JamesPa

I thought that was the case, because there are good installers out there who manage to get things right, but as you say Surely MCS, if there is any point to it at all (other than for the protection of installers which seems to be its main purpose), should get its mind around this and come up with some way to deal with it. Instead, it seems to me, it hides behind a load of stuff which can be interpreted to do the right thing but far too often I do realise I have played fast and loose with the quotes, but the essential point is that MCS are supposed (I thought) to be the guardians of standards yet it appears from what you say (and what others experience) than unless the installer is somehow exceptionally good, it isn't/doesnt, and of course if the installer is exceptionally good, then MCS isnt needed. Im trying not to be negative, but over on Renewable Heating Hub there is a constant stream of people with poor instals, for identifiable reasons (usually unnecessary buffer tank, oversized or wrong controls) who approach MCS which does nothing other than defend the installer because they have followed the procedure. I should add that there are also people, including me, with perfectly good installs, but this seems to be in spite of MCS not because of. So where exactly is the added value?

If you buy the parts yourself you will need to pay the VAT. May still work out better! FWIW the approach I took in the end was to decide what I wanted (in my case a 7kW Vaillant in a particular location, with no external controls, no buffer tank and 4 rads changed plus a UVC) and then seek quotes based on that, providing them with evidence of the house loss. Anyone who said 'well I may have to put in a buffer' or 'I will do my own survey (which I do accept they must) and will then determine the loss - it may be more' or suggested using a pre plumbed cylinder were discarded, leaving a small number who would do what I wanted and were, one way or another, going to take into account the measured loss. Im not saying thats a foolproof recipe, just that it worked for me.

Yes, my fancoil (Mitsubishi i-life2 slim) does both heating and cooling through the same pipes. The reason for 4 pipes (I understand) is to do with the fact some buildings are plumbed this way and perhaps also so that cold can go in at the top and hot at the bottom thus optimising performance.

It can be but it doesn't have to be. In arithmetic grammar exponentiation takes precedence over multiplication and division which both take precedence over addition. Look up BIDMAS. = -35 ie 35- 5 =30. Then divide by 2 = 15, then subtract 20. from left to right after first doing the stuff in brackets. If there is officially another protocol or convention in some fields of design then its important we all know. Sorry thats just wrong, the sum 35-5/2-20 is correctly parsed as 35-2.5-20 = 12.5. Its not left to right after first doing the stuff in brackets its BIDMAS. There isnt 'another' protocol, there is the globally adopted protocol which we would all have been taught at GCSE or O Level as applicable (KS3 I believe), but may well have forgotten. Its not helped by the fact that some early calculators didn't implement BIDMAS (maybe some still don't), but that doesn't change the rule! Incidentally I just checked my Android calculator and it DOES implement BIDMAS, so if you type my formula in exactly as written and without brackets it correctly gives the answer 12.5.

The problem is MCS. They set some rules about how to calculate heat loss, and if installers follow them then the installer is protected, whereas if installers depart from them then they potentially lose the protection. So most simply go with the flow, because its safe for them. Unfortunately the MCS method is quite likely to lead to oversizing in many cases, not least because it uses pretty much worst case values for ACH. The problem is compounded because many surveyors wont account for fabric upgrades that they cant see (eg wall insulation), on the grounds that if they cant see it it may not be there. Its all backside covering at the customers expense. I did once have a written exchange with MCS in which they admitted that the current method for calculating heat loss is unsatisfactory but 'unfortunately there is currently no recognised alternative'. I think this translates to 'we don't want to be responsible for a method, so we are relying on others thus we can blame them if anything goes wrong'. This, in my mind, is inexcusable and irresponsible. The better installers have sufficient understanding to interpret the 'rules' in a way that gets closer to the right answer. Sadly many installers are pure grant-harvesters with little understanding, who 'paint by numbers' and thus depend on the near bomb-proof protection that slavish adherence to the MCS rules provides. Its actually pretty easy to weed out the real dross. Unless your house is very exceptional, anyone proposing to install a buffer tank or use glycol should be immediately dismissed. Anyone fitting (or reusing existing) external controls or smart thermostats other than those specifically designed for heat pumps (ie Homely, Havenwise and Adia only) ditto. Obviously exclude any quotes with silly prices. These tests alone get rid of the real muppets. Then, as @johnmo says do your own heat loss calculations and/or do some sense checks. If you have gas/oil consumption that can be used to sense check, alternatively you can make some rough estimates based on house size/construction. Check that they really did use the right fabric in their calculations, particularly any area which is better than the minimum demanded by building regs for a building of the same age, and ask what ACH they are assuming. If the sense checks and the claimed building loss (whether calculated by them or you) dont stack up, dig deeper unless you are 6kW or less in which case it doesnt matter because you are going to end up with aa 5-6kW pump anyway.

Are they gaining heat from other rooms? My bathroom rad is well undersized but the bathroom temperature is fine because thew adjacent hall is heated.... 100W isnt a lot to gain from elsewhere (if surrounding rooms are warmer of course). 50% makes it seem like a lot but 100W isnt, particularly if you run a bath/shower when you get some instant heat from the water! Sounds like you are more or less sorted, good luck!

Average rad temp =35-10/2=30. Dt rad to room = 30-20 = 10. Correction factor for rads = (10/50)^1.3 = 0.123. Why are you designing for DT 10? Better if you can to design for DT 5 or less and use a heftier water pump if necessary.

That's the average delta t from rad to room. If 35C is the ft and the water temp drops by 5C as it flows through the rad, then the average rad temp is 32.5 ie 35-5/2. Thus the average deltat rad to room if the room temp is 20 = 32.5-20 = 12.5. Does that make sense and if not which bit are you struggling with

Probably the same bollox that led two surveyors each spending 3hrs in my house to conclude that my loss is 16kW. My loss is in fact 7kW confirmed by a proper calculation, gas consumption, the successful replacement of a gas boiler with a 7kW ASHP and subsequent measurements. Be suspicious of the use of assumed high ach values, double counting of room to room losses, and ignoring of any fabric components that are better than building regs at the time your house was first built. Don't believe any survey calculation that isn't somehow sanity checked. The MCS 'rules' appear, in many cases, massively to oversize and do the public a massive disservice as a result. Also suspect anyone offering a pre plumbed cylinder. The principal advantage is that they can employ complete rookies to do the onsite work. In case you haven't already been alerted, reject any quote involving a buffer, phe or llh between heat pump and emitters. The sole purpose of these components, in almost all cases, is to avoid call outs at the expense of a significant increase in running costs and material complication of fault diagnosis for the customer. A 2 port volumiser either on flow or return (but not between the two) is ok. Also no external controls other than those specifically designed for heat pumps namely homely, adia or havenwise. Under no circumstances fit 'smart' thermostats. I and others can explain why if necessary.

I think (if I understand him correctly) that the cycling OP is concerned about is when the HP comes on yet there is no call for heat from the thermostats. This is almost certainly caused by satisfying a tiny buffer in a buffered system. This being the case is raising the LWT really going to make much difference? Certainly it wont guarantee that the system doesnt come on during peak cosy periods when call for heat on the secondary has been disabled.

Actually thinking about it this isnt guaranteed to stop it coming on during peak periods. It will make it less likely because the buffer will almost certainly be warm before the 'switch off', but its not guaranteed to stop it. Its good practice anyway and, by turning down the WC, you will also reduce consumption if the heat pump does come on during peak. Sorry about this.

I would probably do the same because its future proof (in the same vein I have TRVs on all my rads), although I might put in the wiring and save on the actual stats. And then I would turn the stats up to 2C above the desired target and balance the loops (in the same vein all but 2 of my 16TRVs are turned up to max and their heads unscrewed so they almost fall off, thus rendering them inactive; the rooms are balanced on the LSVs)

Im struggling with interpretation of the graph but it looks like short cycling to me. At least 3 ways I can think of to mitigate: Take out the buffer and secondary pump(s) or turn it into a 2 port volumiser in the flow Logically 'or' the call for heat from any stats and connect it (via a relay) to the master call for heat from the heat pump (assuming there is one - which there usually is) Turn the stats up to say 2C above the target and run it on pure WC turned down as low as possible consistent with heating the house, balancing on the LSVs or loop flow regulating valves (heat pump may still short cycle at moderate temperatures if oversized). (1) + (3) is almost certainly the best solution. (1) on its own the next best, (2) involves least disruption but retains the disadvantage of buffer and control-by-thermostat.

that would depend on your definition of a zone my useof the word zone is in relation to room stats and number of manifolds EG one manifold for downstairs ,one for upstairs , I would go with essentially the same definition and indeed it was the definition I had in mind when making the assertion. My understanding is that UFH manifolds generally have flow adjustment valves on each loop so that the flow through each loop can be balanced. There is nothing to stop you tweaking these (per @jack above) so that the different loops end up at different temperatures, just like you can tweak the LSVs on radiators so that rooms end up at different temperatures (even if you effectively take the TRVs/room stats out of the control loop by setting them above the desired temperature so they act purely as limiters). That, combined with properly adjusted weather compensation, is the best (ie most cost effective and most comfortable) way, in most cases, to operate as ASHP and in many cases even a boiler. Of course there are always exceptions such as houses where the external insulation is either poor or not materially better than the insulation between rooms, houses with very low thermal mass, or houses which are of an extreme shape (eg long and thin or physically separated), but most houses aren't like this, they are approximately cubic with reasonably good external insulation and negligible internal insulation. Unfortunately the controls industry has brainwashed us into largely pointless and often counterproductive micro zoning in both time and space. The main contribution this has made (other than to their profits) is to create a lazy heating industry that throws in an oversized heat source, whacks it up to max flow temperature, and leaves the controls to 'sort it out' at considerable expense of comfort and cost for the consumer. Agreed. That said uninsulated space heating pipes within the insulated envelope don't matter much if at all because they contribute to the emitter area. Uninsulated DHW pipes matter even within the insulated envelope, because they are hot when you don't want the space heated. Floor/ceiling voids may or may not be 'within the insulated envelope' depending on construction.

... which is part of the problem. With the possible exception of surgeons we have a thing in this country that 'manual' skills are somehow less valuable than 'intellectual' skills. This is of course nonsense, we need both, they are complementary, and they aren't interchangeable (although some people have the fortune to be good at both). We need to change our mindset and appreciate both equally, and differentiate where necessary. Until we do people with first class skills in soldering, excellent spatial awareness and attention to detail (or not in some cases these days) and body flexibility will continue to be allowed to 'design' heating systems. Madness, as we can see from the results!

nah, they are made for sloppy installers who see buffers as a way to avoid taking any responsibility for the downstream equipment, cant or wont do even approximate head calculations, and who want to avoid call outs due to low flow and several other problems which should be fixed, but with which your system will limp on if a buffer is fitted. There are still, sadly, loads of 'professional' installers who insist on fitting buffers on all occasions, and who should be struck off on account of the (possibly irreparable) damage they are doing to the industry with their poorly performing systems (not just due to buffers, admittedly). There are of course some rare cases where a buffer is a good thing and the only viable solution, but if you start with the premise (a) that it isnt needed until proven otherwise and (b) alternatives that don't involve system separation have been discarded, you wont go wrong. If there was ever any doubt about this - over on RHH the editor has run 2 podcasts on separate occasions where he has invited installers who advocate against buffers and installers who advocate for buffers. Only those in the first category were prepared to take part on either occasion. That says everything you need to know.

Sounds like you have it all sorted! Excellent and good luck. If my experience is anything to go by you wont regret it.

Yes they are doing something wrong, buffers are not needed in almost all cases and in the way they are generally fitted both cripple COP and make fault diagnosis impossible. Electricity prices aren't that different in the UK to those in several other European countries and efficiency is important to everyone so far as I know, irrespective of nationality. There are Vaillant schematics with buffers and schematics without buffers. There are schematics showing things you may not fit. This is intentional as every house is different. Those doing the design need to do the job properly or get out of the business if they are not capable, cant be bothered or haven't bothered to understand how a heating system works, preferably before they destroy the whole industry. PS they aren't engineers, they are fitters. Engineers are professionals who can think about what they are doing and apply intelligence, logic and knowledge to the problem at hand. Fitters do painting by numbers. Absolutely nothing wrong with fitters, we need them and they have valuable practical skills, but they shouldn't be allowed to do design until they have demonstrated that they have the required capabilities. Brunel, Stephenson, Telford and the like would be turning in their graves!

Assuming (a) that the house is well insulated (b) that the insulation between rooms is poor, and (c) the house isnt long and thin, then then anyone who understands a bit about the physics of heating, heat loss and cooling, and hasn't been brainwashed by the controls industry. (a) and (b) are likely to be the case with most newbuilds, (c) is obviously build dependent. Single zone btw does not mean all rooms have to be at the same temperature!

for example ... those flexis look like 22mm connected to 28mm coming out of the heat pump. This maybe OK but given the BS re insulation I wouldn't bet on it. If its not too late Id give the system a good checking over and ask about anything faintly suspicious before paying.

Neither planning (permitted development) rules (in England anyway) nor the BUS grant require this. If MCS do it is a rule of their own making.

TBH I would do the same but I am a bit of a taker of calculated risks and am prepared to work things out iteratively. Many aren't. This is not advice, just how I would approach it. Just be aware 7hrs cheap rate on the immersion may not be enough so some may be at full price and full recovery is going to take a fair time. It depends on how demanding your users are! As you are an electrical engineer you can do the math without our help! Just make sure you are not lumbered with buffer or unnecessary external controls. Vaillant heat pumps come with all the controls you need other than manual (set and forget) balancing valves. If your chosen engineer insists, choose another!

One further thought to above is to consider a cylinder with integral heat pump. They aren't that expensive and it would nicely separate the two systems allowing you to go for the 7kW for space heating. I wouldn't normally suggest this but your extraordinary dhw requirement makes it worth considering imho. Not clear to me whether this is BUS compliant however. It's clearly within the spirit but might require mental gymnastics to convince yourself it's within the letter!

based on that additional info about the house I would withdraw my comment that your house may be (materially) less than 7kW. It may well be a bit less but not enough to provide slack for your DHW at peak space heating load. Even if you top the loft up to 300mm (which I definitely would) then still probably insufficient margin to run the DHW How much DHW do you currently use? I agree given the additional info you have now provided about the house and your DHW intentions. 7kW Vaillant virtually certain to be too small to cope in the height of winter. You have two options (1) go larger eg 10kW or (2) accept you use the Immersion when its (perhaps) 2C or below so the heat pump is used only for space heating at these times. Even then it may be a bit marginal, but chances are you will get away with it unless there are several continuous days at -2 all day and night (which did happen a couple of years ago). re PHE vs new tank. It really depends on the timing of your use. If you can stand a reheat between uses then why not just add a PHE to existing tank. If you cant tolerate a reheat then get a new cylinder, but as @-rick- says you could consider (if you go for new tank) plain tank plus PHE which may well be cheaper than a new large 'heat pump' cylinder. Remember you can heat to >>50C if you want, but efficiency will suffer. That said at 7p/kWh getting best efficiency doesn't really matter, in fact you are quite probably best maxing out the temperature you heat to in order to store more energy, thus reducing the consumption later in the day when leccy more expensive! As to price - I got a 7kW Vaillant , 3 rads, 1 fancoil, 210l tank for 12.5k minus grant = 5k to me; South East England. Two installers quoted that price, others were higher. The two who quoted that price were the ones I would have chosen on quality grounds. This excluded the following the wire (for the temp sensor) from the DHW tank to the heat pump, which I ran. the power supply. Second fix up to the external breaker was done in advance by a local sparks for <£200, after I had run the cable. exposing a void and making good, where the 28mm primaries were to run indoors - I did this myself

If you had both a heat pump and E7 it would be cheaper than E7 alone, by a factor of 2-3. Night time water heating (with E7 or similar) on a heat pump is nearly free, even if the COP isn't the best. (PS I assume you mean 125l not 25l, otherwise its just a footbath)