24V AC Sense?

Sense product manager @HilarioAtSense mentioned on one of my other threads about Weather Awareness that Sense has integration with smart thermostats on their radar. I’m thinking of what information these stats have that Sense can use. Setpoint is probably the most important. After that would be what the call is (Heat1, Heat2, AC1, AC2, Fan etc). What I’m wondering is if a Sense device that was able to read on the other side of the 24 Volt AC HVAC transformer could tell us a whole lot more about what is going on with the largest energy user in most homes. Maybe it would be a “smart” HVAC transformer or integrate Sense monitoring into the stat itself. If Sense knew that the gas valve was open and had information from the user clocking the gas meter Sense could very accurately measure gas usage. Multistage and modulating valves could probably also be monitored for the same purpose. Setpoint could probably be deduced from a connected thermometer if stat integration isn’t possible.

The purpose of knowing when the house uses heating energy is to see how it reacts to different outside temperatures at various setpoints. The smart thermostats give information along the lines of “your furnace ran for 20 minutes less today”. This is not a real useful statistic taken alone. Kind of like saying your car used 5 gallons less gas today. Without distance traveled and maybe speed, you can’t know if it was more or less efficient to know if you need to drive differently or get a tuneup. Monitoring therms per heating degree day would let you know if you need to change behaviors like leaving the door open or playing with setpoint. It would also allow a homeowner or energy auditor to see if improvements like insulation or air sealing worked. It could even be used to prove that replacement equipment was actually more efficient. Imagine being able to compare home energy efficiency when buying a house like you do when buying a car.

My guess is that the people at Sense have already had most of these ideas. I thought it would be fun though to get the community talking about it. Does this spark any other ideas with you?