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Air Source Heat Pumps (ASHPs)

Last Post by batalto 2 years ago

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batalto

(@batalto)

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Topic starter 22/04/2021 1:28 pm

Hi all,

Just wanted to talk you through our upcoming ASHP installation. We live on the south coast, just outside of Portsmouth. The house is a detached home of around 260m2 in footprint. The bottom floor was an extended bungalow and we added a second floor. The first floor is standard construction, brick cavity that's filled and double glazed. The upper floor is made of Structurally Insulated Panels (SIPs) with triple glazing. We had to use SIPs because they are lightweight and so wouldn't affect the shallow bungalow foundations. As an upside SIPS are also extremely efficient in retaining heat and have a very low U value, 0.18. The loft has 200mm of insulation in the middle beneath the floor and 400mm of insulation for everywhere else. We have 8.4kW of solar PV on the roof and 7kWh of battery storage (Pylontech batteries). We also have a Solic solar PV heat controller, which will dump excess solar power into the tank before we export.

We've just had our EPC done and we scored very highly A (93) that also provided a heat demand of 34w/m2 which tallies with our ASHP assessment of 36w/m2.

The ASHP is a 12kw Midea with a stated SCOP of 3.36 supplied and installed by J A Rees, sourced from Freedom Heat Pumps - total cost just under £10k. We will be replacing our current 32kW gas system boiler and hot water cylinder and using the green homes grant for £5k of the cost and I will paying the other £5k. We qualify for the highest RHI so would expect to get roughly £7200 back over the next 7 years. The boiler will be retained as a backup heating system and isolated from the ASHP system. We have been told this is fine with the RHI as its a backup and not hybrid. The heating is currently set to 45 degrees and we have had no problems. Our main living area has a large bifold door system and west facing. This means we have significant heat loss in the winter and for 2 months its very cold and this makes the room chilly, but not cold. All the other months the solar gain is significant, heating the room and the rest of the house. With the conventional boiler the room is chilly, so I am expecting issues in January heating up the room. We might need to come up with a plan for this room, possibly some thick curtains.

The install will be next week and should be very straightforward. The ASHP will go on the drive next to the current power intake. The pipework will go straight through the wall into the current boiler room and tap into the current pipework. The tank will need replacement for one with a larger coil, but more or less everything else will remain the same. The aim is 2 days.

Currently our gas is 2.5p and electricity is 14p and the current boiler is 58% efficient (according to the boiler) - this leads to a bill of around £1250 for both gas and electricity for the year. With the ASHP, boiler efficiency and assuming a worse SCOP of 2.7 on the current tariff we expect the bill to fall to just under £1,000 (34,000kw of gas to 7,000kw of electricity). This cost includes a standing charge for gas even though we wont be using it.

My plan after we have got used to the ASHP is to upgrade the batteries and add 7kw extra, then move to a new tariff. Agile GO is very interesting as I could fill my batteries at night and expend them during the day. The batteries would store 11.4kw (14kW @ 80% Depth of Discharge). I have estimated this would further drop my bills down to £780

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE

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Kev M

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22/04/2021 2:57 pm

Sounds good. Our main living area is large, has a lot of windows and french doors. We ended up with three quite large K2 radiators.

BTW I would double check the RHI situation around backup systems. I thought having a backup system (i.e. a working fossil fuel system you could revert to) meant you had to have metering for payment, even if it wasn't a hybrid system. I looked into this because I had HW heating via my wood burner but I just decommissioned it permanently in the end. @editor Mars might know more as I think he still has his oil boiler. Link below.

OFGEM.GOV.UK "https://www.ofgem.gov.uk/system/files/docs/2018/07/essentialguidetometering_july_2018.pdf"

This post was modified 5 years ago by Kev M

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batalto

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Topic starter 22/04/2021 4:05 pm

@kev-m I think we have those anyway in the main room.

As so the metering, I am just saying what I was told by the installer and freedom heat pumps. I'll have to look into it.

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JulianC

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23/04/2021 8:20 am

Sounds a good solution and price Batalto. Good luck. Please plenty of photos before and after

Daikin Altherma 3H HT 12kWh ASHP with Mixergy h/w cylinder; 4kW solar PV with Solic 200 electric diverter; Honda e and Volvo EX30 Ultra Twin Performance electric vehicles with Myenergi Zappi mk1 & Ohme chargers

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Mars

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23/04/2021 8:54 pm

As far as I'm aware, and bivalent system that utilises fossil fuels will need two metres installed. One for electricity consumed and one for heat generated. That's what we had to do, and the equipment/metres cost £500. Then we need to submit these readings to RHI on a quarterly basis. Knowing what we know now, I wish we'd canned the oil boiler because we just never use. I suppose it'll serve a purpose if anything catastrophic happens to the ASHP. Time will tell.

@batalto, your EPC and system sound great and you should be kept very warm. Our new advice to everyone is to look at the emitter guide and consider K3 rads - they have worked unbelievably well in our property and I think they will improve efficiency and cut electricity consumption. But we will have to wait till this winter to really find out. When are you planning to install everything?

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Derek M

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24/04/2021 6:14 pm

Hi Batalto,

Reading your initial post, it sounds like you are hoping to claim the Green Home Grant and the RHI.

If you claim the GHG, which I am not certain is still available, this amount is subtracted from the RHI, so the maximum that you could claim would be £7200.

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batalto

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Topic starter 24/04/2021 8:21 pm

@derek-m yes we are aware of that. However we are only spending £5k so we should be quids in at the end and should also have lower bills. Win, win and win. If the government want people to change heating it needs to be done once all the houses are nicely insulated. Having lower bills is the easiest way forward. Frankly I'd take a fully subsided system over the RHI just because I'm lazy!

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batalto

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Topic starter 24/04/2021 8:24 pm

@editor the ASHP will be in next week and we'll be fully swapped over. Might just get the boiler capped so it's unusable. Can always get it reconnected if something terrible happens. Also might get the battery islanded so it works in case of a power cut.

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Morgan

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25/04/2021 3:27 pm

@batalto

I think you’ll find that as of April 1st 2021 the GHG is no more.

https://www.homebuilding.co.uk/advice/green-homes-grant-what-is-it

Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.
14 x 500w Monocrystalline solar panels.

2 ESS Smile G3 10.1 batteries.
ESS Smile G3 5kw inverter.

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batalto

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Topic starter 25/04/2021 3:42 pm

@morgan we got it before the deadline, applying in Jan. We have until May to use our voucher!

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Morgan

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25/04/2021 3:46 pm

@batalto

Sorry, I didn’t realise.

Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.
14 x 500w Monocrystalline solar panels.

2 ESS Smile G3 10.1 batteries.
ESS Smile G3 5kw inverter.

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batalto

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Topic starter 27/04/2021 4:21 pm

Looks like we'll be delayed for a week. The DNO hasn't got back to my installer. Until they give the all clear we can't have anything put in. Hopefully shouldn't be more than a week delay... Grumble

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