JohnMo

I would be addressing your insulation values if you need that much power to heat your house. Whatever PV you install will give an abundance of electric April to September and then next to nothing when you need the most. Mid winter you can goes days with zero output. Also you really need to see, what lots of solar will cost you (payment to DNO) and if they actually let you. Your best bet is G99 route to approval, which limits export below 16A. You will need to ask for permission prior to install/ switching on. If you are connected to the grid permission is mandatory irrespective of your intension to export or otherwise. Same can also be true for your battery depending on how it hooked up.

I would think, as they only fit a small selection of heat pumps, analysis of house response to heating inputs and then writing control parameters back to the heat pump controller. Repeat... until it's all calibrated. Then possibly sit there for ever more looking pretty.

Nearly lost the will to live, reading the first post, and still didn't find any details needed. Do you have a buffer or volumiser or neither? What are your flow temps? Typical will do. How many zones, TRVs/ thermostats How do you actually operate the system? Keep it short please.

As @jack says without heat loss calculations you are just shooting in the dark. I am installing a 6kW heat pump and it will heat our house 192m2 and a summer house, 16m2. I expect it to be using around 50-60% of its capacity even on the coldest day. Sounds good, but doesn't really mean anything as far of how much your house is expected to require in terms of heating. There is a calculation spreadsheet in boffins corner on buildhub

Last year I had lots of zone on at differing times, this year I have all zones on if any zone is on and I am using 25% less mostly, in some months 40% less gas. The issue with just one zone on is the boiler cannot get rid of the heat quickly enough, so stop starts runs for a very short period and does this quite a lot. So efficiency drops of a cliff. I tried lots of things a monitored gas consumption and the weather to build a trend so I could understand what worked best.

Atamate_SDAR+Paper+2019+(1).pdf

Think you have answered your own cause. Best two fixes are PIV or MEV. PIV, one central unit in loft or elsewhere, one supply outlet. MEV, centralised extract unit taking air from all wet rooms, can get them so they only when required and close down or open extract points as needed. PIV is either on or off, MEV, ventilation only as required, if specified correctly. You can retrofit trickle vents, or vents in the walls of dry rooms, but get them so they auto open and close based on humidity. MVHR without airtightness is a waste of money.

Think it's good for radiators but not UFH

Pity it's only suitable for a limited selection of heat pumps. But it should be an easy enough algorithm to write I would have thought

I went to a great deal of trouble to fence everything off, in the end no-one seemed to be that bothered. Whether its a case that they see your trying to do the right thing and playing the game. Our architect out together a statement (cut and paste from something he found on the internet) on what we going to be doing, to what BS standard, I cut some words out that were not practical and it went through fine. Basically ours was 4" posted, wired, and orange mesh about a 1m high, with signs from Screwfix say keep out.

Not sure I agree. A house on an open flowing weather compensation system is simple. No actuators, no thermostats, you don't need mixers (in many cases) and in most situations a single pump is used, with the boiler or HP modulating its speed. You can calculate the heating slope etc, so limited faffing getting things correct. There is a study linked to on here, were 3 situations were tested. Heat pump via buffer, buffer control by on/off thermostat - CoP 2.7. Test 2 Buffer with HP on weather compensation, CoP around 3.5. No buffer, open system HP on WC, CoP around 4.2. All tested at 7 degC outside temp and same simulated building loads. So has the UK had WC, but we are too daft to use it. Plumbers install a boiler on Y plan and flow central heating at the same flow temp as a cylinder. Then on UFH mix the flow temp down. We stuff our houses full of on/off thermostats, run a boiler or heat pump way to hot and then wonder why we have gas boilers that run at 80% efficiency, when they are capable and designed to give 110% efficiency. And ASHP that give a CoP of 3 (if your lucky) when they should be getting over 4-5.

So what's that?

It's not an easy one as two identical houses, will have differing heating needs depending on what the owners feel is right. You may be happy with 19 degrees, the next person not happy unless it's 22. This gives a different curve and different heating profile. Mixing in load compensation with WC is fine in concept, but with low temp UFH leads to over and undershooting, the system response is out with the controller parameters.

I think that's one of the key differences, you have a control which grant hide away so you can't mess with it. The original manufacturer uses it as a full function controller

Chofu-Operating-Installation-Manual.pdf Key difference is how they use the controller and generally connect it all up. The manual attached is very similar, just lots of pages longer and features cooling also.

Grant install a modified Y plan, to make it easy for installers. If you went with the Grant badged unit, you need to educate yourself on how they should be installed, or go elsewhere.

Before saying you need xxkW, you need to look at the various performance tables of different heat pumps, as one 3 kW heat isn't he same as another, they give different rating to suit what they want to sell. Main issue isn't really the size anything up to about 6kW should be ok. Main issue will be have a design that doesn't require a buffer for the shoulder season, so engaged always open system water capacity is important, roughly 40L. That will allow the HP to run without short cycling and for defrost. If you can get your head around a single zone heating system, that where you need to heading, simple weather compensation your install can be very simple.

Sorry no photos You will have timber strapping on the wall. Prior to install of cladding, basically close the gaps at the bottom with mesh. So once the cladding is in place there are no gaps.

Good representation of what I was trying to say. Short and fat a good place to dilute supply water with return water. Result hot water from HP going in and warm water going out. With a 4 port there should be no need to have the two pump flow rate matched. They are hydraulicaly seperates, so basically two systems meeting at the buffer. Look at a three port also.

To add a volumiser needs one open loop/radiator downstream of it

A 4 port in normal operation, all water goes in to and out of a buffer. A 2 port only the excess water flows through the buffer. The buffer is always open to the flow and return. If everything is closed downstream of the 2 port buffer all water flows through the buffer. Just the same as a 2 port. A 4 port hydraulic sepereration across buffer a 2 port no hydraulic sepereration. That's the main difference, plus less mixing. So in defrost the heat pump would just pull on your buffer volume in either case. A volumiser either sits in the flow or return circuit only. Does not give hydraulic sepereration. But in defrost the HP can use the stored volume

That is the least efficient way to plumb a buffer for a heat pump as the mixing within the buffer requires the heat pump to operate at a higher temperature than it would otherwise. Better to use the same volume and pipe as a volumiser or as a two port buffer. Or better still don't have one and make sure your zone sizes are big not small.

Those prices are just taking the pi**. The quote says I am not interested in the job, just go elsewhere, or buys the bits you want get the plumber/electrician to hook up. Design help from on here.

Put it on Colling duty, run it off your solar. Heat your hot water 4 times as quick as an immersion, as you get a CoP of 4 ish in the summer, immersion CoP of one. So even on a poor sun day you should get a bigger chunk of your hot water at zero cost.

I looked and you have to an internal and external unit, even on the monobloc, to get them to work. The monobloc has most of its electronics within the indoor unit. The prices gets very large very quick.