JohnMo

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.

Lots of questions The basics and that's where you start from. First it's about pressure drop management, a higher pressure drop the fan in the MVHR have to work harder to give a set air flow. Second when you use a plenum and individual pipes to rooms, the strings in parallel, so you will have one single run which sets the pressure drop - it's generally the longest pipe run and the highest flow rate. This is the route you need to concentrate on and get low. Then make sure all other routes do not exceed that pressure drop. Noise comes from two sources A. Fan noise - as mentioned above B. Duct noise from air velocity. This is generally managed by looking after pressure drops. So get your data sheets, look at pressure drops for ducts, bends and terminals. Get data sheet for fan speed/pressure charts for the MVHR. Before you do that you need to understand each terminal flow rates. You can massively reduce duct length by using coanda terminals. These will throw air from one side of the room to the other following the ceiling before coming down.

I would be doing that anyway - panel are £120 per kW plus mounts, so wouldn't you.

Yes - not really that important l on the design stage, but very important at the 'as build' stage, make sure all assumptions are correct as well as everything else.

Think you maybe over thinking stuff. A heat pump cycling is a reasonably normal thing. If it runs for 10 to 15 mins it over comes any startup losses. As long as it's not 5 mins later you have no issues. Quick restarts are down to setting startup dT correctly. Don't get bogged down, thinking it's bad in mild conditions. It isn't.

I was happy to minimise pipe in floor and designed in loopcad. The insulation values at the time didn't get down to my levels, and even then at -9 had a design flow temp of 35 deg. Actually the highest flow temp I need doing WC is about 32. Just installed a new smaller heat pump, as previous one didn't modulate well at all (it's being reused for hot tub). The last few days the CoP has been (in order they appeared) Average 4.5 day temp CoP 5.11 Average 6.8 day temp CoP 5.68, Average 5.6 day temp CoP 5.8. Still fine tuning WC curve, so performance is improving. Even with 4 poor running days, my weekly SCoP is 4.56. in a weeks time, I expect that to closer to 5+ even with more snow on the way for NE Scotland. Heat striping - pipes are 100mm down and by the time the heat gets to the surface you cannot feel any difference in temperature. It also works acceptably well in cooling.

Either find an installer that will play ball or just cut out the middle man and DIY the install. R290 Haier heat pump 4kW or 6kW from Wolesely are £2100 and £2300 including vat. Do a direct cylinder for DHW heat via immersion on cheap rate and a simple time switch. About £500. Connect ASHP directly to UFH and run WC. Two pipes, strainer on return (supplied with ASHP), couple flex hoses and isolation valves, job done. £200.

We have 200mm of PIR insulation below our bedrooms and carpet, UFH will keep the rooms circa 18, we open the doors if we want them the same temperature as the rest of the house. You may flow up to 35, but surface temp is only a couple of degrees warmer than the room, most the heating season. A nice layer of insulation (carpet and underlay) just stops that temperature reaching the surface. Net effect is rubbish heat output. It doesn't matter how long you wait.

We have standard carpet (wife insisted) and UFH underlay and it kills UFH performance pretty much. It's a bit like wearing a good overcoat on a cold day, you stay warm the cold doesn't get in. We run full weather compensation however. But as you have thermostats run at a set flow temp, you may have to wack the flow temp up x degrees and it should work fine. You would need to fine a happy spot via trial and error. Dig a bit deeper in your pockets and get proper carpet, dump your thermostats, run weather compensation and your energy savings will pay the extra needed for proper the carpets.

Why that much? Over thinking things. You can use passivhaus principles for any build. Main things are thermal bridges, continuous insulation, form factor, airtightness. So you need to consider ventilation.

Add it the outside if you wanted. Do people in the UK buy by the ft² or m², thought they bought by number of bedrooms and that was about it. Hence big builders building shoebox sized houses with loads of bedrooms.

They are very different materials, aerogel is a fibrous soft material, compacfoam, is a solid EPS, looks EPS but rock like. You can drill it screw into it etc. treat it more like wood than insulation. So fixing self drilling screws direct through compacfoam into the steel. Then if you wanted plasterboard screw into to the compacfoam or foam into position. Aerogel I bought it but I ended up using PIR, but @Nickfromwales suggestion of compacfoam is way better. We did upstands for our roof lights with it, easy to use

Observations Just tried to find a price for the Nibe, only price I got near, suggested circa £6k, so 3x the price of my Haier 4kW. Will it perform any better than my Haier, possibly not. Yesterday was between about 4 degs and 8 degs, and it just ticked away all day at an average CoP of 5.6, peak CoP around 6.3 (flow temp around 26-27).

You can work it out knowing your heat loss and then W/m² Just use this as a baseline, you may need to extend the W/m² and the MWT - mid way between flow and return temperature.