【正文】 gh isentropic and volumetric efficiencies can be achieved with screw pressors because there are no suction 11 or discharge valves and small clearance volumes. Screw pressors for building applications generally use either R134a or R22. 12 中文 譯文 空調(diào)系統(tǒng) 過去 50 年以來，空調(diào)得到了快速的發(fā)展，從曾經(jīng)的奢侈品發(fā)展到可應用于大多數(shù)住宅和商業(yè)建筑的比較標準的系統(tǒng)。 本章節(jié)首先對蒸汽壓縮制冷循環(huán)作一個概述，接著介紹制冷劑及制冷劑的選擇，最后介紹 冷水機組 。之后制冷劑經(jīng)過一個熱交換器叫做蒸發(fā)器，它吸收通過蒸發(fā)器的空氣或水的熱量，如果空氣經(jīng)過蒸發(fā)器在流通 ,該系統(tǒng)叫做一個直接膨脹式系統(tǒng)，如果水經(jīng)過蒸發(fā)器在流通 ,它叫做冷卻設備，在任何情況下，在蒸發(fā)器中的制冷劑不直接和空氣或水接觸，在蒸發(fā)器中，制冷劑從一個低品位的兩相液體轉(zhuǎn)換成在正常的工藝條件下過熱的蒸汽。 Zeotropes 和 azeotropes 是混合二種或更多不同的制冷劑，一種 zeotropic混合物能改變飽和溫度在它在不變的壓力蒸發(fā) ( 或冷凝 )。 R410有微小的足夠溫度滑動 (少于 C,10176。 R123擁有的效率優(yōu)勢在 R134a之上 (表 )。在 1998年，第一個使用 R410A的空調(diào)設備的住宅在美國出現(xiàn)。 冷水機組 1995 年，在美國，冷水機組應用在至少 4％的商用建筑中。然后，冷凍水通過各設備 16 傳送到水－空 氣換熱器。在這種循環(huán)中，冷凝器應是制冷劑－空氣熱交換器，空氣吸收來自高壓制冷劑的熱量。在小的應用場合，若低于 100kw（ 30tons）時，使用往復式或旋渦式制冷機組。離心式制冷機的效率最高。往復式制冷機在占滿負荷較小的百分比運行時，效率增加。 1tons 的制冷量等于 或 1200btu／ h。對于大的辦公室建筑或制冷機組需服務于多個建筑時，通常使用離心式壓縮機。冷卻塔將在后一部分講述。 總的系統(tǒng) 大約 86％的制冷機和表所示的一樣用在多臺制冷機系統(tǒng)中（ Bitondo 和 Tozzi，1999）。 R290, 丙烷 , 都有接近 R22的工作壓力，并被推薦來替代 R22 (Kramer, 1991)。 R407C和 R410A是 HFCs的兩種混合物，兩者都是 R22的替代品， |R407C預期將很快地替換 R22，在空調(diào)設備中，它的蒸發(fā)和冷凝壓力接近 R22 (表格 )。 R11， R12， R123和 R134a是普遍用在離心 式的冷卻設備的制冷劑，R11，氟氯碳化物 , 和 R123, HCFC, 都有低壓高容積特性，是用在離心式壓縮機上的理想制冷劑。 C的溫度移動 (12176。 制冷劑的使用和選擇 直到 20世紀 80年代中葉，制冷劑的選擇在大多數(shù)的建筑 物空調(diào)設備中不是一個問題，因為在制冷劑的使用上還沒有統(tǒng)一的的標準，在以前，用于建筑物空調(diào)設備的大多數(shù)制冷劑是氟氯碳化物和氟氯碳氫化物，且大多數(shù)的制冷劑是無毒的和不可燃的，然而，最近的美國聯(lián)邦的標準 (環(huán)保署 1993a；環(huán)保署 1993b) 和國際的協(xié)議 (UNEP,1987) 已經(jīng)限制了氟氯碳化物和氟氯碳氫化物的制造和使用，現(xiàn)在，氟氯碳化物和氟氯碳氫化物在一些場合依然被使用，對制冷劑的理解能幫助建筑物擁有者或者工程師更好的了解 14 關于為特定的設備下如何選擇制冷劑，這里將討論不同制冷劑的使用并給出影響它們使用的 建筑空調(diào)設備和標準。 液體制冷劑在離開冷凝器之后，在膨脹閥中節(jié)流到一個更低的壓力。這些系統(tǒng)的正確設計需要一個有資質(zhì)的工程師才能完成。 8 tons) to the largest centrifugal (18,000 kW。F), which gives it a temperature glide of 7176。英文 文獻 Air Conditioning Systems Air conditioning has rapidly grown over the past 50 years, from a luxury to a standard system included in most residential and mercial buildings. In 1970, 36% of residences in the . were either fully air conditioned or utilized a room air conditioner for cooling (Blue, et al., 1979). By 1997, this number had more than doubled to 77%, and that year also marked the first time that over half (%) of residences in the . had central air conditioners (Census Bureau, 1999). An estimated 83% of all new homes constructed in 1998 had central air conditioners (Census Bureau, 1999). Air conditioning has also grown rapidly in mercial buildings. From 1970 to 1995, the percentage of mercial buildings with air conditioning increased from 54 to 73% (Jackson and Johnson, 1978, and DOE, 1998). Air conditioning in buildings is usually acplished with the use of mechanical or heatactivated equipment. In most applications, the air conditioner must provide both cooling and dehumidification to maintain fort in the building. Air conditioning systems are also used in other applications, such as automobiles, trucks, aircraft, ships, and industrial facilities. However, the description of equipment in this chapter is limited to those monly used in mercial and residential buildings. Commercial buildings range from large highrise office buildings to the corner convenience store. Because of the range in size and types of buildings in the mercial sector, there is a wide variety of equipment applied in these buildings. For larger buildings, the air conditioning equipment is part of a total 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 building sector is dominated by single family homes and lowrise apartments/condominiums. The cooling equipment applied in these buildings es in standard ―packages‖ that are often both sized and installed by the air conditioning contractor. The chapter starts with a general discussion of the vapor pression refrigeration cycle then moves to refrigerants and their selection, followed by packaged Chilled Water Systems。C (–35176。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 chi