Inputs
Example Data Table
| Scenario | Door (W×H) | U-value | Indoor / Outdoor | Openings | Open Flow | Estimated Total |
|---|---|---|---|---|---|---|
| Warehouse entry | 1.2 m × 2.1 m | 2.0 W/m²·K | 24 °C / 35 °C | 10 per hour, 6 s | 0.35 m³/s | ≈ 6.3 kW (about 21,500 Btu/h) |
| Office service door | 0.9 m × 2.0 m | 1.4 W/m²·K | 24 °C / 33 °C | 4 per hour, 4 s | 0.20 m³/s | ≈ 1.8 kW (about 6,100 Btu/h) |
| Cold-room access | 1.0 m × 2.1 m | 0.8 W/m²·K | 4 °C / 28 °C | 12 per hour, 5 s | 0.30 m³/s | ≈ 9.0 kW (about 30,700 Btu/h) |
Formula Used
1) Conduction through the door
Conduction heat gain is calculated from the overall heat transfer coefficient (U-value), total door area, and the temperature difference:
- Qcond = U × A × ΔT
- A = (width × height × quantity)
- ΔT = |Tout − Tin|
- If you provide R-value, then U = 1 / R
2) Sensible infiltration during opening
The calculator applies a duty cycle to represent how long the door is open each hour:
- Duty = min(1, events_per_hour × open_seconds / 3600)
- Average airflow = airflow_open × Duty
Then sensible heat gain from infiltration is calculated as:
- Metric: Qinf = ρ × cp × V̇ × ΔT (W)
- Imperial: Qinf = 1.08 × CFM × ΔT (Btu/h)
How to Use This Calculator
- Select a unit system to match your design documents.
- Enter door width, height, and quantity to set area.
- Enter U-value, or leave it blank and provide R-value.
- Enter indoor and outdoor temperatures for the load case.
- Enter opening frequency, open duration, and opening airflow.
- Press Submit to show results above the form.
- Use CSV or PDF export for submittals and reports.
Project Load Context
Door heat gain is often a hidden driver of peak cooling demand in warehouses, service corridors, and loading bays. This calculator estimates heat entering through the door panel and through warm air pulled inside during openings, giving a practical allowance for HVAC sizing and energy review.
The model focuses on sensible load, which drives temperature rise. If humidity matters, add a separate latent estimate. Use conservative outdoor temperatures for design days, and typical values for annual budgeting.
Key Inputs That Drive Heat Gain
Start with door width, height, and quantity to establish total area. Add insulation performance using U-value or R-value. Temperature difference sets the driving force. Opening events, open duration, and opening airflow establish an hourly duty cycle and an average infiltration flow rate. Select Metric or Imperial units to match schedules.
Interpreting Conduction Results
Conduction is computed as U times area times temperature difference. High U-values, large doors, and outdoor heat quickly push conduction upward. If your design includes insulated sectional doors or upgraded seals, a lower U-value will directly reduce this component. Consider frames and thermal bridges, which can raise effective U beyond brochure values.
Managing Infiltration During Openings
Infiltration typically dominates when traffic is frequent. The calculator applies duty cycle equals events times seconds divided by 3600, capped at one. Multiply that fraction by the opening airflow to estimate average warm air entry. Airflow can be measured with a hood or inferred from opening geometry.
Reduce infiltration using vestibules, air curtains, strip curtains, or operational controls. Scheduling forklifts, limiting hold-open devices, and repairing gaskets often provide fast savings. Wind and stack effects can increase flow, so validate with site observations.
Cost and Design Decisions
After total heat gain is known, the tool converts it into cooling capacity in kW, Btu per hour, and tons. It also estimates annual electricity use by applying operating hours, operating days, and the cooling COP. Use the cost output to compare door upgrades, automation, and traffic management options.
FAQs
1) How should I estimate opening airflow?
Use measured airflow if available. Otherwise start with a conservative value based on opening size, traffic, and wind exposure. If results seem low, increase airflow and compare to observed indoor temperature swings.
2) What if I only know R-value?
Leave U-value blank and enter R-value. The calculator converts using U equals one divided by R, keeping your chosen unit system consistent.
3) Does this include latent humidity load?
No. It estimates sensible heat gain from temperature difference. For humid climates or moisture sensitive spaces, add a separate latent load calculation based on outdoor humidity and ventilation effects.
4) Why does infiltration dominate in busy doors?
Even short openings can move large air volumes. Frequent cycles raise the duty fraction and increase average airflow, which multiplies directly with temperature difference in the infiltration equation.
5) How do I reduce the calculated load?
Lower the duty cycle by reducing events or hold-open time. Improve seals and insulation to reduce conduction. Add vestibules, strip curtains, or air curtains to reduce infiltration during traffic.
6) Can I use this for heating season losses?
Yes, use winter outdoor temperature and indoor setpoint. The absolute temperature difference is used, so the output represents magnitude. Interpret it as heating loss rather than cooling gain.