Air Conditioner

Background

Residential and commercial space-cooling demands are increasing steadily throughout the world as what once was considered a luxury is now seemingly a necessity. Air-conditioning manufacturers have played a big part in making units more affordable by increasing their efficiency and improving components and technology. The competitiveness of the industry has increased with demand, and there are many companies providing air conditioning units and systems.

Air conditioning systems vary considerably in size and derive their energy from many different sources. Popularity of residential air conditioners has increased dramatically with the advent of central air, a strategy that utilizes the ducting in a home for both heating and cooling. Commercial air conditioners, almost mandatory in new construction, have changed a lot in the past few years as energy costs rise and power sources change and improve. The use of natural gas-powered industrial chillers has grown considerably, and they are used for commercial air conditioning in many applications.

Raw Materials

Air conditioners are made of different types of metal. Frequently, plastic and other nontraditional materials are used to reduce weight and cost. Copper or aluminum tubing, critical ingredients in many air conditioner components, provide superior thermal properties and a positive influence on system efficiency. Various components in an air conditioner will differ with the application, but usually they are comprised of stainless steel and other corrosion-resistant metals.

Self-contained units that house the refrigeration system will usually be encased in sheet metal that is protected from environmental conditions by a paint or powder coating.

The working fluid, the fluid that circulates through the air-conditioning system, is typically a liquid with strong thermodynamic characteristics like freon, hydrocarbons, ammonia, or water.

Design

All air conditioners have four basic components: a pump, an evaporator, a condenser, and an expansion valve. All have a working fluid and an opposing fluid medium as well.

Two air conditioners may look entirely dissimilar in both size, shape, and configuration, yet both function in basically the same way. This is due to the wide variety of applications and energy sources available. Most air conditioners derive their power from an electrically-driven motor and pump combination to circulate the refrigerant fluid. Some natural gas-driven chillers couple the pump with a gas engine in order to give off significantly more torque.

As the working fluid or refrigerant circulates through the air-conditioning system at high pressure via the pump, it will enter an evaporator where it changes into a gas state, taking heat from the opposing fluid medium and operating just like a heat exchanger. The working fluid then moves to the condenser, where it gives off heat to the atmosphere by condensing back into a liquid. After passing through an expansion valve, the working fluid returns to a low pressure state. When the cooling medium (either a fluid or air) passes near the evaporator, heat is drawn to the evaporator. This process effectively cools the opposing medium, providing localized cooling where needed in the building. Early air conditioners used freon as the working fluid, but because of the hazardous effects freon has on the environment, it has been phased out. Recent designs have met strict challenges to improve the efficiency of a unit, while using an inferior substitute for freon.

The Manufacturing
Process

Creating encasement parts from galvanized sheet metal and structural steel

• 1 Most air conditioners start out as raw material, in the form of structural steel shapes and sheet steel. As the sheet metal is processed into fabrication cells or work cells, it is cut, formed, punched, drilled, sheared, and/or bent into a useful shape or form. The encasements or wrappers, the metal that envelopes most outdoor residential units, is made of galvanized sheet metal that uses a zinc coating to provide protection against corrosion. Galvanized sheet metal is also used to form the bottom pan, face plates, and various support brackets throughout an air conditioner. This sheet metal is sheared on a shear press in a fabrication cell soon after arriving from storage or inventory. Structural steel shapes are cut and mitered on a band saw to form useful brackets and supports.

Punch pressing the sheet metal forms

• 2 From the shear press, the sheet metal is loaded on a CNC (Computer Numerical Control) punch press. The punch press has the option of receiving its computer program from a drafting CAD/CAM (Computer Aided Drafting/Computer Aided Manufacturing) program or from an independently written CNC program. The CAD/CAM program will transform a drafted or modeled part on the computer into a file that can be read by the punch press, telling it where to punch holes in the sheet metal. Dies and other punching instruments are stored in the machine and mechanically brought to the punching arm, where it can be used to drive through the sheet. The NC (Numerically Controlled) press brakes bend the sheet into its final form, using a computer file to program itself. Different bending dies are used for different shapes and configurations and may be changed for each component.
• 3 Some brackets, fins, and sheet components are outsourced to other facilities or companies to produce large quantities. They are brought to the assembly plant only when needed for assembly. Many of the brackets are produced on a hydraulic or mechanical press, where brackets of different shapes and configurations can be produced from a coiled sheet and unrolled continuously into the machine. High volumes of parts can be produced because the press can often produce a complex shape with one hit.

Cleaning the parts

• 4 All parts must be completely clean and free of dirt, oil, grease, and lubricants before they are powder coated. Various cleaning methods are used to accomplish this necessary task. Large solution tanks filled with a cleaning solvent agitate and knock off the oil when parts are submersed. Spray wash systems use pressurized cleaning solutions to knock off dirt and grease. Vapor degreasing, suspending the parts above a harsh cleansing vapor, uses an acid solution and will leave the parts free of petroleum products. Most outsourced parts that arrive from a vendor have already been degreased and cleaned. For additional corrosion protection, many parts will be primed in a phosphate primer bath before entering a drying oven to prepare them for the application of the powder coating.

Powder coating

• 5 Before brackets, pans, and wrappers are assembled together, they are fed through a powder coating operation. The powder coating system sprays a paint-like dry powder onto the parts as they are fed through a booth on an overhead conveyor. This can be done by robotic sprayers that are programmed where to spray as each part feeds through the booth on the conveyor. The parts are statically charged to attract the powder to adhere to deep crevices and bends within each part. The powder-coated parts are then fed through an oven, usually with the same conveyor system, where the powder is permanently baked onto the metal. The process takes less than 10 minutes.

Bending the tubing for the condenser and evaporator

• 6 The condenser and evaporator both act as a heat exchanger in air conditioning systems and are made of copper or aluminum tubing bent around in coil form to maximize the distance through which the working fluid travels. The opposing fluid, or cooling fluid, passes around the tubes as the working fluid draws away its heat in the evaporator. This is accomplished by taking many small diameter copper tubes bent in the same shape and anchoring them with guide rods and aluminum plates. The working fluid or refrigerant flows through the copper tubes and the opposing fluid flows around them in between the aluminum plates. The tubes will often end up with hairpin bends performed by NC benders, using the same principle as the NC press brake. Each bend is identical to the next. The benders use previously straightened tubing to bend around a fixed die with a mandrel fed through the inner diameter to keep it from collapsing during the bend. The mandrel is raked back through the inside of the tube when the bend has been accomplished.
• 7 Tubing supplied to the manufacturer in a coil form goes through an uncoiler and straightener before being fed through the bender. Some tubing will be cut into desired lengths on an abrasive saw that will cut several small tubes in one stroke. The aluminum plates are punched out on a punch press and formed on a mechanical press to place divots or waves in the plate. These waves maximize the thermodynamic heat transfer between the working fluid and the opposing medium. When the copper tubes are finished in the bending cell, they are transported by automatic guided vehicle (AGV) to the assembly cell, where they are stacked on the guide rods and fed through the plates or fins.

Joining the copper tubing with the aluminum plates

• 8 A major part of the assembly is the joining of the copper tubing with the aluminum plates. This assembly becomes the evaporator and is accomplished by taking the stacked copper tubing in their hairpin configuration and mechanically fusing them to the aluminum plates. The fusing occurs by taking a bullet, or mandrel, and feeding it through the copper tubing to expand it and push it against the inner part of the hole of the plate. This provides a thrifty, yet useful bond between the tubing and plate, allowing for heat transfer.
• 9 The condenser is manufactured in a similar manner, except that the opposing medium is usually air, which cools off the copper or aluminum condenser coils without the plates. They are held by brackets which support the coiled tubing, and are connected to the evaporator with fittings or couplings. The condenser is usually just one tube that may be bent around in a number of hairpin bends. The expansion valve, a complete component, is purchased from a vendor and installed in the piping after the condenser. It allows the pressure of the working fluid to decrease and re-enter the pump.

Installing the pump

• 10 The pump is also purchased complete I h from an outside supplier. Designed to increase system pressure and circulate the working fluid, the pump is connected with fittings to the system and anchored in place by support brackets and a base. It is bolted together with the other structural members of the air conditioner and covered by the wrapper or sheet metal encasement. The encasement is either riveted or bolted together to provide adequate protection for the inner components.

Quality Control

Quality of the individual components is always checked at various stages of the manufacturing process. Outsourced parts must pass an incoming dimensional inspection from a quality assurance representative before being approved for use in the final product. Usually, each fabrication cell will have a quality control plan to verify dimensional integrity of each part. The unit will undergo a performance test when assembly is complete to assure the customer that each unit operates efficiently.

The Future

Air conditioner manufacturers face the challenge of improving efficiency and lowering costs. Because of the environmental concerns, working fluids now consist typically of ammonia or water. New research is under way to design new working fluids and better system components to keep up with rapidly expanding markets and applications. The competitiveness of the industry should remain strong, driving more innovations in manufacturing and design.

Where to Learn More

Other

"HVAC Online." 1997. http://www.hvaconline.com (July 9, 1997).

"Cold Point Manufacturing." 1997. http:/www.coldpoint.com/index3.htm (July 9, 1997).

—JasonRude

AIR CONDITIONING

AIR CONDITIONING. Mechanical air conditioning made its first appearance at the turn of the twentieth century. Defined as the control of temperature, humidity, cleanliness, and distribution of air, it largely grew out of successful efforts to control humidity levels indoors. Systems were custom designed for each installation and were used to either add moisture to the air or remove the excess depending upon the application. Two basic types of air conditioning were marketed: comfort air conditioning for establishing the optimum conditions for human comfort, and process air conditioning for setting the most favorable atmospheric conditions for industrial processing.

One of the first comfort air conditioning systems was designed by Alfred Wolff for the trading room of the New York Stock Exchange in 1902, while Willis Carrier installed a process air conditioning system in the Sacketts-Wilhems Printing Company the same year. Carrier has long been air conditioning's most famous engineer due in part to his pioneering status and in part to the visibility of his company, which established a dominant place in the industry first through its engineering expertise and then through its strong patent position.

For decades mechanical air conditioning systems were used primarily to correct the atmospheric conditions created by deleterious man-made environments such as crowded auditoriums and schools or dry, overheated factories. Process air conditioning far outstripped comfort air conditioning as the most lucrative market for the first fifteen years after its invention. Air conditioning systems were installed in various processing facilities such as munitions, candy, pasta, film, and textile factories to stabilize the handling properties of hygroscopic materials which absorbed moisture from the air. In fact, the term "air conditioning" was coined in 1904 by the textile engineer Stuart Cramer, who advocated the new technology over the old-fashioned practice of "yarn conditioning," which re-lied on adding moisture to the materials themselves rather than the air.

Comfort air conditioning eventually blossomed as an outgrowth of the mechanical ventilation systems required by state law in schools, theaters, and auditoriums. Large crowds of people in a single room invariably created un-pleasant atmospheric conditions that early public health officials believed to be unhealthy as well. However, it was not until builders became more concerned with comfort than with health that air conditioning thrived. One of the first film exhibition companies to exploit the appeal of comfort air conditioning was Balaban and Katz, which in 1917 equipped the Central Park Theater in Chicago with a system that was widely imitated. Operating expenses for these systems were kept low by recirculating a portion of the air from the theater, and the new patent pool, Auditorium Conditioning Corporation (anchored by Carrier Engineering Corporation and four partner companies), controlled that technology, receiving royalties on an estimated 90 percent of new air conditioning installations until the company was dissolved in 1945.

With the onset of the Great Depression, manufacturers of household appliances joined traditional air conditioning companies in pursuit of the residential market. Older air conditioning systems relied upon a water supply to cool either the machinery or the air, but around 1932 engineers at the De La Vergne Machine Company developed the air-cooled compressor, which freed air conditioning from its plumbing connections and accelerated the development of the air conditioner as a discrete plug-in appliance. Residential air conditioning now came in two basic types: a central air conditioning system, tied to the house with plumbing connections and air distribution ducts, and a window air conditioner that the consumer could install anywhere there was an electrical outlet.

Widespread adoption of air conditioning in homes and office buildings waited until the post–World War II building boom. The appearance of new designs, such as the block office building with extensive interior space that had no access to windows, meant that mechanical ventilation was a necessity. Air conditioning, with its provision for cooling, was an advantageous choice to counter the heat of large glass windows, high levels of interior lighting, numerous occupants, and increasing use of office machines. This combination of design and use of modern office buildings meant that nearly all required cooling no matter how moderate the local climate. In the home, the decision whether or not to buy air conditioning was often made by speculative builders rather than the individual consumer. Beginning around 1953, builders of tract homes routinely included air conditioning in their developments, underwriting the cost of the equipment by eliminating traditional design features such as high ceilings, overhanging eaves, and cross ventilation, which had originally helped homeowners cope with hot weather. This conscious substitution of air conditioning for passive cooling techniques made modern homes, like modern office buildings, dependent upon their mechanical systems. By 1957, the use of air conditioning in homes and offices shifted peak usage of electricity from the traditional high mark of December to August's cooling season.

The widespread adoption of air conditioning was accompanied by changes in the public's standard for comfort. Before air conditioning, consumers planned food, clothes, work, and entertainment around ways to mitigate the impact of hot weather. With a technological alternative, those hot-weather rituals declined, and their usefulness has been supplanted by a greater concern with privacy, efficiency, and unconstrained choice which makes them seem poor alternatives. Air conditioning has not only underwritten modern architectural design in the postwar era but also a modern lifestyle.

BIBLIOGRAPHY

Ackermann, Marsha E. Cool Comfort: America's Romance with Air Conditioning. Washington, D.C.: Smithsonian Institution Press, 2002.

Arsenault, Raymond. "The End of the Long Hot Summer: The Air Conditioner and Southern Comfort." Journal of Southern History 50 (1984): 587–628.

Cooper, Gail. Air Conditioning America: Engineers and the Controlled Environment, 1900–1960. Baltimore: Johns Hopkins University Press, 1998.

Ingels, Margaret. Willis Haviland Carrier: Father of Air Conditioning. Garden City, N.J.: Country Life Press, 1952. Re-print, New York: Arno Press, 1972.

GailCooper

air conditioning mechanical process for controlling the humidity, temperature, cleanliness, and circulation of air in buildings and rooms. Indoor air is conditioned and regulated to maintain the temperature-humidity ratio that is most comfortable and healthful. In the process, dust, soot, and pollen are filtered out, and the air may be sterilized, as is sometimes done in hospitals and public places.

Most air-conditioning units operate by ducting air across the colder, heat-absorbing side of a refrigeration apparatus and directing it back into the air-conditioned space (see refrigeration ). The refrigeration apparatus is controlled by some form of thermostat. In water-cooled air-conditioning units, the waste heat is carried away by a flow of water. For recirculation in water-cooled units, a cooling tower is used. This apparatus maintains a constant level of water in the system and replaces water lost by evaporation. The development of small self-contained systems has greatly expanded the use of air conditioning in homes. A portable or window-mounted air conditioner is usually adequate for one room.

Often domestic heating systems are converted to provide complete air conditioning for a home. Usually, this is done by combining a heating device and a cooling device in one unit. In regions where the outside temperature does not fall too low, heat pumps have become popular. A heat pump is a reversible device that does mechanical work to extract heat from a cooler place and deliver heat to a warmer place. The heat delivered to the warmer place is, approximately, the sum of the original heat and the work done. Greater temperature differences between the warm and cold regions require greater amounts of work. In warm weather the heat pump acts like a traditional air conditioner, removing heat from the indoors and delivering heat to the outdoors. In cool weather, it removes heat from the outdoors and delivers heat to the indoors. The efficiency of a heat pump as a heating device depends upon the outdoor temperature. At 50°F (10°C) a heat pump is more efficient than a traditional heating system. Below 32°F (0°C) it is less efficient and requires augmenting with conventional heaters.

In the construction of office buildings in the United States, air-conditioning systems are commonly included as integral parts of the structure. First used c.1900 in the textile industry, air conditioning found little use outside factories until the late 1920s. It is of great importance in chemical, pharmaceutical, and other industrial plants where air contamination, humidity, and temperature affect manufacturing processes.

Bibliography: See D. Abrams, Low Energy Cooling (1988); S. Aglow, Electronic HVAC Controls Simplified (1988).

air con·di·tion·ing • n. a system for controlling the humidity, ventilation, and temperature in a building or vehicle, typically to maintain a cool atmosphere. DERIVATIVES: air con·di·tioned adj. air con·di·tion·er n.

Air Conditioning. See Refrigeration and Air Conditioning.