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Electronics Engineering

How does a ceiling fan work?


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June 11, 2007 11:13PM

A ceiling fan is a type of propeller and also a mixer. The fan is usually composed of flat blades which are attached to an electric motor. The motor,most commonly, has several speeds and can often be operated in a clockwise direction or counter clockwise direction. The fan blades are normally positoned at an angle to the verticle axis of the motor. The result of the angled blades turning is that air will be gathered by the leading edge of the blade and forced to the trailing edge and a breeze is felt coming off of the trailing edge. Withinan enclosed environment such as a room in a home or business,the ceiling fan can be used to accelerate the distribution ofwarm or cooled air within the defined space, reducing energy bills and improving comfort.In the winter, when a warmer interior is required, it is generally considered the most effective operation of the ceiling fan is to"push" the airup toward the ceiling, the loweredge of the blades will be leading as the blades circle. The fan will compress the warmer air in the ceiling forcing it to desend down the walls and pull the cooler floor air up, thus mixing the air within the room and balancing temperature floor to ceiling, creating a more comfortable climate and reducing energy cost bymoving the naturally convected warm air in the ceiling into the living space. The fan operating in the "up" mode also reduces drafts. Because the temperature within the room is the same due to mixing, the controling thermostat will be reading the actual room temperature, not just the stratified temperature at its mounted height.For cooling the opposite applies, the fan should turn with the upper leading edges leading as the blades rotate, causing the air to be blown down, this will pull the hotter air in the ceiling into the cold dense air on the floor and mix it, again balancing floor and ceiling temp, the fan is "pushing" the air down and causing drafts, moving air has a cooling effect on the body, by promoting evaporation. A ceiling fan operating by itself blowing air down will provide some relief on a hot day. A ceiling fan operaing in conjunction with an air condintioner will reduce the run time of the AC unit and allow higher temperatures to be set because moving air is "cooler" than still air.