Prior to the widespread adoption of modern air conditioning in the first half of the 20th century, life was far different than it is now. Summer was often a time of heat-induced doldrums, when stores and factories simply shut down during heat waves. When the temperature and humidity climbed, the only recourse for many people was to spend large portions of the workday lying about on patios or fire escapes. And the farther south you traveled, the more unbearable the heat became; places like Florida and Texas were nearly uninhabitable, and few businesses would consider permanently locating in spots so unconducive to their workers.
Washington, D.C., was so hot and miserable during the dog days of summer that President Woodrow Wilson couldn’t bear working inside the White House. Instead, he set up a large tent in the Rose Garden so he could work in a place slightly more tolerable than the stifling Oval Office.
But that sticky situation would be changed by a New York engineer named Willis Carrier, who designed and built the first air-conditioning system in 1902. Carrier knew a great deal about thermodynamics and in particular, he realized that when fluids changed from a liquid state to a vapor state, they did so by absorbing heat from their surroundings. This process, which is the basis for modern air conditioning systems, makes use of the concepts of phase changes and latent heat.
In a nutshell, when a liquid evaporates (a phase change) into surrounding air, it cools any object or a liquid in contact with it. The amount of cooling varies by the properties of a liquid’s latent heat, which is a physical property associated with the amount of heat that is needed to evaporate the liquid. If more liquid is evaporated, then more heat is pulled from the surroundings, and the amount of cooling provided by the system is greater.
Carrier’s first successful cooling project was a New York City printing plant. The results were so good that soon other factories clamored for a way to cool and dehumidify the air, a process that eventually came to be called “air conditioning.” In 1915, he started the Carrier Engineering Company and before long the company was designing and installing air conditioning systems for office buildings, theaters, and factories across America.
In 1930, Carrier installed a modern air conditioning system that cooled the West Wing of the White House. No longer would presidents conduct the nation’s business in tents on the White House lawn.
Vapor Compression vs. Water Evaporation
It’s not hard to build a DIY air-cooling system that works on principles of latent heat and evaporation. Basically, in our DIY cooler, water is mixed with air and the water is evaporated. As it does so, a great deal of energy in the airstream changes from heat you can sense, called sensible heat, to heat you can’t, called latent energy. The air exiting the blower becomes cooler and more humid.
It’s important to understand that an evaporative cooling machine is not the same as a mechanical vapor-compression refrigeration machine. It is true, however, that both processes make use of the concepts of evaporation and latent heat.
In a mechanical vapor-compression cycle, after the refrigerant evaporates inside the system’s evaporator coils, the refrigerant gas is re-compressed and cooled, which allows it to return to its liquid state. The refrigerant is reused and never enters the atmosphere, which is a good thing because refrigerants are both expensive and polluting.
But an evaporation system is based on the latent heat of water, and the evaporated water is introduced into the space along with the air. So now the air is not only cooled but humidified — which explains why evaporative coolers are best suited for dry, hot environments.
Build A DIY Air Conditioning System
Also known as a swamp cooler, this device is perfect for hot, dry days. (Its cooling potential decreases as humidity increases.)
1. Use heavy-duty scissors, or a cutoff wheel in a handheld rotary tool, such as a Dremel, to make three 9″×4 1/2″ horizontal openings near the top of the bucket, equally spaced.
2. Use a compass to draw a 3 ¼” circle in the center of the lid for the plastic pail. Use heavy-duty scissors to cut out the circle.
3. Insert the round inlet duct of your fan into the hole in the lid, from the top. Fix into place using waterproof tape (Figure A).
4. Connect the flexible metal duct to the outlet of the fan using waterproof tape.
5. Insert the bolt into one end of the vinyl tubing. Use an awl to poke a hole every ½” in the tubing (Figure B), extending back 30″ from the bolt.
6. Insert the cooler pad into the bucket. If necessary, trim it with scissors so it fits neatly around the bucket walls (Figure C).
7. Drill a pair of ⅛” holes in the bucket, one slightly above the other, just above the top edge of the cooler pad. Repeat every 90° around the bucket, for 4 total pairs of holes.
8. Set the plastic tubing atop the cooler pad, and secure it in place by inserting 4 pieces of 4″-long craft wire through the ⅛” holes and tying them off. Take care to keep the tubing section with the holes centered above the fabric.
9. Attach the submersible pump’s outlet to the plastic tubing and place the pump in the bottom of the bucket. Extend the pump wiring outside the bucket by running it under the fabric and out one of the 9″×4½” openings.
10. Fill the bucket with 5″ of water.
11. Place the lid with the fan on top of the bucket. Extend or direct the duct as desired. Connect the pump and fan to the battery (Figure D).
Enjoy your cool air! Depending on weather conditions, you can produce an airstream with 15°F of cooling, or even more. If you use a solar panel to charge the battery, you’ll have made one of the lowest-cost and greenest cooling devices possible.