JamesPa

That's obviously a possibility. To check my understanding (Im a physicist by training not an expert in the capabilities of currently available inverters) - to make this work I would need a CT on the meter tails so that the new inverter shuts down when it senses export, but does so without affecting export from the existing inverter? - is this correct? Its certainly a simple solution (and maybe what I will ultimately do). However I (and the planet) lose out on the potentially exported energy. I'm not averse to having it installed to MCS standards, or to paying a reasonable fee for the installation, just to paying an arm and a leg. I can't say I hadn't considered it the 'just install' option . I have a solar DHW diverter so my current export will be below 'expectations', furthermore I've only just moved from deemed export to measured export, so I doubt the data to spot the difference exists. However its not in my nature to do things 'improperly' if there is a sensible 'proper' solution. Also there are probably people watching this forum! Re battery storage, I will do the sums, but so far have never been able to make them add up. Local battery storage is, so far as I can see, negative environmentally where the alternative is export to the grid, so it would need to work financially to be justified.

Thanks for this, it helps. I have a sneaking suspicion that the condition imposed by the LPA was chosen without particularly careful consideration. Its probably the default one they apply to industrial developments or commercial air conditioning near a residential environment. If it were applied uniformly across the District (which is predominantly suburban/rural) there are very few places where domestic ASHP would be practical! Its not stated as a pre commencement condition and as you say quite likely does not need to be expressly discharged (just met). Practically speaking however one would want to know it could be met before commencing the installation otherwise its a lot of cost for nothing. As well as it being stringent, unreasonably and unnecessarily so having regard to the practical way ashps are used for heating, the burden of proving it is also out of proportion, to my mind, to the scale of development (essentially replacing a gas boiler). Presumably this is another part of the thinking behind MCS, which is a mechanical calculation that almost anyone can do. pleased to hear that!

Wow thanks for that, I was not aware (I wonder how many were). Its a lot of regulation to read, but on a skim it looks like extensions are allowed but the FIT tarrif claim must be prorated unless there is a separate generation meter. That's fair enough, basically you still get paid for the original amount of generation but not the added amount. Practically speaking how might it work though. One could possibly add additional panels to an existing inverter if it has capacity, but how would it react to a mix of panel specs (12 year old 250W panels and new 400W panels). Or I suppose (if combining technologies is a problem) install a new inverter capable of multiple string operation and treat the old and new panels as separate strings? Since the 'old' inverter is nearing the end of its design life (but, so far as I am aware still going strong), this might not be such an extravagant option.

yes but: They would normally be operating below maximum at night because the target flow temp is set back They only operate at maximum when the outside temp is at its coldest, at which time occupiers of adjacent properties will, for the most part, be indoors with the windows closed. If exterior background is quite low, the noise experienced by anyone indoors even with the windows open, will be dominated by the internal background not the external background (the latter will most likely be inaudible). 10dB below background may be reasonable in a dense urban environment (where background is high enough to be relevant) but not so in the 'suburbs.' where the background is itself so low as to be inaudible to those who would be affected when a heat pumps is operating at its maximum. I guess that's, at least in part, the thinking behind MCS 020. Noted, I bet developers ignore this!

Just a note to thank everyone who has responded to my planning consent issue. Its given me lots of ammunition to fight the LPA. Today it was windy and the traffic was busy. Background noise (measured on my phone, so not very accurate) was 47dBA. 10dB below that, as currently required by my LPA, is achievable, about the same as MCS in fact. On a quiet windless day a few weeks ago, measured with the same phone, the background noise was 35dBA. Both are likely to be inaccurate, but the difference is probably quite accurate which frankly makes a mockery of specifying (as the LPA has) that the noise from the heat pump should be 10dB below background. It also makes me wonder if noise consultants working for developers deliberately pick noisy times of day/noisy days to make measurements (why wouldn't you?). Hopefully the LPA will see sense when I feed them some of the pitfalls. I fear, however, they may be reluctant to back down and its headed for an appeal, or caving into installing having an MCS registered installer install the noisier and uglier of the two possible options so I can get it in under permitted development. Either way thanks for the ideas!

I am intending to install 4 panels in 2 arrays, one array of two panels on a flat roof, and one array of two panels at the apex of the pitched roof (of my 2 storey house). This will add to my existing capacity, but as a totally separate system to preserve the FIT payments on the existing. The DNO is happy with the proposed total 5.5kW peak (based on microinverters - probably the best bet anyway as the array on the flat roof is subject to differential shading, so effectively there are 3 'strings' from a shading standpoint). With only 4 panels to install, the economics of a fully 'professional' job aren't great, and I'm anyway happy to do most of the work myself. Im also installing an ASHP, so it makes sense to get an electrician to make the final connections into the CU for both and certify (actually, I cant see a reason why they cant share a connection - but that's a question for later). It would be easy enough to find someone to do this alone at a sane price. However I don't have the head for heights to climb on the pitched roof, and also export payment terms intervene. I'm on octopus outgoing agile, and its a condition that the installation is MCS certified, which of course my existing installation is. So in the ideal world I would find someone to do the work on the pitched roof (is this a task for a roofer or electrician?), make the connection to the CU for the new panels/ASHP, and MCS certify the new installation after I have done all the 'grunt work' other than high up on the pitched roof. Does anyone have any experience of a division of labour of this kind. General electricians are used to 'first fix/second fix' and many are happy just to do second fix (its the high value and interesting bit after all). However I get the impression that most of the (fairly few) MCS contractors locally are pretty much wedded to the idea of doing the whole job and charging an exorbitant amount for the privilege. Any suggestions here of how to avoid being totally ripped off?

I think you are spot on with the arse covering. Problem is, once it's it it's in and is a lot of hassle to remove if anyone did complain (at which point council would be forced to take enforcement action).

In that case perhaps you can appeal that the condition doesn't I think that's pretty much my plan!

59dbA (or 60dBA if I go for the MCS option): Mitsubishi 11.2kW or Samsung 12kW (the new 'quiet' one) 30- 35dbA 6m to the neighbours wall, 7m to the nearest window none respectively. 1 reflective surface within 1m Meets MCS specs (roughly speaking 3dB below an assumed ambient of 40dbA) but not LPA spec (25 dBA ie 10 dB below actual ambient) Would need another 12-17dB attenuation plus to meet the LPA specs. No chance.

Good idea in principle, but one I'm sure won't work. The LPA is pretty insulated against external criticism. To be honest it has to be given the government imposed housing targets which it has to uphold against fierce, repeated and loud criticism from the local nimbys. Unfortunately our LPA has severe trouble recruiting planners because they can't afford to pay enough. Most of the staff are therefore quite junior and I thus doubt that they understand this area well enough to make an informed holistic judgement.

Thanks for that, breach of copyright by WDC surely, but a saving of £298!

That's an interesting one. However gas and oil boilers are generally installed indoors so don't affect the neighbours. They certainly couldn't meet the condition if installed outside. My LPA wants the ashp to be so quiet that the neighbours couldn't hear it if they are outside the property. Thats unrealistic, when it's on full they will be inside sheltering from the cold, or in the swimming pool making a loud noise if I use it for cooling in summer (not currently planned but of course possible). It's a retrofit so, in extremis, I could go for meeting the conditions for deemed consent, but then I have to pay the MCS premium and (ironically) install the louder and uglier of the two alternative units I am considering.

We live in a quiet road so the background is around 35dBA max. 10 dB below this is unachievable. Essentially the requirement as specified by the LPA is (I suspect unwittingly) a refusal dressed up as a consent. MCS (ie permitted development) is effectively (close to) 2-3dB below an assumed background of 40dB. The MCS standard is, unlike the condition specified by my LPA, both deterministic and achievable.

I have just received planning consent for my installation of an ASHP and additional solar panels (which do not clear the hurdles for permitted development because (a) I don't plan to use an MCS registered installer and one possible unit I am considering is marginally too big), but my LPA has seen fit to impose a noise constraint which is both technically significantly more onerous, and also significantly more onerous to demonstrate, than the MCS 020 noise standard applied to heat pump installations which qualify for permitted development. I suspect its ignorance or laziness (notwithstanding that I drew attention to the MCS spec in my application) rather than being imposed for some specific reason; there were no neighbour objections and nothing in an officers report indicating a specific reason of the condition. Has anyone else experienced anything similar or have any comments. I'm minded to appeal the condition (because I don't think its achievable and its going to cost a fortune to determine anyway), but appeals are currently taking 30+ weeks! The specific condition is "The rating level of noise emitted from the air source heat pump (ASHP) system hereby approved shall not exceed 10dB below the existing background noise level as measured or calculated at 1 metre from the façade of the nearest noise sensitive property. The measurement and assessment shall be made according to BS 4142:2014+A1:2019 'Methods for rating and assessing industrial and commercial sound' at the nearest and / or most affected noise sensitive premises, with the ASHP system operating at maximum capacity and be inclusive of any penalty for tonal, impulsive or other distinctive acoustic characteristics

If they are from the same range I am not sure I'd let the sound level difference influence the decision. A 10kW pump running at 7kW is likely to be no more loud than a 7kW pump of a similar design running at max, and its quite likely to be quieter. The amount of air they have to shift (at equal power) is the same so that starting point would be that they would be about the same volume. However larger capacity pumps often have larger air heat exchangers, which for a given volume flow of air will reduce the sound volume. If the manufacturers publish sound vs power curves you could check, but otherwise I would probably ignore this particular factor, unless of course it trips a regulatory issue.

Id definitely go for reviewing the results: partly out of curiosity and also to check my workings I paid for an MCS compliant survey of my house, which resulted in an estimated power demand at -2C of 14kW. The surveyor ignored most of the insulation upgrades I told him about. As a result I've was advised to spec 14kW+ heat pumps My own spreadsheets, taking into account the upgrades (but being fairly conservative about U value assumptions, particularly when it comes to older double glazing) comes out at 10.9kW. For the last few days the heating (still gas) has been ticking along nicely (and the house comfortable) consuming, according to our smart meter, a pretty reliable 7kW (space + water heating) Now there are, admittedly, three rooms we don't heat, so perhaps the demand might go up to 9kW if we heated them, but the 14kW starting point is just nonsense. At least I am now confident that an 11/12kW heat pump, when I fit it (hopefully in the first half of next year), will be sufficient (possibly even a bit to big!). Based on this, if there is any way to take an actual measurement, I would do so. Unfortunately we don't often (in South East England) get a longish period when the temperature is reasonably constant and low. In this respect the last few days have been a bit of a godsend for confidence in my design.

MCS set out a methodology for calculating the noise level taking into account reflective surfaces, obstructed views etc and provide a spreadsheet which does it here https://mcscertified.com/wp-content/uploads/2021/04/MCS-Heat-Pump-Calculator-Version-1.10-locked.xlsm The methodology and the meaning of the various terms is described here https://mcscertified.com/wp-content/uploads/2021/10/MCS-020.pdf I suggest you start with this and put in the relevant factors. When I did mine I found that it was better (and indeed necessary to meet the condition for permitted development) to move the unit nearer to the neighbouring property, but as a result away from a reflecting wall, than the position I had originally intended. Note especially the difference between sound power level and sound pressure level, both of which are quoted in dB. Manufacturers like to quote the latter, often at 5m or 3m distance without telling you the assumptions made) because its a lower figure. Ignore it when comparing models or doing calculations as the figure can all too easily be manipulated by the marketing men (or women). You need to start with the sound power level (which is the total energy per unit time emitted in the form of sound from the unit). This is not dependent on the location etc. and cannot easily be manipulated From that figure you can (using the MCS spreadsheet) calculate a sound pressure level (which is the intensity experienced at a particular point in space) relevant to your particular circumstance. MCS explains it quite well, its worth the read.

HughF you have obviously been doing good work thinking about eliminating unnecessary components - "1 valve not 2". My current design also calls for 2 normally closed (ie closed when unpowered) solenoid valves indoors as part of the antifreeze protection, so that only the external bits, not the whole system, is drained. Have you a design which eliminates one or either of these - they seem like a sledgehammer to crack a nut.

I don't follow the diagram but... The outside unit of an ashp sucks in air at the outside ambient temperature and expels it several degrees colder. The heat extracted is what gives an ashp the 'magic' property that it uses less electrical energy than the heat it delivers to the heating system. For this to work the source of intake air needs to be 'infinite' and likewise the expelled air must be able to dissipate completely from the region of the intake. So any 'confined' arrangement where the expelled air can get back to the intake will not work. Similarly any arrangement where the expelled air ends up in the space to be heated won't work. Does that answer the question?

Pretty similar or identical in our case, so not a major influence on the overall conclusion. Theoretically, if you only consider energy and envisage a seamless distribution and energy storage system. But human beings consume materials also and energy storage and or distribution is non-trivial. I don't think one can logically argue that population growth can be ignored as a factor albeit that it might be politically impossible to affect (so the politicians will instead just let nature take its course, and people will die you unpleasantly as a result of flood or famine rather than not being born as a result of a conscious and planned choice).

I have been doing a lot of work on this 'at work' (the scale of our operation is a bit larger than domestic but not so much larger so the same principles apply) and pretty much come to the same conclusion. Once a building is tolerably insulated (ie do the things that are reasonably practical and reasonably easy given the historical construction - you don't have to aim for passivhaus standards) switching from gas (or resistance electric) to heat pump is definitely the big thing you can do. We have done this for two of our buildings so far and it reduced the carbon footprint (based on measured consumption, not just theoretical) of each by a factor of very nearly 4; nothing else we have done has come anywhere close. Better still the emissions will decrease year on year as the grid decarbonises. Running costs are about the same (as gas) or better (than resistance electric). Looked at that way its a bit of a no-brainer, certainly when the plant is due for or nearing renewal. Having said that ProDave is spot on with his comment as well.

As you say electricity is a is largely of renewables and gas, so prima facie you might expect it to be cleaner than gas. I'm guessing, however, that electricity system losses are much bigger, so by the time its delivered to the consumer that counteracts the 'at source' benefit. The official conversion factors are on the 'fuels' tab (natural gas - gross - 0.182 kg(e) per kWh and on the 'UK electricity' tab ().191 kg(e)/kWh. The electricity figure has come down (got better) in each of the four years I have had a reason to look at these numbers. As you say this makes a difference between heat pumps being something like 70% better or something like 85% better. At this stage that's not a material difference, what is material is that this is a factor of 3 or 4 and will improve during the lifetime of the unit, because the electricity grid is decarbonising. My personal calculations on relative lifetime cost have gas and heat pump coming out roughly equal to within the quite considerable uncertainty on the figures (even more uncertainty since energy prices are essentially artificial). 'Roughly equal' is definitely good enough given the environmental benefits, particularly as the gas boiler is reaching the end of its useful life. Mind you I'm doing some of the work myself!

Yes, but the point is 3-4 times less carbon emissions, ie approx 3-4 times less fossil fuel used.. Furthermore as the grid decarbonises this can only get better. If you are looking for a completely fossil-fuel free solution you are currently out of luck, unless you have sufficient local generation capacity or local heat storage on an annual scale. But a 3-4 fold reduction is an extremely good start and, with the promise of a greener grid, will get us to where we need to be. Doing nothing on the grounds that there is no perfect solution will not.

Er - your conclusion is simply incorrect. It is true that grid electricity is currently very slightly more 'dirty' than gas per unit of energy (kWh) input (https://www.gov.uk/government/collections/government-conversion-factors-for-company-reporting). However an ASHP uses between one third and one quarter as much energy for a given energy output. So for each kWh you put into an ASHP you get between 3 and 4kWh out. This overwhelms the slight difference between the emissions per unit of energy input, and as a consequence an ASHP heating system has roughly a third the carbon footprint (or better) of a gas one. The comparison with oil or resistance electric heating is similar. So to be crystal clear, ASHP reduces the carbon footprint of a traditional home heating system (gas, electric or oil) by a factor of 3-4. That's a pretty spectacular reduction.

Presumably V2House only works when the grid is 'on' to protect against shocking people working on grid faults. So I'm guessing it does not serve as a means to deal with power cuts. Just a guess I admit.