JohnMo

Well done

To put that into reality that is double a passivhaus. Really look at how they have accounted for ventilation heat losses. With MVHR ventilation heat loss drops from big to negligible. Another thing we are 192m² living space plus another 26m² in the insulated space. Our roof area is around 50% more than yours as is our floor area, as we are single storey and every room has vaulted ceilings. All of which (part of form factor) really add to our heat loss per m². We are nearer 13W per m². With a 12kW you may need a volumiser, depending on water volume. You can always get a volumiser with immersion that gives you another 3kW if you really need it. We have an oversized heat pump that doesn't modulate well. I can get acceptable SCoP from it, around 4, if it modulated better I would be getting closed to 5. So a 25% reduction in running costs. So sizing is important. Looking at heat pump monitor a 12kW appears to modulate down to about 4.5kW, cannot see any 16kW on there.

And should be scrapped as well as the wearers of the crown and all the hangers on. But that's a different conversation.

So if that's heated - have you accounted for the net input this provides to the building. If the space has insulated external walls, the heat in this area is added to the building internals.

So how are you heating all of that,is that included as well in heat pump sizing? Depending on how you have calculated ventilation losses there can be plenty of room for error both ways. Is your thermal bridging any worse than the glazing U value? If not impacts aren't much worse than the glazing? If the steel is insulated on the inside most likely not a huge issue.

Even at 490m² at -3 your figures sound high. You possibly have better U values to me, your form factor will definable better than ours. So unless one side of the house is all glass, 9kW maybe a little high. At around 200m² we are 3kW. So 2.5 x 3 is 7.5kW, nudging 8kW (including DHW) at -3. So if Panasonic do a 9kW, I would be looking at that with some wiggle room. The bigger you go the bigger the pipes, flow rates to accommodate etc. So definitely wouldn't be looking at 16kW. But you will build houses big - are you actually going to use all of it? If not why not 2x smaller heat pumps in cascade. Then you can modulate down to 2kW and all the way up to 12kW+ should you need it.

One good thing about plenty of wind power is it's CO2 free. Our current CO2 intensity

Should is very different to are. Some or a lot think, new party in parliament, everything will change tomorrow. That maybe due to the wind density in parts of Scotland being among the highest anywhere. So more bang for your buck. But they are better located offshore, can be bigger, nothing in the way to disrupt laminar air flow for best output. High voltage DC to allow transport of the electric with very little losses.

Just looking back at the original post on this thread the box shown is a combiner box, so takes two parallel strings and brings them into one. So you double the amps. So may not be suitable anyway. Your other question is are you have string fuses? If so have them in a DIN enclosure in loft or anywhere as an easy place to terminate the strings. Terminate the other side of fuse and take to the inverter.

ALL inverters need the AC disconnect, prior DC. Big bangs likely in full sun if you don't. Likely to need a new isolator switch if your lucky, if your not, big volt DC isn't good for ones health.

Details of some of the template sensors This is the import windows defined - have only use morning and afternoon slots binary_sensor: - name: hp_import_window state: > {{ now().hour in [4,5,6] or now().hour in [13,14,15] }} Predicted trigger state sensor: - name: hp_predicted_trigger state: > {% set p = states('sensor.lounge_predicted_temperature_in_1_hour') | float(99) %} {% set setp = 20 %} {% if (p < setp - 0.3) and (is_state('binary_sensor.hp_import_window', 'on')) %} on {% else %} off {% endif %}

So this is the small dash board on home assistant. I have a target temp set at 20 degC. The yaml code for the prediction automation, this just sends a notification to me if we are running to cool.in the house to see how it works. If connected to an output devise and house was likely to be too cold, ASHP would be started at a flow temp higher than the normal WC curve. alias: ASHP Batch Charge Based on Prediction and Slab Temp description: Batch-charge UFH during cheap windows using predicted + slab return history triggers: - at: "04:00:00" trigger: time - at: "13:00:00" trigger: time actions: - choose: - conditions: - condition: time after: "04:00:00" before: "07:00:00" - condition: or conditions: - condition: template value_template: | {{ predicted_min_4h < (setpoint - 0.35) }} - condition: template value_template: | {{ (return_now - return_min_4h) < -1.5 }} sequence: - action: notify.mobile_app_cph2449 data: message: "Batch heat started test " - delay: "03:00:00" - action: notify.mobile_app_cph2449 data: message: Batch charge finished test - conditions: - condition: time after: "13:00:00" before: "16:00:00" - condition: or conditions: - condition: template value_template: | {{ predicted_min_4h < (setpoint - 0.30) }} - condition: template value_template: | {{ (return_now - return_min_4h) < -1.5 }} sequence: - action: notify.mobile_app_cph2449 data: message: "Batch test " - delay: "03:00:00" - action: notify.mobile_app_cph2449 data: message: Batch charge finished test mode: single variables: setpoint: 20 predicted: "{{ states('sensor.lounge_predicted_temperature_in_1_hour') | float }}" predicted_min_4h: "{{ states('sensor.4h_min_predicted_lounge_temp') | float }}" return_now: "{{ states('sensor.emoncms_emoncms_org_heatmeter_returnt') | float }}" return_min_ 4h: "{{ states('sensor.4h_min_return_temp') | float }}"

Been playing with ChatGTP over the last few days, generally going down a rabbit hole. Was looking for a simple way to model Weather Compensation fine tuning and or boosting during low tariff periods. So generally ChatGTP was no help. Had a search for something unrelated on Google and came across this site https://www.diyenjoying.com/2025/04/11/harnessing-the-power-of-predictive-heating-revolutionizing-home-comfort-with-home-assistant-and-derivative-sensors/ And finally a very simple modelling tool became realistic. So using the data on site above to add a couple of helpers to home assistant (hardware is already there - temp sensor). Then fine tuned for my UFH (thick screed etc). You now have a simple hourly and now 4 hourly look ahead at likely room or house temp if nothing changes. The author of that site used the information to start and stop heating, based on a generic thermostat, but taking account of floor inertia to not get swings in room temperature. So start boiler early and stop early, based on likely house temp - not actual house temp. But for weather compensation you just need a simple notification house temp is increasing or decreasing and you can simply adjust the curve. Add a bit of human looking at the day, it's stunning and room temp is increasing - no shocks don't do anything. But if it's dull outside you can decrease curve. So went back to ChatGTP for assistance. I have actually extended everything out to 4 hours to make it a little more meaningful for my house. There are few things this allows Intelligent fine tuning of WC curve. So you can see the likely house temp in 1 and 4 hrs and rate of change as a positive or negative. Options you could implement - you could run a cooler WC curve and boost during cheap periods. Could use it for batch charging alone, add some simple energy calculations based on you heating system store energy etc. Will add a few screenshots later

See this thread also Or have you just moved the problem for now?

Apart from the drawing being wrong - nothing much wrong. I would do - cold water main to PRV, then the check valve, (long bit), flexible, then the short bit. Not sure I would be filling the heating to 3 bar though. Mine currently sits at 0.5 bar.

Easy enough if you plan everything ahead, can get complex and expensive if you don't. Or I just paid someone else to do it, it was fine. Or Never been so knackered, everyone asks you a 101 questions every day. Or I'm broke, house isn't finished, can I have another pint, before I go back to do another 4 hrs, loads to do before the contractors get back tomorrow.

The manufacturers website doesn't even include that detail either.

Your system is reacting the same way as an oversized boiler. The reason it does that, is similar to a kettle, you put a cup of water in it it boils in seconds, fill it it takes an age to heat up. It sounds like you simply don't have enough water volume engaged. Then you have a mixer, this will always mix some of the return water with incoming water, and it doesn't make any different temperatures you set them at they always bypass some return water back to incoming water. If your loops are doing 3l/min, your flow through the Willis is nearer 2l/min. Which is a trickle. The other thing is target flow temp goes out the window with cycling as the target is based on average flow temp. Example, target of 30 degs, is fine if running heat input for hours at a time, but if you are cycling every couple of mins, it's more like 20 then 30, so now your average is nearer 25. So you have to set the target higher to compensate. I would do this first - keep all loops open or closed so run a single circuit. So one control thermostat connected to all loops. And - Crank up the loop flow rate to get more water moved about. Flow each loop at max flow, if making any noise trim them back a little. Then if it's still not ok Delete the mixer, add a pipe stat, for floor protection, to the hot pipe going into manifold. Then finally, add a buffer or volumiser to system.

I've bought DeWalt and Matika, 230V stuff, all good no issues. A Titan SDS from Screwfix, used it plenty further build, no issues.

That is a normal approach, cheap pipe stat.

Your best way to heat almost any house is low and slow, just keep the house heating ticking over. Heat one room, you are really trying to heat the whole house via one room. The external house walls leak heat more slowly than internal walls and doors. So you have one radiator on it runs balls out trying to make up for the heat slipping through the internal walls to adjacent rooms. By low and slow is more about room temps. The normal way is via short time slots, every time to switch heating on, you have to heat the building fabric, all the metal in the heating system etc, so you over compensate with higher room temps. As cold walls suck the heat from you, heavy radiator driven air currents drag cold air about etc. Leaving heating on for long periods with small nightly setbacks, allows the whole house temperature to stabilise, boiler moves to a more tick over mode than flat out for short periods. My sister did exactly the same as you are trying, I convinced to try longer run times with no zoning, the house became more comfortable, rooms that didn't heat well, all became comfortable, heating cost hardly changed.

You can easily heat individual room with enough zone valves or radiator valves. But you get to the point that boiler cannot turn down output far enough and you get short cycling - basically burning loads of gas for little gain. That just means remote access, so nothing smart just an on off device with internet access.

An ASHP feeding UFH will only add heat slowly as flow temp rise is capped by dT between flow and return. If I set mine to batch charge - 35 Deg target point, it will take several hours of full load run to get anywhere that target. So if you set timed windows of one hour for DHW, you will have zero issue, if the 3 port diverter failed. Only cold water coming out the tap.

Can't it - heat loss due to internal 'waterfalling' at pipe connections (tiny little thermal loops where warm water goes into pipe, cools and then falls back into tank, bringing more hot water into pipe). Sounds like a thermosyphon to me. Yes your pipe stays nice and warm at the expense of continuous heat loss, even with good insulation. How many if any seconds it saves you? Just had a shower secondary circulation off, cylinder 20m away from shower, in time it took to take clothes off, I walked straight into warm shower. I will keep the losses in check.

It's a lockable valve. A normal service valve or a motorised valve isn't. @Nickfromwales just beat me to it.