Mechanical revolving blade fans are made in a wide range of designs. They are used on the floor, table, desk, or hung from the ceiling (ceiling fan), and can be built into a window, wall, roof, etc. Electronic systems generating significant heat such as computers incorporate fans. Appliances such as hair dryers and space heaters also use fans. They move air in air-conditioning systems and in automotive engines. Fans used for comfort inside a room create a wind chill by increasing the heat transfer coefficient but do not lower temperatures directly. Fans used to cool electrical equipment or in engines or other machines do cool the equipment directly by exhausting hot air into the cooler environment outside of the machine so that cooler air flows in. There are three main types of fans used for moving air, axial, centrifugal (also called radial) and cross flow (also called tangential). The American Society of Mechanical Engineers Performance Testing Code 11 (PTC) provides standard procedures for conducting and reporting tests on fans, including those of the centrifugal, axial, and mixed flows.