Yea it’s strange because I’ve had a few really good long runs with the flow around 37°C in the last few days.
See the 3rd here Emoncms - app view
Thinking aloud, and not with any deep understanding of heatpumps: I wonder if the input power is dropping for a different reason, and not at the request of the controller. When the compressor is having to work harder to compress the gas, it draws more power for a given speed. As flow temperature increases, so does the power.
So perhaps something is happening to the gas that means it’s suddenly easier to work against, hence the input power dropping?
It would be interesting to see what HeatPumpFrequency is doing during this behaviour.
Here’s a well-behaved example from my system: [Friday 6th Dec]
I learnt from Mitsi that if refrigerant is ‘flooding over’ into the compressor, it will not only close the valve (LEV), but also can rev-up to help get out of trouble. This means the flow,return temperatures overshoot, so the slowing down is understandable, then possibly it gets a ‘wave’ of refrigerant coming back. Is it simply an unfortunate resonance that is probably hard to achieve it you wanted it. I wonder how many other Ecodans are doing this. its only guesswork… not really sure what is happening
The compressor power will certainly drop as the flow temperature drops.
I just found a very rare catastrophic ‘crash’ on my 6kW Ecodan during a DHW session on 8th December. compressor speed steady .
Also veiwable on HPM app
But all the events with no drop of input power should indicate no drop in compressor speed?? no?
The input power does drop a bit each time (in the bit below it is running at 1,179W but drops to around 700W before ramping back up again) but the output collapses to nearly nothing (over 4.5kW down to around 1kW below) .
In cold weather I do sometimes get the DHW cycles where the input power drops back a bit but the output goes to near zero with input power continuing. These are much rarer when I put the hot water into normal rather than eco mode.
It just seems very unstable. Why drop the input power back so quickly when I guess it could slowly back off and find a lower stable input power.
Yea for sure it looks like digging into one might help with understanding the other.
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I had a very quick look through some other 8.5kW Ecodans and found a couple of examples where it is doing the same sort of thing bit not as dramatically as mine. Probably worth having a more extensive trawl through all the R32 Ecodans to see if there are other examples.
Emoncms - app view - from this system: HeatpumpMonitor.org
another
Emoncms - app view - from this system: HeatpumpMonitor.org
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2 posts were split to a new topic: Poor DHW COP on an 8.5kW EcoDan?
I’ve had another complete failure to get up to temperature on a DHW run last night. It was a few degrees above freezing so cold but nothing excessive. Where the flow rate drops to zero the immersion was brought in.
https://emoncms.org/app/view?name=MyHeatpump&readkey=9b87718992b6ed5756d94d4288059a6f&mode=power&start=1734663190&end=1734674220&flow=1
Looks like it backs off to settle at a max flor temperature to give the tank time to get up to temperature but then output collapses. Compressor still consuming for a bit but no output.
Gosh, that is a dramatic ‘crash’. The Carnot COP before and after is quite normal, so surely the refrigerant quantity is not a problem. It sounds like an expansion valve too open, and surely due to a sensor giving incorrect values for this very brief time. Ecodan do tend to slow down as you say, for good reason, but it’s staring to slow at only 53c this seems surprisingly low. Maybe that slow-down is the start of it ‘crashing’… I dont know.
It would be good to get a temperure probe on the discharge and also on the evaporator about 10-20% along the coil. If the LEV closes consideranly, all evaporation occurs in in a small area, hence the temperature drops.
[ Ignore this last comment… an alternative possibility for drop of output would be a closed valve. However, this would cause a pressure fault, and power input would drop. We are not seeing pressure faults here. its not a closed-valve problem]
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Maybe a little correction from me - I expect the EEV to be open more than needed…
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Ah, yes… sorry, too many things on my mind! well… The normal thing we are seeing here (we think) is reduction in heat output due to liquid going to the compressor, and some evaporation happening in the wrong place. However, another possible drop in output could be a closing of the valve. This was common once when mechanical valves fail closed. However, it would stop on the low pressure cutout. Ignore my thought of looking for low pressure, my mind was in the past!!
My DHW is set to 48°C so I guess maybe it goes to 5°C higher than that.
I wonder what the best way of setting something like this up would be.
I guess I could maybe hook an ESPHome with a couple of temperature probes attached.