JohnMo

Maybe I am not suffering from that because I don't use the balanced from the UVC, but instead have prv after the stop cock then the cold manifold. But of the upstream of the stopcock I have a cold water accumulator fed by a borehole pump.

I may be wrong here, but don't you have a fairly large well designed buffer (Nibe) or am I thinking of someone else? Most are not designed well to promote a thermocline, and small ones could not maintain it anyway. So mixing occurs to increase heat pump flow compared to delivery. The way the OP installer is proposing to install the buffer is rubbish and would not comply with any manufacturers design scheme. DHW always should be before buffer, the cylinder does not need a buffer.

Talking out of their butt. Biggest question for me would be, why do I need a buffer at all? One zone or a couple of large zones, zero need. I suspect they will cover your house in thermostats, all third party on off ones, screw up your efficiency and charge you a pretty penny also. If they are not budging on buffer, ask how he is balancing the flow either side of the buffer, if asks why, look to sack him, as they really has no clue what he's doing and why. KISS the heat pumps best friend

If you went that route it would need to big enough to take the cylinder. I would, floor the area under the cylinder and pipes in waterproof chipboard, then small spills and drips can be mopped up easily without damaging other places you can't get at.

Just tried to find details but nothing much to find. Found out there have 14 ASHP planning application ever. The conditions on the planning approvals very from follow manufacturer instructions or follow MCS. Sorry not much to add.

Start with working out your pipe runs. Do pressure drop calculation. If you are connected directly to UFH heating you just need the pressure loss for the longest loop. It should be more onerous than the cylinder coil. Then look at pump curves and get the smallest pump that does the duty. The attached has worked examples Hep2o_Parts_Users_Guide_Australia_2018.pdf

28mm Hep2O at your flow rate is 2m head loss for 100m or about 19.5kPa. So 24m would be about 5kPa. Fittings add metres of head loss, a flow through tee adds no additional resistance

Not sure where you pdi comes from work in imperial or more preferably metric and only metric units. Basically what goes up, must come down, so from head loss perspective they cancel each other out, but you still have the tube they cancel each other out. But don't Samsung use a pump supplied by you - as in it doesn't have a pump in the monobloc. So proper perspective, this is the pump head loss chart from my manual (with pump inside monobloc unit) So my duty point is 75kPa at 1m³/h. So on your case you have about 20kPa going through the ASHP and another 55kPa for your piping and heating system.

Shelly do a leak detector and so plenty of other smart devise manufacturers. To be of any use, it needs to turn off the supply of water. Depending on the leak, you may have to stop a mains pressured cylinder from emptying it's contents, how you do that? If you 60 miles away and a phone alert, what are you going to do?

Have you measured it do you need to preserve it? You need to dynamic and static pressure. On an UVC it just doesn't occur. First image I found - the valve that splits mains water supply. No need. My hot water run is 16mm from UVC, 8m to hot water manifold the 16mm to each wet room longest another 8m then branched from there. By the time you get hot water you will have changed your mind about showering.

Exactly same for me, I built the house, she chose how it was furnished and finished. It's all good quality so should there for the next 20+ years, so really depends on what you define as sustainable.

You really need all the insulation above the wall otherwise the wall will just be huge thermal bridge. I would take the airtight vcl over the mid walls and down the end walls and join with a primed wall and airtight mastic/adhesive designed for joining airtight vcl to wall.

Is it pressurised? if not put some pressure in it and make sure it holds - only way to know is test, use air or water.

Think you are making it over complex. You have lots of big pipe going on, do you need 32 and 28mm in any house system? Cold water I would just run a 15mm feed to each wet room from a central manifold. Then branch from there. With individual isolation to each feed Then if you hit water return circuit just do it to the longest run room. It will then preheat the whole manifold. Remember you need a check valve with the circulation pump. Bring you mpmd pipe to a single stop cock first. Then to outside tap via an isolated tee. Then a whole house prv and onwards from there. Cold water supply to mixer taps needs to come the cold outlet on the UVC inlet group. If it doesn't you need a check valve on the hot water outlet to stop reverse flow. Simplify.

Doesn't comply with building regs.

Do you have pdf drawings? These can sometimes be reversed back to cad, or they should be able scan in pdf to the cad package I believe. If not ask the timber frame the cost to reproduce themselves? Shouldn't be that much, as the architect drawings will be missing loads of detail, they would have to add in and correct a lot of details anyway.

If it's not going outside, then use a waterless drain trap.

You need to take a step back. Mitsubishi and Vaillant looks like it maybe 6kW flow rates, the other numbers are nonsense. The numbers you are looking are the extreme the pump can flow not the target flow rate. The important number is the target flow rate and max pressure rise to achieve that flow. You need to look at the pump curve and where you need to be on it. For those flow rates in most likelihood you will need 28mm. I am flowing around 1m3/h (16.6l/min), the path mine takes is quite convoluted about 12m each way in 28mm in Hep2O and the longest pipe in the UFH is around 110m (16mm pipe), all flowing from the ASHP circulation pump. Plus the same pump also pumps to a single fan coil in 15mm Hep2O another 15m each way in another direction. I would choose something you can get parts for locally, Hep2O is readily available on Sunday morning if you need a bit. Find your target flow rate and the max pressure drop first. Calculate the pressure drop on the proposed run second, size pipe to be under pressure drop max figure. If you piping goes up 4m and 2 that's a 2m head ride when you calculate. Put a bleed at high points, makes life simple when filling and getting of air. A tee will add little or no resistance, Hep2O is good for this also as the pipe inserts are thin wall steel. Or you can do these sections in copper and use straight connector between Hep2O and copper.

I have one at the top of my cylinder (top upwards exit) goes up about 50mm and across cylinder and then down. The downwards pipe is stone cold the top pipe hot.

I never bothered asking, wasn't really aware I had to. But started paying council tax that day. No one seemed to care, so didn't ask questions.

I did a write up on installing a hybrid heating system, not if you saw it? The system is installed so it can have the boiler taken away without any effect on the heat pump system. A low cost version if you don't have a plate heat exchanger kicking about, is a simple close couple tee instead of PHE. If you needed to buy a boiler, as small as you could find would do the job.

It does make it all a nonsense, possibly refilled all holes after leak test, then will the first to complain they have mould everywhere.

Trouble with Scotland MVHR is mandatory for an airtightness of 3 or below. If you hit 2.9 you have to install MVHR before BC sign off. But have to say MEV or dMEV can be made to be incredibly efficient with self modulating trickle vents and dMEV or MEV altering flow rates based on demand. Very low running costs, no filters, no heat recovery but on an otherwise well insulated house running costs are going to low anyway from a heating perspective.

Probably is, maybe one of the reasons a lot of States in the US mandate heat trap, orientation pipe work. i.e. limited length upwards, horizontal and then drop down vertically on all cylinder pipe connections, as soon as practical, to stop thermal gradients moving along piping, leaching the heat away.

But you wouldn't do that in real life. A heat pump cylinder generally has a thermostat within a foot of the bottom of the cylinder. So reheat times are generally manageable in a normal house without the house cooling down to much. Then the reheat volume and time is purely based on thermostat hysterisis and cylinder shape and volume from where the thermocline sits (not total capacity), which could be quite low as it may well be in @Dave Jones case my 6kW reheat times the last couple of days have been around 30 minutes, but the water has to travel about 20m each way so I do loose some efficiency.