This Instructables shows you how I created an evaporative cooler out of a trash can.

"An evaporative cooler (also swamp cooler, desert cooler and wet air cooler) is a device that cools air through the evaporation of water. The temperature of dry air can be dropped significantly [up to 30 degrees under perfect conditions] through the phase transition of liquid water to water vapor (evaporation). In extremely dry climates [example: Burning Man], evaporative cooling of air has the added benefit of conditioning the air with more moisture for the comfort of building occupants."

Source: https://en.wikipedia.org/wiki/Evaporative_cooler

The evap cooler is used for cooling a large tent during Burning Man and other camping trips in dry and hot areas. A few drops of essential oils to the water deodorizes the space as well. The evap cooler is placed outside the tent, hence the use of an optional filter to keep dust out.

Inspiration for this evap cooler came from FigJam's post.

Step 1: The Science of Evaporative Cooling

Evaporative cooling is the conversion of liquid water into vapor using the thermal energy in the air, resulting in a lower air temperature. The energy needed to evaporate the water is taken from the air in the form of sensible heat, which affects the temperature of the air, and converted into latent heat, the energy present in the water vapor component of the air, whilst the air remains at a constant enthalpy value. This conversion of sensible heat to latent heat is known as an isenthalpic processbecause it occurs at a constant enthalpy value. Evaporative cooling therefore causes a drop in the temperature of air proportional to the sensible heat drop and an increase in humidity proportional to the latent heat gain. Evaporative cooling can be visualized using a psychrometric chart by finding the initial air condition and moving along a line of constant enthalpy toward a state of higher humidity.[8]

A simple example of natural evaporative cooling is perspiration, or sweat, secreted by the body, evaporation of which cools the body. The amount of heat transfer depends on the evaporation rate, however for each kilogram of water vaporized 2,257 kJ of energy (about 890 BTU per pound of pure water, at 95 °F (35 °C)) are transferred. The evaporation rate depends on the temperature and humidity of the air, which is why sweat accumulates more on humid days, as it does not evaporate fast enough.

Source: https://en.wikipedia.org/wiki/Evaporative_cooler

Step 2: Materials Needed

For the water reservoir

- Trash Can

- Tools to mark and cut the plastic can (Sharpie, drill, saw, ruler, etc.)

For the wet foam

- Eggcrate Light Diffuser

- Dura Cool Foam

- 12V Water Pump

- Tubing

- Zip Ties

For the fan

- Endless Breeze Fan-Tastic Vent

- Wood scraps

- Motor Speed Controller

For the air filter (optional)

- Air Conditioner Filter

- Aluminum U-Channel

- Tools (rotary tool with cutting wheel, drill, screws, washers and nuts)

For the lid

- Expanding Foam

- Flat piece of wood

- Silicone Caulking

- Plastic Food Wrap

- Masking tape

NOTE: All links are just examples. You should definitely check for specifications and better prices before purchasing from the links provided.

Step 3: Cut the Fan Hole

Trace the body of the fan on the upper 2/3 area of the trash can.
Cut the hole by drilling the corners of the square, then sawing the straight lines that connect the dots.

Step 4: Air Filter Frame

Using the air filter to measure, mark the aluminum at the corner points of the filter.
Cut "V"s (2 x 45 degree angles from folding point) on both sides of the channel at the corner marks.
Fold the aluminum at the "V"s to form a 3 sided frame. Check that the air filter slides snugly into this frame.

Step 5: Cut the Filter Hole

Trace the the aluminum frame (with the filter still inside) on the opposite side of the fan hole, also on the upper 2/3 area. The "opening" of the frame should face down so air filters can be replaced.
Remove the filter and trace the inside of the frame, drawing a smaller 3 sided rectangle inside of the bigger one.
Connect the lines you just drawn to form a complete small rectangle.
Cut the small rectangle out.
Attach the frame to trash can by using screws and nuts.
1. Drill holes small enough through both sides of the U channel and through the trash can for the screw to go in.
2. Drill holes large enough through the outermost side of the U channel for a screwdriver head to fit through.

Step 6: Rewire and Attach the Fan

Rewiring:

Open the body of the fan.
Remove the speed dial and install the motor speed controller.
Rewire the fan, if needed, to ensure that the power cable stays out of the way and outside of the trash can.

Attaching:

Attach wood scraps to the plastic body of the fan, making sure that, when inserting the fan from the inside of the trash can, the wood scraps would prevent the fan from falling out.
Attach the wood scraps to the body of the trash can, making sure that the fan blows towards the outside of the trash can.

Step 7: Create the Wet Screen

Eggcrate base:

Cut the eggcrate to fit snugly insidethe trashcan, as deep as it goes, and as high as the edge of the can. The goal is to create a perfect wall to separate the "fan side" from the "filter side."
Attach the water pump to the bottom of the eggcrate using zip ties.

Wet screen:

Wrap the eggcrate in the Dura Cool foam.
Use zip ties to keep the foam attached to the eggcrate in several spots.
Use foam scraps to cover as much of the eggcrate as possible.

Hose:

Measure the hose to go from the pump to a corner of the wet screen, then across the top.
Cut the hose to the desired length and cap one end.
Using a heated small nail, make holes on the section of the hose going across the top. The goal is to get water evenly distributed on the wet screen. Start with fewer holes than you think you need. Add holes where/if needed. Too many holes will cause one side of the screen to be dry.
Using zip ties, attach the hose to the wet screen, making sure the holes you just made face the screen.

Step 8: Create the Lid

The lid is one of the most important parts of the evap cooler. It not only keeps the unfiltered hot dry air from being sucked in, it also prevents the wet screen from moving forward/backward inside the trash can.

Tape the wet screen in position using masking tape.
Put a layer of plastic wrap loosely on top of the trash can and wet screen as if creating a saggy plastic lid. Add some masking tape to secure it in place.
Cover one side of the flat wood piece with expanding foam, then immediately and carefully invert it on top of the plastic wrap.
Add a weight to the top of the wood piece to secure it in place.
Let it cure for 24 hours.
Remove the weight and open the lid.
Carefully remove the plastic wrap. Some foam may still be soft/uncured in the thicker areas (as can be seen in the picture). Wait for any uncured foam to cure.
Remove the wet screen from the trash can.
Put a layer of plastic wrap around the edge of the trash can.
Spread a bead of silicone in the lid groove that formed around the trash can edge.
Invert the lid back on top of the trash can, add a weight, and wait for the silicone to cure (24 hours).

Step 9: Finishing Touches

Make a small hole as high as possible on the side of the trash can where the pump wires come out.
(Optional) Make a water gauge by making two holes on the bottom of the trash can, vertically aligned. The holes should be as low as possible and as high as the water level can be. Insert a clear air tubing connecting both holes, seal the edges of the holes so water does not leak, and add 1 gallon of water at the time, marking the level at each addition.
Use silicone caulking to seal gaps that would let air to bypass the filter and wet screen (around the filter frame, around the fan, etc.).
Connect all wires to a 12V battery and test that the fan and water pump work. Verify that the wet screen is evenly wet and water is not splashing on the filter or the fan.

If you live in a dry place, you may be able to test if the whole system works by noticing a decrease in temperature of the fan wind.

Enjoy the cool moist breeze!