Ok. That looks the same as what I see when I get a sudden cold snap - it undershoots the set point by maybe 0.5C, remains steady at that value for quite a while and then gradually creeps up to the desired set point over a couple of hours. After a day or so of the new cold weather conditions it has fully adapted and doesn't undershoot.
My understanding is that this is caused by the tuning of the PID controller in the HR92 having adapted to the previous conditions (the degree of heat loss through the walls due to outside temperature thus the amount of heat and valve position required to reach the set point) and when the operating conditions change dramatically (and enabling load scaling would count as a dramatic change in operating conditions from the point of view of the HR92 which is unaware of it) so it will take time for the Integral and Differential factors to adjust themselves to match.
What it also shows is what a good job it was previously doing of predicting how early to start closing the valve to reach the set point quickly and without any overshoot. (As the undershot temperature is so flat) When it gradually creeps up over another hour or two this is the integral action of the controller gradually increasing the valve position and heat demand due to a sustained undershoot.
I suspect another couple of days and it should finish adapting.
My understanding is that this is caused by the tuning of the PID controller in the HR92 having adapted to the previous conditions (the degree of heat loss through the walls due to outside temperature thus the amount of heat and valve position required to reach the set point) and when the operating conditions change dramatically (and enabling load scaling would count as a dramatic change in operating conditions from the point of view of the HR92 which is unaware of it) so it will take time for the Integral and Differential factors to adjust themselves to match.
What it also shows is what a good job it was previously doing of predicting how early to start closing the valve to reach the set point quickly and without any overshoot. (As the undershot temperature is so flat) When it gradually creeps up over another hour or two this is the integral action of the controller gradually increasing the valve position and heat demand due to a sustained undershoot.
I suspect another couple of days and it should finish adapting.
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