Types of Air-conditioning methods

The basic concept behind air conditioning is said to have been applied in ancient Egypt, where reeds were hung in windows and were moistened with trickling water. The evaporation of water cooled the air blowing through the window, though this process also made the air more humid (also beneficial in a dry desert climate). In Ancient Rome, water from aqueducts was circulated through the walls of certain houses to cool them.

Mechanical Cooling

The 2nd-century Chinese inventor Ding Huan of the Han Dynasty invented a rotary fan for air conditioning, with seven wheels 3 m (9.8 ft) in diameter and manually powered. In 747, Emperor Xuanzong (r. 712–762) of the Tang Dynasty (618–907) had the Cool Hall (Liang Tian) 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.

In the 17th century, Cornelis Drebbel demonstrated “Turning Summer into Winter” for James I of England by adding salt to water.

In 1758, Benjamin Franklin and John Hadley, a chemistry professor at Cambridge University, conducted an experiment to explore the principle of evaporation as a means to rapidly cool an object. Franklin and Hadley confirmed that 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 conducted their experiment with the bulb of a mercury thermometer as their object and with a bellows used to “quicken” 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 a quarter-inch 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”.

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. 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 eventually to use his ice-making machine to regulate the temperature of buildings. He even envisioned centralized air conditioning that could cool entire cities. Though his prototype leaked and performed irregularly, Gorrie was granted a patent in 1851 for his ice-making machine. His hopes for its success vanished soon afterwards when his chief financial backer died; Gorrie did not get the money he needed to develop the machine. According to his biographer, Vivian M. Sherlock, he blamed the “Ice King”, Frederic Tudor, for his failure, suspecting that Tudor had launched a smear campaign against his invention. Dr. Gorrie died impoverished in 1855, and the idea of air conditioning went away for 50 years.

Since prehistoric times, snow and ice were used for cooling. The business of harvesting ice during winter and storing for use in summer became popular towards the late 19th century. This practice was replaced by mechanical ice-making machine.

James Harrison’s first mechanical ice-making machine began operation in 1851 on the banks of the Barwon River at Rocky Point in Geelong (Australia). His first commercial ice-making machine followed in 1854, and his patent for an ether vapor-compression refrigeration system was granted in 1855. This novel system used a compressor to force the refrigeration gas to pass through a condenser, where it cooled down and liquefied. The liquefied gas then circulated through the refrigeration coils and vaporised again, cooling down the surrounding system. The machine employed a 5 m (16 ft.) flywheel and produced 3,000 kilograms (6,600 lb) of ice per day.

Though Harrison had commercial success establishing a second ice company back in Sydney in 1860, he later entered the debate over how to compete against the American advantage of unrefrigerated beef sales to the United Kingdom. He wrote Fresh Meat frozen and packed as if for a voyage, so that the refrigerating process may be continued for any required period, and in 1873 prepared the sailing ship Norfolk for an experimental beef shipment to the United Kingdom. His choice of a cold room system instead of installing a refrigeration system upon the ship itself proved disastrous when the ice was consumed faster than expected.

Electromechanical cooling

In 1902, the first modern electrical air conditioning unit was invented by Willis Carrier in Buffalo, New York. After graduating from Cornell University, Carrier, a native of Angola, New York, found a job at the Buffalo Forge Company. While there, Carrier began experimenting with air conditioning as a way to solve an application problem for the Sackett-Wilhelms Lithographing and Publishing Company in Brooklyn, New York, and the first “air conditioner”, designed and built in Buffalo by Carrier, began working on 17 July 1902.

Designed to improve manufacturing process control in a printing plant, Carrier’s invention controlled not only temperature but also humidity. Carrier used his knowledge of the heating of objects with steam and reversed the process. Instead of sending air through hot coils, he sent it through cold coils (ones filled with cold water). The air blowing over the cold coils cooled, and one could thereby control the amount of moisture the colder air could hold. In turn, the humidity in the room could be controlled. The low heat and humidity helped maintain consistent paper dimensions and ink alignment. Later, Carrier’s technology was applied to increase productivity in the workplace, and The Carrier Air Conditioning Company of Americawas formed to meet rising demand. Over time, air conditioning came to be used to improve comfort in homes and automobiles as well. Residential sales expanded dramatically in the 1950s.

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”, using it in a patent claim he filed that year as an analogue to “water conditioning”, then a well-known process for making textiles easier to process. He combined moisture with ventilation to “condition” and change the air in the factories, controlling the humidity so necessary in textile plants. Willis Carrier adopted the term and incorporated it into the name of his company. The evaporation of water in air, to provide a cooling effect, is now known as evaporative cooling.

Evaporative cooling was the first real air-conditioning and shortly thereafter the first private home to have air conditioning (The Dubose House) was built in Chapel Hill, North Carolina in 1933. Realizing that air conditioning would one day be a standard feature of private homes, particularly in the South, David St. Pierre DuBose (1898-1994) designed an ingenious network of ductwork and vents, all painstakingly disguised behind intricate and attractive Georgian-style open moldings. Meadowmont is believed to be one of the first private homes in the United States equipped for central air conditioning. In 1945, Robert Sherman of Lynn, MA, invented the portable, in-window air conditioner that cooled and heated, humidified and dehumidified, and filtered the air.

Refrigerant cooling

The first air conditioners and refrigerators employed toxic or flammable gases, such as ammonia, methyl chloride, or propane, that could result in fatal accidents when they leaked. Thomas Midgley, Jr created the first non-flammable, non-toxic chlorofluorocarbon gas, Freon, in 1928.

“Freon” is a trademark name owned by DuPont for any Chlorofluorocarbon (CFC), Hydro-chlorofluorocarbon (HCFC), or Hydro-fluorocarbon (HFC) refrigerant, the name of each including a number indicating molecular composition (R-11, R-12, R-22, R-134A). The blend most used in direct-expansion home and building comfort cooling is an HCFC known as R-22. It was to be phased out for use in new equipment by 2010, and is to be completely discontinued by 2020.

R-12 was the most common blend used in automobiles in the US until 1994, when most designs changed to R-134A. R-11 and R-12 are no longer manufactured in the US for this type of application, the only source for air-conditioning repair purposes being the cleaned and purified gas recovered from other air-conditioner systems. Several non-ozone-depleting refrigerants have been developed as alternatives, including R-410A, invented by AlliedSignal (now part of Honeywell) in Buffalo, and sold under the Genetron (R) AZ-20 name. It was first commercially used by Carrier under the brand name Puron. Innovation in air-conditioning technologies continues, with much recent emphasis placed on energy efficiency and on improving indoor air quality. Reducing climate-change impact is an important area of innovation because, in addition to greenhouse-gas emissions associated with energy use, CFCs, HCFCs, and HFCs are, themselves, potent greenhouse gases when leaked to the atmosphere. For example, R-22 (also known as HCFC-22) has a global warming potential about 1,800 times higher than CO₂. As an alternative to conventional refrigerants, natural alternatives, such as carbon dioxide (CO₂. R-744), have been proposed.

Types of refrigeration systems

• Air conditioning systems can be broadly classified into 2 types
• Direct expansion systems (DX system)
• Chilled water systems (indirect systems)

Direct Expansion System

In this system the refrigerant is used to cool the air directly. e.g. room air conditioners, packaged units, central direct expansion plants.

Main components of direct expansion system

• Compressor (hermetic or open type)
• Condenser (air cooled or water cooled)
• Evaporator or cooling coil with fan
• Cooling tower or spray panel (in case of water cooled condenser)
• Condenser water pump set
• Air distribution ducting and grills

Chilled water system

In this medium the secondary medium (usually water) is used to achieve cooling objectives. The refrigerant first cools the water and then the water then cools the air.

Main components of a chilled water system

• Compressor (reciprocating or centrifugal)
• Condenser (mostly water cooled)
• Chiller (direct expansion or flood type)
• Air handling unit with chilled water coil or fan coil or water air washers
• Cooling tower
• Chilled water and condenser pump sets
• Air distribution ducting and grills