Finally got some beer in my fermenter, and everything is working really nicely with indirect control, variation on the beer is ±0.05c which is waay better than I anticipated.
But the fridge temperatures is something that I want to have a look to see if they can be improved as from time to time the beer temp starts to trend away from the setpoint, the fridge setpoint seems to overcompensate and it takes up to 4 hours for that to settle back in.
Below is the graph the the fermentation so far, raised started at 19.5 and pitched, raised to 20 for 6hrs for the lag period then dropped to my target temp of 19 over the next 6hrs, been holding pretty steady at 19 since then.
But as you can see, the was couple of time that the beer varied for whatever reason the and the fridge has some large reactions, with some similarities in the setpoint variance, a quick dip, then a small recovery, only to dip again until it settles back in for a long period of time.
My PIDs are mostly set to indirect defaults:
Beer: Kp 20, Ti 2h, Td 0s
Cool: Kp -50, Ti 6h, Td 0s (non-default)
Heat: Kp 100, Ti 6h, Td 0s (non-default)
I set my Heat/Cool Td to 0 as I never saw overshoot with step changes in my testing with water and the default Td of 30m stopped the ramp too early.
So, there are two parts to this question
- Do these reactions seem normal? I zoomed in on one of the larger adjustments
- Under what looks like more steady state, the fridge temp alway stays somewhat below the set point
I kind of expected it to hover around the setpoint, in my testing with water it mostly did that, so I assume it has something to do with the constant absorption of heat from the fermentation.
You can see that all of the temperature control is being done via by the compressor, the heater is only ever on for those large reactions in question 1.
I thought that the large reactions could have been a result of Td of 0, as it’s role is to avoid large change, so I put them back to defaults (15:00) and it introduced a bunch of instability
So I lowered them to 5m for a period, 17:00 to 18:15, where the system seems to hold the variance but didnt trend to no Td component I would kind of expect at steady state.
At 18:!5 I set them to Td 150s, and you can see that it is stabalising.
Does all this look normal? Or is there some optimisation that I should be looking at?