5.5.1 — Energy Efficiency Ratio (EER)
The Energy Efficiency Ratio expresses the cooling capacity of air conditioning equipment in BTU/hr divided by the electrical power input in watts, measured at specific standard rating conditions. EER is the North American rating standard most commonly seen on equipment nameplates and compliance documentation for air conditioning equipment.
EER vs. COP
EER and COP both measure efficiency, but use different units and rating conditions. To convert: EER ÷ 3.412 = COP (approximately). An EER of 10 corresponds to a COP of approximately 2.93. EER is a single-point rating at standard conditions; COP can be calculated at any operating point from measured values.
SEER (Seasonal EER)
Seasonal Energy Efficiency Ratio accounts for varying outdoor temperatures over a cooling season rather than a single rated point. SEER is used for residential equipment ratings and minimum efficiency regulations under the Ontario Building Code and Canada’s Energy Efficiency Regulations. Higher SEER = lower annual cooling energy cost under typical Canadian climate conditions.
Using EER in Practice
EER (and SEER) values are published by manufacturers under controlled laboratory conditions. Field conditions — higher outdoor temperatures, dirty coils, low refrigerant charge — all reduce delivered efficiency below the nameplate rating. EER is primarily useful for equipment selection and compliance verification; for diagnosing field performance, measured COP from operating pressures and temperatures is more informative.
All published efficiency ratings — COP, EER, SEER — are measured under standardized laboratory conditions that rarely match actual field operation. A unit rated at EER 12 in a laboratory test will deliver lower efficiency on a 40°C (104°F) day with a fouled condenser. Use ratings for specification and compliance purposes, but expect and measure actual field performance separately.