Traditionally and simply, a fan can be considered a portable cooler. A fan works by circulating air rapidly across the skin, speeding up the natural process of cooling that the body uses. Normally, sweat is evaporated off of the skin as air passes across it and the action cools the body. A fan increases the speed and amount of air that passes over the skin, cooling the body faster. 
Air conditioners cool the body by reducing the overall temperature that the body is exposed to. However, they are not easily a type of portable air cooler. They can be heavy and cumbersome, making it difficult or impossible to move them around as you need them. Plus, even if you can move them physically, many air conditioners require a special plug that isn’t standard.
Evaporative coolers are a kind of portable air cooler that combines the technology of a fan with the cool air of an air conditioner. An evaporative cooler takes hot, dry air from outside, passes it through a damp pad in order to cool it and then a fan blows that cooler air into the room. Additionally, these coolers act as air purifiers or air ionizers, cleaning the air and trapping particles in the pad before passing the air into the room. The cooler air and the fan action combine the cooling impacts on your body.
Evaporative coolers are also sometimes called swamp coolers, a nickname that probably came from the fact that evaporative coolers add humidity to previously dry air. They are a type of portable air cooler that is easy to use and move around. They come with a standard plug so that you can use them anywhere and some of them even come on wheels so that you can move them quickly and easily.
Not to mention the fact that these coolers are more cost efficient to run than air conditioners. Air conditioners artificially cool the air, and so need a great deal of energy for that refrigeration process. But evaporative coolers use a natural process to cool the air, meaning they don’t need much more energy than a fan in order to work. So if you live in a hot, dry climate and would love to find the best portable air cooler for you, consider evaporative or swamp air coolers.
