Can anyone explain what is happening to the minimum graph in @Timbones set of graphs above? How can the minimum at -10c be 6kw and yet it is only 4kw at plus 15c???
It is odd, I have no idea why. Maybe it just needs to work harder at those temperatures?
I double-checked the databook again incase I copied it wrongā¦ (11.2 kW)
Similar can be seen on the 14 kW unitā¦
ā¦but not so much on the 8.5 kW:
I also noticed these plots that show the COP is best when (this) heat pump is working in the middle of its power range, so aiming to be running at the minimum all the time (as I do) isnāt necessarily the best for performance.
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The sweet spot certainly fits my heat pump experience - it runs very sweetly between 7c and 12c putting out around 5kw for itās minimum input of 910w. Makes sense that they optimised it as this point as the SCOP figure depends a lot on the performance in this band - it represents 57% of the heating year in my area.
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Itās be interested to see the compressor frequency at those minimums - looks like a software minimum limit that gets set higher at lower ambient conditions.
It will be related to avoiding something nasty happening on the refrigerant suffer no doubt.
Mandating that these efficiency maps are published; old at least the best efficiency output and the efficiency at the max/min rated output; would be illustrative
One can then plot āwhat the unit does Vs designā separately from what the load side asks for.
And āhow well the lead behaves with respect to hitting best efficiency pointā thanks to control strategy.
Separating the box from how the box is used to target where performance can be improved.
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Happy to service your Daikin unit.
Give me a shout nearer the time, we have been picking up some of the broken pieces left behind from UK heat pumps.
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Thanks Ken ā probably next June. Sorry to miss you today.
Colin
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Thought Iād add a discovery about my heat pump in freezing conditions. It is currently 0.3c outside and has not really exceeded 2.3c all day. With my old settings that would have been the recipe for a lot of defrosts and a terrible COP as the evaporator would have been running below zero. However after 5 hrs running without any sign of defrost this is what it currently looks like (0.7c remember).
No sign of frost!
Itās running at a max flow temp of 38c and giving a COP of 3.6 and around 7kw output. I am more than happy with these numbers. The evaporator (or at least refrig 2 temp) is between -2 and -3c.
The secret seems to be not to allow it to push too hard to get to the room temp setting or, even temporarily, allowing a higher flow temp than 38c. My previously high modulation setting of +/- 3c was allowing it to do that as was my wd curve which went up to 40c at 0c outside.
As I have a lot of fancoil capacity then I have found that operating in a very narrow 35c to 37c flow temp range (all year round) and allowing the fancoils (with their own RT controls) to PULL the heat that they need out seems to give a good COP at all outside temps. If it keeps getting colder this evening will be interestingā¦
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Can you please confirm which sensors you are referring to? Are you using ESPAltherma?
Sorry for the slow response Jonathan Iām on hols. I use a different monitor that reads the daikin p1/p2 data stream. This then gets the nameā¦ refrig 2 temp ā¦from Daikinā¦which I assume is the evap input temp.
Thanks Colin. Iām not sure what that would correspond to in ESPAltherma. These values are typically around 0C and a defrost usually happens when they are a bit more negative
Suction pipe temp.(R3T) -0.2
Heat exchanger mid-temp.(R5T) 0.2
That would make sense
- Airflow should be perfectly even externally
- Refrigerant distribution should be perfectly even internally
(i.e. it shouldnāt look like a zebra thermally)
Then run the unit with as stable a load as you possibly can without tipping it over the edge into frosting (no setbacks or room influence / rely on the house smooth temperature swings)
One to add to the programming tips perhaps - removal of modulation at the worst temperatures
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