Since the fan motor gives off heat and costs money to operate, you should run the fan only when a person is in that room. When a liquid changes to a vapor, it evaporates and absorbs heat. Evaporative coolers get their name from this process. These devices blow air over a water-soaked pad. As the water evaporates, it cools the air.
Various models are available that mount on the roof, wall or window.
It blows outside air over the wet pad and then into your home. This will increase the humidity. Slightly higher indoor humidity usually isn't a problem for inland areas of southern California. This type of cooler puts no additional humidity into the indoor air. However, evaporative coolers use from 5 to 15 gallons of water per day.