JamesPa

To put some numbers on it a 300l cylinder at 45C with an input CW temp of 10C is storing 12.25kWh of usable energy. If the requirement is to have a flow rate of 20l/min (which some apparently want) then the stored energy is being delivered at a rate of 49kW. Those are both pretty big. 49kW is twice the power available from 100A single phase mains. 12.25kWh is 90 mins heating time for the average 8kW house. If this needs to fit in the size of a combi (volume about 90l) then the energy storage density is 130Wh/l Li ion batteries have a volumetric energy storage density of 0.4 to 1.6 kWh/l (latest research devices) so are capable of storing at the required density. I'm not sure what delivery rate they can sustain but I have the impression it's pretty high. However 12kWh of li ion battery costs a lot more than your dhw cylinder and of course you can't charge them from a water boiler, whether it's a heat pump or fossil fuel. In terms of thermal storage it looks like water has pretty much the highest volumetric heat capacity of any common material https://en.wikipedia.org/wiki/Volumetric_heat_capacity#:~:text=However%2C water has a very,−1⋅m−3. Sofaik it's possible that some esoteric material exists or could exist that has a higher capacity, but esoteric materials tend to have esoteric prices. So in terms of something cheap that can store energy by heating it has greater storage potential than water without a phase change we are probably out of luck. So I think physics/materials science forces us to compromise, or use fossil fuels which have both a very high energy density and delivery rate. If we rule out fossil fuels, which we must, and also rule out phase change then it's compromise on cost or performance or both. Intuitively phase change seems like a potential winner if you want ultimate performance in minimum volume, it's disappointing that sunamp seems to have a poor reputation and also that there are no competitors. Otherwise it's some sort of volume/capacity trade off based on storing energy in water, hence multiple solutions. I admit the above is a bit of a ramble, but hopefully goes some way to explaining why we currently have to compromise and very likely will have to compromise for the foreseeable future.

I think you come up against the laws of physics here. If you want to store energy reversibly in a domestic scenario it's either electrochemical (as in a battery), phase change (sunamp) or just heat. The latter is simplest and you need a cheap material with a high heat capacity. Fortunately water has that property. The alternative is to deliver the energy real time, but because water has a high heat capacity that's a lot of power, more than houses need to heat them. Of course you can combine the two (storage and real time heating) which is what the mini store does. Sunamp with phase change is fundamentally a good idea, but reputationally it appears to have been poorly implemented and of course the material is inherently more expensive than water There are various tradeoffs which can be made, but the physics defines some bounding conditions which don't satisfy the desire of infinite hot water for minimal energy use. That's why we need multiple solutions to fit various scenarios and a killer solution seems unlikely to emerge. If showers were built with waste heat recovery everything becomes much easier, because the power required halves, which brings the requirements nearer to the physical limits with cheap materials. But they aren't (yet) and it's a difficult retrofit.

Congratulations! It's been quite a long journey for you I'm pleased that you have reached this milestone.

If you have the space and an easy route for the G3 drain. 'Best' depends on the circumstances, there is no right answer, the market is big enough and the product simple enough to support a variety of solutions optimised for different users and circumstances.

Because the purpose of the MCS calculation and the MCS standards is to protect installers, not consumers. Simples!

By way of comparison, below is a table of yield in litres of the mini store (with reheat at the rate shown), according to the Newark data, and a conventional cylinder of the same size (no real time reheat). I am assuming 10l/min draw off, the figures for the mini store improve at lower draw off rate and get worse at higher draw off rate. For the conventional cylinder I am assuming that the flow temperature is 5C higher than the cylinder temperature and that there is 10l of dead space at the top which cant be drained at the charge temperature. Bear in mind that the product is aimed principally at smaller properties which would previously have a combi, so the maximum yield is relatively modest compared to that for a more demanding property/family. If I take the example of an 8kW heat pump then the mini store yield is poorer, but this can be compensated in quite a few cases by raising the flow temperature by about 10C. That will incur a performance penalty of perhaps 30%, but the cost of the extra electricity would be significantly less than the cost of an annual inspection for a UVC. My own case (if my LPA ever gives me permission) would be an 8kW pump. My current cylinder is 140l and I run the current boiler at FT55 or FT50. I get enough DHW. Obviously efficiency (with a heat pump) would be better if I fitted a bigger cylinder than I have at present so I can run at a lower temperature, but there is only so much space in the airing cupboard, which is used for airing. With a 130l mini store and an 8kW heat pump I could get the same amount of DHW as I currently get by running at an FT of 65. The mini store clearly doesn't give the most efficient heat pump performance, but the running cost taking into account the annual inspection may be less or similar. The main attraction is circumventing G3. I could install it myself, wouldn't gave to get a plumber to certify and wouldn't have to get an annual inspection. Of course I could alternatively get the G3 qualification myself, but not requiring G3 also means that I wouldn't have to feed a 28mm pipe that will probably never get used in earnest through an awkward route in the house. I must say Im tempted, perhaps more so once they launch one with an immersion boss (which they say is coming in V2). In circumstances of relatively modest demand I don't think the trade-off is crystal clear. Obviously if you want to run showers at 20l/min or several showers in quick succession, then a large UVC is the only practical choice. But in this case you quite possibly aren't replacing a combi, which is one of the use cases at which the product is aimed. My feeling based on this analysis is that it has a place amongst the range of DHW solutions that is needed. It will be interesting to see how the market reacts. Draw off (l/min) 10 Inlet water temp 10 10l/min/10C Mini Cylinder + Conventional Store Temperature 4 kW 6 kW 8 KW 10 kW 12 kW 14 kW Cylinder Mini Store XS - 60 L Yield @40C (l) 45°C - - - - - - 50 50°C - - - - - - 58 55°C - - - - - - 67 60°C - - - - - 50 75 65°C 50 50 55 60 70 80 83 70°C 60 65 70 80 90 110 92 Mini Store - 80L Yield @40C (l) 45°C - - - - - - 70 50°C - - - - - - 82 55°C - - 50 55 60 65 93 60°C 60 65 70 80 90 105 105 65°C 75 85 90 105 120 150 117 70°C 95 100 115 130 150 190 128 Mini Store Fat / Tall - 110L Yield @40C (l) 45°C - - - - - - 100 50°C - - - - 50 55 117 55°C 60 65 70 80 90 110 133 60°C 85 90 100 115 135 165 150 65°C 105 120 130 150 180 220 167 70°C 130 145 160 185 220 275 183 Mini Store XL 130L Yield @40C (l) 45°C - - - - - - 120 50°C 50 55 60 65 75 85 140 55°C 80 85 95 105 125 150 160 60°C 105 115 130 150 175 215 180 65°C 130 145 165 190 225 285 200 70°C 160 175 200 230 275 350 220

In fairness that's pretty much what the Newark literature says. Unless someone beats me to it I intend to do some like for like comparisons to to see what efficiency penalty you pay (because you need to heat to a higher temperature) to get the same amount of water at 40C from a given size tank. If it works out less than about £100-£150 per year it would still be cheaper to pay the efficiency penalty than to pay for the annual uvc inspection. Just from eyeballing the numbers quickly I don't think it will work out this way for a high design dhw flow rate, but might for a low design dhw flow rate. However this needs a spreadsheet!

Full spec and pricelist now published https://newarkcylinders.co.uk/heatgeekministore/

Im guessing cheap electric Is mostly nighttime when it's cold outside. That presumably accounts for high usage, plus of course the need for higher lwt. Double whammy, although if it's cheap it's probably also green, so arguably not bad! I look forward to hearing about the comparison.

I'm not sure why it would do the first unless it had run out of power headroom (in which case then yes I agree, but most of the time we are operating below max power (because the oat is above the design value) so there is likely to be headroom in most practical circumstances). Mitsubishi publishes cop at various loads, it doesn't vary much for any given lwt/oat combo, so I can't see that running at max or thereabouts power materially harms efficiency, provided that lwt isn't increased. Of course you do supply more energy, but thats just making up for energy not supplied during setback. Obviously if oat is lower or let higher then this will cause a penalty. The whole point of the analysis I started on but didn't yet finish is to quantify this. There are some truly wild claims for the energy saving through whole house setback which prima face violate the laws of thermodynamics. Equally there are statements floating around that there is no saving. Experimental measurement is almost impossible without a controlled lab environment. Crude models, both theoretical and numerical, suggest modest savings order 5% are likely but not certain (depends on precise conditions), I was hoping to do (and made a start on) a next level theoretical model, with a hope that it might be possible at least to establish some quantitative parameters for when setback becomes counter productive. But as I say above I got distracted. I assume this is directed at op. I have been thinking about whole house setback where the issue doesn't arise (but I agree with you in the case of room by room setback). Interesting, did the cheap electric not work out or is the aim to compare the two modes before settling on one?

One of the things I realised when playing around with the equations for recovery from whole house setback, is that it happens faster than you might think even if the lwt is not increased above the weather compensation baseline. This is because (without changing the lwt): a. the delta t between emitter and room is higher than the design (because the room is colder) thus the emitter emits more energy at the same lwt b. the delta t between room and exterior is lower than design (because the room is colder), thus the room loses less energy to the outside. These effects combine and the result is an asymptotic convergence towards the design temperature, with the ramp up starting quickly but of course slowing down. The equation for this is in the form T = Td - ae^(-kt) where a and k are constants T is room temperature, t is time and Td the design temperature. This is very different (and much more favourable) to a simple linear convergence model based on the (false) assumption that the power output of the emitter doesn't change. Of course the consequence of an asymptotic recovery is that it never actually reaches the design temperature unless the emitters are at least microscopically oversized. I'm struggling to decide what reasonable assumption to make to continue the analysis. Also I haven't had the time to think about this in the past few weeks, and must confess I have lost motivation a little now that my local planning authority has formalised it's policy of requiring heat pumps to have a noise pressure of only 20dBA at the most affected neighbour which is essentially impossible. I do intend return to this at some point but perhaps @DamonHD will beat me to it!

It sounds like your arrangement mean no RCD protection for the hp circuit, is this a correct interpretation?

Makes sense. Does this sentence from your previous post suggest its a matter for the HP manufacturer to specify? "The characteristics of the HP inverter, and the location of the fault within the equipment, determine the characteristics of the residual current. The selection of the Type of RCD must consider the fault current scenarios identified in the standards and by the HP manufacturer, in their design risk assessment documentation. Electrical installers do not have access to the HP manufacturer’s inverter design characteristics and consequently cannot make the decision to use Type F in place of Type B, without the agreement of the HP manufacturer."

On a early site visit the head of the firm agreed they would fit extra mcbs to my CU and this was echoed on drawings I sent them 6 weeks ago. He didn't mention anything about a Type B RCD then or at any other time. Better I suppose it comes to light now than when their electrician turns up the week after next with the wrong bits. It is not straight forward because (as previously explained to them) the HP has to be fed from the 50A battery inverter output. It can't just be teed off the meter tails with Henley blocks which seems the usual approach. I have also got a DIN rail mounted meter which needs to go in the circuit somewhere. I went through all this with the previous people (who failed to install before Easter as they had promised) and they didn't mention anything about a Type B RCD either. Perhaps some regulatory body has recently issued new guidance/reminder. The new meter goes on the rails and fits correctly through the aperture on the Crabtree Starbreaker CU, which was there in 2007 when we bought the house, maybe I have been lucky. Unfortunately they don't do a Type B which is odd because of their increasing use on EV charging point circuits. Hmm All, I suspect, messy enough that the electrician has decided 'I cant be bothered with this'. I'm not an electrician myself, but can read, think and even do ohms law. I have had variable success arguing technicalities with electricians who propose to do (or have already done) something apparently silly or, more usually, tell me that the bleeding obvious way to do something is not valid but without explaining why.* If attempting to resolve it by amicable discussion doesn't work, my usual approach is to ask them which specific regulation they are referring to to justify their position. Obviously this winds the less able ones up, who then resort to the usual trade bluster to cover up their ignorance and then dig their heels in. The more able ones respond positively, and either rethink (yes it does happen) or point to the regulation in question. The most able ones of course have already worked out what the customer would ideally want, have worked out whether there is a genuine reason to object or whether there is something even better they could propose, and if there is not come forward in the first instance with a sensible proposal. However they appear to be pretty rare, at least in my part of the country. As suggested above see what Vaillant say, but their electrician may have taken one look at the problem and decided that separation was the only way they were prepared to handle it. Houses seem rapidly to be approaching the point of having 'no user serviceable parts inside'; too few people want to touch the existing services for far of downstream claims. In many ways I can understand it since people will all too frequently hold a tradesman responsible for anything even faintly associated with a job they have done, however implausible the connection is. However in the end we all lose from this approach.

How long was the cable? Unless it was very long this seems implausible (provided the cable met the iet wiring regs), not least because they must cope with both UK and mainland Europe mains voltages and their tolerances. For the avoidance of doubt I'm not questioning the requirement for a healthy size of cable, only the explanation for why its required.

The iet wiring regs presumably. I read this as saying nothing more than you must fit the type of RCD locally required (basically it says nothing). That's what I would do too. Although din rails are standard it seems that the dimensions and positions of the apertures in CUs are not (maybe they have been standardised since my cu was fitted in 2010, I really don't know). My personal experience of electricians is that they vary a lot in their interpretation of what is possible/legal! As I mention above your installer may be happy for you to provide the circuit which may be an option if they won't do what you want but another electrician will (obviously always assuming it's safe).

They just don't want to touch your existing cu imho. Perhaps they can't get an RCBO or RCD to fit it, or they just don't touch existing CUs. Nothing I am aware of says you can't run a single phase hp on an MCB with no RCD if you choose although obviously an RCD or RCBO is preferable. And the second circuit is just control electronics = diddly squat power so can run off the ring main so long as you are happy it's sufficiently stable (IE you don't currently get too many trips). Perhaps you can offer to provide the circuit for them and get a real electrician to fit it?

Im reposting this to remind people who 'come in at the middle' can easily find what the post is seeking to achieve. Thanks to all who have replied so far, more replies welcome. I am trying to collate some information of the spread of requirements for noise levels from heat pumps which planning authorities in the UK impose, when planning permission is sought. The principal motivation is that mine has finally published its requirements, and they are quite extreme, so I would like some evidence to compare. However some assembled data might prove more generally useful To kick the table off, here are the requirements for permitted development, and the requirements imposed by East Hertfordshire (the figures being the maximum sound pressure from the heat pump alone at the most affected assessment point) Permitted development: 37dB(A) (figure included for comparison) East Hertfordshire: Town Centres and 'most' locations within 500m of a main road: 29dB(A), Rural areas - 19dB(A) (the actual figures they publish are 6dB higher than this, but they insist on applying a 6dB penalty for tonality/intermittency on top of the calculation) If anyone is willing to contribute figures for other local planning authorities I would be grateful, you can PM me if you don't want to link your name to the locality. I will publish here a table of any figures I collect.

... which should relate, as far as planning law is concerned, solely to noise. All the other stuff in the MCS standards, which has been (wrongly IMHO) imported into planning law by MCS, belongs (if it belongs anywhere) in building regulations not planning law. We also need, IMHO, a fix for the threat posed by the conditions in clauses G3 b and c of the PD rules (England). I say a bit more about this above, and am in the process of writing an article for the Renewable Energy Hub about the risks that these conditions pose.

Thanks I did read this a while ago and I presume that the practical upshot was the consultation on PD rules earlier this year, from which as yet there is no outcome so far as I am aware (although the questions asked made it fairly clear what the likely outcome was).

@MikeSharp01 Thanks for this and also thanks for reminding me I had asked a similar question before, how did you remember? Things move on however so its worth asking again. That's scary really. East Herts think they are 'ahead of the pack', and they are certainly correct that they are ahead of the pack in making it almost impossible to get planning permission for an ASHP. If you put some figures into their newly published tool, its quite easy to demonstrate that a very large number of properties simply wont realistically be able to comply. Reading between the lines (and from FOIs, also in the lines) the officers see them as a significant threat, largely because of the potential for complaints but also because of the rural nature of the area and believe that its necessary to 'control' them quite strongly. I suspect EHDC are not alone in taking this view. We could easily end up with Government relaxing the rules for PD and heaping on incentives, whilst some LPAs try to control them ever more rigidly. I'm also increasingly concerned about yet to be aired flaws in the permitted development rules. The current PD rules contain a loaded gun for LPAs in the form of the conditions in clauses G3 b and c. These conditions are rarely, if ever, talked about but are ambiguous and contain a superlative ('minimise'). An LPA, if it were so minded, could very easily use these to challenge any installation under PD for up to 10 years after it was completed (this figure went up from 4 years earlier in the year) and it could prove quite difficult/expensive to prove they were wrong. If they issue a 'breach of condition, notice' (which is the obvious enforcement route) the only way to appeal is through the High Court, there is no free of charge appeal to a planning inspector. Nasty. I don't find it difficult to imagine this happening if a local authority receives a complaint from a neighbour, however ill founded. Its much easier for a local authority to coerce/enforce (and thus be seen to be doing something) using planning law than it is using environmental health law. This needs to be sorted out from the very top IMHO. ASHPs are very much second class citizens when it comes to planning law, fossil fuels face none of these difficulties.

Are baths inside out boats? Boats are under mostly compression whereas baths are mostly under tension, and material properties tend to differ. Admittedly wood and fibreglass which are common boat materials (and I guess fibreglass is a common bath material) are good at both. Just saying!

Thanks. I agree that the East Herts tool is basically the IoA/EIEH spreadsheet. The optimistic picture you paint of how they might use it doesn't, unfortunately, correspond to my personal experience (if you have a different experience with East Herts I would of course be very interested to hear it). I am 120m from a busy A road and thus would apparently qualify easily as 'Urban'. However they have rejected an application for a Quitemark rated air source heat pump (Quietmark takes into account tonality) which would lead to a projected noise pressure of 33dB(A) (albeit without the tonal penalty - which Environmental Health weren't even prepared to discuss discounting or reducing) and told me that the requirement is 25dB(A). This is as recently as March this year. Furthermore the guidance text provided by East Herts makes it clear that a 'fail' is 'likely to result in a refusal', so its clearly not just to screen the obviously OK ones. If you plug some numbers into the EHDC spreadsheet as it stands, for a typical 8 or 12kW heat pump (which would be fairly normal in a retrofit situation) you will find that the required distances are unrealistic in most cases for anyone with a 'normal' size plot. I take your point about the MCS limit, but the 'MCS Planning Standards' (which define the requirement for PD) mandate that you use the specified calculation method, Note 7 is part of the specified calculation method, so you cant just 'ignore' this table. If you set the result at box 1 to be 37.1dB, box 8 is 2.9dB, leading to decibel adjustment of 2.1dB (according to Note 7), which must be added to 40 to get 40.1dB, a fail. By way of confirmation the The MCS spreadsheet also gives a 'fail' if box 6 is above 37.0dB. I think, therefore that a strict interpretation of the documentation leads to a figure of 37dB(A) being the highest permitted.

Im reposting this to remind people who 'come in at the middle' can easily find what the post is seeking to achieve. Thanks to all who have replied so far, more replies welcome. I am trying to collate some information of the spread of requirements for noise levels from heat pumps which planning authorities in the UK impose, when planning permission is sought. The principal motivation is that mine has finally published its requirements, and they are quite extreme, so I would like some evidence to compare. However some assembled data might prove more generally useful To kick the table off, here are the requirements for permitted development, and the requirements imposed by East Hertfordshire (the figures being the maximum sound pressure from the heat pump alone at the most affected assessment point) Permitted development: 37dB(A) (figure included for comparison) East Hertfordshire: Town Centres and 'most' locations within 500m of a main road: 29dB(A), Rural areas - 19dB(A) (the actual figures they publish are 6dB higher than this, but they insist on applying a 6dB penalty for tonality/intermittency on top of the calculation) If anyone is willing to contribute figures for other local planning authorities I would be grateful, you can PM me if you don't want to link your name to the locality. I will publish here a table of any figures I collect.

Thanks, So far as I can see this only tells you if it needs planning permission not the requirements they will impose if it does. have I missed something.