This University of Waterloo engineering student hacked together a primitive air conditioner from a large fan, garbage can, some copper and vinyl tubing, and a few zipties and hose clamps.
The garbage can is filled with ice water, which is then fed by gravity (a siphon) through the copper tubing coiled along the back of the fan. The hot air passing through the tubing warms the cold water, cooling the air. Waste warm water is then pumped outside.
The system will cool an average room to a comfortable level in approximately 15-20 minutes. Depending on flow rate, a full bucket of water will last approximately 1-3 hours.
It doesn't rip quite as hard as central air, but for less than $30 CAD I'm not complaining.
