Air source heat pumps

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MikeR
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Air source heat pumps

Post by MikeR » Mon Jan 31, 2022 12:06 am

Hi.
Had a Chap round - quoted £14.5k for a Mitsubishi or LG pump, all new radiators and hot water tank and all the work. But keeping existing pipes to radiators. 4 bedroom 1970s house with middling energy rating. Government appear to cover £9100 of it, and with “less running cost than oil” it’s cost neutral over 7 years.

I’d be a bit sceptical of the system maybe, (warm enough, noisy?) except our boiler is about 30 years old, and radiators probably the same so it’s tempting to go new at “no cost”. 🤔

Any experience out there? Pros & Cons?

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Re: Air source heat pumps

Post by MikeR » Mon Jan 31, 2022 4:00 pm

Ah sorry. I thought General Chit-chat might be appropriate for this topic, but now I see it's for "fast cars in general" - sorry! :oops:
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Re: Air source heat pumps

Post by Charles » Mon Jan 31, 2022 6:42 pm

MikeR wrote:
Mon Jan 31, 2022 4:00 pm
Ah sorry. I thought General Chit-chat might be appropriate for this topic, but now I see it's for "fast cars in general" - sorry! :oops:
It's fine here - this section has grown into coverage of many things (cars or otherwise)
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Re: Air source heat pumps

Post by Grumpyjohn1957 » Tue Feb 01, 2022 12:20 am

Is your pipework a single or double system? (Lot of late 60s early 70s used single pipe)
Is it 15,22, or 28mm under the floors with a 15mm take offs to the rads?
All requires serious power flushing prior to coupling up of new gear regardless.
New rads will need to be 30% – 50% bigger as the flow temp’ off heat pumps is much lower.
Without seeing the spec’ of the units I’d suggest temps of 35’ – 45’C max.
I’ve just installed 4 x 16Kw two stage Daikin units in a cascade to produce hot process water. The leaving water temp is 75’C, 3 phase supply and powered by PV when available. It works as predicted.
COP is misleading, always look at the SCOP (seasonally adjusted) At the moment our COP is between 1.2 & 2 due to the winter weather. Icing is a big problem, especially at temps of <5’C. If the air is dry not so bad, in damp or foggy weather the outdoor unit’s ice up very quickly. On a system such as you are being offered it will use electric elements to defrost itself and the cycle time for this could last 45 mins.

Don’t get me wrong, ASHP (GSAP are better) can work very well in the correct application.
Slapping them straight into bog standard houses is not always a recipe for success.

From your gas bills you should be able to get a fair approximation of the energy consumed by your gas boiler. As it’s old assume 70% of the Kw gas that came in (allow more for gas hob?) actually got to heat the house, that will give you a clue how big the heat pump needs to be.

At a COP of 2 you will need 1Kw of electricity to produce 2Kw of heat, with a COP of 4, 1Kw of electricity will produce 4Kw of heat. Electricity is around 25p a unit gas 6p at the moment, do some numbers.
You’ll see COPs of 3 on warm spring days but not cold spring nights!
High summer when you definitely don’t run need to run the heating would give you a COP as high as 5.

LG & Mitsub’ are very good products. I’d expect at least 10 years life hopefully more, they are complex machines and will breakdown.
Pumps, airlocks, and sensor fails are favourite, get a service/breakdown contract.

The price quoted seems very keen – almost too keen for what’s involved.

This is a big decision and you’ll be stuck with it for a long time so please do your research. Ask around, read forums, read technical literature even if you are not that way inclined, get other quotes if you can.
Don’t get rushed into this!


This is what happens on cold foggy days (was +3'C when this was taken)
Iced up Outdoor.jpg
Iced up Outdoor.jpg (449.45 KiB) Viewed 938 times
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Re: Air source heat pumps

Post by MikeR » Tue Feb 01, 2022 11:22 am

Thanks John, most helpful.

The chap said they would power flush the pipework.

Our old boiler is actually oil fired, sorry I should have been clearer. So my "non-researched, you're right I need to get my act together!" guess is that the actual running costs may be similar. Mind you we've had issues with it last 3 winters...

We have electric showers, but Mrs MikeR likes a bath - even in the summer! Would a system be overkill just for bathwater in the summer relative to an immersion heater in the tank? Do you find the constant running to be noisy? I suppose our existing system isn't quiet mind you.

Finally we do have solar panels too, which is maybe a further lean towards this "all electric" option.

Cheers
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Re: Air source heat pumps

Post by Grumpyjohn1957 » Tue Feb 01, 2022 3:06 pm

I realised you use oil when I re read my post this morning! Duh.
Oil boilers are quite a bit more efficient than gas, even old ones, into the 90%+ efficient in fact.
They burn very hot and oil is much more energy dense than gas. Shame about the price variability.
Noise wise on a ASHP? Yes there’s noise, about 40/42 db as rule of thumb on a good domestic system. (Background town noise) In the silent dead of night you’ll hear it as a very faint humming & whooshing if directly under an ajar bedroom window.
They use variable speed fans, very quiet if ticking over on low load. Put it away from the house or even in an acoustic box round the side if possible.
I guess your solar will help a little with the running costs during daylight, I presume you have P.V as opposed to thermal?

It all comes down to the maths and how strong your desire is to reduce carbon emissions. The payback (govt contribution) will trickle back under the RHI every year, it’s worth is derived from standard tables. Get extra insulation in the loft, stop draughts etc,etc and all that.

I can’t emphasize enough the need to for you to thoroughly understand what you are considering.
Be clear about limitations and how well it may suit your property, life style and pocket!
John
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Re: Air source heat pumps

Post by MikeR » Tue Feb 01, 2022 6:58 pm

8)

Thanks!
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No. 097. D3BT Saloon 2010. Manual. Black Sapphire. SOLD
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Re: Air source heat pumps

Post by MikeR » Thu Dec 08, 2022 7:44 pm

Hi John

Your advice of "research beforehand" was spot on.

We ended up with a system that barely got the house above 16C in the spring, and after pulling up floorboards etc. the installers suggested changing to larger bore pipes and converting to two way. At an extra cost of £3000! We argued that they should have pointed out any risks in the beginning, and after about 9 months of wrangling they eventually "upgraded" us to this a couple of weeks back at no extra cost. It now works.

Overall I think we're OK - we paid £14,500 but got over £11,000 back from the government for an all new system throughout. I just wish the price of electric was cheaper now! :shock: We have some new unsightly downpipes in a couple of places now, but we can improve that a little, and maybe a small price to pay to go greener!?!? :mrgreen:
Volvo XC90 T6 Inscription Pro. 2018.
Honda S2000. 2003. SOLD
F31 MSport+ 335D XDrive. 2014. SOLD
No. 097. D3BT Saloon 2010. Manual. Black Sapphire. SOLD
No. 389. D3MT Saloon 2007. Manual. Black Sapphire. SOLD

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