My wife finally convinced me that climbing a ladder while drinking & brewing was a stupid idea, so I decided to buy a second pump and design a single-tier system. Since I've been thinking about adding extra layers of control to my system for awhile now, I figured I'd give HERMS a shot. Being an engineer and, by definition, a lazy cheapskate, I made it my goal to build the HERMS system using as few new parts as possible. This goal lead me to the idea of using my CFC as the heat exchanger (i.e. instead of installing an immersion coil in my HLT).
I put some pictures together and posted them to my Flickr account. I'll apologize in advance for the quality of the pics. I was too lazy to get out the tripod, so I had to free-hand many of them without a flash.
http://www.flickr.com/photos/33275630@N ... 224465695/
I did a trial run last night with 6 gallons of water in the MLT and 14 gallons in the HLT. I primed the HLT to 165F ahead of time (took about an hour) and then started with cold garden hose water in the MLT. It was able to ramp up the MLT from 75F to 160F in about 25 minutes. One interesting thing I observed about a HERMS system is that while you're guaranteed to not overshoot the setpoint temp on the HLT, you're also guaranteed to very slowly approach the final temp. This is because it's a temperature difference between two liquids that drives the energy transfer. I think you could pretty easily do step mashes with this setup, but you would need a source of nearly boiling water to minimize the step transition time. Obviously that presents some problems if you're using an HLT to do the step mashes and also want to use that water for your sparge. I might play around with using the BK, or some other dedicated vessel, as a source of much higher temp water for step mashing in the future.
Note that the BK is absent from the pictures because I was only testing the HERMS system itself. In the final setup, the BK will be located where the MLT is in the pictures, while the MLT will move to the far left on a shelf I still need to build.
I'll bring along some parts from the system to the Tech Meeting tonight, along with a few diagrams.
The only serious downside I've noticed so far with this system is that I can't brew with it until after I move....