JamesPa

Sorry I was imprecise, I should have said/meant minimum system volume, ie the minimum volume that is guaranteed to be in circuit. I guess that in many/most setups is the same as the minimum volume of the shortest loop I confess that I had not realised how little water there is in a UFH system, if it really is that small then I agree a buffer (well volumizer, its not really a buffer in the sense the word is often used) is going to be necessary, if only to power defrost.

How do you reach that conclusion without knowing system volume and modulation capability of the HP? I agree it's incorrect to assume a buffer isn't needed, but surely it's equally incorrect to assume one is needed. I do agree 2 port if you need one and pref in return not flow to avoid any reduction in flow temp.

I would add to the design requirements - get the system sizing right. Not oversized (like many) and obviously not undersized. If you don't efficiency or comfort will suffer. Don't be tempted to 'go big' for safety, you will regret it. I presume that you have a good heat model and a good handle on ventilation rates?

In addition to the comment by @JohnMo, the text quoted above says a lot. It sounds like your system is way oversized (at a guess it should probably be about half the size) and will likely therefore be cycling badly and/or deploying the 'compressor bypass trick' described elsewhere by @markocosic, which potentially kills CoP. It might be worth contacting the developer and making a complaint, but they will doubtless have a wealth of spurious pseudo-arguments to put you off because, lets face it, elements of the construction industry are pretty naff. Its now summer so its going to be difficult to do anything experimental about the heating until later in the year, but some info might help and in the mean time sorting out whats happening with DHW is the thing to do. Thus I suggest you 1. answer @JohnMo s questions 2. answer the following - roughly how much DHW do you use per day. Do you have several people who take a daily power shower or is your use more modest. 14kWh/day at a COP of say 2 (which is low) would indicate a usage of about 800l/day, 6 times the national average per-person consumption of water (hot + cold). 3. find out from your controller (1) what flow temp is set for Central heating and (2) whether weather compensation (which Samsung call 'water law') is enabled, tell us 4. tell us a bit more about your house (floor area, construction) 5. complain to the developer. Not leaving you with instructions is inexcusable, and the high usage suggests it might have been badly set up/specified That's at least a start but fundamentally it sounds like your developer has done a bad job of this aspect of the house, and if that's the case probably also other aspects. Situation normal then, sadly!

I like it, until you need to service it!

Thanks for the tip off. He's not that close but I will make contact.

As your journey continues please feel free to post again here, or perhaps better still (because its probably more actively monitored) in the Heat Pump topic under the Renewable Energy section of this forum. There is an enormous amount of expertise and knowledge here and, whilst people may disagree, at least ideas can be tested.

Thanks. Stainless mesh is a good idea that had not occurred to me, keeps the rats out'

Absolute, at the nearest noise sensitive assessment point (property). The PD requirement is 37dB ditto.

I'm not sure how much science designers/installers really need to know. Some obviously, but nothing much beyond the difficulty of O level physics and maths. They do need a good problem solving brain, a good toolkit of options, some common sense, and some sound techniques. It seems that they aren't currently given this by MCS. On another thread I dispute the idea that system sizing, which is the fundamental building block for the system design, should, in a typical retrofit, be based on purely theoretical calculations. There is ample evidence that the fabric assumptions simply aren't good enough on their own. But it's drummed into them by MCS that the spreadsheet does the job. In a sense it _does_ do the job, in that nobody is likely ever to succeed in suing an installer or getting MCS to take action if the designer has followed the rules, even though it may result in a poor and overpriced system. From an installers point of view, and even more so from the pov of a grant harvester, that's all that matters. The hydrogen ready/fossil fuel sharks must be rubbing their hands with glee.

My personal theory is increasingly that it's not the ashp industry that is doing this, it's the grant harvesting industry. It seems to me that many of the people in the business can't possibly care about the long term, which they must know doesn't matter to them because they are there only to harvest grants and go bust when or before they run out. Of course there are some gooduns, but they seem to be in the minority. So much for the grant stimulating the training of the industry. The question is, how to recover? I've thrown out a few radical ideas on the ASHP forum to try to stimulate discussion but they are, to a significant extent, shouted down.

Thanks, so two ducts and armoured is the basic suggestion if I read you correctly. Is the pipework flexible enough to pull through buried duct or must that be done first? Also - just air surrounding the insulated pipe (presumably with duct sealed at each end with foam)?

In my long standing and extremely frustrating attempt to find a way through the minefield that I am presented with when it comes to finding a legal way to install an ASHP (see other posts for details - mad LPA being the latest) I'm now looking at the possibility of a split with the condenser located about 15 m from the house in the garden. I know that the refrigerant piping has to be insulated with the correct type of insulation, what else do I need to know eg: Can it be buried, if so are there any recommendations for how? Is there a reason not to route the electric cable through the same trench? Are there any restrictions on bends etc? How much roughly am I going to have to pay the f-gas bod to connect it up? Can he just turn up and do it then leave the rest to either a plumber or me? Any info available would be appreciated

That's actually quite a good one. I guess they will argue that its plumbed in so is permanent though, but as the pipes and electric cable are flexible.... Its all getting very silly. The LPA are now demanding that I achieve 25dB(A) whereas PD is 37dB(A). They are completely ignoring the fact that, when its cold outside, people will be inside with the windows closed. I cant imagine that 25dB(A) is achievable in more than a tiny fraction of homes, and certainly not with a monobloc because of the restrictions on pipe length.

Either really. If I size it myself using MCS assumptions but the correct fabric I get to 10.5kW. Actual measured is 7.5kW based on last winter when it was, for 5 days, consistently below the local 'design' temperature of -2C. A similar number is obtained by taking half hour smart meter readings and performing a regression against degree days. I put the difference between my calculations and measured down largely to ventilation. Two MCS surveyors, following in each case a 3 hr survey, came up with 16kW. The difference between this and my calculations is that they ignored the invisible fabric upgrades I told them about. As stated above, Id like to go non-MCS to avoid the constraints, but this is currently blocked by my LPA. And going MCS is blocked by their seeming insistence on fitting a 16kW pump to a 7.5kW house. I'd be happy with 9kW or even 11.2, but not 16, which anyway will be dual fan and so wont get usable planning consent given that my LPA is currently demanding that I achieve 25dB(A) at the assessment point. Im actually interested in two things namely: 1) finding a way to get a heat pump installed for my own house, currently snookered 2) attempting to challenge the industry to do better than it currently is doing, because if it continues as is the fossil fuel and hydrogen ready guys are laughing as a result of the inevitable headlines in the Daily Mail and Telegraph about disastrous rip-off installs, which are already occurring on a regular basis.

At the right time I will. The Planning department of my LPA are still digging even deeper (but at least clarifying their position), so I want to follow this to its conclusion. Furthermore political control of the the LPA changed two weeks ago from Conservative to a Green/Lib Dem alliance, with the Greens in the majority. It seems to me that the members might be rather interested in what is being done in their name. I have already put out feelers and think I need to explore the new political levers before going national. The local paper might also be effective, they wont want the headline that their newly acquired administration is anti-green!. By way of update, the LPA have now confirmed that their requirement is to achieve a sound pressure of 25dB(A) at the assessment points (the PD requirement is 37dB(A)). The one concession that they have made is to allow the calculation to be done using the MCS method, which at least, for now, avoids the requirement to call in an expensive consultant to prove how impractical their requirement. I might just have a way to meet 27-28dB(A), but it requires the LPA to be reasonable in another respect which, based on behaviour to date, seems unlikely. So I have a few more design what-ifs to do before coming to a final conclusion.

I have been clear all that it isnt always a major problem. But, if you believe HeatGeek and the physics, in many cases it is, depending of course on the scale of the oversizing and the circumstances. If the heat pump does not modulate sufficiently to deal with the shoulder season (where much of the heating actually occurs) or if the knock on effects cause unnecessary disruption and cost (which they certainly can do) then it is a major problem. Also it is likely to make the difference between a single fan and a two fan model, which almost certainly means that express planning consent is required when otherwise it could be done under PD. Express consent gives the LPA the opportunity to impose unachievable noise constraints. Brushing the issue under the carpet wont make it go away, knowing the actual figures will allow an intelligent choice to be made. I know which I would prefer. ...if the surveyor bothers to take any notice of the additions then yes. I had 2 full three hour surveys, told the surveyors more than once on each occasion about the fabric improvements, and they ignored any that they couldn't see. Didn't someone on this forum tell us that they had learned a long time ago never to take any notice of what the customer tells them? And even if the surveyor does take notice of the fabric improvements, that doesn't deal with the unknown ventilation loss. Defending the current position is, IMHO, defending pseudo-science. The science is sound but we simply don't, in many cases, have the required data and we also have human beings who choose to ignore it. The impressive spreadsheets make it look scientific, but gigo still applies. I'm NOT saying that the calculation is useless, just that there are, at least in a substantial number of retrofit situations, material factors which are either unknown or not easily verified to the extent that it should be treated with a healthy degree of suspicion.

Thanks for this. The video is basically advocating a specific variant of the general principal I am suggesting (ie actually measuring the heat loss rather than, or in addition to, calculating it from theoretical assumptions about the fabric). I registered for Heatpunk, its basically a same old same old MCS assumption based estimator, which will probably work fine if you have a house that is a) of a consistent construction b) hasn't had fabric upgrades, and c) has the MCS assumed ventilation rates (are there any such houses?) However it will get wrong, in some cases by a massive amount, houses which have been extended to different specs, have had partial fabric improvements or fabric upgrades to variable specs, or are not as leaky as MCS assumes. Newer houses should, in principle, fare better as they are less likely to have variably-specified fabric upgrades. However they may also be less leaky than older houses so I'm not entirely sure that overall the result will be that much better. The heat pump manufacturers, at least those with web connected monitoring, have the stats on this if they chose to look. It would be really interesting to find out what they know! Im surprised that nobody has yet come onto this thread to disagree with the basic suggestion with which I kicked this thread off. Where is the (preferably constructive) criticism?

I will at the right time. I need to get to the end of the road with my second application for planning consent (the first was consented with impossible conditions, they are saying that they will do the same with the second but I am pushing back harder and as yet I haven't had a final determination). I also need to exhaust the local political options, not least because the LPA is now under the control of a Green/Lib Dem alliance, with the Greens in the majority. This is the case only since the local elections a couple of weeks ago, and I am expecting that they might take an interest once they get their feet under the table. I'm already in touch with my ward councillor (Conservative) and a randomly chosen 'Green' councillor who are both showing an active interest. The Council has published their cabinet line up so I will shortly be writing to the (Green) member in charge of planning!

I haven't. Currently I'm unable to find an MCS installer who will quote for a satisfactory system. To resolve this I would like to go non-mcs, but my LPA wants to impose a noise spec way beyond that would apply if the installation were under PD rights and which is not achievable. Since PD installations require MCS and the LPA are being unreasonable so I don't have, and possibly can't get, express permission I'm currently snookered. I am following up a couple of angles so haven't given up yet...

I don't know a way quantitatively to estimate the effect of zoning, it depends on construction, shape and location of the zones. Effectively the unheated room (and its walls) are just another layer of insulation on the heated room. But the 'extra' insulation might be two pieces of plasterboard 100mm apart, and a roomfull of air. Convection currents in either will suffice virtually to eliminate the insulating properties of the air and two pieces of plasterboard offer negligible thermal resistance. A house that is essentially a cube will benefit much less from zoning than a long, thin house where the zones are at either end. You can get some sort of a qualitative feel by asking yourself this question: when its cold outside (say 0C) what temperature are the zoned off rooms at. If they are at 0C then zoning is having an effect. But more likely they are at 13-17C in which case its not having anything like the effect you think it is. Its impossible to tell whether the loss is nearer 6 than 12kW, I wouldn't be surprised if the loss were ~8kW but, as I know very little about your home (and even if I did don't have anything other than a qualitative idea of the effect), this is pure speculation. The qualitative test in the paragraph above might tell you a bit more but not enough to make a decision IMHO. So does this matter? Again it all depends. If the MCS bods fit a 14kW poorly modulating HP on the back of a 12kW calculation and your house turns out o be 8kW and require, say, 3-4kW through most of the shoulder season, you will get rubbish COP. If they fit a 12 or 14kW unit that can modulate reliably down to whatever is required in the shoulder season the COP wont suffer significantly. However even in the latter case you may still be forced, possibly unnecessarily, to do one or more of the following add a buffer tank (cost, space, bad for COP unless properly set up, which it likely will not be) upgrade primary feeds to the CH (cost plus disruption) upgrade primary feeds to the DHW cylinder (cost plus disruption) replace the DHW cylinder (cost plus disruption) replace more emitters than is necessary (although thats not necessarily so bad because you will likely, as a result, to be able to run at a lower flow temp than designed) In addition you will likely end up with a 2 fan unit not a 1 fan unit, which may therefore require express planning consent and, depending on your LPA and surroundings, this may cause problems or render the project impossible. Again without more detail its impossible to know, and even with more detail it depends on which particular preferences the individual installers have. Only you can decide where the trade offs lie. For my, essentially cubic, house with patchy and often invisible fabric upgrades, the knock on differences between the 16kW that the MCS bods (after a full three hour survey - well 2 actually) deem necessary, and the 7.5kW I actually measure, makes the difference between a horrendously disruptive, visually obtrusive and almost certainly poorly performing project for which I would struggle to get planning consent, and a rather simple and relatively unobtrusive one which could be completed within PD rules if it weren't for the pesky requirement to use MCS installers to benefit from PD rights. However mine may well be an extreme example and houses with a more consistent fabric will likely have a smaller discrepancy (having said that ventilation loss, which MCS by default assumes to be rather, likely accounts for about 3kW of the difference between calculated and measured). I have yet to find any MCS installer who will take any notice of my measurements (I do have one lead from another forum - but Im 'out of area' so its unclear if the individual will help), but I'm certainly not going to bow to the pressure and pay 15-20K (after the grant) for an installation that most probably wont work well and will certainly cause lots of unnecessary disruption and cost. From what you have said so far I would, if I were you, seriously consider postponing a year, running your existing heating in 'heat pump mode - ie flow temp as low as you can get it whilst remaining comfortable and on most of the time' through the winter without zoning, and taking loads of measurements of consumption. Also make sure you have access to outside temperature data (you should, its available) or record it. If you have a smart meter get the half hourly readings, if not or you are on oil then find a way to measure consumption (logging flow meter? heat meter?). However I stress that your house is different to mine so I really don't know. But even if you do it and conclude 12kW is correct, you will at least have peace of mind.

Below is my plot of daily consumption vs degree days, calculated daily from half hour smart meter readings. Note the maximum daily total consumption is 165kWh ie average 6.9kW. This is for a house that the MCS bods rate at 16kW. Observations of my smart meter in the cold period (when it was 3C below the 'design temp') indicate 7.5kW and, if I would out the 3 hour average over the entire period it maxes out at 9kW, just once during the whole period, on a day when I turned the heating off at night. So for certain 9kW is sufficient in my house and 8kW would very likely do. Furthermore actual observations indicate that most of the time my house sits at around 4kW. Thus, if I were to do what the MCS bods want me to do and install a 16kW unit or more, I would be into cycling most of the time with the typical modulation ratio* of about 3, a COP disaster. (*excluding units like Samsung which, according to @markocosic, deploy somewhat dodgy techniques to make the modulation ratio appear better whilst actually wasting energy and, in fairness, some of the 'better' units like Vaillant which appear to have a genuine modulation ratio which is greater than about 3) The current way to calculate heat load is, I am fast concluding, pseudo-science because it depends on factors that, in the real world, are not well known (other than in a brand new building) and which make a significant difference to the result. This thread will hopefully stimulate constructive criticism of this view (based on the factors I have stated in the first post). If I am right then the industry method of calculating heat load for retrofits needs to be upended. I am genuinely looking forward to a robust debate on this matter.

Apologies, this is the statement that I would not assume to be true.

Based on my own experience I wouldn't assume this. From a physics standpoint there is little or no thermal separation between rooms, so the whole house loss might not be much less with zoning than without. My measurements on my own house tend to support this. If you can bear to wait, run your current heating next winter at low flow temp 24*7 with at least most rooms heated. You may be surprised. This last winter I did that and consumed 10pc less energy than has historically been the case. Take frequent measurements or get a smart meter. I have gone from 16kW calculated by 2 MCS installers, to 10.5 calculated by me, to 7.5 actually measured during the very cold patch last December (when it was lower than the 'design' temp for five days and nights in a row). This is consistent with a regression analysis of my half hourly meter readings and the maximum three hour average for the entirety of the 2022-2023 heating season. I am now planning to fit a 9kW pump. Of course I may end up cold, but if I need a bit of supplemental heating and as need a bit of supplemental heating on a very few days then that's probably a good trade off.

Im not sure you will find a comprehensive table of U values and anyway there may still be unknowns. For composite layered structures I use this tool https://www.changeplan.co.uk/u_value_calculator.php which also has built in quite a few values for elemental materials. And I ask - because I think this accounts for a 3kW discrepancy in my case - do you actually know your air change rate so you can calculate your ventilation loss? I am guessing those who have 'quoted' you so far will expect to do a full 3 hr survey for which you will be charged, and may change the quote (if my experience is anything to go by upward not downward). But there is absolutely no guarantee that they will use the right data (again based on my experience.) Have you got any real-world info about your consumptio9n that would allow you to do a sense check?