Need to combine both bi-phase control for my espresso group head using peltier elements and heat sinks. The main question, do i need to cool or is heat alone ok?

Background, the 'brew group' is 9lbs of brass in total. it gets heated via a thermosyphon system to keep it hot. The problems start when you leave the machine idle (don't pull shots for a while) the head cools a bit, cools the brew water down from ideal to create bitter shots. It gets back to temp when you begin pulling shots again every two minutes.

I want to match brew head temp to the ideal 95C for espresso, all the time. Since this 95C happens when you pull consecutive shots due to thermosyphon, i would only need to heat the head when pulling shots form idle.. thoughs?

I need to PID control the brew boiler too, right now it uses a std. dead band controller +/- 1C. I want to add a PID to replace it, also add a nice PID to control the low side of brew temps.. as i said, i 'believe' the high side would be controled via feed water (not thermosyphon, that is only for 'off' temp maint.) from the already PID'd brew boiler.

-- Jeff Check (jcheck10@comcast.net), February 08, 2005