The ambient temp. in my apartment is generally around 75 degrees. The optimal temp. of the yeast I use to brew my ales is 70 - 74 degrees. In the past, I have covered the carboy with a wet towel and used an ice tray to bring the temp down 2 or 3 degrees. The beers have been fairly good, but the wet towel is messy, temperature control is spotty, and refilling the ice tray is time consuming. I'm looking for a more elegant solution.
Would the temperature inside a home-made styrafoam/insulated "cooler" be lower than the ambient temperature in my apartment? Or, would I need to add ice to the "cooler"? Keep in mind, I only need to lower the temp. by 2 or 3 degrees.