Sorry, can’t help, but someone will be along shortly I am sure.
Just in case you hadn’t thought of it, plenty of experience on YouTube, and seem to remember Skill Builder has some recent stuff on this.
But some thoughts on this, and they may not be applicable to your situation as you are renovating from scratch so presume have the ability to add lots of insulation to the house.
I am an engineer and have access to simulation software through work to model any process flow sheet, so used it to model and understand the air source heat pump process (basically the reverse of a refrigerant cycle).
Really interesting results and I wanted to get my head around the whole thing from a theoretical point of view, rather than rely on anecdotes and experience, as I am looking at it as a possible future addition.
With gas prices still 1/4 the price of leccy, and unlikely to get ever a COP of 4 or greater (which the model was good for) in winter when I need it, I have shelved any plans for now.
My boiler and radiators will need changing in the next few years, so I will revisit then, especially as the reliability of the technology should improve and if the spread of gas to leccy price narrows.
But, our house is old stock and difficult to upgrade the insulation, so it is always going to be a more difficult candidate for an ASHP.
Just doesn’t make economic sense if you are getting significantly less than a COP of 3 in winter and the leccy costs 4 times the price of gas. Even with the £7,500 grant, and 90%+ gas boiler efficiency.
Fine if you want to decarbonise your house with electrification, but usually you expect and economic reason to ease the decision, and an ASHP currently has no payback or rate of return, as it costs more to install and operate than a gas boiler, even with the grant. And the latter is much established and proven technology, whereas ASHP comes with a lot of challenges, most notably getting the set-up correct for the properties of the house. A gas boiler is very forgiving in this respect.