AIR CONDITIONING
Air conditioning is a combined process that performs many functions simultaneously. It conditionsĀ the air, transports it, and introduces it to the conditioned space. It provides heating and cooling fromĀ its central plant or rooftop units. It also controls and maintains the temperature, humidity, airĀ movement, air cleanliness, sound level, and pressure differential in a space within predeterminedĀ limits for the comfort and health of the occupants of the conditioned space or for the purpose ofĀ product processing.
The term HVAC&R is an abbreviation of heating, ventilating, air conditioning, and refrigerating.Ā The combination of processes in this commonly adopted term is equivalent to the current definitionĀ of air conditioning. Because all these individual component processes were developed prior to theĀ more complete concept of air conditioning, the term HVAC&R is often used by the industry.
COMFORT AND PROCESSING AIR CONDITIONINGĀ SYSTEMS
Articles Related Air Conditioning :Ā
1.Ā CLASSIFICATION OF AIR CONDITIONING SYSTEMS ACCORDING TO CONSTRUCTION AND OPERATING CHARACTERISTICS
2. Who InventedĀ AIR CONDITIONINGĀ ?
3.Ā Heat, Temperature, and Pressure in Refrigeration
Air Conditioning Systems
An air conditioning, or HVAC&R, system is composed of components and equipment arranged inĀ sequence to condition the air, to transport it to the conditioned space, and to control the indoor environmentalĀ parameters of a specific space within required limits.Ā Most air conditioning systems perform the following functions:
- Provide the cooling and heating energy required
- Condition the supply air, that is, heat or cool, humidify or dehumidify, clean and purify, andĀ attenuate any objectionable noise produced by the HVAC&R equipment.
- Distribute the conditioned air, containing sufficient outdoor air, to the conditioned space.
- Control and maintain the indoor environmental parametersāsuch as temperature, humidity,Ā cleanliness, air movement, sound level, and pressure differential between the conditioned spaceĀ and surroundingsāwithin predetermined limits.
Parameters such as the size and the occupancy of the conditioned space, the indoor environmentalĀ parameters to be controlled, the quality and the effectiveness of control, and the cost involved determineĀ the various types and arrangements of components used to provide appropriate characteristics.Ā Air conditioning systems can be classified according to their applications as (1) comfort airĀ conditioning systems and (2) process air conditioning systems.
Comfort Air Conditioning Systems
Comfort air conditioning systems provide occupants with a comfortable and healthy indoor environmentĀ in which to carry out their activities. The various sectors of the economy using comfort airĀ conditioning systems are as follows:
- The commercial sector includes office buildings, supermarkets, department stores, shoppingĀ centers, restaurants, and others. Many high-rise office buildings, including such structures as theĀ World Trade Center in New York City and the Sears Tower in Chicago, use complicated air conditioningĀ systems to satisfy multiple-tenant requirements. In light commercial buildings, the air conditioningĀ system serves the conditioned space of only a single-zone or comparatively smaller area.Ā For shopping malls and restaurants, air conditioning is necessary to attract customers.
- The institutional sector includes such applications as schools, colleges, universities, libraries,Ā museums, indoor stadiums, cinemas, theaters, concert halls, and recreation centers. For example,Ā one of the large indoor stadiums, the Super dome in New Orleans, Louisiana, can seat 78,000 people.
- The residential and lodging sector consists of hotels, motels, apartment houses, and privateĀ homes. Many systems serving the lodging industry and apartment houses are operated continuously,Ā on a 24-hour, 7-day-a-week schedule, since they can be occupied at any time.
- The health care sector encompasses hospitals, nursing homes, and convalescent care facilities.Ā Special air filters are generally used in hospitals to remove bacteria and particulates of submicrometerĀ size from areas such as operating rooms, nurseries, and intensive care units. The relative humidity in aĀ general clinical area is often maintained at a minimum of 30 percent in winter.
- The transportation sector includes aircraft, automobiles, railroad cars, buses, and cruisingĀ ships. Passengers increasingly demand ease and environmental comfort, especially for long distanceĀ travel. Modern airplanes flying at high altitudes may require a pressure differential ofĀ about 5 psi between the cabin and the outside atmosphere. According to the Commercial BuildingsĀ Characteristics (1994), in 1992 in the United States, among 4,806,000 commercial buildings havingĀ 67.876 billion ft2 (6.31 billion m2) of floor area, 84.0 percent were cooled, and 91.3 percentĀ were heated.
Process Air Conditioning Systems
Process air conditioning systems provide needed indoor environmental control for manufacturing,Ā product storage, or other research and development processes. The following areas are examples ofĀ process air conditioning systems:
- In textile mills, natural fibers and manufactured fibers are hygroscopic. Proper control of humidityĀ increases the strength of the yarn and fabric during processing. For many textile manufacturingĀ processes, too high a value for the space relative humidity can cause problems in the spinningĀ process. On the other hand, a lower relative humidity may induce static electricity that is harmfulĀ for the production processes.
- Many electronic products require clean rooms for manufacturing such things as integrated circuits,Ā since their quality is adversely affected by airborne particles. Relative-humidity control isĀ also needed to prevent corrosion and condensation and to eliminate static electricity. TemperatureĀ control maintains materials and instruments at stable condition and is also required for workers whoĀ wear dust-free garments. For example, a class 100 clean room in an electronic factory requires aĀ temperature of 72 (+/-) 2Ā°F (22.2 (+/-) 1.1Ā°C), a relative humidity at 45 5 percent, and a count of dustĀ particles of 0.5-m (1.97 * 105 in.) diameter or larger not to exceed 100 particles/ ft3 (3531 particlesĀ /m3).
- Precision manufacturers always need precise temperature control during production of precisionĀ instruments, tools, and equipment. Bausch and Lomb successfully constructed a constant temperatureĀ control room of 68 (+/-) 0.1Ā°F (20 (+/-) 0.56Ā°C) to produce light grating products in theĀ 1950s.
- Pharmaceutical products require temperature, humidity, and air cleanliness control. For instance,Ā liver extracts require a temperature of 75Ā°F (23.9Ā°C) and a relative humidity of 35 percent.Ā If the temperature exceeds 80Ā°F (26.7Ā°C), the extracts tend to deteriorate. High-efficiency air filtersĀ must be installed for most of the areas in pharmaceutical factories to prevent contamination.
- Modern refrigerated warehouses not only store commodities in coolers at temperatures ofĀ 27 to 32Ā°F (-2.8 to 0Ā°C) and frozen foods at -10 to -20Ā°F (-23 to -29Ā°C), but also provideĀ relative-humidity control for perishable foods between 90 and 100 percent. Refrigerated storageĀ is used to prevent deterioration. Temperature control can be performed by refrigeration systemsĀ only, but the simultaneous control of both temperature and relative humidity in the space can onlyĀ be performed by process air conditioning systems.
Copied by HANDBOOK OF AIR CONDITIONING AND REFRIGERATION by Shan K. Wang