JohnMo

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.