Posted by: @andrewj

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If the hardware limits what can be done then I don't see what an advanced controls mode could actually do.  Currently, it is possible to run as "always on" but only if the necessary flow temperature WC curve lies within the technical limits of the unit.  Do you have any thoughts on what might be possible?

Personally I think its most unlikely that the hardware is technically incapable of operating at a flow temperature <35.  If that is the case then it is pretty nearly unique or certainly very rare.  They may have designed their own compressor (which would be a likely limiting component), but with a wide variety easily available from Chinese factories, I doubt it. 

There are however multiple reasons why they may have imposed the limit in firmware which is what I strongly suspect they have done.  Of course I could be wrong and we may never find out.

I’m betting heavy on that 35C floor being a firmware cap rather than some exotic hardware quirk. It’s pretty standard for manufacturers to slap software limits on these units to play it safe, avoiding things like excessive cycling, oil migration issues in the compressor or just to keep warranty claims down when folks crank settings too low without proper system matching.

On the compressor front, it’s wildly unlikely they’d roll their own when off-the-shelf Chinese units dominate the market. GMCC (Midea’s arm) cranks out millions of rotary compressors annually and they’re in everything from budget UK installs to big-name rebrands. These things are specced for wide ranges… many can condense at temps well below 35C without breaking a sweat, especially inverter-driven models that modulate speed to match load. The real bottleneck isn’t the hardware, it’s system design.

As for advanced controls unlocking more? Imagine firmware hacks or third-party controllers that let you override the min flow temp, maybe down to 25-30C for super-efficient runs in mild weather. But it’d require experimenting with weather comp curves to avoid short-cycling hell.

We might never get the full scoop unless someone reverse-engineers the firmware, but if it’s like most ASHPs, that limit’s there to idiot-proof the system for average installs (and incompetent installers).

@andrewj your right, the loft insulation will keep more heat in the bedrooms, its one of the areas Octopus and me disagreed on. I have kingspan in the loft as I dont want to reboard the loft with legs to allow 300 of rockwool.

ive also removed the downstairs ceiling and im about to refit a new one with rockwool insulation in the ceiling, exactly as you stated to prevent heat from downstairs affecting the heat balancing ive done in the bedrooms.

you dont need to redecorate if you down rate a radiator of the same physical size from 22 to 21 or 11. I did exactly that in one bedroom that was overheating, changed from a 2-2 to a 2-1

In the other bedroom that I have elderly visitors who like more heat, have upsized the 2-1 to a 2-2 version.

@agentgeorge 

it might be of interest I did our vaulted ceiling with 135mm PIR board and a skim and it changed an almost unbeatable room into a sauna. We used to have about 90 mm of wool between the rafters and it seemed to do very little. 

@jamespa Its an emerson copeland, at least what I saw when they installed mine.

Apparently the API can set a static flow lower than the app can, but I haven't tried it yet since mine cycled below 35c anyway, it demolished the COP so was likely doing some protective pauses. I believe generally a HP has to absolutely make sure no liquid refrigerant returns to the compressor, or it will dilute the oil and wreck it. At the same time there will be some maximum recommended starts per hour, to let the unit get the oil return from the sump which is lost during compressor start-ups. I would assume there is no minimum off time because the compressor starts unloaded AFAIK.

I'm hopeful that they will actually be able to nail it, I think they have what they need. In terms of raw, cold weather performance ive been very impressed. (other than the noise), which they could sort with some EPP parts (like loads of other makes) rather than a big monolithic plastic case. If they end up doing this YOU SAW IT HERE FIRST! 🤣 Loads of HVAC stuff using it now: e.g.

@papahuhu thanks for the info, not sure Id want a sauna, Im aiming for a nice background heat from UFH and no draughts. I’m walling in the stairs and fitting a door to isolate the downstairs from upstairs so can control the 2 heating zones independently.

i have kingspan in the eaves aswell to keep the loft area warmer than the outside and reduce draughts.

I also have fire rated down lighters that are fully sealed to the ceiling so you don't get that annoying cold trickle of air from them

@agentgeorge isn’t the idea that about 70% of the heat for the upper floors comes from the lower floor. We did the opposite, changed 3 zone GCH back into one when we added the heat pump and just keep everything open. It seems to help even out any small differences. After a modbus comms niggle was resolved thanks to some help on this forum it now keeps very low flow temps and remarkably good efficiency.

Posted by: @agentgeorge

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The flow temp of my system is set at 36C on the Cosy Hub, the temp gauges on my UFH manifold show a flow of 37C and return of 27C, effective DT10 this gives a comfortable room temperature of 21C thru the downstairs. Upstairs is still radiators all but bathroom have TRV and each room is set at 18 or 19C by adjusting the TRV 1/2 a point until the room doesn't overheat. The bathroom has a towel rail that is adjusted with dual lock valves to give a quiet flow and temp of 21C.

it has taken all year with the system to gradually adjust it for both comfort and peak efficiency; I am now regularly getting a COP 4.5, only in the cold winter months with -6C days being the worst with a COP 3.6

Out of interest, are you running at a set temp of 36c?  Or a minimum temp of 36c at the warm weather end of the WC?  

@kevh 

The App says it choses the top temperature when OAT is above 12C, my system is running at 36C today and its 6.8C according to Cosy HP. Logic would suggest its using the higher temp, but its not.

anyone got an idea how WC is being implemented by Cosy6?

Posted by: @agentgeorge

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The App says it choses the top temperature when OAT is above 12C, my system is running at 36C today and its 6.8C according to Cosy HP. Logic would suggest its using the higher temp, but its not.

anyone got an idea how WC is being implemented by Cosy6?

I had assumed that you were running at a set temp, so That doesn't make sense to me.  My WC is set at 36 / 50 and my rads are definitely warmer today compared with yesterday,  indicating a higher FT and reflecting the cooler OAT today (Staffordshire).

@kevh todays COP is 4.02 (0.5-6.8C), 2 days ago was 4.50 (5.5-8C)

The lower overnight temperature has affected the performance, likely more defrost cycles.

My rads don’t get noticeably warmer when the OAT is below 12C, certainly not 50C.

I have a thermocouple probe so will do some investigating of the flow temperatures