DanDee

You should tweak your pipes such that at low house load(or for the reason you have now) to divert some of the return from the heating through the cold(when it's colder than the return from heating) bottom of the cylinder(coil). No more cycling/reduces cycling. Forget about how much this would benefit, just do it for the guys.

Hydrosplit is a made-up term for every monoblock that doesn't have a pump, just the heat exchanger and paired with an indoor unit that includes everything else, sometimes the nicely squared box DHW. But basically every monoblock with only the heat exchanger, it's a hydrosplit, as even if they don't sell a pairing indoor unit, you have to make it out of parts on the wall/cylinder. If you want the compressor inside, buy a water/water unit, and use any coils with water/glycol you find suitable(you can shape and put them where you want), with PVThermal as extra.

Let's not ignore that the same climate change makes/changes the extremes to the point of normal.

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1133079/Approved_Document_L__Conservation_of_fuel_and_power__Volume_1_Dwellings__2021_edition_incorporating_2023_amendments.pdf

There is someone out there installing A/W that is looking to make a better fancoil than what is on the market now, that would give a better result than having to oversize radiators. There is room for better everywhere.

There's multisplit and then there's mini vrf mini vrf units.pdfmini vrf.pdf

What will be the energy loss under the floor?

there are no limits to what a brain can think of, let it loose

Your best bet is to look at the N. American systems and take ideas from there.

Not mine

I can tell you how to achieve this with any heat pump if: Why do you need this, what is in your mind?

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Well, even if they are capable of higher instant temps, I don't see them as being sold as something to replace a combi boiler/instant heater, and in general a cylinder is still to be used as it makes more sense. I don't think there's a domestic HP designed specifically with that in mind, not to have a cylinder. A combi get's started multiple times a day without the hot water having a change to reach the bathroom tap when tenants are washing their hands turning on the hot rather than cold water for 30seconds. When hand washing dishes, the flow of water that gets the boiler going it's too high, such that if you deem that is too much water/hot water and try to lower it, you pause the heating of the water, thus starting the cycle of death. Old boiler that is. I would want to know a HP is started multiple time more that it already does.

why do you bother writing if you are acting like a yankee that has an army bringing home cheap oil? bring some benefit to the topic/forum discussed