I was discussing a herms design with a friend of mine and we were trying to come up with a heat exchanger. He suggested using a CF chiller for the heat exchanger. This sounds like a great idea. Circulate the wort through the inner tube and circulate the hot water through the outer tube. This of course would require two pumps, one to circulate the hot water and one to circulate the wort. Temp control will come from controlling the flow of hot water through the HEX by either a valve to choke down the pumps discharge or a 3-way valve acting as a face and bypass valve or mixing valve. I do HVAC work and so I could eventually automate this very easly with free parts from the office. We figure we'll give it a shot and if it doesn't work we will have a CF chiller to add to our system. I only have an immersion chiller. This set up seams logical to me because this is how some hot water systems for buildings operate. Surely someone has tried this before.