@dabachata The Operation you described above is common in professional room temperature control. I have a LCN System installed (from German firm Issendorf) which uses 230V (AC) thermo-electric control for radiator control and under-floor heating valves (called LCN-AVN). These valves are controlled by the control module, which could be parameterized to a mode called “PPS” (german: Puls-Paket-Steuerung / engl: pulsed packet control). this mode is an adaption from PWM for AC voltage. You specify a time frame (less than the maximum open/close time of the valve) and the control calculates the on- and off-time of the output for the valve.
For your example it is
Mode 0: 0%
Mode 1: 25%
Mode 2: 50%
Mode 3: 75%
Mode 4: 100%
The LCN system calculates the on-/off-time via a regulator with a resolution of 2% or 0,5% (dependend of the module)…