Project Input Details
Use SI values. Enter design-day conditions and realistic operating assumptions.
Example Data Table
| Input group | Example value | Reason for inclusion |
|---|---|---|
| Floor size | 12 m × 8 m | Defines floor area, perimeter, roof area, and volume. |
| Glazing | 12 m², SHGC 0.45 | Captures conductive and solar window gains. |
| Airflow | 0.50 ACH plus 90 m³/h | Captures infiltration and mechanical outdoor-air loads. |
| Internal heat | Eight people, lighting, equipment | Captures heat released inside the conditioned space. |
| Contingency | 10 percent | Covers reasonable early-stage uncertainty. |
Formula Used
The calculator uses a transparent component method. All envelope terms use SI units. Temperature difference is limited to positive outdoor-to-indoor values. Humidity difference is also limited to positive values.
Q-envelope = A × U × ΔT Q-solar = A-glass × Irradiance × SHGC × Shading factor V̇ = (ACH × Room volume + Outdoor air m³/h) ÷ 3600 Q-air sensible = 1.2 × 1005 × V̇ × ΔT Q-air latent = 1.2 × 2,501,000 × V̇ × Δw Q-design = (Q-sensible + Q-latent) × (1 + Safety margin)Here, A is surface area, U is thermal transmittance, V̇ is airflow in m³/s, and Δw is humidity-ratio difference in kg/kg. The final result is converted into kilowatts, BTU/h, and refrigeration tons.
How to Use This Calculator
- Enter the measured building length, width, clear height, glazing, and door area.
- Use U-values from approved construction details or product data.
- Enter peak outdoor conditions and the planned indoor target.
- Add infiltration, outdoor ventilation, occupancy, lighting, and equipment loads.
- Set realistic operating and diversity factors. Avoid using maximum values for every item.
- Choose a modest contingency. Submit the form to show results above the inputs.
- Download the CSV or PDF after calculation for planning records.
Cooling Load Planning for Construction
Early Estimates
A Pwrmatic cooling load calculator gives an early estimate for conditioned spaces. It combines envelope heat, solar exposure, outdoor air, internal heat, and moisture effects. This approach helps project teams compare options before equipment selection. It is not a substitute for a detailed room-by-room design.
Geometry and Surfaces
Start with geometry. Floor area affects roof gain and internal loading. Ceiling height determines air volume. Perimeter and height estimate gross wall area. Window and door areas are removed from that wall area. This avoids counting the same surface twice.
Envelope Decisions
Envelope inputs describe how quickly heat enters each surface. Lower U-values indicate better resistance. Roofs often receive solar exposure. Glazing can add conduction and solar gain together. Window shading, glass solar heat gain coefficient, and orientation can change results sharply. Enter realistic design values rather than generic assumptions.
Air and Moisture
Air movement matters during hot weather. Infiltration carries sensible heat when outside air is warmer. It also carries latent heat when outside moisture is higher. Mechanical outdoor air creates similar loads. Tight construction reduces uncontrolled airflow. Ventilation still must meet the project requirements. The calculator adds both airflow sources into one cooling estimate.
Internal Heat
Internal gains often become important in occupied spaces. People release sensible and latent heat. Lighting becomes heat inside the room. Computers, motors, kitchen equipment, and process tools can be major loads. Use diversity factors for equipment that will not operate together. Avoid using connected electrical load without checking real operating conditions.
Sensible and Latent Balance
The calculated sensible load represents temperature control demand. The latent load represents moisture removal demand. Their relationship is shown by the sensible heat ratio. A lower ratio means humidity control deserves more attention. Equipment selection should meet both the total capacity and latent capacity. A system chosen only by total tonnage may leave the space humid.
Margin and Review
Apply a sensible safety margin after reviewing all inputs. A modest allowance can cover uncertainty in early estimates. Large margins can create oversizing. Oversized cooling equipment can cycle too quickly. Short cycling may reduce dehumidification and comfort. Review the assumptions when results look unusually high or low.
Final Coordination
Use the report for preliminary budgets, alternatives, and coordination discussions. Check the selected capacity against manufacturer performance at local design conditions. Confirm duct airflow, ventilation, controls, and zoning. Detailed calculations remain necessary for final equipment selection, permits, and high-risk spaces.
Frequently Asked Questions
1. What does this calculator estimate?
It estimates peak cooling demand from envelope conduction, solar glazing gain, airflow, occupants, lighting, equipment, and moisture. It presents a preliminary design capacity in several familiar units.
2. Is this a permit-grade design calculation?
No. It is an early planning tool. Final submissions may require local standards, room-by-room loads, detailed solar geometry, schedules, duct analysis, and qualified professional review.
3. How are wall and roof gains calculated?
The calculator multiplies each net surface area by its U-value and the positive outdoor-to-indoor temperature difference. Better-insulated assemblies have lower U-values and lower calculated gain.
4. Why is solar gain separated?
Glass admits solar energy beyond ordinary conduction. Separating it shows how glazing area, SHGC, irradiance, and shading can change the cooling peak.
5. What is latent cooling load?
Latent load is the energy required to remove moisture. Outdoor air and people can add moisture. Equipment must have enough latent capacity to maintain indoor humidity.
6. What does sensible heat ratio mean?
It is sensible load divided by total base load. A lower value signals a greater moisture-removal demand. Compare it with manufacturer performance data during selection.
7. Should outdoor ventilation be included?
Yes. Enter the required mechanical outdoor-air volume. It creates sensible and latent load when outdoor conditions exceed the indoor design target.
8. How should I select a shading factor?
Use one for unshaded glazing. Use a lower value when external shades, overhangs, screens, or verified controls reduce peak solar heat gain.
9. Why use an equipment diversity factor?
Not all connected equipment operates at full power simultaneously. A realistic diversity factor avoids exaggerated internal gains and unnecessary oversizing.
10. Can this calculate cold-room refrigeration loads?
No. Cold rooms need additional product pull-down, transmission, defrost, door-opening, and refrigeration-system calculations. Use a specialist refrigeration method for those spaces.
11. When should final equipment be chosen?
Use approved designs for final equipment selection and installation.