I am very interested in this, first post here ( I post occasionally over at the Northern Brewer forum, but the DIY section here is much more active - impressive stuff ), I was going to post after doing some experiments, but that might be a while since it is plenty cold enough here for ales in my basement, and I've got some home remodeling projects to finish up. So I thought I'd post before this thread goes 'cold'... so,
to get to the point....
I agree, it should only take a very small amount of stainless tubing in contact with the wort to move the temperature from ambient to fermentation temps (obviously depends on your ambient and whether doing ale or lager). I was planning on taking a thermowell-like tube, running a 1/4" OD plastic tube down into it, and pumping chill water through it with a tiny fountain pump (the smaller the better - less heat generated by the pump). If a 25' tube can remove maybe one degree F per minute at a 25F differential (guessing on that rate), then 1 foot in wort should be able to bring it down ~2~3F per hour. Seems like enough to offset fermentation heat and bring it below ambient with decent insulation.
So, if anyone has a thermowell that could try this before I get around to it, it would be interesting to see some data. You just need to break out the 1/4" tube so you can pump chill water into the thermowell, and drain from the 1/4" tube. I was going to drill out a PVC elbow, run the 1/4" through the hole, run the pump line and 'co-axial' line from the thermowell with the 1/4" inside it through holes drilled in caps on the elbow, and aquarium seal it all up. I'll try to draw this up when I have some time later. Insulate the line, insulate the fermentor in a cooler or just wrap with bubble wrap.
This has so many advantages over the foam boxes:
1) Liquid-liquid thermal transfer with a bit of SS between. Compare to the foam box with ice transferring through plastic bottles to air, transferring through the fermentor walls to the wort. Huge advantage in eff%, which means pump/fan runs less, so less heat added to the system
2) Total surface area could be much less, lower heat loss and less thermal mass to bring to temperature.
3) Should just about eliminate condensation build up - all the coldest parts are internal, or easily insulated (pipe foam insulation on the lines).
4) Other than the thermowell (buy or make) and a bit of low-pressure plumbing hook up, thermostat hook-up, almost no other 'construction' to do (may be a minus for you 'gadget freaks'
).
5) I bought a 12V/.7A fountain pump to try with this - the 12V pump could be wired direct to a house-style thermostat, no need for a high voltage relay.
6) Could run multiple fermentors at different temperatures off the same ice water reservoir (which could be kept in a refrigerator to eliminate/reduce ice re-filling.
There was a thread on this previously, but using a water bath for the fermentor. If I find it I'll link to it. Similar advantages, but I think putting the chiller in the fermentor is even better.
cheers - kenc (no affiliation with Zymurgy mag, I just liked the rhyme)