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Knowing a system will work before we commit to it

Oswiu · 2022-10-19T15:01:35Z

Hi guys, I just want to start by thanking members for their amazing contributions which have very much increased my knowledge, which as we all know is hard to come by for heat pumps. My question is in relation to understanding that a system quoted by an installer will actually perform well for me. I've had a heat loss survey done by a professional installer, but to be frank it had so many issues that it might as well be disregarded, from forgetting an entire room to leaving out external walls and vents. I've therefore done my own heat loss survey in a couple of tools (the official MCS one, Heat Punk, Freedom) and got to about 6kW peak loss for my area and altitude. The living room which is just served by one rad has a heat loss of over 1kW due to two vents for our woodburning stove, and in addition to a normal window, an entire wall of glazing complete with patio doors. A couple of installers have guessed values from our EPC and they've come to about the same, albeit slightly lower values. Our (detached) house is ~140 sq m, and only about 10 years old. This all seems like an efficient starting point for an ASHP, but there are a few complications. Our piping from the boiler is a mere 22mm, and the piping to our 12 rads (no UFH for us) is 10mm. Problems continue in the placement of the heatpump, which due to a confined alleyway on the side of the house would need at least 10 metres of pipe run to the boiler from where the ASHP would go - assuming it would feed into our airing cupboard which is where the current pipes from the boiler in the garage go. So our problems/challenges which of course no salesperson has said are actually blockers are: Heat loss for the house approaches limit of what 22mm piping can provide without hydraulic separation (from what I've read). Heat loss for the living room approaches or is at the limit of what 10mm piping can provide a radiator. A large run of piping (20m there and back) adds significant heat loss if piped outside. Using a formula I found on the internet and 55C outward flow with a DT of 5C, and some outdoor rated piping insulation I found, this would seem to add about 350W of additional heat losses at design temp (c. -4C). This isn't so much a blocker but rather a general grievance that our radiators are woefully undersized for efficient heatpump temps, and almost all of them will have to be replaced. It seems that unlike with every other house in the country, the builders of this one did a heat loss survey and sized the radiators very well for a 70C gas boiler (our current system). We have some comically tiny rads! I suppose my problem is that I just cannot get through to actual heating engineers to discuss this without paying them £1k deposit. They seem to do quotes without surveys or discussion assuming everything will be fine, but I can't take on a quote if I don't know whether the price will double due to insufficient piping etc. The one quote I did get (for a heatpump from a premium German supplier) suggested replacing the 22mm piping with 28mm piping, and that along with replacing the rads was about £2.5k which I thought was actually pretty reasonable. The trouble was that the rest of the quote was eye wateringly expensive. So to the wizards of this forum whose answers I have found so insightful elsewhere, I ask: Will I need to upgrade the piping of the circuit? What can we do with that 1-1.5kW peak loss living room? I've considered filling in the vents and replacing the woodburner with a direct air version, which would lower air changes significantly. Will I need hydraulic separation in the form of a LLH or a buffer? The few installers I've had "estimates" from seem to think so. Is there anything to be done about the long pipe run? Can it go through the house maybe? Is a split or a monobloc system better for long pipe runs? I've heard splits are, but I don't understand why. Could I ever get a good SCOP?

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Air Source Heat Pumps (ASHPs)

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Oswiu

(@oswiu)

Estimable Member Member

Joined: 3 years ago

Posts: 121

Topic starter 23/11/2022 5:19 pm

Things didn't quite go to plan with the install... They can't start this week, but rather next week, so that's a whole extra week without heating. We've had to buy coal to keep the fire going because it burns through logs so quickly it's incredible. Hopefully that is the last time I'll ever buy coal.

We also had a bit of contract back and forth, a fairly hefty price uplift, and still no heat loss survey! They said that the one I sent them looked to a good standard so they're using that to design, and will do their heat loss survey afterwards. It seems a bit shady to me, but then again I know that's only because they don't have the time to do it at such short notice.

We agreed to upgrade the model that was going to be installed to a newer model. The one originally listed isn't even in Daikin's product catalogue anymore, so certainly a bit outdated. I'm hoping that it gives some basic statistics to work out COP. It's not entirely clear from the installation manual that this is guaranteed. I'm also in discussions over where the controller should be installed, as they have planned to shove it in the garage. I'm planning on running on weather compensation only to see how that goes, but I still don't want to be heading out to the garage to get to the controller, and also if it has the WiFi module in then I don't think it'll get signal.

I also got from the Daikin manual that if my heat emitters are radiators, which they are, then DT is fixed at 8C. Reading that has made me completely scrap my plans for changing pipes from 10mm to 15mm in my living room, since it should now allow much higher power output even if it requires a bit more balancing - 2.9kW with DT8 vs 1.8kW with DT5. I was under the impression that heat pumps always aim for a DT of 5, so it's worth checking a specific model if this comes up for anyone else.

Also we had to arrange our own radiator delivery and installation, and it might clash a bit with the ASHP installation. The installers don't seem bothered, but it's all a bit stressful, especially because no one has looked over my radiator changes list, and it could leave me without heating for longer.

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HughF

(@hughf)

Honorable Member Member

Joined: 4 years ago

Posts: 489

23/11/2022 7:27 pm

Don’t feel too bad, I bought half a ton of Welsh anthracite last week to run my Rayburn through this winter. 🤣

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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Oswiu

(@oswiu)

Estimable Member Member

Joined: 3 years ago

Posts: 121

Topic starter 09/12/2022 12:49 pm

The pump has been in for over a week now but still hasn't been turned on, and won't be until next week because we've been having a nightmare installing the new radiators and we couldn't get it commissioned until the end of next week. It's getting quite chilly now!

The installers were originally going to set up the Daikin tank (which includes a buffer/volumiser) as a buffer, but I managed to catch it and they agreed to change to using it as a volumiser which was the original plan anyway. There's a couple of things I'm not overjoyed about with the installation, so I might have to work a bit to resolve these things. I don't understand why they attached the exterior piping with metal clamps directly on the piping as opposed to lagging first and clamping the lagging, surely that would be so much more effective.

I'm unsure whether I should by Daikin's Madoka thermostat to modulate the heat pump with weather comp, or just run on full weather compensation with my current thermostat as a limiter set to something pretty hot like 23C, with the idea being that I'd never reach that. I've seen a few ways online to connect my heat pump to my home automation system so I could do the modulating myself and save a few hundred pounds on a complex install of the Daikin thermostat which would have to be wired all the way to a living area.

What I'm really worried about is when the plumber changing our radiators fills the system up, will it just all drain out the freeze protection valves, or if the incoming water warms them up enough, will it just freeze inside the heat pump and break it? The frost is lasting all day at the moment, so it's a real concern. I asked the installers and they said they've never filled up a heat pump in freezing temperatures so didn't know what would happen.

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