sharpener

And he wants to change the cylinder but curiously not any rads (until I queried it). Came as a recommendation from the Vaillant find-an-installer so its a bit of a disservice to them if other things are equal which I think they are, his calcs show 12.5kW which is probably about right and within its capability. Has put Mechanical Ventilation = No even though we have MVHR in all bedrooms, has been told not to allow for it but cannot explain why. At least he is prepared to design for OAT -0.2 as per CIBSE and MCS table and 55C flow (which is odd as the Stiebel Eltron has a poorer CoP at 55 than the Vaillant). Whereas tomorrow's man would under no circs design for more than 45 and OAT of -3.0 though he will re-consider the latter at -1.4C now. MCS design process at its finest!

Been looking at this. That's for the single fan models. The Arotherm + 12kW is 60. Have just been quoted for a Stiebel Eltron 25 which is about the same output but only 54 or 55 dB so only needs a partial screen. Installer said the Vaillant wasn't quite big enough which is odd as the difference is very small (and changes sign with flow temp). Not keen on it as the refrigerant is R410a which is already obsolescent, will I be able to get it re-gassed in 5 yrs' time? Been there with car aircon. Want to have R32 at least, pref R290, Viessmann looks another possibility for that. Another installer coming tomorrow, we shall see.

If reasonably deep you can assume a mean temperature of 10C not 0 which will improve the result somewhat. Also the additonal pumping losses serve to heat the water so are not completely wasted. Start collecting surplus packaging materials, polystyrene squiggles, bubble wrap, bags filled with air, that kind of thing to use when backfilling the trench if it isn't in a heavily trafficked area, or put it down the path under the slabs.

Or centred on the blank wall to the left of the window. Installing HPs below windows is not recommended, presumably because of noise.

Hi Judith, Try this link then https://totalhomeshop.co.uk/CLI/THE001/Images/Group-Aero-Install-Manual-March-2017Web.pdf If these are right for your unit then E11 denotes a fault in the refrigerant circuit so it may need re-gassing. Looking at that pic I wonder if there is no physical 2nd immersion and what he has done is wire a second direct connection into the original immersion heater. This might be OK but either piece of kit might object to the other. The illustrations in the above handbook don't show any port for a second immersion. The diagram on p17 for solar heating appears to be connections for solar thermal pipework, not electrical connections: Sorry but Brighton is a long way from my patch but am happy to help remotely.

That sounds atrocious! Can you not put some ikoustic fencing in front of it where it is currently? That looks a reasonable product to try in the first instance.

Good, it doesn't sound like an underlying comms problem. Let us know if re-pairing solves the Marlec issue. Can we compartmentalise the problems a bit more. Is the above behaviour the same if you isolate the supply from the diverter to #2 immersion at the dp switch or spur box which I assume they have fitted (I am wondering if the Joule can detect the voltage coming from the Marlec)? What has happened between it running for a week and it running for 1 hour? Have you got a record of the settings after this engineer's visit and can you check they are still the same as he left them? What exactly does the error message say? Are these the right instructions for yr Joule Aero? See 1. interpretation of error codes p 36, 2. configuring the legionella cycle p32. What happens if you disable it temporarily to eliminate it as a factor? Or try a factory reset (note all the settings first, then add them back one at a time and re-test as you go) There doesn't seem to be anything about fitting the second immersion in the text or the exploded view on p41. Is it external like a Willis heater? Can you post a pic of how/where it is installed and the wiring to it. Whereabouts in the country are you?

Promising, looking at what they say 20dB sounds about right and if it already complies with MCS then would reduce level to 17 dB which is really quiet. Would you mind telling us what they quoted you? We might need something similar for a Vaillant two-fan 12kW, depends if the window next door is a "habitable room". Also I imagine of interest to @JamesPa who as you have gathered has a similar issue.

Is that Delta T = 30? Will work with a high temp HP. Delta T = 25 would be better, latest installer I have contacted will not design for flow temp more than 45. For a smallish property the circulating pump in the HP will be sufficient, unless you have a buffer tank which are anyway to be avoided on efficiency grounds. Water circuit will be pressurised so you would need a small expansion tank in a corner not a header tank in the loft. Some mfrs have a complete indoor hydraulic unit designed to go on a kitchen wall like a boiler, but for what they are they are expensive.

I would guess the enclosure, because assuming the 20Pa back pressure criterion is met there will be little or no additional power required whereas the heat losses on the extra pipe run will be small, but very real (and quantifiable). But I doubt anywhere near the 20% you mention upthread. Can you provide a link to the specific enclosure you have in mind? Do they warrant its performance with your particular HP and what dB reduction do they state it will achieve? Also how does it vary across the spectrum?

So it is probable that - whatever was done originally - the Joule technician put the second immersion in so that it could/would be electrically separate from the original one. If that is so it sounds like you have two separate faults, one with the Joule setup (maybe it still thinks there is a separate supply to #1 immersion) and the one with the Marlec diverter. If the wireless link has failed then it might manifest itself as an (incorrect) battery low message. Or the batteries genuinely failed and it lost its pairing as a result. (Honeywell wireless TRVs do something similar.) In either case re-pairing it might resolve it if you can make sense of the instructions. I would expect you would put the master unit (the diverter itself) into a "pairing" mode and then press a button on the Sender or activate it in some other way. The instructions here would seem to confirm this. How far is the sender from the diverter and is there much in the way? Was it 100% reliable before? Sorry I have no suggestions about the Joule problem but getting someone to verify that the #2 immersion is not connected electrically might be helpful. What does the error message say? Has it always been the same? Did the Joule work properly before any attempt was first made to connect the Marlec diverter to it?

It's potentially all there, but AFAICS I would need to download the average temp for a whole year (ideally 5 years) and then sort the numbers into 1 degree bins to fit into @JamesPa's spreadsheet, is there a better way?

I think the psychology of moving it where the neighbour cannot see it is more likely to have the desired effect.

@SteamyTea / @JamesPa can either of you suggest a ready source for temperature distribution by # of days in 1 deg bins for Plymouth? I have found some data in the CIBSE Guide A but it is concentrated around and below freezing and does not cover the warmer days where the HP will I hope spend most of its time.

Doesn't seem to have stopped them though. I get direct mail through my letterbox about once a month as well as seeing their full page ads in the paper every weekend. Environmentally irresponsible IMO, I can't see any benefits at all for any class of user. Might as well heat the house with radiant two-bar fires like my grandparents.

And their high profile advertising for fancy electric heaters which offer to heat your house using peak rate electricity are nothing short of scandalous.

Thanks @DanDee, that seems to work now and the article is very much the kind of explanation I was looking for. The method takes account of the reduced load at higher OATs by assuming the HP is part-loaded at the same flow temp, whereas with WC it would in practice be run at a lower flow to achieve the same end at a better CoP. My climatic situation is a good deal warmer than the "Average" climate based on data for Strasbourg. And since mfrs typically don't publish figures for the optional "Warmer" (Athens) climate I can't easily correct for this with e.g. a weighted average of the two. Very much the kind of result I was anticipating, do you by chance still have a link to that thread @JamesPa? Several possible installers have now converged on an overall heat loss of about 12.5 - 13.5 kW at -0.2 to -1.4C, my principal concern now is defining the correct rad surface area vs flow temp. In the past I have already more than doubled the rads in the living room and master bedroom, and I am planning to change the rads on landing and two other bedrooms and fit one in the en-suite. But I am not going for the gold-plated solution of installing a further five in utility, kitchen and shower room as suggested by one firm. If a subsequent buyer re-does the kitchen and rips out the AGA then fitting an extra rad will be small beer, the pipework is already there on the other side of the wall. And it is not a disaster if I do not get them totally correct first time provided the HP is big enough to start with.

Purpose of this thread is to try and understand how SCoP is arrived at short of buying and wading through the whole of BS EN 14825. In particular it seems to me that the averaging process might not/does not take account of weather comp. It appears to be some kind of weighted average of the test points at -7, -2, +2 and +7 for two cases, low temperature operation and high temperature, which is not (now) really a high temperature anyway. Maybe using the performance tables here https://www.vaillant.cz/downloads/projek-n-podklady/kl-06-e2-verze-01-18012023-2564719.pdf and weather statistics from e.g. CIBSE I can build a more appropriate model but was hoping to avoid this. Yes from Table 6.3.11 in this link the CoP is about 2.2 at A0/W55C but these conditions will prevail for a small part of daily cycle over a very small fraction of the year. As mentioned elsethread we have a s/h barn conversion, it has D/G and MVHR but scope for wall insulation is virtually nil. The building is long and thin so zoning works well in it. Of course I am canny with oil purhasing, belong to a local buying group and buy nearly all I need in the summer, but the boiler is over 25yrs old and I would rather replace it at a time of my own choosing, ideally with an HP because of the 7kW of PV. Have considered Veritherm assessment of heat loss coefficient but they cannot do it until August or September when the nights are again long and cool enough, and given the lead time for P/P that will be too late for W23/24. There is a lot of free PV in the shoulder seasons so outright efficiency is not the main driver however and as always in these matters there is a balance to be struck between capital outlay and running costs. Here the best is the enemy of the good and as @JamesPa has also discovered installers are extremely conservative and are wont to overdesign to avoid callouts e.g. chooosing -3C as a starting point in coastal Devon. Whereas I have a taste for elegance in design, have years of experience in engineering projects, and can afford to take some risks because I have an AGA and WBS as supplementary means of heating even if the benighted MCS process will take no account of them. So all-in-all and with due thanks for the contributions so far I am still after a good explanation of how the SCoP figures are arrived at in the first place!

I think this might be an old link? It now redirects to what appears to be the landing page for a discussion forum in Swedish. I assume you meant a specific thread @S2D2 but it doesn't seem to be there any more.

My point exactly, what is it I "expect"? If I design for 99% worst case OAT (-0.2C for the SW) then using weather comp I expect the flow temp to vary from say 30C in spring and early autumn to say 55C in the depths of winter. I don't anticipate spending a high proportion of the time at 55C but I think it is a reasonable corner case to design for. At this temp the Vaillant Arotherm + 12 is still producing more than the nominal 12kW output and the claimed SCoP (whatever that turns out to mean) of 3.63 is enough to beat the price I am currently paying for oil. Problem is that the Vaillant installer I spoke to recently won't under any circumstances design for flow higher than 45, which seems not to take advantage of the machine's capbility on the limited number of days it might be needed. And chose a -3.0C worst case OAT which increases the required emitter sizes even further. IMO it should be my choice how to trade operating efficiency in extreme conditions against investment in 12 new radiators.

So I read that SCoP is formally defined as total heat output over a year divided by total electrical energy input. As the instantaneous CoP is a function of Flow Temperature and Outside Air Temperature this leads to performance tables like this: Are the OAT figures in the table then the design minimum figures, and so already take account of the variation through the seasons of the actual OAT. If so, what is the source of the OAT probability tables used for this (e.g. CIBSE?), which will vary from region to region? Furthermore, with Weather Compensation (which is mandatory under MCS rules) the flow temperature is itself an inverse function of OAT. So do these tables already take that into account as well? If not then they will underestimate the year-round average CoP as the flow temp needed to achieve a constant ambient temp inside the house will also vary with the seasons so will be less that the figure in the table. Thanks for any enlightenment!

So I find the Heatpunk software has some worrying inconsistencies. As well as the swapped rad selection boxes noted upthread, it seems that going back and changing the wall materials gives unreproducible results, if I reverse the changes I get an answer about half of what I started with. To get a true comparison between the stock "610mm solid stone" and the custom "sandstone 600mm" I needed to start again and build a new model identical save for the wall materials - which is annoyingly time-consuming as there does not appear to be a "copy floorplan" feature. Result is that the "610 mm solid stone" (U=1.86) needs 12180W whereas the "sandstone 600mm" (U=2.27) needs 13776W. So it is clear which one the surveyor needs to use to get the "right" answer!

Yes, it will. This is what I meant by generously specced (columns are 35/40/45/50/55C flow), the superiority of the R290 is obvious cf the Samsung R32 offering: One issue is the design OAT, the heatpunk s/w gives -1.3 for my postcode whereas the MCS table has -0.2. Another is making sure they do not apply any uplift for near a river (should be an advantage IMO), or intermittency. Fortunately the EPC surveyor was generous in assessing the loft insulation thickness to avoid disqualification for BUS. (Makes damn all difference to the overall picture, payback for adding more is ~10years if DIY, awful job, ?twice that if contracted). Have just spotted I can reduce the U value of the walls from 2.27 to 1.86 by selecting the stock "610mm solid stone" instead of 600mm "sandstone". But it only reduces the heat loss by a few 100 W, further investigation of this required methinks!

In my case, very closely indeed(!) I have now done a more comprehensive heatpunk model including internal walls and individual rooms, which showed that for some reason the previous shell model was only half my house [it is two barns end-to-end]. Now it has been fixed, the total MCS heat requirement is a shade under 15kW. Since the Vaillant A+ 12 is very generously specced (unlike the Samsung HT 14 which is positively mendacious) I think that will suffice. There is MVHR and additional heating in the form of an AGA and a WBS which of course MCS won't allow for. Result is remarkably close to the central figure from the Heat Geek cheat sheet, 75 W/m^2. And reasonably consistent with the parsimonious 6kW average oil consumption required to heat only the zones I am using at any one time (kitchen plus two bedrooms or the living room). Still nothing heard from the two installers who came a week ago. A third contacted me courtesy of the Vaillant "find an installer" scheme, Daikin seem to have given up completely.