Drawing No. EH–TH–004 // Thermal Engineering & HVAC
Chiller COP / EER Calculator
Reviewed August 2026
Convert freely between the three most common ways chiller and AC efficiency are reported — COP, EER and kW/ton — and see input power or cooling capacity for a given rating.
What problem does this solve?
Cooling equipment efficiency shows up in three different units depending on the manufacturer, region and equipment class: COP (dimensionless), EER (Btu per watt-hour), and kW/ton (electrical kW per ton of cooling — lower is better for this one, unlike the other two). This calculator converts between all three from any single known value, and shows the resulting electrical input power for a given cooling capacity.
Inputs
Results
Background
COP = cooling output (kW) ÷ electrical input (kW), a dimensionless ratio. EER = COP × 3.412, expressing the same ratio in Btu/h of cooling per watt of input. kW/ton = electrical input (kW) ÷ cooling capacity (tons), where 1 ton = 3.517 kW — note this metric runs the opposite direction: lower kW/ton means more efficient, unlike COP and EER where higher is better.
COP is the natural thermodynamic ratio used in engineering calculations worldwide. EER became standard in North American residential/light-commercial ratings, largely for historical reasons tied to Btu-based HVAC industry convention. kW/ton is common in large chilled-water plant specifications, where it directly states electrical demand per unit of installed cooling capacity — useful for utility and demand-charge calculations.
Frequently asked questions
Practical questions about inputs, assumptions and interpretation.
Yes, for both EER and COP, a higher number means more cooling delivered per unit of electricity — more efficient. For kW/ton, it's reversed: a lower number is more efficient, since it measures electrical demand per unit of cooling rather than cooling per unit of electricity.
Older or smaller chillers often run COP 2.5–3.5; modern efficient water-cooled centrifugal chillers can reach COP 6–7+ at design conditions. Air-cooled chillers typically run lower than water-cooled equivalents because rejecting heat to air is less efficient than rejecting to water.
No — this calculator uses a single rated efficiency value, typically the full-load design-condition rating. These are steady-state efficiency conversions at one operating point. Real chillers vary strongly with load and entering/leaving temperatures, which is why manufacturers also publish IPLV/NPLV or other part-load performance data for seasonal assessment.