JohnMo

MVHR dies summer bypass automatically cannot change it, not sure how it helps, unless it increases heat demand, which not sure below the back pocket

Nope not enough cooling effect. UFH in cooling mode leads to a nice house

It's minimum modulation is near 4kW, house demand is only 3.5kW max. Normal run of things I wouldn't change it, but we have just bought a wooden hot tub, so will repurpose the old unit to heating the hot tub, instead of the normal wood fired heater. So get a heat pump more appropriate to the house demand. Should make a decent dent in running costs, with better CoP in summer and winter, for very little money.

Didn't answer fully before

There is the inverter controller outside but I think the indoor wiring centre controls most things The relay is for cylinder immersion control. You can drive a couple of secondary pumps, mixer valve, 3 port valve etc. plus lots more.

Yes and Wolesely don't tell you any different. They want a restocking fee to take it back. They do sound small, I keeping my 50L volumiser in system so will retain the existing expansion vessel in circuit.

Just need some warmer weather to allow old heat pump to be removed and this one installed. Have had to add antifreeze valves, part of the warranty conditions. Have got Inta Zero ones that reference water temperature not air temperature. Brand new half price bargain from eBay.

Some photos Indoor wiring centre with controller installed (no wiring installed). Simple install screened cable to outside unit and power. Cover on and wing complete, all metal casing and very heavy duty. No sharp edges. Outdoor unit, for a 4kW unit it's pretty big, the condenser and fan are very big compared to the Maxa unit currently installed which is a 6kW.

So took delivery of the 4kW Haier ASHP today. So far first impressions are very good. Consists of an outdoor unit, complete with expansion vessel and pressure relief valve, inside the monobloc. Inside the packaging is also a controller and indoor wiring unit. So can return the one I thought I had to buy. So total cost is £2100 delivered to the door from Wolesely. Photos to follow with full install story

Heat output is governed by mean floor temperature or mean radiator temperature. A heat pump that can modulate down to match heat energy required and not cycle, the target flow temp will always be lower as it can run steady state. So to deliver a mean flow of say 30 degs with a delivery temp of say 32 and return of 28. A cycling ASHP no matter how minor, to deliver the same mean flow temp will have to operate a higher target flow temp to compensate for the periods when the compressor is off, so CoP takes a hit. Also data table assume steady state running not any cycling. So do not take account of any energy wasted reheated cooled down components. But as previously mentioned, if a oversized heat pump has a suitable depth of modulation your only hit is capital costs. Which could be in the thousands as everything becomes bigger to accommodate the increased flow rates and electrical loads. Which aren't the dominant use case. The coldest days are the few and more average 7 degs days are the many.

So are new one

Run in DC not AC, then volt drop isn't an issue

Heat pump cylinders are generally big because they store water at 45 to 50. A typical direct cylinder could just as easily be at 70 degs, so effectively a much smaller cylinder holds just as much energy.

Can you not surface run it?

Get your finger out!

I would just a decent dMEV system.

That's the trouble with this country - lowest standards possible. And a general public that are willing to accept that. So a cheap 30kW combi that only modulates down to 10kW, thermostat in every room, boiler that lasts about 5 years because it cycles so often. That'll do

Nope. Fact any cycling requires a higher flow temperature to compensate. Example my install is cycling 4 degs outside, runs for 1.5 hours off for a hour. Flow temp max 29.4 degs. Overall CoP so far today is 4.55, but heat input is approx 500W higher than it should be (2.5 compared to 2kW). Steady state running flow temp required is 23-24, also need 2kW heat input, reduced flow temp increases CoP to around 5.2 to 5.5, reduced electricity input by 500W, so should yield something like a 30% reduction in running cost, just by a using a heat pump that covers full heating range by modulation. Apply that to 80% of the heating season it's not small change.

What make model - boiler or heat pump?

Depending on the controller it may be configured as the master thermostat unless it's just a time switch. Your sitting room maybe has no zone control it's just an open zone. The controller may be asking the system to do stuff based on what it sees in the garage?

The installation I am talking is simple. You will need a room by room heat loss calculation, then size emitters to room heat loss at same flow temperature. Direct cylinder with immersion timer. Set timer to any low tariff periods. ASHP, outside unit power cable via isolator switch. Two core screened cable between outside and wiring center. Power to wiring centre. Controller within wiring centre. No room stats. That's it no need for 2 port or 3 port valves.

Pipe sizes are simple for a heat load of say 5-6kW, I would just run 28mm until pipe splits for downstairs and upstairs then 22mm to each manifold. UFH pipes 16mm, and rads from manifold 15mm

But I would just delete all the zones, it's just going to make your heat source cycle and use more energy anyway. Zones add no value

Where is your boiler controller is it the sitting room?

So assume about 188m² (can't be arsed converting ft²) so 5kW sounds high. Would have expected 3 to 4kW. You can go grant, but by the time you're adding the MCS markup you will paying out as well. PV just couple to a 2x mppt string inverter. At a later date this could have an AC coupled battery added without touching much on the solar side. Or hybrid would replace the inverter. A 6kW Hiaer heat pump is £2100 including vat and you need to add a wiring center and controller for £550 Inc vat. It will modulate down to 1.6kW. (the 4kW down to just under 1kW) Sling in a direct UVC and run DHW from immersion (off peak), heat to 60 degs and install a smaller cylinder. Run UFH and radiators at same temperature, all one zone. Simple install, minimum materials, cheapest to run. Makes wonder - I would just ignore him and don't get him anywhere near your install. Don't bother with the grant, not worth the hassle and fighting over someone saying you need a 10 to 12kW ASHP.