I'm looking to build a system which will monitor the heating system this winter in a building I own. 3 units with 3 zones each and one common zone.
The heating system currently uses two Taco ZVC406 zone valve controllers to monitor 10 thermostats and control 10 zones via three wire zone valves (see:
http://www.taco-hvac.com/uploads/FileLibrary/102-397.pdf)
By monitoring the presence of 24vac I can log the following events:
t-stat call for heat start/end (presence or disappearance of 24vac on R or W on the thermostat connections - need to check w/ my multimeter to see which line carries 24v from the transformers in the ZVC to the t-stat and which is the return line)
zone-valve open/close (presence of 24vac on zone valve controller line 1/2)
zone-valve opened / zone call for heat (presence of 24vac on line 3)
ZVC request for heat from boiler (presence of 24vac on isolated end switch)
The pumps and what not are controlled by the boiler controller, so at the moment I'm not worried about that.
With 10 zones, I see 30 monitoring points (3 for each zone) plus the ZVC's call for heat from the boiler, for a total of 31 monitoring points.
This guy (
https://www.instructables.com/id/Log-and-Graph-24V-Thermostat-Events-Optocoupler-Ra/) built a circuit to monitor a single tstat. While I could duplicate this 31-fold to monitor each of the data points, I'm wondering if someone may have a better idea.
Once I have a method of monitoring the presence of voltage on each of the data points, I can use a Raspberry PI with a I2C Hat and an ADC to do the actual data collection and feed the information into a database.