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Air source heat pump with ground air pre heat

Air Source Heat Pumps (ASHPs)

Last Post by robl 3 years ago

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Oxo2oxo

(@oxo2oxo)

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Topic starter 23/02/2023 4:42 pm

We have a reasonable garden but not quite big enough for ground source. Anybody ever installed underground air pipes to pre-heat an air source heat pump?

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Under ground air pipes

Derek M

(@derek-m)

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23/02/2023 5:03 pm

Posted by: @oxo2oxo

↑

We have a reasonable garden but not quite big enough for ground source. Anybody ever installed underground air pipes to pre heat air sourced pump ?

Many, many years ago, I remember watching a TV program about a test house that was built, I think in Sweden, with not a heat pump, but MVHR.

The incoming fresh air was being supplied via pipework under the garden, which then went through a heat exchanger, and was being additionally heated by the warm air coming out of the building.

I suppose the same idea could be used to pre-heat the air going into an ASHP, but if you are digging up the garden to lay pipework a GSHP would probably be more efficient.

On a post within the forum, I previously proposed the idea of using stored heat energy using water heated by solar thermal, to pre-heat the air supply to an ASHP during the colder nighttime period.

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Oxo2oxo

(@oxo2oxo)

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Topic starter 24/02/2023 10:54 am

@derek-m Hi garden not big enough for ground source but we could get a reasonable amount of pipe in to pre heat the air. We are doing an extension so will have digging going on. Just trying to see if any body has any experience

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Mars

(@editor)

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24/02/2023 5:37 pm

@oxo2oxo, have you considered drilling a borehole if you're wanting to invest in a ground source heat pump? You don't need much space at all for the boreholes and the rigs they use for drilling a the size of vans so they're quite compact. It's an option.

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robl

(@robl)

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24/02/2023 5:52 pm

Posted by: @derek-m

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Many, many years ago, I remember watching a TV program about a test house that was built, I think in Sweden, with not a heat pump, but MVHR.

The incoming fresh air was being supplied via pipework under the garden, which then went through a heat exchanger, and was being additionally heated by the warm air coming out of the building.

I think that did use to be a thing, but it is fraught with difficulty. Mice getting in, mould, stagnent water pools. All of these can be tackled - grills, special silvered pipes, sloping and drained. The reason to do it for MVHR is to improve the efficiency - but MVHR efficiencies are so high now there's little point.

I can sort of understand for ASHP, but you'd have to be careful that the pressure drop wasn't too great, it sounds difficult in practice.

👍

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