The simple integrating controller in my non-modulating Thermia ground/underfloor heatpump works well. The greater the demand, the longer the compressor stays on.
In process control language it’s a cut-down PID controller (Wikipedia). Here’s a real-life example:
-
Choose a target for the circulating water. Right now the outside temperature is 3 degrees C and the target is 26 degrees.
-
Calculations
-
The integral is an accumulator which starts at 0 at switch-on.
-
Once a minute, measure the difference between the flow pipe to the underfloor and the set point. (Not the return because that varies less.) This difference is the “error” in process control.
-
If the flow temperature is X degrees below the set point, subtract X from the accumulator.
-
Or if the flow is X degrees above the set point, add X to the accumulator.
- Decisions, also once per minute
- If the accumulator is -60 or below, turn on the compressor.
- If the accumulator is between -60 and 0, leave the compressor in its current state (on or off).
- If the accumulator is 0 or greater, turn off the compressor.
- If the error is greater than 10 (i.e. too hot) turn off the compressor.
The thresholds at 0 and -60 provide hysterisis, and are adjustable.
The relationship between outside temperature and set point is also adjustable - typically a drop of 1 degree in outside temperature should increase the set point by 2 or 3.
Might be some ideas for you heat pump owners there.