4 times now during the hot weather periods, (outside temps over 24oC) the DHW heating cycle stops short of heating the full mixergy DHW tank.
Today the ASHP turned off after hitting a flow temp of 49.2oC , return of 44.9oC after a short 30min run.
The Mixergy tank started with 90% cold water with a target temp 48oC for 100% of the tank. 56% of the tank got to 48oC. ASHP turned off at this point. As the Mixergy tank hadn’t reached its 100% it then switched to immersion and proceeded to heat to 100%.
Any other cooler day the ASHP gets to a flow temp of 55oC with return of 52oC, and Mixergy tank goes from 90% cold to 100% target temp of 48oC. This roughly takes an hour.
Any thoughts on why the ASHP stops it run? The Mixergy continues to call for heat and ultimately has to resort to heating via its immersion heater.
See dates 12th aug, 10th Aug, as examples of failed heating. I’m the Octopus Daikin in Marlborough in heatpump monitor.
Thank you David
I could be wrong, but I’m sure I’ve read that DHW on the Daikin stops when outside temperature (as read from the internal sensor on the unit, even if an external sensor is fitted) reaches 30C.
I’m not sure why it works that way, but I recommend trying to do your DHW outside the temperature peak of the day and when the sun is not on the outdoor unit.
That’s quite possible as the unit would have been in the sun and internal temp would likely to have been over 25oC whilst external was registering slightly lower. I’ll have a look for the guidance on temps that you suggest.
Unfortunately the Mixergy calls for the DHW cycle when internal levels reach 90% cold, which gives a nice long efficient run. I over ride this in winter as the cold temps hit harder on cop.
I observed a similar effect - when scheduling the DHW at a time of day when I would have plenty of surplus PV, on the hottest days the DHW doesn’t complete.
So now I have moved the DHW schedule to a cooler part of the day - during my off-peak electricity hours.
As we move into Autumn I’ll shift it back to DHW when the outside temps are mildest.
Tempted just to leave it but if there’s some config settings on the Daikin I can set so that it overrides or is less sensitive to that temp I’d prefer to leave my Mixergy to self demand when at its lowest.
A quick look online and I can’t initially see any detail about a temperature cut off for the Daikin, but there must be something.
The only references to “ambient” and “DHW” in the Field Settings table refer to the limits of the WD curve you can set on DHW if you want. I assume you’re not using that?
Daikin’s brochure page 10 suggests an upper limit of 35c for both low and high capacity units. I can confirm my 11kw ran and topped up the DHW while it was 32c outside yesterday, according to it’s own sensor.
Thanks @chrisg my unit was in the sun on the last run so I’m wondering if that has also played a factor in getting it to a higher ambient temp. and caused it to cut off after 30 mins. of running and not reaching the required 55oC flow temp. The outside ambient temp was 24 oC, the OEM temp feed suggested 30 oC, which was too high. My unit is East facing and this run started at 11am, so not peak temp either.
I wonder if it’s the large delta between the flow and return as this grew and hit 5oC, is there a setting to increase the delta in the Daikin DHW cycle settings?
Or the fast climb rate of flow temp? This failed run saw 1oC every minute where as a successful run is 0.5oC every minute over 1 hour.
My system seems to operating as expected, in that it cuts out at 45 when ambient temp is above 25. I don’t believe I have a booster in my ASHP EDLA06E2V3 so heating falls to the Mixergy immersion to complete.
From Daikin;
With this hot weather you may notice that the booster heater / mixergy is coming on to do hot water,
With the small Daikin units E series eg 4,6 ,8 kw units and a ambient temp above 25deg the hot water schedule will use heatpump to heat tank to 45deg then booster heater will then take over and take it to cm setpoint, For ambient temperature above 30 +deg the booster heater will only come on
Things to check on site are that the booster heater is set to compressor off and that there is no booster heater schedule set ,as said above this only effects the smaller Daikin, so as the weather gets warmer you may see more booster heaters coming on to do hot water.
This graph shows when the booster kicks in. On the y axis is outdoor temp. On the X axis is tank temp. If we take 25 c outdoor temp for instance trace across you can see the line hits a hatched area at 45 c tank temp. The hatched area is when the booster kick in over the compressor at a given external temp.
