Underfloor heating hack

I have tried to find some basics how a standard underfloor control system is regulating the heating, but haven't, so started with checking up our own temperature control system from LK(TCS).

I used Node-Red, with Raspberry Pi(RPi), sensing when the TCS applied voltage to the actuator. Since the actuator is running on 24 VAC and the input on a GPIO PIN is maximum 3,3 VDC I used a optocoupler to level shift. Schematics below

Please find another post here where I realized, using Shelly 1 and NodeRed, the regulating of the underfloor !!

Lesson learned 
according to the first picture.

• The top image
• Covering a timespan of 2 hours, shows that when calling for heat, there is a time proportional output with the cycle of 10 minutes
• The middle image
• Shows that the actuator "on time", measured in seconds, increases with an increasing demand for heat.
• In an normal condition, outdoor temperatur around 5 C, the "on time" is never more than 300 seconds
• Once a day, around 19:00, the actuator is activated for almost 600 seconds
• The bottom image
• Is showing the measured temperature in C. Sun is shining in the middle of the day making a quick rise in temperature.

Thoughts for further development
Reading the manual for LK:s latest TCS, the above observations and control system theory gives some thoughts for building Your own;

• The running time for the actuator is approx 6 minutes. (The time from applying actuator voltage until the valve is fully opened)
• Use a time proportional output with cycle time of 10 minutes
• Once a day activate the valve, for 600 seconds, so it doesn't get stuck
• Use a PID controller
• A "Holiday function" is setting the target temperature to 12 C
• Circulation pump control, which activates 6 minutes after the system wants heat

Valve sensing

The following circuit is used to detect the voltage applied to the actuator. Via the optocoupler the actuator circuit is totaly isolated from the RPi. The output from the optocoupler is a transistor with open collector which is connected to a RPi GPIO pin. The pin is set up as input with a pullup.