JohnMo

On a public forum no. You can take what I say or ignore it. Just look at the theory of how a heat pump works. Basics are - refrigerant is at a much lower temp than the surrounding air. Air is forced through a heat exchanger by a fan. Inside the heat exchanger is refrigerant, it absorbs the airs heat (hot moves to cold). The warmer the air the more energy it allows to be transferred the refrigerant, so better the CoP. The sun being out doesn't change the localised air temperature (in open space), heat pumps will move many 100s of m3 of air each hour, so it makes zero difference if the heat pump is located in the sun or not - air will be moved from everywhere.

The only bit I would take away from that is doing DHW heating when the day is at its warmest.

Depends if the person saying 100mm is ok, is the one that has to pay the bill, for the additional downwards heat loss. I would treat be boiler in the same way you would a heat pump. Design the radiators for a max flow temp of 35 to 40 deg, they will be big and never feel hot, but you basically run them continuously on weather compensation, house is always warm. Also if you are installing a cylinder, get a heat pump one installed with a 3m2 coil. X plan will allow two different flow temps to be used, both set to get the best form the system. Some reading material https://www.intergasheating.co.uk/homeowner/2022/07/13/the-knowledge/

Hope you get all your ducks aligned before committing, would not be very good if the DNO imposes a limit of 16A on exports, because the local grid cannot handle anything more than that..

That is still massive

Wikipedia, is a site any tom dick or Harriot can upload too. Nothing scientist about that site. If I wanted to upload and say the world is flat and made of chocolate I could. 5 ACH is pretty rubbish, especially if wanting MVHR. ASHP in sun is a daft idea, an ASHP doesn't use radiated heat, it takes air temperature so make no difference if located in sun or shade for efficiency. Being in the sun messes with the temperature probes, so not the best idea. Not done the heat loss calculations obviously, as there is almost zero cold bridging with durisol blocks.

With 100mm insulation stick with radiators, but oversize for low flow temperature. You really need 150mm (ground bearing) insulation under UFH to make viable from a downward heat loss perspective, block and beam makes matters worse with downwards heat loss. Assuming you have a gas boiler get that changed to run X plan if you can, one temp for hot water and the other weather compensation for heating.

About 40 to 50mm thick, weight no idea per m2

Why - Computherm are way better, you just need to control on a single zone, pump controlled by thermostat. Thick screed doesn't need remote inputs from work, it needs to run continuously to batch heat (4 to 12 hrs) depending outside temp and flow temp, or continuously at a low flow temp. Why what are they going to do? If your floors is getting to 26 your flow temp is way to high and you are trying to do things too quickly, without knowing anything about your house, suspect you flow temp should be in the 26 to 30 (continuous) or 35 (batch) range With a 140mm floor thickness if you are getting hot, it has taken you 24 to 48 hrs to get there, you ain't stopping with a floor probe, way to late. Example, my heat pump is set to a target flow temp of 35 degs, after 12 hrs of running it's flow temp is 33. Would take me another 12 hrs to reach the flow temp of 35. The floor surface temp when I stop heating is around 22-23. You have 50% more floor height to heat up. Your floor will be super slow to do anything.

Generally ok, but could be rubbish, depends on make really. Ivar good and very adjustable, ESBE electronic good, most other not so good. Set the flow initially to match the pipe length and adjust up and down there. Plenty of calculators online. Thick slab is best heated by batch heating to a very low (0.1) hysterisis thermostat, or running continuously, all on a single zone.

Not sure how you would be allowed to do any work yourself, as the work has to be done by MSC contractor to get the grant. All things being equal the cost delta on a new build is the difference in cost between decent boiler and heat pump, everything else is basically the same. So really should be £1000 or less. My cost delta if I hadn't installed the gas boiler first, would be around £500.

Sorry slightly off topic, really consider an ASHP. My build started with a gas boiler and although not passive, getting the gas boiler to work efficiently in a low energy demand house isn't that easy. Our max heating demand is 3.5kW, but most the heating season you need less than half of that. Had two heating seasons with gas boiler and then self installed an ASHP. We have plenty of solar, battery and on E7, but even in Dec and Jan when solar is rubbish the ASHP is cheaper to run than gas. And it's easier to get running well on low heat demands.

Bad idea - You would have to very careful doing that. Would need to be copper or stainless and very clean, otherwise it would not be healthy to drink the water later. And certainly don't want to get carbon steel corrosion products in you unvented cylinder as you start to get pin hole corrosion in a couple of years. We had an 1830 build last, that had a cold room, thick stone floor, walls and 50mm thick stone shelves, never changed temperature year on year. A passivhaus doesn't necessarily mean exactly the same temperature everywhere. Really depends how you build the space.

So to be pedantic, it's not fully installed. Not sure what temperature you currently have, but we had -3 the other night and a few nights hovering around zero, snow and sleet yesterday, -2 tonight. So the system will generate plenty of condensation, if only half insulated.

My view is install fully, then run. Don't run part installed.

I would expect it's a secret. Localised reduced bore has little real effect on system pressure drops, if you do the pressure loss calcs. Would think there will be a pressure drop table in the install manual, just a matter of finding it online.

How are you trying to set it up? What flow temps and for how long etc? Big heat pumps are really best run on weather compensation or a low set flow temperature for very long periods. Do you have lots of zones, buffer cylinder, explain your setup?

Looking good. Nice to see it's able to run constantly at 25 degs.

After quite awhile messing with WC, I actually find it cheaper to run a set flow temp of 35, and let it run as long or short as required by a 0.1 hysterisis thermostat. Low heating demand and WC doesn't make that much difference, my curve was something like 0.3 per Deg OAT starting at 10 degs down to -5. I get a consistent CoP of just over 3, but only because I make it heat during the night when it's coldest - because my tariff is cheapest then. Bathroom towel rails, we did electric. If you do UFH in bathrooms cram as much pipe into the floor as can, as floor surface area ends up quite small. If you want to do intermittent bathroom heating the output needs to quite a bit higher than you think you need. Especially if the ensuite if attached to bedroom at 16 to 18 Deg.

You said earlier that the aga had an external air feed? If that is the case it doesn't draw air from the house. So the ground floor only has a utility fan that is light switch activated with no over run timer? And upstairs only one fan that is actually used. If you aren't replacing air and you are developing humidity your house will get damp.

So your only forced ventilation for the whole house is a single bathroom fan. So you really need a fan in the other bathroom and kitchen. The Greenwood ones mentioned can be really from eBay. Adding a humidity activated trickle would ensure the cross ventilation is occurring when and where needed. Example bedroom vents normally closed in the day opening during the night when you are sleep etc.

Why? Bit like leasing your TV in the 70/80s, 4 years later you could have bought it twice over.

For new builds it is already cheap enough, unless you insist on paying a premium for a Vaillant heat pump. The UFH should already be being installed, so it operates on very low temps, a cylinder is most likely being installed, then the only cost added is the difference in heat source price. A new build should almost never need a heat pump above 8kW, most a 5/6kW is bigger than really required. Plenty of decent heat pumps on the market for reasonable price. Retrofits are always going to more expensive, with microbore and or small radiators etc. to contend with, they should get the grants. A heat pump should really be made mandatory for all new builds anyway (without a grant) and any other reason you need planning permission. If you don't like it, don't do the new build or extension etc.

Biggest joke is it says the same for wind turbines, bet there aren't any MCS installer, as there are no grants. Once grants stop, there will be very few MCS heat pump installers either.

That fan looks ideal also. Set to run continuously, with automatic humidity sensing and you could minimise the overrun timer as the unit would look after itself. However 10l/s isn't enough to ventilate the house. I had a look and the AGA requires a 30cm2 air inlet grill permanently open, is this in the kitchen? Your ventilation strategy will have to take account of the air requirements of the Aga so you don't start to depressurise the house.