The problem is as follows, my friend and I want to make a fridge that uses cold air from outside, instead of an electrical compressor. We plan to simply use a fan, and pipe to bring cold air from outside into the fridge. So if our variables are: - Pipe length / Diameter - Fan speed / CFM - Wind temperature outside - Temperature inside the fridge - Desired temperature to reach inside the fridge - Heat capacity of fridge contents - Volume of fridge / Volume of contents How do we calculate, how long the fan needs to run, at what CFM to bring the temperature in the fridge from its current temperature down to the desired temperature in a particular amount of time? Assuming the outside temperature is always below the desired temperature. Thanks.