JohnMo

Another option could be a Tesla Powerwall3, keeping the 3 theme. This should take all you pv directly

Every other house we have owned, except this one, the bedroom window has remained open all year (except a couple of very cold nights) and radiators switched off. That includes a very old poorly insulated, and brand new at the time houses. So how do you keep rooms at different temperatures Current house everything is on one floor, bedrooms are generally cooler/colder, we do this by putting less heat into those rooms and closing the room door. If we want the room the same temp as the rest of the house we open the door for 30 minutes. And we still have everything on single zone. You make any room, any temperature you want, with flow balancing. More flow, smaller deltaT across the emitter equals higher output.

Bit of a long post, but I would say there are two things that don't hang together. One weather compensation and having radiators opening and shutting. When running WC the flow temp is matched to the heat loss, so what energy flows into the radiator is equal to that lost by the room. So a room takes an age to change temp. You seem to want to hang on to a gas boiler operating regime, which is high flow temps and very immediate, but install a heat pump which is the polar opposite. Embrace simple, limited controls, very long run times. Really don't understand the Cosy tariff and how it helps a heat pump.

I say dump 3 phase, for the solar, do it all single phase, go G99, to see what they allow you to export if that's what you want. Or, slightly less efficient each array its own inverter, then something like a Givenergy All in one, all you pv is connected in to a gateway, the mains goes into the same gateway, as does car charger and battery. Full house power in a blackout (6kW, with 10 seconds at 7.5kW), PV stays online also. The installer can limit output to grid from 0 to 6kW.

We started with 6 zones, first years heating bill was huge, boiler just couldn't cope when only one or two zones calling for heat. Ended up adding a huge buffer. Then a light bulb moment, made the whole lot a single zone. This year ASHP, one zone, no actuators on manifold, no mixer or pump on manifold. Thermostat gives a direct start permissive to ASHP. Set up for cooling and heating. Cooling this summer no issue long run times, most or all electric from PV, CoP (or SEER), during cooling between 6 or 7. Not as effective as A2A, but good enough.

They are pressure treated. They guy that did the work said he did one 20 years ago and it's still ok. The odd post has been replaced. But on our side the bank is free draining sand, so water doesn't sit for long if at all, with a layer of top soil on the top.

During construction

We used wood strangers, basically 240mm dia by 4m long wooden posts. Dig trench circa 1.5m deep, concrete in posts.

It's linked to my Givenergy App for the battery. You do national average or by post code.

Good old - moth balls.

Plenty of time limits in the scheme. The grant is supposed to be applied for prior to install, all prices are supposed to go to you with the grant money removed by the the installer. There are plenty time limits imposed. Something doesn't smell right Have read https://www.ofgem.gov.uk/environmental-and-social-schemes/boiler-upgrade-scheme-bus/property-owners

OP base case was gas system boiler and cylinder (although stated on another thread). Granted the cost of a combi install would be cheaper. But it's a huge house, not sure a combi would be the best fit. So would be having a cylinder either way anyway

As a new build does even need the as built SAP and air test? Can't he just use the pre build sap report?

Same is true for a lot of heat pump installs they are not 400% efficient, but get rid of zones, run on weather compensation, no reason they shouldn't run at over 100% efficiency for gas and 400%+ for a heat pump.

Current energy mix for my post code A modern A-rated gas boiler will emit 215 grams of CO2 per kWh of heat delivered. So on face values pretty similar, except the SCoP of a heat pump should be over 4, so CO2 emmisions a 1/4 of gas.

Which are you saying is cheaper gas or ASHP? I have two years heating data on gas, will have an ASHP running this winter. So can tell you the real world comparison. What you can't do with gas is use off peak energy. Now I have a battery, time of use tariff or even E7 make sense. You can batch charge the floor most of the heating season in the 7 hours, you take a slight hit in CoP, but the electric is half price and you only need to run the heat pump for 7 hours.

I am at 300mm, but I am a brave (or foolish). You need good floor installation for that wide and low overall heat loss. Generally 200mm would be fine, but really depends on your heat loss figures. You don't want to be flowing more than 35 deg on the very coldest day (for me that's -9).

Start with heat loss calculation, that will give you your ball park ASHP size. Number and bathrooms will determine the cylinder size. Once you know the cylinder size and heat loss, the rest will fall into place. But really you are comparing the actual cost of an ASHP and comparing to a boiler. Just every bit of plumbing will be the same, either way.

UFH could take several hours to get a meaningful room temp change. So dream on if you think UFH is an on or off magic button. If you want that, you need high temp radiators, but not sure current building regs allow that, as everything is supposed to heat pump ready. Even with a gas boiler to get good efficiency you need low flow temperatures. I got a completion certificate in March, had used the gas boiler for two heating seasons, have just installed an ASHP, mostly for cooling, but the heating should be cheaper also than gas. Cylinder prices are about the same for gas or heat pump, plumbing about the same, good boiler that does weather compensation and ASHP are about the same cost.

Exactly what I would say also. But do you really need UFH upstairs? Wet rooms yes, bedrooms? UFH is very slow by nature to heat up and cool down, when most likely you need a blast of heat first thing and just prior to bedtime. Once in bed you want it cool down for sleeping. UFH will keep pumping out the heat for hours. Most well insulated houses with an upstairs will just take the heat, that is rising from downstairs. I would, UFH downstairs and upstairs wet rooms only, electric panel heater with timer and thermostat, just in case you need it, in bedrooms. Also electric towel rads in bathrooms. UFH - Run the whole lot on a single zone, no actuators, thermostat to give boiler or really assume ASHP the start/stop permissive, run the whole lot from the ASHP circulation pump. Comments on ground floor plan Hall and cloakroom delete those loops. Your hall already has loads of pipes going through it, spread them across the floor and borrow their heat. Cloak and utility do as a single loop, flow through cloak then to utility.

The one I'm thinking about is a monobloc, with two additional connections for refrigerant. https://www.appliancesdirect.co.uk/bct/heating/monobloc-heat-pumps You need to go into the installer instructions to find the detail, you also need to use their cylinder.

There's an Italian ASHP A2W that can do cooling and hot water heating at the same time. The cylinder has an additional coil for refrigerant, the refrigerant is diverted to cylinder during cooling mode.

I would say if the pipe is at the bottom of concrete, compared to middle the heat would be felt at the surface quicker if mounted in the middle. The logic is the heat radiates from the pipe, almost evenly (almost as it will always prefer to travel towards the lowest temperature). The heat as it spreads would have lost some heat to concrete each mm it moves from the heat source, the further way from the heat the more time it takes to get to the surface. However saying all the above, thick screed requires long slow heating regime, either 24/7 or use as a storage heater over 7 plus hours. Hoping to put on the heating when you get home or an hour or so before you get home will lead to a cold house. Thick screeds make a simple heating system, one thermostat for the whole house, no need for so called smart controls, run on weather compensation or a modified curve to allow storage heating over 7 hours. It actually 50mm from the surface and bottom of concrete, minimum, to prevent corrosion, not really much to do with reinforcement properties.

You either need to tell UFH it's in cooling mode, or turn the thermostat up to full so the the actuators open. Not sure cooling and radiators works.

I am not sure, it seems to move about from minute to minute sometimes importing others exporting. Not sure if some is to with the conversation from AC to DC and back to AC converter losses. Rather than real export. Or if it's using the grid as small resource to make up for an ever moving PV supply power and the variable of house demand.