ASHP sizing advice for a thermal store.

Discussion in 'Plumbers' Talk' started by Dam0n, Aug 5, 2022.

  1. Dam0n

    Dam0n Screwfix Select

    Hi all,

    I’m looking to install an ASHP directly to my 300ltr thermal store and need some advice on sizing from the knowledgeable folk on here.

    Currently the store is heated by 9kw of immersions which are able to keep the house warm enough and provide enough hot water for our needs. The water is set to 60° in the winter months however.

    The house has solid walls - loft insulation and double glazing.

    Three radiators upstairs and underfloor heating downstairs. I’m willing to increase the size of the upstairs radiators to account for the lower temperature output of the heat pump.

    I’m leaning towards a 9kw- 11kw ASHP for the store but am a bit worried I may be over doing it. I’ve heard that you shouldn’t really overspec a ASHP due to the issue of short cycling and a waste of electricity. Any ideas? Will short cycling be an issue as I’m heating up such a large mass of water anyway?

    Has anyone got any experience of plumbing in a heat pump to a thermal store? Is it as easy as connecting it up (I have inlets and outlets on the store ready for a heat source) and wiring it up. I have an 6kw programmable feed from the stores’ controller which is usually used as hot water “top up” which can be used to power the pump instead. I’ll still have 9kw of immersions to use with the controller if for whatever reason I need a quick boost of power.

    Any input would be appreciated on this. I just want to make sure I haven’t got it all wrong.


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