Introduction: Portable Evaporative Cooler (swamp Cooler)

In areas with low humidity, regular air conditioners don't work very well. A simpler solution uses water evaporation to cool and humidify air. These are called evaporative coolers or swamp coolers and are used in homes all over the Southwest U.S. Air is pulled by a fan across a wet pad, which lowers the air temperature by 20-30 degrees, and provides much needed humidity as well.

We attend a week-long festival in the remote Nevada desert, where daytime temperatures climb well over 100 degrees F.In this situation, it is necessary to be completely 'off the grid', self contained, and self reliant. In order to remain comfortable, we made portable swamp coolers out of common materials, powered by solar panels, to cool our enclosed living spaces. They have also been used at home in more permanent installations to cool greenhouses. Additionally, they could provide temperature regulation to desert homes where electrical power is not available.

Step 1: Materials

36-44 gallon heavy duty trash can with lid
Evaporative cooler pad x 12 feet x 29 inches
Hardware cloth or chicken wire x 6 feet x 24 inches
Submersible 12 volt bilge pump x 1
1/2 inch irrigation tubing x 10 feet
1/2 inch T-connector for irrigation x 1
Automobile radiator fan or solar fan x 1
16 inch diameter HVAC tubing
Large drain pan
U-bolts x 3
Solar panel and deep cycle battery

Step 2: Examples of Materials

With the exception of the fan (and solar panel if you use one), most everything can be found at a Big Box Hardware-type store (Lowes, Home Depot, etc). Much of it can be scrounged for free, as well, if you are patient and resourceful.

Step 3: Assembly

First you need to make a way for the air to pass thru wet padding:
Cut 2.5 inch diameter holes in sides of garbage can. A drill bit made for cutting doorknob holes works perfectly.  Leave the lower 10 inches of the garbage can intact, without holes. Line the inside of garbage can with blue evaporative cooler padding x two layers. Keep it in place with hardware cloth or chicken wire on the inside. Keep that in place with the U-bolts drilled thru the garbage can sides. Now you have a garbage can with ventilation holes, lined with evaporative cooler pads which are kept in place with hardware cloth wire.

Now you make a dripper to keep the padding moist:
Make a circle with the 1/2 inch diameter irrigation pipe; join with a 1/2 inch T-piece. Drill very small holes about every 2 inches in bottom side of circle for water to drip from. (If you want to get really fancy, you can insert drip irrigation emitters in the holes, which will give you a known gal/hour drip rate. )

Now we need to get the water up to the top of the pads:
Place 12 volt submersible pump in bottom of garbage can. Connect the pump to the drip ring with 1/2 inch tubing. Feed wiring thru one of the holes so you can connect to battery power later

Next, we need a fan at the top, which will suck air in, thru the holes in the sides of the garbage can, thru the evaporative cooler padding, and out the top into the HVAC tubing which will deliver cool, humidified air to the location of your choice:
Cut out a circle in top of garbage can lid and mount fan.Make sure it blows upwards! Used auto radiator fans are cheap, blow lots of air, but use a LOT of amps. So we eventually bought a solar-type fan for about $200 that runs forever on a 45 watt solar panel hooked to a deep cycle 12 volt battery. An auto radiator fan  will use more juice than this system puts out, and only runs about 20 hours before draining the battery faster than the solar panel can charge it. However, if you have enough solar panels, the auto fans REALLY put out lots of cool air, compared to just a breeze from the solar-type fan.

Wire it up! Soldering connections is a good idea, but you may want to make the wires to the top lid/fan/HVAC tubing component unpluggable so they can be removed for easier packing for transport. I also installed a switch to cut off the pump in the cool morning hours and just have a fan. It gets too cold, otherwise!

The entire unit will need to sit in a catchment basin, to collect water that drips out from the sides (this dripping is inevitable). Big black tubs from a garden center work well. you may need to drill holes in the bottom of the garbage can to allow this water to percolate back inside to the pump.

Step 4: Where Stuff Goes

First photo shows completed body without top.The next three views are looking down into the cooler, showing the pump and drip tubing. Next is a view of the top with fan installed. Then, a view of the whole thing put together, and one of it in use. Solar panel is not in view.

Step 5: Running It

You'll need about 6 gallons to fill it and wet the pads. Afterwards, uses about 2 gallons/hour, depending on the humidity and temperature. More holes in the drip ring may lead to more water usage. And that's why the emitters might help decrease water use. For home/permanent use, install a toilet float valve hooked up to a permanent pressurized water source.

Step 6: Swamp Cooler in Action in the Nevada Desert

The camper is called a Flip-pac, the sleeping area is over the cab of the truck. The swamp cooler HVAC tubing is directed to our sleeping area. The solar panel (it is pretty dusty, here) keeps the deep cycle 12 volt battery charged. The battery provides a consistent flow of electricity to the swamp cooler pump and fan. By the way, the green structure behind the truck is our fancy shower.