JohnMo

So not really on the agenda, not even worth discussing it so far in to the future, so much can change in that time. 12 years ago I moved in to my forever home - since built a house elsewhere and sold the forever home. All your equipment could be ready for scrap heap if you don't install well in 15 years time. Have actually sized the heat loads you need? No idea the insulation levels of the additional building or the house? The heat pump could be big or it could be way undersized?

First not enough insulation really You either do no insulation and use ground as a heat store, then run heating low and slow for the whole heating season, or at least 150mm PIR, but the more the better. This limits heat seeping downwards never to return. Do yourself a favour and swop to Pert-Al-Pert, easier to manipulate. 16mm is the size to use. Flow dT is likely to either 4 or 7 rather than 10. Layout looks good, making use of pipe to and from rooms to heat halls etc. Easy way to fix that, pull the hall pipes closer together then use a longer pipe length for room A-02 and make an addition loop or two in the hall.

I was thinking more like this, way less noise, possibly a better quality of manufacture. 9443_EN_Unico_Next-F_REV2.pdf One place selling them, not price checked etc. https://aircareappliances.co.uk/collections/olimpia-splendid/products/olimpia-splendid-unico-2-1kw-evo-f-16hp-pva-9000btu-all-in-one-air-conditioning-unit-and-heat-pump

So reality check - spending the same price on piping as an ASHP? If you are knocking down why are spending a fortune on ASHP and heating system? Pipes you linked to are pretty small dia. The pipe sizes will not support your huge heat pump, they are too small for you cold water main with the booster. I have a long run from ASHP to house and use 28mm pipe for that, your 18kW will have to support 3x the flow! You really would need a secondary return loop for DHW to make hot water usable in the house. So you need an additional pipe. If you are knocking down and rebuilding, your heat pump will be huge and no longer appropriate for new house. A new build to slightly better that building regs is unlikely to need any more than 6kW. While your house is being built the 18kW ASHP will not support your rental and workshop - it will be too big and short cycle to an early death. Suspect some more thinking time is needed, your current plan doesn't work!

There is a review of different makes and models in 'Which' some are really good others are pants. Best one cooled the test room from 35 to 25 in around 30 mins the worst was over 3 hrs.

If running opentherm does the UFH even need a 2 port valve. Could the UFH pump just be wired direct to thermostat. UFH zone hot, UFH pump stops?

I said pulling, as in pulling in electric. The graph of our ASHP was pulling in 840W it's a 6kW that modulates poorly. So see no reason why a 4kW ASHP would need anything more than 500W, should be way less. 1.8kW is output heat I suspect. So doing cooling could be pulling in 360W or less

That would heat my house at -9 outside. Even poorly insulated a 1 to 1.5kW through wall ticking away would be good. It would only take 300W electric. Or about 7-8p an hour to run

Why bother with a split system, just get a through wall Aircon unit. They are generally smaller.

Buy Greenwood CV2 or CV3 dMEV. They are best part of silent, they have smart auto boost on rising humidity levels (so taking a shower for example) and cost pennies a year to run. Then install humidity activated trickle vents in place of the your manual ones. Any trickle vents in wet rooms seal up. Then you will have a simple demand activated ventilation system.

Good possiblity is no. If you have intermittent fans currently I would consider changing to dMEV, these run continuously at a low level and are silent. In our last house the utility fan didn't come on for the 10 years we were there.

I would leave it alone for a couple of hours and see if it fixes itself. Are you running weather compensation? But some alarm bells You have ASHP which is great, but your house is zoned and this will mean inefficient running If you need thermostats flow temp is too high. If you have zone it may also mean you have a buffer again driving inefficiency.

Not got the money at the moment, to change car, so a bit of a sacrifice to save a hundred quid or so.

You won't need much sun to make it super hot. Add blinds/curtains to room lights, window and bifold, and manage temperature by closing as needed. If you an ASHP can it do cooling?

Video to watch Thread to read

So where is that mentioned?

as I said you need to read building regs, have assumed you are in England. Not sure where your figures align with what BR asks for? From building regs Mechanical ventilation with heat recovery Ventilation rates 1.67 For dwellings using mechanical ventilation with heat recovery, each habitable room should have mechanical supply ventilation. The total supply air flow should be distributed proportionately to the volume of each habitable room. 1.68 Mechanical supply terminals should be located and directed to avoid draughts. 1.69 The minimum total continuous rate of mechanical ventilation with heat recovery is the whole dwelling ventilation rate in Table 1.3 1.70 For dwellings using mechanical ventilation with heat recovery, each wet room should have a minimum continuous mechanical extract ventilation high rate as given in Table 1.2. Tables are

Without fully check AI answers, I wouldn't trust them at all. The answers just change depending how you ask. Go to the core document - building regs - what does that say? Understand BR, it makes life way easier, no one can pull the wool over your eyes. I could read it for you - but...

Have you looked at coanda effect supply terminals? They look like this and move air across the ceiling about 4 to 5m, before coming down. Maybe easier than floor ducts.

Save £1000+ and buy a humidifier? When you look at Aircon, some will monitor the humidity and draw in fresh air to manage RH%.

Do you actually need a feed in the dining area, does your dining area have a door to elsewhere in the house? Or a vertical wall connected to an accessible area in the existing house?

How? from reading up on it, it doesn't do it it's a heat exchanger in the air stream. Just AI says yes, doesn't make it real. Download the manual and have a read. If I am wrong I will happily eat my words. I did look at an evaporator unit (different make) for the MVHR you need very dry incoming air for it being if any use. UK humidity made as good as useless. That's how it works needs cold water through a heat exchanger to cool the air.

Datasheet extract -

We have exactly the same overheating issue. Prime reason for finding a reasonably price ASHP, and cool via the floor. According to data sheet at a water flow temperature of 7 degs, and 400m³ h you get 1.5kW cooling - pretty much a waste of time in my opinion. Not sure it does evaporation cooling according to reading the data sheet, it needs cooled water.

But I would add, have it only on the heating side of the 3 port diverter valve. Otherwise when heating DHW you are also heating an unnecessary high volume of water. Plus if you have UFH pushing 50+ degs water directly into the floor once the 3 port diverter swings back to heating duty - not good.