Every industry has its set of acronyms but it often strikes me that the heating, ventilating, and air conditioning (HVAC) industry has more than its share of arcane and indecipherable abbreviations. Unfortunately, nearly all of us are going to be confronted with HVAC acronyms throughout our adult lives since everyone needs to heat and cool their homes, condos, and apartments. This article is intended to offer some handy definitions.
The four acronyms in the title all refer to efficiency characteristics of a particular piece of heating and cooling equipment. SEER is used for air conditioning equipment and stands for Seasonal Energy Efficiency Rating. It is calculated using the total cooling output during a typical cooling season divided by the total electrical input over the same period. Higher is better when it comes to SEER.
The US government has mandated that any air conditioning system manufactured after 2005 have a minimum SEER of 13. Energy Star central air systems must have a minimum of 14.5. The most efficient systems will boast SEERs as high as 21. Window units are not SEER-rated so their SEER hovers around 10. They may have an Energy Efficiency Ratio, or EER. Again, higher is better.
Since I just mentioned EER, let’s go over what it means. This ratio is calculated in a different manner than SEER. It is the ratio of output cooling energy (in British Thermal Units – BTU) to input electrical energy (in watt hours – Wh) at a given operating point. EER is generally calculated using a 95° outside temp and an inside return air temperature of 80° and 50% relative humidity. But SEER and EER are related. For the same piece of equipment, SEER will always be higher than EER. Here’s the formula to calculate it for yourself, EER = .875 x SEER
COP stands for Coefficient of Performance and is frequently used with heat pumps. COP measures how many times more efficient the heat pump is than electric resistance heat with an efficiency of 100%. COP ratings range from 1.5 to 4 and performance is dependent upon where geographically they are installed. A system with a COP of 2.1 delivers 2.1 units of output for every 1.0 unit of input. For once, output exceed input.
The fourth rating is the Heating Seasonal Performance Factor, HSPF. This rating is included on the Energy Guide label of all heat pumps sold in the United States. It is a combination of the cooling performance of the efficient compressor with the less efficient performance of the electric resistance heat elements that are required for back up heat and defrosting. The more efficient heat pumps will generally have a HSPF of around 10 although technology is changing fast so expect ratings to climb.
I thought it would be interesting to pass along the theoretical maximum efficiency a system can achieve. Dictated by the laws of thermodynamics, the most efficient refrigeration process is the Carnot Cycle. Operating with an outdoor temperature of 95° and an indoor temperature of 80°, the Carnot Cycle COP is 36 and the SEER 120. It will be quite some time before we see those ratings. But it would be nice to cool and heat your home with a handful of AA batteries…just kidding on the power requirement.
What you want to take away from all this is that the ratings are better the higher they go. And with advances in technology, especially for heat pumps, we can expect to see some major efficiency improvements in the future, and a great return on your investment. Still, it pays to be cautious. If a contractor’s claims of performance sound too good to be true, ask to see the Energy Guide labels on the equipment or research the manufacturer’s site.