JamesPa

Returning to the question of retaining existing dhw cylinders discussed upthread, para 5.6.7 of mis 3005-d might wipe that idea out. It's ambiguous, but one reading says that, if the primaries to the retained cylinder aren't already insulated, then insulation needs to be fitted to the primaries. This might involve accessing pipes under solid flooring that can't be lifted easily like carpet/floorboards can, together with all associated works on skirting and fittings, in some cases (including my own) adding thousands to the cost. I have taken this up with the MCS helpdesk. Their initial reaction was to confirm that this unreasonable interpretation was the correct one, but on further questioning admitted that they weren't actually sure and had escalated it to the technical team. I am awaiting further feedback which I will post here. If they confirm the unreasonable explanation then that's another nail in the coffin for a reasonably affordable ashp retrofit. Let's hope they see sense! Has anyone else queried this in the past?

Nice one. If Im not too much mistaken its a Stiebel Eltron, so somebody paid a pretty penny for this. I suspect many householders may be more sensitive to appearance that planning authorities, except on flats of course where the visual prospect of lots of different, differently placed, wonky units on the visible elevation is pretty naff albeit invisible to the occupants. Its a shame that MCS and PD discourages front placement, which in many cases is the least noise sensitive location. Is there really a problem with an HP on or adjacent to the front drive. It has much less physical volume than a car and could be equally a status symbol. Several HP manufacturers illustrate their models proudly displayed in front of a modern Scandi/Modern Germanic style house.

Agree. Remember that most of the time the unit will be running at perhaps 60pc of peak capacity and either end of the season one quarter or less. The downside of under sizing is that you may need some source of secondary heating if it's persistently very cold. Depending on where in the country you live, this may happen very rarely. Good luck though trying to persuade an installer to downsize. The advantage to the installer of oversizing is that they get fewer call outs and definitely meet the BUS requirement to deliver 100% of the load. From an installers pov it's almost a no brainer. I'm in exactly the same situation. In the depths of last winter 7.5kW 24*7 did the job, based on smart meter recordings. The calcs say 10-11kW. A '7kW' vaillant is really about 8.5kW at my design FT and the -2 design temp. It's a nice unit. Do I go for it or something 'safe'. I may even be forced to a spreadsheet to work out the penalty for a top up at COP 1 for the few days per year it might happen. Still TBD, hopefully in the next couple of weeks.

They might add it to stop flow/temp errors either end of the season. It probably doesn't cost much, is a well known technique, and anything which avoids call outs is good. Alternatively their compressor modulation might be rubbish.

I spotted this. The internal piping diagram shows that it does have hot gat bypass. The question, which I don't believe has been answered, is the hot gas bypass there to extend an otherwise respectable modulation ratio (in which case its arguably OK) or is it there because, without it, the modulation ratio is poor (in which case its definitely not OK). Maybe @markocosic knows. Some part load figures for Samsung would help, but so far I haven't seen any.

Well they will still have all the MCS overhead, but the won't have to submit the grant application. So you might get a bit better 'deal. The job is vastly simpler and less risky without DHW so the reduction should be substantial. It might depend on how a job without DHW fits around other jobs in a week. Currently I'm pretty sure many plan for one week x 2 people which is very 'neat' Of course if MCS weren't a government supported closed shop an ordinary plumber could just fit it in around other jobs.

Thats the conclusion I now reach. You can do space heating only under MCS (and thus permitted development), but you then cant get the grant.

I cant find this in MIS3005-D which is the defining document for both PD and grant. Where is this please? Having said that neither can I find in MIS 3005-D a requirement that the heat pump serves both DHW and Space heating. I thought there was one, but I cant find it. It doesn't help that MIS3005-D is not searchable! However it is a requirement for the BUS grant https://www.legislation.gov.uk/ukdsi/2022/9780348232349/regulation/9 So a HP can be installed to MCS rules under PD for space heating only, but you cant claim the BUS grant in this case.

Contact closure for dhw seems to me to be perfectly ok if you choose to run dhw at ft 65-70 and thus are able to retain the existing dhw system, which is a condition for a low cost install. Many if not most seem to have this capability. Combine this with weather compensated space heating which afaik all do natively with their controller and surely you are good to go. I'm pretty sure grant now implement weather compensation so if you treat the room thermostat as a temp limiter not a temp controller that should be ok too. Prices of the more powerful and higher spec units (which look nicer) are still quite high though, I guess time will fix this.

Why not write to your MP. Here is the response from MCS when I challenged them on the point. Basically they are saying that DLUHC approved the text. "Department for Levelling Up, Housing & Communities (DHLUC) developed the permitted development rights as a way for heat pumps to be installed legally without having to go through full planning permission. DHLUC set all the requirements to meet permitted development rights, including all noise specifications, not MCS. However, as a way for contractors to understand whether their installation will meet permitted development rights, DHLUC approached MCS to develop a methodology for installers to calculate whether the installation meets the thresholds. Therefore, MCS developed MCS 020 via our technical working group (made up of installers, manufacturers, certification bodies etc) and in conjunction with DECC (pre-ancestor to BEIS, now DESNZ). Just to be fully clear, all requirements to meet permitted development rights are set out by DHLUC, however, MCS were responsible for developing the methodology set out within MCS 020, which was accepted by DHLUC as it delivered a way of contractors being able to meet permitted development rights. It was also DHLUC’s decision to mandate the installation is installed in accordance with MCS 007 and MIS 3005 as a way to ensure quality and reduce the risk of poor noisy installations."

Interestingly it may also even be more, or at worst no less, carbon friendly. Off peak electricity is cheap because there is excess capacity before gas/coal fired power stations are switched on. Mass load shifting will become increasingly important as we move from fossil fuel heating and transport to electricity.

All, or at least mostly true however... Unfortunately MCS have written their installation 'standards' into planning law. They shouldn't be there, if they belong anywhere they are part of building regulations. But that's not what has happened. Basically the government has outsourced writing the rules for permitted development to MCS. MCS is funded by a limited installation industry whose interests are, at least at present, aligned to low volume high price. It doesn't take a genius to work out what happens. The alternative is express consent which is down to LPAs. LPAs have been subject to 10plus years of council tax caps imposed by the government. It doesn't take a genius to work out that that frustrates their ability to hire people who have the skills needed to deal intelligently with new technology. Underfunded government, whether local or national, hasn't got a chance against well funded private vested interests. Underfunded government with politicians whose personal interests align with the worst of the vested interests even less so. That's what you get if you bang on about low taxes without regard to the need for public services, don't hold governments to high moral standards at the polling booth, don't evaluate the plausibility of arguments made by politicians and others, and have a press which is in bed with those who seek to prolong their personal privilege at the expense of the long term good of the population.

That's crediting the government with a greater degree of competence than is reasonable. However others, more competent or more to the point better funded, do have interests which align with the current situation, including many in the grant harvesting/heat pump installation industry. Their influence on a government that really isn't up to the challenge is all too evident.

Sadly not entirely. To install a hp under permitted development requires MCS. So if you want to avoid the faff you need express planning consent which, depending on your LPA, makes it nearly impossible to install a heat pump.

Exactly. We are discussing engineering alternatives, but at the level we are discussing I'm not sure it's about engineering. The real question with dhw is what can you persuade an installer to do. So it needs to be guaranteed by someone else, meet all the regulations, save enough time to mean they can do more than one per week and still give them a reasonable profit. A HT pump with dhw run at 65-70 has the potential to do this. A more nuanced solution which might be a few percent better from an efficiency standpoint currently doesn't, I fear. I will be testing this in the next couple of weeks as it happens. I have 3 more flexible installers poised to give me quotes. I will see how they react to a HT dhw solution.

As it happens I agree. Now try persuading an installer to do that, no chance. So I can do it for myself at home (but only with express planning consent) but it's not a solution for mass deployment.

Exactly. In a retrofit situation you need to design around what is already there as well as consider the 'ideal solution', then find a cost/performance/disruption sweet spot. Replacing a perfectly good DHW cylinder can add a lot more than 2K to the price, because a) thats often the price of the cylinder alone if the HP manufacturers cylinder is specified (the easy option) and b) many installers will want to upgrade the primary feeds to the cylinder to 28mm, upgrade the CW feed to 22mm, and of course run the thermocouple lead, and it almost inevitably involves a lot of taking up of floorboards and uncertainty = cost. There is also a horrible tendency to fit the HP manufacturers pre-plumbed cylinder which makes any subsequent changes even more difficult. Then there is legionella to worry about because you are running at low temperature. I also have a nasty suspicion is where a lot of margin is hidden. I reckon the added cost may in practice be nearer 4k which, together with the £1200 for the MCS design fee, more than wipes out the grant. So if you can avoid doing it then its well worth considering doing so. Running the HP at 65-70 for DHW only means that you don't have to replace the DHW cylinder and, in a typical house, might add £100 per year to the running cost without materially impacting the climate change mitigation. The DHW cylinder upgrade can be done at a later date if needs be. Im actually beginning to convince myself that its a no brainer.

The latter was basically what I was thinking of. Smart, or even dumb but electronic, trv actuators with alternative firmware have all the required control function. I don't know if trv valves (by which I mean the bit that interacts directly with the water) are linear or basically on/off. But designing a linear one isn't beyond the wit of man. Alternatively make an adaptor to enable an electronic trv actuator with the alternative firmware fit a lockshield. Working out a solution which is manufacturable and requires minimal investment by the householder is the key. To do that you need to know more about the actual detail of plumbing components than I do. Again these only really work in the heating season so some more off the wall thinking needed to find something more universally practical. I suppose you could just automate what plumbers do (or don't do), but this balances for delta T not room T.

Lots of good ideas here, many of which are readily implementable!. Fundamental goal for me is 1. If there is an existing stored DHW system, it should not be necessary to replace it 2. If there is a combi, then the replacement needs to fit in the same space as the combi, or thereabouts. If we can achieve this then the installation should come down to 2 men*2 days, or even 2 men * 1.5 days, as opposed to 2men*1 week which seems to be the current norm. Sadly I'm not optimistic about a common protocol for communication, but surely they could at least agree on a common physical layer. Currently some require 2 wire, some 2*5 wire, and doubtless there is everything in between and more besides. At least if they could agree on that, only boxes not infrastructure need to be replaced when something fails. In addition to the packaging questions, I believe that there are two other matters which need to be addressed namely: A quick, robust way to estimate whole house load, the current gigo spreadsheetery is not helping at all. A less time consuming and more robust way to balance emitters The whole house load thing has been aired on this forum several times; I don't think we have found a universal solution yet but there are a couple of options. The most robust is probably to use smart meter readings where they are available, and some intelligence around the patterns of consumption and local weather data. It needs some software eventually, for now some people to play with it and develop some simple techniques (which some are doing) and acceptance that the current method cant work for retrofits where you have no reliable way to determine the fabric. Balancing radiators seems to take on more importance with ASHP than with fossil fuel, because of the drive to low and slow. The first question is, what are we balancing for? Heat Geek does a bit on this and eventually they come down to 'balance for equal room temperature (with open TRVs)'. This makes sense, balancing for equal delta T assumes rad sizing is correct, which we know it isn't. Balancing for equal (or correct) room temperature takes out this error so Im going with that as the actual requirement. There seem to be all sorts of auto balancing valves around, but none I know of actually do this. To my mind an adapted TRV (certainly an adapted electronically driven TRV) must surely be able to achieve this. What you need is some kind of slow reaction linear adjustment of the flow, which settles on a flow that delivers the correct temperature over the long term. The problem of course is that you have multiple control systems fighting each other and the risk of oscillatory behaviour is clearly real. I haven't yet got my mind round this, and to be honest don't know enough about valves to do so from a solid knowledge base. More thought needed. Perhaps a 'fit for a week then remove' solution is appropriate, however, so far as I can see, this will only work during the heating season which creates an issue for installers that probably rules it out.

If you read the source documents , ie the actual legislation and the 'MCS Planning Standards' to which the legislation refers, I'm personally 100% convinced that MCS is required for PD. MCS seem to have caused this to happen because it's a consequence of the way the 'MCS Planning Standards' are written. I'm used to finding loopholes in regulations but in this case I can't find one that I am convinced by. I have challenged MCS on the immorality of creating a closed shop by the backdoor in this way; they don't deny it is the effect of the documents, but claim that others were responsible for this effect - the 'it's not my fault gov' defence which is only one step removed from, or possibly equivalent to, the Nuremberg defence.

Well that's almost certainly Bow Locks. So, after a good wash, it's got traces of copper, iron, rust and very, very, very dilute inhibitor in. Probably a lot safer than your local swimming pool on kids day!

But ... Are any systems plumbed with separate flow for dhw yet common return. Probably, if so better not get that mixed up!

Sounds sensible. What will it take, I wonder, to persuade installers to reuse primaries for hot water?

As an option yes, but forced not sure. In a retrofit situation the win is a simple water connection to the existing primaries at the existing boiler location, retaining the dhw tank if there is one or colocating a small tank where the combi was (or very nearby). Or have I misunderstood (perhaps a diagram would help!). Further thought, so are you suggesting repurposing the primaries between boiler and cylinder for carrying heated cylinder water? If so then I can see where you are going, depending of course on where existing diverter valves are located. Also, let's factor in that 15l of stored hot water doesn't need all the safety precautions. Can we make a heat pump combi replacement using your ideas and this?

Good ideas. I would add (for retrofit) the ability to run the flow temp for the DHW at 65/70 so you dont have to replace the cylinder, even if its vented, and as you say leigionella fixed a plate heat exchanger 'add on' to an existing DHW cylinder so that you dont need to replace a cylinder just to get a large coil (already offered by Mixergy) (only necessary if you run DHW at a low temp, not necessary if your run it at 70) Monobloc option also available All of this and what you have listed is already available from the market, but the installation industry wont fit it!