JohnMo

And an ASHP - why. Keep systems separate, ventilation keep to ventilation, heating keep to heating. So a normal MVHR unit, a normal monobloc heat pump. If you have a choice of heat pump, go Panasonic. Go Heat Geek cylinder (300L) you should be able to get a CoP of around 5 compared to the 3.5 I get with a more normal 3m² coil heat pump cylinder. UFH on ground floor and fan coils in bedrooms all as a single zone.

I would try it first, UFH maybe too hot at 45. If it turns out it's not getting hot enough dump mixer and pump and it all fully open off the heat pump circulation pump. Last thing you want is thermostats switching big sections of the heating system off, because the flow temp is way to high. Flow rate is king with heat pumps

From trying myself no. There is always mixing going on. But having radiators and UFH your radiators will need a higher flow temp anyway (45) and floor maybe closer to 30. I would Assuming you run the rads on weather compensation, get the curve set for that, set the UFH mixer at say 35 see what happens? Adjust from there. Concentrate on radiators first, then balance the flow temp on the UFH.

It's a Maxa i32V5, same as a Viessmann 100A. Just started with a target 5 degs higher than normal, to see what happens - was pulling quite a large dT at start up, so heat pump went to max power trying to get either the flow temp or dT to target. I then started moving the target temp back towards the more normal. Moved the target temp down in one degree increments, after a couple of steps the heat pump tone changes and it runs a lot quieter and the heat pump started modulating downwards. Gets to about 5.2 kW During a normal run, you see the heat pump adding and subtracting power to maintain a 5 dT. I think the floor will happily take 5 to 6kW or more, even on 300mm UFH loop spacings. Think the ASHP has just found it's happy place, it can control dT and is running at point where heat given is equal to the absorption of the concrete floor, which is about 50 to 60 Tonnes of concrete to heat. Cycles are very controlled, certainly doesn't have short runs and restarts every few hours. Thick screed floors are just strange respond differently to a radiator or thin screed floor. More like a storage heater.

At that flow temp and outside temp max is about 6.2kW, so modulating down to 84%.

Mine is supposed to modulate down to about 3kW, but it never seems to drop below about 5.2kW, but is delivering a COP above 6 when running and runs a reasonable time. Most heat pumps have setting you change which alter cycling time and frequency.

Have attached an UFH design chart, it shows the relationship between pipe centres, heat demand and mean flow temp (average between flow and return). Draw a line from pipe centres through heat demand W/m² and you get mean flow temp required with a floor coverings with a Tog value of 0.1 (different floor covering materials will add or subtract actually flow temp required, depending on chosen materials). Notes: You actually have to extend the chart downwards below 20W/m². ASHP have a min flow temp allowed it is generally 25 degs. ASHP generally have a dT of 5. Using 20W/m2 as an example 300mm centres requires a mean flow of 27. While 100mm centres a mean of about 25. The difference in CoP from the heat pump is in the region of 0.15 advantage to 100mm centres over 300mm centres at -7 outside.

I would be wary of doing that, just because of the amount air drying that will go on - you could get an unhealthy humidity level mid winter. Even just below normal levels of ventilation last year we were getting to 30% humidity. Bumping up ventilation rates and heating the air - not sure I would. Heat pump and fan coils kor UFH and fan coils in bedrooms) or A2A and separate MVHR.

But once you get below about 15-20W/m², we are talking around 2 degree difference in flow temperature, when changing from 300 to 100 centres.

They are wrong. I get some cycling, which I can manage, because I have 300mm centres. By default closer centres has way more water in the system, this prevents cycling to a good degree. You also have more contact area with the screed so heat gets carried away easier. You manage energy by flow temp. Which can go down to a flow temp of 25.

It's actually air changes per hour not air tightness, that goes in the box in the spreadsheet. Different things. If you have MVHR that air change figure is close enough.

GRC Aquatech from Insch in Aberdeenshire

This is where we got all our UFH from, if your local they install as well.

Don't arse about, have all water filtered. Get a company to install, so you are covered for wholesome water. They will disinfect as required also. If your water isn't pH neutral the last thing you want is to spray that all over your car or plants. Servicing, day to day, there is none. We have just had an annual service done, everything reset as required media topped up, filters replaced etc. £160 incl. VAT. Filter changes (10, 5 micron and UV) are an annual task unless water source is really mucky. Last year watering 800m of banking (2 hose pipes for around 2 hrs continuously) every other day throughout summer added an extra 10 and 5 micron filter change, so about £10.

No G3 requirements for these cylinders. But if you have room for a cylinder use a cylinder. If there is an issue doing the drain side of things for an unvented cylinder, look at a harlequin cylinder, they also require no G3. Or go full UVC but specify a heat pump cylinder, store at lower temperature your boiler will condense throughout the full heating cycle due to the big coil.

Air changes can set at 0.3 to 0.5. A big house not many people set at 0.3 so the air doesn't dry too much in winter. If you want to heat the house house from just the ground floor you are likely going to need 150 to 200mm centres. Maybe time to look at a different supplier?

Other than UFH, where are you installing radiators? Your low energy house should be running pretty cool flow to the UFH, circa 30 ish at your lowest outside temp. If you are have radiators 1. Do you really need them? Upstairs bedroom unlikely to need them 2. make sure they have a design temp pretty close to your UFH Then run the whole system open loop. Remember No buffer No mixers or UFH pumps in the system. Both the above will have a direct impact on CoP

I enjoyed the whole process. But I rarely look back, just keep looking and moving forward. Did lots myself, when I had trades I spent all the time on site, clearing up, being on the spot to make the 1001 decision. We were in almost a year to the day from starting, but 3 years later my to do job list is nearly complete.

So sprinklers needed in every new house in Wales! That must be the fire engines having to do 20mph. So takes an age to get there.

Our neighbour has an underground tank that he will divert rain water too for fire fighting. It's a condition of a habitation that it's full. Not sure you will need sprinkler system unless you are open plan from kitchen to stairs. Or lots of floor levels.

You can download all sorts here, including the build manual, which is where the calcs came from. It also has all the thermal thermal bridging calculation for all standard details with are all SAP EPC approved. https://durisol.uk/technical-resources/

Starter fir your calcs on U value calcs for 300 and 365mm blocks

Assume Ecobrix is the new name for Durisol? We used 365mm with a 50mm service void inside and that will give a U value of 0.14 without anything else. Not sure I would bother (I didn't) with the 300mm nor the additional external insulation on either. Your into the territory of diminished returns. Biggest issue with both blocks is design of your air tightness layer. Do you have thoughts?

Same view as myself That is what I am using. Installed between MVHR unit and distribution plenums. You have to have at full stretch and then they are fine, not sagging or loose. I have just plain steel distribution plenums and no further attenuation. No issues - don't over think it. Install filter G3/4 cones in the extract terminals, these add to the noise attenuation anyway. But install before commissioning to keep all the dust out of the ducts.

Your starter for 10 https://www.planningportal.co.uk/permission/common-projects/decking/planning-permission Then have a read of Approved Document K: Designed for what loadings and why?