I received a notice today that my always on had increased significantly. I have both a heat pump water heater and a Mitsubishi mini split system I use for heating and cooling. It’s cold this time of year so the heat pumps run almost continuously. I’m wondering how the Always on plays into device detection? At this point now that some of that power is seen as always on, will sense continue to learn these devices?
I should mention both heat pumps have been detected, but don’t register the full amount of power they consume. Also, now that I see the always on figure has increased I’m not seeing the heat pump detected.
Always On is Sense’s way of categorizing power usage from a range of devices (or device components) that steadily and continuously use energy, without much transition/change. Realize that Sense looks for roughly 1/2 second or so changes in power usage to identify devices turning on or off. If a device, or one component of a device, is continuously on or only slowly changing for long periods of time (more on time later), Sense isn’t going to easily detect the continuous power usage as a device, so it uses Always On as a way of accounting for that usage, though that usage is aggregated with all the other devices that have a continuous use component.
I use the term component when talking about device usage, since many devices will have some kind of standby/continuous usage component as well as one or more on/off behavior components - one good example is my electric garage door opener. My opener uses 7W continuously, just to listen for the remote opener signal. When it received an open/close signal, a second component that opens or closes the door appears. Sense never “sees” the standby component since it only shows up in transitions when I first plug the opener or flip a breaker on or off. But the second component has been detected by Sense and looks like this:
I mentioned “continuously for a period of time” since time is a critical part of calculating Always On. Sense calculates Always On by looking at the near minimum (1% bin) power usage over the past 24-48 hours (Sense uses 24 hours when fist starting up, but I think moves to 48 hours for continuing operation once it has measured 48 hours work of data). To put it more specifically, during 48 hours, Sense takes 8,294,400 samples that you see displayed in the Power Meter waveform. Sense looks at the 82,944th smallest sample during those 48 hours and uses that value for the Always On power for that half second in time. As new data flows in, if it is larger than the current Always On more than 99% of the time, Always On will increase, as smaller values disappear outside of the 48 hour sample. If the incoming data has the same statistical mix (99% larger, 1% smaller than the current Always On), Always On will stay about the same, and if more than 1% of the new data is smaller than the Always On, it will go down. Whew ! Here’s the way Sense expresses how Always On is calculated:
Two more wrinkles - Per the definition, Sense looks at each of the mains separately for the 1% bin calculation, then adds them together, so you might see occasionally see Always On data that is lower than the Power Meter, because Always On is looking at the 1% bin point on both mains, over the whole period and not necessarily occurring at the same time. Plus you will notice that it is using the mains power, not the mains power minus detected devices. This means that Sense is mainly using the “quietest” energy usage times in your house to determine Always On. One way to think of it is that Sense is looking for the “quietest non-contiguous” half-hour of usage. Now suppose you have a new device or device component that comes on for long periods, especially during the night and early morning hours, when most houses typically have lower electrical usage. That new device or component is going to raise the 1% bin on both mains, raising your Always On.
One way of getting insight into the breakdown of your Always On data is to use a smart plug. Sense will do roughly the same calculation on each smart plug to break out the the Always on component stemming from the device(s) on that smart plug. But some devices, like AC units or dryers, can’t be used with smart plugs because they have too high a current draw, are 240V and/or are wired (no plug). For those, there are other techniques for looking at their Always On draw.
Finally, you probably hope that Sense will detect your mini-split some day. The good news is that there is hope. Sense appears to be seriously tackling mini-splits. From the article below, my takeaway is that mini-splits do run continuously over long periods, but they do have transitions. Unfortunately, those power transitions are longer in time than the short window Sense uses for most of their detections. Note that the transition times in the graphs at the bottom are in 10s of seconds, or really slowly and continuously changing over the entire cooling cycle.