JamesPa

The important thing with ashp system design is KISS. You just need a correctly sized (not grossly oversized) ashp connected directly to the emitters with a diverter valve to the UVC, maybe a volumiser, (almost) never a buffer. No external controls, not even a thermostat. No glycol, use anti freeze valves. Use the ashp controller to set the weather comp curve as low as possible and leave ticking over 24*7 (unless you plan to batch charge your slab to use it like a storage heater which is a whole different design). Choice of ashp itself not so important, but some have better controls, quieter, less ugly etc than others. Many of the ones with poor (personally I would say inadequate) controlled can use homely, an external physical controller, or havenwise, a virtual controller service) as an overlay. Under no circumstances fit any smart thermostats etc other than these (or adia) which are designed specifically for heat pumps. Reject any installer who is going to install a buffer, phe or llh between ashp and emitters, or external controls other than those mentioned above. Be suspicious of any installer who specified a 'pre plumbed cylinder'. This is often an indication that they are employing rookie plumbers and some pre plumbed cylinders come with built in llh. Post back for explanations of the above if needed.

... Which, if I follow through on the logic above, is apparently entirely fair, because they wouldn't have charged Roger as much for the infrastructure upgrade needed to support his load had there been an additional house on the pole.

I agree there is little point in continuing the debate because you appear to think that a utility that we all pay for should provide infrastructure to support what you want free of charge to you, so the rest of us have to pay, even though your requirement is out of the ordinary. Like it or not its your load that is abnormal and it's entirely irrelevant to the argument that there are some hypothetical circumstances in which the dno could accommodate you cheaply. Those circumstances don't exist. What does exist is your abnormal load and the rest of us shouldn't have to pay for it. Hopefully one of the suggestions others are making will work.

How do you know that the money isn't to pay for infrastructure upgrade. I'm not a power engineer, but I can think conceptually of two ways to spend the money and solve the load balancing problem namely: Fit a 3 phase transformer (and any necessary supply from the next station up the line) and insist you run split your load between at least two of the phases or Retain single phase but upgrade the return (neutral) cable to the next splitting point so the phase imbalance is statistically diluted and the cable loss reduced. There are probably other ways. Did you actually confirm that the figure you were quoted involved NO infrastructure upgrade at all? Even if there is no infrastructure upgrade then your abnormal load still costs the rest of us money unless you contribute, because the phase imbalance results in network losses which we all pay for. It could be that they take a view on that but charge it as a one off fee. I'm sorry but the bottom line, which I know you don't like, is that you have an abnormal requirement and so you should pay an abnormal fee, which is what you are asked to do.

Pay for the necessary infrastructure to support your unusual load?

No of course not. But neither should we all pay for their indulgences. The reason you need more than a normal domestic load is because of your unusual needs, not because of a heat pump. You have chosen to prioritise the former. In an ideal world the dno would charge you more for your unusual needs whether or not you need an upgrade, then do the upgrade to support the heat pump as well foc. But that gets very complex, it's a niche case, so it's unlikely to make sense overall even if it does in your case. One possible solution is probably the French one where you tarrif depends on peak consumption, but doubtless that also creates anomalies. You can't expect the whole world to be designed around your niche circumstance. You will have to live with the fact that your choice to have unusually high needs and not to be willing to pay for the supply required means your options are now limited.

It adds little or no value unless there is a very specific reason for it, and it's another component to pay for, go wrong, and complicate any problem diagnosis. Also complicates weather compensation (are you planning a weather compensated mixer for heating, if not how do you plan to achieve this?) Heat pump still has to produce the higher (or lower in the case of cooling) of the two temperatures, so that defines the efficiency you will get. What's the added value of running at two temperatures? I agree that getting them to fit the ASHP then doing the associated cooling parts is probably the best solution here

There is a further side to this. If the demand is such that 3phase is either advised or required, then dno will be concerned about phase imbalance if they supply it all on a single phase. Having alerted them to a 3phase requirement it would be entirely reasonable of them to be suspicious of a revised single phase specification which exceeds the domestic norm. Hiding behind it being a spur off of a connection to the house isn't going to help. DNO had a duty to protect the (shared) network for the benefit of all. There are good technical reasons behind restrictions on single phase supplies.

I agree with @JohnMo, but installer may still refuse even if you run above dew point because he won't know anything about cooling and wouldn't want the responsibility and you probably haven't paid him to do a design for cooling. So don't tell him, make sure he fits a system that is capable of cooling and which can measure and control to dew point (check specs yourself if necessary), then run above dew point also without telling him. If you are worried this will invalidate your warranty, which it just might, then you may need to pay for a cooling design!

80A is surely enough for your ashp, EV and domestic needs, even 60A could be made to work. If you need more for non/abnormal domestic purposes it's right that you should pay. Earlier on this thread you used the DNO position to justify your statement that government isn't serious about carbon reduction. Was that really a fair statement given what you have subsequently told us about your use?

Can you clarify please, I thought I'd addressed your comment but maybe I didn't understand it!

Sorry I agree with @JohnMo. Eliminate the zoning (and the heatmiser), balance the loops, let the Mitsubishi controller do what it was designed for. Your problems will likely vanish and equally likely you can turn down the flow temperature, save yourself money and have a more comfortable house. Unfortunately the manufacturers of controls have, over the years, seduced us into thinking that micro zoning in time and space saves money and is somehow desirable or necessary. Even with a boiler (and excepting very lossy or very long and thin or otherwise oddly shaped houses) this is unlikely to be true, and is certainly not true to the extent we have been told by those with a vested interest in us buying their products. With a heat pump (admitting the same exceptions) it's almost definitely not true. Likewise ignore me if you wish!

This is true, but is a consequence of our grid not habug the right interconnections - it was.set up to supply power from a few concentrations of coal plants in the Midlands and North. Shifting power from thr coast is harder. Sometimes there isn't enough capacity to shift the power I am told by someone I trust on these matters is that this is not the principal reason. The same person says that the principal reason is that there is a type of gas powered station that can't economically be turned down for less than about 24hrs, so to balance the grid other more flexible sources must be attenuated. He also says that NESO's green objectives mean that by 2030 these will have to be eliminated. In other words there is a plan. This is fair enough, infrastructure takes time to change and the future demands are not fully predictable particularly with a volatile political climate. Sometimes, if you bother to find out the facts, actions of government become much more understandable than click bait sound bites, motivated by self interest, would like us to believe. For this reason my personal opinion is that it's best either to ignore or take with a pinch of salt such mischievous reporting designed solely to undermine experts and the government but actually with little foundation. And yes @MrPotts it gets added to our bills, as it should because it's part of the cost of providing the ever present access to exactly the amount of electricity we want precisely when we demand it. If we were more flexible then some of the infrastructure costs would reduce, but we aren't. He also says that the elimination or reduction of these sources will likely result in nighttime TOU tarrifs becoming less favourable.

Some do for sure, but some don't. If you want to go mad there are some really swanky looking ones available in Italy, at correspondingly swanky prices. Actually the Mitsubishi ones are made in Italy and IMHO look better in 'real life' than in their publicity leaflets, because the stylistic curves have more impact. Thats the one niggle with the Mitsubishi model. It does have different thresholds for heating and cooling, but they are not adjustable. The cooling one is fine (18C I think) but the heating one, at 30C, is a bit high at the beginning and end of the season. For me that hasn't yet been a problem because the room its in has solar gain, so when the fancoil doesnt come on because of the threshold, the sun is heating the room anyway. However that wont be the case for everyone and, personally, I think they should allow the threshold for heating to go as low as 25. You need to set the coolant temperature above the dew point. My Vaillant measures dew point and does that by default (once you have enabled cooling with their overpriced dongle, or the with the exact same dongle, but at 1% of the price, sold also for coding their gas boilers). Doubtless at least some other makes will also control for dew point. @JohnMo is of course spot on about power output. Mine and many others modulate their fan according the the settings and/or the set temperature compared to room temperature. It seems to work well. The one thing to watch is that they have essentially zero water volume, so if you have a lot of them you are likely also to need a volumiser.

I cant see why, with a little ingenuity and assuming no industrial power tools, 60A isnt sufficient anyway. The baseload can be taken as 10-20A for an EV, 32A for a Heat pump (only when its really cold and even then probably only for relatively short periods) plus the standard 400W=2A that we all have as baseload for our misc electrics. That fits within 60A. This will of course be exceeded when washing machine, iron, cooker, immersion heater or dishwasher are doing heating, but during these periods, which typically last an hour or two max, either the EV or the heat pump could be turned down/off. Many EV chargers are capable of measuring supply current to limit output, and all heat pumps can be switched off temporarily either by a dedicated contact or using the call for heat. To my mind there is a very strong argument that we should all be compelled (or very strongly incentivised) to limit our demand to 60A to reduce the need for expensive electricity network infrastructure upgrades. France already, I am told, has tariffs which depend on max load, no reason why we shouldn't. To do things 'sensibly' as opposed to at unnecessary great expense both in terms of money and resources, we have to get out of the mindset that says we can have anything we want whenever we want it and into a mindset which allows some, very modest, compromise! As it happens I don't think I have seen my total instantaneous house consumption exceed 5kW since my heat pump was installed and my EV acquired, but that's influenced by the fact that I only have a granny charger and a 7kW heat pump.