JohnMo

The first video, had two distinct zones, UFH and radiators, which is different from you are doing. The primary circuit was at the boiler with secondary circuits for radiators and UFH each requires it's own pump. You will be running both areas (UFH and rads) on unison, so you really don't need hydration seperation to keep boiler happy. Whether you need dT20 to keep boiler on side with a max flow temperature of 50 is debatable, and something that can be set anyway. Trouble with dT20 thing, is when you are running WC and it's mild your flow temp could be 30 for the radiators, so dT 4 or 5 works, dT20 definitely doesn't as return temp is lower than room temperature. Discussion here on dT settings

So is the left manifold feeding the radiators? The right the UFH? The tee being your mixing valve?

Flow rate goes down with multiple showers on at same time, but you are only delivering what the water main will flow at a max anyway. Two showers is fine, 3 usable but unlikely 3 people would shower at same time. Never noticed any noise ever.

Do you need the tee and join between flow and return between the two manifolds? You will need two circuits, but they are going to stay on all the time. You will need two different WC curves one for the radiators and one for UFH. If you applied the same curve to both circuits it wouldn't work. Mainly because the design day flow temps are different by a big margin.

For £2k you buy a heat pump! But, do what the regs say. They do not mean the same. Double skin is just a additional external layer to the tank, more for protection from impact. A bund is an oil tight area below the tank, which should the tank leak would catch the contents and not allow it to leak to the environment. A bund done correctly allows water (rain) to drain away, but not oil.

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?