1、附 录 附录 A 外文翻译 Air Conditioning and Refrigeration Technology Air conditioning has rapidly grown over the past 50 years, from a luxury to a standard system includedin most residential and commercial buildings. In 1970, 36% of residences in the U.S. were either fullyair conditioned or utilized a room a
2、ir conditioner for cooling (Blue, et al., 1979). By 1997, this numberhad more than doubled to 77%, and that year also marked the first time that over half (50.9%) ofresidences in the U.S. had central air conditioners (Census Bureau, 1999). An estimated 83% of all newhomes constructed in 1998 had cen
3、tral air conditioners (Census Bureau, 1999). Air conditioning has alsogrown rapidly in commercial buildings. From 1970 to 1995, the percentage of commercial buildings withair conditioning increased from 54 to 73%. Air conditioning in buildings is usually accomplished with the use of mechanical or he
4、at-activatedequipment. In most applications, the air conditioner must provide both cooling and dehumidificationto maintain comfort in the building. Air conditioning systems are also used in other applications, suchas automobiles, trucks, aircraft, ships, and industrial facilities. However, the descr
5、iption of equipment inthis chapter is limited to those commonly used in commercial and residential buildings. Commercial buildings range from large high-rise office buildings to the corner convenience store.Because of the range in size and types of buildings in the commercial sector, there is a wide
6、 variety ofequipment applied in these buildings. For larger buildings, the air conditioning equipment is part of atotal system design that includes items such as a piping system, air distribution system, and cooling tower.Proper design of these systems requires a qualified engineer. The residential
7、building sector is dominatedby single family homes and low-rise apartments/condominiums. The cooling equipment applied in thesebuildings comes in standard “packages” that are often both sized and installed by the air conditioningcontractor. The chapter starts with a general discussion of the vapor c
8、ompression refrigeration cycle then movesto refrigerants and their selection. Chillers and their auxiliary systems are then covered, followed bypackaged air conditioning equipment. Even though there is a large range in sizes and variety of air conditioning systems used in buildings, mostsystems util
9、ize the vapor compression cycle to produce the desired cooling and dehumidification. Thiscycle is also used for refrigerating and freezing foods and for automotive air conditioning. The first patenton a mechanically driven refrigeration system was issued to Jacob Perkins in 1834 inLondon, and the fi
10、rstviable commercial system was produced in 1857 by James Harrison and D.E. Siebe (Thevenot 1979). Besides vapor compression, there are two less common methods used to produce cooling in buildings:the absorption cycle and evaporative cooling. These are described later in the chapter. With the vapor
11、compression cycle, a working fluid, which is called the refrigerant, evaporates and condenses at suitablepressures for practical equipment designs. The four basic components in every vapor compression refrigeration system are thecompressor, condenser, expansion device, and evaporator. The compressor
12、 raises the pressure of therefrigerant vapor so that the refrigerant saturation temperature is slightly above the temperature of thecooling medium used in the condenser. The type of compressor used depends on the application of thesystem. Large electric chillers typically use a centrifugal compresso
13、r while small residential equipmentuses a reciprocating or scroll compressor. The condenser is a heat exchanger used to reject heat from the refrigerant to a cooling medium. Therefrigerant enters the condenser and usually leaves as a subcooled liquid. Typical cooling mediums usedin condensers are ai
14、r and water. Most residential-sized equipment uses air as the cooling medium in thecondenser, while many larger chillers use water.After leaving the condenser, the liquid refrigerant expands to a lower pressure in the expansion valve. The expansion valve can be a passive device, such as a capillary
15、tube or short tube orifice, or an activedevice, such as a thermal expansion valve or electronic expansion valve. The purpose of the valve is toregulate the flow of refrigerant to the evaporator so that the refrigerant is superheated when it reachesthe suction of the compressor. At the exit of the ex
16、pansion valve, the refrigerant is at a temperature below that of the medium (air orwater) to be cooled. The refrigerant travels through a heat exchanger called the evaporator. It absorbsenergy from the air or water circulated through the evaporator. If air is circulated through the evaporator,the system is called a direct expansion system. If water is circulated through the evaporator, it is called
