1、英文翻译 Chilled Water Systems1 Chilled water systems were used in less than 4% of commercial buildings in the U.S. in 1995. However, because chillers are usually installed in larger buildings, chillers cooled over 28% of the U.S. commercial building floor space that same year (DOE, 1998). Five types of
2、 chillers are commonly applied to commercial buildings: reciprocating, screw, scroll, centrifugal, and absorption. The first four utilize the vapor compression cycle to produce chilled water. They differ primarily in the type of compressor used. Absorption chillers utilize thermal energy (typically
3、steam or combustion source) in an absorption cycle with either an ammonia-water or water-lithium bromide solution to produce chilled water. Overall System Figure 4.2.2 shows a simple representation of a dual chiller application with all the major auxiliary equipment. An estimated 86% of chillers are
4、 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 7C) (39 to 45F). The chilled water
5、 is then distributed to water-to-air 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 shown in Figure 4.2.2 a
6、re water-cooled 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
7、section. Chillers can also be air cooled. In this configuration, the condenserwould be a refrigerant-to-air 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
8、the U.S. are electric and utilize vapor compression 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 combustion engine or steam drive in
9、stead of an electric motor to drive the compressor. 1节选自 James B. Bradford et al. “HVAC Equipment and Systems”.Handbook of Heating, Ventilation, and Air-Conditioning.Ed. Jan F. Kreider.Boca Raton, CRC Press LLC. 2001 浙 江 海 洋 学 院 毕 业 设 计 2 FIGURE 4.2.2 A dual chiller application with major auxiliary
10、systems (courtesy of Carrier Corporation). The type of chiller used in a building depends on the application. For large office buildings or in chiller plants serving multiple buildings, centrifugal compressors are often used. In applications under 1000 kW (280 tons) cooling capacities, reciprocating
11、 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 Table 4.2.5 shows the nominal capacity ranges for the four types of electrically driven vapor compression chillers. Each chille
12、r derives its name from the type of compressor 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 (R-22 and R-123) or HFC (R-134a) refrigerant. The steady state efficiency
13、 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 3.52 kW or 12,000 btu/h. With this measure of efficiency, the smaller number is better. As seen in Table 4.2.5, centrifugal chillers are the most efficient；
14、 whereas, reciprocating chillers have the worst efficiency of the four types. The efficiency numbers provided in the table are the steady state full-load 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 0.06 to 0.31 kW/ton to the numbers shown (Smit et al., 1996). Chillers run at part load capacity most of the time. Only during the highest thermal loads
