Air Conditioner

An air conditioner not only controls the temperature, it also regulates the humidity, circulation, and purity of the air within a room or a building.

An air conditioner is a group of equipment that "conditions" the air by controlling not only the temperature but also the humidity (moisture level), circulation, and purity of the air within a room or a building. It usually consists of a pump called a compressor, a condenser, an evaporator, and a refrigerant (see below). Most people associate air conditioning with cooling the air during warm weather. However, air conditioning also involves heating the air during cold weather. In both cases, air conditioning provides human comfort.

The cooling capacity, or size, of an air conditioner is rated by the number of British thermal units (Btu) of heat it can remove per hour. Btu is the amount of heat required to raise the temperature of one pound (0.45 kilogram) of water one degree Fahrenheit (0.56 degree Celsius) per hour. Air conditioner sellers and contractors help consumers determine the size of the air conditioner unit needed using published calculation procedures recommended by industry experts.

Keeping cool through the ages

Since early times, people have looked for ways to keep cool. Ancient Greeks and Romans built public baths, which were community facilities that accommodated hundreds of people. Some people cooled the air entering their homes by hanging wet grass mats over windows and doors. Others used big leaves to fan themselves.

The powerful and wealthy beat the heat in different ways. Roman emperors reportedly ordered mountain snow transported to their palaces during the summer months. Some people had their servants pack snow between the walls of their homes. Still others had slaves fanning blocks of ice. Around 1500, Leonardo da Vinci (1452–1519), noted for his many clever inventions, constructed a mechanical fan to circulate the air in the home of a duchess.

The first air conditioners

The first attempts to condition air within enclosed spaces occurred during the eighteenth and nineteenth centuries. The purpose of the air conditioning was not to cool people but to provide humidity in textile factories so that fabric thread would not break due to the dry air. Water sprays and pots of hot water were used to keep the air moist. In 1842, American doctor John Gorie (1803–1855), having invented mechanical refrigeration, applied the same principle to cool patients' rooms. In 1902, the first air conditioner designed for human comfort was installed at the New York Stock Exchange. The term "air conditioning" was coined in 1906 by textile engineer Stuart Cramer (1868–1940), who invented a device to freshen and humidify his textile factory by adding moisture to the surroundings.

Father of air conditioning

Mechanical engineer Willis Carrier (1876–1950) is credited for developing the formulas that form the basis for the air conditioning system. He first created an air conditioner for a printing factory in Brooklyn, New York, in 1902. Fluctuating temperature and humidity caused changes in paper size so that the colored inks did not line up properly during printing. Carrier solved the problem by devising two sets of cooling coils (groups of tubes) over which he passed the air during hot weather. During cold weather, he piped in steam from the factory boilers. By 1907, Carrier's air conditioning system had been installed in several textile factories, a shoe factory, and a drug company.

In 1921, Carrier invented the centrifugal refrigeration machine, which enabled the air conditioning of large areas. While industries were the first to use Carrier's machine, commercial buildings, including department stores, hotels, and movie theaters, soon followed. In 1930, the White House became air conditioned. Although Carrier introduced the residential air conditioner called the "Weathermaker" in 1928, it was not until the end of World War II (1939–45) that it was installed in American homes.

Raw Materials

Air conditioners are made of different types of metal, including copper and aluminum. Plastic, which is lightweight and inexpensive, may also be used. Copper and aluminum are important raw materials in many air conditioning components (parts), because they are good heat conductors, contributing to the efficiency of the system. In addition, these two metals can be easily shaped and bent and are resistant to corrosion (the slow wearing out of a metal by a liquid or a gas). Aluminum's light weight is an additional benefit.

Other air conditioner components are made of stainless steel, which is also resistant to rusting and other environmental changes. Self-contained units that house the refrigeration system are usually encased in sheet metal, produced by flattening steel with rollers. The sheet metal is covered with a powder coating to protect it from environmental conditions.

The refrigerant is the working fluid that circulates through the air conditioning system. Refrigerants used include hydrocarbons, ammonia, and water. Hydrochlorofluorocarbon (HCFC), which goes by the trade name R-22, is the refrigerant most commonly used in air conditioners. However, its global manufacture is being phased out (reduced in stages over a period of time) because of its negative effect on the ozone layer (oxygen layer that protects the earth from harmful ultraviolet rays). Scientists are researching suitable replacements for HCFCs. New air conditioners that are being manufactured use a chlorine-free refrigerant called Puron®, or R-410A.

Design

An air conditioner has four basic parts—a pump called the compressor, an evaporator, a condenser, and an expansion valve. It also contains a refrigerant, or a working fluid, that continuously moves through the air conditioning system. Most residential air conditioners get their power from a combination of an electric motor and pump. Some may use a gas engine and a pump.

The process of air conditioning involves the drawing in of heat from the air inside the home and then releasing that heat outdoors. These functions are performed by the refrigerant as it circulates through the air conditioning system. The pump is designed to increase system pressure and circulate the refrigerant.

ENVIRONMENTAL CONCERNS

Scientists have found that certain chemicals, such as hydrochlorofluorocarbons (HCFCs), currently used as refrigerants in air conditioners, are diminishing the ozone layer above the earth. The ozone layer, made up of oxygen, blocks most of the sun's harmful ultraviolet rays. Scientists believe that holes in the ozone layer have resulted in increased numbers of certain cancers (for example, skin cancers) and decreasing fish populations and plant growth.

The refrigerant, in the form of a low-pressure vapor (gas), starts at the compressor, in which it is "compressed," or squeezed, changing into a hot, high-pressure vapor. The hot refrigerant vapor travels through a condenser coil, which has metal fins all around it. The fins help the refrigerant transfer heat to the outside, causing the refrigerant to change to a liquid.

Next, the liquid refrigerant flows into the evaporator through a narrow expansion valve called a capillary tube. The capillary tube allows the refrigerant's pressure to drop, causing it to evaporate. In the meantime, the hot air in the room is drawn to the evaporator surface through its metal fins. The refrigerant circulating in the evaporator coil absorbs that heat and thus cools the room. In the process, the refrigerant changes into a low-pressure vapor, returns to the compressor, and restarts its circulation through the air conditioning system.

The Manufacturing Process

Most air conditioners start out as sheet metal and structural steel shapes. A sheet metal is usually steel and is made by pressing the metal under pressure between rollers. A structural steel shape is a basic construction material. It is a very strong steel that has been shaped.

Constructing the casing, brackets, and other supports

1 The casing that houses the air conditioner unit is made of sheet metal. The sheet metal has usually been galvanized, or coated with a thin layer of zinc to protect it against corrosion. The galvanized sheet metal is also used to form the bottom pan, face plates, and various support brackets. A shear press, a machine that cuts by using a mold and applying pressure, is used to cut the different air conditioner parts.

Structural steel shapes are used to make some of the brackets and supports. The steel shapes are cut and mitered. Mitering refers to the process of forming a perpendicular joint, usually at a 45-degree angle, so that it could be attached to a similar piece to form a 90-degree corner.

Punch pressing the sheet metal forms

2 From the shear press, the sheet metal is loaded on a CNC (Computer Numerical Control) punch press, which uses two matching dies, or molds, to form a shape using pressure. The punch press may receive its computer program from an independently written CNC program or from a drafting program called CAD/CAM (Computer-Aided Drafting/Computer-Aided Manufacturing) program.

The CAD/CAM program will convert a drafted or modeled air conditioner part on the computer into a file that can be read by the punch press. The program tells the punch press where to punch holes in the sheet metal. The dies and other cutting instruments are stored in the punch press and can be mechanically brought to the punching arm for use in cutting the desired shape. The computer-controlled press brakes bend the sheet metal into its final form. Different bending dies are used to make different shapes.

3 Some support brackets that are made from sheet metal are produced on a hydraulic press or a mechanical press. A coiled sheet metal is unrolled as it is fed into the press, producing different shapes. High volumes of brackets can be made because the press can often produce a complex shape with one hit.

Some brackets, fins, and other air conditioner parts are manufactured by outside companies. They are brought into the assembly factory as needed. (Fins are thin aluminum strips that are bonded to the outer surface of evaporator and condenser coils. They help in the transfer of heat to and from the coils.)

Cleaning the parts

4 Different cleaning methods are used to remove dirt, oil, grease, and lubricants from the cut shapes that will make up the air conditioner. The parts may be soaked in large tanks filled with a cleaning solvent, which is stirred to remove the oil. Spray-wash systems using pressurized cleaning solutions may be used to knock off dirt and grease. Vapor degreasing may also be used. It involves hanging the parts above a harsh cleansing vapor, usually made of acid. As the vapor condenses (changes to liquid) on the metal surface, the grease and lubricants are removed.

Air conditioner parts that are manufactured by outside companies arrive at the assembly factory already degreased and cleaned. For additional corrosion protection, the parts may be put in a phosphate primer bath.

Powder coating

5 Before casings, pans, and brackets are assembled, they undergo a powder-coating process. First, the metal parts are charged with static electricity so the powder will stick to the bends and small openings within each part. As the parts are fed through a booth on an overhead conveyor belt, robotic sprayers cover the parts with a paint-like coating. Using the same conveyor system, the powder-coated parts are passed through an oven where the powder is permanently baked on the metal.

Bending the tubing for the condenser and evaporator

6 The condenser and evaporator are made of copper or aluminum tubing. Tubing arrives at the manufacturing factory in a large coil form. Before it can be processed in a bender to make the individual condenser and evaporator coils, the tubing goes through an uncoiler and straightener. Some straightened tubings are cut into desired lengths with an abrasive saw.

7 The tubing is formed into U-shaped bends with an computer-controlled bender, using the same principle as the press brake (see Step 2). A mandrel (a supporting bar) is inserted through the tubing, which is bent around a fixed mold. When the desired bend is achieved, the mandrel that kept the tube from collapsing during the bending process is pulled out. The finished evaporator and condenser coils are transported to the assembly area, where they are stacked on guide rods.

Aluminum plates are punched out using a punch press and formed on a mechanical press to place waves on the plates. These waves help in the transfer of heat.

Finishing the evaporator and condenser coils

8 Joining the evaporator coil with the aluminum plate constitutes a major part of the air conditioner assembly. The coil is mechanically fused to the aluminum plate by first inserting a mandrel through the tubing to expand it. Then the tubing is pushed against the inside part of the hole of the plate.

9 The condenser, on the other hand, is simply attached to a flat metal surface and is held in place by brackets. The condenser is connected to the evaporator with connecting devices, such as fittings and couplings.

Evaporator and condenser coils may be covered with aluminum fins. The fins are very fine precoated strips that are mounted all around the surface of the coils and are designed to transfer heat efficiently.

10 The expansion valve, also called a capillary tube, comes as a complete component. It is purchased from a vendor, and is installed in the piping after the condenser is in place.

Installing the pump

11 The pump, or compressor, is also purchased from a vendor. It is connected to the air conditioning system using fittings and couplings, and anchored in place by support brackets. It is bolted together with the other structural members of the system and is housed in the sheet metal casing. The casing is fastened to the base to protect the inner components.

Quality Control

Each component of the air conditioning system is checked at various stages of production. The different groups of workers responsible for specific stages of production typically have quality control plans to ascertain that the components they are working on are properly constructed. Once assembly of the air conditioner is complete, a performance test is done to ensure the whole system operates efficiently. Components purchased from outside vendors undergo inspection by quality assurance personnel before they are incorporated into the final product.

The Future

The Air Conditioning and Refrigeration Institute reports that almost half of all American homes have air conditioning. Industry experts predict that the market for air conditioners will continue to grow because manufacturers are quick to respond to consumers' changing needs.

EFFICIENCY RATING

Each air conditioner is assigned an energy-efficiency rating. This rating indicates the amount of energy the air conditioner needs to produce a specific cooling effect. Central air conditioners are assigned the Seasonal Energy Efficiency Ratio (SEER), while room air conditioners use the Energy Efficiency Ratio (EER). These ratings (indicated as numbers) are displayed on a yellow label attached to the air conditioner. The higher the rating, the more efficient the air conditioner. By law, the minimum SEER allowed is 10 for a split system (the compressor and condenser are outdoors) and 9.7 for a single-package unit. The best available SEER is 18. Consumers are advised to look for a SEER of 12 or higher. The minimum EER is 8. Consumers should select an EER of at least 9 if they live in a mild climate, and an EER of over 10 in a hot climate.

Manufacturers continue to face the challenge of improving energy efficiency and lowering costs. Some manufacturers are producing systems with the highest SEER efficiency rating of 18 (see sidebar). High-powered compressors and alternate refrigerants that will eventually replace hydrochlorofluorocarbons (HCFCs) are being developed.

In the area of designs, new room models include compacts that do not take up much window space, technology that prevents water condensation, lightweight remote control, and soft-touch control pad. Outdoors units for central air conditioning come with a condenser coil that has specially coated aluminum fins and zinc-clad housing to prevent corrosion.

The competitiveness of the industry is not limited to just developing new designs and cost-effective systems. In 2001, Carrier Corporation took this competition to another level. The company has teamed up with IBM (International Business Machines Corporation) to introduce the first Webenabled air conditioner that can communicate with personal computers and mobile telephones. Some of the features include consumer capability, when they are away from home, of turning their unit on and off and setting temperatures using the Internet. Repair persons will also be able to access air conditioner data and anticipate problems in the unit.

compressor:

The part of the air conditioner that pumps the refrigerant through the system.

condenser:

The part of the air conditioner that removes heat from the refrigerant and helps transfer that heat to the outside.

conductor:

A material that lets heat pass through it.

corrosion:

The slow wearing away of a metal by a liquid or a gas. For example, rusting of iron can result from exposure to moisture.

evaporator:

The part of the air conditioner through which a refrigerant vapor flows, absorbing heat and cooling the surrounding air.

fins:

Thin aluminum strips on the outer surface of an evaporator or condenser, enhancing the transfer of heat.

galvanized steel:

Steel that is coated with a thin layer of zinc to protect against corrosion.

refrigerant:

The working fluid that circulates through the air conditioning system, absorbing heat indoors and discarding it outdoors.

stainless steel:

Steel that does not rust.

For More Information

Books

Althouse, Andrew D., Carl H. Turnquist, and Alfred F. Bracciano. Modern Refrigeration and Air Conditioning. Tinley Park, IL: The Goodheart-Willcox Company, Inc., 1996.

Killinger, Jerry, and LaDonna Killinger. Heating and Cooling Essentials. Tinley Park, IL: The Goodheart-Willcox Company, Inc., 1999.

Periodicals

"IBM and Carrier Team to Launch First Web-Enabled Air Conditioner." Appliance (May 2001): pp.15–16.

Ivins, Molly. "King of Cool." Time. (December 7, 1998): p. 109.

Web Sites

"Energy-Efficient Air Conditioning." U.S. Department of Energy.http://www.eren.doe.gov/erec/factsheets/aircond.html (accessed on July 22, 2002).

"Stay Cool! Air Conditioning America." National Building Museum.http://www.nbm.org/Exhibits/past/2000_1996/Stay_Cool!.html (accessed on July 22, 2002).