JohnMo

Also think the misinformed population think an airtight house is a house ready to rot and suffer from mould at worst or you are talking meaningless words at best. So who cares what the EPC says? a bunch of self builders and those chasing free money from grants and that is where the list stops.

I would spend that money replacing the high temperature radiators with radiators designed for dT 15. That would allow you run the whole system at a single flow temperature. Install limiter trv's on the radiators. Run the whole lot as a single zone with a 2 Deg setback if you want at night. So all heating is either on or off. Everything on a typical winter day will be running a very low flow temps 25 to 30 and to a large degree self modulating. If room temp increases output decreases to keep room temp quite stable. No additional pumps required, no LLH or mixing sets, run the whole system from the boiler pump on WC run from the Vaillant controller, no additional thermostat required. If it looks or sounds complicated, it usually is with little or no advantage. Your shopping list reduces to Valiant kit: Boiler Valliant Ecotech Plus (new model) sized to suit heat loss - definitely not just a big one. Wiring centre Weather Comp Unvented cylinder - install a heat pump cylinder with 3m2 coil. This will give super quick recovery at low flow temps. Size cylinder the same as a heat pump and store water at about 50 degs. So 210L to 300L for 3/4 bed. VR10NTC temp sensors: Unvented Cylinder pocket 2 Port Diverter splitting the flow from the boiler to A) the DHW (for hot water priority) and B) Rads and UFH Some radiators and plumbing. The above will give continuously condensing running conditions and efficiency of around 105 to 110%. Compared to closer to 80 to 85 with the other design mixing down from hough temperature. The first step is a heat loss calculation for whole house and the radiator rooms. This will allow a suitable boiler and radiators to be specified.

Correct

That's a life time, tech wise, in the future. Why are you worried about it now?

Just translated the text Depth between 2 and 6m, Length between 30 and 60m. That's long and deep!

Hope your ready for the drop in hot water flow. Isn't this a degrade. Make sure you get one with a good hot water flow, some are absolutely rubbish flow rates. Choose wisely, not any old one will do. You will need cold water inlet control group, basically a small expansion vessel and over pressure relief, and a condensate drain. Some reading of how to improve performance. The cylinder referred to in the document looks like this.Combi-SuperFlow-White-Paper-v1-2-4.pdfCanetis-SuperFlow-Product-Sheet-WE-050318.pdf

We were away this weekend staying in a log cabin heated by an 8kW ASHP. The friends we stayed with didn't mention anything about the noise, because it was pretty much silent, even while doing DHW heating from a couple of metres away.

We were away at the weekend in a log cabin. ASHP heating which was nice to see, and intermittent fans in the bathrooms - forgot how noisy the fans were. ASHP seemed to run well, and nice quite, but the plumbing was so needlessly complex. The friends we stayed there with were looking everywhere to find the air outlet for the heated air - completely confused when I said the heated water just like a gas boiler and really didn't believe me.

The basics are here https://www.open.edu/openlearn/nature-environment/energy-buildings/content-section-2.4.1

Why - does what you were given allow you get the grant? If yes move on. Are you wanting to sell, don't pay the bill/complain.

I would calculate it yourself as that sounds big, 30% of the heat loss sounds better - unless you have an extremely leaky house or you are flowing way too much through the piv system. Then adding MVHR would just make heat loss higher due to the additional ventilation. Having a ducted pre heat will only preheat to 7 degs at best (if very long and a reasonable depth) but possibly closer to a couple of degrees above ambient. Spend a couple of days optimising the flow settings of the piv. Get a CO2 monitor, set it the bedroom first and get so you hit a max of just under 1000 ppm overnight with the bedroom window closed. Don't worry to much about humidity levels as they will be all over the place at the moment.

Heat loss calculation for house at your lowest practical outside temperature, normal to do it at about -3. But what you are being offered sounds huge. Not true, you run UFH continually at a low flow temperature, if you find a room is too warm or cool you tweek the loop flow rate to compensate, once set it is self regulating to a large degree. Only time you need lots of control is if are trying to blast it with really high temps for short periods. WC is the opposite to that. Would suggest you find a different plumber. Have you thought about increasing bedroom radiator size so you can flow all the house at the same low. temperature? With WC you don't really need them, but if you insist you have them as over temperature limit stops. So target room temp is say 21, set them to 23. Install the correct sized boiler and you don't need this. Have a watch of this video on a Vaillant boiler install.

Not sure you are being realistic on the cost v reward

I did look, no one wanted to come this far north, so just did standard stripped footings and stub walls and did plenty of insulation below and sideways to stop heat loss as much as practical. Easy to get contractor to do that without much learning curve.

Because you want vertical cladding and have 300mm wall thickness. My ICF blocks started at 365mm thick before internal service void and external cladding.

Do you have the land for it, thought you needed quite along run to get the benefits bit like a GSHP. A short run (a few metres) is zero benefits

What is the current ventilation strategy used for the property? Not cheap, could be used to move air from these rooms to wet room adjacent to these rooms, then use a dMEV fan in the wet room to provide continuous ventilation. https://www.ventilationland.co.uk/en_GB/p/brink-indoor-mixfan-co2-controlled--up-to-70-mh/17927/

If you want MVHR instead of PIV, look into cascade MVHR. Supply is pretty much the same as the PIV - one supply, possible some through (internal) wall vent fans to move air towards the extract points as you require. The only difficulty comes in getting ducts to all wet rooms. But you would be better spending your time getting you your existing system to work more efficiently on an as required basis instead of set speed.

Because the press tell people they are noisy, so they go looking for the noise? Some people try to run them like a gas boiler so they run flat out and make more noise than they could?

If doing that plan for a suitable sized buffer within the heating system and the added inefficient running it brings. I did that initially until I started to get the heating bills. Now run as a single zone no buffer and one thermostat. Works well.

We have ours behind a shed and you have to go to back of the shed to see if it's running. Not silent but not noisy either when running. Some click and clonk when starting.

Not a fan, too slow to heat up and collect down unless you mean just in wet rooms (I know as we have it everywhere). You should not need any in bedrooms, especially if well insulated and bedrooms are upstairs, just electric heater just in case you feel the need. Or an oversized radiator when we talked to builders around us, some didn't even want us on site, unless specifically invited.

That's where we started, until the prices came in, then moved to other ways to build. We bought with planning permission and ended up with a house design better than we would have done. We just tweaked it, to get the interior better suited to us.

Are you trying to get elected or something.

Remember that's only external walls, internal construction if studs can 70mm studs and 12.5mm plasterboard each side and taped. Also if horizontal external cladding and using 25mm battens and chasing in electrical and plumbing elements and plaster skim you could reduce quite a bit. If doing block walls 200mm (2x 4" blocks) plus cavity, plus 25mm vertical external battens, plus cladding and plastering. Even with 150mm cavity your down to 400mm.