Editing Ceiling fan (section)

==Uses==
Ceiling fans have multiple functions. Fans increase mixing in a ventilated space, which leads to more homogenous environmental conditions. Moving air is generally preferred over stagnant air, especially in warm or neutral environments, so fans are useful in increasing occupant satisfaction.<ref>{{Cite journal|last1=Arens|first1=Edward|last2=Turner|first2=Stephen|last3=Zhang|first3=Hui|date=2009|title=Moving Air for Comfort|url=https://escholarship.org/content/qt6d94f90b/qt6d94f90b.pdf|journal=ASHRAE|volume=Journal 51|pages=18–28}}</ref> Because fans do not change air temperature and humidity, but move it around, fans can aid in both the heating and cooling of a space. Because of this, ceiling fans are often an instrumental element of low energy [[HVAC]], [[passive cooling]] or [[natural ventilation]] systems in buildings. Depending on the energy use of the fan system, fans can be an efficient way to improve [[thermal comfort]] by allowing for a higher ambient air temperature while keeping occupants comfortable.<ref>{{cite journal |last1=Schiavon |first1=Stefano |last2=Melikov |first2=Arsen K. |title=Energy saving and improved comfort by increased air movement |journal=Energy and Buildings |date=January 2008 |volume=40 |issue=10 |pages=1954–1960 |doi=10.1016/j.enbuild.2008.05.001 |bibcode=2008EneBu..40.1954S |s2cid=55323785 |url=https://escholarship.org/uc/item/6xg815xj }}</ref><ref name=":0">{{cite journal |last1=Lipczynska |first1=Aleksandra |last2=Schiavon |first2=Stefano |last3=Graham |first3=Lindsay T. |title=Thermal comfort and self-reported productivity in an office with ceiling fans in the tropics |journal=Building and Environment |date=May 2018 |volume=135 |pages=202–212 |doi=10.1016/j.buildenv.2018.03.013 |bibcode=2018BuEnv.135..202L |s2cid=55365037 |url=http://www.escholarship.org/uc/item/0g35d3hk }}</ref> Fans are an especially economic choice in warm, humid environments.

Ceiling fans can be controlled together in a shared space, and can also be individually controlled in a home or office setting. 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.<ref name=":0" /> Ceiling fans aid in the distribution of fresh air in both [[Ventilation (architecture)|mechanically ventilated]] and naturally ventilated spaces. In naturally ventilated spaces, ceiling fans are effective at drawing in and circulating fresh outdoor air.<ref>{{cite journal |last1=Song |first1=Jiafang |last2=Meng |first2=Xiangquan |title=The Improvement of Ventilation Design in School Buildings Using CFD Simulation |journal=Procedia Engineering |date=2015 |volume=121 |pages=1475–1481 |doi=10.1016/j.proeng.2015.09.073 |doi-access=free }}</ref> In mechanically ventilated spaces, fans can be focused to channel and circulate conditioned air in a room.

===Direction===
The direction that a fan spins should change based on whether the room needs to be heated or cooled. Unlike air conditioners, fans only move air—they do not directly change its temperature. Therefore, ceiling fans that have a mechanism for reversing the direction in which the blades push air (most commonly an electrical switch on the unit's switch housing, motor housing, or lower canopy) can help in both heating and cooling.

While ceiling fan manufacturers (mainly Emerson) have had electrically reversible motors in production since the 1930s, most fans made before the mid-1970s are either not reversible at all or mechanically reversible (have adjustable blade pitch) instead of an electrically reversible motor. In this case, the blades should be pitched with the upturned edge leading for downdraft, and with the downturned edge leading for updraft. Hunter's "Adaptair" mechanism is perhaps the most well-known example of mechanical reversibility.

For cooling, the fan's direction of rotation should usually be set so that air is blown downward—usually counter-clockwise from beneath, but dependent upon manufacturer. The blades should lead with the upturned edge as they spin. The breeze created by a ceiling fan creates a [[wind chill]] effect, speeding the evaporation of perspiration on human skin, which makes the body's natural cooling mechanism much more efficient. 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. Since the fan works directly on the body, rather than by changing the temperature of the air, it is recommended to switch all ceiling fans off when a room is unoccupied, to further reduce power consumption. In some cases, like when a fan is near walls like in a hallway, updraft may cause better airflow.  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.

For heating, ceiling fans should be set to blow the air upward. Air naturally stratifies, i.e. warmer air rises to the ceiling while cooler air sinks, meaning that colder air settles near the floor where people spend most of their time. A ceiling fan, with its direction of rotation set so that the warmer air on the ceiling is pushed down along the walls and into the room, heating the cooler air. This avoids blowing a stream of air directly at the occupants of the room, which would tend to cool them. This action works to equalize, or even out the temperature in the room, making it cooler at ceiling level, but warmer near the floor. Thus the heating thermostat in the area can be set a few degrees lower to save energy while maintaining the same level of comfort.

Though reversible models of industrial-grade ceiling fans do exist, most are not reversible. High ceiling heights in most industrial applications render reversibility unnecessary. Instead, industrial ceiling fans typically de-stratify heat by blowing hot air at ceiling level directly down toward the floor.

===Blade shape===
Residential ceiling fans, which are almost always reversible, typically use flat, paddle-like blades, which are equally effective in downdraft and updraft. Industrial ceiling fans typically are not reversible and operate only in downdraft, and therefore are able to make effective use of blades that are contoured to have a downdraft bias.

More recently, however, residential ceiling fan designers have been making increasing use of contoured blades in an effort to boost ceiling fan efficiency. This contour, while serving to effectively boost the fan's performance while operating in downdraft, can hinder performance when operating in updraft.

===Air conditioning===
The most commonplace use of ceiling fans today is in conjunction with an air conditioning unit. Without an operating ceiling fan, air conditioning units typically have both the tasks of cooling the air inside the room and circulating it. Provided the ceiling fan is properly sized for the room in which it is operating, its efficiency of moving air far exceeds that of an air conditioning unit, therefore, for peak efficiency, the air conditioner should be set to a low fan setting and the ceiling fan should be used to circulate the air.

===Flicker and strobing===
Ceiling fans are usually installed in a space with other lighting fixtures, but if the fan is positioned too close to a light panel or fixture, a strobe or flicker effect may occur. 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.<ref>{{Cite journal |last1=MK Think |date=2017 |title=Ceiling Fan Study: Literature and Market Report. |url=https://www.hnei.hawaii.edu/wp-content/uploads/Ceiling-Fan-Study-Literature-and-Market-Report.pdf |journal=Hawaii Natural Energy Institute |pages=50–51}}</ref> 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. The rotating area of a moving fan blade can commonly obstruct the light source when a ceiling fan is positioned underneath an artificial lighting fixture, which can be increasingly distracting to occupants within the space.<ref>{{Cite patent|number=US4382400A|title=Combined ceiling mounted fan and lighting fixture|gdate=1983-05-10|invent1=Stutzman|inventor1-first=Clarence|url=https://patents.google.com/patent/US4382400/en}}</ref> To ensure that the ceiling fans seamlessly co-exists with the lighting fixtures to avoid strobing, it is recommended that the horizontal separation between the blade and the lighting fixture is maximized. In addition, increasing the vertical distance between the light and the blade will reduce the concentration and frequency of strobing. Never position a light fixture directly above a ceiling fan's blades, and downlight and point source fixtures should be set such that their beam angles do not cross them. Generally, to ensure uniformly adequate light levels, any recessed ceiling lighting and fixtures that emit light above the level of the fan blades should be placed as far away from the ceiling fan as possible.<ref>{{Cite journal |last1=Raftery |first1=Paul |last2=Cheung |first2=Toby |last3=Douglass-Jaimes |first3=David |last4=André |first4=Maíra |last5=Li |first5=Jiayu |last6=Kent |first6=Michael |last7=Huynh |first7=Nam Khoa |last8=Sultan |first8=Zuraimi |last9=Schiavon |first9=Stefano |date=2023 |title=Fans for cooling people guidebook |url=https://cbe-berkeley.gitbook.io/fans-guidebook/ |journal=[[Center for the Built Environment]]}}</ref> Another recommended strategy is to ensure that the light’s angle of dispersion or the field angle is reduced, which minimizes the strobing effect from the fan blades. It is well known that human eyes can detect flicker at low frequencies (between 60 and 90 hertz), but not at high frequencies (beyond 100 hertz), which is also known as non-visible flicker. The strobe effect can have significant physiological and psychological effect on humans.<ref>{{Cite book |last1=Yang |first1=Jin |last2=Zhang |first2=Tianchi |last3=Lin |first3=Yandan |last4=Xu |first4=Wei |title=2019 16th China International Forum on Solid State Lighting & 2019 International Forum on Wide Bandgap Semiconductors China (SSLChina: IFWS) |chapter=Effect of Illuminance and Light Strobe on Attention and Visual Fatigue in Indoor Lighting |date=November 2019 |chapter-url=https://ieeexplore.ieee.org/document/9019810 |pages=149–152 |doi=10.1109/SSLChinaIFWS49075.2019.9019810|isbn=978-1-7281-5756-6 |s2cid=212637051 }}</ref> 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.<ref>{{Cite journal |last1=Kent |first1=Michael G. |last2=Cheung |first2=Toby |last3=Li |first3=Jiayu |last4=Schiavon |first4=Stefano |date=2020-09-01 |title=Experimental evaluation of visual flicker caused by ceiling fans |url=https://www.sciencedirect.com/science/article/pii/S0360132320304406 |journal=Building and Environment |language=en |volume=182 |pages=107060 |doi=10.1016/j.buildenv.2020.107060 |bibcode=2020BuEnv.18207060K |s2cid=225305290 |issn=0360-1323|url-access=subscription }}</ref>