JohnMo

Multi meter?

Thin screed of almost any type is fast warm-up. It also cools quicker as there is less heat capacity. You going to have to explain the less heat loss below bit? Not sure that makes much sense.

Read product websites with caution. Sand cement screed, isn't the same as concrete, the thermal conductivity changes dramatically with material make up. Same as some screeds are insulation. Big range of thermal conductivity in most material. Various grades of concrete for example.

There are 6 sets of doors inside/outside in kitchen alone. Ditch at least one door to hall. From outside to utility 2x doors, ditch the internal one and the wall and make utility bigger. Same with front door. If you are airtight (MVHR would suggest you are) you don't need double doors.

Not saying it doesn't work, but travel path can be quite short and it's better to wash through general areas also - gym is under ventilated anyway

I have never seen a good reason to have a supply in an extract area - kitchen. I would supply more to the gym instead. You need to calculate the most onerous run, not all of them. You need to calculate from MVHR to and including the terminal. Nothing wrong with F7, although I have never had any issues with just G4. Map where the air travels to and from, do you have the whole area covered, with flow going through hallway and stairs.

No way are you pressurised that high. In the 10s of Pascal's, maybe. 10kPa - no. Are you sure you don't mean 0.1psi maybe, not sure I would want to open a door against that.

A sketch of your proposal would make it clearer what you propose. An idea of distance also would be good.

Do you close the cap at the top to close the AVV off? Post a pic of what you have and where the issue is.

It would be worth checking the voltage at both CUs they should be about the same. Check them at different times of the day to see the difference.

How far is the inverter from the consumer unit? If a long distance you could have a big enough voltage drop, that the inverter is producing enough volts that it goes off because it's hitting max voltage point for trip.

If the system is running mostly from excess PV, no point doing anything that will cost anything. Trimming back flow temp on heat pump will give the best CoP. Make sure the heat pump return is a low in the TS as possible. All a bit of a balancing act really. Don't run the ASHP when it's likely to go through lots of defrosting unless the electric is free. CoP takes a hit during defrost.

Not sure why you want it pressurised? But you would normally equalise flow and extract, this equalises pressure. If it is pressurised you would struggle to open an inward opening outside door. So I doubt you are actually pressurised, you would also need an airtight house. Any ventilation system will bring your humidity levels down to 35 to 40% in a period of sustained cold outside.

With a fan coil running for long durations how do you manage indoor humidity levels in winter, if using for heating. I know some expensive versions of A2A are connected to allow fresh air in to prevent humidity dropping too low. If we get a prolonged cold snap heating with UFH and have MVHR ventilation we can get as low as 35% humidity.

I assume you are overthinking stuff. Never seen any signs of mould been running for about 3 years. Keep unit on, change or cleaning every six months, open up every year have look clean up. That's it. Airflow rates should be way to high for mould to form. What cube are you talking about?

You wouldn't have many health issue with plenty of that. No reason to breath anymore.

I would be careful as HVAC means many things, which bit are you thing about HVAC - Heating, Ventilation, Air Conditioning?

Sounds about right It is, but so is the surface area available. Our house about 192m² so that approx 6kW of cooling power. A set of fan coils may be slightly more effective and targeted, but my heat pump only puts out 6kW of cooling power. As I said above fan coils are better than UFH, and UFH takes the edge off and allow quicker recovery to normal temps. If you have UFH already moving to cooling with a heat pump is zero cost option, which makes the house more comfortable than it would otherwise be. Adding fan coils can make a more comfortable house, but at a cost. If starting from a blank sheet, install fan coils. Why would need to be that high? We flow between 12 and 14. The heat pump will generally cycle. Running for about 40 mins. Manifold does get just below dew point, as I see dulling of bright stainless. But not enough to bother about. To get floor surface temp to 17 you have to flow cooler than that.

Sort of, but looks more like a car radiator that a house radiator.

Not disagreeing - just adding full contextual details. There are several mechanisms at play for both fancoils and UFH (cooling). Fan coils are way better if you have them, that is a given. But if you don't have them, cannot justify the costs or you are retrofitting a HP and cannot justify moving away from UFH. When UFH is in cooling mode, it does make a warm house feel cooler, even if actual air temp is quite high. But also allows cools the house down quickly (compared to not having cooling) when the sun goes away.

Sorry you are not comparing apples with apples. UFH flow temps are warmer than fan coils in the cooling mode - you should be flowing a temp to UFH system, that doesn't generate condensation. At most I have seen a little dulling of the stainless steel UFH manifold at the end of cooling cycle. Never seen a drip or drip forming. Why are using a mid position valve on a heat pump system? Assume you actually mean, diverter valve? Only when discussing radiators - not UFH. And radiators don't do cooling at all well - not really applicable to a cooling thread

You should get a structural design certificate from one company for the whole property including everything from the foundation to the roof top. If the glazing company (and any other company) is providing structural design calculations, the company issuing the structural design certificate should review, comment and approve as appropriate. This should be standard working on the structural drawings and/or notes. Your architecture tech, is misguided.

That is only part of the mechanism. UFH cooling works in the most part by pulling the heat from the body. The floor temp being substantially below the body temperature. So your body radiates heat to the floor.

Most are, but you need to read the datasheet. Some need additional parts (e.g. Vaillant). Simple answer heat pump doesn't care or know what it's pump too. You set flow temperature according to likely dew point within the house. So if you target a house temperature of say 21-22, then your flow temp is set around that. But it is floor surface temperature that is affected by dew point. We flow at around 14 degs. No issues in 2 summers. Fan coils are more effective as you can run 6 deg water through them.

A video to watch https://youtu.be/kVaxAfXQPDU?si=nIsu2BUM-O5wMIQM