I am building a pump speed controller for my hydronic floor heat system. I have copper pipe wrapped around my wood stove and chimney to heat the coolant then its piped through my concrete floor with a variable speed pump. Problem is that there is a large lag in the system which will likely cause an overshoot in temperature as by the time the pump speeds up there is still a lot off coolant still in the stove system and by the time it gets to the outlet its too hot.
Is there a way to program the controller to also monitor the rate at which the temperature rises so the pump can head off a sudden increase in stove temperature to prevent overshoot and reduce cycling and add hysteresis at the same time?
Why do you think that hysteresis alone would not be enough? Alternatively, or in addition, instead of "monitoring the rate", couldn't you just also slow the reaction time of the system?
You haven't tested it? This is speculation? Just implement a simple hysteresis and you will have a much better view of what, if anything, you need to change.
Also, I think pump speed should depend on stove temperature, not room temperature. But it's your project...
Currently I am just leaving the pump on a highish setting so that it hits the top temp during a hot burn but this means the water temp is low the rest of the time. Operating the pump speed manually is tough as the temp tends to run away quite easily due to the lag when you let it get up to the 60 degree C mark, once it hits 70 it takes a full minute at full pump speed to clamp the temperature rise and for it to start going back down again. It is a long loop around the stove and chimney to get the water temp up high enough which is causing a longer lag time, when the water is allowed to gets too hot its still takes time before it hits the outlet so the temp continues to rise.
Yes this is speculation as I havent tried automation yet but I forsee boiling issues that I would like to avoid.
LM35 temperature sensor is mounted right on the outlet pipe as close as I can get it to the heat exchanger I built so it measures the water temp as it comes off the stove. I couldn't find any temp sensors that could handle the full wood stove temps directly so I am measuring the temp of the coolant coming off the stove, hoping to keep it around 60-70C. Its a presurized system so it should be good up to 100C same as a vehicle with the pressure release valve at 15 psi.
Ideally it would be nice that the pump accelerate if a sudden rise in water temp is seen to maintain a steady temperature to prevent overshoot but I guess I could just try it first and see what happens
Is there a programing option that increases the reaction rate based on how far the measured temp is off the setpoint? If the temp is way over then the pump speeds up quick but as it gets closer to the setpoint the PWM adjustments increment slowly type of thing?
Have you looked into a PID controller. The reaction is greater the further you are away from a set point. There is a PID library you can download in the library manager, complete with examples.