Designing ASHP syst...
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Designing ASHP system using the Freedom toolkit spreadsheet

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6918 kWhs
Joined: 2 years ago
Posts: 1391

@hughf - it is definitely on the cards, but I haven't quite got to the Oscar Wilde moment yet ('either the PHE goes, or I go') as I am still a bit in favour of the pros of separating the two circuits, and now we have warmer weather, it is less easy to investigate the cons, losses due to the PHE. Mine also got hampered by the installer's plumber's well intentioned but unwise habit of reversing the flow, ie removing the contraflow by rotating the pump through 180 degrees, in a bid to improve radiator heating (they tend to be too cold, even with adequate primary flow temps). I think this is most likely inadequate circulating flow rate, despite the pump being on its max flow rate setting, water in effect stagnates in the rads and cools down, and it will be easier to fit a higher flow rate circulating pump if the two circuits are separate. There is also the question of the adequacy of the circulating pump in the heat pump, if it has to maintain a fast flow round all the rads, rather than just the PHE.


Midea 14kW (for now...) ASHP heating both building and DHW

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2928 kWhs
Joined: 2 years ago
Posts: 480
Topic starter  
Posted by: @jezzaf

@hughf Hi.. just read your comment and the last line caught my attention and if I understand you correctly  .. so many years ago I did a self install of a Trianco Active Air Heatpump .... it was a rebadged  chinese made machine anyway the compressor failed I can't now remember if it was in warranty or just out. The point was that as I was not an "approved installer" the manufacturer "Trianco" would not even talk to me or assist in any way.  Ended up scrapping the unit and now happy with air to air. But moving to G2 listed Farmhouse in Somerset in two weeks so its  full circle for me back to oil 🙂        

That's unfortunate, but the nature of the beast with any sort of refrigeration in a domestic environment over here. Look at the US, HVAC tech's everywhere, perfectly capable of changing all the parts inside your average split ac/heatpump unit. Compressors, 4 way vavles, expansion valves, filters, all available from the spares suppliers or kept on the van.

To be honest, I like to write down my tech at a reasonable rate, so if I can get 10 years out of something that costs £3k, I'm happy with that. I wouldn't expect any issues within 10 years, perhaps a regas, but that's easy enough for anyone with F-gas to do.


Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

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