I agree! The main reason I use HA is for monitoring and alerts, I have pets, so on a hot summer day an AC failure can be lethal, and in the winter it can get down to -30F, where heat failure can get dangerous VERY quickly.
The next step on my end is to add a temp probe to the surface of the HVAC output vents, so I can detect within maybe 1 minute if the heat or AC is not functioning properly. I have had the device hooked up for a few days, so far it is working 100% on all 3 inputs (heat/fan/cold). I have yet to mount it in a permanent location, I am still deciding if I want to wire it to the output terminals of the zone controller or the input terminals of the HVAC, either way I was going to replace my wiring to use brown thermostat wire.
Or maybe not, the red wire makes it very obvious which one is the device! Here are some more details of how it works and what I used to build it.
Power
The Shelly i3 operates on 24 to 60VDC, so a spare 24V passive POE injector from some Unify equipment did the trick, where VDC is provided to the blue conductors and Ground to the brown. I pulled some CAT6 wire apart to connect the ethernet jack to the i3 and the DC side common block. I did run into an issue with polarity, my i3 wiring does NOT match the diagram on the Shelly site:
You may notice from the first set of images that my i3 has the N at the end… and I did need to connect that to ground to get it to function properly. My best guess is they changed the design at some point, but attention needs to be paid to the polarity. I used Wago lever nuts to connect the stranded wire from the i3 to the solid wire going to the terminal blocks.
The AC relays need… AC, and you may be able to tell from the image, but the zone controller has no “common” AC wire terminal, however it is fully powered by the HVAC transformer so there are power terminals on the right side, I ran an insulated jumper closer to the red wire instead of a bare wire across the device. Took about 5s with a multimeter to figure out which one was common relative to the Rhc wire, and I connected it to the blue conductor in my red wire, which is the standard color for 24VAC common. With that in place the relays function properly.
Signals
I connected the fan wire to the center relay, then connected the cold to yellow, which happens to be the standard color, and heat to red. Once I get some thermostat wire I will probably replace those so it is more consistent with the standard colors, but for now the wire I am using is for fire protection systems (hence the read insulation) and does not include white or green.
The DC side of the device connects the i3 inputs to the relay NO relay contacts, and the blue common block wiring to the COM relay contacts. The relays are Form C but I am not using the NC contacts.
When a zone controller relay trips to send a signal to the monitored wires, the device’s relay is also tripped, closing the relay and energizing the respective input wire on the i3. HA receives the change from the i3 a fraction of a second later. Interestingly, my blower fan will turn off during the heating cycle for 35s or up to 4 and a half minutes… that may be completely normal but it is inconsistent.
Parts
I had most of the parts to build this in my stash of spare parts and supplies, but needed the DIN mounted relays. I chose Phoenix Contact 2900300 relays, 24VAC with only 11ma coil current. They are very narrow which allowed me to use individual terminal blocks for every wire on the small rail.
The terminal blocks themselves are Dinkle DK2.5N series, I had a ton of blue and yellow left over from my security system wiring project so I used those.
The wire was pulled out of an 8 conductor bundle, nothing special there, the DIN mount for the ethernet jack is also pretty standard, but it did have a plastic end cap that allowed me to adhere the i3 in a way that was removable in case I needed to adjust any of the wiring.
Next Steps
In addition to the temp probe for early warning of system failure, I was going to make a couple of general alerts based on the state of doors, windows, outdoor temp, and other environmental monitoring:
IF the heat or cold turns on AND there is a door or window open AND carbon dioxide/voc are within tolerance AND the target temp trend is NOT in the direction of the outdoor temp THEN send an alert
What that basically means…
It may be 70 degrees outside, but it is 74 inside and going up, so the AC turns on, but I have the deck door wide open. Since the target trend is temp down, and the outdoor temp is below the current temp, do not send me an alert
OR
It may be 50 degrees outside, but it is 68 inside and dropping, so the heat turns on, and I have the deck door wide open. Since the target trend is temp up, and the outdoor temp is in the opposite direction, send me an alert, UNLESS there is high CO2 or VOC, in which case the door is open to air out the house, so the alert will be skipped.
After winter, If I have collected enough cold weather data, I will work on interruption of the main zone thermostat signals to either send heat earlier if the temp trend is down and low, or delay it if the tread is expected to go up in the near future.