JohnMo

MVHR will be around 0.5ACH, with an efficiency for heat recovery, of say 80 to 90%. You sound like you will be better than 3 m3/m2 @ 50Pa airtightness, so you will be needing mechanical ventilation of some sort, so the next is MEV or dMEV, so that would be same ACH, but 0% heat recovery. MEV or dMEV would require trickle vents also, within wall or windows.

Your ach seems very high, you need less than half that, when you have finished. I would extract from the kitchen and bathroom only, and supply an equal amount to bedroom and wardrobe. The living room will be continually washed with fresh travelling from the bedroom and wardrobe as it travels to the extracts points So do 47 and 29 m3/h in the kitchen and bathroom as extract, and supply the same to bedroom and wardrobe. Short runs will only need one 90mm duct. So bathroom and wardrobe. Once you get signed of by building control, you could have those rates. Get a CO2 meter to monitor.

Ground floor yes, in bedrooms not the best to slow to respond. So never really the right temp when you get up or go to bed. In wet rooms it's good, but add an electric towel rad also. Solar - thermal or PV? ASHP can do UFH and all DHW. No additional heating required, but if there is the cylinder will have an immersion. 12kW why that big, do your heat loss calculations then select the size. To big makes life difficult, cost more need more equipment to keep it happy.

+1

I would think it's more likely to do this. A ceiling extract terminal, will pull the air across the whole room The extract above the hob will throw the air across the room in red. The blue lines will pull that air and the air from the supply to the dining area and the downstairs toilet.

Been like that for years in Scotland, doesn't stop you installing PV. Very little wind today, overcast, so not much wind or solar electric today. But our PV is generating enough, to cover background loads and has spiked at 1kW for short period - but saying that our grid is still zero carbon today.

The heat pump will be makings air pass through itself when online, the air will be ambient, so would any wind. It's an inanimate object, not affected by wind chill, as humans are.

HiI would just do dMEV fan set on the lowest rate. Here is what I would recommend, have done a comparison of running cost and heating savings below. https://www.ebay.co.uk/itm/110918389829?var=0&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338749401&toolid=20006&customid=GB_11700_110918389829.141234980085~1871630609920-g_CjwKCAjwkY2qBhBDEiwAoQXK5d0Y4QsG2U9JPC4jZvEMGuxN-nZ8u5PCl84Yx8sUrwsA3kzKB7p8xhoCLtUQAvD_BwE Advantages of dMEV Silent in operation, no filters to change, one hole in the wall, will manage humidity boost out the box. Next to no power input. Doing MVHR will cost way more install and run, require loads more labour to install, require frequent filter changes as the flux, will mess with the extract filter. If you are pretty well insulated your typical (14 deg delta between inside and outside) would require 500W with dMEV, and if MVHR is 70% efficient about 400W per hour heat input. (Used a heat loss calculations I had already as indicative) 180 heating days for 8 hours a day about £30-40 a year difference in heating cost. But add in running costs, MVHR is 40W 24/7 so that is £94 per year, and additional filter changes - running at a low speed would possibly half that to say £40 per year. The dMEV would be running 24/7 all year also, but only requires between 0.5 and 1W at it's lowest set speed. So costs £2.30. Costs are based on 27p kWh. So difference in heating saving is taken up in running costs, plus it costs way more to install MVHR (equipment and labour). I went through the same dilemma earlier in the year, and want Greenwood dMEV. No regrets

Not sure the location of the kitchen extract is good above the hob. I would bin supply in the dining area and make that the extract for the kitchen. Secondary air for the stove being pulled from the room, could depressurise the room, allowing fire fumes to enter the room, so you need to be careful.

Knauf Frametherm 32, on a roll, easy to cut, self supporting. Makes it easy to get a gap free install. Assume to get a decent U value, you have additional insulation going into the structure?

The warm south, currently 7 here, been that hot all day mixed with continuous rain.

Welcome

So using passivhaus or English rules the ventilation rate is around 400m3/h, from the bottom row on the table. But really depending on how many people are in the house, that could be over ventilated in reality, so the 4br/5p at 90m3 or somewhere in between. Your trouble is the amount extracts you have and if you do the passivhaus rates for those that are actually wet rooms, 3 x shower rooms at 31m/h 1 x Kitchen at 46m3/h 1 x Utility at 15m3/h So already at 156m3/h, plus you still have a further 4 extract points to consider. Pantry and kitchen do those to match the kitchen rate between them so say 10m3 in the pantry the rest in the kitchen, plant room as small a flow as you get. Temple a low nominal number. You then need to match the supplies to an equal extract flow rate overall. Basically the more people you are likely to have in a room the higher flow required. I do a quite high flow in a lounge, a low flow in a single bedroom, big areas where very little happens day to day, a low nominal flow.

@Lloyd Adams has all the information now, different views on what is or isn't allowed, and only he knows how the space will be used, in the end. So really up to him to decide, which way he proceeds. Not me, you or anyone else.

Sorry you can't read the 'or' If I was asking the question the OP is asking (and by the way I wouldn't ask, I would just do it), then reading the technical guideance it reads as, planning permission is required. But people ask too many questions, to get answers, they don't really want to hear.

That's a blast from my past, when I was doing a degree, 30 years ago. Certainly a lot of countries will have major issues, not just with land loss, but mostly from ground water (drinking water) being contaminated with seawater. Back then the major concern of global warming was water or lack of suitable water. Talk of the next wars being over control of water. That issue has been buried, in the very difficult basket, I assume.

So instead of the short read here is the longer one direct from the government if that suits you better. Ok straight from the government instead, Technical Guidance to permitted development rights - bit of a longer read but what's allowed is concerned in Class E. Page 41 states A purpose incidental to a house would not, however, cover normal residential uses, such as separate self-contained accommodation or the use of an outbuilding for primary living accommodation such as a bedroom, bathroom, or kitchen. So having a kitchen is not permitted with planning permission. 190910_Tech_Guide_for_publishing.pdf

I wish - 600 mile further north and it's currently 2 degs, had around 5 degs this afternoon.

Wrong, as detailed below, if you don't know don't answer someone's question. https://www.crownpavilions.com/blog/garden-room-with-kitchen/ "Can you put a kitchen in a garden room? In short, the answer is yes. You can install a kitchen in your garden room so long as you follow building regulations and apply for appropriate planning permission. For a working kitchen, plumbing and electricity is a must-have. As such, your garden building will now be classified as a dwelling rather than an ancillary building and will require planning permission. Read our planning permission guidelines for more information."

Or a Willis heater?

Would add, that our assessor only applied min building regs junction details, so if you have better min allowable, you have to proof it, as well

I would check, if your that bothered, as soon as you start to add mains water and drainage, the planning rules start to change. Get more onerous.

Not sure it makes a huge amount of difference, you just need to shop around to get good prices.

What about the fans? What about filters to keep the HE clean? I only paid £250 for a new unit on eBay, so not sure you will be saving much but if it's project/hobby don't flag it as a money saver. Would it be easier to have a square box with a heat exchanger at 45 deg, then the inlet outlets can be on a straight face instead of a lot of different angles?

Only thing I would worry about is the kitchen does not seem to be covered by ventilation? Is the bedroom also having dMVHR? If it is, really confirm noise levels, anything above 30 to 35 may sound noisy in the middle of the night. But I would really concider a simple condition based dMEV setup. Put humidity activated vents near patio doors and in bedroom, these are silent in operation and need no power. Then a dMEV in kitchen and bathroom that runs at all times at a very low background ventilation rate and is automated with humidity sensor to boost only when needed. Greenwood dMEV is silent in operation while doing background ventilation and have a humidity sensor built in.