mechanical engineering

he 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).

These are defined by the cooling effect in Btu (not in tons) divided by the power use in watts (not in kW) for the peak day (EER), or the seasonal average day (SEER).

For room air conditioners, the commonly used efficiency ratio is the

EER - Energy Efficiency Ratio

For central air conditioners, it the ratio used is

SEER - Seasonal Energy Efficiency Ratio

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

Some of the air conditioner manufacturers participate in the voluntary EnergyStar labeling program where EnergyStar-labeled appliances mean that they have high EER and SEER ratings.
EER - Energy Efficiency Ratio

Room air conditioners in general range from 5,000 Btu per hour to 15,000 Btu per hour. Select room air conditioners with EER of at least 9.0 for mild climates. In a hot climates, select air conditioners with EER over 10.
SEER - Seasonal Energy Efficiency Ratio

For central air conditioners there is units with SEERs reaching nearly 17.
Example - EER

A cooling unit operating at 1 kW/ton would have an EER of 12,000 Btu 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 kW (1000 watts) per ton is equivalent to a COP of 3.516, or an EER of 12.