Fans and air coolers are both used to cool down a room, but they work in different ways. A fan simply circulates the air in a room, creating a breeze that can make you feel cooler. It does not actually lower the temperature of the room. On the other hand, an air cooler uses water to cool down the air in a room. It works by drawing in hot air and passing it through a filter that is soaked in water. As the hot air passes through the filter, the water evaporates, which cools down the air. The cooled air is then blown back into the room by a fan.