EER stands for energy efficiency rating and is mostly used to rate the energy performance of appliances like air conditioners. It’s useful when you want to compare the energy efficiency of different air conditioners and different air conditioners sizes.
In most cases, a portable air conditioner has the best EER rating. A good EER rating for an air conditioner will be a rating over 8.5.
How to Calculate EER
You can calculate the EER rating, for any air conditioner, by dividing the useful cooling output (BTU/h) by electricity input (Watts).
Air conditioner BTU is 6000.
Air conditioner Watts is 800.
EER Rating: 6000 (BTU) / 800 (W) = 7.5 EER.
With a 7.5 EER rating this would be classified as an air conditioner which is not efficient. As stated previously we would prefer an air conditioner with an EER of over 8.5.
In this example, based on the EER rating, this air conditioner will provide 8.5 BTU of cooling for every 1 W of energy input.
Keep in mind that EER is based on a fixed set of conditions:
- Outdoor temperature: 95F
- Indoor temperature: 80F
- Relative humidity: 50%
This means the EER isn’t necessarily always 100% accurate. The industry is adapting to this with the addition of SEER, for central air conditioners, and CEEP, for window air conditioners. EER is now generally used for room air conditioners.
The Best Possible EER Rating
Scientists have been able to use the laws of thermodynamics to determine the best possible EER rating an air conditioner can achieve, based on the coefficient of performance or COP rating.
COP rating formula:
COP rating = Tcold / (Thot – Tcold)
EER = 3.41 x COP
Thot refers to the hot temperature outside and Tcold refers to the cold temperature we want to air conditioner to provide inside. In this example Thot and Tcold will be listed in Kelvin.
Tcold: 75F (297K)
Thot: 90F (305K)
COP rating: 297 / (305-297) = 37.12
EER = 3.41 x 37.12 = 126.6
And there you have it, a simple way to calculate EER (energy efficient rating) for your room air conditioner. Use this value to compare the energy efficiency of your next air conditioner purchase.