sharpener

If it were to improve the heat transfer by 2x then this would double the output the HP would run at for the same delta T from LWT to DHW. I wish I could devise a simple experiment though.

I was encouraged that the Good Energy online enquiry form gives the choice of opting out of the tank replacement, with a warning that recovery times may not be what they used to be. re a) you wrote <There are at least two solutions. The first is what Mixergy do with their Heat Pump kit. Essentially its to add a PHE in series with the coil and use a pump to pump the DHW through the PHE, thus increasing the effective size of the flow water -> DHW water heat exchanger. > I also proposed using a pump on its own to stir the tank and so increase the effective coil area by improving the heat transfer from the outside of the coil over that achieved by convection alone. Can't now find the link to this discussion. Still needs the potable water pump, but less plumbing involved and no PHE required so significantly cheaper. It would be nice to find some way of determining how much benefit this might bring, my feeling is that it might be 2x. Downside is no stratification so you would need to re-heat the whole tankful. Personally I would heat the water last thing before E7 ends in the morning. This might not suit people who have lots of children/baths in the evening but what I am suggesting would work no less well at teatime and combine ideally with PV.

I don't think this is a likely scenario. Having employed architects and structural engineers (@JamesPa's analogy) and also having run my own technical consulting business I think I can say that it is unlikely that the designers would want to be prime contractors to cover the installation work. There are just too many extraneous factors that could go wrong even with a known and trusted installation partner. Even if things went OK the inevitable contract variations (consumer add-ons, emergent work) would then have to be renegotiated via the design house which they would not want to get involved with. Also the professional indemnity insurance would not be likely to cover the extra exposure.

From what I have read the thermodynamic properties of r290 mean easier to achieve LWT of 70C for drop-in replacement market so hotter water and better CoPs than R32 in that application. https://viessmanndirect.co.uk/files//c0caf059-853e-4207-909d-ae8a00cd0c22/Technical Guide.pdf p69 says it requires a safety zone of 3144mm at ground level so in practice 1572mm from centre of HP to nearest door opening which is not too onerous and I can certainly live with. Not a split system so no propane inside the house anyway. Did you have something else in mind @PhilT? As of yesterday there was at least one supplier with the 16kW unit in stock. But as said upthread it may be better to wait until the technology is not bleeding edge, there isn't such a price premium and the generic mfrs are doing them without all the bells and whistles.

Viessman Technical Guide available here says on p85 the following: If frost protection mode is permanently enabled (e.g. in a holiday home), the secondary circuit temperature can drop below the mini- mum heat pump flow temperature. The heat pump compressor does not then start independently. As a result, even with a mono mode heat pump design, an additional heat generator must always be included in the design; e.g. an instantaneous heating water heater. Also on p88 it says not to use antifreeze. I can't now find the reference to 20C min compressor temp but I am sure I read it somewhere as recently as yesterday.

It will be more efficient to heat the water with the HP while the temp is low enough. You might need to arrange a timer and/or a tank stat so that you close the valve from the HP to the coil and switch on the iBoost or off-peak when the tank gets as hot as the HP can achieve. This will also overcome @ProDave's objection as the water will still get as hot as it used to. Gledhill have an enormous range of tanks in lots of configurations and IIRC will also make specials to order.

Starting on another tack I am now looking to see if there is an R290 HP with a simple interface so I can just call for heat at either 65C or 35C from my existing controls (like the Grant mentioned recently in another thread but that is R32). Ideally a DIY install. So far it seems the major manufacturers (Panasonic L-series, Mitsubishi, Vaillant arotherm plus, Viessman vitocal 150 etc) have got R290 models already but some of them are only <10kW and most of them have their own relatively sophisticated but un-interfaceable controls. To judge from the Viessman literature downloadable here the restrictions (safe zone of 3144(!) mm wide) are not too onerous. Using the usual model of technology diffusion I imagine in time the no frills brigade (Grant, CoolEnergy) will introduce R290 HT units but has anyone got one on the market yet? I expect @markocosic will have something to say on the topic<g>!

Yes, once again they go for what is on trend and then only the low-hanging fruit. I spent 6 months of last year trying to find someone to fit 8 more panels. My "mistake" was to fit my own Victron battery system first. I lost count of how many people I told I do not need/want/intend to buy an inverter but no-one was prepared to install the panels on their own because of (they said) warranty implications But I think also because of the thin margins on the panels when the profit on cheapo Chinese battery hybrid systems is much better.

That's all very fine until it happens when you are away. So I prefer the idea of antifreeze in the system. Read yesterday that Viessman R290 units don't allow it, you have to enable their frost protection, also these units won't start from cold so there is a 6kW inline heater in the indoor unit to warm the compressor up to 20C before starting it up.

Not that difficult. My oil tank has a sight glass which I read quite frequently. When I embarked on this heat pump journey I had winter readings which equated to 6kW continuous input round the clock (and about 2kW for the Aga, which heats the kitchen and by extension the master bedroom above, the MVHR system also recovers some heat from the flue). Armed with this info I spent a lot of time discussing what I wanted with a firm who appeared to be sympathetic to my aims, but in the end would only quote on an MCS-procedure basis so I stopped dealing with them.

Thanks, eventually found it here, very informative. They have suggested the 16kW model to me but I see it can only provide a 65C LWT over the range 5C < OAT < 15C. With a LWT of 60 and an OAT of 0C the o/p is only 9359W, CoP is 1.72(!) and I wonder if these will be sufficient. In practice if below zero we would fire up the wood-burner but IIRC that is not allowed for MCS calcs. Maybe I should ask for a design temp of 0C as we are on the coast in the SW and it rarely goes below freezing as this table shows. Also the turn-down ratio is disappointing, only about 1.6 over much of the operating range. Maybe this explains why the diagrams all show a four-port "balance tank" and secondary pump, I will ask about that as they are not included in the quote. The diagrams also show a blending valve used to drop the temp to the UFH if you have rads as well, but since I will have them on at different times this is not a good arrangement. (I already have a blending valve but it seems to be stuck in the full flow zero bypass position. However the floor never gets very hot, balancing the flow in the loops is difficult because the valves clag up).

Well they have chased up the quote today and tell me that they defo can install in my area (SW) and it is the web site that needs updating. From the practical nature of the conversation I sense I am dealing with the organisation that will actually do the job, not sell on the lead. It seems that last December, Good Energy bought Igloo Works for £1.75M as reported here ?from the ashes of Igloo Energy Supply which went bust in 2021, and have renamed it Good Energy Works Ltd. Apparently I need an EPC before they will do the survey in case it recommends loft insulation (which I have in abundance) or cavity wall insulation (which I can't, having no cavities). Funnily enough they can recommend an EPC company, PropCert. The background material they sent includes the statement that they have as of February done over 80 installs which does not sound a great number for a national company. It also appears that Midea HPs require 300mm clear space behind them, which is twice what some others need and seems a lot for a unit only 410mm deep itself. Anyone got proper technical specs for the Midea M Thermal Arctic range? They are suggesting the MHC-V16 with an SCOP of 3.59 at 50C, what is its maximum flow temp? Am still pursuing alternative options with Octopus (not in my area yet) and a Daikin HT installer (local but slow to get back to me).

Back to the numeracy/understanding of science topic once more then!

Surprisingly well. You have a standard ducted MVHR setup which sucks the air out of the warm wet spaces (kitchen, bathrooms, toilets) and pre-heats the air fed to the bedrooms and living rooms. But by using a heat pump instead of a plate HX or a heat wheel you can cool the exhaust air to well below the OAT and apply this higher delta T to the same volume of inlet air. See this write-up. The ultimate limit is probably how much you can cool the exhaust air before condensation and defrosting become too much of a problem. There is a one-sided and highly critical Wikipedia article which focuses on the shortcomings of a particular Nibe setup. Not perhaps surprising, as I would not expect the MVR/HP concept to work well with the temperatures required for hot water supply. I have not done much of a survey of the market but this system from Joule looks quite interesting.

I think for well-insulated airtight new build houses the anwer is none of the above. Have been musing ever since I put our MVHR system in in 2008 that a comparatively small HP would recover a great deal more that 100% of the heat that goes to waste in the exhaust air. The trouble is, the specific heat of air is so low compared with water that you need to move enornmous volumes of air to get any reasonable heat output. Hence it will not work as a retrofit solution without massive ductwork*. But for new build I think it could be a no-brainer because the exhaust air is so much warmer than ambient that the CoP will be way better than with conventional A2A. *Even 160mm ducts required a serious amount of diamond drilling in a stone barn conversion.

Did you get it in the end?

This is the nub of it. Planning departments use the word "Planning" to cover different things (environment, noise) from MCS (system design, hp sizing). Not easy to fix now the confusion has arisen. In principle I think it should be possible to argue that the latter aspects are of no concern to the planners and so PD should apply provided the relevant parts of the MCS standards i.e. wrt noise and external appearance (if any) are met, and enforcement action against someone who met them whilst not being an MCS-certificated installer did not achieve any planning control objective and was therefore not in the public interest. But local planners are capricious and might require one to apply for retrospective p/p as a remedy. And then impose conditions which as you have found make no sense or defy the laws of physics - but they can be seen to have done their job and it is you that are non-compliant. Neighbour has a cellar with a window onto our property. MCS definition of "habitable room" does not mention cellars, just says (from memory) any "room" other than kitchen, toilet or bathroom. What about descriptive terms like library, study, studio, scullery, pantry, lobby, attic at least some of which would usually be regarded as "rooms", do we have to consider them or not? Or hall(way), corridor or landing - which are not normally thought of as "rooms" yet might be affected by noise? Or box room, store room, shower room, wet room, boot room, gun room, darkroom - which are "rooms" by their very nomenclature but not at all likely to be affected? IIRC there is someone on this forum who is a noise consultant, I wonder if he will tell us what the case law is on these definitions, they cannot be unique to ASHPs.

Yes, I agree with all the foregoing and if they can only paint by numbers then a standardised set of connections - ideally colour coded like a motorised valve - would seem to be the answer. Actually I think all it needs is two inputs (ideally at mains potential not voltage free), one to call for the DHW set point and one for the heating (which might or might not be the same temp). Most existing time controllers already provide these outputs. And WC of course, inhibited by the call for HW. My Vokera boiler didn't do this and the plumbers had no idea how to go about it because (in 2009) they had never even heard of WC. Easily fixed with a small mains relay inside the wiring centre.

As I wrote upthread <Or are they merely harvesting my data for a leads database which they are then going to auction to the highest bidder?>

So having been on the receiving end of the "bait" part of the tactic, what do I expect to get in the future as the "switch" element? I still don't understand their business model. Perhaps they don't either, although IIRC the founder of Good Energy seems to have something of a reputation as a businesswoman.

I agree, sounds daft, they do quite a good job of the fact-finding and survey and then come up with a proposition that is commercial nonsense. (Hence my earlier comment about banana boats.) Two heat pumps is in any case not permitted development whatever the noise level. Part of the explanation may be that the surveyors seem to be mostly self-employed sub-contractors who have no skin in the game provided their fees are paid by one party or the other. Can't find any retail prices or detailed specs or performance figures/graphs of Midea units for comparison. My concern would also be that the sole importer is claimed to be Freedom who have form for poor recommendations regarding buffers with Samsung HPs. No mention of a buffer with the Midea though, maybe they have better turn-down. @markocosic probably knows. Am still waiting for a Daikin HT quote from an installer highly recommended by ther distributors, but worry that the indoor unit has a 6kW inline heater in it, IIRC this will cause the DNO to suck their teeth and/or require an upgrade to 100A supply (which would be really disruptive because it would need new (25mm^2) meter tails through a very thick stone wall with other cables embedded in it). Scottish Power who are my supplier also invite HP enquiries but similarly don't have installers in Devon. They too know my address already so what is point? I am beginning to think it is like last year where I started looking for more PV in May and after contacting 20+ installers finally got 8 panels put up in November. Difference here is it is only April but OTOH no way am I having anyone disconnecting the oil boiler after 1st October.

As a Good Energy customer for my 2011 FIT installation they sent me an email today. It says Our engineers are already installing heat pumps in your area! They already have quite a lot of information about me in their database. So I click on the link in the message which takes me to their online estimating form. The first question is my address, which they already know. The rest of it is quite detailed, existing heating type, sq m, insulation and d/g, # of bedrooms, # of baths, # of showers. So far so good, I click on Continue. The wizard recommends a 16kW Midea M Thermal which is probably about right, "Continuous water supply temperature, 60°C even as low as -20°C" sounds good, installed with Magnafilter for £10582 inc VAT less the £5000 BUS grant. It says the 250l cylinder is optional for £2128 but warns that heatup may be slow without a new one. The Tado controller I decline for another £706. They guess I will need a typical 4 radiator upgrade for £1152 which sounds reasonable vfm so I tick that, bottom line is £6734 which is the best offer I have had on my house and I have been able to opt out of all the things I don't want. Conditional on a Zoom survey for £50. One click more to download the whole thing and BOOM! We are not installing in your area...yet Unfortunately this means we cannot progress your enquiry at this time. We are growing the team and as soon as we can install in your area we will email you to let you know. So what is their business model? They knew my address to begin with. So are there any areas where they are installing yet? Is it a fishing expedition to find out where best to deploy their limited resources? Or are they merely harvesting my data for a leads database which they are then going to auction to the highest bidder? (Though detailing Midea seems a bit specific for that.) Answers on a postcard please...

Well I guess we all did. But it's scandalous that even now it's not part of official advice on fuel economy. If you don't have condensing operation anyway you might as well have the Ideal Mexico which was simple, robustly built, and easy to service. <It's just sad that we don't get to make an informed choice, instead the industry does what it thinks is right (and for the majority of customers probably is right) rather than presenting customers with options. I suspect those in the industry will say, doubtless with some justification, that giving customers choice with trade-offs to evaluate is too complex for most customers. We are victims of our wealth (and perhaps our laziness?)> If "The industry" means the manufacturers then (having consulted for them) I think they are mostly OK but there is a total gulf between them and installers, be they one-man bands or national networks.* Ultimately I fear this is a lack of numeracy and basic scientific understanding on the part of the latter, which leads to over-simplification and playing safe in installation guidance. This is a far-reaching problem, underlying UK plc's poor productivity growth over the last decade and more. *According to a major manufacturer, condensate drain installation problems account for a large proportion of warranty callouts. I had to ask the plumbers who installed my gas boiler to re-do the drain as the pipe had a dip in it. When they had finished, it had a slightly smaller dip in it so in the end I sorted it out myself.

Do they think you came up the Clyde on the last banana boat or what?

Have seen the Samsung warranty stuff before e.g. here. From what I have read elsewhere you might as @JamesPa says do better with it as a 3-port buffer, as a compromise between too much mixing and not enought engagement. Ideally with the 1 port teed off the flow and the 2 ports on the return. If you can then tune the pump settings so there is least flow through the tank when the demand is greatest I think you will have better efficiency. Fortunately you seem to have better instrumentation than the installer!