JohnMo

So cosy is cheaper and you get better user experience if you need to speak to anyone etc.

You can circumvent the system if you want. By simulation of the temperature probe and external control. You need a normal cylinder thermostat - not the probe that is normally used, something with an adjustable hysterisis (e.g. EPH EDBS), and a timer. You then need two resisters 5.6kΏ and 4.1kΏ. A 5.6kΏ resister is equal to 41 degs, you put this across the heat pump terminals where you probe originally connected. The timer/thermostat (zero volt connection, and normally closed) needs to connected in parallel to the 5.6kΏ resistor, and you add a 4.1kΏ resistor in one of the wires from timer. The time/cylinder thermostat then simulate two cylinder temps 41 and 51 degs. You set the ASHP to DHW always on. You use timer and thermostat to achieve what you need. If you cannot wire zero volt switching, you need to add a relay to do that for you.

Think you may need to install a staircase. If they have done that what have they done you don't see? Run away unless super cheap.

I added mine after sign off, just incase they said variation. Then did what I felt was ok. Most batteries for houses seem to be a safer rather than less safe battery technology now.

But if you need to go that level detail, that's ok, but do you really need too? If your that marginal and you need in depth calculations, good chance you are putting an additional pump in anyway. Or someone will add glycol and screw up the theory anyway. Or existing piping has some scale or biofilm which changes roughness and dia and turbulence factors, from poor chemical treatment in the past, and then all bets are off anyway.

Simple diagram to use, join the dots as demonstrated with the red line

You only need to take the single most onerous UFH loop, as the UFH run in parallel. Plus the feed and return pipes to manifold from ASHP and manifold.

We bought loads at the start of COVID, boiler, solar, cylinder, MVHR, all our floor insulation etc. Most came from sales prior to shutting down for lockdown. But it's sensible, if you know what you need, to look out for seasonal sales anyway.

So if you use 2 zone control, you may need the volumiser with a 7kW heat pump, but if you just run as a single zone I would just take the buffer out the pipe work and slot a couple of spool pieces in. Why - General rule of thumb, and a specific requirement for some heat pumps is 20L per kW of heat output at min ASHP turn down. The 20L is calculated on the smallest zone that can call for heat. If you have a well zoned house (lots of thermostats), leave the buffer as it is.

I could have asked, but you posted an image that stated 1/2", so would have been a wasted question. But as your using 16mm, all is good. But your loops are really only designed to fit the space, not to match the room heat loss. The loops per room, should be matched to heat loss. Balancing is possible with manipulation of flow rates through each loop, but there is a limited effect, if your circulation pump modulates.

Never meant to be aggressive.

All I can say is they are pretty pictures. But unless both spaces are fully open plan, there is zero design work going on. Pipe sizes is questionable. 1/2" pipe isn't really suitable, you should be using 16mm. Your loop length can be around 100m, so the smaller loops can be deleted and incorporated into other loops if you wanted. For info I am doing 7 loops in total for the same heat load.

Move on to another, one that brings their own tools - will treat their own tools correctly.

I would suspect for 90% of the year velocity will below min rates anyway. Most heat pumps will modulate circulation pump flow to match heat demand, heat demand will vary and only duty demand rate being required on the coldest days. The rest of the time heat pump should be running close to minimum modulation. Example -my heat pump this morning was circulating at 7L/min, so pretty much well below and min velocity rates.

Have you cast the concrete yet? Do you have insulation below it? Are your waste pipes there already? Is this a new build or renovation?

All our trades supplied their own tools, they were responsible for accuracy. If they were after additional costs for tool hire - bye bye, would find a different company. Yes, and the digger and everything else they need. I would expect the basis of the scope to be fully coated and an agreed fixed cost.

But you may have issues doing DHW - I say this from experience, the heat pump circulation pump runs full speed in most situations. My system drops from 28mm to 22mm for the run to the cylinder - around 10m each way and it needs an additional pump to get adequate flow.

But it is within flex conduit not directly embedded, - for clarity States similar to this - https://www.multipipe.co.uk/knowledge-base/do-you-install-your-hot-cold-pipes-in-floors/?srsltid=AfmBOopxxCCySW4Q1pdnV0rpxDKf6TCdk71yIPUyWcaBhL6S0K1AMi5D

So minimum is going to be 28mm piping. Ideally in copper, Hep2O should be ok, 22mm the pressure drops will be too high. Depending on heat pump you may need to add a boost pump. MLCP in 32mm I would check the cost of pipe insulation - min wall thickness 19mm it could cost quite a bit.

Not sure that helps, I tried a flat curve, to see what happens and it got a lot worse. The heat loss reduces, so still throws the controller out. That sounds like too much intervention and faff. I would be setting to manage coldest outside and then have a thermostat, used in an energy limit mode. So basically a permission for boiler to run, but cut out when curve doesn't exactly match house needs and house starts to get a higher temperature than target.

This is ours heated via 3kW immersion. 210L slimline cylinder. Temp messing about 1/3 up from bottom. Basically 1hr or 3kWh to heat.

I have a very similar issue with my heat pump and working through it, I think I know what causes it. Mine occurs when the heat pump hasn't really got any work to do or on an upward outside temperature change, with a warm house. The controller wants to keep the heat pump running but it not getting the return temperature doing what it expects. It's trying to pull return temp down, but the floor isn't willing to change quickly. In our situation the floor is saturated with heat and return temperature is very stable. So the logic starts to loose control - acts like a spoilt child. Not willing to switch off, but really has nothing to do. The control logic, being to manage a dT and upper flow temp (with an over temp hysteresis). So return is stable, dT cannot be maintained with reducing target flow temperature, so controller starts to work, counter intuitively and it's normal programming isn't working. Here is a plot over 50 mins. The previous hour to this outside temp rose a couple of degrees, plus the sun was starting come through from dark and below zero. I have set up a simple thermostat to kill the heat pump, when house hits a given level, about 0.2 above target room temperature. This limits this behaviour quite well. Your radiator system could be doing exactly the same thing, it just cannot shed the heat, so return temperature stays stable. You boiler control system isn't setup by Viessmann to cover this situation? The same as my Hiaer one isn't. This is a problem 99.9% of users will never notice, I monitor mine to death, so see everything, so do you.

I found it in there somewhere, but did the design 6 years ago now, so no longer have to hand. May not even be in the latest edition.

We have our cold water pipes embedded in the concrete sub floor. Scottish building regs say the pipes need to be replaceable. So used 20mm flex conduit, tie wrapped to the rebar. Good thing we always have nice cold water, summer and winter. DHW pipes could have gone in the insulation but they are run elsewhere. But no joints below ground.

Why not heating, what will you use? If you have a heat pump use it. 2+kW means you need heat. Not been on buildhub for a few days. Our Haier 4kW will kick out over 6kW, even though the datasheet doesn't state it does. So will easily heat a big cylinder. But we use the immersion.