JohnMo

Low points - outside, if that at the heat pump, that's where they go.

Really! Missing a trick if you don't, the heat exchanger becomes unbalanced and you don't get the heat recovery you should. Do properly or really don't bother wasting your time, effort and shed load of cash on MVHR.

Not standard, but best practice, especially if you are doing cooling as well. Make sure the two products are from same manufacturer. I use Adey MCP1+ and MC10+ rapide, can be sprayed into the filling loop, takes 30 seconds. Do once you have all the air out the system and no leaks.

Seen the video, yes you can get a good CoP, but you still have the downward heat loss. Two schools of thought, loads of insulation or none, nothing in-between. Zero insulation you keep the UFH on all the time to keep ground charged. No, unless heat pump is huge. 6kW and 210L is a recharge time of 45 to 60 mins, 300L cylinder would take 50% longer again. DHW heavy usage, gas boiler running against a heat pump cylinder, would give really quick reheat times.

One each side, so two, you then ensure the piping and heat exchanger within the heat pump are protected

Look on eBay - half the price

After the existing filter last thing in the return loop on its way to heat pump. Altecnic 1” Filter Ball Valve - 124-6005 CST or Inta Full Bore Ball Valve with Filter Cartridge - 28mm Comp.

You building must be massive to need that size heat pump, as effectively a new build? 5-600m²?

If you are going for heat pump grant, photograph and record every insulation and airtightness improvement you make. Many will ignore these improvements otherwise. Get an official air test at the end of works. If you are doing UFH add at least 150mm of insulation (PIR) under and screed above or don't bother with UFH. A retrofit I would just do radiators, heat pump or PDHW boiler setup running Weather Compensation and/or room compensation. The boiler set up in PDHW will give almost instantaneously and endlessly available hot water. Others on here, have similar age building and with upgrading some insulation aspects run radiators at 35, with boiler or heat pump.

If it's all new nothing much, enough to get air out. Circulation pump on for an hour, cleaner filter and strainer

Again check your install instructions - mine explicitly stated a strainer must be installed and you’ve provided one. It also says if you have magnetic filter they also had to be installed

True, but do any modern ASHPs say glycol is the only option?

Best ratio - is no glycol at all - why are you adding. It just degrades system performance. If you really want freeze protection for warranty, buy two anti freeze valves. But ones that respond to water temperatures not outside temperature. The flexible hose by the expansion vessel, should tee into the cold water main and act as filling loop. But you UFH loops will need filling and air got out of the system - you would use a hose on the UFH manifold for that, one loop at a time. Not seeing many useful auto bleed points

Just a point worth thinking about. Heat pumps the SCoP (annual measure of electricity in, to heating energy out) is directly proportional to flow temp. For a given house heat loss, a heat pump designed around a max flow of 55 degs compared to 35 degs will cost 75% more to run (SCoP are approx 3.85 and 5.10). So a low design temp will cost less than gas. But sizing the heat pump correctly is really important. As you can see, insulation isn't the important thing when installing a heat pump, correct design is. Gas or heat pump insulation and air tightness reduces the heat loss only - it doesn't make one better than the other.

Energy counter 1 is showing 1.88 / 0.3 that is a CoP of 6.26, but it's reported as 6.8? Or is it showing an average over a time period and reporting that as the CoP?

Hoping - well happy for NE Scotland. Yep, need a couple of nice cold days to finish, got a couple coming later this week

He doesn't attempt, they film a team doing it and does a little bit of hands on. It was interesting but...

We have similar floor buildup in our summer house, not parquet but is and laminate flooring, the performance is pathetic even at 40 degs. In the end I decommissioned it. You need the pipes in close contact with something that fully envelopes the pipe so you have zero air gaps. So a screed or self levelling compound will improve things. Your thickness needs to thick enough to stop cracking from small movements. So will depend on make and exact product you use. I would looked to a self levelling but flexible compound.

If you can only afford to do the extension why are planning gutting the house as well? Cut your cloth according to budget. I would have an air test done and ask the guy to spend a hour going around the house finding and identifying air leaks first. Then make a plan of action to fix. Understand your current insulation and see how to upgrade cost effectively. Lofts are easy to upgrade, floor? (New floor or insulation to original), walls? (Internal or external) You plans have zero details on build up of walls, roof, flour etc, so are just a pretty picture. To get what you want the builder needs to quote based on exact specs, hoping for the best isn't going to get what you need. If you aren't airtight don't bother with MVHR, a well designed MEV or dMEV system will be more appropriate. And cost many thousands less. I would step back and get everything planned and realistic to your budget.

I have done all sorts of modes of heating, including just heating during E7 period, Cosy periods etc, and by far cheapest (with battery and ASHP) is just letting the heat pump run on WC. A 5 degree day today and it's ticking away at a CoP of 5.78 so far today. Any sort of batch charging, can drop CoP to the mid 3s

Work out your heat loss at your design outside temp, then get a heat pump that will modulate to half that or less. Then it should just tick away all day. If you have a secondary heat source like a wood stove, it will cut any peaks in demand, so size it tight to the calculation heat load or even slightly smaller. But then you need to consider DHW, I just do immersion then heat pump sizing doesn't matter. Closer pipe spacing decrease flow rate for a given heat demand, but only by a little, but generally not by as much as people make out when your house is already a low heat demand.

Mainly because it was a 10kW unit software limited and badged to 6kW, so generally min output was close to 4kW.

You can buy materials from anywhere, just get a VAT receipt, places like B&Q (can be way cheaper for some things that trade outlets), you have to ask for a VAT receipt. For best prices just shop around, trade account doesn't mean best prices, you can be royally ripped off. You can also get cash accounts with companies if you want, basically they have all your details you can haggle prices as they can see your buying history etc. Some jobs it's just easier to leave contractors to quote for the job, if you find the quote acceptable, they get the job, leave them to source and do the job, then invoice less VAT. That's life, get on and don't over think it.

For our build I considered speed of build first, then got stupid quotes. Looked at SIPs and there was quite a bit of key stuff by others, steel being one plus to get to the values I want, plenty of additional insulation was needed. In the end I went Durisol ICF, two of us both DIYers, built the walls of the house in 4 weeks (during end Nov to Christmas), not small either, lots of angle changes and 70m perimeter. 0.14 U value out the box, thermal bridge free, only basic hand tools needed. Build six blocks high, fill 5.5 blocks with concrete, repeat. No lintels needed they are self formed with the blocks, some rebar and concrete fill. Parge coat walls, service void and plasterboard or wet plaster direct, gives an airtight structure. External render, brick or stone slips or timber cladding are all easy to do, directly fixed to woodcrete ICF. It doesn't burn, doesn't rot. The blocks are made from end of life wooden products like pallets etc.

https://www.epicair.co.uk/products/zehnder-circular-decorative-coanda-effect-grille-renoventil-dia-90-mm-white?srsltid=AfmBOorHC-MEWuXyI--gEQUSlx8LQK3shpT2LxaOQzhu9pieFmeKZ3ak £7 each, I have 6 in the house and they will clip on directly to 90mm duct or you can get adaptors. They an extract version as well at a similar price point. You can either adjust flow rate at the plenum with restriction plates or a zehnder do a slip into duct one for the terminal end.