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Heat pumps - What’s your experience of the benefits and downsides to an ASHP?

  • 10 January 2022
  • 77 replies
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Heat pumps - What’s your experience of the benefits and downsides to an ASHP?

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Just a few observations.

TRVs and zoning

Turning radiators down or off, zoning parts of the heating, or running the heating intermittently will reduce the average temperature of the house and hence reduce the heat losses from the house.

Operating the heat pump at a higher flow temperature will reduce its efficiency, so running it for longer at a lower temperature should make it more efficient.

The question is does the increase in efficiency outweigh the increase in house losses?

In some ways this is like comparing taking a bath or a shower. Baths are much more efficient because the energy in the bath far exceeds the losses in the pipework, but showers use maybe a quarter of the energy, so they are by far the most economic.

If the load on the heat pump is much less than its rating (excessive zoning), then the heat pump will be continually cycling, pulsing heat in, then waiting for the return flow to cool. Think filling a bowl with hot water in the kitchen, then taking it upstairs to fill the bath, then returning to the kitchen to repeat the process.

Heat up times.

The time for a room to re-heat is determined by the power output from the radiator. If the radiator has been resized so that it outputs the same power (at the reduced flow temperature) as the original radiator (operating at gas boiler temperatures) then the room will reheat in the same time.

Weather compensation may mean that the (initial) flow temperature may be less than the design flow temperature (for -3°C ambient), so the cooler radiator outputs less power and the room heats slower. 

However a "TPI" thermostat on a gas boiler system will adjust the heating duty cycle to run the boiler cooler (to increase efficiency), so it too will heat slower on warmer days.

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Those are some really thoughtful observations @BeePee

I don’t know if you have seen this article yet but I would definitely recommend giving it a read 

Keep us updated with your findings

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