JamesPa

That seems logical I'll check this out. MIS 3005-D could be interpreted to require you to insulate the primary feeds (ie take up all the flooring including any solid flooring) if you retain the dhw tank, but not if you replace it, which is perverse. I have asked MCS for clarification, if they confirm the perverse interpretation then... well I'm hoping they dont

If we must pick one thing, it won't be personal transport or housing. I think I would argue that 1. we need each individually to fix our own heating and transport 2. we need each individually to reduce the quantity of goods and services we buy 3. the manufacturers need to reduce the carbon content of the goods and services we sell If we rely on (3) alone we are saying that we have no individual responsibility, which is clearly immoral. its interesting that the emissions from UK goods and services have fallen quite dramatically. Sadly I fear that maybe because less of the goods and services we purchase is UK produced rather than because our industry is especially green, but I cant evidence that at present and would dearly love to be proven wrong..

My experience with my boiler is that running 'low and slow' makes for a more comfortable house because the room temperature variations with time are less as are the thermal gradients. So if you decide to run the heat pump at a constant 55C and accept the loss in efficiency (at 55C constant you will require about 25% more energy input compared to 55C with weather compensation, based on some modelling I did a while ago) then it still might be worth weather compensating the output from the buffer for comfort.

This is getting interesting. We are well into the realms of 'good enough as opposed to perfect' once we talk about operating heat pumps at 55C for domestic heating. Whilst we are at it, why not operate mains pressure DHW as a thermal store at 65 (70C flow temp with PHE or large coil) and avoid G3 and legionella cycles? Or is that one step too far?

The problem with running the CH flow through the DHW cylinder, which I agree seems initially like a good idea, is weather compensation. A friend of mine had to build some (simple) circuitry to fool his weather compensating boiler into upping the flow temp when it was heating the DHW. Fortunately heat pumps natively distinguish, but that alone doesn't solve the problem.

On the general topic of 'good enough' to simplify/de risk/reduce price of installs, I have just suggested to an otherwise cooperative and flexible prospective installer that I keep my existing DHW tank and run the HP at say 65 (or even 70) for heating the DHW (it will be run at 45 for CH). The claimed cop at 65 for the Daikin unit in question is over 2, and DHW is a small proportion of the total consumption. He point blank refused to not replace the DHW tank, on the grounds that he has got into trouble in the past with the BUS people for not doing so. When I interrogated his reasoning he was adamant that it was BUS related. He has already accepted that a pre-plumbed cylinder is not feasible, so his real reason is not that he employs idiot plumbers who cant cope with anything other than a plug together system. I read both the MCS and the BUS legislation and cant find any material reason why what I have suggested is not legitimate. I fully accept its not necessarily 'the best' and may well do a DHW upgrade in the future, but that's not the point Is the installer just giving me a load of BS or does anyone know of a genuine reason that the BUS mandates replacement of the DHW cylinder?

Thats a good point. Personally Im mostly concerned about retrofits (a) because thats my personal situation and (b) because retrofit is the majority need case for Heat Pumps (1.4M per year required - being the number of gas boilers replaced each year, vs 200K new build if you are lucky). But you are of course right in a new build the cost of the supply matters also. James

Definitely. It should be possible to achieve better than 2.5 at 55 check the latest Vaillant specs. I think we need to talk a bit more about dhw also. Replacing existing dhw tanks is an overhead we could do without. With modern high temp heat pumps we can reach a sufficient temp to reuse existing, or worst case splice in a PHE and pump. Is this good enough? Obviously this won't work for a combi retrofit but if we could crack the case where there is already a dhw system it's a good start.

It was always going to happen, because the boiler industry risks extinction (and must become extinct), but as others have said the Heat Pump (installation) industry is complicit. As @JohnMo says, MCS has made it too difficult and too expensive (in a way which protects the installer not the customer), and there is too much focus on optimum efficiency and not enough focus on good enough. Too few system designers have been trained and far too many of those are just grant harvesters, so we end up with over specified, over engineered over priced quotes with too much disruption for most to contemplate, and so much system complexity that the monkeys who install it get it wrong, leading to poor performance. Our planning regulations aren't up to the job and, if my LPA is anything to go by, nor are at least some planning authorities (I did a bit of a web search and mine is not alone in making it inordinately difficult to get express consent). Its not entirely their fault, they have been starved of funds by the governments council tax cap (sorry 'referendum') so cant recruit people with sufficient intelligence and engineering know how to get their heads around new technology. My Green Party run LPA is about to declare a climate emergency, having effectively made it impossible, by imposing unachievable and wholly pointless noise constraints, for me to install a heat pump under express planning consent, both at home and at work. The irony is shocking. All very depressing and, with a government that is asleep at the wheel on almost anything of consequence, unlikely to get better soon. On a slightly positive note I actually received a faintly reasonable (by heat pump standards) quote for an install today. A mere £9800 (after grant) for a not too over-specified Daikin monobloc and UVC, fully supplied and installed. That's way better than many I have so far turned down. The guy who visited is a regular middle aged plumber, decided to get into heat pumps, and has trained with Daikin and Samsung. He was lamenting how MCS has made the task difficult and the officials running the government grants even more so. The only problem I can see with Daikin is that they make it very difficult to find detailed literature (eg a table of capacity and COP by OAT and flow temp, which the guy who visited had but I have yet to find). Nor can I find anything out about their modulation capability (perhaps someone here knows)? I'm hopeful I might get another quote next week as well.

Begs the question, why not just run both dhw and Ch at 55 and use the dhw tank, as you imply, intelligently as a buffer. The volume of a washing machine, subtracting 50mm all round for insulation, is about 170l which should be plenty of dhw/buffer if people could get used to showering for a sensible amount of time.

You and I know that. The Daily Mail and the Torygraph probably also know that, but it doesn't suit them to tell people. Nor does it suit most politicians. And many if not most are happy to put their head in the sand if it saves them a few pounds. Like it or not price at the point of delivery does matter.

I agree but...for many it's about price. Particularly for those who campaign against change.

First point noted and the route I'm still trying to take. Second point (mortgages), you are surely kidding. No I guess you aren't. This should be outlawed immediately.

I just checked the current gas and electricity prices (average). Gas is now 7.5p and electricity 30.1p so somehow what was, prior to the energy crisis, a 3:1 ratio between the prices has become 4:1. Not sure if thats a seasonal effect, obviously the demand for gas increases in winter disproportionately to the demand for electricity. However its (hopefully temporary) bad news for heat pumps, at 4:1 most retrofits wont achieve cost parity. the EU average ratio remains about 3 (10c vs 26c) figures from Eurostat; how did the government get us to this point?

Yup, good enough is good enough. Better is still better, but can be sold as a business case led upgrade. They already can. Check out the Vaillant R290 units - flow temp goes to 75C. One wouldn't necessarily design for this, its almost certainly preferable is to retrofit a PHE to the existing cylinder to increase the 'coil' area without having to rip out the cylinder yet still allow the flow temp to be 55/60. The technology for mass retrofit is here now; we need fit-for-purpose regulation (or better still scrap MCS altogether) fit for purpose planning rules (PD requires MCS and excludes most if not all 2-fan units. MCS-rules-based over sizing drives installs for larger retrofits to a 2 fan unit, LPAs then object to the noise even though it meets the PD noise rules so legal install becomes impossible or impossibly difficult a fit for purpose system design industry By the time the UK has those, the technology will have advanced even further, perhaps to the point where our under-educated construction industry can cope with it without completely messing it up. There are no excuses left, its all within UK control.

Would this work, I thought that the pressure differential across a PHW was quite high?

The latest version of part L makes it mandatory to size for 55C. I guess that won't change again for a few years. The latest R290 heat pumps (eg Vaillant) have a scop of between 3 and 3.6 at 55C (the larger ones have a higher scop). SCOP=3 makes it about the same cost as gas even at todays gas/electricity price ratio, so is good enough. Put a 5 or 7kW Vaillant in a new house insulated to modern standards and you are good to go in most cases I would think. Possibly you need a small volumiser, (not a 4 port buffer, because its bound to be connected wrongly and/or undersized) if the house is small or particularly well insulated. Bear in mind most new houses are built to standard designs so it's not that difficult to get it right if you can be bothered. It's all doable now. But builders won't do it until they are forced to do so. Obviously this is an urgent must-do, but by far the majority of our housing stock is the more difficult retrofit job. Here we need to sort out the regulation, and in particular MCS and planning rules, and the system design industry (part of installation if you will, but actually there are plenty of competent plumbers and electricians around, just not many people who can do a practical system design for retrofit). This industry barely exists in any competent form, albeit that there is a flourishing grant harvesting industry.

Absolutely 100%. Lets hope the decision sticks and we can, as you say, stop wasting time.

Just rescale after importing, using whatever known measurement is available.

Too complex I fear. The expectation is that thing just magically work. Alternatively we could invest in properly educating our population. Unfortunately that would mean that certain unscrupulous, self interested, politicians, supported by their friends in the gutter press, couldn't convince large numbers of people to vote for fantasy concepts which damage the lives of those voting for them to benefit the interests of a small minority. Education education education.

I have seen several second hand models on eBay!

Mine is on hold at my request while I go through all the design options with two prospective installers. I'm not optimistic though, they seem determined to insist on 27dB(A) at the most affected assessment point which is nigh on unachievable unless I put it 20m down the garden at a trenching cost of 3-5k. Political pressure on the ruling green party has so far failed, their exec member in charge of planning takes the view that greening up should be permitted subject to the condition that it doesn't inconvenience anyone at all, particularly someone like her 'a keen gardener'. Mine is equally picky about plans. I created mine by downloading (from the LPA website) and modifying plans of the neighbours extensions and a survey of my house I had done. Libre office draw is remarkably good at importing and has quite powerful drawing tools. It's no CAD package but it works.

Units with R290 refrigerant have restrictions because it's heavier than air and flammable. They will be detailed in the instructions, suggest you check them.

Hopefully, but Im not counting chickens yet.

My vote, based a bit on logic and a bit on gut feel, is still for recirculation with a PHE instead of a cylinder coil. Hopefully I will get to try that soon.