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Z-Wave Thermostat for 120VAC (self.homeassistant)

submitted 1 month ago by white_nrdy to c/[email protected]

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Hello all, I am moving into a new apartment, and was planning on replacing the thermostats with Z-Wave ones. I currently have a Honeywell T6 Pro Z-Wave in my current apartment, and was planning on picking up a couple more.

When I was at the new place today, I took a look inside of one of the thermostats and saw something I was not expecting. They are all 120VAC line voltage thermostats. The heating and cooling is shared between the building, and whether heating or cooling is on is a whole building schedule. The person in the leasing office that was touring us around the new place when we got our keys said that it switches to heat in october or November.

Attached are a couple of photos of the thermostat and a photo of the vent in the wall (although not sure if that is helpful). The thermostat is a Honeywell T651A. I am not sure of what the actual HVAC equipment looks like.

This obviously throws a hamper in my plans, and now I have to look for alternatives. I am not super familiar with 120VAC HVAC, so I wanted to get some advice from others. I believe it is a heated/chilled water system, and the thermostat simply controls the pump/blower in the wall panel (one of the photos). The fact that there is both heating and cooling is what is confusing me, since all of the 120VAC thermostats I have seen are only for heating. Obviously it all boils down to how the temperature is compared to the set point. If the building switches to cooling (which won't be a problem for about 6 months after it switches I am guessing), the comparison will be backwards.

If anyone is able to point me to any resources on how I can learn about this control system, that would be great. I found the Stelpro KI Z-Wave Thermostat which I think will work, but I am not sure what happens when it switches to cooling in the spring. I prefer Z-Wave since I have found it to be far more reliable (especially in a larger building. This is a 7 floor building with ~15 units on each floor. So there is a lot of 2.4GHz traffic I assume), however if anyone knows of a product that will work for this (if the Stelpro one won't) I'm all ears.

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[–] [email protected] 5 points 1 month ago (1 children)

If it’s like one I rented a few years ago, yes the thermostat just controls a fan, and the radiator is always hot or cold as it’s controlled by the building. I’d be inclined to use a Shelly or other dry relay with a virtual thermostat in home assistant now.

[–] white_nrdy 2 points 1 month ago* (last edited 1 month ago) (2 children)

Yeah, this is something I'm also toying with. Just get a relay and temp sensor and fake it out.

However this is not my first choice, as I prefer to still have control of things if HA is down or something. So I wonder if I could wire it in with the existing therm to provide the ability to override. Like when adding a real to a switch.

[–] [email protected] 2 points 1 month ago (1 children)

The thermostat should be a passive device and is really just a relay on its own. It could be connected to the switch pins on a Shelly.

I don’t know of a compact zwave dry relay though - so this does mean 2.4ghz wifi.

[–] white_nrdy 2 points 1 month ago (1 children)

Yeah, this was my thought (the fact that it's just a relay), and I figured I could connect it's output to the load to the switch pin on a relay instead. I am gonna look into this possibility, since it would allow for some sort of local control if things go down. My thought is I could set the temp on the physical therm to way below the target temp (in the heating months, above the target temp in the cooling). This way it kinda also acts as a fail safe. And if HA is down and we need to override it, we can. Might need to put more thought into this though.

Also, here is a Z-Wave relay I use for another project and it works well, just FYI Zooz ZEN51

[–] [email protected] 2 points 1 month ago (1 children)

Ohhh I haven’t seen that Zooz relay before, hopefully I can get it in Canada. Going to see about replacing the Shelleys I’ve got deployed then

[–] white_nrdy 2 points 1 month ago

They're great. I already have one, and they also make a double one. They also have energy monitoring as well, which is nice. I use it for control my Christmas tree around Xmas time. I have it wired together which a foot switch thing, which is great.

[–] [email protected] 1 points 1 month ago (1 children)

Or maybe something like this:

https://www.securemeters.com/uk/product/room-thermostats/hrt4-zw-asr/

The unit with the buttons on is a simple relay, which hass can control to turn things on and off, and use a heating control with a temperature sensor.
But if you hit the button on the front, it also gives 30 minutes of on, which can be handy if the system had issues.

Or you could have a hass controlled relay, but also leave the old controller wired in on a manual switch.
So if there was a failure, you could go back to the old control by manually flipping it over.

[–] white_nrdy 1 points 1 month ago

Thanks for the link. That one wouldn't work for me as I am in the US, so the Z-Wave freq for that is wrong.

I think that I settled on something like the relay and a manual override switch, if I do anything at all.

[–] [email protected] 2 points 1 month ago* (last edited 1 month ago) (1 children)

Maybe I'm wrong, but if it's whole building heating, doesn't that mean it's some sort of boiler and radiator system situation? I don't think you have actual control of the heat temperature with a thermostat in that case.

I'm not sure how AC would work in this situation if it was also via water cooling and such if you also flushing cold water through the radiators system. I don't think you'd want any kind of "smart" thermostat on it if so.

[–] white_nrdy 1 points 1 month ago (1 children)

I don't have control of the water temp, but I have pseudo control of the heating cooling by just turning it on or off. Which is pretty much the same premise as "normal" HVAC.

[–] [email protected] 2 points 1 month ago

Well there's plenty of smart radiator controllers out there if you care to go that route. If the unit you've linked to does the right wiring and replaced the existing one, then go for it.