JamesPa

I have never understood how Cosy is a good fit to a heat pump unless you also have a battery. Sure you get cheap leccy for a few hours per day, but at relatively poor COP because you are trying to get the same amount of energy into the UFH in one third of the time, so have to jack up the flow temperature (49C for UFH apparently, I'm running at only 43 on radiators). Obviously you also need a heat pump which is a factor of 3 oversized. However, that notwithstanding (almost) everything above, is also true. Its very cold at present so consumptio9n is at its max, (as it would be with any heating but who monitors gas or oil daily?) If you have only just switched it on you have got a lot of making up to do. It might be best to just monitor it for a few weeks and see how its averaging. Also consider whether cosy plus jacked up flow temp is more cost effective than a different tariff plus running the UFH at a more typical 30-35C flow temp. What COP is your heat pump reporting?

Thanks everyone, great discussion. Lets leave aside the financial for a moment (I accept its a sound argument but its another dimension which different people will view differently). Lets just consider the physics and what the urban plumber said. He said that (in round numbers), for a room at 20C, its DT 10 to the floor (because the soil is at say 10C), and DT20 to the room (because the outside air is at 0C). But for the walls and ceiling its the internal air that is in contact with the cold elements whereas in a floor with UFH its heated pipework that is in contact with the cold elements. So it may be DT from room to soil but its DT20-25 from pipework to soil, and that's what matters because that is where the heat is lost from. He also said he has no evidence to support his assertions and 'gets good scop'. Well yes, you can get good scop with a house that consumes 10kW or with a house that consumes 3kW, the SCOP is not dependent on the loss, its dependent on the flow temperature. Im not saying he is wrong, but he admits he has no evidence to prove it and some of his arguments do appear to be wrong. There has to be a thermal gradient from the pipe temperature of 30-35 to the soil temperature of 10, and heat will continue to fall down that gradient. So I accept its a thermal buffer but it is a lossy buffer, same as a river, the river level stays constant but water still pours out of the estuary and has to be replenished at the source. Not convinced, I wonder if anyone has actually modelled this?

This is just mad right? Or is there some part of the physics I don't yet understand which means that its somehow sensible? Just checking, I don't have it nor do I plan to, but I have been asked and want to check whether my immediate reaction is right or not.

Its very cold at present, this is the time it will be at its most expensive (roughly double what you might normally see most of the season), Dont forget to factor that in! With a cost of £6 presumably about 24kWh? - difficult to tell as you are apparently on agile (do you have a battery? If not agile might not be the best tarrif) For comparison Im currently consuming about 28kWh/day in a house with a loss of 7kW @ -2 and on the few days when its consistently sub zero I can consume as much as 50kW. The heating is still cheaper and more comfortable than the gas boiler it replaced was, so Im not complaining! You seem to have your WC set to 49@-2 and 39@20. Does it need to be that high (answer no, certainly at the high OAT end)? Are you operating 24x7 with WC adjusted and zones balanced, thermostats/trvs set to max so they have no effect or alternatively 2C above desired so they act as limiters? Tell us a bit more and someone may be able to give some specific suggestions.

Now you are expecting people to take responsibility for their own actions. How dare you, don't you realise that everything is the fault of the Government/the Council, the EU/immigrants/whatever other target for hate somebody chooses to invent. If course there definitely are people who can afford neither home improvements nor 'expensive holidays and weddings'. Assuming that they are trying to improve things for themselves then they deserve help with improvements to make their houses more efficient IMHO. Here are some stats from ABTA. Nearly 60% of people in the UK (according to ABTA) take one or more foreign holidays in any given year (allowing for Covid recovery).

I run the numbers for batteries at least every 3 months and can never quite get it to work out after accounting for cost of capital (even if I allow for tax on savings). I want them to and its close, but they don't for me. A decent nighttime tarrif, doing washing and charging ev overnight, and running the heat pump 24x7 without setback still works out the best bet. Drop the price by 20% and it changes, but the installers don't drop the prices. Even factoring in arbitrage doesn't tip the balance.

There have been a couple of posts recently about recirculating loop DHW. I dont have it and thought it was confined to hotels etc, but it appears not, so I'm intrigued. The issue seems to be one of control. If you have the pump on continuously you drain the heat out of the DHW. In summer this adds unnecessary heat to the building, in winter the lost heat goes towards heating the building, but at a lower efficiency particularly if you have ASHP. Some people seem to put the pump on timer, I have seen one who puts the pump on manual switches and then waits for the water to come through before turning on the tap (thus saving the water from going down the drain) but I cant see how thats going to work with teenagers. One could imagine a smart tap which, when you switch it on, starts the pump but then only opens when the water comes through hot. However you dont get the 'instant hot water' that surely is the main attraction, it needs a mind reading tap to do this. Overall it feels to me like a bit of a dogs breakfast in a domestic scenario. Has anyone got the perfect control strategy and if not, what control strategy do you use? Is this a technology looking for a problem?

Who says you would even fit it? If you are allowed to retain your existing system then all that needs to happen is that the new unit is delivered to your house. Then you can sell it on and, unless there are backup checks, nobody is the wiser. And dont imagine that the removal (if it were fitted) would conform to f-gas regulations, snip the pipework, allow the gas to escape, unscrew 4 screws, bit of polyfilla, job done nothing spent. Sell it wholesale, abroad or wherever, there is always a market! Im assuming, I accept, that people are crooked, but the fact is that a proportion are! We have almost the whole political class running round like headless chickens over only a few 10s of thousand of illegal migrants shipped around in deadly conditions by a bunch of crooks to evidence that!

Hmm Not sure about grants if old system is left in place. Obvious thing to do is take the grant, get the system fitted, then sell it almost new. Perfect opportunity for both organised crime and small time scammers. It would certainly need rigorous follow up and significant easy to apply penalties to be even reasonably proof against the slime bags in our society.

SOFAIK its just a change to index linking to CPI (instead of RPI). FIT contracts are contracts and the Government cant change them (or any other contract) unless they were to pass specific legislation to do so (or the counterparty agrees). They are most unlikely to do this because undermining the reliability of government contracts would crash the economy. The video says its happening quietly, which couldn't possibly be the case if legislation were being passed. So they will only do what the people who receive the FITS signed up for! I believe the contracts said 'inflation', thus leaving open which measure of inflation. If the beneficiaries didn't like the ambiguity at the time, they didn't have to sign up! But guess what, they did, because it was so lucrative! Like @johnmo my heart bleeds (full disclosure I do get FIT albeit only at about 25p, jumped too late!). Sorry but the graphic is just demonising for unjustified and unjustifiable political or commercial gain.

Yet half the installers can't manage it. The they should be compelled to go back to school as a condition of continuing practice, or confined to pipe bending and soldering duties only under the direct supervision of someone who can manage it (and have their pay adjusted accordingly). The physics is mostly the same whether its a heat pump or a boiler, and a basic understanding is essential to efficient system design and maintenance and to giving professional advice to customers. In many jobs CPD is compulsory, but seemingly not in the construction industry. Why do we tolerate this level of ignorance?

That was my initial reaction but, with the right management, they may be a sensible solution for small properties/flats where a heat pump isnt a practical solution. Im thinking dense newbuild flats, which probably have a demand sub 2kW. Our electricity is already on average lower carbon per kWh than gas and that can only get better still, if heat batteries are filled so far as possible when the grid is greenest then not such a silly idea. So I wouldn't rule out the possibility that they have a niche role to play.

Not any more they don't if you want them to be efficient You mean unlike condensing boilers that are set up so they rarely if ever condense, which so far as I can tell is common practice. My plumber, when he visited to do the last annual service before it was superseded by and ASHP, had the cheek to reset the flow temp to 75C (without telling me) even though I had deliberately turned it down to 50C. We have a long way to go it seems in terms of CPD or am I missing something?

Having a heat pump is a disadvantage. Primarily because of cost, secondly, finding someone who can do it properly, and, to a much lesser degree, reliance on the grid being available, which for most is a non issue, but a small issue for me. Given, as per my ramblings elsewhere, i end up with a bigger generator, that problem goes away. The eco4 scheme, assuming i qualified, would fund the HP, solar and insulationl at no cost to me at all. Im sure you can appreciate, that fundamentally changes things. OK. If I understand you correctly you may fit a heat pump if (because?) its paid for by the taxpayer, even though you believe it may cause you hassle and don't believe there will be any comfort or running cost benefits and also mention above several other features that you consider are disadvantages. That, particularly given the strength with which you express above your views on the disadvantages, is probably why I'm confused. Furthermore I don't really know how to respond to this position (other than to pity any contractor who gets involved) so I wont comment further on this particular matter.

Yeah but a car is very high loss, small and has thermal characteristics known to the designer of the heating. Houses are none of these, so the problem is much more difficult. I agree but...I spoke to the clearly knowledgeable guy from Hive at the most recent installer show. They had a go, but gave up, not because its impossible but because the interfaces are all different and not guaranteed to stay constant, so it wasn't commercially viable for them. Thats not difficult to understand. We need an EU regulation to force an open interface to the basic parameters. I believe there is talk of same, but no date or certainty it will happen. I agree, and not. An uneducated population is a gift to a poor installer, a scammer, a would be despot, and any of the other disgusting slime that humanity throws up. I can see no reason why people need to understand the physics of how their heating systems work, but even the most basic understanding of a few key concepts would surely be beneficial. For WC it amounts to, when its cold outside radiators will feel warm, when its warm outside they will feel cooler, there is some clever technology that makes that happen and the result is a more stable house temperature and lower running costs.

I believe Havenwise offers exactly that for £50 per year (other heat pump optimisation services are available). Even without Havenwise, all you have to do on my heat pump to adjust the WC is turn a (digital) dial up if the house is too cold, or down if its too warm. Not exactly rocket science! Changing the set room temp actually shifts the WC curve behind the scenes, the user doesn't need to know that if they don't want to so once again, hardly a difficult concept!

Not all sadly, far too many just throw in plastic push fit elbows.

Well perhaps your posts have succeeded in confusing me. So far as I can tell from what you have said above you see no advantage in having a heat pump, only disadvantage. Yet you have/are investigating getting one? I can only apologise for my confusion.

They dont need a physics degree to turn a single temperature dial up or down, which is the control on mine. Not that it needs changing often, just leave it alone and it does its thing. I don't have or need batteries, the business case doesn't stack up for me and there is no environmental benefit so far as I can tell. There would be a convenience benefit so, when prices come down a bit I may, but not yet. Which is fine, nobody here is trying to sell you a heating system. Like most things, including boilers, they have some good points and some not so good points. You obviously recognise the not so good points, all I (and others) are doing is setting out some of the good points so the discussion is better informed. Sometimes we dont know what we dont know!. Somehow, however, I get the feeling that you don't want to hear anything good about heat pumps, only the bad. That's also fine, you are entitled to block out things you don't want to hear. However blocking things out doesn't change reality. What I know is that mine is more comfortable, much more comfortable. I also know why, and also why the same is highly likely to apply to many houses and that other people report similar. I also know that I went as far as I could to make my previous system as comfortable as possible.

I actually went down the sequential route as part of the discovery phase for my ASHP. I first reduced my boiler temp to the lowest it would go (50C), then started operating 24x7. That was as far as I could take it without changing radiators, in fact I needed to up the FT to 55 in the depth of winter. I also limited my boiler output to the minimum possible (8.5kW in my case). This arrangement was indeed more comfortable, and used less gas (it wasn't cheaper because prices went up at the same time, but it used less gas). Upsizing radiators, swapping to an ASHP (obviously with WC) and thus getting max FT down to 45, and FT most of the time to 35 or less, together with removing all but one TRV head made the big difference in comfort though. One day I will tot up how much I have spent on wholly unnecessary heating control equipment over the years (yes I too was suckered into trying 'smart' TRVs at one point - what a waste of time and money!).

I don't think you wont have to wait long. My 4 year old Kia e-Niro reliably does >240miles in the worst of winter, 300 in summer. That's not much less than you need and thats a car from 4 years ago.

... and the heating industry is content not to inform them, because it is so easy to whack in a 28kW boiler without thinking and let the controls 'sort it out'. This is of course at considerable cost to the customer both in comfort and expense, and with the added benefit to the industry that they get to sell lots of unnecessary controls! We are stunningly backward in the UK. Some continental european countries mandated weather compensation decades ago. I presume our heating industry lobbied against and unfortunately our Government wouldn't have had the technical knowledge to overrule them. I confess that, despite having a degree in physics, I was ignorant of this myself until I started researching heat pumps (and thus heating systems in general) about 3 years ago. Its only slowly dawned on me how misled we have been by the industry in this country and how backward it is. For the avoidance of doubt Im not saying we are unique, but we could be a lot better.

I know that and acknowledge it in my post - I quote: 'Low temperature heating (the conversion to which makes up a major part of the differential cost) is just so much better, but how many people who haven't experienced it know that?.' However the cost comparison that you do is with your typical 'shove in a 28kW boiler, whack the flow temp up to 75, ignoring the fact that it wont condense, and let it cycle like mad on the TRVs and Thermostats, with the consequent temperature gradients across rooms and temperature swings with time' crap that our heating industry has been installing, its not the well put together low temperature system you speak of above. The latter needs the same care, and mostly the same components, as an ASHP system. So yes if you want a crap heating system that costs more to run than it should go for the cheapest to install, which is undoubtedly to shove in a 28kW boiler, whack it up to 75C, and let the TRVs 'sort it out'. If you want a system that keeps you comfortable then go for something much better, which will cost about the same to install whether the heat source is ASHP or gas and, if you get it right, will be a bit cheaper to run in the latter case (a lot cheaper if you have batteries and/or solar PV) and much greener. Obviously there are many that can only afford the capital for the first of these, but equally there are many who would happily pay for better if (a) they knew the option existed and (b) our heating industry were capable of delivering it at scale, which at present I doubt it is.

As a recent ASHP owner I would probably agree (although I do save a significant amount of money with mine) However I would also say that, if you want a much better heating experience with a house the whole of which is comfortable 24*7 for about the same or possibly less running cost then do bother. (Obviously also if you want to reduce the carbon footprint of your heating by a factor of 3 they do bother) Low temperature heating (the conversion to which makes up a major part of the differential cost) is just so much better, but how many people who haven't experienced it know that?. Just be sure to do your research so you avoid the cowboys, as you must for absolutely anything which involves any of the building trades which, lets face it, are in parts about as dodgy as it gets.

It hasn't. However in the thread concerned the complainant was blaming his ASHP (because thats what people do) for problems clearly caused by a poorly insulated circulation loop running continuously. I suppose with a boiler the problems wouldn't be so easily noticed, because the boiler would just carry on chucking heat into the loop.