JohnMo

Depends on a number of factors, screed thickness being one. Wide pipe spacings give a ripple temperature across the floor, the closer the spacing the smaller this ripple becomes. The floor loop pipes emit heat radially, the wider the spacing the more the heat is diluted before getting to the surface where it is used to heat the room. But reducing that ripple is in the form of diminishing returns. And when running low temperature UFH cannot be felt. Examples 100mm screed, with 18mm oak floor covering for 20W/m2, on 300mm spacing you need a flow temp of 30 degs For 23W/m2 on 300mm spacing you need a flow temp of 31 degs Same conditions but 50mm centres, you drop the flow temp by about 2 degs, so 28 and 29 for the above outputs. For every m2 300mm centres has about 3.3m of pipe, while 50mm has circa 20m. Our 192m house has a loose 300mm spacing and 7 loops in total. Moving to 50mm centres would increase the number of loops to about 40, so 4 or more manifold instead of one. ASHP circulation pump would require several other pumps to supplement it. The gain in efficiency from boiler or heat pump would be spent on stupid amounts of pipe, pumps to buy and run for ever more. LoopCad does analyse the bunched pipes, our utility showed a huge overheat just by transiting pipes, I added insulation to the flow pipes the overheat went away. If you can't do the floor at 150mm centres your target parameters are wrong - increase flow temp, sort the design for your worst room first, then it is easy to sort the balance of the house, with wider spacings if needed, to get a balance output in all areas.

So take that in the round, we are 192m² and have a heat loss of 3kW, you are about 50% bigger, so that puts you to 4.5kW. We also have MVHR, triple glazing and very good insulation, so you aren't going to far away from 9kW. I would concentrate your effort finding out depth of modulation, that is possibly the more important aspect.

Never seen that requirement in any MCS documents! But are you not just paying MCS (suppliers tax, more profit) to go that route. If you are insulated as we as you say, you should only be needing a circa 6kW heat pump? High ceilings affect form factor, so you have a bigger surface area exposed to the outside. You just do the room by room heat loss calculation as normal, you will just have more wall and more roof exposed (if vaulted). Small impacts on a well insulated house. Depends on where you are in the country for ventilation, just follow building regs guidance to size, England is different from Scotland. You will be turning the system down after completion anyway, because you end up over ventilating at BR rates. Bathroom heating, you normally want bathrooms warmer than bedrooms, so you need heating in them. Bedrooms can be ok at 18-19, bathrooms will feel very cold at that. With a cooler bedroom they suck the heat from ensuites, so you need bigger than calculated towel rails.

So are you just making up the exterior, as you go? Surely you need a structural engineer for the outside, to specify lintels, ensure wind loads are accounted for etc. Who designed the foundations and have the blockwork walls be allowed for?

What flow temp are you trying to achieve that needs 50mm centres?

I just have 15mm from UVC to manifold and then 15mm for each wet room, then branch from there. Flow is more adequate. Wouldn't do 22mm for any hot water, you will waiting too long for hot to come out of the tap. Did similar for cold water.

You will gets of solar gain through the big windows at the rear, unless you have some mitigation.

Hasn't your structural engineer specified what you are to use?

Not really that obvious, nor the best. My view is a simple one, run weather compensation, you then need no control. Looking at your schematic, there are no mixers, which is good, so means the radiators and the UFH have the same flow temp, so should be easy to do just straight WC. Gives the best CoP generally, so lowest running costs. your other option is to do WC with set forwards in cheap tariff periods, here you would use a timer to up the WC curve to second set point 1 or 2 degs warmer, this then means when outside the cheap period the heat pump works less hard, so a little less likely to run down the battery too quickly. Fully open system (nearly) gain good. Your buffer is a 3 port, so a good compromise. Do a search on 3 port buffers to see the advantages and disadvantages.

You just need to look at the practicality of installing. It's been done, but by overlapping various loops, so more like a 100mm or something spacing then a second loop straddling the first. Little bit of a pain to do, but doable. But why, are you trying to flow stupid low flow temperature, that may not even be practical to run? If sounds wrong it normally is What depth of screed are you using? Our room with the most loops is fully glazed one end, 6m tall fully vaulted and we can manage on 300mm centres and we have to heat down to -9 on a regular basis.

If you need 50mm spacing I would go back to basics and see what you have done wrong. Increase flow temp, change floor coving. Are you sure you have insulation values correct?

I pumped everything excess until I got export into my immersion. But I now get 15p for export so why bother. ASHP can heat DHW at a CoP of 3 all year round. So as I pay 12.79p for import that's about 4p per kWh so makes perfect sense to export. You just need to own maths based on your own circumstances and tariff. What's right me, may not be you.

Perhaps it would be better to post a sketch of how you propose to hook this all up. Still confused how you will hook up only 4 loops to a 9kW heat pump. You may not able to meet the main flow rates required.

So buffer makes sense big ASHP not doing it's full duty. A decent write up here https://blog.heatspring.com/2-pipe-versus-4-pipe-buffer-tank-configurations/ And here https://kensa.co.uk/installer/resources/buffer-tank-sizing-heat-pump

Do I care - no😇

Why? If so how are you configuring it.

Export excess and run pure WC on ASHP. Time cylinder heating early afternoon and other off peak period if needed Don't bother using immersion, you get better value exporting. Go on something like Octopus Cosy to give you three chances to charge battery in mid winter.

Not sure why they such a bee in their bonnet about it. This is what building regs says about https://www.gov.scot/publications/supplementary-topic-notes-review-domestic-non-domestic-energy-performance-certificates-scotland/pages/3/ The thermal Mass, or the heat capacitance, of a material reflects its ability of a material to absorb and store heat. It's basically the internal heat capacity of the building. Timber frame and PIR insulation has a low thermal capacity, block work and plaster applied directly it's huge. Pretty simple really.

What am I missing 9kW to only 4x loops of UFH, what's on the rest of the system? Expansion vessel on the DHW cylinder is for fresh water only. You need one for the central heating water, this is close to the ASHP on the return side, after the tee where the cylinder joins the return pipes. This then covers all water that goes through the ASHP for heating cylinder and for central heating.

Why bother - is it going to make any difference how it runs really?

Sounds like a plan. Mist spray joints and use expanding foam. Allow to gel and push together this should give bridge free joint. Forming a single wall of EPS. You could use a similar method to stick to substrate plus mechanical fixings.

First thing that jumps out is the lounge is small compared to other rooms, the hall looks bigger. Maybe move stairs towards kitchen diner would balance things a little and possibly a narrower hall, would give a nicer lounge. Utility looks a little small to be practical. Office looks wrong in the corner of the kitchen. The island in the kitchen looks a little close to the door, so is a bit of a pinch point. From a practical perspective would the kitchen in a L shape be better or even swapping kitchen and dining rooms around? So not filling a whole wall. Washing up against a blank wall is just sad, so maybe re-home sink. Have a trip to a beach and draw each floor in the sand full size, walk through the build to see how it really feels. Make changes as needed, photo update plan. I found that to be best for our build.

Pretty much what @Beelbeebub did, but with some flashing to joint to tiles system. Looks way more adaptable/flexible to different sizes of PV panels. Especially if the panel has reduced in size like I found.

This video shows you what you need and how it works https://youtu.be/iHRdlLeqm7Q?si=R62xc2Xma48Hjr-U

After you have done that you need to address a few other things to get best efficiency. Assume a mixer valve and additional pump are on manifold, look to remove them so you can operate on WC. The mixer will always add distortion to system as there is always mixed in return water to flow. If you have a buffer you need to delete or ideally modify to be a volumiser on the return line only. Then look at your circulation pump logic. You need to it switch on off with the ASHP compressor, not be on 24/7. Look at you 3 way valve that diverts flow to cylinder or heating, check make and model, then find kvs value from manufacturer datasheet. You for a kvs no lower than 6, but the bigger the number the better, if 10 or above that is great. Strainers in system, replace with a low pressure loss central heating filter. Strainers have a pretty huge pressure loss, ball valve strainers are the worst.