Here I am responding to Gideon who wants to understand heat pumps. We are only discussing the science and engineering of them, and whether domestic use is a good and economic idea.
Here I am responding to Gideon who wants to understand heat pumps. We are only discussing the science and engineering of them, and whether domestic use is a good and economic idea.
The heat loss in the electric motor is probably about 5% of the electrical input. Remember though that any heat lost from the compressor itself and is not in the gas is largely wasted because it is difficult to collect. The heat of compression you want is the pump output, provided that it is lost in the output heat exchanger to the air or water, etc. It doesn't matter in a fridge, but in a heating pump, it is very significant.
If you carefully read the specifications of the various systems on sale you will see that the COP figure is not well described. There should be a graph of the temperature differential between hot and cold sides and the COP, and ones of the electrical consumption against temperature differential, and also the useful heat output in kW. As usual, you will see the best case COP given, not the one you really need to know for very cold weather!
In large systems used in hot countries, you will see that the hot side has wet cooling towers, similar to a power station. The reason for the water is because the evaporation energy can be used to vastly increase the cooling capacity, just like the cold side of a power station steam turbine. Unfortunately, you cannot do this for heating, as the inside of your house would have 100% humidity, but doing so would help to use the output heat very effectively. Ducted air is obviously the best solution as the temperature differential is small, and consequently the COP high. Fitting ducts under suspended floors is a good idea, but the noise silencing and disruption of probably taking all the floors up to fit insulated quite large ducts would be a problem. Don't forget too that the circulating fan would also take power, probably at least 1kW, so even more electrical consumption! It is likely that a 3kW pump would provide sufficient heating this way for a normal semi without much additional insulation, but it may not be available yet, and I don't see the installation cost as being low, and upstairs would probably have to be heated by circulating air around the whole house, in other words, more ducts in the roof space and then back to the heat pump heat exchanger.
As an example, I have seen a very large system for cooling in Las Vagas, cooling a vast exhibition hall, about 100,000 m2 and 10 metres high, so 1 million cu metres. It cooled the whole place from 35C ish to 20C in about 10 minutes, which feels fantastic, but it did take 2MW! COP theoretically about 20 so 40 MW of cooling, in reality probably 30MW allowing for efficiencies.
The heat loss in the electric motor is probably about 5% of the electrical input. Remember though that any heat lost from the compressor itself and is not in the gas is largely wasted because it is difficult to collect. The heat of compression you want is the pump output, provided that it is lost in the output heat exchanger to the air or water, etc. It doesn't matter in a fridge, but in a heating pump, it is very significant.
If you carefully read the specifications of the various systems on sale you will see that the COP figure is not well described. There should be a graph of the temperature differential between hot and cold sides and the COP, and ones of the electrical consumption against temperature differential, and also the useful heat output in kW. As usual, you will see the best case COP given, not the one you really need to know for very cold weather!
In large systems used in hot countries, you will see that the hot side has wet cooling towers, similar to a power station. The reason for the water is because the evaporation energy can be used to vastly increase the cooling capacity, just like the cold side of a power station steam turbine. Unfortunately, you cannot do this for heating, as the inside of your house would have 100% humidity, but doing so would help to use the output heat very effectively. Ducted air is obviously the best solution as the temperature differential is small, and consequently the COP high. Fitting ducts under suspended floors is a good idea, but the noise silencing and disruption of probably taking all the floors up to fit insulated quite large ducts would be a problem. Don't forget too that the circulating fan would also take power, probably at least 1kW, so even more electrical consumption! It is likely that a 3kW pump would provide sufficient heating this way for a normal semi without much additional insulation, but it may not be available yet, and I don't see the installation cost as being low, and upstairs would probably have to be heated by circulating air around the whole house, in other words, more ducts in the roof space and then back to the heat pump heat exchanger.
As an example, I have seen a very large system for cooling in Las Vagas, cooling a vast exhibition hall, about 100,000 m2 and 10 metres high, so 1 million cu metres. It cooled the whole place from 35C ish to 20C in about 10 minutes, which feels fantastic, but it did take 2MW! COP theoretically about 20 so 40 MW of cooling, in reality probably 30MW allowing for efficiencies.
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