JohnMo

We have 200mm of PIR insulation below our bedrooms and carpet, UFH will keep the rooms circa 18, we open the doors if we want them the same temperature as the rest of the house. You may flow up to 35, but surface temp is only a couple of degrees warmer than the room, most the heating season. A nice layer of insulation (carpet and underlay) just stops that temperature reaching the surface. Net effect is rubbish heat output. It doesn't matter how long you wait.

We have standard carpet (wife insisted) and UFH underlay and it kills UFH performance pretty much. It's a bit like wearing a good overcoat on a cold day, you stay warm the cold doesn't get in. We run full weather compensation however. But as you have thermostats run at a set flow temp, you may have to wack the flow temp up x degrees and it should work fine. You would need to fine a happy spot via trial and error. Dig a bit deeper in your pockets and get proper carpet, dump your thermostats, run weather compensation and your energy savings will pay the extra needed for proper the carpets.

Why that much? Over thinking things. You can use passivhaus principles for any build. Main things are thermal bridges, continuous insulation, form factor, airtightness. So you need to consider ventilation.

Add it the outside if you wanted. Do people in the UK buy by the ft² or m², thought they bought by number of bedrooms and that was about it. Hence big builders building shoebox sized houses with loads of bedrooms.

They are very different materials, aerogel is a fibrous soft material, compacfoam, is a solid EPS, looks EPS but rock like. You can drill it screw into it etc. treat it more like wood than insulation. So fixing self drilling screws direct through compacfoam into the steel. Then if you wanted plasterboard screw into to the compacfoam or foam into position. Aerogel I bought it but I ended up using PIR, but @Nickfromwales suggestion of compacfoam is way better. We did upstands for our roof lights with it, easy to use

Observations Just tried to find a price for the Nibe, only price I got near, suggested circa £6k, so 3x the price of my Haier 4kW. Will it perform any better than my Haier, possibly not. Yesterday was between about 4 degs and 8 degs, and it just ticked away all day at an average CoP of 5.6, peak CoP around 6.3 (flow temp around 26-27).

You can work it out knowing your heat loss and then W/m² Just use this as a baseline, you may need to extend the W/m² and the MWT - mid way between flow and return temperature.

Run in WC mode everything is always calling for heat. The fan coils just modulate their output to match room conditions by changing fan speed not water flow rate. So all good

Looking at room temperature the line is steady climb, which is good, but suspect your flow temperature is way to high. A 2 Deg rise over 12 hrs is very fast for thick screed. Your +15 degs I would be setting sub 25, maybe 20 to 23, your -5, 28 to 30. Start low, and move up. A hot house is a horrible place to be, especially when it's a thick floor and it doesn't cool for an absolute age. At 10 degs your house will not need or very unlikely to need heating, when dried out. Your running 30 degs, that is nearer what you will need at -5.

Nibe (and others) use an energy integral, so if they are cycling they use a fancy time, to degrees of heat delivered calculation, so they can provide a higher than target temperature, to get a decent run cycle and time off, while still managing the energy delivery to house. Basically ensure short cycling is never an issue and energy delivery is on target.

Your form factor is good, it's a rectangular box. So U value effect is different from a poor form factor (like our house). I would look at a slight bigger scale than just the walls, so floor windows/doors and roof. Get a bigger picture. Note: Passivhaus required U value changes with form factor.

I say look at modulation - can it run all day long at most weathers? As in not cycle?

Our new heat pump has the "App", I did connect to it, you can set time scheduling, set quite mode, turbo mode and holiday, but an utter waste of time when you do WC, so killed the connection.

Very unlikely for it to be any warmer than the room itself. The heat from the pipes will only migrate so far before it runs out of energy

We have our UFH manifold in there, so whole house UFH pipes pass through it. No additional loops needed there, so why put them in?

Who in right mind remodels a kitchen in under 10 years, 20 years isn't that likely. Most kitchen units have a decent long warranty. We have been in our house for 5 years now, redecorating isn't even on the horizon, remodeling a perfectly good kitchen is unlikely ever in my life time. I would possibly build another house first, that's unlikely also. May upgrade a laminate work top but nothing else likely. Your just planning for thing unlikely to occur, adding complexity likely to go wrong.

For me the following comments The floor array hasn't been sized for room output - they have just filled the floor with pipes, so zero design effort. You should really design output to match room design loads just the same as you do with radiators. As it is designed, you may/will need room thermostats to manage overheating, this drives a buffer and other complications. Suspect you will not be able to set room temps by water flow balancing alone. As mentioned dedicated hall loops aren't needed. But may be needed if you need to manage each room temperature via a thermostat. WC and bathroom are next to each other, you could easily share loops. So one loop serving both rooms. To add to this, suspect the utility could also share the same loop. Take into bathroom first, then WC and the utility and then back to manifold. WC will actually need little or no heat as it's internal room surrounded with heat areas. Spiral or up and down makes very little difference as dT (flow return temperature difference) is only 3 or 4 degs, plus floor temp is way below body temperature, so you will not feel it.

Our 4kW can put out around 20L/min of flow if required. It's currently doing around 2kW and the flow rate is around 6-7L/min. So zero need for additional pumps. We are heating 192m² UFH floor area plus a fan coil in another 24m². So do you need the pumps, possibly not, assuming you are flowing the same temperature to each floor area covered by each manifold and don't need mixers. Even then your ASHP should be able to drive an electronic mixer to reduce temp to the lowest flow temp temperature, and do it all without additional pumps/buffers etc. Maybe start a thread, with your details and bottom out what you do and don't need?

Bigger is better, but only if all are the same % oversized, so don't over egg one room and neglect others. Otherwise you end up gagging back one room and still flowing a higher temp at ASHP.

But you would do that to all internals walls anyway, so no different. We have an office the other side of the wall were the UFH manifold is located, timber stud wall - nothing the other side of the wall. Correct

Yep A 21st century essential, just like thermostats were in the 20th and still are to many - that isn't essential and doesn't add value. It's all needless tatt. I do have home assistant, but use it as a simple go to place to see stuff, never found control over the long term reliable. If it stopped working, I wouldn't replace it.

150mm for insulation and any screed above just isn't enough, you should be doing 150mm if PIR insulation at least with UFH, ideally 200mm. Then screed above that, would look at the minimum 50mm.

First time we lit ours, we melted. BUT, treat it low and slow, one log at a time, min air for a clear burn, let it burn almost completely repeat. 3 or 4 logs will heat whole house with ease, without melting you Go through doors not under wall - minimise risk. Ours is flowing through 7 loops, but heat pump has circulation down at 7L/min, can't hear a thing now and when flow is 3x that. No pump though and do you need one - no.

I had some high spots on our concrete slab, used a diamond disc and a hoover attachment/guard attachment on an angle grinder. Used a Henry hoover which survived. Worked well enough, but time consuming. You will still need a face mask.

150mm allowed for insulation and screed? Insulation below and around the structural slab? Where are you in the project - just planning or kart way through build?