Good heat loss calculator for ASHP with UFH? - Air Source Heat Pumps (ASHPs)

RE: Good heat loss calculator for ASHP with UFH?

Anonymous 5011 — Thu, 15 Aug 2024 18:17:48 +0000

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

RE: Good heat loss calculator for ASHP with UFH?

Jancold — Thu, 15 Aug 2024 17:50:13 +0000

@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.

RE: Good heat loss calculator for ASHP with UFH?

Anonymous 5011 — Thu, 15 Aug 2024 17:01:38 +0000

@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/

RE: Good heat loss calculator for ASHP with UFH?

Jancold — Thu, 15 Aug 2024 15:46:22 +0000

RE: Good heat loss calculator for ASHP with UFH?

ash2020 — Wed, 14 Aug 2024 08:12:19 +0000

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

RE: Good heat loss calculator for ASHP with UFH?

Anonymous 5011 — Wed, 14 Aug 2024 07:18:53 +0000

@johnmo You couldn't do an unvented cylinder yourself though.

I did the UVC course at a local college, so now qualified.

RE: Good heat loss calculator for ASHP with UFH?

ash2020 — Tue, 13 Aug 2024 22:54:56 +0000

@johnmo You couldn't do an unvented cylinder yourself though.

RE: Good heat loss calculator for ASHP with UFH?

Anonymous 5011 — Tue, 13 Aug 2024 20:44:53 +0000

Except the floor, sounds good, did the heat punk calc take all this into account?

RE: Good heat loss calculator for ASHP with UFH?

Jancold — Tue, 13 Aug 2024 20:00:31 +0000

@johnmo We have cavity insulation double glazing and loft is mostly well insulated, all except a walkway down the middle. Also the chimney stacks have been removed. Floating floors with no insulation.

RE: Good heat loss calculator for ASHP with UFH?

Anonymous 5011 — Tue, 13 Aug 2024 19:48:03 +0000

We are going to install underfloor heating

Hope you plan for plenty of insulation under the pipes. Otherwise the downward heat losses can be pretty big. General recommendation is 150mm PIR.

Have you considered fan coils? More expensive than radiators, less faff than doing UFH correctly. Can do cooling in summer if you want it.

stupid MCS thing

I just didn't bother, we are a new build originally with gas boiler. As soon as house was signed off, I installed the ASHP. Cylinder was £1000 (210L slim line), 6kW Maxa heat pump £1300 from ebay, around £500 for stuff. So around £3k all in. When I bought the ASHP, Viessmann were selling a rebadged Maxa unit for around £4k.