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EER & COP vs. SEER & HSPF
Let's get through all of the jargon and get to the point as quickly as possible. These ratings are a calculation of how much energy you have to put into a system to get a BTU of heating or cooling out.
But the problem is that each piece of cooling or heat pump equipment has a bunch of variables that impact the numbers, so each one is a little different.
Here is a quick summary:
EER (energy efficiency ratio) = BTU/h of output ÷ Watts of Energy Input
The nice thing with EER is you can measure it in real-time if you know the watts being used and the BTUs being produced. No conversions needed, no fancy math. Measured EER is an easy snapshot, but rated EER is another matter, based only on RATED conditions. It doesn't take into account seasonal temperature or runtime variations.
COP (coefficient of performance) = BTU/h output ÷ BTU/h of Energy Input
In other words, COP is the same as EER, but you convert the input to BTU/h from watts by multiplying watts by 3.413. That one is also easy but has one more step of math added in. The same issue is that it is a snapshot of performance and is based on only one set of operating conditions.
SEER (Seasonal Energy Efficiency Ratio) = BTU/h output ÷ Watts of Energy Input / Averaged over an entire cooling season
So, SEER is just like EER, but it would theoretically be the average EER if you measured it all through the cooling season and then averaged it. The PROBLEM is that it isn't the same everywhere, so it is still based on a set of conditions meant to replicate an average.
HSPF (Heating seasonal performance factor) = BTU/h output ÷ Watts of Energy Input / Averaged over an entire heating season
This equation makes HSPF exactly like the SEER, but it's the winter (heating season) version where the EER is calculated and then averaged out. The same challenge exists in that not all places have the same set of operating conditions.
The solution lies in understanding each efficiency measure and the requirements of the particular market you work in to provide your customers with the best possible products to serve their needs. If you live in a market with very high outdoor temps like Phoenix, AZ, you want to look at the extended performance data on the equipment you see and find systems that continue to perform well at high temperatures.
If you are installing a heat pump in Maine, the same is true but in reverse.
Ratings are great. Being situationally aware is greater.