JohnMo

Couple of things Bigger DT means lower mean temperature, which means lower output. Mixer like the flow temp 10-15 hotter upstream than downstream of the mixer. Boiler condensing is a function of return temp not flow temp, if your return temp is below 53 deg your are condensing. You say it worked, then you changed stuff, put it back the way it was. If it reaches temp, all good. Then change things one at a time. If you reduce flow temp, to get the same heat out the floor you DT needs to reduce. If you decrease boiler flow your mixer may need adjusted to keep.the same floor flow temp.

Maybe it's not level

Sounds like you have the flow temp set too high. The floor response is such that you are overshooting the thermostat. How thick is the insulation and screed, what flow temp?

The other issue maybe you are just running the UFH for to shorter time, running longer may do the job without increasing the flow temp.

You are living in a barn and you have left the doors open, or your heat emitters are undersized. But looks like a controller suitable for both a heat pump, but also a gas boiler.

I had so called self learning thermostats, but they just couldn't cope this the heat up and cool down times of thick screed and low flow temp. So next to useless. House was to hot or way to cold never the correct temp. So got used as on/off.

Not really clear what you are asking? All really depends on what state the house is in, if you are living, showering in the house mould could be an issue, especially if not heated also. Or if there is no real humidity being developed, mould issue not really there. If you are building and living in property a good chance the duct work will end up with a good coating of dust if you start the MVHR. If you are heating and living, I would crack the bedroom window open at night and open a window after a shower and take a hit on heating costs until building work is complete. Better than filling MVHR ducts with dust.

You're been watching the freedom heat pump install video's, I watched them yesterday

If the flow rate is increasing at each loop, that would suggest DT would come down, so mean flow temp would increase. The easiest way to get heat in the floor is to just increase flow temp. Instead of making a pump work harder.

Have you worked out your design heat loss. Although the heat pump says it 5kW as it get colder that figure drops. So you need to know your heat loss. Unfortunately that heat pump only has a single flow temp. You would really need to charge the buffer from the heat pump. The ch or cylinder would call for heat from the buffer as they required from the buffer. The heat pump would automatically charge the buffer as needed.

To have the same UFH across two different floor buildups could work badly, as they may or very likely require different flow temperatures to counteract the differing downward heat losses. If you are doing this, you want to think about different manifolds for the different floors, the flow temp for the new floor could be in the high 20s to high 30s, depending on the overall heat loss. The old floor flow could be in the mid to high 40s, and still not heat the room well. I would do as Nick suggests, and I really would not want UFH in an uninsulated floor. It will be a money pit for running costs, perform badly and generally disappoint.

I used 70mm. The only real place mine was exposed was at doorways. Due to strapping the walls out 50mm, plasterboard and skirting. Tiler was a bit surprised, but used a very flexible tile adhesive, we have thick commercial tiles, no issues a year later. The carpet fitter didn't even comment, but I did use a self leveling screed at those doorways. Again no issues.

My be worth doing a calibration, the instructions tell you how to do it. When you do it looks like it takes about 10mins, but in reality it takes about an hour, some of which the flow will be zero.

Would have thought you would simply put an electric meter between the consumer unit and the heat pump? An interface units sounds like a unit that allows one bit of kit to speak or communicate with another. Rather than a read out?

To have a grid connected system you have to completed G98 install certificate. If you don't you need to do it. Then you just use that. Simple

This is what used benn on a summer, single coat so far, looks as good as it went on. Basically a cedar oil at a very good price. It say decking oil, but suitable for anything made of wood. All our cladding and a couple sheds done in it. Dead easy to apply. https://www.ryeoil.co.uk/shop/deckingoil/

It's good you can smell it, means the parts per million is still quite low. As ppm increases your nose cannot detect it, but the concentration is at a level where quite short/medium exposure can kill you or do you no good what so ever. Even after dilution it may have a smell. Concentration (ppm) Symptoms/Effects 0.00011-0.00033 Typical background concentrations 0.01-1.5 Odor threshold (when rotten egg smell is first noticeable to some). Odor becomes more offensive at 3-5 ppm. Above 30 ppm, odor described as sweet or sickeningly sweet. 2-5 Prolonged exposure may cause nausea, tearing of the eyes, headaches or loss of sleep. Airway problems (bronchial constriction) in some asthma patients. 20 Possible fatigue, loss of appetite, headache, irritability, poor memory, dizziness. 50-100 Slight conjunctivitis ("gas eye") and respiratory tract irritation after 1 hour. May cause digestive upset and loss of appetite. 100 Coughing, eye irritation, loss of smell after 2-15 minutes (olfactory fatigue). Altered breathing, drowsiness after 15-30 minutes. Throat irritation after 1 hour. Gradual increase in severity of symptoms over several hours. Death may occur after 48 hours. 100-150 Loss of smell (olfactory fatigue or paralysis). 200-300 Marked conjunctivitis and respiratory tract irritation after 1 hour. Pulmonary edema may occur from prolonged exposure. 500-700 Staggering, collapse in 5 minutes. Serious damage to the eyes in 30 minutes. Death after 30-60 minutes. 700-1000 Rapid unconsciousness, "knockdown" or immediate collapse within 1 to 2 breaths, breathing stops, death within minutes. 1000-2000 Nearly instant death

Seems you may have a huge gap in the insulation called a cat flap. Don't sound that compatible.

Sorry attached the wrong spreadsheet. Have added the Emura 3 details MoreDetailPerformance2.xlsx

You can do by calculation, that is the easiest way. Got the calculation somewhere on my PC, but on my phone now. Down to about -3, double glazed (1.2 U value) actually meet the comfort criteria set by passivhaus because the inert pane, stay above a given temperature. Did all the calcs as part of the house design process, but then went triple glazed anyway. Our roof lights are Passivhaus institute approved and certified. U value is 0.93 https://database.passivehouse.com/en/components/details/skylight/roof-maker-ltd-fixed-flat-1153sk03

I found this on here and have added to it. The micro difference come from the temp set points and outside air temp, some perform well across the board others don't. There is link at the top of spreadsheet, this is where test data comes from, all registered and tested units are there. MoreDetailPerformance Aircon.xlsx

No issue with a single supply terminal. But you need vents to direct the flow through the rooms. You could retrofit something like these https://www.bpdstore.co.uk/glidevale-energy-saver-humidity-sensitive-trickle-ventilator/p/182 You can't get old air out without getting new air in. If you want heat recovery two options MVHR, rip house apart to install. dMVHR, fan unit required in each room, hole in each room through outside wall. Will need power run to each fan. A single unit not that expensive, but several starts to get expensive. Without heat recovery PIV, will replace old with new air, humidity controlled vents will help mitigate heat loss by closing when ventilation is not needed.

Not sure it's anything to do with the buffer. If the trvs are closed the radiator volume is excluded from the heating circuit, so the flow route closed. Then you are trying to dump xxkW through a single radiator and a buffer. Ideally you would reduce the flow temp, the heating would take longer to heat a room, but you Trvs would remain at a more open position as there would be less likely hood of overshoot. The alternative is to balance the system to reduce overall flow through the radiators so you get a larger delta T and radiators give less heat to the room, trv remain open unless you get solar gain. Or do weather comp.

Looked at my boiler this morning 2 degrees outside, and there was white smoke. Not much, just a general stream out the flue. Return temp at that was high 30s. There will always be some water vapour, even if the flue temp was 30, flue gas would hit the cold air, exceed the dew point and water vapour would appear.

It's certainly not going to rot in the short term. Our cladding was on the house for 9 to 12 months before it was coated, with no issues. Wait til you have a nice day or spring. UV strength during the winter is poor - length is day also short.