Mini split and window AC on constant cool

First my house does not have enough AC btus. So, when it climbs to 90 outside and there are no trees shading my house, the AC is on constantly. Plus, I make it worse because the hotter it is outside the colder I want the bedroom.
When the single mini split and the single window ac is on constantly, Sense can’t find them. I don’t think there is a way around this (unless I turn down the AC) but I figured I would ask if others have seen this.
Overall I’ve been presently surprised how well Sense has found items, even duplicates, in only 3 weeks of running.

You’re on to something there. Sense needs to see a range of on-transitions and off-transitions before it can detect a device. If your AC compressor is on for long periods without any stoppage, then there are no transitions or very few transitions to learn. And if your AC is on for extremely long periods, approaching 48 hours, then the AC usage will even flip into the actual Always On category (I’m not sure AC units are designed for 48 hour duty cycles, and I that most controllers will insert some break times).

Here in the Bay Area, we’re fortunate in that even hot spells are cool at night, so the AC has a break after 8-10pm. Sense has been pretty good at detecting my simple (non variable speed) AC units, perhaps with some assistance from the Ecobee integration. I do still see a somewhat similar issue, though, during hot spells when the AC is running for 4 or more hours. In that situation, I think Sense times-out on the AC detection, thinking it might have missed and off transitions.

I investigated the hours when my Ecobee runtimes and my Sense AC for my upstairs AC unit diverged the most (lowest Pearson correlation) and found that Sense was dropping off during long runs.


My upstairs AC is an old-school traditional unit and even when it’s really hot, it turns off and on multiple times an hour. Sense has found both you mini split and window unit?

Yes it found both and reports them mostly correctly all the time, except when I blast them. Maybe because of the difference in size? The mini split is a Mitsubishi 12Kbtu outside and inside paired unit and my window AC is 5Kbtu. Or what I guess makes it easier is that the mini split is 230v and the window ac is 115v.

@kevin1 has addressed your detection issue in detail so here are some thoughts on “comfort”:

Most people like sub-50%RH (relative humidity).

When outside humidity is high, unless you have a really well sealed house, the moisture in the air will find it’s way into your house … there is essentially a sucking action that wants to balance the humidity inside and out.

Most window AC units, especially oversized ones, are pretty bad at removing humidity as a consequence of cooling. In fact, cooler air also tends to “attract” humidity from the outside. Mini-splits and conditioners with a DRY mode can be reasonably effective at removing moisture from the air but there is a caveat that not all mini-splits seem to be set to avoid – you have to set them on a LOW fan speed.

(I have discovered that a firmware bug in the Mitsubishi MUZ-FH06NA actually allows you to run DRY mode at full fan speed … which makes the drying action ineffective)

You also need to consider how different cooled Zones of air might interact. If you want a DRY bedroom (probably more comfortable) then it may be that if it’s connected through, say, an open door to another cooled area then that adjacent air should be kept COOLER than the bedroom otherwise the bedroom will suck in the moisture from the surrounding warmer air.

My personal take is that below about 74F you’re in the realm of “it may feel cool at first but the humidity rise is probably the thing that makes you feel like it’s still sticky … so you turn the thermostat down … which makes it even more humid … which …”.

And I’ll end with a quandary: The most efficient cooling runs at the lowest possible btu for the longest cycle … so Sense isn’t going to see frequent starts and stops with easily recognized signatures. Quiet, smooth, modern HVAC makes for tough detection: “Can you hear me now?”

First thanks.
Got myself a humidity meter and my house is at 60% with both AC units running. I will do some experiments with a dehumidifier, especially when the heat comes back in a couple of days.
But I might be an outlier. I want snow on the ground from late October to the beginning of March, and never to have temperatures above the mid eighties especially with dew points around and above the high 50s.

You may want to investigate the new(ish) dual-inverter LG window models. Unfortunately the smallest unit is hard to find at the moment I believe. The dual-inverter models have dehumidification performance, even in COOL mode, approaching a good mini-split and they are reasonably efficient.

Dehumidifiers are one of those things that are sometimes necessary but in the long run their low cost is eclipsed by the running cost. The inkjet printers of HVAC!

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