Formula & Calculator
Energy Efficiency Ratio (EER)
Rates the cooling efficiency of an air conditioning unit relative to its electrical power consumption.
Interpretation
Energy Efficiency Ratio (EER) = Cooling Output (BTU/hr) / Power Input (W).
Higher EER means more cooling per watt of electricity – used for air conditioners.
Example: 12,000 BTU/hr cooling with 1,000W input → EER = 12.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| EER | Energy Efficiency Ratio | BTU/(hr·W) |
| Q_cool | Cooling output (cooling capacity) | BTU/hr |
| P_in | Power input (electrical consumption) | W |
What it means
The Energy Efficiency Ratio (EER) is the ratio of cooling output (in BTU/hr) to power input (in watts) for an air conditioner. Higher EER means more cooling per watt. Example: An air conditioner with 12,000 BTU/hr cooling and 1,000W input has EER = 12. EER is used to compare the efficiency of cooling units. A higher EER indicates lower operating costs. The EER is a standard rating for window and portable air conditioners. It differs from SEER (Seasonal Energy Efficiency Ratio), which is averaged over a cooling season.
Worked example
Energy Efficiency Ratio – Practical Example
Real‑World| Parameter | Value |
|---|---|
| Cooling output | 12,000 BTU/hr |
| Power input | 1000 W |
| Formula | EER = Cooling Output (BTU/hr) / Power Input (W) |
Common mistakes
Watch for unit mismatches (W vs kW, single- vs three-phase) and remember to include power factor or efficiency where the formula requires it.Applications
Energy Efficiency Ratio (EER) = Cooling Output (BTU/hr) / Power Input (W) measures air conditioner efficiency. Higher EER means more cooling per watt. Engineers use it to select AC units, to compare systems, and to meet energy standards. This metric is critical for HVAC design.
- HVAC equipment selection and efficiency comparison
- Energy compliance (e.g., SEER, EER standards)
- Building energy modelling and cost analysis
- Air conditioning system design
- Educational understanding of cooling efficiency
Frequently Asked Questions
EER is the ratio of cooling output in BTU/hr to the electrical power input in watts: EER = Cooling Output (BTU/hr) / Power Input (W). It is used for air conditioners.
Typically 8‑12 for older units, 12‑15 for newer high‑efficiency units.
COP = EER / 3.412 (since 1 W = 3.412 BTU/hr).
Common errors: 1) using the wrong units, 2) comparing EER values at different operating conditions, 3) confusing EER with SEER (seasonal), 4) using the input power without including fan power.
Power (W) = Cooling Output (BTU/hr) / EER.
EER is measured at specific conditions (95°F outdoor). SEER is the seasonal efficiency averaged over a cooling season.
Selecting energy‑efficient air conditioners and comparing models.
EER decreases as the outdoor temperature increases because the cooling capacity drops and power consumption increases.