@jamespa sorry for the confusion. Simply. Battery was holding 16kW at 5:30 and at 7:30 it was showing 11.5kW. I can see the house load usage stated in kW: I've seen that move from 1.6kW to 3.2kW (mostly towards the latter) but this is clearly a point in time figure.
Currently, at 11:19, it is showing a load of 0.5kW on the house which is in line with normal background load so it would imply the Cosy is not running right now. I daresay it will start up again before too long and I'm glad I have solar as it does help a lot on these sunny days.
I have spoken to Octopus and it requires an engineer visit to enable a drop of the Cold Weather flow temp min below 50c. I've explained the whole situation to the After Care team and an engineer is going to visit next Thursday and hopefully I can have a more in-depth discussion with him/her. Given what I've documented so far, and not being an expert, is there anything specific I should be asking them?
I have also managed to get into the Cosy Controller which gives me some minimal info - other data requires an installer code which I don't have. The flow temps at 10:12 are shown in the image and are at a deltaT of 3.8c. Unfortunately After Care can't see the flow rate so I have to wait until next Thursday for the engineer to tell me.
I haven't screwed all the LSVs down - none are fully shut and two are fully open. I'm not going to make any more changes to the WC curve until I see the engineer as I don't see the point. I am going to have to use the TRVs on the Study and the Landing as I'm sitting here at 25.2c and sweltering! I'm also going to turn it down in the bedroom as 24+c is too hot. I presume that is unlikely to affect anything with 15 radiators in the house plus a volumiser but is there anything I should look out for?
I have spoken to Octopus and it requires an engineer visit to enable a drop of the Cold Weather flow temp min below 50c. I've explained the whole situation to the After Care team and an engineer is going to visit next Thursday and hopefully I can have a more in-depth discussion with him/her. Given what I've documented so far, and not being an expert, is there anything specific I should be asking them?
Well that sounds like a win, hopefully. Nothing else to ask I dont think (other than the installer password if there is one - which is probably the default and which they probably wont give you). you obviously understand the concepts, the problem is this pesky and wholly unnecessary limit.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
Often the default password is in the installation manual, which is on manualslib. Its unlikely to have been changed or personalised to the installer because other Octopus engineers will need to know it for servicing. If the default isnt stated in the manual its usually available somewhere on the internet!
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
Interesting temperatures this morning: this is what I'm concluding so please correct me if my thinking is wrong!
From a high of 23.5c at 11pm last night, the living room has dropped down to 22.0 at 9am this morning as the outside temperature warmed up - it's now 5.5c here. Other rooms downstairs followed suit, with the Study dropping to 22.6 from 23.5c (I have turned down the TRV in this room because it was constantly at 25c+) Upstairs is still over 23c apart from one room which has always been cooler than others and its radiator wasn't swapped out. Bathrooms are warmest at just over 24c.
If I had to make an interpretation, I'd say the Warm Weather flow temp point of 32c is having an effect here. In which case as it gets warmer still I'd expect the downstairs temps to drop; if they don't then I think it would be reasonable to assume that give or take a small tweak, this could be a good set point. On the 18th Nov we had OAT of 5c - 7.5c and temps slowly dropped by 0.5c over 9 hours at a flow temp point of 33c. In any case, the temperature is due to rise to 8c and remain at 6c/7c overnight so should be a good day for adjusting that end. I guess the only issue is the time it takes to take effect.
It thus seems reasonable to draw a conclusion that I need to drop the Cold Weather end below 50c (potentially with tweaks to the Warm Weather end) in order to stop the internal temps rising when the temperatures drop again. I'm not going to be in a position to do that until next week when I can hopefully persuade the engineer to alter the Cosy Controller settings.
Clearly with upstairs temps remaining high I may end up having to resort to some rooms remaining warm and using the TRVs on the 3 rooms regularly used to control the temperatures in them.
@andrewj Watching with interest. I think that your interpretation of your data makes sense, in that the cold weather end of the WC curve does appear to be too high for your heat loss.
I am interested in your thoughts that the warm end needs a further tweek (upwards?) and it will be good to know how that unfolds.
Looking back at your original postings in this thread, your goal seemed to be to achieve continuous running rather than cycling...how is that conundrum going I wonder?
Thanks for picking me up on my FR / FT faux pas recently, I did indeed mean FT, and yes, my guess at what the Cosy WC curve looks like is simply a linear relationship between one end and the other, much as your images show.
I do hope that you will share anything juicy that the Octo engineer tells you at the forthcoming visit, though if I am honest I imagine that permitting a lowering of the cold end set point below 50c would be admission of an overpowered HP install, ie of an error on their part.
Good luck and thanks for sharing your journey on here.
@andrewj Watching with interest. I think that your interpretation of your data makes sense, in that the cold weather end of the WC curve does appear to be too high for your heat loss.
I am interested in your thoughts that the warm end needs a further tweek (upwards?) and it will be good to know how that unfolds.
Looking back at your original postings in this thread, your goal seemed to be to achieve continuous running rather than cycling...how is that conundrum going I wonder?
Thanks for picking me up on my FR / FT faux pas recently, I did indeed mean FT, and yes, my guess at what the Cosy WC curve looks like is simply a linear relationship between one end and the other, much as your images show.
I do hope that you will share anything juicy that the Octo engineer tells you at the forthcoming visit, though if I am honest I imagine that permitting a lowering of the cold end set point below 50c would be admission of an overpowered HP install, ie of an error on their part.
Good luck and thanks for sharing your journey on here.
My intention is to move away from a thermostatically controlled system. The problem we have, and was the same with the gas boiler, is that with heat supply determined by a set temperature and hysteresis, it tends to go off when we are in the room with the thermostat because just two bodies can add an additional 500W - 600W. This means the rest of the house cools down. Unfortunately there isn't a good place to put the thermostat which prevents this: other locations just stay warm and the living room would then cool down below comfort. I had to install a Hive Smart TRV on the bedroom radiator so it could call for heat late evening. Can't use that as a solution now but if I can keep the heat ticking over then the problem goes away.
Today, the temperatures down stairs stayed pretty stable. The living area did drop to 21.7c around 6pm but is now back up to 22.5 because we're sitting in there (and there's been some cooking in the whole open plan area. So this is the tweaks I mentioned: it may need to move up from 32c to 32.5c or 33c but I shall leave alone for a couple of days to see how it goes. It's given me a COP of 4.26 today.
It definitely doesn't have a regular weather curve control algorithm. Unless you "force" it too by setting a room target very high.
@swwils I don't know what you mean or what I'm looking at, could you provide an explanation please? A few posts ago I asked you a couple of questions that I hoped your insight could help with if you could take a look please.
@andrewj Certainly mine cycles alot below 36C, it seems "happier" with the weather compensated minimum flow temperature at 36ºC or above. I think the really old manual also mentions this.
If you go back to generic basics, you must have correct pressure differential for as-designed compression, you need to avoid suction flooding, keep the inverter in its stable torque region. So if you go "too low" the pressure ratio becomes too small, and the compressor is basically pumping nothing.
Looking at some of my data, the pump really wants to maintain a set ΔT, so as you drop the minimum LWT really low the return water might only be 1–3 °C lower and destroy your COP.
At mild outdoor temps, your house may need <2 kW. So for my 9, the system must cycle and minimum flow temperature being too low makes it worse, because the compressor surges on start, return water spikes, unit trips off, repeat.
This is why dropping the minimum WC temp only increases cycling and reduces efficiency.
