So, the government has included air-air heat pumps in the BUS (see https://www.gov.uk/government/news/discounts-for-families-to-keep-warm-in-winter-and-cool-in-summer ), which has set me thinking about them again. Does anybody have any ideas about whether this will decrease or increase prices, and when. Or how to find a competent and trustworthy installer? (in Suffolk if it matters) And about any specific products?

PS They've also included subsidies for 'heat batteries', but since heat batteries are now more expensive than electrical batteries for the same capacity, it seems like another poorly thought-out scheme!

Posted By: Doubting_ThomasNowadays for DHW I guess you'd pair the battery with a heat pump to get more out of it?

If I was going for an "ASHP" then yes, but if I'm going for air-air I'm tempted to leave the thermal store and immersion heaters in place; at least for now.

We put some extra insulation around the thermal store, and being next to an MVHR extract vent with the MVHR having automatic summer bypass, the heat loss hasn't been a problem for us.

Posted By: owlmanHow is your thermal store currently heated.

Two immersion heaters. One at the bottom powered by a solar diverter. One half-way up controlled by a timeswitch. The lower one is set to a higher temperature.

During the summer and most of spring and autumn, solar gives us all our hot water. Off-peak mains tops it up at other times of year.

Posted By: owlmanThat sounds fairly similar to my accumulator tank although mine has a spare internal coil too.
Does yours supply both space heating and DHW? Does it have an internal coil?

Our space heating is presently all direct electric. No wet heating at all. There're no internal coils AFAIK. DHW is produced by an external PHE.

IIRC the BUS grant eligibility for air-water heatpumps is they must provide 100% of the space heating load of the home (as calculated by the dubious MCS method) AND they must provide 100% of the hot water. This was to stop people claiming the grant, installing a token-sized heatpump, then retaining/using a non heatpump system in parallel.

The consultation for adding air-air heatpumps to BUS had a line where they noted that air-air heatpumps generally can't do hot water and so this requirement would need to be changed. They wanted suggestions how to change it.

They also said they won't fund dedicated air-to-DHW pumps, such as the integrated heatpump cylinders that come up occasionally.

Edit: the consultation has closed and the government response is
"To be eligible for BUS funding, AAHPs will
need to be installed to provide space heating. They will also need to be MCS certified
products, as well as meeting ecodesign requirements for heating and cooling. We will allow
AAHPs to be installed alongside other electric appliances that provide supplementary space or
water heating.
To ensure AAHP installations maximise potential carbon emission savings, AAHPs installed
alongside existing fossil fuel heating appliances will not be eligible for funding"

Home batteries are available from a number of different suppliers, ours is Givenergy's All In One but we had quotes with prices for other companies that did not line the pockets of Elon Musk.

Sunamp do a phase-change solid battery thermal store https://acarchitects.biz/self-build-blog/self-build-blog-sunamp-heat-batteries

Posted By: ChrisGTI've just had a quote for £1350 for a 2.5kw air to air HP for my passivhaus retrofit. I don't have much room for a cylinder so am tempted just to combine it with instantaneous water heating. Is this sensible?

I think it might be. It depends on how much hot water you use, and also whether you have solar panels and suchlike.

Who's the quote from, if you don't mind my asking, and which heat pump?

Interested how fast can these home batteries be discharged? Looked a while ago and a 10kWh battery could discharge at about 0.5C = 5kW, which was useless for instant hot water for a shower or bath.

Seemed then that the advantage of a hot water cylinder over an electric battery and instant heater, was rapid hot water delivery, difficult to fully electrify homes without this. Larger sunamps are also good for instant hot water at shower flow rates.

In principle an electric battery could discharge at high enough kW rate, like in an electric car, but that might need a bigger battery and/or battery coolant systems.

What's the current state of art?

(Sorry if this is sidetracked thread)

Hi DJH its a Haier AS25RBAHRA4
2.7kwh R32 wall mounted unit.
We use about 1100kwh/pa for hw.
For heating we use about 550kwh pa. We don't mind if the temp drops a bit in winter and find the oven will heat the house.
.

If you had enough electric batteries to enable instant water heating instead of hot water storage (let's say 10kW to drive an electric shower), would you need a 10kW G99 cert from the DNO in case it was diverted to export? Or do they come certified to do export limiting?

Posted By: WillInAberdeenIf you had enough electric batteries to enable instant water heating instead of hot water storage (let's say 10kW to drive an electric shower), would you need a 10kW G99 cert from the DNO in case it was diverted to export? Or do they come certified to do export limiting?

Dunno; good question. I'll add it to my list of things to ask the installer who's quoting.

Consider too battery system siting, as connections between Inverter and CU can get onerous.

Posted By: GarethCthe big battery, charged with cheap, green off peak leccy ... would deliver super cheap, super green heat?

would cost far more to run than a heat pump.

Ah. Gd thought - what do our boffins say about running a HP on off-peak stored elec? Off-peak's not all that cheap, the batts would cost a lot (but getting cheaper?), maybe spend their cost on fabric retrofit, save more elect consumption that way than the off-peak saving; and/or spend it on ASHP-system optimisation for example UFH if not already, for consumption saving via maximal COP.

Posted By: djhif I decide to go for one

Hasn't your house already got its heating system? - or re-doing it just for fun?

Posted By: djhNo way is wet heating economical

Now you tell us - we're listening.