> before cheap, reliable internet access was widely available

Cheap and reliable Internet access is still not widely available. You don't want to have your HVAC stop working because ISP botched something up. Frankly, IMO there should be zero reason for any of the HVAC control loop to extend beyond the building. Sending data from your controller to your device next to it through half the world and back is insane, and yet it is what's happening with IoT right now.

You couldn't be more right. To this day, I encourage the use of radio, dial-up, closed-circuits, cheap leased lines... anything but the Internet... for mission-critical transmission. Just way too many issues from reliability to security. Using simple lines and protocols with little to no routing let's one use equally simple hardware. If resources are left over, one can use them for boosting manageability, reliability, or security.

This is so true. As someone who worked at a company that did power monitioring and wanted to (and did) expand into thermostat control.

1) Reliable internet isn't everywhere, it cuts out a bit.

2) A lot of internet enabled thermostats are just not that great at reconnecting when the eventually loose their connection.

Though to be fair the thermostats generally will just continue on the normal schedule if they loose connectivity.

The company ended up using on a different wireless protocol to talk from the base station to the thermostats. (z-wave or zigbee fwiw).

Ironically we had a 80s error programmable thermostat in the office, which worked pretty well.

Well as far as the cheap part goes, my thinking was that these buildings definitely already have internet service in the first place, may as well just utilize that.. I supposed you make a point about reliability, but then again they're putting up with the whole 2-way radio interference, seems like the bar is already set low :P

I don't know, again I'm just thinking out loud, I'm no HVAC professional. We do use the internet to manage off site devices in my company and we tend to have more issues with power outages than we do with our ISP uptime, it's been a good solution for us.

If it is a really critical system, the proper way would be a T1 circuit between the two buildings. The circuit would only go from one building to the local telephone office, back to the other office. They tend to be pretty reliable, but expensive. You could then run a lan over this.

Funnily enough it likely is already using TCP/IP: https://en.wikipedia.org/wiki/AMPRNet

Man I really hope someone out there has streamed Spotify or NPR over this. Recurs-inception.

Whoa that is funny! Ha I had no idea