Advanced Cooling Load Calculator
Enter room, envelope, air, and internal gain values. Use project data when available.
Formula Used
Area: floor area = length × width
Envelope conduction: Q = U × A × ΔT
Solar glass load: Q = window area × solar radiation × SHGC × shading factor
Lighting and equipment: watts × 3.412 = BTU/h
Infiltration CFM: room volume × ACH ÷ 60
Sensible air load: Q = 1.08 × CFM × ΔT
Latent air load: Q = 0.68 × CFM × grains difference
Final design load: (sensible + latent) × diversity factor × safety factor
How to Use This Calculator
- Measure the room length, width, and ceiling height.
- Enter design outdoor temperature and desired indoor setpoint.
- Add U-factors for walls, roof, floor, and windows.
- Enter window area, solar coefficient, radiation, and shading factor.
- Add people, lighting, equipment, infiltration, and ventilation values.
- Use diversity and safety factors to tune the final design load.
- Press calculate and review sensible, latent, tonnage, and kW results.
Cooling Load Planning Guide
Definition
A cooling load calculation estimates heat that must be removed from a building space during peak conditions. It is not only a square foot rule. It studies heat transfer through walls, roofs, floors, and glass. It also includes heat from sunlight, people, lights, appliances, outside air, and moisture. In construction work, this definition matters because the result guides duct sizing, equipment capacity, insulation choices, glazing choices, and comfort expectations.
Important Inputs
The first input is the size of the room. Floor area and volume affect almost every part of the estimate. The second input is the temperature difference between outdoor design conditions and the indoor setpoint. A higher difference creates more heat gain through the envelope. U-factor values describe how fast heat passes through building materials. Lower U-factors usually mean better insulation. Window area, glass type, shading, and solar exposure can change the result quickly.
Internal And Air Loads
Internal gains are also important. People add sensible heat and latent moisture. Lights add heat based on wattage. Computers, cooking equipment, pumps, and other devices may add large loads. Infiltration and ventilation bring outdoor air into the space. That air can carry both heat and moisture. Moisture load is called latent load. Temperature load is called sensible load. A good estimate shows both parts, because an air conditioner must manage comfort and humidity.
Using Results
The final design load is commonly shown in BTU per hour, tons, and kilowatts. One cooling ton equals 12,000 BTU per hour. Engineers often apply diversity and safety factors after checking the base load. Diversity prevents oversizing when not all loads peak together. Safety factor gives a modest allowance for real field conditions. Too much safety can create short cycling and weak dehumidification. Too little capacity can cause warm rooms during hot weather.
Construction Value
This calculator helps compare options before procurement. You can test better roof insulation, lower glass gain, reduced infiltration, or smaller lighting wattage. Use the result as a planning guide. Final equipment selection should follow local codes, manufacturer data, climate files, and a qualified design review. Record assumptions beside each number. This makes later checks easier for owners, site teams, and inspectors. It also helps compare bids, substitutions, and value engineering proposals without losing the original comfort target during coordination.
Example Data Table
| Input | Example value | Meaning |
|---|---|---|
| Room size | 30 ft × 20 ft × 10 ft | Defines area and volume. |
| Temperature difference | 20 F | Outdoor design minus indoor setpoint. |
| Window area | 120 sq ft | Glass exposed to conduction and solar gains. |
| Occupants | 6 people | Adds sensible and latent loads. |
| Infiltration | 0.45 ACH | Uncontrolled outdoor air leakage. |
| Safety factor | 10% | Allowance added after base calculation. |
Frequently Asked Questions
What is cooling load calculation?
It is the estimate of heat and moisture that must be removed from a space to keep the desired indoor condition during design weather.
Why is cooling load important in construction?
It supports equipment sizing, duct planning, insulation review, glass selection, electrical coordination, and comfort planning before installation begins.
What is sensible cooling load?
Sensible load is heat that changes air temperature. It comes from walls, roofs, windows, people, lights, equipment, and warm outdoor air.
What is latent cooling load?
Latent load is moisture removal. It comes from people, ventilation, infiltration, cooking, wet materials, and humid outdoor air entering the room.
Why are U-factors used?
U-factors show heat transfer through building assemblies. Lower values usually reduce conduction load and improve the cooling performance of the envelope.
How does window area affect cooling load?
Windows add conduction and solar gains. Large unshaded glass areas can raise the cooling load more than insulated opaque walls.
What does ACH mean?
ACH means air changes per hour. It describes how often room air is replaced by outdoor air through leakage or planned airflow.
What is the role of safety factor?
A safety factor adds a controlled allowance for uncertain field conditions. It should be modest to avoid oversized systems and poor humidity control.
Can this calculator size final equipment?
It gives a planning estimate. Final selection should use local code, climate design data, manufacturer performance tables, and professional review.
Why include diversity factor?
Diversity factor adjusts the load when all internal gains are unlikely to peak at the same time. It can reduce unrealistic oversizing.
What units are shown in the result?
The result shows BTU per hour, cooling tons, kilowatts, and load per square foot for quick construction planning.