Measures of Energy Efficiency
The air conditoning industry and the Department of Energy (DOE) have developed standards for measuring energy efficiency.
The terms used are EER, SEER, COP and HSPF.
It sounds like Alphabet Soup, but below is the meaning for each.
EER - Energy Efficiency Ratio
EER is the ratio of the cooling capacity divided by the watts at full-load design conditions.
For example, let's look at a 3-ton system using 3KW at 95F.
Since 1 ton of cooling = 12,000 BTU/HR,
EER is measured at the Design Temperature of 95F.
The problem with EER is that it does not consider the complete operating temperatures of an air conditioning system.
In many climates, 95F is the high temperature for a few hours on a hot day.
The system operates at lower temperatures the other 20 hours a day.
What is the efficiency at those operating conditions?
In some cases, the equipment is more efficient at lower temperatures.
A more realistic measure was needed, so in the 1980s SEER started being used.
The SEER is higher than EER because it includes conditions where the equipment operates more efficiently.
SEER - Seasonal Energy Efficiency Ratio
SEER is a more realistic measure of performance than EER because capacity and power consumption vary at different outdoor temperatures.
Most systems have reduced capacity at warmer temperatures of 95F and greater.
In general, higher temperatures mean lower efficiency, lower capacity and higher operating costs.
COP - Coefficiency of Performance
Coefficiency of Performance (COP) is used to determine the efficiency of electric heat and heat pumps.
COP for a heat pump excludes any supplementary resistance.
Because the fan motor adds heat to the air, it is included in this rating.
A heat strip's COP is usually very high (.96 perhaps), but very expensive to use.
A heat pump's COP could be around 2.7, which means that the heat pump is 2.7 times more efficient than standard electric heat.
In general, a higher COP rating means more efficient operation and less cost to operate.
HSPF - Heating Seaon Performance Factor
HSPF was developed as a tool to evaluate the efficiency of a heat pump.
HSPF is the total heat output of a heat pump (including supplementary heat) during the heating season divided by the total electric power in watts.
A lower rating is better for this measure (unlike COP).
Note that this method requires historical data for an entire season to calculate a ratio.
Any estimate based on a shorter period of time is called a "Projection", and could be defined as a "Best Guess".