jack

I skimmed through that this morning and wondered which BuildHub members were involved.

Welcome to BuildHub. No reason it can't work. We had the same thought when we saw what the cement board we have in a few places looked like (before it was tiled). You could buy a piece and experiment with different finishes. I'm sure you could make it look more interesting with a waxed or lacquered finish, or even ragging or coarsely thinly/randomly trowelling on some tinted plaster or cement. Even some offcuts that we left outside developed an interesting patina after a few rain and drying cycles.

I remembered less than 20 mins ago - bloody phone was somehow on silent so I didn't hear the reminder! Ran around and turned off what I could, but have just now learned that the washing machine has been on the whole time as well. Also, it appears the car's been plugged in to charge until right now (partly my fault - we came home together, my wife plugged it in while I got the dog out of the boot. I'd planned to put it back onto the cheap tariff so it wouldn't start until after midnight, but I got distracted and didn't do it). If anything, we're going to have used more than our average consumption during this period. Bugger.

Not really. The most common mistake is to use kW where kWh is intended, but kW is often used appropriately too. I don't think AI is at the stage where it could handle the distinction perfectly, but even if it were, the forum software isn't capable of doing this.

From the original email introducing the scheme: We seem to be roughly on target for that order of magnitude, especially taking into account the late start to winter.

Perhaps sit on BuildHub typing "The correct unit is kWh" over and over?

I'm somewhere north of £8, nearly all of which was over two sessions.

Should be fine. They always seem to end up with a few bent fins one way or the other.

You really need to know the heat losses to determine the appropriately sized heat pump. For a house with excellent insulation and airtightness, you could comfortably get by with a 5 or 6 kW unit. Several on here have done this successfully. If you're planning minimum insulation and not paying attention to airtightness, you could well need a hell of a lot more.

Great news!

I agree with the general thrust of your comments, but the problem isn't "impossible", it's just going to take a generation to sort out. People said that about operating a computer 40 years ago but look where we are.

Yes, and it gets worse as the temperature reaching the mixer falls as the tank empties. For those not familiar with how this works, the issue here is that you're effectively using the heat of the drain water to preheat incoming cold water. The "System B" approach involves you only heating the cold water feeding the shower. The closer the incoming hot water to the shower is to the target output temperature, the less cold water you need to mix in. The edge case is where the hot water is supplied at the target temp: in that case you'd get no recovery, because you don't need to mix in any cold water. It's not all bad. If you're using less cold water, then what you are using should have plenty of time to absorb heat as it passes through the unit. Since it's warmer, you'll need to mix in more of it (and hence use less hot water) to keep the mixer at the desired temperature. I can't remember which way around they go, but System A and C involve preheating the cold feed to hot water tank, or cold feeds to both the tank and the shower. Preheating both can offer higher recovery rates - probably quite a bit higher where the average tank temp is lower due to being heated by an ASHP rather than a gas boiler. Annoyingly, I allowed our plumber to talk us out of connecting the cold feed to the DHW as well as the showers, due to complexity. For others reading, it's imortant to go for this type of connection if you have a low temperature DHW source such as an ASHP. One other thing: other than through the worst of the winter months, our immersion diverter often heats the tank well above what the ASHP is set for (50 degrees at the moment). On Wednesday, for example, the tank reached 63 degrees. In that situation, we do get more waste water heat recovery. Obviously this is much more common outside of the dark winter months.

There is no technical or practical reason why it needs to be a disaster. ... but based on all evidence of what happens when government and/or big business tries to implement complex things for civilians, yes, the net result would be disaster.

We have a 5 kW ASHP in a 289 m2 house with PassivHaus levels of insulation and airtightness. It does fine, although during this time of year, it'd be great to have a higher maximum output so we could do more with the 4 hours cheap period we have on Octopus Go.

Absolutely go for 300 L (minimum). We have a 4 bedroom house, and with four of us (including two teenagers) living here, our ASHP-heated 250L tank can struggle some days, even with waste water heat recovery on the two main showers that are used. Admittedly that's partly because it's programmed to only reheat water during the Octopus cheap period from 12:30-04:30 - we'd rarely have an issue if we reheated continously, or at least during another period (couple of hours in the afternoon, say). It sounds obvious, but the larger the tank, the more energy you can store at a given temperature. It probably doesn't make much difference if you have a gas boiler that can get the water up to 80 °C, but it you're maxing out in the 50-55 °C range like most heat pumps, that's a drastically smaller amount of stored energy. If I were doing it again, I'd go with a much larger tank so I could heat it to an even a lower temperature. That would both help with COP and reduce standing heat losses. Do look into waste water heat recovery. It might add ~£1000 (installed), but it'll signficantly reduce the amount of hot water your showers use for a decade or more without maintenance. I was absolutely certain that you had to meet both, but you're right, it's one or the other. Every day's a learning day on BuildHub!

Ha, no, but my neighbour is a cameraman and has a massive drone he uses for work. Might ask him to get some shots next time he has it out in the garden.

I'm not sure whether you mean a literal PassivHaus or one designed using PassivHaus principles, but the heating demand you've shown exceeds the PassivHaus standard of 15 kWh/(m²a). Still a great result by any measure.

No, sorry. That's just a grab from Google maps. Bing is no better. I really just posted it to roughly show that an 8.5 kW array takes up more than 50% of a large flat roof. We're tantalisingly close to having vehicle batteries form part of the grid. Our EV has only a 38 kWh battery, but that's nearly three times the capacity of the Tesla Powerwall 2. I know you wouldn't use it in the same way, but when EV batteries eventually come with two or even three times that as standard, that's a lot of energy on tap. My main concern is complexity. We have PV, an EV, an immersion diverter, an ASHP doing DHW and heating, FiTs, and a cheap overnight rate. The complexity involved with optimising that lot is already bewildering. What happens when we move to a more complex situation where you have all that lot, plus batteries, plus vehicle to grid, plus variable half-hour pricing both in and out?

If your hose isn't frozen, you could try spraying it with water. Even cold water (maybe 8 degrees at this time of year?) is pretty efficient at melting ice.

Is there any particular reason to specifically target "covering our own usage"? I get why it's a target conceptually, but it's actually pretty arbitrary - there's no logical reason to assume that this is the optimal target when you take costs into account. I assume you're going for batteries too. Have you modelled how changing battery and array capacity changes the numbers? Is it possible that a smaller array with more battery capacity allows better usage? Where are you going to put the array? 22 kW is physically huge. For comparison, we have 8.5 kW and this is what it looks like on the (flat) roof of our house. For reference, the house footprint is roughly 160 m2: I assume have three phase? If not, you'll struggle to get approval to connect an array that big to the grid. Apologies if you've already worked through all of these questions, but 22 kW is the largest domestic array I've ever heard of!

If you're anywhere near Guildford in Surrey, I'd heartily recommend the guys we used a few years back: https://techforenergy.co.uk/ Unlikely to be the absolute cheapest, but they definitely know what they're doing (not always a given in this industry).

Most likely correction of a typo or formatting in the title.

Ah yes. Got the email yesterday, signed up, planned to turn everything off at 9 o'clock, forgot to set a reminder, and have just noticed that my wife decided to plug the car in this morning to charge. It's been sat there sucking up over 2 kW for the first 40 mins of the session. Even if I turned the entire house off now, there's no way I can make up that deficit!

The costs regularly being quoted for these jobs is just eye-watering. I get that it's more than just a day rate for the installer, because the company needs to turn a profit etc, but we regularly see installation quotes that suggest there's weeks of work involved. I had our ASHP installed by the plumber and electrician who did the rest of the house. Neither could possibly have spent a full day on their part of the work.

Yup, all good.