It could bring an additional level of anticipation, by changing the gains depending on the weather, for example. But this would be really complex to manage.
I have a Netatmo thermostat to control my boiler, it uses a PID too, and probably the external temperature grabbed from internet. But to get the best efficiency, I configured my boiler (a model with condensation system) to regulate the water output temperature based on external temperature (with a sensor plugged directly on the dedicated input of the boiler, water temperature increases when external temperature decreases). I just had to adjust a bit the gain an offset of the boiler control rule to match my house insulation.
Coupled to the PID of the Netatmo, the temperature of the living room on the first floor is perfectly regulated (±0.1°C max) except on sunny days when heat is coming from the sunlights through the large windows.
But it already exists on this system. How to build it and add it to the smart thermostat ? It would require an additional loop with its own PID to modulate the thermostat PID output… For sure it would be a hard work, for probably low benefits.
I would rather consider this Smart Thermostat as a (low cost) room temperature regulation for people already having home automation equipment to improve systems with poor regulation performance. As example, I’m using this thermostat to regulate my bathroom temperature.
My towel dryer was already equipped with a Qubino flush pilot wire dimmer, and I have a Zwave temperature sensor in the room. The towel dryer thermostat being basic with the pilot wire :
- Level 5: Comfort mode. Regulates the temperature based on the potentiometer (inaccurate there is no temperature indication).
- Level 4: Comfort temperature -1°C.
- Level 3: Comfort temperature -2°C.
- Level 2: Eco mode. Regulates at Comfort temperature -4°C.
- Level 1: Frost protect. Regulates at 7°C.
- Level 0: Off.
But 1 step of the towel dryer thermostat does not change the set point by 1°C. So the comfort temperature was either too hot or too cold (I’m also suspecting my daughter damaged the potentiometer by playing with it).
With the PID thermostat the pilot wire is switched from frost protection to comfort (with the towel dryer thermostat being on the max setting) and the regulation is much better.
To have an even better regulation, for example for the central heater system of a house, I would definitely prefer buying a dedicated solution like Netatmo or Tado°, it’s not so expensive compared to sensor’s and relays (160€ for the Netatmo without special offers, Vs 100€ for my Zwave sensor+dimmer) and it’s really efficient.