JamesPa

Probably best not to do that. Many heat pumps (it is said) want to be exactly horizontal to balance the fan bearings. I certainly wouldn't tilt the pump without asking the manufacturer if its OK.

probably not, just use the immersion or fit a phe & pump as suggested by @JohnMo

One thing to add to the above. If your heating load at OAT 10 is only 750W, then your house loss at -2C is nowhere near the 8kW+ that the Vaillant 7 is capable of at -2/45C. Probably more like 3-4kW. You could very likely have got away with the next size down. This might have given a bit better COP at mild OAT. However with an electricity consumption of only 250W the other factors would still be significant, so perhaps not!

That's an interesting observation. Looking at OPs figures eg 12Oct total energy consumption 6kWh, which is only just over 250W. 7th Oct was half that. At this level water pumps, control electronics, trace heaters etc all start to matter. Looked at this way its not surprising that high loss houses get better COP, at least when it's mild. I guess the supplementary question is, how much does it matter. If your house is warm for 250W input that's a good result in many ways, perhaps there is a point where chasing COP becomes a bit academic. The better approach might be to look elsewhere to reduce the electricity baseload (which is typically ~250-400W). This will push up heat pump load but at a cop of 3+ rather than 1 (I'm assuming that all or most electricity consumed in the house eventually appears as heat, which I would think is highly likely).

Its good to see somebody is now offering this as a kit, which sort of brings the option a bit more mainstream.

By 'wiring box' I mean one of those typical central heating 'wiring centres' that many use to do all the interconnections between thermostat, valves, call for heat for the boiler etc. Not necessary so far as I can see for the Vaillant, or indeed most ashps, as almost all wires go back to the ashp control, unless you are doing something silly with external controls (which I'm not). Yes the ac isolator is fitted and wired already. Actually a 32 A one with a 6mm feed (but a 16A MCB) just in case it needs to be upgraded in future. I put the cable in, sparky fitted the isolator and connected to the cu. They are. The current boiler is run off the ring main. I'd ideally prefer to have it separate as we do get the occasional nuisance trip, but not worth the effort until I replace the cu for some other reason.

BTW I recall you too were trying to avoid replacing the HW cylinder. Should be easier for you with a smaller HP. How has that worked out? I could have avoided replacing the DHW cylinder (one installer, still in the frame, was willing to work with existing), but I eventually decided to replace. TBH I'm fed up of the two pumps I have to boost the DHW pressure (particularly galling since my mains pressure is about 9bar) and the mess of pipework in the airing cupboard, plus I finally found a do-able way for the D2 vent (which is the key issue). So it will go UVC. Still TBD whether its a 'Heat pump' UVC or a 'direct' UVC with a PHE on the side - that depends who wins the job which I'm (hopefully) sorting out with final questions at present. I'm pretty sure plumbers connect these up if they choose to, and I'm pretty sure there is no regulation that says it has to be an electrician, its just connecting to an existing circuit via the 'wiring box'. But then again that's why I still think an electrician may turn up and disagree with the signed-off installation. However if the installer has in fact budgeted for a day of electrician time, its not going to take more than a couple of hours to splice a small CU into the current circuit that my electrician was perfectly happy with, so its hardly a disaster if that does happen. No (because I didn't ask him to) and No. There is a switched fused spur and typical heating wiring where all the electronics will be, and the one installer that specified what he wants didn't specify any sockets, because he presumably reckoned he could connect to what was there. That said, thanks for the tip-off, I might just put a double socket on the end of the fused spur before anyone turns up😀 its a wonder anyone ever gets a heat pump installed given how difficult the industry manages to make it.

Interesting The two candidate installers have both said that so long as mine has been signed off by an electrician they are happy. However I can easily see that changing when they get on site if their electrician (assuming they bring one - I dont think there is now anything to do for which an electrician is mandatory, circuits are all in place its just a case of making a connection) looks into it in that much detail.

Thanks for posting this and I'm pleased to hear it mostly went well. Do you have any control at all over dhw. Is that regulation or technical. My electrician (not connected to the hp installers, a separate bit of prep) has just provided an MCB and no RCD because he couldn't find an RCD to fit my cu (which is an older model where some of the circuits are just on mcbs not RCDs) and didn't consider it worth upgrading or necessary to do so. My suspicion is that he may strictly be right but perhaps I would have preferred an RCD in a separate cu for maximum safety.

I can't decide whether I violently agree or violently disagree. It's clear that, as we electrify, there are real opportunities (and a need) for grid demand management which probably are best managed centrally not locally, and equally clear that the new infrastructure costs, which ultimately we all have to bear, will be enormous if we don't manage demand. On the other hand, like you, I value independence. My considered view is that we need infrastructure build out and demand management that acts solely in the public interest, not commercial interest. But we also need the option to opt out of demand management. However if you do opt out of demand management then you should bear the full cost including making a significant personal contribution to the infrastructure in addition to any contribution through tax. That will translate to very high electricity charges if you don't want demand management, but so be it. With a bit of luck that should focus minds on what matters individually in a way that doesn't prejudice choices others may wish to make

Thanks for the explanation. I cant find a business case for batteries, at least for me, and the power round here only fails rarely for short periods. So if a battery doesn't help the environment then there is absolutely no reason to have one. Thats why its so important to understand if it actually helps the environment, as some people claim If I understand you correctly, your conclusion is that local storage, where the choice to store or not is based essentially on retail price, is currently (and wont be for perhaps a decade) of benefit to the environment, and in fact is probably harmful. Is it possible to envisage a chart that demonstrates this simply without going through all the arguments?

Sorry to be dense, but I'm still not seeing how to interpret that to work out if retail price and carbon intensity correlate or not

So far as I can see its going to work with a gas boiler, as would a conventional thermal store (which also doesn't need G3). The reason UVCs are preferred for ASHPs over thermal stores are that, for any given stored water temperature/volume combination, you will get much more DHW from a UVC. With an ASHP you want to keep the flow temperature (and thus the stored water temperature) low, so a UVC is the obvious way to go. Gas boilers are typically run at a higher FT (although in fact also perform better if run at FT of 55 or less), so a thermal store becomes a more realistic possibility. In performance terms the Heat geek mini cylinder is a bit 'in between'. Because it has a large coil the temp difference between the stored water and the output DHW is less (so you get more DHW than with a typical thermal store that has a smaller coil). Furthermore there is no temperature difference between flow and 'stored' water, because the 'stored' water is actual water from the central heating system. Yet more it is designed to be used with real time re-heat (so again you get more DHW than with a thermal store). None of this is enough to make its yield of DHW equal to a UVC of the same size run at the same temperature (unless the DHW is run off slowly) but it still gives a better DHW yield than a conventional thermal store for the window of parameters it is designed to work in. Dont assume however that its a drop in replacement for an existing cylinder, you may have to play with the system controls a bit.

Excellent plots thanks, can you tell us what conclusions you reach from this in relation to price and carbon intensity (these are wholesale prices I presume, Im guessing agile follows wholesale prices).

If that's the case for you then I grant a battery may help. However most people reputedly use a battery to minimise cost and, in the absence of a good correlation between cost and carbon intensity then that's not the same as minimising carbon. We could really do with some solid information on this, nothing would please me more than to find evidence that domestic batteries do minimise carbon as it would make the case for me to simplify my energy management! That said it may well be that consumer batteries are needed to reduce the infrastructure costs of a decarbonised grid to acceptable levels. Without a doubt electrification places strains on the grid which will require expensive infrastructure upgrades. These can be mitigated in part by load management. Whether we need batteries to do this or alternatively the combination of the management of car charging and using houses to store heat energy by managing heat pumps, I don't know. I'm not even sure that the industry has yet reached a position on this. My understanding is that, until recently, they were focussed on grid reinforcement (at our considerable expense) not demand management. I also understand that this may change now that NESO has been brought into public ownership.

If they had batteries and solar then yes, on days it's sunny. But unless there is no local real time use for excess PV generated, the batteries aren't helping. This will likely occur when we have a lot more PV than we currently do, but at present there can't be many places in the UK where that is the case (we will know when we start getting charged for export not paid). In the absence of PV saturation and unless price and carbon intensity correlate, or they specifically charge and discharge their batteries to minimise carbon intensity not cost, then probably not.

How far back in time have you looked? I plotted UK carbon intensity Vs east of England agile price for Oct 2023 - sept 2024. I then repeated the exercise with carbon intensity as a percentage of average carbon intensity on the same day, which I think is a metric more relevant to batteries. In both cases there was a weak positive correlation (r squared =0.2). Visually they look close to uncorrelated. I couldn't download regional carbon intensity for more than a day at a time, which is why I used UK figures. I would be delighted to be proven wrong. Others may have more information.

Actually I have a feeling that the problem in the UK may be absence of regs. When I did a bit of research a few months ago, it seemed pretty conclusive that there were no regs and the current situation arises from risk aversion by the manufacturers. I may be wrong of course but if I'm not then the introduction of regs may be necessary to deal with the problem you identify. The problem isn't helped by the conventional drawings that appear in most manufacturers instructions, which don't make it clear that it's ok (afaik) to put an r290 heat pump underneath a window. Some installers seem to interpret the regs as prohibiting this. Samsung (I think it's Samsung) have a variant of the most commonly seen diagram that makes it clear that the exclusion zone does not extend above the case of the unit.

Sorry but the battery doesn't help carbon emissions. If excess generation is exported instead of being used by you then others on your street 'cause' less carbon emissions as a result of a proportion of 'their' electricity coming from your PV rather than a power station. The global (and even local) outcome is (more or less) the same with or without a battery. The only carbon benefit would be if you can store in a battery and use at times when carbon intensity is higher (in lieu of import). So far as I am aware batteries don't yet respond to the carbon intensity of the grid, they respond to price which does not appear to be a good proxy for carbon intensity (unless someone can show that carbon intensity and price are well correlated which hasn't occurred to date).

..and the European Commission is proposing a ban from 2027 on refrigerants with gwp >150 in split systems, which includes R32. I am not sure if the ban extends to monoblocs, but which manufacturer wants two different designs unnecessarily. It looks like it's on its way out. They will imho need to get more realistic about the 'exclusion zone' for R290. I still don't understand why I can have 13 kg of propane more or less inside a boat or caravan, but < 2kg outside a house is considered a serious hazard.

Your are right to consider PV as (more or less) carbon neutral. However I think you are wrong to conclude that this means that the battery helps reduce carbon emissions: If you generate 1kWh of PV and use it yourself at the same time (ie without a battery) then that's 1kWh less that the grid must supply and therefore the carbon associated with 1kWh is 'saved'. If you generate 1kWh of PV and use it yourself wholly or partly after storing it in a battery then that's (with a little loss) 1kWh less that the grid must supply and therefore the carbon associated with 1kWh is 'saved'. If you generate 1kWh of PV and export it (whether or not you are paid) then it will be used by your near neighbours and that's (with a little loss) 1kWh less that the grid must supply and therefore the carbon associated with 1kWh is 'saved'. This is the case until the local solar density is so high that all of the local load is satisfied, which, just by casual observation of rooftops, is a long way off in most places in the UK The carbon reduction is due to the PV not the battery, and the battery doesn't make a material difference, its the PV that matters. So this is emphatically not (at present) an argument for the environmental benefit of batteries. Absolutely and I think its the future. This will reduce the scale by which the grid capacity needs to be increased (saving shedloads of money) and indirectly save carbon emissions. The later is because of the embodied carbon in the infrastructure that will not need to be built as a result of using a resource that was going to be created anyway (the car) to do two jobs not one.

I agree carbon neutrality is important, but how are you saying a battery becomes carbon neutral. You seem to be linking it to solar and I confess I don't understand the linkage, unless for some reason you can't export any excess solar generation you may have to the grid and so, in the absence of a battery, it is wasted.

So it does. I probably was thinking that I couldn't easily apportion between the various rates given that they are somewhat interleaved, although the probability of Solar displacing consumption in the peak rate period is relatively low. In reality a better model might be 50% exported (at 15p) and the rest apportioned. If I plug that in Cosy without battery becomes about £90 less attractive.

I expect you will be offered a half hour slot with Henri, which is where I got my info from. They are taking customers now.

er Im now confused, isnt that what I have (in the first model, which is the only one that uses these numbers) or am I going mad?