All this discussion of correlation coefficients is a little abstract, though it provides a wealth of information. But now it’s time to get a little more concrete and look at a few comparison scatter plots where positive correlation is good, bad and ugly. A quick summary from ggplot2 (a package for R) can give us a little help. Here are plot summaries for every pairing of the AC devices with the upstairs (CoolUp) and downstairs (CoolDown) condenser runtimes, over the past year. We only need to look at the first column of plots for each, since that is the column that looks at Sense device energy results for each hour vs. Ecobee runtime. I’m using Ecobee runtimes as the golden reference since they are exact views on condenser activity. As usual, plots are somewhat colored by month to see correlations at different points in time.
Here’s the summary for the downstairs condenser - One can see the strong correlation line between CoolDown (Ecobee) and the Sense AC 3 device. Also visible is a slight line, in black between CoolDown and AC Down, representing the month or two of good correlation back in Sept 17. Points lying along the bottom of the plots in the first column of plots represent hours when the downstairs condenser was on, but the associated devices were not recognized.
The plot summary for the upstairs condenser shows a much less clear set of relationships, as expected. AC shows reasonable correlation with the upstairs condenser, CoolUp, for at least a couple of months (in black), but a lot of non-recognition as well (point on the bottom of the plot). And, as the correlograms indicated, there is also relatively strong correlation between the upstairs condenser runtimes and the AC Down device later the year being monitored. AC Spike is also well-correlated with the condenser, but shows a change in slope, really power usage over time.
What I want to do now is examine more detailed full year plots for the 5 pairings that showed strong correlation, at least in one point in time. First CoolDown and AC 3, no surprises. No identification in late 2017 through Mar 18. Great correlation after that. Looks like AC 3 runs at about 4.7kW.
CoolDown vs. AC Down is just the opposite. Good correlation in late 2017, but demising correlation thereafter, once AC 3 took control. Note all the 2018 vintage points on the bottom (missed identification of CoolDown) and on the left side (Sense identifying some other signature as AC Down). When it was recognized, AC Down looked like a 5kW device.
On the upstairs front, AC (part of the AC Up pairing or AC Up and AC Spike), correlated well from late 2017 into Apr or May 18, then pretty much gave up on any recognition (pink and purple dots on the bottom, missed identifications, but none on the left side, which would indicate identifying something else in those months). AC looks like a 3.5kW device.
Correlation between AC Down and the running of the upstairs condenser is much murkier. There’s a correlation line visible but an awful lot of missed identifications as well, all during the same time period. The correlation line points at a 3kW AC Down device, quite different than the original 5kW perspective on AC Down.
Final mystery - what’s happening with AC Spike and how does it relate to it’s original betrothed, AC and CoolUp, as part of AC Up ? Here’s CoolUp vs AC Spike. It’s the most mysterious since there is a visible correlation but the correlation is driven by a time-dependent set of lines (or one line of varying slope over time). When it first appeared in Sept-Oct 17, AC Spike appeared to be around 500W, but has diminished in consumption as time has gone on to about 250W.
I can see the drama over time now, but can’t really say why things happened. I do wonder if my AC condenser signature characteristics changed over time leading to a varying AC Spike and a swap of identifications. And did Sense introduce a smarter better model (AC 3) for my downstairs unit in Dec that eventually took over leaving my existing models to battle for “ownership” of the upstairs unit ?
Any ideas on how to probe more deeply ??