HVAC Controller

  • Howdy, wanted to share a project I am working on because I think its super cool. So I have a MySensors setup with home assistant with sensors through our my new house. We have split our house into 4 zones and want to use Home Assistant to control the zones. Each zone is being controlled by a honeywell thermostat and I refuse to use their cloud stuff to integrate. So here we are. The end goal for Phase 1 is to have a setup so that the if Home Assistant is down or broken we can turn on the Honeywell thermostat and it would function as normal.
    So I have 2 MySensor controllers one for wireless devices and the other for wired through RS485. I bought this board which has a RS485 connector, 8 inputs, 8 relays, 4 buttons, and a lcd display. 8DI-8DO-Relay-Shield-Module-Modbus-RTU-RS485-PLC-IO-Expanding-Board-Delay-Timer-Switch-for.jpg_.jpeg

    Boy was this fun to program and get working. Essentially I have it set to 3 modes.

    • Off - No Relay interactions
    • On - Relays are controllable
    • Passthrough - Relays are controlled by the inputs only - dampeners are all opened

    I wired the inputs up to the Honeywell thermostat and when the thermostat is switched on and calls for heating or cooling this board auto switches to Passthrough mode, ignoring the states coming from the controller. The only way to get out of passthrough is to set the thermostat to system off and the click button 1 to go back to on.

    Buttons are programmed as the following:

    • Switch to On mode
    • Switch to Off mode
    • Switch to Passthrough mode
    • Run the presentation and send the current state of the device to the controller (cause Home Assistant :/)

    Boom it works.

    Screenshot 2023-09-21 at 10.15.54 AM.png

    Now I just need to configure Home Assistant. As you can see I have 3 open relays for dampeners on the zone. That is for Phase 2 where we had dampeners installed in each room so that each person can control the temperature of their room/office currently building out the environmental sensors.

    Just wanted to get thoughts, suggestions, etc before I start building the sensors.

  • Wow, you're going to be busy. Hope all goes well. Give us an update when you're finished.

  • We are of like minds, Don't like the cloud based controls (that's another discussion).

    In my case I have a Bryant/Connex system, heat pump, variable speed fan and 4 zones. There's a lot going on: the 4 zones creates 16 profiles. The fan speed for a profile will depend on the indoor and outdoor temperature. The thermal fluid pump also has to be controlled. A profile will have an optimal air pressure, so there's a sensor there.

    The controller works just fine not being connected to the cloud. But I want to set the parameters remotely, Bryant/Connex can do this. I also wnat the status of the various actuators and sensors to show up in Home Assistant.

    The signals sent over the RS422 are proprietary. My plan was to reverse-engineer the signals. After doing this I'll have to experiment to get the right mix of air pressue, fan speed and thermal fluid flow for each profile.

    I'd like to do the same for my AO Smith heat pump water heater.

    I'd like to follow your progress.


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