JamesPa

fair point, particularly given my experience referred to above with my gas boiler, albeit down to my stupidity!

Two because the two circuits are totally separate. The reason for the one on the primary circuit is to prevent overpressure due for example to forgetting to turn off the filling loop properly. I actually did that with my old boiler (where the PRV was) isolated. It blew a radiator quite spectacularly, fortunately it didn't blow anything under the floor otherwise it would have been an expensive mistake. If your mains pressure is low then its perhaps less important although a fault in the immersion could conceivably cause boiling in the primary (through heat transfer to coil) so there is (just) a way to get overpressure even with low mains water pressure, albeit very unlikely. If there is one in the heat pump then I cant see you need another.

Indeed. The Ideal R32 range looks suspiciously like Mitsubishi pumps to me, albeit with Ideals own control system. The physical dimensions are a perfect match.

I thought that their R290 products are rebadged Midea, at least thats what the people at Adia told me. I (and they) could be wrong of course! Otherwise agree with everything you say above, check EON tariffs as well as Octopus if you have an EV (and possibly if you dont).

Interesting discussion. Having recently got my heat pump installed, and possessing an EV charged from a 13A socket only, I am in the process of moving from Octopus to EON Next which gives 7 hrs at 6.7p/kWh without any requirement to have a dedicated charger. I don't do that many miles but the negative comments about OVO influenced me away from them and my calculations suggest EON works out cheaper than Cosy or OVO, in the latter case at least in part because of their poor export tarrif. Its also a lot less faff having a block of cheap electricity rather than 3 blocks. If anyone has any tips for 'getting on with' EON I would be grateful, otherwise I will report back in a few weeks.

My 15 year old Worcester Bosch (presumably now in the skip) actually had a WC add on available (I don't and didn't have it). Totally analogue so far as I can tell from the limited information now available!

There are clearly some 'perception' factors at work (we experience the same) which control systems ignore. I do wonder if humidity is one factor at work. If we do some washing and dry it indoors, even though we put the dehumidifier on and the measured house temperature is the same, it feels colder!

Noted. I think its WC that is the game changer in terms of stability, a technology thats been around for decades and is mandatory in some countries. It seems illogical to some, given that its room temperature that matters, but of course its perfectly logical because it means that the control system is ahead of the game rather than always playing catch up and the emitter temperature and hence output is more closely matched to the demand. Its something of an indictment of our heating industry that the technology was shunned in the UK until heat pumps forced it to happen!

For what it's worth my ashp was finally fitted a fortnight ago following a two year long and very painful planning saga. Installer set it up in a mode combining wc and control based on room temperature, all using the heat pumps own system controller with no external controls. After the first week I disabled the room temperature element of the control, and now have it set up on wc only, trvs fully open with heads unscrewed so they can have no effect. The result so far, in my house and with my pump, is a more stable house temperature than with the mode in which the installer left it, and much, much more stable than was ever achieved with my gas boiler operating at fixed flow temp with a thermostat and trvs. I have rads, not ufh with a massive slab BTW. Obviously this is one case only, however its doing what the theory says (and what should be the most cost effective), so it's not really a surprise. I would suggest that those who are sceptical of wc might wish actually to experience it if they haven't already!

Thanks. I was coming to that conclusion myself (and its the general approach I have been preaching for some time - get the WC curve right before you anything more sophisticated). My installer is back today to fit two rads that weren't available when he did the main job last week. I don't want to touch too much while he is still around, but once he is gone I consider it to be open season! That said, I can see why he has set it up the way he has. Most wont bother with or understand the tweaking of WC curves and the way he has set it up will get somewhere close eventually I think, without human intervention.

Reading the expanded mode description I think the controller may ignore energy integral if this mode is active, relying on oat to restart. My installer has also enabled adaptive WC (which requires expanded mode). I guess his thinking is that this will eventually sort out the WC curve, which is probably true!

My boiler, now siting on the driveway waiting to be removed, had a pump anti-seize function doing exactly this. I imagine heat pumps do also. Mine seems to be varying by about 0.2bar around 1.7bar One thing I have noticed is very long cycle times in the mild weather - too long in fact - the heat pump can be off for more than an hour and the house cools by 0.5C in that time which is noticeable. I thought this was governed by the 'energy integral', but it seems that the room temperature mode (inactive/active/expanded) may be dominating the cycling as the compressor doesn't switch on even when the energy integral is as low as -150 degree minutes (I have a suspicion that it comes back on at -180 degree minutes but cant prove it).

I think that maybe a bit strong. Heat geek have a lot to say about rad balancing and they correctly point out that the real objective is to balance for room temperature not deltaT. They aren't the same because the rads won't be perfectly sized. Their comment therefore is not that spend large amounts of time balancing for deltaT on the grounds it's not actually what we want. It's a fair comment imho.

Depends on your heat pump model. Pure WC should be fairly close to fit, adjust and forget, but adjustment may take several weeks or more. If your heat pump features an adaptive WC mode this should be closer with shorter adjustment time. Some heat pumps can be paired with external control eg homely, havenwise or the like. The first is, by repute, fit, forget and enjoy cost optimised operation. The second is a newcomer but can deal with Vaillant heat pumps which homely can't (but then Vaillant heat pumps feature a native adaptive WC mode). What do you have?

That's the cop of hydrogen production by electrolysis. We were discussing hydrogen at the time I thought.

But not a lot more difficult But with a COP of about 0.7 as opposed to a COP of 3 for a heat pump. Excess wind etc should be used to produce hydrogen first and foremost for applications where there is no realistic (and better) alternative, for domestic heating there is. Aside from the cost, there is a real challenge with grid capacity, making it 4 times worse is not going to help. 'Hydrogen ready' boilers are simply greenwashing

Not entirely true, there are some get-out clauses where the 99.6% requirement 'cannot be met'. The installer and the neighbour could reasonably argue that the requirement cannot be met because planning permission for a bigger and louder pump was refused, whereas the one chosen fits within PD rules.

Yes but... generally optimised for cost not carbon, so why should we subsidise it? I cant see how using electricity to create green hydrogen can ever compete cost wise with using electricity to power a heat pump. Hydrogen for domestic heating is, so far as I can see, pure greenwashing. I don't dispute it may have a place in transport though.

Yes it is indeed, but of course the secondary heat source is guaranteed to be more expensive to run than the heat pump, so there is no incentive to use it unless absolutely necessary, and the control is fully integrated to guarantee that. Perhaps this is the only form of hybrid that should receive any public subsidy. On second thoughts, silly me, it doesn't satisfy what I suspect is the industry objective for hybrids, namely to perpetuate the use of fossil fuels. Or am I being cynical?

Quite probably not, depends on make and how it is set up. With a heat pump you have to re-learn how to use heating controls because, stupidly (and unlike many more enlightened countries), the UK didn't implement weather compensation on our boilers, which has increased the running cost of our boilers by about 10% for many, possibly most people (I can explain why). In general dont set the TRVs - see below instead. if you tell us what make your heat pump is we may be able to give more specific help but... Basically you have four options, of which 3 are reasonably efficient and the fourth is definitely not unless you have UFH and are already operating at a low flow temperature, say 30C or less. 1. Operate pure weather compensation: Leave TRVs (or at least most TRVs/TRVs in the main rooms) and any room stat set at least 2C above the desired temperature so they operate as temperature limiters, and the main control is the WC. Balance rads. Adjust WC curve as low as possible consistent with keeping your house warm. Leave alone Trvs will shut down the room where you have the fire. 2. Operate room-sensor-tweaked weather compensation: Leave TRVs (or at least most TRVs/TRVs imn the main rooms) and initially any room stat set at least 2C above the desired temperature so they operate as temperature limiters,. Balance rads. Adjust WC curve more or less as low as possible consistent with keeping your house warm, aiming to get it within a couple of degrees of the 'ideal' (which is scenario 1). Then use one pure on/off room stat or better still the heat pumps internal sensor (but NOT any room stat that attempts to be smart by applying a pulse width modulated signal to the heat pump) to control. This will result in long on cycles and short off cycles when its cold, and will be ~3-6% less efficient than (1) depending on how close the curve is to (10 3. If your heat pump supports it, operate in adaptive/AI/Smart mode (terminology differs - and this feature is NOT available on some heat pumps including Samsung, Midea and several others) Leave TRVs (or at least most TRVs/TRVs in the main rooms) and any room stat set at least 2C above the desired temperature so they operate as temperature limiters, and the main control is the Heat pump. Turn off adaptive mode. Roughly set up a WC curve according to the recipe in (1). Make sure that the bit of your heat pump controller with the temperature sensor (usually the one with the flashy UI) is in a suitable reference room). Turn on adaptive mode 4. Operate at fixed flow temperature using a room stat to turn the heat pump on/off like a (UK) boiler Unless you have UFH and are already operating at say 30C flow temperature, this is 20-30% less efficient than any of the above and may cause flow rate errors if you also have lots of TRVs. Not recommended. Hope that helps, Im sure if you tell us about your heat pump and which of the above you prefer people can give you some guidance. Once you get used to it you will most likely find that the levels of comfort are higher with WC activated. This is because there will be reduced temperature gradients across the room and less up and down of temperature with time. Low temperature heating (which is the essence here and its not specific to heat pumps) is actually more comfortable for most, its unfortunate that our heating industry has been up till now/still is rather backwards compared to many other countries.

Exactly that. Also works a dream with HA. So far so good. Dhw done and system is working on the immersion, no heating today, switch over early tomorrow. Literally a one man 'team' on the install. Only 3 rads to touch which helps of course (I did the majority myself a year ago) and electric feed to breaker was also pre-installed. Someone close by has theirs done last week by a different company, they were without heating for 4 days However they had a lot more rads changed, the installation looks good so I think they are happy. Interestingly this one had 'designed-in' under sizing with backup heater to make up the difference.

Probably The next step is that Elon Musk will be 'autocorrecting' so that it says what he wants you to say.

I have one of Shelleys 16A relays to switch on and off the charger for my EV. It looks and feels like quality and it works a treat. Obviously the product you are looking at is a different one, but if my experience of Shelley is anything to go by I would give it a try.

Agreed But then some plumber will turn up (or there will be some flashy TV or Facebook ad) explaining how fitting Hive (or the like) will mean that they can control the heating remotely and save a fortune, and so they will buy Hive. Perhaps less likely in a rental property, but in an owner-occupier situation the industry has done an absolutely fantastic job of selling us over-hyped 'smart' controllers of various which don't (and cant) save anything like as much as claimed whilst failing to sell us weather compensation for gas boilers which would and which would improve our comfort levels. I'm sorry for my cynicism!

The Government report posted by @JohnMo summarises it thus 'Heating schedule can also drastically alter the share of demand met by the heat pump component, and could account for some of the variation seen in Figure 8-1. A twice a day heating profile has high peaks in heat demand which require high flow temperatures, and must therefore be met by the boiler instead of the heat pump. This reduces the emissions savings of the HHP relative to a gas boiler. For example, Figure 8-2 shows that the annual emissions savings that could be achieved by a HHP installed in 2017 would be 55% under a continuous heating schedule, but only 18% for a twice a day heating schedule. So I dont think the average will be 60%, more like 30% because most will inevitably be set up to be and actually used like boilers. Only if they use them like heat pumps, otherwise not. I fear its an exercise by the fossil industry to perpetuate the use of fossil fuels. In which case there is also no saving in carbon emissions. Why should any contribution at all to such an arrangement be made from taxation? I think I am for 'no grants' for hybrid systems, other than in extremely rare cases, on the simple grounds that the probability that significant carbon reduction is achieved is too low. (Unless the integrated control, as @JohnMo says, can be and is locked to the 'minimise carbon emissions' setting and there are penalties for any installer that changes this). The end game, bear in mind, isn't installing heat pumps its materially reducing carbon emissions! Only if this is achieved is the expenditure of any 'public' (in other words our) funds justified.