"HERMS" design with CF chiller.

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.

It seems like a hassle to run a second circulatory pump when an immersed coil in the HLT only requires one. Not to mention you can fill the HLT with ice water for cooling later.

That is much simpler, however I think I could get better temp control with the CF chiller. I could be less precise the the water temp in my HLT and never have to stop the flow going through MT.

p-nut said:

That is much simpler, however I think I could get better temp control with the CF chiller.

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I agree. The problem with using the heat exchange coil inside the HLT is that the volume of water in the HLT is huge, so it's not easily controllable. I've seen people either bypass it, or simply shut the pump off to try to get around this problem. Even then there is a small amount of liquid from the MLT gets heated above the desired temp when in 'bypass', which is not desirable.

But by using a CFC, when you turn off the 'heat pump', the hotter water would very quickly reach equilibrium with the MLT water due to it's low thermal mass. Not sure if you'd even need to choke/mix it. I've been pushing around the idea of using a plate chiller for this same concept. Currently, I'm using a small heat exchanger, with about a gallon of volume, based on
http://sdcollins.home.mindspring.com/HX.html
http://sdcollins.home.mindspring.com/Logic.html
(i've seen the author on this board before, cheers!) This works amazingly well, but I still get some overshoots because of the poor efficiency of my heat exchange. The smaller the volume, the better!

eccsynd said:

But by using a CFC, when you turn off the 'heat pump', the hotter water would very quickly reach equilibrium with the MLT water due to it's low thermal mass.

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That is exactly what I was thinking. My friend originally suggested a plate heat exchanger like a therminator, but we both agreed that it would have more mass than the CF.

Yeah, the Therminator is pretty big. Maybe a Shirron plate chiller would be smaller than a CFC? Guess we'd have to do the math. In either case, I agree that a CFC or plate chiller would give superior temp control over an HLT coil based solution. Plus, it's has a dual use, which is always good.

I'm thinking of piping everything in 1/2" and just before the choke valve placing a 1/2" x 1/2" x 3/8" tee. If I make the 3/8" bypass line tall enough then as I choke down the discharge of the pump it will force the hot water up the smaller pipe and return to the HLT. This is assuming the water will take the path of least resistance. I hope this makes sense. This would eliminate the need for a three way valve. The question is how tall the 3/8" line would have to be above the CF chiller.