JohnMo

But the scheme is different in Scotland - heat pump mandatory on a new build so no grants for us.

That also increases U value, I looked at additional PIR on our build but the difference between an unventilated air space and actual PIR is too small to worry about.

At 0.26 your wall insulation must be very poor. I would look to add 50mm or more externally, if the figures are correct. Floor is likely to be around 0.08 U value. 32W/m² is huge. Similar build to ours is closer to 15W/m² at -9. Heat loss at 7.3kW sounds excessive.

Timings as @ProDave says is pretty real. If your using a ToU tariff, I do and have the following 4kW heat pump - Hiaer monobloc. Then a use a direct UVC, so is charged via immersion (have plenty of solar also). Heat pump is then not trying to do heating and DHW in a cheap period, they are independent of each other. Going that route Heat pump under £2k when you claim the vat back. Cylinder £600 incl vat. Drive via simple time switch. £20. Plumbing very simple. You have loads of water volume.

I went down the route of looking at CO2 sensors etc. 5 years in none of it is really needed - nice sales accessories. We need a CO2 monitor in master bedroom (Scotland) and I used to monitor it, all the time (very rarely look at it ever now) I tweaked MVHR flow rates to get CO2 max I was comfortable with overnight, and that's it. We have dry contact switches outside each wet room to boost and a humidity sensor in the MVHR unit. MVHR almost never goes in to boost. It just doesn't need to, house humidity doesn't rise much for long.

150mm is fine, but filling just floor is lazy. A new build requires so little heat. Layout on software, you can simplify it a little by making the angle 90 degs between the two wings. One manifold or two the supply and return will be similar lengths. I would aim to use one manifold. You will not need a pump and mixer on the manifold, so don't let anyone sell them to you. Just run supply and return in 28mm you will have zero issues. Would suspect heat loss is below well 4kW, do don't let anyone sell you a big heat pump. I had a 6kW and found it too big, so swopped it out to a 4kW last winter. Note on your loops A-1, move manifold in room and all pipes passing through room do the heating - delete dedicated loop. A-2 and A-6 delete and use pipes passing through that area, spread them out instead of bunched up. Pipes can be 100m long. Loops A-10,11 and 13 add up to less than 200m, so could be 2 loops instead of 3. But if using 1 manifold that may not be possible, however an optimised design may allow 200 or 250mm centres do then that room and room next it could reduce the loop count.

I used loopcad via a trial app. UFH is very similar in a lot of respects to a radiator. A radiator you size to the room heat loss and target room temperature, each room has a radiator of a suitable size for the heat loss/temperature and the system as a whole is just about balanced out the box. The exact same applies to UFH, you size your loops in the floor to match heat loss and target temperature for that room. You can fill the floor with pipes but it's a bit like sizing a radiator to fit your longest available wall - you wouldn't do that. Can't see the dimensions on your drawings but guessing around 200m²(?). If so we are about the same size and only 7 loops. Our flow temps are also super low.

Do yourself a favour and do your own design - there is zero room balancing by design. The design is for multiple zones/multiple thermostats, not single or limited zones for ASHP. Suspect you can easily delete a few loops by spreading pipes that transition through various areas.

Obvious question, is why do you even need a controller - once set what is there to adjust. MVHR commission forget, except filter cleans/changes

But do you really need a dehumidifier with MVHR is winter. Our humidity levels are pretty low anyway. Overnight and they are dry next morning. MVHR doesn't even go into boost. We only dry stuff that doesn't going the heat pump dryer.

Yep, even in Somerset. UFH is so cheap to install, why wouldn't you, insurance even if not connected. Good for cooling as well. Passivhaus still allows 10W/m² for heating demand so a 200m² house that's still 2kW heat demand on the coldest day (48kWh). I would rather that supplied via the floor than and electric panel heater being moved about. Sensible in ALL houses

@MPx is this Passivhaus or "a passivhaus" as certified or sort of a Passivhaus? ASHP is now about £2k for a 4kW Hiaer. UFH shouldn't cost more than £1k. Do a direct UVC for domestic hot water, about £600. £60k is a lifetime of direct electric heating on a decent tariff.

Unless you are in Scotland and then a score better than 3m³/m² @ 50Pa has to have MVHR - so applicable to any low energy loss house, so not an extra really for Passivhaus.

But have you gone back to designer and asked what is the minimum spec you need and still comply with what heat loss loss that applies - it's not black and white. The door by definition is protected and in a different environment to an external door. Nothing in a Passivhaus has to be Passivhaus certified just perform to a defined standard (which is variable dependant on form factor and many others). If you can only get a £7k door that is a stupid way to build a house (and doubt that is true).

That works, but save some money and just use Thermolites. They are in a nice dry area, so will.work well.