JohnMo

Thought you said balance wasn't needed? Looks like classic mixing and distortion going on. The Lazer may not be accurate on different surfaces but is repeatably on the same surface as a comparison. The two degs makes a decent difference in running costs

So the thermocline is obviously not that robust. Contrary to what you state below. Do not disagree - but also doesn't mean it's efficient. You can actually end up with the heat pump cycling to keep the buffer happy and provide zero energy to the house.

It happens when you have lots of zones. Control by either less zones, have the zones open longer by reducing the need for the thermostat to react by reducing flow temp or flow rate or both. My UFH system went from thermostat in every room, big buffer, multiple pumps, to no thermostat, no buffer and one pump. More efficient, more stable room temps.

Agreed, for heating system, but cylinder pipes from diverter valve need to be insulated and primary pipes from heat pump to diverter valve need insulation, and DHW piping.

Sorry - if flow rates are different you get mixing, if flow rates are the same or close, you get a thermocline form. With different flow rates that thermocline doesn't occur. So you get inefficiency as return temp to ASHP gets distorted and is higher than it needs to be.

If you run with all open loops (no room thermostats - all on or all off), you could just bypass and remove the buffer and the second pump. If you want need room thermostats, keep the buffer. The thing with buffers is both the primary and secondary flow rates need to be balanced otherwise you get mixing in the buffer which isn't good, that is maybe why you are seeing different temps to what you expect. I would if with buffer, run straight WC, keep as many zones open as possible all the time, ideally all of them and balance flow rates on the UFH. More flow warmer room, lower flow for a cooler room. Balance the flow rates on both pumps

Do you also have a mixer valve and pump on the UFH?

This very much is for a normal leaky house without MVHR. Possibly test at 50Pa to get a meaningful repeatable result for all houses. Any lower may not get anything meaningful any higher not needed. Still a flawed assumption. It assumes you have house at ambient outside temp and its the coldest day and you never recover any heat until until at full temp. As dT increases between outside and inside temps, the heating load increases. Its when you get to an inside temp of say 21 and outside at say -3 when your heat demand is highest. Your real heat loss is around 3kW, but as said above you will most likely install a 5kW heat pump, anything bigger will be harder to manage. I would doubt you will actually flow that high, your MWT will be closer to 30/32.

Basically as @ProDave says use the spreadsheet on here. 5.7kW sound massive, which would indicate you have something very wrong, for that sized house. Mine is about 3kW at -9. And heat meter shows that to be true, and matches the spreadsheet almost spot on. I don't have the best MVHR, best airtightness, a rubbish form factor, and loads of glass. 2m³/m² @ 50 Pa, is at a very elevated pressure, compared to real life (high winds from every direction at the same time). Using SAP calculation that becomes an infiltration rate of 0.1358. Will come back to that later So your MVHR will have an air change rate of 0.5ACH. the MVHR unit will have a 80 to 90% efficiency. So effective air change rate drops to 0.075, plus 0.1358 infiltration rate. So 0.2. Use that figure in your heat loss calculation for ventilation rate and you won't be far off. But once built you are likely to reduce the MVHR flow rated to about 0.3 other wise you end up over ventilating the house, so the figures are likely to reduce a little. You do the calcs, in Scotland you have to do it as part of the planning process, they even want my UFH design and supporting calculations. Good thing with UFH and well insulated is that wide or narrow pipe spacing makes very little difference to flow temperature. If I installed 100mm centres or as I did 300mm centres, it adds about 2 degs to flow temp. 300mm centres is just little less responsive, but heating is always on low, so who cares. When you get around the calcs you will end up with a 5kW heat pump. No need for MVHR to factor in heat loss he is just adding ventilation. Heat engineer that doesn't factor in MVHR heat recovery, should just be sacked and told to get off the project. He is not fit for purpose. Just design it with loopcad. Our living room has 7m wide and 6m tall at the peak of glazing at one end, it's the warmest room of the house on 300mm centres, because its designed to be the warmest. It's designed to be 21, when bedrooms areas are designed for 17/18 at the same flow temp. Get the basics in order Proper heat loss calculations use the one in boffins corner. Once you have your head in that headspace everything else starts to slot in to place.

Sounds a rip off. Explain your system, is this the heat exchanger in the outdoor unit or one inside the house?

Of sorts, yes, dedicated no, dispersed where it best resides yes

Never really been convinced with plant rooms. Our UFH manifold is in a walk-in cupboard in the utility - makes it an airing cupboard. Our second MVHR is in the hall cupboard, then cylinder is in a insulated loft with primary MVHR and a gas boiler. Mostly use the loft for storage - like most lofts, but is fully insulated. ASHP obviously outside.

I just use this Does what it needs to, mine just installed in the cold water line to cylinder. Was originally on the combi boiler. https://www.bwt.com/en-gb/products/protection-for-heating-systems/combi-care/15-mm-combi/

So you boost every time you switch the light on? Isn't that a bit OTT? Can't remember the last time we used boost

Yes Use correct screws for fixing the boards. Plenty of fixings for plasterboard that can be used for high loads. More a matter of using the correct fixings for the job.

Mine were just a simple spreadsheet with individual inlet and outlets based on building regs. If your paying for MVHR design this should be part of the design delivery from contractor. If DIY look at building regs for the gross numbers, plenty of give away spreadsheets on here. Basics are, use Passivhaus as your starter for bedrooms. When you build it near completion, you have the system commissioning done and a certificate is issued, the numbers should match.

Big brother is here and working. Even starting to control your heating system. Slippery slope. Think I will stay with my dumb E7 and have control myself.

Mine (not the same make) and every other manual I have read (loads), once temp goes to 16 and above it just stays on the same flow temp. Your 25 degs is probably the lowest set point you can go. I would really read your manual on this subject because get this wrong it could be very expensive. Most heat pumps look for zero volt contacts. You should have a setting or mode within the unit thermostat controller to do this function itself. Sort of a hybrid thermostat and WC control mode.

Disability access is missing from the design altogether. No toilet facilities either on ground floor, in fact unless I am missing something a guest has to go into some ones bedroom, to nip to the loo. Quite a bit to sort really to get through planning.

I finish the UFH pipe installation on the Sunday, filled with water and antifreeze and pressurised. Covered on the Tuesday with 100mm concrete. No damage etc. within a week or so we were getting zero temperatures no issues. Makes for a comfortable house. Some perspective, a heat loss of 2kW is 48kWh per day, via a heat pump that's 12kWh of energy, so £3. Can also cool Via gas about £2.5, can't do cooling via electric heat mats or any direct heating about £12. Can't cool

Never heard of decoupling mat before, so never used it. UFH been working for 3 years, tiles no cracks. Ours was a concrete floor laid before the house walls were started so had a 9 month dry time. So what is it supposed to stop? Or is a means of screed one day do tiles a few days later?

Shop around if other selling for similar or more it may be good value. £60/year

Nice looking place but not convinced by a number of things that seem strange. Loads of bedrooms (2 floors worth) and limited living space in comparison. Not all those people housed in the bedrooms should want to crouch up on a couple of sofas. But sorry that size build everything will all be astronomical. 1200m² is just huge it's 6x bigger than our very roomy 3 bed house. Hope you proof read and facts everything, so you don't make yourself look a foolish. Chat bots make a good looking document that may or not be factually correct.

We are in a similar position on a hill over looking a Loch, we have loads of glass also. We use UFH in cooling mode and it effective in knocking the thermal gains down a bit, but importantly reduces the recovery time to normal temps, quite quickly. It not Aircon, but effective enough, for no cost.

Unless you live in Scotland 😁