Posted by: @andrewj

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@kevh It's something I'm trialling at the moment - I've set the Cold Weather Max Flow temp to 50c at -10c and left the Warm Weather Flow Temp at 36c.  You can adjust the warm weather end below 35c, it has the effect of steepening the curve but the 35c minimum modulation (of the Cosy 9, don't know about Cosy 6) cuts in at a lower temp.  The attached image is my attempt to map the WC curve from -10c to +12c at different settings.  It's probably mostly right as the curve is linear.  I was advised not to drop the warm weather end below 36c but it's not really clear to me what actually happens to the Cosy if you do so and I don't have a means to measure data points not shown in the app, which is extremely limited.

I have plotted myself that exact same chart, and have assumed that the FT levels off beyond the set points, which I think personally is a weakness in the design.  So I too have been running with the FTs set at 50c and 36c, cold and warm respectively.  This heats the house adequately however the effect is to run like a boiler, off and on.  

I am intrigued by your decision to position the primary pod in your coldest room. Mine is in the room that we spend most time in (it's where the boiler thermostat was). I can't quite get my head around the consequences of putting the primary pod in the coolest room, and as my coolest space is a large extension off the kitchen with no way of segregating the two, and with a design target temp of just 16c, I am not sure how this might play out.  

There are just too many variables to consider, it seems.

Thanks for your ongoing reports of your progress with Octopus, it all serves to inform. 

Posted by: @andrewj

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@harrisonc I've not seen that, it's not coming up on my feed.  

I definitely think you want to be careful playing around with the interface areas that you aren't supposed to be in! It's interesting to see data or control points though.

 

 

Bearing in mind that Octopus can apparently monitor our every move in regards to the hub, I would be concerned about invalidating the warranty.

Posted by: @kevh

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I have plotted myself that exact same chart, and have assumed that the FT levels off beyond the set points, which I think personally is a weakness in the design.  So I too have been running with the FTs set at 50c and 36c, cold and warm respectively.  This heats the house adequately however the effect is to run like a boiler, off and on.  

I am intrigued by your decision to position the primary pod in your coldest room. Mine is in the room that we spend most time in (it's where the boiler thermostat was). I can't quite get my head around the consequences of putting the primary pod in the coolest room, and as my coolest space is a large extension off the kitchen with no way of segregating the two, and with a design target temp of just 16c, I am not sure how this might play out.  

There are just too many variables to consider, it seems.

Thanks for your ongoing reports of your progress with Octopus, it all serves to inform. 

The FT levels off at either the set point OR the minimum flow temp it can reach, so once the FT is 35c for the Cosy 9, it levels off irrespective of the set point.

The heat pump is running on/off like a boiler because you have a Target Temp it can reach: if you set it beyond that, e.g. 30c, you will find it stays on and runs like you would expect a heat pump to do.  What happens in this scenario will depend on the flow temp vs radiator sizing vs heat loss of the rooms and I don’t know how efficiency is affected because it won’t use the pods as modulation sensors.  If the radiators have been well sized, you will find that the rooms maintain a stable room temp that you want and tweaking the Flow Temp can help you achieve that and fine tune it.  However, Octopus set the lock shield valves so that each radiator puts out the same heat, at least in theory, so you may find that some rooms overheat or underheat.  All you can do here is tweak LSVs to temp match rooms or tweak the FT.  You can see that I had problems overheating and a re-survey has decided that the original heat loss was over specified by 1kWh and all the radiators are oversized, hence the adjustment of the 50c set point from -3.4c to -10c.  There are 2 radiators that are undersized and I’m hoping to get these changed, although the surveyor thought these were sized correctly!

The Primary Pod is in the coolest room with a target temp of 19c because this keeps rooms in the rest of the house at around 22c - 23c and we find that comfortable.  This is because, despite the surveyor’s view, the radiator is undersized.  It is running on/off but isn’t influenced by humans or electronics in the room.  With it placed in the living area or hallway, the difference in heat loss across the room or influence from body heat just threw out the comfort of the house.  For example, in the living room it would heat to 22c quite happily, but with the wife and I in there in the evening the temp would rise to 22.5c or so and thus heating would not come on until we went to bed.

I’m still working with Octopus on resolving the problem so don’t want to make too many changes without referring back to them but I feel we’re honing in on the right settings.  At that point I may well try running on just flow temps to try and keep it ticking over.  We are due cold weather for a few days from Christmas Eve so that will be a good test of how well the FT is set.

@andrewj they will release smarter controls, its been mentioned lots of times now.

@andrewj Many thanks for taking the time to explain, it is much appreciated.

I am learning so much through following your postings and your exchanges with @jamespa.

i now get your point about positioning the primary pod in a cool room. 😀 
i also get the principle of hiking up the target temp on that pod and moderating the room temperatures by reducing flow temps and use of lock valves.

My stumbling block is that my upstairs rads are barely open (using the lock valves) to balance the rads overall, and I am running a WCC of 35:50, so I am not sure how I can boost the target temp with so little room to adjust the FT or rads. 
Having said that, the house is cosy when operating the primary pod as a switch. 
Maybe I should just accept that I can't have my cake and eat it? 😜 

Merry Christmas everyone.

@kevh Thanks for the season’s greetings which are reciprocated. Regarding the upstairs radiators and the fact that the LSV’s are only a nadgers (technical term y’know😉) off the completely closed position, if you have decorator’s caps hanging around, you could try judicious extra control by partially closing the valves to further restrict the flow. I should add I have not ever tried this but would have thought that this method would give you further trimming control of an over-eager heater rad! Toodles.

@kevh it's worth remembering that many lsvs only actually control the flow in the last half or quarter turn, so they may seem 'completely turned down' but actually they aren't.  As @toodles says you may get better control using decorators caps on the trvs (first removing the heads).  These are typically much more linear.

Heat geek did a video about 'valve authority' which explored how good or bad (mostly bad) lsvs are.

Merry Christmas!

@toodles Thanks for your advice.  I am down to a quarter turn open on the three LSVs on the three upstairs rads, so maybe there is a little (a smidgeon, a tad, a whisper) more to play with?  I'll give it a go.

@jamespa Thanks for this...do you mean take the control knobs off the TRVs and replace with a decorators cap?  In addition to virtually locking down the LSVs?

@kevh Yes, I reckon a millinadger is just a few degrees so you have some scope remaining…. Toodles.

@kevh The body of the valve remains - what you remove is the screw-on top that contains the thermostatic mechanism. All the TRV does is push the pin of the valve itself down in stages into the valve body as the temperature rises. When you remove the ‘top’, you leave the valve mechanism in place and can then use the decorator’s cap to push the pin down gradually - once you reach the degree of restriction required, you stop screwing the cap down any further. Regards, Toodles.

Posted by: @kevh

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@jamespa Thanks for this...do you mean take the control knobs off the TRVs and replace with a decorators cap?  In addition to virtually locking down the LSVs?

Yes.

In addition or instead.  The point us that trv bodies with decorations caps offer an alternative (or additional) and more linear adjustment mechanism.