JohnMo

You can get around the DHW temperature probe with an on off thermostat and two resistors. I works and is working currently for me. https://forum.buildhub.org.uk/topic/36003-pt100-cylinder-probe-wireless-connection/

You can do gas. We started gas and 3kW of PV. Gas boilers are difficult if you have a low energy requirement house, as they are just too big. Now we have 7+kW PV, battery and ASHP. March is still heating season for us, but electric import yesterday was £1.60, today looks to be 65p (best cost days so far this year). Heating run overnight on both nights. That is only possible because we have the battery and can run E7, cost effectively. With the good and bad days of the winter, the battery and E7 have been £386 cheaper than running the house on just normal rate electric and a similar amount cheaper than gas and electric last year. Looking to make even greater savings during the summer. (I don't get paid for exported electric)

Think you are all trying too hard, tried various ways of doing WC, so far the most accurate (house temp stability) and cheapest to run is a set flow temp and a good 0.1 hysteresis thermostat. Cooling just flow at 15 to 16 degs, which is above dew point generally and you get a CoP of about 6 or 7.

Now take your calculations to the next level and work out the downward heat loss.

DHW heating doesn't really help, because the heat pump either does heating or DHW not both at the same time. Modulation isn't really too much of an issue. As long as you have enough water capacity open the heat pump will cycle, but not short cycle. The biggest issue will be supporting the flow required for all the loops you have. So will be worth checking. A 4kW heat pump will have a max flow rate of about 0.7 to 0.8m3/h. A couple of fan coil units may be a better and easier solution to implement.

I just use a filter on the down pipe https://www.celticwater.co.uk/downpipe-filter-rainus/

Why wouldn't you just use the controller that comes with it. If doing UFH basically run long and slow or if on a longish time of use tariff like E7 and batch charge, having a battery helps keep flow temps low as you can run longer and still keep cheap tariff effective. Anything else is just making it complicated for the sake of it.

Are you correct with your assumptions you need 4kW? Have done heat loss calculations? A 100W/m2 at 35 flow isn't going to happen. Even at 100mm centres you will need 47 deg mean flow temp. It just will not work well or cost effectively. Something is not right with your calculations. As said

Big Red heat pumps used to do them. Spoke to Harlequin about them, but the heating coil wasn't that big and you lost quite a bit of cylinder volume with that and the DHW coil. So moved to UVC, which is a good solution, either big coil, or existing cylinder with PHE and pump.

So will get full low sun mid afternoon onwards. Plan for overheating. We have 36m2 of glass in out living room, which is southwest facing. It can get very hot if you are not careful. Not to bad in the winter, with triple glazed 0.6 U value, but the lounge looses as much heat as the rest of the house.

Why not just get a quote from MBC, instead of going around different groups, what ever answer you get, will not be the same answer given for your design.

Choose your battles, foundations have time scales. Dig, building control inspection, fill with concrete. Leave it too long or take too long, they fill with water or the sides collapse. Access starts to become an issue, once you start, depending on the site layout.

Because they have an excellent turndown ratio. By that I mean minimum output which is something like 1.8kW, compared to must which have nearer 6kW for the same boiler rated max output. This helps minimise short cycling which can use lots of gas. Other good things you get with a good boiler are two flow temps one for heating a cylinder and the other for central heating. With gas boilers the lower the return temperature back to boiler the higher the efficiency. Irrespective of heat source chosen I would design the heating system and the hot water the same (unless you want a combi boiler). Heating system design for low flow temps and hot water storage design around a heat pump cylinder with storage temperature of 50 and below. If you go combi, get one that will take preheated water (Atag, Ideal, Intergas to name a few). And read the papers below - been there and it works well. Combi-SuperFlow-White-Paper-v1-2-4.pdfCanetis-SuperFlow-Product-Sheet-WE-050318.pdf

Ambient temperature during the heating season is very different between the two countries. So therefore the SCoP for ASHP during the heating season is very different. Building and population density are also very different. You are comparing apples to oranges.

https://mixergy.co.uk/news-and-insights/plate-heat-exchanger-vs-coil-the-great-debate/ Interesting read, but does generalise with respect coils, making the assumption that all coils are just a single coil. Most coils are now multiple coils run in parallel, so you could have 4 to 6 separate coils fed from a manifold to make up the coil stack. It assumes the coil starts a fair way up the cylinder. My nothing special off the shelf cylinder, the coil starts as low down as practical, being just above the immersion. Not as low as the mixergy but not 20% higher as indicated in the text. I do believe the extra heat transfer efficiency. But you have an extra pump in the system also. The bit I find worrying for the real world is this - 4 hours to reheat the cylinder. https://mixergy.co.uk/news-and-insights/real-world-performance-of-mixergy-and-heat-pumps/search

Decent digger driver, job done. Worth their weight in gold. Digger and normal laser.

Noticed a few fan motors on eBay, may be worth asking for the part number...

In fact they would always trump any building standards requirements. Except a noise requirement and anyone with half a brain can work through MCS-020 noise flow sheet.

As above no. If you specify a suitably size UVC and water is sitting for weeks. If the contents of the cylinder don't get used, then there maybe a case to heat once a week to 60 Deg or if you someone in the house with a suppressed immune system. There are two of us in the house and we have a 210L cylinder it gets heated to 50 usually twice a day. If mains water, or borehole with suitable treatment system and in a closed system where air, debris etc. cannot get into the system, no contamination can occur.

But MCS standard done by anyone other MCS is the equivalent. After all a MCS Main Contractor can dish out just about the whole scope to any third party, sub contracted by an MCS main contractor.

Unvented cylinder, heated by ASHP to 47 to 50 degs.

Really depends on what the supplier pays you per kWh export. If you have a smart meter you could get 15p if you don't or live in a area where they don't function it's 4p. So even then it's best to self consume as much as possible.

We started with a combi boiler, driving UFH, thought nice, easy, cost effective. But getting a big gas boiler to work well in a low energy house isn't easy. They just short cycle, using way more gas than they should. Eventually got it working well. But swopped it last year for an ASHP, all self funded. Doing it again, ASHP every time, 3m2 coil UVC for hot water. House heated as a single zone. Three ways to heat Fan coils not the cheapest option, but good for cooling and heating Big radiators run on weather compensation or UFH on the ground floor and any upstairs bathrooms. Add provision for electric panel heaters in bedrooms, just in case you need them. If doing UFH do a 100mm thick screed and charge on a cheap tariff the same as a storage heater, or thin screed and run on weather compensation. MCS grant scheme should be the cheapest, but just seems a rip off get quick scheme for installers. From everything I've seen Panasonic ASHP seems very good, something like a 200L cylinder, and heat emitters is all you need. £4-5k all in, plus install, and there is nothing complicated. Insulation and ventilation will have an impact on heat source sizing. Best advice I have seen. We have done many kitchens in many houses, back in 1999 we spent 25k on a kitchen, latest one in 2022 was about £7k and way nicer.

Once you get below 15W/m2 there basically nearly no difference in flow temp between different centres. Something like 2 or 3 degs between 300 and 100mm centres. As mentioned the only difference is response time. With thick screed the response time is many hours per 0.1 Deg anyway. So I just did 300mm centres. Easy to install, 8 loops over a 195m2, batch charge overnight on E7 at 35 deg flow temp.

Possibly a good solution. Would keep your options open to makes and models, while R290 may give high temps nothing wrong with R32. I laid £1300 and some else just got a Daikin for £1200. Same Vaillant is circa £3500.