[phasetransition]

Upvoted,

BACnet already exists as an ISO standard: https://www.iso.org/standard/37298.html https://bacnetinternational.org/

The example application in the Ethernet Alliance one-pager on single pair Ethernet is HVAC: https://ethernetalliance.org/wp-content/uploads/2020/10/EA_T...

[amluto]

FWIW, if this were my startup, I would probably use 10BASE-T1L. The programming model is simple, and cloud or other “smart” integration is natural if the system already uses IP. For that matter, one ought to be able to support wired 10BASE-T1L and wireless Matter/Thread thermostats without much duplicate effort.

This could be prototyped on a BeaglePlay :)

[phasetransition]

FWIW,

BACnet allows multiple PHY implementations, including 802.3

I suspect that 802.3.cg is also kosher, but haven't looked in detail. It's been 5 years since I looked seriously at whether BACnet was the correct solution for a product family.

Single pair Ethernet is indeed cool tech.