I work in a medical lab and we get a lot of reagents delievered to us in styrofoam coolers that will fit a 5 gal carboy perfectly. In these styrofoam coolers come reusable ice packs. Now keep in mind all of this is thrown out once we put the reagents away. So I had an idea. I took about 50 of the ice packs and 2 of the styrofoam coolers and started to have a brain storm while I should be making sure this patients lymphs are not atypical. Anywho i digress. My idea is to place a primary carboy nearing the end of its fermentation stage in one of the coolers standing upright on its side. At the same time load up some kind of ice water bath in the other cooler sourrounded by the ice packs. Place a aquarium pump in the ice bath in the other cooler and with it somehow rig up some type of tubing that will run into the other cooler and wrap around the carboy. This will give me 2 insulated areas, one with the carboy with the tubing wrapped around it with the cold water flowing thru and the other cooler with the water,ice packs and aquarium pumps. I think this will probably get the beer to right above freezing and keep it there for a few days while only changing out the ice packs maybe once to keep the water cold. You could probably crash cool in 3 days or so without having a spare fridge like most of us dont. My guess is that this will probably also work with lagering. But im a n00b and dont really know all that much about the lagering process.
My idea for the pump was backed up by Edworts circulating chiller post. Ill take some pics of the coolers when I get home from work tonight to show you what i mean. And below is Edworts chiller post.