JamesPa

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.

How much of that do you believe will actually happen. Liability will stop meaningful reuse of anything and installers will pocket the grant. We only have to look at what's currently happening to get a flavour of what can, and so probably will, go wrong. Don't misunderstand, I see the argument in principle, but sadly I genuinely can't imagine it being properly implemented in the UK given the starting point (high temperature heating with no wc), the poor level of public understanding and an industry which certainly has many good people but also, sadly, a load of chancers who exist solely to harvest grants. Perhaps any grant should be available to self-installers only!

Thanks for posting the report which I will read in full. I skipped to the conclusions and this one struck me as particularly poignant '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. Obviously the industry will sell the hybrid as being just like a gas boiler, so people will operate it that way, more or less negating the savings! I fear that the government may be suckered into this by the industry desperate to continue selling gas boilers at any cost to the environment. If they can somehow get it right so that the fears I and others express above aren't realised, then great. I had read, but have not verified, that some other countries do this, but then other countries have had weather compensation for decades unlike our backward approach! However if they cant its another nail in the environmental coffin.

I think the other probable gotcha, based on what we currently see in the market as reported here, is that installers are unlikely to do what you suggest. They will want to sell a 'hybrid system' complete from a manufacturer. Bear in mind we are talking about an industry that, as a matter of course oversizes heat pumps and sells us buffer tanks and low loss headers that compromise system performance. I fear that yesterday's Telegraph article headline 'Now David Miliband wants us to install a boiler and a heat pump' (or something very similar) actually got it right, albeit for all the wrong reasons. As I say I think the principle is likely OK in some circumstances, I just don't see how our installation industry is going to do a good job given their (lets face it pretty poor) track record and fear it will become just another delaying tactic.

What makes you say that? Zero need to switch to boiler until it hits about 3 degs. How many days a year do you get below that? Depends on how it is set up! Since the introduction of condensing boilers the industry has ignored the fact that, to work as designed, they need to be set up with a sufficiently low return temperature that they actually condense. Why? Because its easy for the installer to whack it up to max and leave TRVs to sort the mess out. Any guess what will happen with hybrid systems? My bet is on installing the cheapest possible heat pump with the most rubbish possible controls, a buffer tank to provide hydronic separation/poor performance, and setting it up so the boiler does most of the work then pocketing any grant available. Furthermore those of us who have gone for a heat pump risk losing out because the political incentive to fax the electricity/gas price ratio will be reduced. From a purely technical point of view in some circumstances I tend to think its not a wholly bad idea, my concern is the practice.

If your installer wont accept the figures, find another installer. It appears that there are now some MCS installers out there who will do sensible things with heat loss, whilst still conforming to the letter of the MCS requirement. If a 6kW unit is what you need, you really don't want a 16kW one and even less do you want two units with the (almost) inevitable complex (and very probably highly inefficient) plumbing system that will accompany this arrangement.

That's my guess, but it would be good for the industry to confirm or not. Maybe wind effects eg are such that a multiple RC model only is sufficient.

Thanks. Is anyone doing any work on it. It's surely much less complex than weather forecasting but arguably at least as important. Isn't that what BRE is for?

Thanks. I was thinking beyond steady state heat loss, which could, more or less, be measured. I was thinking about the dynamic effects (eg what happens when the conditions, eg oat or iat, change). I was also thinking about retrofit of older houses with composite constructions, not just new ones. Is any of this understood, even roughly? This is a serious question. I vividly remember a friend of mine embarking on a PhD, sponsored by the met office, to study the air flow over one isolated conical hill, followed up by a study of the air flow over two conical hills. That was 40 years ago and, crude though it is, I suspect it's contributed to the fact that weather forecasting has advanced dramatically since then, albeit that it's still not perfect. Weather forecasting is also a situation where the physics is well understood but the dynamics are complex (albeit much more complex than domestic heating). Are we at the 'conical hill' stage in understanding thermal dynamics in houses, or are we further forward? This isn't a trick question or a value judgement, just a genuine curiosity about how deep (or shallow)or understanding of houses is.

That's good to know thanks. Obviously it's not cost effective to theorise/model each house individually, but is there any prospect that the behaviour of several broad classes of house could be described in a way that moves us forward for the purposes of understanding our heating? Also is there any prospect that those who could model their individual house (which I suspect includes almost any electrical engineer who has used some flavour of SPICE - which I would have guessed is a good modelling tool for the purpose) could get some insight from those who do understand houses on how to do so?