glazing plane at design time. If you lack site data, use conservative peaks and apply realistic shading and orientation factors. Detailed hourly simulation is recommended for critical projects.
What does the safety margin cover?
It buffers uncertainty in U-values, schedules, infiltration, and future plug loads. Use smaller margins when drawings and schedules are reliable. Use larger margins for early estimates, retrofit work, or poorly documented envelopes.
Can I size equipment directly from tons of refrigeration?
Use the adjusted tons value as a starting point, then check manufacturer capacity at your entering air and condenser conditions. Confirm airflow, coil selection, and sensible heat ratio so the system meets both temperature and humidity targets.
Why are my results higher than rules of thumb?
Rules of thumb ignore ventilation, solar peaks, and latent moisture. If the tool shows higher loads, recheck outdoor design conditions, infiltration, equipment watts, and window assumptions. Oversights in these inputs commonly inflate or deflate results.