HVAC experts: What in the world is going on with my ecobee?


#1

I’m allowed to ask for help here too, right? :smile:

I recently installed an ecobee and it’s pretty fantastic. I was dealing with some issues with my aux (electric) heat running too frequently and I’ve pretty much solved that…well, except for the following issue.

I have aux set to run below 30 degrees. That’s all fine and dandy and it seems to do that without issue. However, the ecobee doesn’t want to register it as aux heat. When I set it to Aux mode, it shows as Stage 1 Aux, but when I set it to Heat, it doesn’t want to show aux at all, even when it is obviously running.

These images are from the other night. The cycles match up perfectly. In the power meter screen shot, you’ll see two cycles of my heat pump followed by 12 cycles of what is obviously aux heat. This matches up with the shot from ecobee: the first two cycles are above 30 degrees and thus purely heat pump and the rest are below 30 and thus aux.

So…why in the world would ecobee not register them as aux? Someone on Reddit suggested that they might all be aux triggered by a defrost cycle and not aux triggered by ecobee. But these are all 14 minute cycles and I would think there’d be some visible ramp from heat pump to aux in the power meter. I’m not seeing that at all. I have since reached out to ecobee support but figured I’d toss this puzzle your way as well. I know you guys like puzzles.


#2

One suggestion - try an export of that day to see what shows up in the system mode column. Sometimes I find slight differences between what Ecobee displays vs. what I see in export.


#3

Good call. I didn’t think of that. Unfortunately, they’re marked “compressorHeatStage1On.”


#4

It looks like you’re set up to use heat strips under 30F and heat pump over 30F. Do you only have an air handler + electric heat strips or do you have a heat pump exchanger + furnace + elect. heat strips? If you have an air handler + electric heat, i think you may have setup your thermostat for a furnace application, in this mode heat pump and furnace can’t run at the same time (often call “add-on” in thermostat litterature). So it switch from heat pump to aux at a selected change over setpoint which is 30F in your case. In Air handler mode, both heat pump and electric and can run together. However i’m not familiar with ecobee. I could try to look at the manual if you tell me your particular setup.


#5

Thanks, Marc.

Yes, at that time my aux would be locked out until outdoor temps hit 30F. I’ve since changed it to 20F to see what happens and aux hasn’t been triggered since (seemingly neither from an ecobee call nor from a defrost cycle, and it has been in the mid 20s at night here so I’d expect some need for defrost).

As for the system, it’s pretty basic: electric furnace with (I think) 7kw strips and a single stage heat pump — I don’t remember the specific models off the top of my head and I’m not at home. Per the ecobee settings, it is set to run both simultaneously if need be, via the “Heat Pump, Aux Heat Simultaneous Operation” setting. I pretty much used all of the settings here, as I’m really trying to optimize for cost savings rather than ultimate comfort. Luckily, my wife and cat are on board with that :smile:.

I’ll add that I’ve also reached out to Ecobee support and while they’ve been very responsive, ultimately they’re not all that interested in looking at third-party data (i.e., my Sense Power Meter grabs) as verification. But I’ve since spoken to some other folks and the defrost theory is starting to seem more feasible and would explain why ecobee wouldn’t see the call.

Here’s a couple other power meter grabs that may also support the defrost theory. It looks like there actually is some stepping up from normal heat pump usage, to something happening in the 5kw range, and then to the 10kw heat strip range. The first picture is the first time it switched over to aux, and the second is an example of a subsequent time (missing the 2kw normal heat pump usage).



#6

Well, 99.9% sure that the mystery is solved. In a bout of curiosity, I opened up the heat pump control panel to find an outdoor thermostat set to 30F. I turned it down to 10F and we’ll see what happens during the next cold spell.


#7

i came here to post that your old thermostat most likely did not have an outdoor sensor to control the aux heat, so that outdoor sensor is connected to the control board (with the necessary intelligence) in your air handler… but you found it.

sorry, i dont visit this forum often…