Heat Pump (inverter-based) Air Conditioner tracking, control & detection

After some significant hurdles I finally installed a heat pump mini-split in my 6,000 cubic foot apartment (i.e. small space). Appropriately perhaps I chose a Mitsubishi MxZ-FH06NA for the task, the unit is rated at 6kBTU cooling (and 8kBTU heating).

I have a dedicated Sense (the Main CTs) clamped to the 208V supply phases for the outdoor unit. The indoor unit, as for most small mini-splits, is powered directly by the outdoor unit.

Sense capture has been up-and-running from the initial startup of the unit.

Meanwhile I have an iQAir AirVisual temperature+humidity+CO2+PMx particle detector INSIDE the space sampling at 5 minute intervals and a PurpleAir monitor OUTSIDE (in the shade) near enough to the outdoor unit to capture the micro-climate of the outdoor unit but not so close that it will be influenced by the heat (or cold) thrown off by the unit.

I will be posting some ongoing analysis here as I tool up to build some coherent, and hopefully useful, charts. In the meantime, here are some initial thoughts based on the first few days of data:

  • A mini-split presents Sense with a really complex waveform! (I am reminded of my OLED TV signature)

  • The ramping power is everywhere for this system. Look at the startup load for example … 7 seconds to go from zero to the initial 223W! Note: When you look at the startup signature in anything other than the full resolution and fully expanded you would think the unit simply draws 223W, boom. At full resolution you might ask yourself how Sense would determine “When exactly the unit is ON?” … remember that Sense, when doing native device detection (disaggregation) is seeing a much more complex waveform than this – the aggregation of all the devices in my house.

  • Sense registers almost no current spikes for any startups but there are some interesting peaks at the ends of cycles.

  • Looking in Signals you can see that the unit is using a single phase (120V) to power certain components. Seems like in “idle” it’s consuming around 13W (on one phase), probably for the controller boards. This should all be fairly easy to correlate with the detailed specs but it does make me think: An installer empowered with detailed Sense data, maybe even including per-phase loads at high resolution, could quickly determine component-related startup issues. A dedicated Sense in some sort of capture mode in theory has plenty of free processor cycles because it doesn’t need to be doing any disaggregation or device integration (smart plugs and so on) processing.

Here’s the first few days from the very first system activation.
The standard commissioning procedure (which I carried out) sets the thermostat to 75F and runs for 30 minutes.

Apologies for the rough rendering. I’ll work out a more coherent charting method soon.

TEAL = Sense
BLUE = inside temperature, left vertical scale
RED = inside humidity, left vertical scale
YELLOW = inside CO2, right vertical scale

ON cycle begins …

ON cycle ends …


Wow ! Very complex waveforms that probably hide the fundamental physics of the underlying motors / compressors quite well. As you suggested, looks more like a OLED or QLED TV, or a washing machine with a DC motor, than my dumb old-school AC units (that are detected by Sense).

ps: Not sure the last two pictures highlight the features you intended - I can’t see an OFF in the second one.

Bad nomenclature on my part … was trying to convey the nature of the on ramping, i.e. the “ON cycle ends” meaning after 7 seconds of ramping the unit is at a 223W plateau and operating.

There are more dramatic examples but that was the very first activation of the unit and if by some miracle Sense was able to do native detection at that point you would assume, based upon what I understand of the realtime on/off chunks (“on” only in the case) that Sense ingests for the DSP, that it would be looking at at least 7 seconds of data.

This all speaks to the difficulty of realtime detection. As a thought experiment, it’s easy enough with the dedicated Sense to say, from the waveform, “my AC is on” but I was just playing around with the fan speeds and moving the vanes (tiny DC motors!) to see whether Sense would tag any of the wattage changes or, more importantly from a human vs Sense perspective, whether I could see those changes in the waveform and say something like “I turned up the fan”. Sense is definitely beating me on those little changes.

[Interesting: It’s as though some of the small motor loads are being absorbed by some capacitor charging. It’s very hard to see any load change in the waveform as I’m moving the vanes or changing fan speed. “Components” in modern devices, that one needs to detect, really starts to mean “components at the solid-state electronics level”, not just motors and such]

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Ahh - understand the intent of the ON waveforms now. My 2c is that virtually all manor of DC electronics plus electronically controlled DC motor are pretty much unfathomable to Sense. Not because of any Sense shortcomings, but because power supplies obscure actual power usage in the time domain. But love seeing the education the instrumented mini-split is providing !


The extreme case is maybe an EV. You would know, since you’ve been bravely trying to pick apart the charge cycles. Meanwhile the big motors; pumps; hydraulics; tens of tiny motors (something like 35 in the average US car); DC-DC transformers; lights; you name it in the EV are completely hidden from view! Small mercies.

SensEV gonna drive us crazy!

if you are curious this is the data from my HVAC items as well consisting of 2 3ton fully variable inverter heatpumps, 2 fully variable furnaces/air handlers, 1 heatpump water heater. i have zero anticipation that sense will ever detect these. i am pulling this data from my smart load center by leviton

and this is Saturday when we had some people over and where cooking so we actually had to have the down stairs unit on

Digging the clarity of the Leviton semi-transparent overlay on black. I might steal that for future rendering.

Thanks for sharing.

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ixu… My PurpleAir id… k8ger… Enjoy… Gerry

BTW… Solar powered…