Air Conditioner Efficiency

The ratio between heat removed - to watt of power used - EER and SEER

Cooling equipment systems used in residential and small commercial buildings often express cooling system efficiency in terms of the Energy Efficiency Ratio - EER - and/or Seasonal Energy Efficiency Ratio - SEER.

For room air conditioners the commonly used efficiency ratio is the

EER - Energy Efficiency Ratio

For central air conditioners the commonly used ratio is

SEER - Seasonal Energy Efficiency Ratio

These ratings are posted on the Energy Guide Label attached to all new air conditioners.

Some air conditioner manufacturers participates in the voluntary Energy Star labeling program where the Energy Star label indicates higher EER and SEER ratings.

EER - Energy Efficiency Ratio

EER is a measure of how efficient a cooling system operates in steady state (over time) when the outdoor temperature is at a specific level (outdoor conditions commonly used are 95 oF).

  • the higher EER - the more energy efficient system

EER can be expressed as

EER = qc / P         (1)


qc = output cooling energy (Btu)

P = input electrical energy consumption (watt-hours, Wh)

EER is commonly used for room air conditioners ranging 5,000 Btu per hour to 15,000 Btu per hour.

  • 1 Btu/h = 2.931x10-4 kW = 0.0299 kpm/s = 0.252 kcal/h = 3.986x10-4 hk = 3.939x10-4 hp = 0.2163 ft lb/s

In mild climates air conditioners with EER of at least 9.0 should be selected. In hotter climates air conditioners with EER over 10.should be selected.

Note that EER is sometimes expressed with cooling power and electrical power consumption

EERpower =  qc / P      (1b)


qc = output cooling power (Btu/h)

P = input electrical power consumption (W)

SEER - Seasonal Energy Efficiency Ratio

SEER  - Seasonal Energy Efficiency Ratio - can be expressed as

SEER = Qc / P         (2)


Qc = seasonal cooling energy (Btu)

P = seasonal electrical energy consumption (Wh)

SEER should be at least 10 -  there are units where SEER reach ate least 17.

Example - EERpower

A cooling unit operating at 1 ton/kW would have an EERpower of 12,000 Btu per hour divided by 1000 watts or 12. This is mathematically equivalent to multiplying the COP by 3.413. Therefore a small cooling unit operating at 1 ton per kW (1000 watts) is equivalent to a COP of 3.516, or an EERpower of 12.

Related Topics

  • Air Conditioning - Air Conditioning systems - heating, cooling and dehumidification of indoor air for thermal comfort

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