JohnMo

You have a start and stop hysterisis for the compressor. So for a target of 25, the return flow will drop by a predetermined amount below the target flow temp, once at that point compressor starts. It will run until the shut off hysterisis temp is reached. How long it runs depends on system volume, heat demand and how deep the heat pump modulates. My settings are based on my system and what it does and doesn't do. Mine at a target flow of 25, start up hysterisis is 5.1, so return temp is allowed to fall to 19.9, before compressor start. Cut off hysterisis is 2.3 so cuts off at 27.3. My total hysterisis is 7.4. All this changes with different heating systems and houses. Mine is 300mm spacing UFH in 100mm concrete screed. Heat pump is a Maxa i32V5. Today excluding DHW the compressor has started 5x times up to 10pm, shortest run time was 18 mins (9 degs OAT) and longest run 2.5 hrs (5 Deg OAT). WC is all about running just enough to top up the energy in the house, so I use the hysterisis and a WC curve to play with the floor heat output. Based on the floor average temperature, to get the correct heat output. The WC curve starts at 15 Deg OAT at 25, this gives a floor minimum temperature of 19.9 (don't want the heating on really at that temperature), at -9 the WC curve stops at 30.3, so floor temp is a minimum of 25.2 (not tested this temp yet). So far this is working fine down to +3 degs. Depending on actual run times at sub zero this will affect where WC stops and at what flow temp. But once set it's set for ever.

Think I saw all the various wiring schemes on the Homely website

Cascade is a system configuration used by people like Fresh-R also a configuration used by Brink. Just as effective as normal MVHR, infact most MVHR is using cascade to a lesser extent. For example lounge is supplied with air, air then moves though the hall and is extracted in the kitchen, the hall is ventilated via cascade.

No more Q's You need to have think about how you actually operate the system. Timed heating slots will drive up your heating cost most likely as the heating system has to run hotter than ideal to play catch-up. more further down I would suspect you have two control methods in each room - a radiator thermostatic valve, so this controls the radiator output based on room temp, plus what sounds like a room thermostat that possibly calls for heat from the heat pump. Your UFH will also be calling for heat randomly, so the whole system is likely to run rubbish and cost huge amounts to run. My advise Bedroom wall thermostats set very high so they are unlikely to stop calling for heat. Set radiator valves fully open for now. Set all UFH thermostats high, so they always call for heat. Remove all timers and set to run 24/7 Now you need to get access to your heat loss calculations and the weather compensation setting in you controller. Read your manual At the warm weather end of the WC curve, set to 25 deg flow at 20 degs outside, the cold end set per your heat loss calculations, so design outside temp to max flow temp. If you have predefined curves to select check and adjust as required. Now you need to adjust the WC curves to get the lowest flow temp and a stable comfortable house temp. Now adjust your bedroom radiator valves to get a comfortable bedroom temp. This will take a few days at least. You are now at the cheapest running mode, then adjust slightly to get the comforts you need. Never switch off, just have small 1 to 2 deg setbacks.

MVHR and dMVHR does not need trickle vents. You have to have dMVHR in every room, for it to be sound ventilation strategy, so stupid expensive and you have to meet the minimum whole house flow rates. Have to you considered cascade MVHR instead? Or proper MVHR with coanda effect terminals, or a combination of the two to limit ducts?

Interesting thought, but not sure I agree, many ASHP don't have that functional control. We are currently putting in less than an average of 1kW into the house with a 6kW heat pump, so well below any modulation, controlled on hysteresis and pure WC. House fluctuating a massive +/-0.25 degs and daily CoP generally around 5 for heating, as I get thing optimised. Generally cycling is good, its an easy way to control capacity, when below min modulation. The only caveat the run time needs to be long enough to do some useful heating, this varies with different systems, this is easy to tweak with hysteresis.

Tell us more about the system. UFH do have lots of thermostats (so plenty of zone on that also) Do you have a buffer? Do you run weather compensation? I suspect you are running the system similar to a gas boiler, as in timed running slots for heating?

Change the solar fixings to ballast trays or ballast system for different angles, so no roof welding needed?

Big question - do you need the Energy Integral? Does add to system efficiency or house comfort? Suspect the answer is maybe or sometimes. But generally a good marketing tool, has kept this thread talking about it for a few years.

I would and try and log electric data and actually work out costs, then switch off in the expensive period and again work out costs and compare. You may see very little difference most of the year, you may see a big difference depending on your house.

Yes it would. WC really doesn't need anything in the house except a balanced heating system. That's the thing with weather comp, it doesn't need any more info, just outside temp to set target flow temperature against the defined curve. In fact all the boiler is interested in target flow temperature and return temperature. It then modulates output based on management of dT, it doesn't even even care about flow rate unless it actually modulates flow rate.

Isn't that just 4pm to 7pm, so only 3hrs, not 16hrs you have programmed to be off?

I would strongly suspect a lot of your issues are related to setup and operating. Rather than anything else. Would bet your immersions are doing a lot of the work instead of the ASHP. Tell us more on your set up and how you operate it? Weather compensation continuously, thermostat(s) and set temperature, on and off via a timer. UFH, radiators or a mix, buffer or no buffer etc etc Doing a hybrid set up is pretty straightforward. Radiators in front of the ASHP, sound like a lot of energy in (gas or oil) and not a lot of gain in heating energy.

Or leave them as a placebo devise, just don't have them connected to anything functional.

Was saying this instant, I was implying when it is working.

Or just delete them. Just run WC. Put normal TRVs in bedrooms. If you have radiators randomly switch on and off you just end up short cycling the boiler and undo any savings made.

Even though the times are set, is there a thermostat overriding, so during the none heat periods if a thermostat still believes its not warm enough is it still making the system run? The other issue you will have on cosy, with a heat pump sized to match your house heat demand, is the heat pump cannot deliver 24 hrs of heat in 8 hrs. So if you have a heat demand of 5kW (so 5 x 24 hrs is 120kWh required in 24hrs), you need a 15kW ASHP (so 15 x 8hrs is 120kWh) for Cosy to work at design temp. Or have a battery to allow the heat pump to run during expensive times.

WC normally has the circulation pump pump running 24/7. Room stats are also either deleted or set a few degrees warmer than room target. Maybe the circulation temp is above the set point controller hysterisis. That's the thing with WC, it's not always heating, mine spends most it's time just circulating. Add heat for 20 to 40 mins takes a few hrs off. As the day gets warmer the set point for the water lowers so the boiler or heat pump doesn't need to add heat. If in doubt switch off for a few minutes and switch back on. Sometimes lots of setting changes just confuse the controller and it's needs a reset.

I would airtight layer under ceiling joists, counter batten to form service cavity all wiring in service cavity, down lights in plasterboard. 50mm cavity will leave room for led transformer also. Plan to have no wires in the loft. Not ugly, airtight and insulated ones are also available. Can you do it so the plenum for each room penetrates as easier to seal-up. Tyvek Supro BBA certificate mentions a drying out procedure to be followed during first heating season. So perhaps dig that out also.

Just what we did, vaulted everywhere except one area, that became plant room come store room. Big loft hatch with integral ladder.

The other way and in my option better, is make the loft space warm. Insulation is then done at roof level.

Flooring manufacturer instructions normally give explicit instructions. Ours had to be glued down on top of UFH. Doesn't mean yours will. If in doubt ask the supplier.

The window really needs to straddle the insulation Some notes on here https://nhbc-standards.co.uk/6-superstructure-excluding-roofs/6-7-doors-windows-and-glazing/6-7-3-in-service-performance/#:~:text=In cavity masonry walls%2C doors,layer of the external wall.

I would consider EPS beads, they will self drain any water away and gravity will fill any voids fully.

What's going inside the house or within cavity with respect insulation? Ideally the window should straddle the insulation