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Comment by trebligdivad | Hacker News Reader

How are the COP values so high? The spec on the Vaillant aroTHERM+ says ~2.9 but that is showing well over 5 on some; what's the difference?

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COP depends on the temperature difference.

A single COP is some yearly average usually but in these measurements it is probably a shorter period.

In europe there is a somewhat more rigorous measure of Seasonal COP (SCOP) where the typical climate (in my case nordic) is taken as a standardized test. So x number of days outside temp 0C, y -5C, z -10C, w +10C etc.

So in case of Air source heat pump if the outside temperature is +10 or +15 you can easily get COP numbers that are 9 or above.

Better technical documentation usually has rated COP for some different outside temperatures or even a graph.

Thanks! At the top of that webpage is a drop down to select the date-range; you can select a year (although there aren't that many entries) - and that is lower, I guess averaged over it.

note also, that the temperature difference is also influenced by the outlet temperature: if you have a radiator system, you'll need a higher outlet temperature than say a floor or ceiling heating system. this is because the energy transported is proportional to area of the delivery system. so that's also something to optimize. add in a decent insulation (less units of heat required to replace lost heat units) and you get a higher COP.

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