Where I’m at, the temps flip-flop day to day, even hour to hour. In the morning it’s 35° outside, and by evening it’s 79°. I gave up keeping up with the temps and shut my unit off for the time being.
My question is why can’t HVAC units be programmed to say that if the outside temp reaches n° and the inside temp reaches m° cold, turn on the heat; conversely, if the outside temp rises to n° and the inside temp reaches m°, then turn on the AC?
My thermostat already knows the outside and inside temp, but I still have to manually switch it back and forth. I want a system that I can just set it and forget it all year round.
You don’t really need complicated control theory for HVAC (at least, on a per-room or house basis) , since the system has such a huge heat capacity and takes a long time to change. Simple set point control with 100% on/off operation and a 2 degree dead zone gets the job done
That’s generally true for most HVAC applications. Bang-bang control creates limit cycle behaviour and as long as a small oscillation in temperature is acceptable, it’s a nice simple solution.
OPs problem seems to be a discontinuity between the two limit cycles, heating and cooling. The way to tackle this is to make time series vectors of all measurements and compare them with the subjective sensation of the room temperature. That should inform the relevant set points for the control actions.
“Bang-Bang”, the simplest feedback controller in control theory.