Immersion fermentation temp control?

Most of my beer projects are quickly wrapping up, which means I've been spending a lot of time thinking about new things to try.

An idea just came to me after reading through some of the more creative fermentation chiller threads and looking at jacketed conicals. I'm sure this isn't anything new, but my search magic failed me on tracking down related discussion.

Anyways, my idea is, basically, to use an immersion chiller to circulate cool/cold water to maintain fermentation temperatures (using a bucket, keg/carboy would be tricky to get the chiller in). A temp controller hooked to an aquarium pump pumping ice water (possibly stored in a nearby chest freezer) would maintain the desired temperature.

My rationale for this is that the footprint would be roughly equal to my bucket anyways, and the cost would be relatively low (coil of copper, STC-1000, aquarium/sump/fountain pump). And should be considerably more efficient than pumping cold air from the freezer into an insulated box (my original plan).

Copper being immersed in the wort for that amount of time is potentially problematic to the longevity of the copper (?), but should be good for the yeast. Temperature stratification is always an issue, but I wouldn't expect it to be bad. Sanitation, well sanitize the thing and seal it all up (modified lid). Scalability is definitely an issue, but I very rarely ferment more than a single batch at a time anyways.

So, collective intelligence of HBT, what say you? Crackpot scheme or pure genius?

Don't use copper.
Extended contact with acidic wort will cause the formation of copper sulfate, which is poisonous.
Use stainless and you'll be fine.

Thanks for the reply, definitely valuable info!

As fate would have it, I returned to the search box and found a couple of related discussions:

https://www.homebrewtalk.com/f11/immersion-lagering-coil-345265/
https://www.homebrewtalk.com/f51/immersion-coil-fermenter-308885/

Takeaways: copper = bad.

Stainless coil definitely ups the cost of this idea depending on the length needed.

I'm working on the same project right now. I have a 25' roll of stainless coil coming from NY brew supply. I'm using the 15 gallon plastic conical inductor tank and still working out the details of getting the coil through the lid. I'm planning to roll something similar to the brewhemoth design, probably a tight coil of 3-4" in diameter. I bought a 5000btu air conditioner that I've dismantled and already tested placing the condensor in water. It brought 3 gallons of water from 80 to 50 degrees in about 15 minutes.

The plan is:
Cooler with 5-7 gallons of water / glycol mix cooled by a/c unit controlled by STC-1000. Submersible pump, controlled by another STC-1000 pumping chilled fluid through the coil to cool the wort. I've also purchased 100W silicone heaters that can easily be placed on the side of the conical with aluminum tape to warm the conical when my shop gets cold in winter. I'll be sewing up a jacket to insulate the conical whether I'm heating or cooling. I've been trying to decide how to measure temperature of the conical and believe I'll just tape and insulate the sensor to the side for now. If that doesn't provide satisfactory results, I'll investigate a thermowell.

I'm building my cooling unit large enough to cool two separate conicals because I have another in a box which I'll build up after I make all the mistakes on the first one.

Stainless coil: http://www.ebay.com/itm/300309687912?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Heaters: http://www.ebay.com/itm/360404955919?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

I'll be following your progress.

Your best bet will be to control the temp of the water flowing through the coil, and run the pump constantly. If you run ice water, and measure the temp on the outside of the vessel, you'll get a ton of carry over. By the time the controller shuts the pump off, the core temp will be way below target and you'll get wild swings. I ran into this exact problem. If you control the water temp flowing through the coils, you'll get table top flat wort temps.
You will get temp stratification, unless the coils are top to bottom, but by then active fermentation is done and it shouldn't matter as much.
I'm doing the opposite of you. I put the entire fermentor in a temp controlled water bath. Chilling with ice water and measuring the carboy temp was a huge mistake. Controlling the water bath was night and day better. Same problem in reverse.

Awesome input, thanks!

Like i said, I knew this wasn't an original idea. Cool to see others implementing similar ideas.

I may look into a self-contained aquarium heater/cooler for coolant temp control to keep the footprint down. 5g batches shouldn't require too big of a cooling system (AC unit is likely overkill here).