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Air Conditioners

Air conditioning is the mechanical process of cooling air to maintain optimal temperatures within a room, building, or facility. Air conditioners range in size from compact units designed for window installations to large-scale systems capable of cooling entire skyscrapers or specific sections within them. These systems operate using a combination of compressors, condensers, fans, refrigerant gases, and thermostats, with some incorporating ductwork to distribute cooled air. Whether for human comfort or industrial applications, air conditioning plays a crucial role in regulating temperatures for sensitive materials, such as electronics and volatile chemicals, ensuring proper storage and operational conditions.

he History of Air Conditioners

Early History of Air Conditioning

Evaporative cooling marked the first step toward air conditioning, with ancient Egyptians using wet reed curtains to cool air as breezes evaporated water. The Romans developed a system that channeled cool water from aqueducts through walls to regulate building temperatures, while the Persians designed cisterns and wind towers to facilitate cooling.

During the Han Dynasty in 2nd-century China, prisoners operated a series of rotating fans to cool the Imperial Palace. This manually powered system remained in use, largely unchanged, through the Song Dynasty in the 13th century.

In 1840s Florida, Dr. John Gorrie sought to combat "the evils of high temperatures," believing that cooling hospital air could help prevent disease and provide relief for malaria patients. Initially, he relied on shipping blocks of ice from the northern states and using fans to circulate cooled air, though this method was expensive and only mildly effective. Inspired by Michael Faraday's 1824 discovery that liquefied ammonia could chill air as it evaporates, Gorrie experimented with mechanical cooling and invented a rudimentary compressor capable of making ice. He patented his invention in 1851, but after losing financial backing, his dream of large-scale cooling remained unrealized.

Air Conditioners in the 1900s

In 1902, Willis Carrier faced the challenge of controlling humidity for a Brooklyn lithographer whose magazine pages were wrinkling due to excess moisture. Carrier's work led to his patented "Apparatus for Treating Air," which used tubular coils filled with water to either humidify or dehumidify a room. Further advancements included an automatic control system to regulate temperature and humidity in textile mills. Recognizing the potential of his innovations, Carrier launched his own company to develop large-scale industrial air conditioning.

Air conditioning saw its first major breakthrough in the 1920s with its introduction to theaters. Early systems, adapted from heating units with refrigeration compressors, pushed air through floor vents, leaving theatergoers with cold feet and warm heads. In 1922, the Metropolitan Theater in Los Angeles installed a more effective ventilation system, while the Rivoli Theater in New York introduced a centrifugal chiller, which featured fewer moving parts, improved reliability, and lower manufacturing and operating costs.

The earliest refrigerant gases used in air conditioning—ammonia, methyl chloride, and propane—posed significant safety hazards due to their toxicity and flammability. In 1928, Thomas Midgley, Albert Henne, and Robert McNary synthesized the first non-flammable refrigerant gases, known as chlorofluorocarbons (CFCs), including Freon. The development of CFCs, hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs) allowed manufacturers to produce safer and more efficient air conditioning systems. While many of these refrigerants were later phased out due to their impact on climate change and ozone depletion, they played a crucial role in making air conditioning widely accessible.

In 1929, a split-system room cooler was developed for home use, but its size, cost, and requirement for a separate condenser made it impractical for most households. Frank Faust refined the design, and by 1931, a self-contained room cooler was introduced. The following year, H.H. Schultz and J.Q. Sherman developed the first window-mounted air conditioner, though its high cost initially limited consumer adoption. Henry Galson improved on the concept, creating a more compact and affordable window unit, and by 1947, 43,000 units had been sold.

The introduction of the rotary compressor in 1957 made air conditioners smaller, lighter, and easier to install. By the late 1960s, nearly all new buildings were constructed with central air, fueling rapid population growth in hot climates such as Arizona, Texas, and Florida.

The energy crisis of the mid-1970s led the U.S. Department of Energy to implement energy reduction laws and efficiency standards. By 1992, conservation regulations required home air conditioning units to meet minimum energy efficiency levels. As microprocessing and semiconductor technology advanced in the 1990s, high-efficiency, low-energy air conditioners emerged, along with programmable thermostats to further reduce energy consumption.

Added Air Conditioner Requirements in the 2000s

Since 2006, air conditioning units in the U.S. have been required to meet minimum energy efficiency standards, measured by the Seasonal Energy Efficiency Ratio (SEER). This rating is calculated by dividing the annual cooling output in BTUs by the total energy consumption in watt-hours over the same period. The minimum SEER rating for air conditioning units in the United States is 13, ensuring greater energy savings and environmental sustainability.

Workings and Design of Air Conditioning

Modern air conditioners recirculate air within a space rather than continuously cooling warm air from outside, making the air progressively cooler. Many units are also equipped with a heat pump, enabling them to provide both heating and cooling as needed.

Air conditioning operates on the principle of evaporative cooling in a vacuum, a concept first observed by Benjamin Franklin and John Hadley at Cambridge University in 1758. They discovered that the evaporation of volatile liquids such as ether or alcohol could chill objects to temperatures below the freezing point of water.

Typically, cold moves toward heat, which can be observed when placing a hand near an ice-cold beverage on a hot day. The cold radiates outward, and moisture from the air condenses on the outside of the glass. However, in the refrigeration cycle, "work" must be done to remove warm air from an enclosed space to maintain a cool temperature. This process relies on refrigerant gases that circulate through a closed-loop system of pipes or tubes, with separate fans controlling airflow for both the cooling and heating cycles.

The refrigeration cycle begins when the refrigerant gas enters a compressor, where it is pressurized and heated. The hot gas vapor then moves into the condenser, where air passing over the coils cools the gas and causes it to liquefy. Still under pressure, the condensed gas flows through an expansion valve, which can be a simple hole in the piping or a pressure-activated valve. As the gas expands rapidly, it undergoes flash evaporation, drastically lowering its temperature.

The chilled refrigerant then moves into an evaporator, where a fan blows warm air across the evaporator coils, cooling the air. As the refrigerant absorbs heat and evaporates, it turns back into a gas and is cycled back to the compressor to repeat the process. The most commonly used refrigerant in home air conditioning systems is R-22, chlorofluoromethane, while HFC R-134a is widely used in automotive air conditioning.

Heating and air conditioning performance is measured in British thermal units (BTU), a unit of energy that quantifies temperature changes. One BTU represents the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit. In heating, BTUs measure the energy required to add warmth to a space, while in air conditioning, they measure the energy needed to remove heat. A 15,000 BTU air conditioner, for example, removes 15,000 units of heat from an environment.

Air Conditioner Location and Sizing

Where to Find an Air Conditioner

Air conditioners are used in vehicles such as cars, airplanes, trains, and cruise or cargo ships. They provide essential comfort in office buildings, restaurants, shopping centers, apartment complexes, sports stadiums, hospitals, and schools. In industrial settings, air conditioning is crucial for both worker comfort and equipment safety, preventing overheating and ensuring optimal operational conditions.

Air conditioners are widely implemented in residential, commercial, and industrial settings, with manufacturers designing a range of models to accommodate diverse environments and needs. These units are typically installed in locations where natural ventilation or fans are insufficient due to extreme temperatures, air disturbances, or pollution. Many systems also incorporate air filters to maintain air quality, preventing the spread of germs, pollutants, and other airborne contaminants.

Air Conditioner Sizes

Variations in size, power, and air delivery capacity help consumers select the most suitable unit for their needs. Some of the most common types include cabinet air conditioners, ductless air conditioners, central air conditioners, and split air conditioners. The size and power of an air conditioning system are the most critical factors when determining its suitability for a specific space.

Portable air conditioners, also known as spot coolers, are compact units that can be easily moved to different areas within a facility. While convenient, they provide only limited cooling and are often used in spaces where a primary air conditioning system does not reach or where additional cooling is required.

Cabinet air conditioners, housed within a protective enclosure, are slightly larger and designed to safeguard internal components from dust, water, liquid spray, and accidental contact. These units are often connected to air ducts or air-handling equipment, which distribute cool air throughout a building. However, in cases where ductwork installation is not feasible or cost-effective, ductless air conditioners provide an alternative by delivering cooled air directly into a space. These systems can cool larger areas than portable or window-mounted air conditioners, as multiple evaporators can be connected to a single compressor.

Central air conditioners are powerful enough to cool an entire building. In residential settings, the main unit is typically installed outside, while commercial and industrial systems often position air conditioning units on rooftops for efficiency and space conservation.

Split air conditioners separate the hot condensing unit from the cool air-handling unit, with the hot components placed outdoors to enhance efficiency. These systems may feature a single large condensing unit or multiple smaller units, allowing different areas of a building to be cooled separately. However, split air conditioners are less effective in multi-level structures, as larger buildings require more robust cooling solutions.

Commercial air conditioners are specifically designed to regulate temperatures in office buildings, retail stores, and other commercial spaces. These systems generally rely on central air conditioning to maintain consistent and comfortable indoor temperatures throughout the facility. Similarly, industrial air conditioners are essential in manufacturing plants, warehouses, and shipping facilities, where precise climate control is necessary for both equipment protection and worker safety.

Types of Air Conditioning Systems

Split Air Conditioner System

A split air conditioner system separates the evaporator, or inside heat exchanger, from the condenser, or outside heat exchanger, placing them at a distance from each other. A mini-split system is a ductless air conditioning system designed to heat or cool a single zone, though it can be configured with multiple evaporator units to serve up to eight zones from a single condenser.

Multi-Split Air Conditioner System

A multi-split system uses a single, high-capacity outdoor condenser equipped with multiple ports in a manifold to distribute refrigerant to several evaporators. This configuration is ideal for cooling large buildings with multiple zones or rooms while minimizing outdoor unit space requirements.

Multi-Zoned Conditioner Systems

These systems provide flexibility with their compact evaporator units and diverse installation configurations. While the initial installation cost is higher than some other air conditioning options, the lower operating costs of split air conditioning systems often make them a worthwhile long-term investment.

Central Air Conditioner

Also known as ducted air conditioners, central air systems are standard in modern construction. They utilize a forced-air system to distribute cooled air from a single unit through ductwork, with louvered vents directing airflow throughout the building.

Industrial Air Conditioners Uses and Proper Care

Air Conditioners and Avoiding Overheating

Industrial air conditioners serve as the first line of defense against declining worker productivity and equipment failure. Studies indicate that employees perform less efficiently in overly warm environments, whereas even a slight reduction in room temperature can significantly boost productivity. Additionally, electronic equipment generates substantial heat, which must be dissipated to prevent overheating and the cascading failures that power loss or service interruptions can trigger.

Beyond temperature control, industrial air conditioning systems are essential for maintaining precise humidity levels, reducing static electricity, preventing the over-drying of textiles, minimizing paper warping, and ensuring the proper flow of powdered materials. Effective air filtration is also critical in cleanrooms and manufacturing environments, helping to remove contaminants and maintain air quality standards.

Proper Care for Industrial Conditioners

The mass cooling and air distribution process is carefully calculated to meet the specific needs of each industrial application. Factors such as space size, shape, function, and structural integrity must be evaluated to ensure adequate cooling capacity. Additionally, the quality of the air being circulated is a crucial consideration.

Industrial air conditioning ductwork can extend hundreds or even thousands of feet, making it susceptible to accumulating dust, fumes, mold, and other contaminants. If left unchecked, these pollutants can spread throughout a facility, causing poor air quality and potential health issues. In severe cases, prolonged exposure to such conditions can lead to "Sick Building Syndrome," where occupants experience illness simply from being inside the building.

Regular maintenance, including proper filtration, routine cleaning, and thorough inspections—particularly of ductwork—can prevent the spread of disease and create a safer, healthier work environment.

Contacting a HVAC Specialist

The ideal heating, ventilation, and air conditioning (HVAC) system depends on the specific needs of each application. While air conditioners are readily available at department stores and home improvement retailers, an off-the-shelf unit may not always be the best solution. A professional assessment of your unique requirements should be the first step in the air conditioning selection process.

Evaluating and calculating factors such as air volume, temperature control, humidity levels, and installation and operational costs are essential to designing an efficient system. An HVAC specialist can guide you in developing a solution that aligns with both your performance standards and budget.

Air Conditioner Terms

Accumulator
A shell-shaped device integrated into an HVAC (heating, ventilation, and air conditioning) system within the suction line to protect the compressor from liquid damage.

Active Cooling
Air conditioning that operates using a compressor-driven system.

Adsorption
The process of drying air or gas by trapping moisture vapor on a desiccant surface without altering its molecular structure.

Air Handler
The indoor unit of an air conditioning system responsible for delivering conditioned air into a space. It consists of a heat exchange coil, filters, and a fan.

BTU (British Thermal Unit)
A unit of heat or energy measurement. One BTU is the amount of heat required to raise or lower the temperature of one pound of water by one degree Fahrenheit.

Capacity
The maximum amount of heat energy an HVAC system can remove from or add to a medium.

Compressor
Often called the "heart" of a refrigeration or air conditioning system, a compressor is a pump that pressurizes refrigerant, moving it between an outdoor condensing unit and an indoor evaporating unit.

Condensation
The process of converting air into liquid form.

Desiccant
A substance designed to absorb and retain moisture.

District Heating and Cooling
A central utility system used to provide heating or cooling to large residential or industrial areas.

Duct
A passage or conduit used to distribute air in an HVAC system.

Filter
A device designed to remove solid and liquid particles from the air or gas stream.

Gravity Cooling
A cooling method using an evaporator that does not rely on a fan for air circulation.

Heat Exchanger
A device that facilitates heat transfer from one place or medium to another.

Absolute Humidity
The total mass of water vapor present per unit volume of air, typically measured in grains/ft³, lbs/ft³, or grams/ft³.

Inlet Pressure
The total pressure at the compressor’s inlet flange.

Load
The required rate of heat removal to maintain a specific temperature.

Moisture Separator
A device used to extract condensate from an air stream.

Precooler
A heat exchanger that lowers the temperature of incoming air using the outgoing cold air while simultaneously reheating the outgoing air with the incoming air.

Refrigerant
A heat transfer medium in a refrigeration system that absorbs heat by evaporating at a low temperature and releases heat by condensing at a high temperature.

Silica Gel
A regenerative desiccant used to absorb moisture.

Vapor Pressure
The pressure exerted at the interface between a liquid and its vapor.