Cooling and Heating Load Calculator
Example Data Table
| Room |
Area m² |
People |
Summer °C |
Winter °C |
Window m² |
Lighting W/m² |
| Office Zone A |
120 |
12 |
35 |
2 |
22 |
10 |
| Training Room |
85 |
25 |
38 |
4 |
18 |
12 |
| Small Lab |
65 |
6 |
34 |
1 |
9 |
14 |
Formula Used
Envelope load: Q = U × A × ΔT ÷ 1000
Solar gain: Q = Window Area × Solar Irradiance × SHGC ÷ 1000
Internal sensible load: Q = People Sensible + Lighting + Equipment
Outdoor air sensible load: Q = ρ × Airflow × Cp × ΔT
Outdoor air total cooling load: Q = ρ × Airflow × Δh
Latent outdoor air load: Qlatent = Qtotal − Qsensible
Cooling total: Cooling = Sensible Load + Latent Load + Safety Reserve
Heating total: Heating = Transmission Loss + Ventilation Loss + Infiltration Loss + Safety Reserve
Tons of cooling: Tons = Cooling kW ÷ 3.51685
Heating BTU/h: BTU/h = Heating kW × 3412.142
How to Use This Calculator
Enter the room size first. Add ceiling height to estimate air volume. Enter summer and winter design temperatures. Add indoor and outdoor humidity for cooling moisture load. Fill wall, roof, and window areas. Enter U values from drawings or material data. Add SHGC and solar irradiance for window heat gain.
Next, enter people, lighting, and equipment loads. Add infiltration in air changes per hour. Add ventilation in CFM per person. Choose a supply air temperature difference. Add a safety factor for early design uncertainty. Press Calculate. Review the result above the form. Download the CSV or PDF report when needed.
ASHRAE Cooling and Heating Load Planning Guide
Overview
Cooling and heating load work starts with a building picture. A room gains heat through walls, roof, glass, people, lights, equipment, outside air, and leakage. It loses heat during cold weather through the same envelope paths and through incoming outdoor air. This calculator follows the same planning idea used in many load manuals. It separates each source, then combines the parts into one practical estimate.
Why Load Separation Matters
A single total load can hide the real problem. Solar gain may be the largest issue in one room. Ventilation may dominate another room. Internal equipment may control a small server space. Separate lines help a designer choose better insulation, glass, airflow, or zoning. They also make review easier before equipment is selected.
Cooling Method
The cooling side includes sensible and latent heat. Sensible heat changes air temperature. Latent heat comes from moisture. The tool estimates humidity ratio from dry bulb temperature and relative humidity. It then compares outdoor and indoor air enthalpy. This gives a more useful outdoor air load than a temperature-only method. Solar gain uses window area, solar intensity, and SHGC. Envelope gain uses U value, surface area, and temperature difference.
Heating Method
The heating side focuses on transmission and outdoor air warming. Wall, roof, and glass losses use the winter temperature difference. Infiltration and ventilation air are warmed from outdoor winter temperature to indoor design temperature. A safety factor can be added for uncertainty, duct losses, or rough early data.
Design Use
Use the result as an early sizing guide. Check every input before making purchases. Use local weather data, accurate drawings, and verified construction values. Large buildings, hospitals, labs, kitchens, and critical spaces need a detailed professional load study. This calculator is best for education, comparison, and planning. It shows how each heat path changes the final answer. Try several cases. Lower window gain, improve U values, change outdoor air, or adjust occupancy. The side-by-side results can reveal the most effective design change.
Practical Checks
Do not size equipment from peak load alone. Consider part load operation, humidity control, ventilation rules, duct pressure, and room balance. Oversized systems can short cycle. Undersized systems may miss setpoints. A balanced result supports comfort, efficiency, and engineering discussions.
FAQs
1. Is this a final equipment selection tool?
No. It is a planning and education tool. Use it for early estimates, comparisons, and review. Final design should include local codes, drawings, schedules, ventilation rules, and professional judgment.
2. What is a U value?
U value shows heat flow through a surface. Lower U values mean better insulation. Walls, roofs, and windows each need their own U value for better load results.
3. Why does humidity matter in cooling?
Humidity creates latent load. The system must remove moisture as well as heat. High outdoor humidity can raise cooling size, even when the dry bulb temperature looks moderate.
4. What is SHGC?
SHGC means solar heat gain coefficient. It estimates how much solar heat passes through glass. Lower SHGC usually means lower solar cooling load.
5. What does ACH mean?
ACH means air changes per hour. It describes how often room air is replaced by leakage or infiltration. Higher ACH raises both cooling and heating loads.
6. Why is a safety factor included?
A safety factor covers early design uncertainty. It can allow for rough dimensions, duct gains, unknown schedules, or conservative planning. Avoid using it to hide poor data.
7. Why are cooling tons shown?
Cooling tons are common HVAC capacity units. One refrigeration ton equals about 3.51685 kW. The calculator shows both units for easier comparison.
8. Can this handle large buildings?
It can estimate a single zone or simplified area. Large buildings need room-by-room schedules, diversity, solar orientation, ventilation standards, and detailed simulation or manual review.