Energy Efficiency Ratio (EER )

Energy Efficiency Ratio, EER

The EER is the ratio of output cooling energy (in BTU) to electrical input energy (in Watt-hour).

The units are therefore BTU/W/h or more formally BTU.W-1.h-1.
The bizarre units of measurement originated in the US to measure the efficiency of an air conditioning system in a steady state. The units are therefore not dimensionless and EER can be measured only over time. Typically, with the system stable, one can measure the energy used over an hour period. One measures the amount of cooling the system has performed during that time.
Many writers erroneously consider the EER to be a ratio of power, not energy:

The units are the same, but now we are dividing the power of the air conditioning unit (in BTU/h) by the power to operate it (in Watt). Although incorrect, this view does have the advantage of allowing us to easily estimate the power used for a certain size of air conditioning unit.
As an example, consider an air conditioning unit that is five tons and has an EER of 11.6. 4 If we want to find out how much power is used we rewrite equation 5:

Where the multiplication by 12,000 converts tons of air conditioning to BTU/h. The EER can be specified only at a specific delta temperature (between inside and outside the space being cooled), because as we see from equation 2, the efficiency changes with this delta temperature. The EER is usually specified under the conditions shown in table 1.

To convert EER to COP, we need to accommodate for the units used. We convert the BTU energy and the electrical input energy to a common energy unit, namely Joule. 5 One BTU equals 1055 J. One Wh equals 3600 Ws or 3600 J. So: