I have a Trane XL 850 that I have controlled through Hubitat. This controls a variable speed system. The thermostat sucks. The AC can run for hours and hours and I can watch the "current temp" that it shows go up a degree. It does not accurately read the air temperature. My conjecture is that the system itself generates heat that interferes.
Anyway, I have Zooz temperature sensors everywhere now and have a good idea of what the temperature should be, vs what the thermostat says it currently is. The thermostat scheduler/controller combo is working great at keeping the house at the actual temperature I want it at.
What happens though is this. Let's say I have the TC set to 74. The temperature goes up to 75 and so it wants to tell the actual physical thermostat to make cold air. It might set the thermostat to 66 and then turn it off once then temp reaches 74... which is what I want. Actually, what happens is because of how much the XL850 sucks, the actual house temp might be 75, but the TS says 78 and then TC sets it to something like 68 so it thinks there is a huge demand for more cooling when there really isn't.
The issue is that I have a variable speed system and I would rather the temperature of the thermostat be set just a couple of degrees lower (than what it currently thinks the temperature is) so that the compressor maybe runs at 20% for an hour instead of 100% for 15 minutes. It has basically turned my variable speed system into a regular single stage unit.
EDIT: I actually just realized I will probably have the same issue in Winter but worse. Instead of running the heat pump the high wattage electric heaters will be engaged. So definitely need to know if this can be changed.
I know it can be calibrated. The issue is not really that it's off by X number of degrees. Let's say the air temperature is 76 and the air has not been running for a while. The thermostat might correctly show 76, or within a degree.
But now lets say I set the air down to 72. The AC will kick on and it runs and runs and runs, all while we can feel the temperature dropping and the sensors show the air dropping... the thermostat might say the indoor temperature is still 76 degrees. I have even seen what it thinks is the indoor temperature creep upwards, so it might now say it's 78 degrees when in reality it's dropped down to near 70. We get around it by just manually changing the setpoint temperature a bunch. So I might set it back to 76 at this point.
Where is your thermostat installed? Is it very close to a return or a supply, or does it perhaps have a remote device that reads the return temperature?
Sounds like you are getting false heat around the thermostat. Where is it located? Any lamps or pulldown stairway near it? Also make sure the hole behind the tstat where the wire comes thru the wall is plugged. Toilet paper works well. I was in HVAC 45 years until I retired 4 years ago.
I don't think it's the location. Google "Nexia XL850 inaccurate" and you'll find lots of complaints. I installed a Zooz ZSE44 right next to it and the temps it records rises and falls as expected.
As an example of the behavior I want to change, here is what the thermostat looked like after I adjusted the TC down by 1 degree.
It would have been much better if it had set the thermostat to 75 instead and the compressor would have probably come on at like 25%. I suppose I will need to turn off the thermostat scheduler and build my own schedule in RM using time triggers and setting the TC based on what the thermostat thinks the temperature is. I think it's doable.
Seems like you really just want to set the thermostat's target to [thermostat reported temp] + [actual temp] - [desired temp]. So the thermostat sees the actual direction and magnitude of the desired change, regardless of what the numbers themselves are.
Yeah, actually I think that would be the best way to do it. I was thinking I'd be able to do it in RM fairly easily but the more I think about it, it's more complex than just setting the thermostat setpoint to be the difference between the two. I would basically be trying to recreate the whole Thermostat Controller app.
@bravenel Is this a feature that could be added to thermostat controller? I think the above quote sums up what I need to happen pretty well. If the magnitude of the change made to the actual thermostat was the same as what was made to the virtual thermostat, I believe that fixes this problem. Maybe with a note suggesting it only be turned on if you have a variable speed system.
TC doesn't have a lot of choices for what it can do to push the real thermostat into heating or cooling. Are you using the real thermostat as one of the TC temperature sensors? How are you managing the Control Offset, since that's the key to how it sets the real thermostat.
Yeah, that's the intent of TC. TC has no understanding of variable speed systems, or how to manage them.
Right now if it's 76 and I set the temperature to 75 (the actual temperature according to TC) it will set the real thermostat to a temperature way less than what it's currently set to. The thermostat might be reporting the air temp as being 78 and then TC sets the cooling set point to something like 70. The thermostat then thinks I'm calling for a 8 degree temperature change so spins up the air handler and compressor both at 100%. In reality, I wanted a 1 degree temperature change. The thermostat could have been set to 77 and then maybe the compressor kicks on at 20% and the air handler at 40%. It'll then run at a lower speed, for a much longer time, which actually feels much nicer.
So a feature to make the magnitude of change on the real thermostat match the magnitude of change made to the virtual thermostat.
No, several Zooz temperature sensors.
I'm not sure what you mean. It asks for a number. The default was 2 degrees and I left it there. The documentation doesn't really say what this setting should do. Is this the amount it's supposed to change the setpoint of the real thermostat?
Correct. Above, you said " and then TC sets the cooling set point to something like 70". This value is determined by the Control Offset and the current setpoint of the Controller Thermostat.
Is the delta of the real thermostat sensor error roughly constant? Is it always reporting 2° too high? If so, the fix is probably as simple as just biasing your other sensors by the same amount, and then seeing if 1° Control Offset does the trick.
In other words, make TC have the same error as the real thermostat. For your example, with the real unbiased temperature being 76, real thermostat says 78 and you want to only push it by a single degree due to variable speed -- you'd set TC to 77, one degree cooler than the biased average.
When you say controller, do you mean the controlled or controlling thermostat? Sorry for being pedantic but that's the terminology in the app so I just want to make sure.
I'm guessing it's the controlling thermostat and that's exactly my problem.
Unfortunately not and I'm locked into this stupid thermostat because of Trane's proprietary communication protocol. But the thermostat sucks (Trane XL850). The prevailing theory on the Internet when you search about it is the thermostat generates enough heat to interfere with the temperature sensor. Sometimes, the AC comes on and runs and runs and runs and we can feel the temperature dropping, and the Zooz sensor that is literally 6 inches to the left of it can see the temperature dropping, and then the air temperature the thermostat thinks it is will tick up a degree warmer instead of down. When the AC hasn't been running much, it's actually pretty accurate.
Looking at the logs from yesterday, during the night and coming into the morning, the delta was a constant 1.5ish degrees. As it got warmer and the AC started running, the delta peaked at 6 degrees when the thermostat reported it being 80 degrees and the temp sensor was reporting 74.2 (set point on TC was 74). TC does work really well at keeping the actual temperature to what I set it to, but makes the AC run at 100% all the time.
The TLDR is the longer the AC runs, the delta often increases.
Sorry for the somewhat long replies. My ADHD makes it hard for me to parse out what info is relevant to the other person.
I have a screenshot in the middle of the thread. I changed the temperature on the TC thermostat down by 1 degree (AC was off) and the actual thermostat was set 6 degrees lower than it's
OK, so with a faulty temperature sensor, you're going to have a problem no matter what you do, including your suggestion for a feature that uses the thermostat temperature as the starting point for applying a smaller delta (to overcome the variable speed problem). I think the best you can do is to get all of the sensors, including the one in the thermostat, to read roughly the same (even if actually wrong). You can put in offsets in the TC app for each sensor. Once you get them all roughly agreeing, then the current TC method of pushing the controlled thermostat into calling for cooling or heating is as good as you're going to get.
I empathize: We live in Arizona, and had to replace our 3 AC units a year or two ago. They wanted to sell us variable speed with proprietary thermostats, but I knew that would probably make automation of the thermostats impossible. I've got Lutron RadioRA2 thermostats, which are really Honeywell thermostats with conventional wiring. The HVAC company came up with an alternative manufacturer who has high end systems that use conventional thermostat wiring, instead of proprietary. The executives at these HVAC manufacturers who got it in their head that somehow the world would beat a path to their door for all HA to run through their app, should all be fired for gross incompetence of not knowing what business they are in. Variable speed is nice (saves a very small amount of energy/money), but at what cost? The manufacturer we found was Lennox.
It's not just variable speed, that typically has 3 speeds. It's inverter driven units that have an infinite number of speeds...and to be fair, those are needed for a minisplit to operate properly. 1000% agree that these things should not be proprietary.
There are 3rd party devices that allow you to convert your proprietary t-stat to a common t-stat. Although most on this forum could probably handle installing these 3rd party devices, they are not intended for the average consumer to install. These devices allow the user to connect, for example, and Ecobee to a proprietary air handler. The challenge is that every device has unique features, and those are usually lost when using these converters and a standard t-stat, either at the converter level or the t-stat level. Example: Many Mitsubishi units have a dehumidification mode, in addition to heat, cool, auto and off. The converter may or may not be able to communicate that mode, but the Ecobee t-stats definitely do not handle that mode, so some functionality is lost. And then you have that added challenge of needing to go through the cloud to control the d--- tstat or have the tstat communicate with Hubitat.
