sharpener

Interesting. Thanks for the link. Seems to be an elaborate stick to beat boiler manufacturers with, as if that will improve the supply side or bring down costs. Obviously still have immense faith in MCS: <Where work fails to meet these standards, consumers must have confidence that work will promptly be put right. The requirement set out in this consultation that in order to generate credits under the CHMM heat pump installations must be notified via an appropriate certification scheme (i.e. the Microgeneration Certification Scheme (MCS) or an equivalent scheme) will help to ensure that this is the case.> Talks about encouraging UK heat pump manufacture but then 10 years ago the DTI were wanting a UK solar panel industry to spring into existence(!). Nothing I could see about how to increase the skilled workforce, or relaxing planning constraints. (See Matthew Parris in today's Times) All in all a narrow, uninspriring and mechanistic approach to the issue IMHO.

Yes it's a nonsense. While it is understandable that the DNO should have a say because they have legitimate concerns e.g. if you export more than your license you might push the voltage too high*, my experience and quite a few others over at https://camelot-forum.co.uk/phpBB3/viewforum.php?f=11 is that they are happy with DIY installs of both panels and batteries. In which case if the technical standards are met why should the companies trading in the power care who installed the means of production. * Have never understood why they are concerned about me suddenly supplying more than 3.68 kW yet do not care (or even know) if I turn off an electric shower drawing 9.5.

I think if they were either strong or turbulent in the first place then you would never get stratification.

Here is the experiment as proposed by jrmichler here Or you could run a simple test. Get a piece of copper tube about the diameter of the tubing in the heat transfer coil, and solder a cap on one end. Drop the sensor from an indoor/outdoor thermometer into the tube and fill it with water. Fill a bucket with hot water. Insert the tube into the water, and measure the rate of temperature rise in the tube. Do this while holding the tube still, then while swishing it back and forth. This test measures the rate of heat transfer of the total system. It also gives you a good idea of how fast you would need to circulate the water in order to get the water filled tube to heat up 3 to 4 times faster. OK so the result is useful. Without any agitation the initial rate of rise inside the tube is about 6C/min and with agitation it is about 10. Without agitation the temp is still rising slowly after 10 mins and with agitation it reaches a plateau at 7. However while the swishing motion is effective at mixing the water in the bucket it is not clear to me if it is effective at mixing the water in the comparatively narrow tube. Conclusion: the heat transfer is improved by a factor of at least 1.5 and it might be more if the regime on the inside of the tube were continuously flowing as in the real-life situation. This would make the difference between keeping a 6kW HP from short-cycling and a 10 kW ditto so I think a worthwhile improvement for the cost of the pump. @JamesPa you wrote <I read it the same way.> Not sure what your "it" is, the most important things for me were that many of the claimed advantages for the expensive Mixergy tank disappear when you connect a heat pump to it and their CEO is less than truthful about this on youtube.

Have posted this as a query on another forum. Most of the replies are off topic/unhelpful as per usual but one has proposed an experiment. I will report back to both fora and hopefully before too long (once I have reclaimed a length of 22mm Cu pipe from being a dinghy trailer axle. 1/2 in galv steel pipe (which I have) will be a better fit for the new wheel OH has just bought). BTW I have just viewed this Mixergy video and at 1'50" Pete Armstrong the CEO says heat pump conversion retains all the features and benefits. But I see from the Mixergy User Guide that the heat pump conversion kit almost completely destratifies the tank (presumably a result of pumping it all round throught the external PHE). So it is hard to believe that the principle of heating only the water you want to use etc is maintained with a Mixergy/HP combo, the fancy user interface app becomes largely pointless and you are no worse off fitting the pump to a conventional tank, with or without the PHE.

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.