JohnMo

Or you can always go AC coupled instead.

There are a couple of things that maintain water pressure. No leaks, and an expansion vessel. Water contracts as it is cooled and expands as it's heated. Depending on system volume, the volume change when heated and cooled could be a reasonable amount. Setting and sizing the expansion vessel and system pressure is important. Your expansion vessel needs to be pressured with the system flat with zero pressure (or at least the leg with expansion vessel in it). You need charge to the correct pressure for the system set pressure. If you set the pressure too low or the vessel is too small every time you go into cooling mode your system pressure is likely to drop to zero.

If doing new cylinder, just do one with a big coil, less to go wrong, one less pump to run less for installer to do

Why wouldn't you have them in ANY house. Bonkers not too. MVHR is just a ventilation tool, not some magic bullet.

Just choose a direction and sticks with it. Left to right for all rooms and halls or up down for all. I prefer them running from windows instead of across the main windows, so my case all would run left to right.

It is, but heat pump cylinder or a normal cylinder has to sized per MCS guide lines. BUS just states heated by a heat pump, doesn't mean it can only be heated by one heat pump at the property. Only thing with integrated heat pump cylinders is they generally have a long recovery time, due to the dinky heat pump they use

Two schools of thought, one lag everything, the other lag nothing. But your best to lag everything that goes to DHW, so you are not adding heat to house during summer. The lag nothing, comes from, with an ASHP, the ideal for good CoP is to run WC and a single zone fully open system. So what is the pipe insulation doing, everywhere in the house, the voids etc are also at a similar temp to rooms. Obviously if you don't run the heat pump like just described, insulation needs added to all pipes. Anything outside the heated envelope insulated to death in both cases.

You will now storing DHW at 50 or below, what do you currently store at? But plate heat exchanger would be able to heat cylinder, the current coil wouldn't be used any more. You need to concider defrost cycling, this will bring down the 10kW quite a bit. There was some testing done on a Vaillant ASHP and the conclusion was the 7kW output in a UK setting was correct, the datasheet was ok for mid European location, where defrost isn't so much of an issue.

If that price after grant, a rip off from what you say. That is a fair comment - add another DHW heat in the afternoon, it will have lost the battle and you will have a cold house and large energy draw at the end. You need to size ASHP based on how many hours you are heating DHW (3x 90 mins), so 4.5 hours. Take that away from 24 hrs. So you now have 19.5 hours to provide 24 hrs of heating. So (7kW x 24 hrs) / 19.5 hours, so heat pump size minimum is 8.6kW at your design outside temperature. So realistically you are looking at a 9 or 10kW heat pump.

The issue with mixing valves on the manifold is they always mix return water with incoming warm water. So if for instance you are flowing 30 degree water to the radiators, you may be getting enough return flow mixing to drop the water to 20 deg irrespective of the knob setting. Issue is most mixers are deigned to see 70 deg water at the inlet and have minimum predefined mixing and the knob just makes that more not less. The only ones I have seen that are any good are - IVAR low temp mixer, but that still has a predefined mix - or use an ESBE (other makes available) electronic mixer, your Vaillant may (VR71 should) already have the controls built in to control the mixing valve. The Vaillant VR71 should be be able to let you run two WC curves one for radiators and one for the UFH. To get this function working - delete the existing mixer, install ESBE mixer, add temperature probes to piping at UFH and wire back to VR71 , split system in to two zones within the controller radiator and UFH. The set the two WC curves and then run both zones together

Don't even think about what occurs in England as it is quite different. Planning permission is one aspect it just defines the look and basic practical aspects of the build and lets other policy makers have an input. Building Warrant, is the nuts and bolts of the build all the details of how you will build the approved house from planning permission. You need an as design EPC, a full build structural certificate that covers everything in the build. Once approved you can start the build. Building control in the most part, is done by local council, not third party company, they will define hold points for inspecting. The whole system, I found to be very black and white and easy to follow.

How do you stuff 10 people into 165m²? Are they all on camp beds?

Your 300L just isn't big enough for that at heat pump temperatures. With 10 people in the house DHW will be the dominant demand for 95% of the year. Are your quote companies aware you have 10 people in the house? Ideally you would size radiators to flow same temperature as the UFH and have a single flow temp and no mixers. Not sure what this is?

Sounds like a bodge - not a Just find a better location or a different delivery method of cold air

You can get various grades of mineral wool or fibreglass, something like Knauf Frametherm 32. I used multifoil in a summer house supported with loads of other insulation material. Not sure it would find a place in my house.

That is for under sizing the heat pump. So in extreme weather if after a given time not reaching flow setpoint it will fire the immersion. The heat pump will manages itself in those circumstances, it just starts the circulation pump on a continuous or intermittent basis based on outside temperature. So your heat tracing isn't really doing anything.

Do you actually think this is a serious thread? Good guess it's someone just flinging daft questions about. You can buy a 2.4m long worktop from B&Q for £60.

If they can't afford laminate - no idea why anyone thinks stainless is affordable.

Wouldn't you just be better fixing the half arsed job left by others. Been involved in lots of poorly installed heat tracing in my past. Heat tracing that isn't extremely well insulated, may as well not be there. Even with insulation you need to have suitable Watts per metre rating for it to be effective. Was this all calculated or was a stab in the dark? What powers it in a power cut, so does it actually afford any protection? Or is a sticky plaster that isn't really needed and isn't very effective?

But how many hours do you need and how low below freezing Nice simple to read article here https://renewableheatinghub.co.uk/do-air-source-heat-pumps-really-need-glycol/

Run my system without glycol and without anti freeze valves. Why do you need either? Both are there to protect the heat exchanger in the ASHP casing from freezing. It's a big chunk of metal that will not freeze easily, it's also insulated by the manufacturer and in a casing. It isn't freezing any time soon irrespective of temperature outside. Are antifreeze valve or glycol used in external oil boilers - no. Other disadvantage of anti freeze valves. Is they are directly exposed to air, so will activate way before any damage would occur if heating is off. Once activated you have drained out part of the water from your heating system, how do you fix if you are not hands on and your plumber isn't available?

None, materials and labour contract should be charged at zero vat - I assume a barn to house is zero vat

Not water proof or water resistant. External ply would be better. Or don't bother use and old door or old table, get inventive.

Most airtight expanding foams only expand a little. Someone will come along soon and give what makes and types to use

I would scrape out what you can and replace with a good airtight expanding foam. The foam will discolour with UV, but generally not an issue, especially as we move to winter.