Heat Pump system efficiency - heat losses?

[GilesM]

I have a ~90,000 BTU Arctic Air heat pump installed in newly replastered pool last summer. It services a 600gal spa and 22k gal pool, both indoor. I don't have any previous operating behavior yet (new house). This unit heats the spa at about 8F/hour which works out to about 40k BTU (just considering the heat going into the spa water). I don't know if that means half the heat is being lost heating piping and spa walls, etc or what. Assorted online rule of thumbs suggested this HP is undersized for this pool. I'm thinking it is slow for heating but will be very efficient maintaining temp once reached.

Another hypothesis is that the new plaster resulted in scale on the copper piping (?) inside the HP. I see a jump in pressure from 17 to 25 PSI when I open the valve to the HP so certainly something smaller diameter in there. Can someone else post spa-scale BTU losses on a HP or even gas heater?

 

[ajw22]

Heat pumps do not use copper heat exchangers.

Heat pumps have smaller pipes and are more restrictive to water flow than gas heaters. The PSI rise you see is normal for a HP.

HP BTUs are at a theoretical 80/80/80 environment which is rarely the case. Actual BTU output is usually less.

 

[1poolman1]

I have a ~90,000 BTU Arctic Air heat pump installed in newly replastered pool last summer. It services a 600gal spa and 22k gal pool, both indoor. I don't have any previous operating behavior yet (new house). This unit heats the spa at about 8F/hour which works out to about 40k BTU (just considering the heat going into the spa water). I don't know if that means half the heat is being lost heating piping and spa walls, etc or what. Assorted online rule of thumbs suggested this HP is undersized for this pool. I'm thinking it is slow for heating but will be very efficient maintaining temp once reached.

Another hypothesis is that the new plaster resulted in scale on the copper piping (?) inside the HP. I see a jump in pressure from 17 to 25 PSI when I open the valve to the HP so certainly something smaller diameter in there. Can someone else post spa-scale BTU losses on a HP or even gas heater?

yes, heat pumps are much better for maintaining heat. For fast heating you need gas. They have a constant BTU output of about 82% of the input rating. A heat pump, though very efficient, is dependent on how much heat is actually in the atmosphere at a given time. In a laboratory test center your 90KBTU rated heater may in fact output that amount. In the real world that seldom happens.