| Scenario | ΔT | Airflow total | Envelope conduction | Internal + solar | Total sensible |
|---|---|---|---|---|---|
| Office, moderate insulation | 8 °C | 0.17 m³/s | ~1.04 kW | ~1.75 kW | ~2.99 kW |
| Retail, high ventilation | 10 °C | 0.35 m³/s | ~1.60 kW | ~3.20 kW | ~6.00 kW |
| Residential, low air leakage | 6 °C | 0.08 m³/s | ~0.55 kW | ~0.90 kW | ~1.45 kW |
- Select a unit system that matches your project inputs.
- Enter the design temperature difference between indoors and outdoors.
- Add envelope areas and U-values for walls, roof, and windows.
- Enter ventilation and infiltration flow for air exchange.
- Provide internal sensible gains for people, lighting, and equipment.
- Press Calculate to see totals and the full breakdown.
- Use Download CSV or Download PDF to export results.
1) Meaning of sensible load
Sensible load is the portion of cooling demand that changes air temperature without changing moisture content. It includes heat entering through walls, roofs, and windows, plus temperature change from outdoor air brought in by ventilation and leakage. People, lights, plug loads, and solar also contribute sensible gains.
2) Typical data you may enter
For early estimates, ΔT is often 6–12 °C (or 10–20 °F) depending on climate and indoor setpoint. Outdoor air rates vary by use; offices may be modest, while retail and classrooms can be higher.
3) Envelope conduction drivers
Conduction follows U·A·ΔT, so large areas and poor insulation dominate. If you only know R-values, remember that U ≈ 1/R (after unit conversion). Roof loads can be significant due to solar-heated surfaces and large exposed areas, especially for top floors and lightweight constructions.
4) Windows and solar considerations
Window conduction is captured with U-value and area, but solar heat can exceed conduction during peak sun. If you have a solar heat gain estimate, enter it directly as “Solar through glazing.” Shading, glazing type, orientation, and blinds can reduce solar gains substantially during occupied hours.
5) Ventilation and infiltration impacts
Outdoor air adds sensible load because it must be cooled from outdoor to indoor temperature. In metric mode, the calculator uses standard dry-air properties (ρ and cp) with ρ·cp·V̇·ΔT. In imperial mode, it applies the common approximation 1.08·CFM·ΔT.
6) Internal gains and diversity
People sensible gain depends on activity; seated work is lower than active retail. Lighting power is often tied to floor area, then adjusted for control strategies. Equipment loads can be highly variable, so apply realistic diversity factors and occupancy schedules to avoid over-sizing and cycling losses.
7) Practical sizing and margins
Use the breakdown to identify what matters most before applying safety factors. Oversizing can increase humidity problems and reduce comfort, even though this tool focuses on sensible load. Pair the sensible result with a latent load check and select equipment based on real operating conditions, not peak-only assumptions.
8) Using outputs for decisions
Compare scenarios by adjusting one driver at a time, such as tighter infiltration, improved U-values, or reduced lighting power. The CSV export supports quick sharing, while the PDF is useful for submittals. If solar dominates, explore shading; if air exchange dominates, verify ventilation requirements and sealing quality.
1) Does this include latent cooling?
No. This tool estimates sensible load only. Add a separate latent load calculation for moisture removal from ventilation, infiltration, and internal sources to complete equipment selection.
2) What should I enter for ΔT?
Use the design indoor setpoint minus the design outdoor dry-bulb temperature for cooling. If you are comparing scenarios, keep ΔT consistent across runs.
3) How do I estimate infiltration flow?
If you lack test data, start with a conservative leakage assumption and refine later. Improvements like weatherstripping and vestibules can meaningfully reduce infiltration-driven sensible load.
4) Can I use this for heating sensible load?
Yes. The same sensible heat relationships apply. Use a heating ΔT and interpret the total as required sensible heating capacity, while still accounting for ventilation air warming.
5) Where do U-values come from?
Use code tables, manufacturer data, or assembly calculations. For layered constructions, calculate overall thermal resistance and convert to U-value after including film resistances when appropriate.
6) Why is solar entered directly?
Solar heat through glazing depends on orientation, shading, and glazing properties. Entering a known solar gain lets you use outputs from other methods or software without double counting.
7) How accurate are the results?
Accuracy depends on input quality. Early estimates guide decisions, but final sizing should use validated ventilation rates, envelope data, realistic schedules, and a full sensible-plus-latent load calculation.