Ceiling fan

Fans do not reduce air temperature or relative humidity, unlike air-conditioning equipment, but create a cooling effect by helping to evaporate sweat and increase heat exchange via convection.

Originally operated manually by a cord[1] and nowadays powered electrically using a belt-driven system, these punkahs move air by going to and fro.

Instead, a stream of running water was used, in conjunction with a turbine, to drive a system of belts which would turn the blades of two-blade fan units.

He continued to make improvements to his invention and created a light kit fitted to the ceiling fan to combine both functions in one unit.

From the Great Depression of the 1930s, until the introduction of electric air conditioning in the 1950s, ceiling fans slowly faded out of vogue in the U.S.,[2] almost falling into total disuse in the U.S. by the 1960s; those that remained were considered items of nostalgia.

Meanwhile, ceiling fans became very popular in other countries, particularly those with hot climates, such as India, Pakistan,Bangladesh and the Middle East, where a lack of infrastructure and/or financial resources made energy-hungry and complex freon-based air conditioning equipment impractical.

The fans became the energy-saving appliances for residential and commercial use by supplementing expensive air conditioning units with a column of gentle airflow.

Other American manufacturers of the time included the Hunter Fan Co. (which was then a division of Robbins & Myers, Inc), FASCO (F. A. Smith Co.), and Emerson Electric; which was often branded as Sears-Roebuck.

Smaller, short-lived companies include NuTone, Southern Fan Co., A&G Machinery Co., Homestead, Hallmark, Union, Lasko, and Evergo.

However, important inroads have been made in design by companies such as Monte Carlo, Minka Aire, Quorum, Craftmade, Litex and Fanimation—offering higher price ceiling fans with more decorative value.

In 2001, Washington Post writer Patricia Dane Rogers wrote, "Like so many other mundane household objects, these old standbys are going high-style and high-tech.

Because of this, ceiling fans are often an instrumental element of low energy HVAC, passive cooling or natural ventilation systems in buildings.

In an office environment, individually controlled ceiling fans can have a significant positive impact on thermal comfort, which has been shown to increase productivity and satisfaction among occupants.

In naturally ventilated spaces, ceiling fans are effective at drawing in and circulating fresh outdoor air.

As a result of this phenomenon, the air conditioning thermostat can be set a few degrees higher than normal when a fan is in operation, greatly reducing power consumption.

Another example of how updraft can cause better cooling is when the ceiling fan is in middle of a bedroom with a loft bed near a wall, meaning breeze can be felt better when airflow is coming from the top.

This action works to equalize, or even out the temperature in the room, making it cooler at ceiling level, but warmer near the floor.

Residential ceiling fans, which are almost always reversible, typically use flat, paddle-like blades, which are equally effective in downdraft and updraft.

A strobe or flicker effect is a phenomenon which occurs when light brightens and dims consistently as it penetrates and passes through a moving ceiling fan.

[8] This is due to the fan blades intermittently blocking the light, causing shadows to appear across the room's interior surface leading to visual discomfort.

[11] Two test rooms were utilized in an experiment to compare the effects of visual flicker induced the ceiling fan.

The findings revealed statistical proof that one out of three cognitive performances (digit-span task) may have been reduced slightly as a result of an increased effect of visual flicker.

In addition to improving thermal comfort and reducing energy consumption from air-conditioning, ceiling fans have also been studied as a tool that could potentially affect airborne transmission and distribution of infection.

[20][21] An experiment using gas to simulate exhaled droplet nuclei found that ceiling fans could reduce the concentration of aerosols at the exposed person's breathing zone by more than 20%.

[21] The benefits of ceiling fans are highest when the room is well ventilated, when masking measures are in place, and when the pathogen is not highly contagious.

It is a common mistake for homeowners to replace a light fixture with a ceiling fan without upgrading to a proper junction box.

Building codes throughout the United States prohibit residential ceiling fans from being mounted with the blades closer than seven feet from the floor;[22] this sometimes proves, however, to not be high enough.

If a ceiling fan is turned on and a person fully extends his or her arms into the air, as sometimes happens during normal tasks such as dressing, stretching or changing bedsheets, it is possible for the blades to strike their hands, potentially causing injury.

Building codes throughout the United States also prohibit industrial ceiling fans from being mounted with the blades closer than 10 feet from the floor for these reasons.

However, a severe wobble can cause light fixture shades or covers to gradually loosen over time and potentially fall, posing a risk of injury to anyone under the fan, and also from any resulting broken glass.