JohnMo

What happens with wiring for lights and plumbing etc? Really see zero advantage to block and beam for anything especially for first or mid floors.

Would think you are making life difficult and possibly way more expensive. You will have a structural oak frame AND a structural ICF doing nothing more than window dressing. I make a decision on ICF or oak frame and go from there. Not sure I would mix. Oak is flexible and will move about initially or will in the green state, the ICF is concrete there is no flex.

That's the issue doing UFH, the floor can suck the heat away really quickly, this means return temp stays low, as heat pump wants to manage dT first, target temperature second. So if you try to run UFH for short periods, you never achieve a stable operating point. This means UFH can happily absorb most heat given to it, and big flows of return water keeping the return temperature low, never achieving target flow temperature. Run UFH long a long time the return temp increases, smaller quantities of hot water are taken into the mixer, more water is recycled within the mixer. Return temp increases because, more flow is routed to radiators and less to UFH. Heat pump achieves target.

Unlikely as an ASHP normally will supply a minimum of 25 Deg in heating mode. Then at deltaT 4, plus restart hysterisis for the heat pump, you need the floor temp to drop below 20. If that's the case your floor would provide zero heat to the house. Tried that with mine (25 Deg flow) it ran fine, but never restarted, floor just never cooled enough to allow ASHP to restart. Thermostat you need a hysterisis of 0.1 or less if you can one. It has to be on/off not TPI. I have 100mm concrete with UFH pipes at the bottom - I am also 300mm pipe centres, response is slow. But if you are prepared it's something you can use to an advantage. But don't expect setbacks to work, they won't. WC works fine. If you use a tou tariff, get a bigger heat pump and batch charge the floor storage heater mode. I am at a out 3kW at -9 and have a 6kW ASHP, will run without stopping buffering into the floor if I want it to. If your heat loss is 2kW, you need 48kWh of heat, if you only have 7 hours to heat you need 7kW of heat input, plus it may need defrost or modulate down to manage dT, so even 8kW would be fine.

Both are correct, over 30 Deg flow it's 7dT, while under that is 5dT.

Think that's half your issues, running more like a boiler than a low and slow heat pump. You have a mad blast to heat in short bursts, Trying to stuff loads of hours of heat in 3 hrs just doesn't work, may do with a boiler but not a heat pump. That would indicate your flow temps are way to high.

We heat with a fan coil, but it only really gets secondary heat from the house UFH, ASHP circulation pump runs 24/7. So we generally have a min of 16, but it can get as high as 20 (currently) due to solar gain.

Just do wireless thermostat, easy, battery lasts a couple of years. You can also move it about. We are running WC but use a thermostat to trigger a second operating point, basically WC plus 2 degrees. Use the thermostat to force the heat pump to run hotter during cheap rates period and also shelly relay across the terminals of the receiver to drive the heat pump hotter during excess solar production periods. Converted 3kWh of excess solar in to 11.5kWh of heat today for free.

dMEV fan install now and then forever more let it run 24/7. Cost about £1 a year to run. Set to min speed, buy a Greenwood CV2 from eBay pretty cheap. This last year's humidity of our garden room

You are just scared mongering now. So now you are worried about a lots of steel plates that are insulated inside an insulated box freezing. If that is the only concern, remove insulation, wrap with 12v heat trace, re insulate, and use simple relay to switch the heat trace on in event of power outage when heat exchanger drops to 3 degs.

UFH needs plenty of insulation to be efficient, otherwise you heat the flat under you - they will like it - you won't like the energy bills! Or you will heat the worms under your flat if on ground level. Really wouldn't bother.

Did you do the print out? It should give you model for your design and build regs design so you can compare. What did you put in for airtightness at 50 Pa? What did it give you as an infiltration rate? Would compare target house with your inputs, check your inputs are not strange. Would also add another 50mm insulation to the floor. Check MVHR inputs, different duct types can make a big difference in efficiency etc. Heating controls make difference, can you select pure weather compensation?

Mostly, longest is 12 hrs, some we don't even notice because the battery hides them, which is good

Questions to ask yourself 1. How often do I get a power cut? 2. How long do they last? 3. How long to totally freeze a pipe? 4. Do I have a generator and or battery? My answers are (we have insulated buried pipes) 1. 4 to 6 times a year 2. Up to 12 hrs 3. With no circulation I think to freeze a pipe or the parts inside the heat pump, when tested was about 18 to 24 hrs at -20 (in freezer) when tested. 4. Yes and yes I have NO, antifreeze valve or glycol. In normal use the ASHP circulation pump runs 24/7, even if off the antifreeze running protection in the heat pump will look after the unit and pipe. Observations My outside cold water pipes have never frozen they start from cold (not warm) they aren't insulated and are buried to a similar depth. We have had -9 for several days over the last couple of winters. You need to get extreme cold and power outage for a prolonged period at the same time. External oil boilers don't use antifreeze etc. Have read here https://renewableheatinghub.co.uk/do-air-source-heat-pumps-really-need-glycol

Just occurred to me, you just paid an arm and leg to get this system installed, get the installer back to rectify. You have an MCS performance guarantee.

Then you need internet to get your heating to work - not good Something like this, which an RF relay not WiFi. https://mainsswitch.co.uk/ You can get them for £43 on eBay

I used CV2, super cheap on eBay. No app, do you need an app? Set and forget

The rule book said max 6 high then concrete fill to 5.5 block level. Only screws were used to part lengths blocks as belt and brace. Bracing - Corners and all part block joints had 6mm OSB screwed to each block. Basically each sheet of OSB was made into 4 patch panels, 4 panels per corner (2 inside, two outside). That was all the bracing needed. No blow outs. Rebar, above and to side of each opening, long rear wall had a rebar wind post formed midway along. But in general not much rebar. Think the fill concrete was max stone size of 5 or 10mm, quite high strength concrete, but with a huge slump value, bit like cream. You can see the clear water free flow out the bottom blocks after the pour. I think this is what seals the blocks and the holes in the block become quite well sealed with concrete.

Another view I did a self build with Durisol, never done it before, two of us did a 70m perimeter wall house up to 3.5m, plenty of internal and external corners etc. was very simple, took us 3 to 4 weeks. Total cost was about £7.5k in 2020 at the height of COVID. An internal parge coat was applied over 2 days, joint between floor and wall sealed with liquid air seal. No water leaks anywhere, even had an exposed external wall for a couple months after moving in - not a damp spot anywhere.

Or even fan assist radiator?

Had one in the summer house, which my wife uses for massage etc. for about 18 months. I do have them set quite low and even then the humidity is never high

What is the target room temperature? How many thermostats are in the house? Run less setback overnight and during the day, then the radiator and boiler has less work to do next morning. Try running the same temperature 24/7 does that fix the issue? You may find the boiler in general has less work to do so operation is at a lower max temperature and uses less gas.

Simple question - Greenwood CV2 or CV3, which ever you can get at the best price. Nothing else. They are silent, so much so I have to remove the cover to check it's working. The are smart also, in that they only boost if they need to. So just 3 wires needed. No manual boost required or light switch activation etc. Do as simple install as possible - as said they make no noise, they use almost no power either. Remember to undercut all doors to allow cross flow of air throughout house. No trickle vents in rooms that have dMEV fans. Ideally couple with self regulated trickle vents in dry rooms. You should have a dMEV fan in every room that has a water, utility, bathroom and kitchen.

I would just keep the plumbing simple. Manifold good for hot and cold, locate in central location, with easy access, feed in pipes 15mm. Take cold water to cold manifold from combined valve on UVC. Cold feed to DHW UVC combined valve in 22mm.

We have secondary circulation also to our ensuite is about 15m from the cylinder. It's only switched on in the morning for a couple of hours. So when you want to use the sink hot water is nearly instant. Pump has built in timer and thermostat, so only runs when needed. Not really needed for the shower as by the time you are undressed the water is already started coming out warm, so only a short wait.