JohnMo

You could, but unless you have considered and worked on airtightness, it not likely that airtight. Another alternative is dMEV, same as MEV (nearly) but no ducts, just a silent fan in each wet room and the same inlets.

MVHR is supply and extract so every room needs an air supply. But by using a cascade system some of this air doesn't need to be directly ducted to the room. This is my house and what it would look like in a cascade system, I did do this in the end for various reasons. In the above there are only two units and two supply terminals and three extracts and one through wall fan unit. It uses the principles of what goes must come out, and fans to force air wherexit wouldn't otherwise travel. Those units where Fresh-R, but any normal MVHR unit can do the same thing with a little thought. MEV would only extract from wet rooms, and use cross flow ventilation to sweep the house. Supply points would be either trickle vents on windows or through wall ducting.

The air travels all the way across the room, approx 5 to 6m depending on flow rate. A normal door needs about 8 to 10mm, some of ours area little smaller, but doesn't seem to affect anything.

New build - nearly all my supply terminal are these https://www.epicair.co.uk/products/supply-air-valve-coanda-effect-8960-90mm Not really true, but mandatory anyway. You just have a supply in the bedroom, the air travels out of room by undercut, to the nearest extract point h as you balance flow and return it's not an issue. Silent in operation, connected direct to 90mm duct.

But does either work on a small scale?

We try not to don't get paid for it. We do cool as required in summer, if it's sunnier the house is generally warm enough it needs to be cooled - free cooling. Not sure about We don't do legionella cycle, as we consume enough hot water not to require it. But we do heat the cylinder to 70 via diverter. Reduces or stops any requirements to heat via heat pump. Our primary excess goes to battery first.

Really depends on if you did any airtight details to ensure the property is reasonably airtight. If it isn't you are just adding more ventilation in a additional to what would normally occur, so it is likely to increase heat loss. I would look at demand controlled MEV with demand controlled inlets first. Runs to keep humidity levels stable, otherwise it's off or at very low rates. Easier to install cheaper to run. If set on MVHR you should consider a design that is a cascade system and it could also make use of coanda effect supply and extract terminals to minimise duct runs.

I was quoted about £700/m2 based on double glazed windows, with a large percentage of the money due 28 days prior to delivery. This was for a wind and water tight, kit of parts. This excluded, all ground work, and all site assembly. But didn't go that direction on the end

If can walk on it even if not designed for walk on it needs fall protection. So you need to stop them going on the green roof. Remember you cannot use horizontal bars etc that a child could climb up and over

That can be attenuated with suitable vents that knock the noise transfer down to nothing.

Greenwood CV2GIP, silent, smart humidity stat, easy to install, commission etc. cheap off eBay sometimes available. But to work any fans need somewhere to draw from, so you need something on the other side if the room like a trickle vent always open. But I would list what ventilation is actually installed now and look at the whole house ventilation strategy in the round, before fixing one thing.

I saw them for sale in a garden centre a couple of months ago, they are still sold. It didn't come with the fire place, but was under £50.

But not for an airtight house with the MVHR off or no windows open!

Or the other alternative is a combi storage boiler such as a Viessmann 111-W it has the cylinder built in to give the same effect in a compact package, 25kW boiler will modulate down to 3kW. Will 20l/min DHW flow rate. Install is the same as a standard combi, no complications.

All true, but it keeps the wife happy knowing we could light the fire.

This was mine for ICF build (external insulation), I added a 70mm up-stand to the the screed edge also, not shown on the drawing

Overall less expense than a UVC and boiler combination. No servicing required unike an UVC, pretty simple to install overall. If OP doesn't have space leave it out. But for anyone with a Combi boiler great performance for nor money, and easier cheaper than an UCV

At no-where near that age, I will still have enough wood left from our build, I suspect by the time I get there. So for the amount of time we use it, generally only once in a while and only two logs each burn, I will still keep it. Also I think we have had about 10 power cuts in the last 12 months, one for over 24 hrs, the others a few hours each time. So its nice to have the secondary heating system.

Depends how far is it travelling 1m or 100m or something in-between?

Why hasn't your architect not already planned this out and structural engineer not done the supporting drawings?

Higher flow rate than you would otherwise get from a combi, due to a lower dT required to be added to the warm instead of cold water, especially in winter. Consistent output flow rate winter and summer. In fact our hot water flow hasn't changed since we installed an unvented cylinder for the ASHP compared to the combi and pre heat. Simple additions, big performance improvement. What's not to like.

Another read https://www.heatgeek.com/viessmann-vs-worcester-boilers/

Not sure how else you would do it. Block work and lintel over, pea gravel around pipe... Assume you mean by private drain, you mean waste pipes from your own house and not some other buildings? Another buildings waste would be rerouted around the new foundation not through or under it.

You can just as easily design a standard strip foundation to be just efficient and can be completed by your local ground workers

For radiators use this to get a decent radiator size https://www.heatgeek.com/do-i-need-to-upgrade-my-radiators-for-a-heat-pump/