JohnMo

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.

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 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.

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.

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.

The HE mini store, is a part of the central heating system, in it can be included in the already in place expansion vessel (recheck sized based on increased system capacity) and relief valve etc. Assume ministore has an immersion, it could be heated by that, but will not take much energy depending on the volume. To get the most out of it, you need to set your boiler up to do priority domestic hot water. Which isn't as straightforward with a combi, but can be done. Then you can blast the ministore with high temp (80 Deg) water to ensure you actually have endless DHW in winter and top as needed in summer. Your immersion will hold the temperature while idle, but on hot water draw, will not keep up especially if running on excess PV via a diverter. So get your tin hat ready "the blo@dy hot water cold again" moments with the other half.

That's mixers, they mix, they mix all the time like it or not, always a fixed amount of mixing. They are really designed to operate with high flow temps from boilers, generally not suited to ASHP systems. If you need to mix because of different flow temp needs for two different manifolds it's better to use an electronic mixer driven by the heat pump controller. I had the same issues, deleted the mixers and additional pumps, the actuators on the manifold and just left room sensors in place for monitoring.

So you really need something that does remote access as an add-on, instead of out the box. Then everything is local, with the ability to look at stuff and adjust settings. I have a polypipe system with room sensor main hub and and external WiFi access point. Everything is local, WiFi link of it works or doesn't has no effect on the work of the system. Heatmiser and Wiser I believe are the same. You need an add-on for remote access. Anything that mentions clouds walk away

If you have the space put a proper UVC in. The mini store is unlikely to perform much better than your combi except immediate draw of would be quicker.

£1400 isn't modest in my book. Plus if used the way you are suggesting you would need a full safety group. You may have a few things to resolve. If water flows through the combi it will fire up, so use gas anyway. If heat store isn't heated, sun not playing ball, it would just cool the water already heated by gas boiler. So no hot water! I would install cylinder upstream of the combi, heat by solar, if water is above 45 divert around boiler direct to tap, if below 45 let it be heated by boiler. Saves boiling firing when not needed etc.

Really depends how it's setup. Would think every parameter you mentioned can be adjusted. But neither way mentioned sounds an efficient way to run a heat pump.

Or a dry trap? One or the other sounds contradiction, or your client has money to waste🤔

Where is your structural design? Should be zero need for such questions, if your building is designed.

So is your heat pump oversized to allow this?