暖通空调专业外文翻译---空调系统-暖通(编辑修改稿)

暖通空调专业外文翻译---空调系统-暖通(编辑修改稿)内容摘要：

water systems were used in less than 4% of mercial buildings in the . in 1995. However, because chillers are usually installed in larger buildings, chillers cooled over 28% of the . mercial building floor space that same year (DOE, 1998). Five types of chillers are monly applied to mercial buildings: reciprocating, screw, scroll, 6 centrifugal, and absorption. The first four utilize the vapor pression cycle to produce chilled water. They differ primarily in the type of pressor used. Absorption chillers utilize thermal energy (typically steam or bustion source) in an absorption cycle with either an ammoniawater or waterlithium bromide solution to produce chilled water. Overall System An estimated 86% of chillers are applied in multiple chiller arrangements like that shown in the figure (Bitondo and Tozzi, 1999). In chilled water systems, return water from the building is circulated through each chiller evaporator where it is cooled to an acceptable temperature (typically 4 to 7176。 C) (39 to 45176。 F). The chilled water is then distributed to watertoair heat exchangers spread throughout the facility. In these heat exchangers, air is cooled and dehumidified by the cold water. During the process, the chilled water increases in temperature and must be returned to the chiller(s). The chillers are watercooled chillers. Water is circulated through the condenser of each chiller where it absorbs heat energy rejected from the high pressure refrigerant. The water is then pumped to a cooling tower where the water is cooled through an evaporation process. Cooling towers are described in a later section. Chillers can also be air cooled. In this configuration, the condenserwould be a refrigeranttoair heat exchanger with air absorbing the heat energy rejected by the high pressure refrigerant. Chillers nominally range in capacities from 30 to 18,000 kW (8 to 5100 ton). Most chillers sold in the . are electric and utilize vapor pression refrigeration to produce chilled water. Compressors for these systems are either reciprocating, screw, scroll, or centrifugal in design. A small number of centrifugal chillers are sold that use either an internal bustion engine or steam drive instead of an electric motor to drive the pressor. The type of chiller used in a building depends on the application. For large office buildings or in chiller plants serving multiple buildings, centrifugal pressors are often used. In applications under 1000 kW (280 tons) cooling capacities, reciprocating or screw chillers may be more appropriate. In smaller applications, below 100 kW (30 tons), reciprocating or scroll chillers are typically used. Vapor Compression Chillers The nominal capacity ranges for the four types of electrically driven vapor pression 7 chillers. Each chiller derives its name from the type of pressor used in the chiller. The systems range in capacities from the smallest scroll (30 kW。 8 tons) to the largest centrifugal (18,000 kW。 5000 tons).Chillers can utilize either an HCFC (R22 and R123) or HFC (R134a) refrigerant. The steady state efficiency of chillers is often stated as a ratio of the power input (in kW) to the chilling capacity (in tons). A capacity rating of one ton is equal to kW or 12,000 btu/h. With this measure of efficiency, the smaller number is better. centrifugal chillers are the most efficient。 whereas, reciprocating chillers have the worst efficiency of the four types. The efficiency numbers provided in the table are the steady state fullload efficiency determined in accordance to ASHRAE Standard 30 (ASHRAE, 1995). These efficiency numbers do not include the auxiliary equipment, such as pumps and cooling tower fans that can add from to kW/ton to the numbers shown Chillers run at part load capacity most of the time. Only during the highest thermal loads in the building will a chiller operate near its rated capacity. As a consequence, it is important to know how the efficiency of the chiller varies with part load capacity. a representative data for the efficiency (in kW/ton) as a function of percentage full load capacity for a reciprocating, screw, and scroll chiller plus a centrifugal chiller with inlet vane control and one with variable frequency drive (VFD) for the pressor. The reciprocating chiller increases in efficiency as it operates at a smaller percentage of full load. In contrast, the efficiency of a centrifugal with inlet vane control is relatively constant until theload falls to about 60% of its rated capacity and its kW/ton increases to almost twice its fully loaded value. In 1998, the Air Conditioning and Refrigeration Institute (ARI) developed a new standard that incorporates into their ratings part load performance of chillers (ARI 1998c). Part load efficiency is expressed by a single number called the integrated part load value (IPLV). The IPLV takes data similar to that in Figure and weights it at the 25%, 50%, 75%, and 100% loads to produce a single integrated efficiency number. The weighting factors at these loads are , , , and , respectively. The equation to determine IPLV is: 8 Most of the IPLV is determined by the efficiency at the 50% and 75% part load values. Manufacturers will provide, on request, IPLVs as well as part load efficiencies. The four pressors used in vapor pression chillers are each briefly described below. While centrifugal and screw pressors are primarily used in chiller applications, reciprocating and scroll pressors are also used in smaller unitary packaged air conditioners and heat pumps. Reciprocating Compressors The reciprocating pressor is a positive displacement pressor. On the intake stroke of the piston, a fixed amount of gas is pulled into the cylinder. On the pression stroke, the gas is pressed until the discharge valve opens. The quantity of gas pressed on each stroke is equal to t。