Why we shouldn't insulate the brew boilers of PID machines
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Insulating a boiler, any boiler, is to reduce the rate at which energy is lost. This is great for steam boilers, it means more of the energy you put in is retained, and it looses heat much more slowly. In addition the innards of the machine run cooler as ventilation is more effective. All fantastic for steam boilers. For brew boilers, generally…not so good.
We go to the expense of fitting a PID to that shiny dual boiler machine, to give us brew temperature stability. We want the temperature to remain as close to the set point as possible before and during a shot. The brew boiler tends to be smaller, so heating it is not a problem and it cools pretty quickly too (unless you insulate it). With non insulated boilers, your PID parameters can be more aggressive. With insulated boilers, this gives a brew boiler that when programmed aggressively overshoots the set point and takes a while to come down. If programmed conservatively, just becomes slow in responding to depressions in brew temperature and slow to return to the set point.
You might find some manufacturers insulate the brew boiler, some because they subscribe to the theory, "insulating boilers is good". Well it's not for the brew boiler! I suppose there might be machines with a smaller brew boiler that had to be insulated to get an acceptable response or prevent wandering around the set point when idle, the message there would surely be…….use a larger brew boiler. It also creates a new problem on DB machines that use shared PID parameters, because the less aggressive parameters have a knock on effect on steaming, see pid-and-steaming-why-we-should-care
I think for most machines with programmable PID parameters, I would be inclined to remove any brew boiler insulation.