How to Build a Portable Swamp Cooler

A swamp cooler uses an air mover to draw hot, dry air through a wet pad, causing the water to evaporate, which in turn lowers the temperature of the air. The same air mover then blows the treated air into the space that must be cooled. In optimum conditions this process can lower air temperature by as much as 30 degrees. Because it is difficult to supply portable swamp coolers with pressurized water, they are typically constructed so that you can easily and conveniently wet down the evaporative pad from the outside. You may need to do this as often as once every three hours to maintain maximum efficiency.

Things You'll Need

• Craft knife
• 45-gallon trash can with lid
• Evaporative pad
• Duct tape
• Nylon thread (optional)
• Clothes dryer ducting
• Air conditioner sealing foam
• Car radiator fan
• 4 "U"-bolts
• Reducing hub (optional)
• Deep cycle battery
• 8-gauge wire

Instructions

1. Use a craft knife to cut a 20-by-12-inch hole in one side of a heavy-duty 45-gallon trash can with a lid and handle clips to secure it in place. This hole will accept a 22-by-14-inch evaporative pad, which you can fix in place using duct tape or by threading nylon thread back and forth through the pad and the trash can at 10-inch intervals, effectively "sewing" the pad to the inside of its hole. Use an aspen wood evaporative pad, which will be much more effective than a blue synthetic one of the type that is more aggressively marketed.

2. Cut a much smaller hole in the opposite side of the trash can to accept the insulated concertina trunking (clothes dryer ducting); this hole will transfer the treated air from the portable swamp cooler to the duct work serving the location to be cooled. Slip the ducting two inches inside the trash can, secure it in place with nylon thread or duct tape, then use air conditioner sealing foam to close any leaks around the ducting so no treated air can escape around the edges.

3. Install the fan from a car radiator as an air mover. Use the most powerful unit that fits your budget, case size and tolerance for operational noise, balancing relatively small physical size with the ability to move a useful volume of air. Attach the car radiator fan to the inside of the trash can so that it covers the exit hole to the duct work. Fix it in place using "U"-bolts threaded through its integral mounting flanges; pass them through the body of the trash can and bolt them tightly to the outside. If necessary, obtain a reducing hub from the HVAC aisle at a home improvement warehouse to step down from the size of the car radiator fan to the duct work; a 20-by-6-inch reducing hub will usually be ideal.

4. Connect a fully charged deep cycle marine or recreational vehicle coach battery to the terminals of the car radiator fan, using 8-gauge wire. If the fan sucks instead of blowing, simply reverse the connections. Soak the evaporative pad, clip the trash can lid in place, and within seconds cooled forced air should be coming from the open end of the ducting.

5. Allow air to escape from the opposite end of the cooled area to keep back pressure from building up; back pressure will stifle the effectiveness of the portable swamp cooler. Experiment with opening a window to allow air out. Too meager an opening will cause humidity to build intolerably in the room; too large an opening will allow the treated air to escape too rapidly.

Tips & Warnings

• Place woven screen material over the outside of the evaporative pad's hole to keep insects from entering the cooled space along with the treated air.

• Use a solar panel fitted to the top of the portable swamp cooler to recharge the deep cycle battery.

• A portable swamp cooler will work only if it is located where it can draw fresh hot, dry air in from outside.

References

• Consumer Energy Center: Evaporative Cooling

Resources

• Metafilter: Good Portable Swamp Coolers