Commercial HVAC operating-cost calculator
Convert cooling tons and EER into an estimated electrical load, monthly kWh, peak demand, and operating cost. This is a screening model for cooling—not a replacement for equipment selection or building-load calculations.
Commercial HVAC operating-cost calculator
Estimate cooling electricity from equipment tons, EER, part-load operation, fans, hours, and commercial demand charges.
A 100-ton system rated at 10.5 EER
A 100-ton cooling system at 10.5 EER has an approximate full-load cooling input of 114.3 kW before the separately entered fans and auxiliary loads. At a 60% average cooling load, with 12 kW of fans for 312 monthly hours, the model produces about 25,138 kWh. At $0.12/kWh and a modeled 114.9 kW peak at $18/kW, the illustrative monthly energy and demand cost is $5,085.
What the EER calculation represents
The Department of Energy defines energy efficiency ratio as cooling capacity in Btu per hour divided by electric input in watts. Using 12,000 Btu per hour per ton gives the calculator's full-load relationship: tons × 12 ÷ EER = approximate cooling kW.
That value is not a prediction of every hour. Real systems cycle, unload, stage, or vary speed. Outdoor conditions, humidity, ventilation, occupancy, controls, and maintenance change the load and efficiency. Integrated or seasonal metrics can be more useful for comparing part-load performance when applied under the correct test method.
Choose inputs that match the equipment boundary
| Input | Where to find it | Common mistake |
|---|---|---|
| Cooling tons | Nameplate, schedule, or design documents | Assuming installed capacity equals building load. |
| EER | Certified product data at a stated condition | Mixing EER, SEER, IEER, COP, and kW/ton. |
| Average load | Trend data or engineering estimate | Using 100% for every operating hour. |
| Fan and auxiliary kW | Measurements, schedules, or motor data | Double-counting loads already inside the rating boundary. |
| Demand coincidence | Utility and building interval data | Assuming HVAC alone always establishes billed demand. |
Improve the estimate before approving a project
- Confirm the efficiency metric and its test condition.
- Trend outdoor temperature, cooling command, and equipment power.
- Separate compressor, supply fan, pump, and condenser loads.
- Compare occupied, startup, setback, and unoccupied periods.
- Use utility interval data to identify whether HVAC sets the peak.
DOE's air-cooled chiller calculator similarly treats energy savings as a comparison between equivalent products under stated assumptions and distinguishes full-load from part-load design conditions. PowerCost Lab follows that same transparency principle: the result is only as specific as the inputs.
Frequently asked questions
How do you estimate commercial cooling kW from tons and EER?
One ton of cooling equals 12,000 Btu per hour. Because EER is cooling capacity in Btu per hour divided by electric input in watts, approximate full-load cooling input is tons multiplied by 12 and divided by EER.
Does HVAC run at full load for every operating hour?
Usually not. Cooling load changes with weather, occupancy, solar gain, ventilation, internal equipment, controls, and building condition. This calculator uses an average-load input for screening rather than assuming continuous full load.
Are fans included in an EER rating?
The boundary of an efficiency rating depends on the equipment and test procedure. This calculator provides a separate fan and auxiliary input so the user can add measured or estimated loads consistently with the rating being used.
Can this calculator compare replacement equipment?
It can screen two scenarios if you record each result and change the EER or operating assumptions. A purchase decision should also consider part-load efficiency, climate, maintenance, controls, service life, installation, incentives, and actual load profiles.