I'm looking for simple ways to keep my beer a stable temperature, lower than room temp, during fermentation. Are there any simple ways of doing this besides buying a refrigerator for the purpose of doing this. Any tips are welcome. If any one has built homemade cooling systems i'm interested in that as well.
There are a lot of products that are available. Most are a heatsink or piezo electric coolers, claiming to cool 30° below ambient. Really depends on your fermenter type carboy, bucket etc. It's worth a Google. Having not tried them I can't point you to a good one.
BrewJacket is the only one that I've seen that interest me.
If by simple, you mean free, I would use tap water, an instant-read thermometer, and ice. If you're trying to ferment at say, 50 degrees for some type of lager, run a tub or large trash can full of water, check the temp, put the carboy in, then add ice and stir till you get to the desired temp. It will warm over the course of the day, so you'll have to keep checking and either adding ice or water to even out the temperature, but it'll give you a more stable environment, thanks to water's high specific heat, than just leaving it out in the open. If you don't have a tub or can't monopolize it for weeks fermentation, maybe check the temperature in your basement or cellar, or that of a friend.
That said, the best method would be to actually buy a fridge and a basic thermostat, especially if you plan on continuing to brew. The stability, ease of use, and peace of mind will be well worth the small investment, and are also a good chunk of what you need for a draught beer system ;)
You can put a wet tshirt or towel over your fermenter and have the evaporation cool the fermenter. Like with the ice water bucket, you'll have to check back on it every once in a while and change the tshirt or towel.
I use the brew bag here.
I throw a couple of 12oz frozen water bottles in there, and it drops the temp from room temp about 4-5 degrees. I switch them out 1-2 times a day.
In my case, since I'm only doing ales, that works as I keep the temperature about 66-68 degrees.
I place the fermentation vessel in a room that naturally has lower temperature than I desire for fermentation. Then I place a small heater inside the room and control power to the heater with a temperatur sensitive socket insert. That way I use the rooms natural temperatur to lower the fermentation temperature, and the heater to increase it. This works nice and is a very cheap solution, as long as you have a cold room.
For lager beer I place the fermentation vessel in a old fridge, and place the temperature sensitive socket insert between the fridges and the house power. That way I use the fridge to cool the vessel and the ambient temperature in the room where the fridge is to rise it.
Brewpi and an old fridge that someone has given up on and has set on the side of the road waiting for trash pick up. Hack the fridge with brewpi like components and control your fermentation remotely.