JohnMo

Should of added if low temp system and/or you do cooling you also add biocide and chemistry should match your inhibitor.

If it's not a building of historical interest (listed) and you are doing insulation internally and externally, not sure why anyone needs to be involved. Photograph everything good for future reference. Only thing other than the above, if the wall is currently breathable keep it that way, so add mineral wool wood fibre etc not PIR. I would be adding another 150mm on top of that.

I used a blunt fine tooth wood handsaw. But also a plunge saw or bench makes light work of it. You can also get specialised insulation saws.

But you also need to buy the correct grade for appropriate compression strength. Not all are equal. Not sure I get that, why is it a pain? I have cut PIR and EPS,both are equally a pain or easy.

And don't trust your builder to make engineering decisions - he isn't qualified

Are you sure your maths is correct? Have another coffee and retry? You would need to use your mean UFH flow temperature, not room temperature for the heat loss downwards. That would be around 24 to 25 averaged across the heating season

Don't you have a design from either the structural engineer or architect or both? You normally have a stepped strip foundation, but this is normally detailed on your drawings.

Only thing I would add, watch modulation levels especially at or around 7 to 10 degs. If you have a unit that doesn't modulate well at this temperature your overall SCoP will suffer. Even healthy cycling has a direct impact on achievable CoP, due to the impact of standby energy usage. The lower the overall heat loss the bigger the impact on CoP. So if you have a design heat loss of say 3kW at -3, you want a heat pump that at 7 degs has a min output of 1.5kW or lower, so it can tick away all day if it wants.

What will achieve?

You don't but the high number is an instantaneous air flow rate for intermittent fans. Or maybe a house leakage rate at 50Pa, which isn't the actual air movement through a building. You can have good controlled ventilation without MVHR. MVHR is the icing on the cake, when you have done, wall, floor and roof insulation to death, triple glazed and made house airtight. Most houses don't need it, don't benefit from it. But they do benefit from a well thought out and appropriate ventilation system.

You seem dead set on two units, so you have a few options. Do ground floor in isolation with ASHP, but unlikely to get any grants, as you haven't covered upstairs heating demand. Add upstairs later when and if permitted development rules change to two units and they also allow cooling under permitted development. Get your noise survey stuff done and press on with planning permission, sounds expensive and they may still say no. Or change to something different, talk to other installers, there are plenty of water based ducted fan coil systems out there,to allow one outside unit.

You can already get it it's called epoxy resin. But plastic sheet is way cheaper. Can remember my dad doing a house up in the 70s, it had some pumped under the ground floor to just below floor level, black but I think that was bitumen based.

Unless your actually pretty much airtight I read wouldn't. What are your current fans in wetrooms? You just need to promote a cross flow ventilation from dry rooms to wet. It doesn't need to be howling gail just a gentle flow. You also need to make sure you can close doors by have a small ventilation gap at the bottom of all doors. What I have written many times Greenwood CV2 or CV3 fans in all wetrooms including kitchen. They run all the time at a very low rate, they are almost silent. They automatically visit on rising humidity. Automatic trickle vents that respond to humidity in all dry rooms. Seal all trickle vents in wet rooms. Undercut all doors. You then have a system that automatically responds to where people are in the building minimising ventilation. Easy to retro fit, pretty cheap implement, zero maintenance.

I was looking at a Haier heat pump tech data, they had all the outputs for all outside temps and flow temps, and min, middle, nominal and max output for each data point. Trouble most manufacturers don't give this level of detail.

No, that is off the lowest price I could get locally.

I thought that, and god you had a load of excess, I would allow 1-2%. I saved more than that by shopping about, without compromising on quality. What was on the plan was bought, but at good rates. Saved 50%+ on insulation alone by shopping about.

Looking at a technical manual today, HiSense monobloc, and split system. It gives all the parameters to help size the heat pump and for the first time I have seen a manufacturer take due diligence for defrost. Giving derate required for various outside temps

Stop faffing, get PIR, spend once, save for ever more. Once in you cannot upgrade. I shopped around, bought online saved a small fortune, it came on lorry direct from factory - I had a full lorry load of 100mm thick, so 2 layers.

Well you don't need two heat pumps, anyone that says you do, well!!! I have house heating connected to a summer house, it has a very different heating characteristics to house. So I would just install a through wall Aircon unit in the out building - these are not subject to planning or permitted development as there is nothing visible (no box outside). Then do one ASHP, to drive UFH, via an electronic mixer (driven by ASHP controller) and a second zone running fan coils. Get a heat pump that does cooling out the box (Vaillant don't), then have UFH - in cooling mode for summer and fan cols in upstairs. All done under permitted development and all allowed under the grant scheme.

Is that whole house?

Why make life difficult for yourself. Just do normal, why reinvent the wheel? Future proof is normal stuff, not novel. Leave DC to cars and and small boats.

I've started to do something similar. Found down to about 5 degs normal WC is just fine. But once I get into defrost mode, battery takes a bit of a pounding, especially with a couple of days sub-zero. So set the WC curve to stop at 5 degs, my old UFH controller has an outside temperature reference. So use it as a cheap rate boost controller, so when its 5 degs and below outside and below 20.5 inside, it activates a second set point for the ASHP and allows a higher boost flow temp, for cosy cheap slots. Rest of the time the ASHP ticks away at a low flow temp. Use the same amount of energy, get similar CoP, but moves the majority of the energy usage to the cheaper time slots.

I would temp back and really ask yourself why you need 2x heat pumps. Blown air in bathrooms will not be the most comfortable way to heat, especially if you are wet. Have you done a full heat loss survey?

Think the trouble with a lot of these questions and issues, they are raised after the event, when it's basically too late. People expect wonders to occurs without pre planning and deep discussion on expected outcomes. Thermal bridging isn't great, but we have a work force of poorly trained labourers, not skilled crafts people. Only things open to you without taking everything out and starting again, fill all gaps with expanding foam, seal the outside with mastic to form a waterproof seal. But looking at the thermal images, I would comment Door cill area doesn't look that bad, worst bridge appears to be at the side lights, most likely caused by air movement. Your doors most likely need adjustments as you appear to have drafts at the door seals. So as mentioned fill any remaining gaps with expanding foam, seal with mastic and move on with your life.

I wouldn't bet against you. Low gas prices really mean more profits for big corporate entities, not much passed on to the man on the street.