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Good heat loss calculator for ASHP with UFH?

ash2020 · 2024-08-07T09:41:43Z

Hi all, new here and very excited to be starting on our project. We are buying a modern-ish bungalow with good insulation in Cornwall and are going to install an ASHP with underfloor heating. Long story but the property shares an oil tank with the vendors next door and currently has an oil boiler and rads. We told them we didn't want them to install a new oil tank so from the day we move in, will have no heating or hot water. Therefore I want to try and get all the design work done so we can hit the ground running on day one.Is there a good calculator, maybe an Excel spreadsheet I can use? Thanks, looking forward to lots of interactions here. Andrew

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Air Source Heat Pumps (ASHPs)

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ash2020

(@ash2020)

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Topic starter 14/08/2024 9:12 am

@johnmo Excellent. I'm going to try and re-instate my Part P electrical qualification which lapsed when I retired.

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Jancold

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15/08/2024 4:46 pm

@johnmo I revisited the Heatpunk project which I did back in May and put in the data for the floor and ceilings which I had not done and revised the heat loss up to 5070 or 70W/m2. Does that seem reasonable?

Daikin 6Kw ASHP.
MG4 EV
1926 Semi with loft and wall cavity insulation, all radiator.

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Anonymous 5011

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15/08/2024 6:01 pm

Posted by: @jancold

↑

@johnmo I revisited the Heatpunk project which I did back in May and put in the data for the floor and ceilings which I had not done and revised the heat loss up to 5070 or 70W/m2. Does that seem reasonable?

Seems high to me

Take a look here

https://www.heatgeek.com/how-to-size-my-heat-pump-or-boiler-heat-loss-cheat-sheet/

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Jancold

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15/08/2024 6:50 pm

@johnmo Thanks, yes I have that cheat sheet and was a bit surprised it was higher than expected. Maybe I should start the Heatpunk project again. Still awaiting Octopus report promised this week but we will see.

Daikin 6Kw ASHP.
MG4 EV
1926 Semi with loft and wall cavity insulation, all radiator.

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Anonymous 5011

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15/08/2024 7:17 pm

There is a lot said about perfect sizing of heat pump to heat loss, but if you run open loop, there is flexibility. Our house heat loss at -3 is about 3kW at 7 degs about 1 to 1.5kW, but we have 6kW heat pump. It cycles, at min load and I get about 10 to 12 mins on and off an hour. So doesn't short cycle. We are currently doing cooling it has been a mostly wet day so almost no load required and the heat pump compressor has started 8 times in 18 hrs.

Opposite to what a lot will say - I think you are better to be slightly big on heat demand, your radiators end up bigger, so you can run lower flow temperature, your heat pump has some flexibility, if it gets really cold outside. Get it the other way round, you end up running higher temps and the immersion on if it gets really cold.

No zones (well one) is the best for flexibility, and oversized, you may get a very slight CoP hit when it's mild, but not much, when it's cold it runs fine.

So I wouldn't fret to much, 5kW or 4kW you really should be running a 6kW ASHP. Remember you still need 2 to 3 hrs for DHW each day mid winter

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