Interaction between Thermostat Controller and Honeywell T6 Pro Z-Wave + 2 Stage Heatpump

I recently installed a brand new true 2 stage heatpump. At first, I tried using it it with a centralite pearl thermostat, but as it turns out that tstat can't effectively operate 2 stage compressor heatpump on the heat side, but can on the cool side.

So, I did some research and the Honeywell T6 Pro seems well supported by HE, so I picked one up, installed it, configured it, and created a Thermostat Controller to manage it so I could use some temperature sensors I've got scattered around the house to feed into the average temp.

What I'm noticing is the new tstat is seemingly always calling for second stage heat, even on relatively warm days like today where it hit 49F outside. I read over on this post that the Honeywell T6 Pro bases its calls for heat based off the cycles per hour setting. On these warm days the heat pump doesn't cycle all that often, so I'm guessing it's slightly more complicated than that (open to being told otherwise here - what the algorithm here is seemingly an enigma). Note my second stage is a compressor second stage, not electric heater strips or any other aux heating method.

So I guess what I'm trying to figure out is - does anyone else have this setup or something similar? My working theory is that the +2.0 default temperature offset that the HE's Thermostat Controller uses is too aggressive for the Honeywell and so it thinks it needs to run the heatpump at stage 2 heat to catchup. To test this I am going to try disabling the thermostat controller for now and see if I can get my tstat to just call for stage 1 heating during these warmer days and potentially switch into stage 2 if it needs. But I would love to hear if anyone has any familiarity with these tstats on 2 stage compressor heat pumps?

I would agree with your theory.

I encountered the same issue. After experimenting with the control offset value, my conclusion is that the thermostat calls for 2nd stage due to the large difference between set point (determined by the Thermostat Controller) and the T6 Pro thermostat-sensed temperature.

Lowering control offset can prevent this, but then that increases the odds that the T6-sensed temperature will satisfy the thermostat (and shut off heat/cool stages) instead of the average temperature as computed by the Thermostat Controller app.

2 Likes

Same. I ended up replacing the T6 Pro a couple weeks ago with a GoControl GC-TBZ48. Like the ecobee I used previously, the GoControl lets me choose between Stage 1 and Stage 2 for both heating and cooling based on the delta between the temperature set point and the ambient temperature at the thermostat.

In my experience, this works way better, and also completely predictably. Predictability was especially important for my use because my heat-pump is configured to run on my generator; when that happens, it is important for it to start in Stage 1 and not Stage 2.

1 Like

Thanks for the confirmation @Guffman that puts my mind at ease a little.

I wonder if potentially there's a feature request in here where we could have the Thermostat Controller adjust its final temperature offset dynamically to avoid this kind of a scenario? That probably requires decent hardware that reports frequently enough so the HE could make the necessary adjustments and not cycle the equipment like crazy (although any half decent thermostat should have compressor protection to prevent that). Battery operated thermostats would probably have issues with that.

@aaiyar I wish I had found your post about your T6 issues before I bought mine :sweat_smile: otherwise I probably would've gone with the GoControl.

1 Like

@aaiyar , thanks for the GoControl info - I might grab one and see if I can set it up similarly.

@m.smollinger , in my case, the T6 temperature sensor reacts a lot faster than the averaged temperature in my downstairs HVAC system, just due to the T6 placement and the room thermal response in which it is located. In cooling mode (only single stage), the Thermostat Controller offset can be set pretty high, to guarantee that the average temperature is effectively always in the feedback loop. So all was well until heating season, since I have a two stage gas furnace. So when the Thermostat Controller calls for heat, the variable speed blower and furnace quickly ramp up to ‘11’ - noticeably louder register noise and heat output. Since I live in the south, and the downstairs is thermally efficient, the unit very rarely needs 2nd stage heat.

Not sure if a dynamic offset would solve my problem. The algorithm set point would have to chase the T6 temperature reading, staying just outside of it to try and remain in control of the call for heat/cool. Maybe it would work…

1 Like

Just dropping a related thread...

@aaiyar , would you mind sharing where you purchased the GoControl thermostat? I would like to try one on my heat pump.

I didn't. It was gifted to me by a fellow Hubitat user. Here's a link to the specific zwave+ model I use:

@aaiyar , thanks for the info. I grabbed one off of eBay and installed it on my upstairs heat pump/heat strip/variable speed air handler yesterday. So far so good, I would be grateful if you could comment on the following…

  1. Noticeably slower response to Zwave commands than the T6, based on watching attribute changes on the HE device web page - have you observed this?
  2. I was using the Thermostat Controller app to overcome compressor short-cycling (my system is oversized, so inadequate dehumidification). Given the GoControl has a minimum run time parameter, what are your thoughts/experiences with tuning this parameter in lieu of the Controller app?
  3. Which device driver are you using? Generic Zwave Plus Thermostat, GoControl Zwave Thermostat, or the Advanced GoControl driver available via Package Manager (authored by djdizzyd)? Why did you choose one or the others?

Thanks!

1 Like

Can't say I have. I have noticed that this thermostat is connected to the hub at 40 kbps, while the T6 used to connect at 100 kbps (same location etc).

Ultimately, I trust the thermostat itself over software running on a computer that is another point of failure. So I set mine to 9 minutes, which I think is the maximum time setting for a minimal compressor on time.

This one. No special reason. It does all I need. And was built-in.

Thanks very much!

1 Like

another solution for the t6 is possibly putting temperature sensors in other rooms so it averages the readings.. unfort. I am not sure if th t6 pro accepts wiresless sensors it appears to only have wired ones which are a pain..

at home i have the vision pro 8000 redlink with wireless sensors and it averages all of them

1 Like

@kahn-hubitat
You can use the thermostat controller to do this to aggregate averages for the T6 (or any thermostat really)``

1 Like

Yes I know but I prefer a Therm to also work independently of any automation if possible as heat in colder climates is such an important attribute. I don't mind monitoring and alerting on.top of that however.

1 Like

It does allow the use of a hard wired external temp unit.

So quick update from me:

I've been running the t6 pro uncontrolled by Thermostat Controller and like we all suspected, thermostat controller's method of operation by increasing the stat's temp by 2 (or more depending on config) degrees does, in fact, kick in the stage 2 every single time. Unmanaged, I do hear the stage 2 operation kick in after several minutes of stage 1 running, like you'd expect a 2 stage heat pump to do.

@rlithgow1 yeah my original point with this post was exactly that: to use my array of zigbee temperature sensors to create a weighted average for Thermostat Controller to then manage the t6 pro. However because the thermostat always thinks it needs to "catch up" from the change, it's basically not being efficient with how it works.

As for the hard wired external temp unit, that is pretty much solely used to inform the tstat what mode to run the heat in, i.e. if its above 30 degrees outside it'll use the heat pump (if i'm recalling the settings correctly), and if its lower than that it'll rely on either aux heat or emergency heat depending on what is configured/installed.

It does also support 1 wired indoor sensor but I don't recall if it'll create an average of the wired and built in sensors or if it overrides the built in sensor (basically if your thermostat is in a terrible spot for HVAC needs but can't be relocated).

2 Likes

Same observed here. That’s what I really like about the GoControl. With a delta of up to 3, the heatpump can be configured to come on in stage 1. At a higher delta, it comes on in stage 2.

In addition to the finer degree of control, this has the advantage of letting me heat or cool at different rates depending on whether or not there’s company at home.

Download the Hubitat app