Has anyone seen a graph of efficiency vs Flow Temp. Trying to achieve FT of 45C when it’s-12C outside sounds like a step to far. 
with my setup, ive noticed when the OAT is below 3C, the Cosy6 is running at 100% most of the night and until mid morning 

@agentgeorge 35C ScOP 4.36, 50C ScOP 3.6, 65C ScOP 2.99.

@swwils good results supporting running heat pumps at lowest FT that will keep the home warm and not overheat it

@andrewj are you able to adjust your cosy9 flow temp down to 45C?

@agentgeorge these are just the declared figures. I need to check but I think I have seen better real world results especially after the August update.

@agentgeorge Probably, but temperature change at -10 has little effect without a warm weather change as well.  It just flattens the curve out: I haven't plotted, say 45c/36c, but I suspect the temperature difference at design temperature of -3.4 won't be much different to 50c/36c.  As it stands, I don't really have the adjustment in the radiators to run fully on and my COPs are already reasonable.  Today is 4.33.  4th of Feb with temperature range from 2.3c  to 7.5c over the 24 hours was 3.76.

It’s been consistently warm over the last couple of days and I’ve found temperatures in the house have dropped off a bit.  The landing is 22.4c and I haven’t seen that below 23c since mid-October.  Living room is around 21.4c and many other rooms are hovering just below 22c.  I’m assuming this is a result of my warm weather end of the WC curve being 36c and the heating going off for 2 hours overnight whilst the hot water cycle occurs. So 36c isn’t quite enough to bring temps back up, or maintain them, given the thermostatically controlled nature of this thing - although we’re not cold obviously.  In cooler weather, where temps are more consistently around 4-5c with occasional rises to 7-9c house temperature is more stable, with rooms at around 22.5c.  I haven’t made a change to the WC curve since early December, and that was to move the design temp point from 50c at -3.4c to 50c at -10c.

@andrewj I couldn't imagine living in my house at the temperature your seeing, mines set at 20.5C for a comfortable environment downstairs and 19C upstairs.

Everyone who visits remarks how warm the place is when they walk in too.

The conclusion is your original heat loss survey didn't take into account your scandi design house with super insulation.

Also Im always intrigued being a calibration engineer in my younger days, you state temperatures of 21.4 etc. 

Do you have calibrated sensors or are you trusting those mickey mouse ones have an accuracy of +/- 0.1C

I have 1 calibrated temp meter and the others are rarely anywhere near accurate, sometimes over 1C out.

@editor With your contacts, do you know someone at Heat Geek who would like to experience a sauna heat pump installation and comment on the original heat loss survey, if the HP is over specified, and how to better control the temperatures within this example of a Scandi House.

Posted by: @agentgeorge

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@andrewj I couldn't imagine living in my house at the temperature your seeing, mines set at 20.5C for a comfortable environment downstairs and 19C upstairs.

In fairness, I would find those temperatures too cold and uncomfortable.  One of the differences might be related to thermal mass:all our walls are plasterboard, there is no block work on the warm side of the insulation, and any brickwork on the cold side is really just decoration.  Therefore we really do rely on how warm the air feels.  Not heat pump related, but summer months can be very warm inside - our windows will now open to essentially give us a wall sized hole in the living room.

Posted by: @agentgeorge

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Do you have calibrated sensors or are you trusting those mickey mouse ones have an accuracy of +/- 0.1C

nothing so fancy, I think they are +-0.3 sensors. I also don’t know how accurate the Cosy Pods are either.  When I obtained these I ended up with 3 Pods and 12 temperature sensors.  I placed them all in the same spot and looked at the readings once they had time to settle.  IIRC 8 of them read the same value, 3 read 0.1c different, 3 read 0.3c different and 1 read 0.5c different.  None of them are likely to be “calibrated” and when I state temps, it’s just what they are reading and against actual temperature are likely to be off. For all intents and purposes, they are accurate enough though.

Posted by: @agentgeorge

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@editor With your contacts, do you know someone at Heat Geek who would like to experience a sauna heat pump installation and comment on the original heat loss survey, if the HP is over specified, and how to better control the temperatures within this example of a Scandi House.

It’s not a sauna now, at least in my view and definitely not in my wife’s view - she would keep her dressing gown on in bed going “brrrr” even when the room was 22.5c 😀 Still, I’d pay for a day’s time for someone IF it actually provided useful insights for myself and this site - although I’d be a little worried I’d end up in a he said/she said scenario.  Also Octopus haven’t been an “installer from hell” and I wouldn’t want any implication of that.  I don’t have access to any operational data either, just an hourly breakdown of input, output and average OAT.  It’s worth mentioning that I had a survey from Octopus and Heat Geek and they both came up with a heat loss within 200w of each other - around 8.5kW.  Octopus have since resurveyed and come up with 7.5kW and their suggested radiator spec with 4 smaller radiators (for bedrooms) and 2 larger output (for porch and downstairs WC which were undersized) resulted in 1kW MORE total output than originally!  

Really I’d say the only real issue now is controlling the heat output.  I get these house temps with the Primary Pod in the downstairs loo irrespective of the target temp.  In other words, I don’t really know how I would implement a setback or what I would do if I really wanted a cooler house.  I think moving the Primary Pod to the living room would work for a holiday mode as the rest of the house would probably follow that.

I've had a few more good runs with 33 - 45 weather comp. I also did a few max load tests that I put on HPM.

Ive notice the cosy targets dT5 until you reach about 55c flow, then it targets dT 10. Which makes sense and might be useful for some people here.

@swwils Similar here, though it has been very mild.

It will be interesting to see what happens over this weekend as the temperature outside drops again.

With the current outside temperatures I'm finding that I don't need heating on at all during the daylight hours.  The schedule is set at 22c from 18:00 to 09:00 and 20c 09:00 to 18:00.  What I'm finding is that the heating will probably come on around 23:00 and be on/off during the night - this morning, the last heat run was sometime between 08:00 and 09:00 (closer to 08:00 but I can only break down runs by hourly increments); hot water is created 02:30 to 03:30.  Solar gain is raising internal temps of the house to around 22.5c downstairs and 23.5c upstairs and it only drops under 22c around 23:00!  

Strange state of affairs though, with the east side of the house above 22c from some time after sunrise but the west side of the house fluctuating around 21.8 - 22.3c (heating on so keeping it at that range), which of course adds further heat to the east side, until late morning when solar gain starts to take effect.  I made the 20c daytime setback today because even with the room at 21.5c or so it still felt comfortable because of the blue skies outside (21.5c in winter with rain and cloud felt cold...) but because it was still calling for heat it started to feel too warm.

Clearly, this is a good cost saving and I can't argue with that.  With the heating only required over night during colder hours though, the COP is quite low - to be fair, it's ok given the OAT but on other days with larger OAT swings the warmer periods would drag the COP up which isn't happening now.  I've attached an image of usage today to show what I mean - note that the SPF = SCOP = quite reasonable and is currently "flicking" between 3.89 and 3.90, with a full year's calculation only available on 9th May.

The system runs thermostatically, as I've already reported, and I haven't bothered previously with setback temperatures.  I may give that a go now, perhaps setting overnight to 20c with a raise back to 22c for 05:30.

I'm guessing that this time of year involves more fiddling with settings as the OAT temps fluctuate.  If we hit a cool spell again, the schedule will have to revert back.  

@andrewj 

Same here.  I have a slight setback between 21:00 and 4:00 and have found that during this warm spell the Cosy has been kicking in at around 2:00 until around 9:00, then nothing until a DHW blast in mid-afternoon.  

Despite this the COP is only down a little (still above the SPF though) and, remarkably, the SPF is sitting at 3.62, almost exactly where it was forecast to be after 12 months (installed 25 March last year).  

All things considered I am pretty pleased with overall performance and I expect that the SPF will improve in year 2 now that I think I know how to get something approaching the best from it.

And, given the current situation in the Middle East, I am so pleased that I took a punt on the fixed Cosy tariff last October.