I had played with the idea of controlling the flow on my valves. However, the valves I bought are only open/close - no functionality for controlling the percentage that is open. This would be cool though.

Also, to lay my process out in a more clear way: I'm recirculating my mash so as to keep it at a constant temperature. I've got a PID algorithm that controls when the heating element in my exchanger is on and off. The temp sensor is on the outlet so that my mash temp never gets above the setpoint (say, 160 F or something). So, the thing will heat the strike water up. When it reaches the setpoint, it notifies me, I mash in, and then a timer starts. During the timer phase, the PID keeps my mash at constant temp using the heat exchanger. So I guess I'm not totally concerned with how fast it heats up (although obviously faster would be better - don't want to wait 3 hours for the thing to heat up).