JohnMo

You need to look and see how things connect in the cellar. If the lintel is connected to another cold source (e.g. wall then floor), the lintel will stay cold no matter how much insulation you put under it. So you may need to install insulation in house floor instead. 25mm (or more) under the floor finish would make a big difference.

Possibly will, but the kWh used, no matter if UVC or Sumamp would be pretty much the same on a daily basis. You have more flexibility with an UVC, you just heat to different temperature, to alter capacity. A Sumamp has defined max capacity based on PCM melt temperature, so less flexible on that basis.

EER/SEER is cooling, CoP/SCoP is for heating. Why would you design a system around 18 Deg house heat temp? Way to cold. Suggest you are over thinking the whole thing. Calculation of heat loss is needed, but that isn't difficult. Add 10% for DHW and/or defrosting, which generally occurs between +3 to -3. Design to cover 99.8% of likely outside temperatures. It is unlikely the heat pumps on offer, will exactly match the kW required exactly, so you choose the one one up. Cycling isn't an issue generally and the worst can be fine tuned out. Most issues with A2W revolves around distribution system in house being split into many zones, poorly installed and designed buffers and way to high a design flow temperature. Then home owners ignorant of how to operate and wanting to operate how they did with a gas boiler. Most these issues are not relevant A2A as the equipment and how it runs is factory designed and set, and the home owner cannot mess with it.

PV is cheap, batteries aren't Actually PV including mounts should be around or less than £200 per kW. An inverter to support couple of hundred pounds.

I doubt that, as you have a heat meter so will pay by the kWh.

But it is unlikely you would ever have to replace the whole contents. Thermostat is low down, the rest of the cylinder will be at a higher temperature. Bottom of our cylinder can read 12 at the thermostat, but it's actually 45 at the top of the cylinder. My average input to a 210L by immersion is 4.5kWh.

Our houses at a very stable temperature, but there are some days that it just feels cooler. We had the fire on yesterday. Small load to get it started, then one small log. Burn was about 3 hours on very low. Soap stone gave off heat until bedtime. Small log shed would keep us going for a couple of years.

Call cool energy they will open now. Have you tried switching the whole lot off and on?

I would just keep it simple One hot and one cold manifold in plant room. Then one of the two options below. Option 1. Looks like a 5 port manifold for hot and cold. A single 15mm feed from manifold to each wet room, in hot and cold. From 15mm pipe in wet rooms, teeing off to users - sink, toilet, shower etc. (this what I did and have seen no issues. 2. Bigger manifold in plant room, with individual (suitable sized pipes) to each user in the house. So a mix of 10 and 15mm.

That assumes your house almost no decrement delay. So you need to be careful with assumptions. In a well insulated house new or old house your weather compensation curve almost flat. Weather doesn't really change much in a hour, maybe drop or increase a couple of degrees. Plus the output of a floor modulates (thick or thin screed) depending on the dT between floor and room. So when room temperature drops floor output increases. You design your system for what you want, it's flexible, there are advantage and disadvantages to every system. No right or wrong answer. So testing done with our 100mm thick screed I have used pure WC and not had an issue, except expensive electricity outside ToU cheap periods. Batch charged the floor overnight and that works fine down to a just below zero (7 hrs charging and rest of the keeping house pretty stable), below that it needs a top up early evening. Running against a thermostat works, but you can overshoot and undershoot a lot with cheap thermostats and higher than ideal flow temperature. With thick screed you have to use 0.1 hysterisis thermostat. Certainly with a thick screed you have no need for a buffer as the floor is a huge one.

You may get a blank look from the window people, they are generally clueless. Do a Google search on here and you will find a few people using different ones. We have MVHR it has humidity sensing and boosts as needed. No idea when it last boosted, fairly steady temps and continuously running ventilation is key. Once the house settles down the background ventilation is mostly all that's needed. No really correct they are always partly open so room always gets some ventilation. No, size is irrelevant really it's the usage, it's there for background ventilation. You will have your cooker hood as well.

Less than half the volume of the house an hour, all very slow. I would really consider dMEV. Greenwood CV3 or CV2, they will only do background ventilation unless needed. They are silent out the box. One in each wet room (including kitchen). No trickle vents in wet rooms. Trickle vents in dry rooms with humidity activated vent control. Undercut all doors for easy cross flow with doors closed. 4 fans cost about £4 year to run. You only have enough ventilation, not over or under vented. No ducts, no filters.

If you have read that somewhere, they generally don't move heat about, the flow rates are too low. Oversizing to do that makes no sense, as although they recover heat, its not 100% efficient, so you are actually pumping out more heat than you should. MVHR is ventilation, not heating or a make shift heat mover.

No you don't, direct cylinders will have two immersion heaters, so you can heat all or part of the cylinder. For the price difference for a normal direct cylinder and sunamp, you could heat a normal cylinder for free for a decade.

Post up you roof buildup, what materials air gaps etc

Post a drawing of your extension/house

So what happens when you sell, if you "need" breathable paint. And the next owner covers with normal emulsion paint? What do you do with ceiling?

Think it needs a big dT, unlike most refrigerants. But you can get them from Mitsubishi I believe.

CO2

No wouldn't work. Trouble is without extracting to the main MVHR you don't have a well balanced system, so not that much energy to recover. So assume not on a new build? If your not super airtight (you may be) MVHR is pretty much a waste of time and you are better with on demand dMEV.

Are you talking 1 Barg or 1 Bara? (as in gauge or absolute).

Should be able too, as there are no breaks in the system.

Have you thought about using solar PV panels. Move so you have one side of roof facing east the other west. 2m2 of PV is about £50 to £60

why not use something like this - other makes are available https://www.ventilationland.co.uk/en_GB/p/brink-indoor-mixfan-co2-controlled-up-to-70-m3-h/17927/ You use the MVHR to dump air in to the hallway instead of the room directly. This fan is installed above the doorway or in wall and sucks air from room based on humidity and/or CO2 levels. Air is drawn into room via door undercut.

First is depth of screed. Then choose a screed. Look at product datasheets Here is a bunch of different materials, some useful most not so. https://help.iesve.com/ve2021/table_6_thermal_conductivity__specific_heat_capacity_and_density.htm