Are PIDs effective on heat exchanger coffee machines?
A PID (electronic temperature controller) isn't necessary for stable brew temperature on a heat exchanger (HX) Italian espresso machine. Any HX espresso machine with a well engineered thermosyphon (water reticulation system) can be stable with either PID or with pressure stat control.
When PIDs first arrived on the scene for HX Italian coffee machines many manufacturers crudely replaced the pressure stats. In engineering terms these machines were a failure as without a thermosyphon modification water in the HX tube would super-heat. This mean't that before pulling a shot you need to flush the super-heated water through the group head. Obviously, the PID on these machines was ineffective for setting of brew temperature control on these Italian espresso machines machines.
This is all different with PID HX coffee machines that have been engineered for a PID from the ground up. With these Italian espresso machines you can get fantastic thermal stability as well as effective brew temperature control from PID adjustments.
Most people will set and forget, but espresso aficionados will love the ability to play with brew temperature. If you want a more chocolatey, bitter-sweet espresso you can set the temperature up into the high 90s. If you want something brighter and more acidic you can set the temperature down in the low 90s. Awesome!