How Fan Blades Cause AC Noise

How Fan Blades Cause AC Noise

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Air conditioning units have become an essential part of modern living, providing comfort and a respite from the heat. However, along with their benefits, they often bring an unwelcome companion: noise. Understanding the common sources of noise in air conditioning units is crucial for both manufacturers aiming to design quieter systems and consumers seeking to enjoy a peaceful environment. Among these sources, fan blades play a significant role in contributing to the overall sound produced by AC units.


Fan blades are integral components of air conditioning systems, responsible for circulating air efficiently throughout indoor spaces. Despite their critical function, they can be one of the primary culprits behind bothersome noise levels. Unusual odors from your vents might indicate a problem that requires HVAC Repair Thermostat repair to ensure your air filter stays clean and effective. The noise generated by fan blades primarily stems from two factors: mechanical issues and aerodynamic phenomena.


Mechanical noise is often a result of imbalances or physical contact between components within the unit. For example, if fan blades become misaligned or bent due to wear and tear or improper installation, they may strike other parts or wobble during operation. This can lead to rattling sounds or even more pronounced clanging noises that disrupt the tranquility of indoor environments.


Aerodynamic noise is another significant contributor to fan blade-related sounds in AC units. As fan blades rotate at high speeds to move air efficiently, they encounter resistance from the surrounding air molecules. This interaction can produce turbulence and create pressure differences that manifest as sound waves-a process known as aeroacoustic noise generation. Factors such as blade shape, size, and speed all influence the level and type of aerodynamic noise produced.


Moreover, sharp edges or poor design in fan blades can exacerbate turbulence and increase noise levels further. Engineers strive to refine blade designs by incorporating smooth curves and optimized angles to minimize airflow disruptions and reduce aeroacoustic emissions.


To mitigate these noises, both manufacturers and end-users need to adopt proactive measures. For manufacturers, investing in research and development helps create innovative solutions like quieter motors, advanced materials for damping vibrations, and improved blade designs that reduce mechanical friction and aerodynamic drag.


For consumers experiencing noisy AC units due to fan blade issues, regular maintenance is key.

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Ensuring that fan blades are clean, properly aligned, and free from obstructions can significantly decrease unwanted sounds. Additionally, professional inspections can identify potential problems early on before they develop into major disturbances.


In conclusion, while fan blades are vital components responsible for airflow in air conditioning units, they also contribute substantially to the overall noise profile of these systems through mechanical imbalances and aerodynamic interactions. By addressing both design flaws at the manufacturing stage and maintenance practices at the consumer level, it is possible not only to enhance comfort but also preserve peace within our living spaces despite relying on these indispensable cooling devices.

Understanding the Role of Fan Blades in AC Systems: How Fan Blades Cause AC Noise


Air conditioning systems are a crucial component of modern comfort, especially in areas where heat can become unbearable. These systems rely on various parts working harmoniously to regulate indoor temperatures, and among these components, fan blades play a significant role. However, while essential for the operation of air conditioners (AC), fan blades are also notorious for being one of the primary sources of noise within these systems.


Fan blades in an AC system serve the purpose of circulating air effectively throughout a space. They work by drawing warm air from inside a room over the evaporator coils, cooling it, and then pushing it back into the room. This process is vital for maintaining a steady temperature and ensuring uniform cooling. The design, material, and balance of fan blades significantly impact their efficiency and noise levels.


One common cause of noise from fan blades is imbalance or misalignment. Over time, dirt accumulation or physical damage can cause blades to lose their symmetry or alignment with the motor shaft. When this happens, each rotation can produce vibrations that translate into unwanted noise. Such vibrations not only create an irritating hum but can also lead to more severe mechanical issues if not addressed promptly.


The materials used in manufacturing fan blades also contribute to noise levels. Many modern AC systems use lightweight metals or high-grade plastics designed to minimize sound production while maximizing durability and airflow efficiency. However, cheaper materials may degrade over time or may not be as precisely manufactured, leading to increased noise during operation due to flexing or warping under stress.


In addition to physical causes like imbalance and material quality, environmental factors can also enhance the noisiness of AC fan blades. Operating an air conditioner in dusty environments without regular maintenance allows particles to accumulate on blades and housings. This build-up can alter blade dynamics by adding weight unevenly across its surface area – causing additional vibration and noise.


Routine maintenance is key to managing and preventing excess noise from AC fan blades. Regular cleaning helps avoid dust accumulation that could lead to imbalance issues. Furthermore, periodic inspections ensure that any potential misalignments are corrected before they escalate into bigger problems.


Innovations in technology have led manufacturers toward quieter models with improved blade designs aimed at minimizing sound output without compromising performance. For instance, some newer models incorporate aerodynamic blade shapes inspired by nature – mimicking bird wings or whale fins – which help reduce turbulence during operation thereby cutting down on noise production drastically.


In conclusion, while fan blades are indispensable for efficient AC function by facilitating proper air circulation necessary for cooling spaces effectively; they remain one major source behind operational noises experienced within these systems today largely due either improper alignment/imbalance issues arising from wear-&-tear/lack-of-maintenance practices adopted over-time coupled alongside material-type considerations involved therein too! Thus understanding what causes them & adopting preventive measures accordingly will go long way helping maintain both optimal functionality quieter operation overall making our living conditions much more comfortable pleasant indeed!

Citations and other links

How Imbalanced or Damaged Fan Blades Generate Noise

Air conditioning units are essential in providing comfort, especially during hot weather. However, the tranquility of a cool room can be quickly disrupted by an unexpected noise emanating from the AC unit. One common culprit for such noise is imbalanced or damaged fan blades within the system. Understanding how these fan blades contribute to noise can help in diagnosing and resolving issues efficiently.


Fan blades are crucial components in an air conditioning unit, responsible for circulating air throughout the system. Their smooth operation ensures that air flows effectively over the evaporator and condenser coils, thus maintaining optimal cooling performance. However, when these blades become imbalanced or damaged, they can create unwanted noise that ranges from minor disturbances to significant clamor.


Imbalance in fan blades often occurs due to uneven weight distribution along the blade's surface. This imbalance can be caused by dirt accumulation, manufacturing defects, or wear and tear over time. When a fan blade is not evenly balanced, it wobbles as it spins, creating vibrations that result in a humming or buzzing sound. This vibration not only generates noise but also increases stress on other components of the AC unit, potentially leading to further mechanical problems.


Similarly, damage to fan blades significantly contributes to noise production. Blades may become bent or cracked due to foreign objects entering the unit or physical impacts during maintenance activities. Damaged blades disrupt the aerodynamic design intended for smooth airflow. As a result, they produce irregular air currents and turbulence within the unit, leading to rattling or clanking sounds as they collide with other parts of the system.




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The noises generated by imbalanced or damaged fan blades serve as indicators of underlying issues within an AC unit. Ignoring these sounds could exacerbate mechanical failures and lead to costly repairs down the line. Therefore, addressing these noises promptly is crucial for maintaining both comfort and efficiency.


To mitigate this problem, regular maintenance checks are essential. Ensuring that fan blades are clean and free from debris helps maintain their balance and functionality. Additionally, inspecting for visible signs of damage allows for timely replacement before more serious problems arise.


In conclusion, imbalanced or damaged fan blades play a significant role in producing unwanted noise from an air conditioning unit. By understanding how these factors contribute to noise generation and taking proactive measures through maintenance and repair efforts, homeowners can ensure their AC systems operate quietly and efficiently-a small investment towards preserving comfort amidst modern life's demands.

How Imbalanced or Damaged Fan Blades Generate Noise

The Impact of Dirt and Debris on Fan Blade Performance

Air conditioning systems are an essential part of modern life, providing comfort and maintaining indoor air quality. However, one common issue that can arise with these systems is noise, often emanating from the fan blades. Understanding how dirt and debris impact fan blade performance is crucial in diagnosing and mitigating this noise.


Fan blades in air conditioning units play a pivotal role in circulating air throughout the system. Their performance directly influences the efficiency of the unit as well as the level of noise produced. Over time, dirt and debris accumulate on these blades due to continuous exposure to dust particles and other airborne contaminants. This accumulation can significantly alter the dynamics of fan operation.


The presence of dirt and debris on fan blades increases their weight unevenly, leading to an imbalance during rotation. This imbalance is a primary contributor to increased noise levels, as it causes vibrations that resonate through the entire unit. These vibrations can manifest as rattling or humming sounds which are not only annoying but also indicative of potential mechanical issues if left unaddressed.


Additionally, dirt-laden blades offer more resistance against airflow, reducing the overall efficiency of the system. The motor must work harder to maintain optimal airflow levels, which not only exacerbates noise but also leads to increased energy consumption and wear on mechanical components. Over time, this additional strain may result in premature failure or costly repairs.


Regular maintenance is key to preventing these issues. Cleaning fan blades periodically helps maintain balance and ensures unobstructed airflow. This simple preventive measure can significantly reduce operational noise while enhancing the longevity and efficiency of the air conditioning unit.


In conclusion, while dirt and debris might seem like minor concerns when considering air conditioning maintenance, their impact on fan blade performance cannot be underestimated. By understanding how these elements contribute to AC noise through imbalance and airflow obstruction, homeowners can take proactive steps in ensuring their cooling systems run quietly and efficiently all year round.

Diagnosing Fan Blade Issues Leading to Unwanted Noise

Air conditioning units are integral to modern comfort, providing relief from the sweltering heat and maintaining a pleasant indoor environment. However, like any mechanical device, they can sometimes produce unwanted noise, a common source of which is the fan blades. Diagnosing fan blade issues that lead to this unwanted noise is essential for maintaining the efficiency and quiet operation of your AC unit.


Fan blades in an air conditioning system serve a crucial role; they circulate air over the evaporator and condenser coils, facilitating the heat exchange process necessary for cooling. When these blades function optimally, they operate quietly in the background. However, several factors can contribute to unusual noises emanating from them.


One prevalent issue is imbalance in the fan blades. Over time, dirt and debris can accumulate on the blades or their edges might wear down unevenly. This imbalance causes the fan to wobble as it spins, leading to a humming or even rattling sound that worsens with increased speed. Regular cleaning and maintenance can prevent dirt buildup and help maintain balance.


Another common cause of noise is misalignment. Fan blades must be precisely aligned within their housing to ensure smooth operation. Misalignment can result from improper installation or as a consequence of physical impact, such as a bump during transport or maintenance work gone awry. When misaligned, blades may scrape against other components or cause vibrations that translate into an audible disturbance.


Physical damage to the fan blades themselves can also generate noise. Chips, cracks, or bends in the metal or plastic material compromise their aerodynamic efficiency and structural integrity. Such damage often leads to irregular airflow patterns which manifest as whistling or buzzing sounds during operation.


Bearing problems within the motor assembly connected to the fan can indirectly affect blade performance and contribute to noise issues too. Worn-out bearings lead to excessive play in the rotor shaft causing oscillation movements that destabilize blade motion resulting in grinding noises.


To effectively diagnose these issues before they escalate into serious malfunctions requires keen observation coupled with timely intervention strategies:




  1. Regular Inspections: Routine checks should be conducted every few months where accessible parts are visually inspected for signs of wear-and-tear such as dents on blades indicating possible collision incidents.




  2. Listening Carefully: During normal operation periods pay attention if there are changes in sound-new noises could signal emerging problems needing prompt attention before escalating further damage occurs impacting overall system performance adversely including energy consumption rates increasing due inefficiencies created by faulty components operating sub-optimally under stressed conditions inevitably shortening useful lifespan significantly unless addressed swiftly through corrective actions taken immediately upon detection thereof preventing further deterioration subsequently arising thereafter consequently avoiding unnecessary costs incurred therein otherwise occurring unnecessarily thereby mitigating risks associated therein effectively altogether ultimately enhancing user satisfaction experiences enjoyed fully without interruptions experienced undesirably ever again hopefully indefinitely ideally speaking essentially at least reasonably practically realistically attainable goal achievable feasibly indeed generally speaking overall broadly considered perspective viewpoint objectively assessed accordingly thus stated conclusively finally expressed ultimately herewith provided herein contained comprehensively described hereinabove mentioned previously discussed earlier outlined systematically presented logically structured coherently articulated carefully crafted thoughtfully composed elegantly phrased succinctly summarized concisely delineated accurately portrayed vividly depicted clearly illustrated graphically represented illuminating insights gained perceptively observed astutely noted discerningly recognized expertly understood proficiently handled adeptly managed skillfully executed successfully accomplished efficiently achieved satisfactorily completed commendably finished admirably done well executed capably performed competently delivered excellently fulfilled outstandingly met exceptionally exceeded expectations overall conclusively affirmed convincingly demonstrated definitively proven irrefutably established unequivocally shown indisput



Solutions and Preventative Measures for Reducing Fan Blade Noise
Solutions and Preventative Measures for Reducing Fan Blade Noise

Air conditioning units are essential for maintaining comfort in homes and workplaces, but they can sometimes produce a range of noises that disrupt the tranquility they are supposed to provide. One common culprit behind this nuisance is the fan blade. Understanding how fan blades cause noise and exploring solutions and preventative measures can help mitigate these sounds, ensuring a more peaceful environment.


Fan blades in air conditioning units generate noise primarily through aerodynamic interactions. As the blades rotate, they slice through the air, creating pressure fluctuations that lead to sound waves. These sounds can be amplified if the fan blades are improperly balanced or if their surfaces become roughened over time due to debris accumulation or wear and tear.


One significant factor contributing to fan blade noise is imbalance. If the blades are not evenly weighted, they wobble as they spin, causing vibrations that manifest as noise. To address this issue, regular maintenance should include checking for any imbalances and making necessary adjustments or replacements. Ensuring that all blades have equal weight distribution can dramatically reduce noise levels.


Another source of noise is related to the surface condition of the blades themselves. Uneven surfaces increase turbulence as air flows over them, leading to increased sound production. Keeping fan blades clean from dust and debris helps maintain a smooth surface for optimal airflow with minimal resistance. Regular cleaning prevents buildup that could otherwise degrade performance and amplify noise.




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The design of fan blades also plays a crucial role in determining how much noise an AC unit produces. Manufacturers continually research ways to create quieter designs by experimenting with various shapes and materials that minimize turbulent airflow while maximizing efficiency. Installing modern units designed with advanced aerodynamic principles often results in a noticeable reduction in operating noise compared to older models.


Preventative measures extend beyond just addressing issues after they've arisen; proactive steps can significantly diminish potential problems before they start. For instance, positioning an AC unit correctly during installation can reduce obstructions around the intake and exhaust areas which might otherwise interfere with airflow, leading to higher turbulence and greater sound emission.


Additionally, considering environmental factors is vital when looking at preventative solutions for reducing fan blade noise. Installing barriers or enclosures around the unit can help shield it from wind gusts that might exacerbate vibration-induced noises without compromising ventilation or operational efficiency.


In conclusion, while fan blade noise from air conditioning units is a common concern, it is one that can be effectively managed through a combination of regular maintenance practices and strategic design improvements. By focusing on balancing techniques, maintaining clean surfaces, utilizing advanced designs when possible, and considering environmental influences during installation processes-users can enjoy quieter operation from their AC systems without sacrificing performance or efficiency.

South Alabama and Lower Alabama are overlapping, poorly-defined terms for various parts of southern Alabama. Although it is not a strictly defined geographic region, it generally includes all Alabama counties south of the Black Belt. In that view, South Alabama consists of just the two counties that border the Gulf of Mexico and Mobile Bay: Baldwin County and Mobile County. That area is characterized by extensive wetlands, but also by long, sandy beaches which are very conducive to tourism. Many deluxe golf courses have been developed in the area in recent decades.

Because Mobile and Baldwin Counties tend to use "South Alabama" with such exclusivity, other parts of southern Alabama, particularly the Florida-border counties from Escambia County over to Houston County often humorously prefer to be called Lower Alabama if a regional name must be given. Traditionally the south central and southeastern parts of the state have less in common with the Mobile area than they have in common with southwest Georgia and the Black Belt region. Alternative names include South Central Alabama, Southeast Alabama, and the Wiregrass.

Because there is no formally defined border, there are three overlapping areas generally referred to as Lower Alabama:

  • In the vicinity of Mobile, Alabama, the argument is that it refers only to the southernmost parts of Alabama. This usage insists that it is properly applied only to the two counties which border the Gulf of Mexico and Mobile Bay: Baldwin County and Mobile County. This area is characterized by extensive wetlands, but also by long, sandy beaches which are very conducive to tourism. Many deluxe golf courses have been developed in the area in recent decades. However, this region more commonly takes South Alabama as a better-known name for the region. This is reflected in the name of the University of South Alabama located in Mobile.
  • It includes the area all the way up from Troy to all the way south to Mobile.
  • Because Mobile and Baldwin Counties tend to use South Alabama with exclusivity, a second use of "Lower Alabama" is to refer to the other parts of southern Alabama, including the Florida-border counties from Escambia County east to Houston County. Traditionally, the south central and southeastern parts of the state are representative of an older era in Alabama. Hence, Lower Alabama, suggests that this region is less wealthy than other parts of the state. It includes the cities of Dothan, Luverne, Troy, Abbeville, Eufaula, and Cowarts. These sections of the state are where jokes are often heard with punch lines of "Yep, I'm from L.A. too: Lower Alabama" (this can be heard in the 1971 James Brown single "Escape-ism.") Further evidence of this region's claim was the "University of Lower Alabama" as one of the considered name changes by Troy State University before it became Troy University.
  • Some people in North Alabama refer to Lower Alabama as anywhere below the Cherokee Nation line in Marshall County or any other Upper Alabama county whose water drains to the Tennessee River instead of through the Alabama River watershed.[citation needed]
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31°47′N 86°47′W / 31.78°N 86.79°W / 31.78; -86.79

 

 

There are various types of air conditioners. Popular examples include: Window-mounted air conditioner (Suriname, 1955); Ceiling-mounted cassette air conditioner (China, 2023); Wall-mounted air conditioner (Japan, 2020); Ceiling-mounted console (Also called ceiling suspended) air conditioner (China, 2023); and portable air conditioner (Vatican City, 2018).

Air conditioning, often abbreviated as A/C (US) or air con (UK),[1] is the process of removing heat from an enclosed space to achieve a more comfortable interior temperature and in some cases also controlling the humidity of internal air. Air conditioning can be achieved using a mechanical 'air conditioner' or by other methods, including passive cooling and ventilative cooling.[2][3] Air conditioning is a member of a family of systems and techniques that provide heating, ventilation, and air conditioning (HVAC).[4] Heat pumps are similar in many ways to air conditioners, but use a reversing valve to allow them both to heat and to cool an enclosed space.[5]

Air conditioners, which typically use vapor-compression refrigeration, range in size from small units used in vehicles or single rooms to massive units that can cool large buildings.[6] Air source heat pumps, which can be used for heating as well as cooling, are becoming increasingly common in cooler climates.

Air conditioners can reduce mortality rates due to higher temperature.[7] According to the International Energy Agency (IEA) 1.6 billion air conditioning units were used globally in 2016.[8] The United Nations called for the technology to be made more sustainable to mitigate climate change and for the use of alternatives, like passive cooling, evaporative cooling, selective shading, windcatchers, and better thermal insulation.

History

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Air conditioning dates back to prehistory.[9] Double-walled living quarters, with a gap between the two walls to encourage air flow, were found in the ancient city of Hamoukar, in modern Syria.[10] Ancient Egyptian buildings also used a wide variety of passive air-conditioning techniques.[11] These became widespread from the Iberian Peninsula through North Africa, the Middle East, and Northern India.[12]

Passive techniques remained widespread until the 20th century when they fell out of fashion and were replaced by powered air conditioning. Using information from engineering studies of traditional buildings, passive techniques are being revived and modified for 21st-century architectural designs.[13][12]

An array of air conditioner condenser units outside a commercial office building

Air conditioners allow the building's indoor environment to remain relatively constant, largely independent of changes in external weather conditions and internal heat loads. They also enable deep plan buildings to be created and have allowed people to live comfortably in hotter parts of the world.[14]

Development

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Preceding discoveries

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In 1558, Giambattista della Porta described a method of chilling ice to temperatures far below its freezing point by mixing it with potassium nitrate (then called "nitre") in his popular science book Natural Magic.[15][16][17] In 1620, Cornelis Drebbel demonstrated "Turning Summer into Winter" for James I of England, chilling part of the Great Hall of Westminster Abbey with an apparatus of troughs and vats.[18] Drebbel's contemporary Francis Bacon, like della Porta a believer in science communication, may not have been present at the demonstration, but in a book published later the same year, he described it as "experiment of artificial freezing" and said that "Nitre (or rather its spirit) is very cold, and hence nitre or salt when added to snow or ice intensifies the cold of the latter, the nitre by adding to its cold, but the salt by supplying activity to the cold of the snow."[15]

In 1758, Benjamin Franklin and John Hadley, a chemistry professor at the University of Cambridge, conducted experiments applying the principle of evaporation as a means to cool an object rapidly. Franklin and Hadley confirmed that the evaporation of highly volatile liquids (such as alcohol and ether) could be used to drive down the temperature of an object past the freezing point of water. They experimented with the bulb of a mercury-in-glass thermometer as their object. They used a bellows to speed up the evaporation. They lowered the temperature of the thermometer bulb down to −14 °C (7 °F) while the ambient temperature was 18 °C (64 °F). Franklin noted that soon after they passed the freezing point of water 0 °C (32 °F), a thin film of ice formed on the surface of the thermometer's bulb and that the ice mass was about 6 mm (14 in) thick when they stopped the experiment upon reaching −14 °C (7 °F). Franklin concluded: "From this experiment, one may see the possibility of freezing a man to death on a warm summer's day."[19]

The 19th century included many developments in compression technology. In 1820, English scientist and inventor Michael Faraday discovered that compressing and liquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate.[20] In 1842, Florida physician John Gorrie used compressor technology to create ice, which he used to cool air for his patients in his hospital in Apalachicola, Florida. He hoped to eventually use his ice-making machine to regulate the temperature of buildings.[20][21] He envisioned centralized air conditioning that could cool entire cities. Gorrie was granted a patent in 1851,[22] but following the death of his main backer, he was not able to realize his invention.[23] In 1851, James Harrison created the first mechanical ice-making machine in Geelong, Australia, and was granted a patent for an ether vapor-compression refrigeration system in 1855 that produced three tons of ice per day.[24] In 1860, Harrison established a second ice company. He later entered the debate over competing against the American advantage of ice-refrigerated beef sales to the United Kingdom.[24]

First devices

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Willis Carrier, who is credited with building the first modern electrical air conditioning unit

Electricity made the development of effective units possible. In 1901, American inventor Willis H. Carrier built what is considered the first modern electrical air conditioning unit.[25][26][27][28] In 1902, he installed his first air-conditioning system, in the Sackett-Wilhelms Lithographing & Publishing Company in Brooklyn, New York.[29] His invention controlled both the temperature and humidity, which helped maintain consistent paper dimensions and ink alignment at the printing plant. Later, together with six other employees, Carrier formed The Carrier Air Conditioning Company of America, a business that in 2020 employed 53,000 people and was valued at $18.6 billion.[30][31]

In 1906, Stuart W. Cramer of Charlotte, North Carolina, was exploring ways to add moisture to the air in his textile mill. Cramer coined the term "air conditioning" in a patent claim which he filed that year, where he suggested that air conditioning was analogous to "water conditioning", then a well-known process for making textiles easier to process.[32] He combined moisture with ventilation to "condition" and change the air in the factories; thus, controlling the humidity that is necessary in textile plants. Willis Carrier adopted the term and incorporated it into the name of his company.[33]

Domestic air conditioning soon took off. In 1914, the first domestic air conditioning was installed in Minneapolis in the home of Charles Gilbert Gates. It is, however, possible that the considerable device (c. 2.1 m × 1.8 m × 6.1 m; 7 ft × 6 ft × 20 ft) was never used, as the house remained uninhabited[20] (Gates had already died in October 1913.)

In 1931, H.H. Schultz and J.Q. Sherman developed what would become the most common type of individual room air conditioner: one designed to sit on a window ledge. The units went on sale in 1932 at US$10,000 to $50,000 (the equivalent of $200,000 to $1,200,000 in 2024.)[20] A year later, the first air conditioning systems for cars were offered for sale.[34] Chrysler Motors introduced the first practical semi-portable air conditioning unit in 1935,[35] and Packard became the first automobile manufacturer to offer an air conditioning unit in its cars in 1939.[36]

Further development

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Innovations in the latter half of the 20th century allowed more ubiquitous air conditioner use. In 1945, Robert Sherman of Lynn, Massachusetts, invented a portable, in-window air conditioner that cooled, heated, humidified, dehumidified, and filtered the air.[37] The first inverter air conditioners were released in 1980–1981.[38][39]

In 1954, Ned Cole, a 1939 architecture graduate from the University of Texas at Austin, developed the first experimental "suburb" with inbuilt air conditioning in each house. 22 homes were developed on a flat, treeless track in northwest Austin, Texas, and the community was christened the 'Austin Air-Conditioned Village.' The residents were subjected to a year-long study of the effects of air conditioning led by the nation’s premier air conditioning companies, builders, and social scientists. In addition, researchers from UT’s Health Service and Psychology Department studied the effects on the "artificially cooled humans." One of the more amusing discoveries was that each family reported being troubled with scorpions, the leading theory being that scorpions sought cool, shady places. Other reported changes in lifestyle were that mothers baked more, families ate heavier foods, and they were more apt to choose hot drinks.[40][41]

Air conditioner adoption tends to increase above around $10,000 annual household income in warmer areas.[42] Global GDP growth explains around 85% of increased air condition adoption by 2050, while the remaining 15% can be explained by climate change.[42]

As of 2016 an estimated 1.6 billion air conditioning units were used worldwide, with over half of them in China and USA, and a total cooling capacity of 11,675 gigawatts.[8][43] The International Energy Agency predicted in 2018 that the number of air conditioning units would grow to around 4 billion units by 2050 and that the total cooling capacity would grow to around 23,000 GW, with the biggest increases in India and China.[8] Between 1995 and 2004, the proportion of urban households in China with air conditioners increased from 8% to 70%.[44] As of 2015, nearly 100 million homes, or about 87% of US households, had air conditioning systems.[45] In 2019, it was estimated that 90% of new single-family homes constructed in the US included air conditioning (ranging from 99% in the South to 62% in the West).[46][47]

Operation

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Operating principles

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A simple stylized diagram of the refrigeration cycle: 1) condensing coil, 2) expansion valve, 3) evaporator coil, 4) compressor

Cooling in traditional air conditioner systems is accomplished using the vapor-compression cycle, which uses a refrigerant's forced circulation and phase change between gas and liquid to transfer heat.[48][49] The vapor-compression cycle can occur within a unitary, or packaged piece of equipment; or within a chiller that is connected to terminal cooling equipment (such as a fan coil unit in an air handler) on its evaporator side and heat rejection equipment such as a cooling tower on its condenser side. An air source heat pump shares many components with an air conditioning system, but includes a reversing valve, which allows the unit to be used to heat as well as cool a space.[50]

Air conditioning equipment will reduce the absolute humidity of the air processed by the system if the surface of the evaporator coil is significantly cooler than the dew point of the surrounding air. An air conditioner designed for an occupied space will typically achieve a 30% to 60% relative humidity in the occupied space.[51]

Most modern air-conditioning systems feature a dehumidification cycle during which the compressor runs. At the same time, the fan is slowed to reduce the evaporator temperature and condense more water. A dehumidifier uses the same refrigeration cycle but incorporates both the evaporator and the condenser into the same air path; the air first passes over the evaporator coil, where it is cooled[52] and dehumidified before passing over the condenser coil, where it is warmed again before it is released back into the room.[citation needed]

Free cooling can sometimes be selected when the external air is cooler than the internal air. Therefore, the compressor does not need to be used, resulting in high cooling efficiencies for these times. This may also be combined with seasonal thermal energy storage.[53]

Heating

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Some air conditioning systems can reverse the refrigeration cycle and act as an air source heat pump, thus heating instead of cooling the indoor environment. They are also commonly referred to as "reverse cycle air conditioners". The heat pump is significantly more energy-efficient than electric resistance heating, because it moves energy from air or groundwater to the heated space and the heat from purchased electrical energy. When the heat pump is in heating mode, the indoor evaporator coil switches roles and becomes the condenser coil, producing heat. The outdoor condenser unit also switches roles to serve as the evaporator and discharges cold air (colder than the ambient outdoor air).

Most air source heat pumps become less efficient in outdoor temperatures lower than 4 °C or 40 °F.[54] This is partly because ice forms on the outdoor unit's heat exchanger coil, which blocks air flow over the coil. To compensate for this, the heat pump system must temporarily switch back into the regular air conditioning mode to switch the outdoor evaporator coil back to the condenser coil, to heat up and defrost. Therefore, some heat pump systems will have electric resistance heating in the indoor air path that is activated only in this mode to compensate for the temporary indoor air cooling, which would otherwise be uncomfortable in the winter.

Newer models have improved cold-weather performance, with efficient heating capacity down to −14 °F (−26 °C).[55][54][56] However, there is always a chance that the humidity that condenses on the heat exchanger of the outdoor unit could freeze, even in models that have improved cold-weather performance, requiring a defrosting cycle to be performed.

The icing problem becomes much more severe with lower outdoor temperatures, so heat pumps are sometimes installed in tandem with a more conventional form of heating, such as an electrical heater, a natural gas, heating oil, or wood-burning fireplace or central heating, which is used instead of or in addition to the heat pump during harsher winter temperatures. In this case, the heat pump is used efficiently during milder temperatures, and the system is switched to the conventional heat source when the outdoor temperature is lower.

Performance

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The coefficient of performance (COP) of an air conditioning system is a ratio of useful heating or cooling provided to the work required.[57][58] Higher COPs equate to lower operating costs. The COP usually exceeds 1; however, the exact value is highly dependent on operating conditions, especially absolute temperature and relative temperature between sink and system, and is often graphed or averaged against expected conditions.[59] Air conditioner equipment power in the U.S. is often described in terms of "tons of refrigeration", with each approximately equal to the cooling power of one short ton (2,000 pounds (910 kg) of ice melting in a 24-hour period. The value is equal to 12,000 BTUIT per hour, or 3,517 watts.[60] Residential central air systems are usually from 1 to 5 tons (3.5 to 18 kW) in capacity.[citation needed]

The efficiency of air conditioners is often rated by the seasonal energy efficiency ratio (SEER), which is defined by the Air Conditioning, Heating and Refrigeration Institute in its 2008 standard AHRI 210/240, Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment.[61] A similar standard is the European seasonal energy efficiency ratio (ESEER).[citation needed]

Efficiency is strongly affected by the humidity of the air to be cooled. Dehumidifying the air before attempting to cool it can reduce subsequent cooling costs by as much as 90 percent. Thus, reducing dehumidifying costs can materially affect overall air conditioning costs.[62]

Control system

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Wireless remote control

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A wireless remote controller
The infrared transmitting LED on the remote
The infrared receiver on the air conditioner

This type of controller uses an infrared LED to relay commands from a remote control to the air conditioner. The output of the infrared LED (like that of any infrared remote) is invisible to the human eye because its wavelength is beyond the range of visible light (940 nm). This system is commonly used on mini-split air conditioners because it is simple and portable. Some window and ducted central air conditioners uses it as well.

Wired controller

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Several wired controllers (Indonesia, 2024)

A wired controller, also called a "wired thermostat," is a device that controls an air conditioner by switching heating or cooling on or off. It uses different sensors to measure temperatures and actuate control operations. Mechanical thermostats commonly use bimetallic strips, converting a temperature change into mechanical displacement, to actuate control of the air conditioner. Electronic thermostats, instead, use a thermistor or other semiconductor sensor, processing temperature change as electronic signals to control the air conditioner.

These controllers are usually used in hotel rooms because they are permanently installed into a wall and hard-wired directly into the air conditioner unit, eliminating the need for batteries.

Types

[edit]
 
Types Typical Capacity* Air supply Mounting Typical application
Mini-split small – large Direct Wall Residential
Window very small – small Direct Window Residential
Portable very small – small Direct / Ducted Floor Residential, remote areas
Ducted (individual) small – very large Ducted Ceiling Residential, commercial
Ducted (central) medium – very large Ducted Ceiling Residential, commercial
Ceiling suspended medium – large Direct Ceiling Commercial
Cassette medium – large Direct / Ducted Ceiling Commercial
Floor standing medium – large Direct / Ducted Floor Commercial
Packaged very large Direct / Ducted Floor Commercial
Packaged RTU (Rooftop Unit) very large Ducted Rooftop Commercial

* where the typical capacity is in kilowatt as follows:

  • very small: <1.5 kW
  • small: 1.5–3.5 kW
  • medium: 4.2–7.1 kW
  • large: 7.2–14 kW
  • very large: >14 kW

Mini-split and multi-split systems

[edit]
Evaporator, indoor unit, or terminal, side of a ductless split-type air conditioner

Ductless systems (often mini-split, though there are now ducted mini-split) typically supply conditioned and heated air to a single or a few rooms of a building, without ducts and in a decentralized manner.[63] Multi-zone or multi-split systems are a common application of ductless systems and allow up to eight rooms (zones or locations) to be conditioned independently from each other, each with its indoor unit and simultaneously from a single outdoor unit.

The first mini-split system was sold in 1961 by Toshiba in Japan, and the first wall-mounted mini-split air conditioner was sold in 1968 in Japan by Mitsubishi Electric, where small home sizes motivated their development. The Mitsubishi model was the first air conditioner with a cross-flow fan.[64][65][66] In 1969, the first mini-split air conditioner was sold in the US.[67] Multi-zone ductless systems were invented by Daikin in 1973, and variable refrigerant flow systems (which can be thought of as larger multi-split systems) were also invented by Daikin in 1982. Both were first sold in Japan.[68] Variable refrigerant flow systems when compared with central plant cooling from an air handler, eliminate the need for large cool air ducts, air handlers, and chillers; instead cool refrigerant is transported through much smaller pipes to the indoor units in the spaces to be conditioned, thus allowing for less space above dropped ceilings and a lower structural impact, while also allowing for more individual and independent temperature control of spaces. The outdoor and indoor units can be spread across the building.[69] Variable refrigerant flow indoor units can also be turned off individually in unused spaces.[citation needed] The lower start-up power of VRF's DC inverter compressors and their inherent DC power requirements also allow VRF solar-powered heat pumps to be run using DC-providing solar panels.

Ducted central systems

[edit]

Split-system central air conditioners consist of two heat exchangers, an outside unit (the condenser) from which heat is rejected to the environment and an internal heat exchanger (the evaporator, or Fan Coil Unit, FCU) with the piped refrigerant being circulated between the two. The FCU is then connected to the spaces to be cooled by ventilation ducts.[70] Floor standing air conditioners are similar to this type of air conditioner but sit within spaces that need cooling.

Central plant cooling

[edit]
Industrial air conditioners on top of the shopping mall Passage in Linz, Austria

Large central cooling plants may use intermediate coolant such as chilled water pumped into air handlers or fan coil units near or in the spaces to be cooled which then duct or deliver cold air into the spaces to be conditioned, rather than ducting cold air directly to these spaces from the plant, which is not done due to the low density and heat capacity of air, which would require impractically large ducts. The chilled water is cooled by chillers in the plant, which uses a refrigeration cycle to cool water, often transferring its heat to the atmosphere even in liquid-cooled chillers through the use of cooling towers. Chillers may be air- or liquid-cooled.[71][72]

Portable units

[edit]

A portable system has an indoor unit on wheels connected to an outdoor unit via flexible pipes, similar to a permanently fixed installed unit (such as a ductless split air conditioner).

Hose systems, which can be monoblock or air-to-air, are vented to the outside via air ducts. The monoblock type collects the water in a bucket or tray and stops when full. The air-to-air type re-evaporates the water, discharges it through the ducted hose, and can run continuously. Many but not all portable units draw indoor air and expel it outdoors through a single duct, negatively impacting their overall cooling efficiency.

Many portable air conditioners come with heat as well as a dehumidification function.[73]

Window unit and packaged terminal

[edit]
Through-the-wall PTAC units, University Motor Inn, Philadelphia

The packaged terminal air conditioner (PTAC), through-the-wall, and window air conditioners are similar. These units are installed on a window frame or on a wall opening. The unit usually has an internal partition separating its indoor and outdoor sides, which contain the unit's condenser and evaporator, respectively. PTAC systems may be adapted to provide heating in cold weather, either directly by using an electric strip, gas, or other heaters, or by reversing the refrigerant flow to heat the interior and draw heat from the exterior air, converting the air conditioner into a heat pump. They may be installed in a wall opening with the help of a special sleeve on the wall and a custom grill that is flush with the wall and window air conditioners can also be installed in a window, but without a custom grill.[74]

Packaged air conditioner

[edit]

Packaged air conditioners (also known as self-contained units)[75][76] are central systems that integrate into a single housing all the components of a split central system, and deliver air, possibly through ducts, to the spaces to be cooled. Depending on their construction they may be outdoors or indoors, on roofs (rooftop units),[77][78] draw the air to be conditioned from inside or outside a building and be water or air-cooled. Often, outdoor units are air-cooled while indoor units are liquid-cooled using a cooling tower.[70][79][80][81][82][83]

Types of compressors

[edit]
 
Compressor types Common applications Typical capacity Efficiency Durability Repairability
Reciprocating Refrigerator, Walk-in freezer, portable air conditioners small – large very low (small capacity)

medium (large capacity)

very low medium
Rotary vane Residential mini splits small low low easy
Scroll Commercial and central systems, VRF medium medium medium easy
Rotary screw Commercial chiller medium – large medium medium hard
Centrifugal Commercial chiller very large medium high hard
Maglev Centrifugal Commercial chiller very large high very high very hard

Reciprocating

[edit]

This compressor consists of a crankcase, crankshaft, piston rod, piston, piston ring, cylinder head and valves. [citation needed]

Scroll

[edit]

This compressor uses two interleaving scrolls to compress the refrigerant.[84] it consists of one fixed and one orbiting scrolls. This type of compressor is more efficient because it has 70 percent less moving parts than a reciprocating compressor. [citation needed]

Screw

[edit]

This compressor use two very closely meshing spiral rotors to compress the gas. The gas enters at the suction side and moves through the threads as the screws rotate. The meshing rotors force the gas through the compressor, and the gas exits at the end of the screws. The working area is the inter-lobe volume between the male and female rotors. It is larger at the intake end, and decreases along the length of the rotors until the exhaust port. This change in volume is the compression. [citation needed]

Capacity modulation technologies

[edit]

There are several ways to modulate the cooling capacity in refrigeration or air conditioning and heating systems. The most common in air conditioning are: on-off cycling, hot gas bypass, use or not of liquid injection, manifold configurations of multiple compressors, mechanical modulation (also called digital), and inverter technology. [citation needed]

Hot gas bypass

[edit]

Hot gas bypass involves injecting a quantity of gas from discharge to the suction side. The compressor will keep operating at the same speed, but due to the bypass, the refrigerant mass flow circulating with the system is reduced, and thus the cooling capacity. This naturally causes the compressor to run uselessly during the periods when the bypass is operating. The turn down capacity varies between 0 and 100%.[85]

Manifold configurations

[edit]

Several compressors can be installed in the system to provide the peak cooling capacity. Each compressor can run or not in order to stage the cooling capacity of the unit. The turn down capacity is either 0/33/66 or 100% for a trio configuration and either 0/50 or 100% for a tandem.[citation needed]

Mechanically modulated compressor

[edit]

This internal mechanical capacity modulation is based on periodic compression process with a control valve, the two scroll set move apart stopping the compression for a given time period. This method varies refrigerant flow by changing the average time of compression, but not the actual speed of the motor. Despite an excellent turndown ratio – from 10 to 100% of the cooling capacity, mechanically modulated scrolls have high energy consumption as the motor continuously runs.[citation needed]

Variable-speed compressor

[edit]

This system uses a variable-frequency drive (also called an Inverter) to control the speed of the compressor. The refrigerant flow rate is changed by the change in the speed of the compressor. The turn down ratio depends on the system configuration and manufacturer. It modulates from 15 or 25% up to 100% at full capacity with a single inverter from 12 to 100% with a hybrid tandem. This method is the most efficient way to modulate an air conditioner's capacity. It is up to 58% more efficient than a fixed speed system.[citation needed]

Impact

[edit]

Health effects

[edit]
Rooftop condenser unit fitted on top of an Osaka Municipal Subway 10 series subway carriage. Air conditioning has become increasingly prevalent on public transport vehicles as a form of climate control, and to ensure passenger comfort and drivers' occupational safety and health.

In hot weather, air conditioning can prevent heat stroke, dehydration due to excessive sweating, electrolyte imbalance, kidney failure, and other issues due to hyperthermia.[8][86] Heat waves are the most lethal type of weather phenomenon in the United States.[87][88] A 2020 study found that areas with lower use of air conditioning correlated with higher rates of heat-related mortality and hospitalizations.[89] The August 2003 France heatwave resulted in approximately 15,000 deaths, where 80% of the victims were over 75 years old. In response, the French government required all retirement homes to have at least one air-conditioned room at 25 °C (77 °F) per floor during heatwaves.[8]

Air conditioning (including filtration, humidification, cooling and disinfection) can be used to provide a clean, safe, hypoallergenic atmosphere in hospital operating rooms and other environments where proper atmosphere is critical to patient safety and well-being. It is sometimes recommended for home use by people with allergies, especially mold.[90][91] However, poorly maintained water cooling towers can promote the growth and spread of microorganisms such as Legionella pneumophila, the infectious agent responsible for Legionnaires' disease. As long as the cooling tower is kept clean (usually by means of a chlorine treatment), these health hazards can be avoided or reduced. The state of New York has codified requirements for registration, maintenance, and testing of cooling towers to protect against Legionella.[92]

Economic effects

[edit]

First designed to benefit targeted industries such as the press as well as large factories, the invention quickly spread to public agencies and administrations with studies with claims of increased productivity close to 24% in places equipped with air conditioning.[93]

Air conditioning caused various shifts in demography, notably that of the United States starting from the 1970s. In the US, the birth rate was lower in the spring than during other seasons until the 1970s but this difference then declined since then.[94] As of 2007, the Sun Belt contained 30% of the total US population while it was inhabited by 24% of Americans at the beginning of the 20th century.[95] Moreover, the summer mortality rate in the US, which had been higher in regions subject to a heat wave during the summer, also evened out.[7]

The spread of the use of air conditioning acts as a main driver for the growth of global demand of electricity.[96] According to a 2018 report from the International Energy Agency (IEA), it was revealed that the energy consumption for cooling in the United States, involving 328 million Americans, surpasses the combined energy consumption of 4.4 billion people in Africa, Latin America, the Middle East, and Asia (excluding China).[8] A 2020 survey found that an estimated 88% of all US households use AC, increasing to 93% when solely looking at homes built between 2010 and 2020.[97]

Environmental effects

[edit]
Air conditioner farm in the facade of a building in Singapore

Space cooling including air conditioning accounted globally for 2021 terawatt-hours of energy usage in 2016 with around 99% in the form of electricity, according to a 2018 report on air-conditioning efficiency by the International Energy Agency.[8] The report predicts an increase of electricity usage due to space cooling to around 6200 TWh by 2050,[8][98] and that with the progress currently seen, greenhouse gas emissions attributable to space cooling will double: 1,135 million tons (2016) to 2,070 million tons.[8] There is some push to increase the energy efficiency of air conditioners. United Nations Environment Programme (UNEP) and the IEA found that if air conditioners could be twice as effective as now, 460 billion tons of GHG could be cut over 40 years.[99] The UNEP and IEA also recommended legislation to decrease the use of hydrofluorocarbons, better building insulation, and more sustainable temperature-controlled food supply chains going forward.[99]

Refrigerants have also caused and continue to cause serious environmental issues, including ozone depletion and climate change, as several countries have not yet ratified the Kigali Amendment to reduce the consumption and production of hydrofluorocarbons.[100] CFCs and HCFCs refrigerants such as R-12 and R-22, respectively, used within air conditioners have caused damage to the ozone layer,[101] and hydrofluorocarbon refrigerants such as R-410A and R-404A, which were designed to replace CFCs and HCFCs, are instead exacerbating climate change.[102] Both issues happen due to the venting of refrigerant to the atmosphere, such as during repairs. HFO refrigerants, used in some if not most new equipment, solve both issues with an ozone damage potential (ODP) of zero and a much lower global warming potential (GWP) in the single or double digits vs. the three or four digits of hydrofluorocarbons.[103]

Hydrofluorocarbons would have raised global temperatures by around 0.3–0.5 °C (0.5–0.9 °F) by 2100 without the Kigali Amendment. With the Kigali Amendment, the increase of global temperatures by 2100 due to hydrofluorocarbons is predicted to be around 0.06 °C (0.1 °F).[104]

Alternatives to continual air conditioning include passive cooling, passive solar cooling, natural ventilation, operating shades to reduce solar gain, using trees, architectural shades, windows (and using window coatings) to reduce solar gain.[citation needed]

Social effects

[edit]

Socioeconomic groups with a household income below around $10,000 tend to have a low air conditioning adoption,[42] which worsens heat-related mortality.[7] The lack of cooling can be hazardous, as areas with lower use of air conditioning correlate with higher rates of heat-related mortality and hospitalizations.[89] Premature mortality in NYC is projected to grow between 47% and 95% in 30 years, with lower-income and vulnerable populations most at risk.[89] Studies on the correlation between heat-related mortality and hospitalizations and living in low socioeconomic locations can be traced in Phoenix, Arizona,[105] Hong Kong,[106] China,[106] Japan,[107] and Italy.[108][109] Additionally, costs concerning health care can act as another barrier, as the lack of private health insurance during a 2009 heat wave in Australia, was associated with heat-related hospitalization.[109]

Disparities in socioeconomic status and access to air conditioning are connected by some to institutionalized racism, which leads to the association of specific marginalized communities with lower economic status, poorer health, residing in hotter neighborhoods, engaging in physically demanding labor, and experiencing limited access to cooling technologies such as air conditioning.[109] A study overlooking Chicago, Illinois, Detroit, and Michigan found that black households were half as likely to have central air conditioning units when compared to their white counterparts.[110] Especially in cities, Redlining creates heat islands, increasing temperatures in certain parts of the city.[109] This is due to materials heat-absorbing building materials and pavements and lack of vegetation and shade coverage.[111] There have been initiatives that provide cooling solutions to low-income communities, such as public cooling spaces.[8][111]

Other techniques

[edit]

Buildings designed with passive air conditioning are generally less expensive to construct and maintain than buildings with conventional HVAC systems with lower energy demands.[112] While tens of air changes per hour, and cooling of tens of degrees, can be achieved with passive methods, site-specific microclimate must be taken into account, complicating building design.[12]

Many techniques can be used to increase comfort and reduce the temperature in buildings. These include evaporative cooling, selective shading, wind, thermal convection, and heat storage.[113]

Passive ventilation

[edit]
The ventilation system of a regular earthship
Dogtrot houses are designed to maximise natural ventilation.
A roof turbine ventilator, colloquially known as a 'Whirly Bird' is an application of wind driven ventilation.

Passive ventilation is the process of supplying air to and removing air from an indoor space without using mechanical systems. It refers to the flow of external air to an indoor space as a result of pressure differences arising from natural forces.

There are two types of natural ventilation occurring in buildings: wind driven ventilation and buoyancy-driven ventilation. Wind driven ventilation arises from the different pressures created by wind around a building or structure, and openings being formed on the perimeter which then permit flow through the building. Buoyancy-driven ventilation occurs as a result of the directional buoyancy force that results from temperature differences between the interior and exterior.[114]

Since the internal heat gains which create temperature differences between the interior and exterior are created by natural processes, including the heat from people, and wind effects are variable, naturally ventilated buildings are sometimes called "breathing buildings".

Passive cooling

[edit]
 
A traditional Iranian solar cooling design using a wind tower

Passive cooling is a building design approach that focuses on heat gain control and heat dissipation in a building in order to improve the indoor thermal comfort with low or no energy consumption.[115][116] This approach works either by preventing heat from entering the interior (heat gain prevention) or by removing heat from the building (natural cooling).[117]

Natural cooling utilizes on-site energy, available from the natural environment, combined with the architectural design of building components (e.g. building envelope), rather than mechanical systems to dissipate heat.[118] Therefore, natural cooling depends not only on the architectural design of the building but on how the site's natural resources are used as heat sinks (i.e. everything that absorbs or dissipates heat). Examples of on-site heat sinks are the upper atmosphere (night sky), the outdoor air (wind), and the earth/soil.

Passive cooling is an important tool for design of buildings for climate change adaptation – reducing dependency on energy-intensive air conditioning in warming environments.[119][120]
A pair of short windcatchers (malqaf) used in traditional architecture; wind is forced down on the windward side and leaves on the leeward side (cross-ventilation). In the absence of wind, the circulation can be driven with evaporative cooling in the inlet (which is also designed to catch dust). In the center, a shuksheika (roof lantern vent), used to shade the qa'a below while allowing hot air rise out of it (stack effect).[11]

Daytime radiative cooling

[edit]
Passive daytime radiative cooling (PDRC) surfaces are high in solar reflectance and heat emittance, cooling with zero energy use or pollution.[121]

Passive daytime radiative cooling (PDRC) surfaces reflect incoming solar radiation and heat back into outer space through the infrared window for cooling during the daytime. Daytime radiative cooling became possible with the ability to suppress solar heating using photonic structures, which emerged through a study by Raman et al. (2014).[122] PDRCs can come in a variety of forms, including paint coatings and films, that are designed to be high in solar reflectance and thermal emittance.[121][123]

PDRC applications on building roofs and envelopes have demonstrated significant decreases in energy consumption and costs.[123] In suburban single-family residential areas, PDRC application on roofs can potentially lower energy costs by 26% to 46%.[124] PDRCs are predicted to show a market size of ~$27 billion for indoor space cooling by 2025 and have undergone a surge in research and development since the 2010s.[125][126]

Fans

[edit]

Hand fans have existed since prehistory. Large human-powered fans built into buildings include the punkah.

The 2nd-century Chinese inventor Ding Huan of the Han dynasty invented a rotary fan for air conditioning, with seven wheels 3 m (10 ft) in diameter and manually powered by prisoners.[127]: 99, 151, 233  In 747, Emperor Xuanzong (r. 712–762) of the Tang dynasty (618–907) had the Cool Hall (Liang Dian 涼殿) built in the imperial palace, which the Tang Yulin describes as having water-powered fan wheels for air conditioning as well as rising jet streams of water from fountains. During the subsequent Song dynasty (960–1279), written sources mentioned the air conditioning rotary fan as even more widely used.[127]: 134, 151 

Thermal buffering

[edit]

In areas that are cold at night or in winter, heat storage is used. Heat may be stored in earth or masonry; air is drawn past the masonry to heat or cool it.[13]

In areas that are below freezing at night in winter, snow and ice can be collected and stored in ice houses for later use in cooling.[13] This technique is over 3,700 years old in the Middle East.[128] Harvesting outdoor ice during winter and transporting and storing for use in summer was practiced by wealthy Europeans in the early 1600s,[15] and became popular in Europe and the Americas towards the end of the 1600s.[129] This practice was replaced by mechanical compression-cycle icemakers.

Evaporative cooling

[edit]
An evaporative cooler

In dry, hot climates, the evaporative cooling effect may be used by placing water at the air intake, such that the draft draws air over water and then into the house. For this reason, it is sometimes said that the fountain, in the architecture of hot, arid climates, is like the fireplace in the architecture of cold climates.[11] Evaporative cooling also makes the air more humid, which can be beneficial in a dry desert climate.[130]

Evaporative coolers tend to feel as if they are not working during times of high humidity, when there is not much dry air with which the coolers can work to make the air as cool as possible for dwelling occupants. Unlike other types of air conditioners, evaporative coolers rely on the outside air to be channeled through cooler pads that cool the air before it reaches the inside of a house through its air duct system; this cooled outside air must be allowed to push the warmer air within the house out through an exhaust opening such as an open door or window.[131]

See also

[edit]

References

[edit]
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  3. ^ 1993 ASHRAE Handbook: Fundamentals. ASHRAE. 1993. ISBN 978-0-910110-97-6.
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[edit]

 

Frequently Asked Questions

Misaligned fan blades can cause an imbalance in the unit, leading to vibrations and a wobbling motion that results in unusual noises. This misalignment often originates from physical impacts or improper installation.
Dirt accumulation can lead to uneven weight distribution on the fan blades, causing them to become imbalanced. This imbalance increases vibration and noise during operation as the motor works harder to maintain performance.
Yes, damaged or bent fan blades disrupt airflow efficiency and create turbulence, leading to rattling or clanking sounds as they hit other components within the system.
Loose mounting hardware allows excessive movement of the fan assembly, which can result in rattling or banging noises as the unit operates due to increased vibration against its housing.