>It's not technically a measure of "efficiency", we call this the "coefficient of performance" instead.
I have to disagree. At its most general, the concept of efficiency means "desired output achieved per unit of scarce good expended" and can be applied in a variety of contexts: new users per dollar spent on marketing is a measure of your marketing efficiency, treasure value found per hour spent searching is a measure of your treasure-finding efficiency, etc.
Heat pumps are just a case where a) we use the same units for output and input even though they're different things, and b) in that unit system, the value for the output can be greater than the input. Since people can be unnecessarily suspicious of >100% efficiency, they use different terms for it.
If you expressed the efficiency as "2 joules of heat moved per joule of mains electricity consumed" you eliminate the canceling that would let you phrase the ratio as 200%.
> If you expressed the efficiency as "2 joules of heat moved per joule of mains electricity consumed" you eliminate the canceling that would let you phrase the ratio as 200%.
But that's the performance. Efficiency is usually a measure of how good the performance is.
In this case there's a practical reason not to call it efficiency, because there is a well understood maximum performance which is the Carnot limit, so for practical purposes (to avoid confusion) PumpedHeat/Power is called "coefficient of performance"and CarnotLimit/PumpedHeat is called "efficiency", and it has the usual properties that it cannot exceed 100% and it measures how well your system works in a more or less absolute sense.
Heat pump takes energy from two sources, power grid and outside environment: air, landmass or water (there are even air+land models etc). Their energy output is always less than sum of sources, so their efficency is never over 100%. But as the ambient land/air/water heat is generally ”free” then we seem to get 3-500% economy. I have never even seen the technical/physical efficiency numbers for heat pumps as consumers do not care about this.
I have to disagree. At its most general, the concept of efficiency means "desired output achieved per unit of scarce good expended" and can be applied in a variety of contexts: new users per dollar spent on marketing is a measure of your marketing efficiency, treasure value found per hour spent searching is a measure of your treasure-finding efficiency, etc.
Heat pumps are just a case where a) we use the same units for output and input even though they're different things, and b) in that unit system, the value for the output can be greater than the input. Since people can be unnecessarily suspicious of >100% efficiency, they use different terms for it.
If you expressed the efficiency as "2 joules of heat moved per joule of mains electricity consumed" you eliminate the canceling that would let you phrase the ratio as 200%.