Industrial dehumidifiers remove excess moisture from the air in order to prevent rust, mildew, and damage to electrical components. They also add heat to the area being treated, further reducing the relative humidity of the surrounding air. There are four basic types of industrial dehumidifiers. Air cooled devices force moist air over a cold, dehumidifying coil. The moisture condenses out of the air onto the coil and drains from the coil into a container. Water cooled dehumidifiers derive their name from how they remove excess moisture by circulating cool water through a system of coils and pipes. Industrial dehumidifiers with solid desiccant rotors use ceramic wheels or disks whose surface is covered with a specialized desiccant. Electric or gas-fired heaters are often used remove the trapped condensate from the desiccant. Other removal methods include steam and positive temperature coefficient (PTC) heaters, self-regulating devices that do not contain doped, polycrystalline ceramics. Unlike other industrial dehumidifiers, liquid absorbent devices use substances such as lithium chloride to remove moisture from air.