When you think of air conditioning, I bet you think of Willis Carrier inventing the Air Conditioner 115 years ago, don’t you? It turns out, like many things, people have been chilling since long before 1902. This raises the big question: “How do you get cool without a compressor, a heat exchanger, and a whole lotta watts?” People are clever and crafty about manipulating the world to do their bidding.
The Egyptians are believed to have been one of the first, if not the first, to use Evaporative Cooling. Paintings dating back to 2500 BC show royalty being fanned in front of jars of water. Commoners would have put wet reeds in their windows and let the wind do their cooling. Cold air would blow in the window and be slightly chilled by the cold water on the reeds.
The whole concept here relies on water’s amazing thermal properties. We’ve mentioned some of them before. In this case, it is the Enthalpy of Vaporization. When water changes states, it takes a lot of energy with it. In a hot, dry desert environment, the lack of humid air makes it easy for water to make that phase change. Any open water source will readily change states into a vapor at its surface.
With a cold breeze, whether natural or artificial, more air is exposed to the water. More cool air is exposed to the room’s occupants. More heat can be shifted from the air to the water, and the people to the air, to provide a cooling effect. The increased humidity would also be an added benefit, making the air less harsh to those in the desert.
Notably, Evaporative Cooling is still a big thing today. It’s more energy efficient than AC Systems and it’s simple enough to make your own cooler in a sink with some ice water and a fan. More ambitious, you can build one in a drink cooler with a fan: https://www.etsy.com/listing/500302082/12v-portable-air-conditioner-cooler-30. The concept is simple, durable, and well tested by time.
The Ancient Romans developed two approaches that we still use today. The famous system of Aquaducts supplied their ancient cities with a constant supply of cold water. This cold water would be sent to the public wells, to the bathhouses, and to the homes of the wealthy. This constant, flowing supply provided all the water a city needed for heating, cooling, and living off of.
In the homes of the wealthy, the cold water would be sent through pipes in the walls, cooling the walls and the home at large. We’re quite familiar with this approach because it is still used today. A number of schools and offices pipe water through industrial chillers and then back through the same radiators they use for heating in the winter.
The commoners in the bathhouses were treated to a second, incredibly popular way of getting cool: cold pools. While we know the bathhouses for their heated flooring and baths, they also had cold water baths. These cool pools were called the Frigidarium. If that sounds a little too close to our modern Frigidaire, welcome to the powerful impact of Rome and the Latin language. We still have pools and pipes in our walls. Some things really do last the test of time.
Science Tackles Air Conditioning
The Romans and Egyptians didn’t study their cooling technology. For them, it just worked and that’s pretty much all that mattered. By the 16th Century however, Science would begin taking a real grip on the world. Real research would start going into how the world worked. Leonardo da Vinci would create what is believed to be the first Hygrometer. He used a ball of wool to measure humidity. His work would lead to a mechanical air cooler using a water wheel.
The 17th century would see Natural Laws emerge defining the volume and pressure properties of fluids. There were observations that water transmitted force evenly and measurements of the volume of a ‘dry gas’ such as air. This would lead into the 18th century’s discovers on fluid dynamics and evaporation. It became possible to calculate what would happen, when, and why it would happen with gasses and fluids.
The 19th century would bring with it wide spread adoption of steam engines and the push to study thermodynamics. For the first time in history, researchers were working to discover how energy was moved and transferred. This would eventually lead to our compressor driven air conditioners in use today.
The 20th century brought with it Willis Carrier’s first air conditioner. It was an industrial-scale dehumidifier developed to ensure consistency in printing with a guaranteed year-round 55% humidity. These early cooling systems were large, expensive, and clunky, but over the decades to follow, would become compact, reliable, and simple. The air conditioner we know today.
Things are going to get wild in the future. Researchers have developed a number of machines that will make the air conditioners of today into antiques of a bygone era. Special applications today can take advantage of Solid State Cooling, essentially computer chips that get cold. These have enormous potential to be more efficient and reliable than what we have today. In other areas of research, thermo-acoustic compressors have been built and experimented with. These are devices that use soundwaves to compress a refrigerant. These could very well cool the air so efficiently, a traditional refrigerant would not be needed.