So,
I wouldn’t have seen the below without heatpump monitor. It hasn’t done this before (minor fluctuations - nothing this erratic). I’ve bled the system on the buffer tank, very little air came out and the system remained at the same pressure on the gauge.
That’s about it for my knowledge of what to do.
So any thoughts appreciated.
This is from early on in the day
This is something that has been seen on some heatpumps…
…though those typically see a matching oscillation of the electrical input at the same time. That makes me wonder if the fluctuations are real, or some noise on the flow temperature sensor.
What model of heat pump have you got, and how is performance being measured?
Interesting. I would except your power input erratic as well. To me it looks like some flow temperature sensor issue. On my pump I have this pattern when flow temp is reached and the pump is not able to maintain it properly for some reason. But then power input is jumping easily by 300W. I believe it’s some bug in controlling firmware because there is no reason why compressor oscillates between 22Hz and 14Hz all the time instead of 22 - 20 - 21 - 22 or such for example.
@Timbones I have an Acond Pro-N unit. Monitoring wise I have SDM120 Modbus/MBUS Single Phase (class 1) and Sontex heat meter (class 2)
@Michal_S I’ve had the unit for a few years now and this is the first time I’ve noticed it, it will go as low as 460w usage. It has always been steady though without fluctuations.
It’s last run is now back to normal.
Thanks for your replies.
Yeah, it’s strange so good it’s back to normal. I wish I have such a graph as you have 
I got mine from Level 3 Heat Pump Monitoring Bundle (emonHP) - Shop | OpenEnergyMonitor Now half the price I paid, well worth it though.
Silly question, but don’t you have some sort of zoning, or local thermostatic valve in your system? It appears to be the flow temperature rising and falling rapidly, without change to the return temperature. Can you monitor your flow rate?
I don’t have any zoning or thermostatic valves in the system, must be thinking of someone else.
Flow rate is monitored by heatpumpmonitor.
I’m sure that it’s a real effect. My Samsung does it.
Both input power and output power vary in sync.
I found that I’m inadvertently logging compressor frequency and fan speed and they also oscillate in sync with the power fluctuations.
My surmise is that this occurs when the power demand is low and the heat pump hunts between 2 states trying to match output to demand and failing. It doesn’t seem to cause a problem so I just ignore it, but it might be possible to stop it by adjustments to the WC curve, maybe by raising the flow temps.
Possibly my mistake, but to be fair I cannot see your flowrate on your graphs, only flow temperature. If you look at my graph, the flow rate and the heat output oscillate together, but neither the flow temperature or the energy input not changing. This is in order to keep the delta T in range. On your graph, the heat output and the flow temperature oscillates in pair. Heat output is a calculated value and we only can see two of the variables, the return temperature is more less constant, so we can ignore both of these. To determine the cause of your oscillation we need the flow rate. There is a great possibility, your circulating pump targeting the return temperature, and trying to maintain it, rather than the delta T (like mine).
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I’m not sure how / if I can get flow rates on the graph. However, I retook the screen shot with the readings in show and flow rate is fluctuating.
The raph not showing the flow rate. The list blow the graph has some data called flow rate, but that is very low value. For example my one is up to 33l/minute. Yours is below 1.
Mine is m3/hour so about 14.3l/minute which is about right for the heat output of the unit.
Now including flow rate, doesn’t look as erratic as I thought it might.
anyhow it’s not done it since, I’m going with it just being a combo of heat demand and outdoor temp, putting in between two settings and switching between the two of them.
I see, the outside temperature is definitely on the “high end”, however I saw a few days on your feed, you even run the system when the outside temperature is around 14 degrees, but I could not capture the issue you have. Anyway, you also mentioned the system is running for a few years now and this is the first time you noticed this… Just out of curious, did you clean your strainer (filter) recently/at all?
