Posted by: @agentgeorge

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Question to the Forum:           Do we believe 8pus that there’s no requirement for 1 radiator to be always open as was the regs for a Gas Boiler system?

Heat pumps should always be run with most (preferably all) of the system open.  Shutting down 10-20% is unlikely to be a problem, shutting down more is likely to cause a problem, depending on the specifics of your house.

I set the cosy 9 to 70C fixed flow today and let it have at it.

Super interesting, when it reached 60C flow it began widening dT instead of flow temp.

Posted by: @swwils

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Super interesting, when it reached 60C flow it began widening dT instead of flow temp

I'm not so sure this is a great surprise, there is not much it can do about DT unless it can ramp up the water pump speed, which at some point it will be unable to do even if it tries!   Perhaps more interesting is that it manages to manages to maintain 70C ft, suggesting a fair margin in capacity.

@jamespa it seems to run at max 27L/min until 45C and then ramps down to 14L/min at 60C then stays there at 60C 14L/min.

I was absolutely cooking so I'm sure maybe my TRV had closed I couldn't emit 10kW possibly.

Posted by: @swwils

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@jamespa it seems to run at max 27L/min until 45C and then ramps down to 14L/min at 60C then stays there at 60C 14L/min.

I was absolutely cooking so I'm sure maybe my TRV had closed I couldn't emit 10kW possibly.

Curious that it reduces the flow rate at higher flow temp.  I wonder what the logic is of that?  If it were looking to maintain a specific DT then it would need to increase it.  Perhaps its trying to ensure that the return temp isn't too high for some reason?  Reverse engineering control systems for heat pumps (and many other things including doubtless boilers) can be fascinating!

@jamespa https://emoncms.org/app/view?name=Cosy+9&readkey=9c733f17f0fd7a3816ec0db72d96e857&mode=power&start=1764066130&end=1764069780&flow=1

Run starts at 11.

It didn't do a defrost the blip in the middle is me canceling a HW call.

@andrewj the Cosy6 cycles on and off like a gas boiler, I don't think it can be set to run low and slow unless you force it by deliberately retarding your radiators so they cannot under any situation reach a temperature too hot for you in that room.  Then I think it would run much longer.  You would have to spend much time adjusting the warm/cold points of WC curve too.

I don't think Octopus really do radiator balancing, they didn't balance mine - they fit TRV and you use them.  It's a different design model to "heat geek" 'esq systems.

wreckguru

Posted by: @swwils

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@agentgeorge I don't need too because I sniff the modbus

can you share how, even in private message?

Posted by: @wreckguru

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@andrewj the Cosy6 cycles on and off like a gas boiler, I don't think it can be set to run low and slow unless you force it by deliberately retarding your radiators so they cannot under any situation reach a temperature too hot for you in that room.  Then I think it would run much longer.  You would have to spend much time adjusting the warm/cold points of WC curve too.

I don't think Octopus really do radiator balancing, they didn't balance mine - they fit TRV and you use them.  It's a different design model to "heat geek" 'esq systems.

wreckguru

They certainly commission their Cosys to work like that and I suspect they do it because everyone will understand that operating model.  It also uses WC to modify the flow temps so ultimately, its default commissioning is like a condensing boiler with a WC control module fitted.  I further suspect that they do this because they design to the MCS guidelines for room temps rather than a consistent temp across the house.  The problem with this is that heat is only generated when the Primary Pod calls for it which means the whole house is heated based on the heat loss of the area that the PP is located.  Again, for most people who are used to a gas boiler and found that comfortable enough that probably isn't much of a concern - indeed, I expect it probably runs longer once at temp than a gas boiler so may actually feel more comfortable.  In terms of efficiency, there's probably not a lot in it in terms of this operating approach vs a WC/FT only approach.  Whether it is as comfortable is debatable.

I have found, in my house that it doesn't work very well.  When I had a gas boiler there was nowhere that the thermostat could go that wouldn't cause inconsistent heating and cool rooms because of the way the house heated and cooled.  In fact, I ended up getting a smart TRV for the bedroom so it could call for heat later in the evening because the house would just cool down given 2 people's presence in the same room as the thermostat.  You may say, "put it in a different room" but there isn't one - all other rooms would stay warmer once at temp and our main living area would become too cool.  This was the primary reason to move to a heat pump based system.

I have it running on WC/FT right now, but I need to get some further adjustments to the WC curve which I can't do given the defaults set in the Octopus App.  I'm hoping that an engineer visiting tomorrow can sort that.  In warmer temps (say, >4c) it's fine but as it gets colder than that the house starts to heat up so I end up with rooms around 23c.

With UFH downstairs, I couldn’t let my Cosy6 go for it at 70C.

I have adjusted the settings over the past 12 months, chose different positions for the Cosy Pod and determined best place for my system is middle of the lounge/kitchen area.

I regularly check the flow temperature to my UFH manifold and have seen it peak at 37C, this is reasonable as I have the UFH open loop, no blend valve and flow rate 0.5-1.5l/m depending on room size.

8pus designed my system for bedroom RT of 19C and it achieves that, mostly, I had to swap a rad between 2 rooms as I found they named the rooms wrong. Bedroom 1 and Bedroom 2 got swapped between survey and fitting planning. I tried to point that out but they said it had to be installed to plan for MCS approval. I also changed the radiator in the “office 21C” for one that’s “bedroom 19C” compliant. I had a home office for many years but since being retarded it’s a “hobby room” now.

The engineer visited this morning and checked everything over.  He agrees that everywhere is too warm but he cannot drop the Cold Water Flow Temperature min value below 50c as the system doesn't allow it.  He's going to refer it back to a Technical Support Engineer to get involved to determine what needs to be done.

Today, with it being so warm, the flow temps are obviously a bit lower and that has brought the upstairs room temps to below 23c (just!) and downstairs closer to 22c, with the living area at around 21.8c to 21.9c.  It feels like my Warm Weather Flow Temp value of 32c is right, or close enough.  COP is 4.71 so far.

Yesterday, with it being very cold for the first part of the day, temps everywhere in the house were hot.  Upstairs was pretty much all over 23c with some rooms at 24c; downstairs rooms were getting close to 23c.  There was an obvious drop in Input power of 66% with an OAT change from 1.5c to 3.2c.  This helped drag the COP up to 3.38 for the whole day.  During the early hours of yesterday the input power is mostly indistinguishable between hot water heating and house heating.

So now I have to wait for the next engineer to get involved.  I guess the one positive is that the house is too warm rather than too cold.

Posted by: @andrewj

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 He agrees that everywhere is too warm but he cannot drop the Cold Water Flow Temperature min value below 50c as the system doesn't allow it.  He's going to refer it back to a Technical Support Engineer to get involved to determine what needs to be done.

Now that really is nuts.  Hopefully tech support dont suggest to downsize the radiators!