【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(yīng)用于大多數(shù)住宅和商業(yè)建筑的比較標(biāo)準(zhǔn)的系統(tǒng)。 本章節(jié)首先對(duì)蒸汽壓縮制冷循環(huán)作一個(gè)概述，接著介紹制冷劑及制冷劑的選擇，最后介紹 冷水機(jī)組 。之后制冷劑經(jīng)過一個(gè)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(gè)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(shè)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(gè)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(dòng) (少于 C,10176。 R123擁有的效率優(yōu)勢(shì)在 R134a之上 (表 )。在 1998年，第一個(gè)使用 R410A的空調(diào)設(shè)備的住宅在美國(guó)出現(xiàn)。 冷水機(jī)組 1995 年，在美國(guó)，冷水機(jī)組應(yīng)用在至少 4％的商用建筑中。然后，冷凍水通過各設(shè)備 16 傳送到水－空 氣換熱器。在這種循環(huán)中，冷凝器應(yīng)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(yīng)用場(chǎng)合，若低于 100kw（ 30tons）時(shí)，使用往復(fù)式或旋渦式制冷機(jī)組。離心式制冷機(jī)的效率最高。往復(fù)式制冷機(jī)在占滿負(fù)荷較小的百分比運(yùn)行時(shí)，效率增加。 1tons 的制冷量等于 或 1200btu／ h。對(duì)于大的辦公室建筑或制冷機(jī)組需服務(wù)于多個(gè)建筑時(shí)，通常使用離心式壓縮機(jī)。冷卻塔將在后一部分講述。 總的系統(tǒng) 大約 86％的制冷機(jī)和表所示的一樣用在多臺(tái)制冷機(jī)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(yù)期將很快地替換 R22，在空調(diào)設(shè)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(shè)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(jī)上的理想制冷劑。 C的溫度移動(dòng) (12176。 制冷劑的使用和選擇 直到 20世紀(jì) 80年代中葉，制冷劑的選擇在大多數(shù)的建筑 物空調(diào)設(shè)備中不是一個(gè)問題，因?yàn)樵谥评鋭┑氖褂蒙线€沒有統(tǒng)一的的標(biāo)準(zhǔn)，在以前，用于建筑物空調(diào)設(shè)備的大多數(shù)制冷劑是氟氯碳化物和氟氯碳?xì)浠?，且大多?shù)的制冷劑是無毒的和不可燃的，然而，最近的美國(guó)聯(lián)邦的標(biāo)準(zhǔn) (環(huán)保署 1993a；環(huán)保署 1993b) 和國(guó)際的協(xié)議 (UNEP,1987) 已經(jīng)限制了氟氯碳化物和氟氯碳?xì)浠锏闹圃旌褪褂?，現(xiàn)在，氟氯碳化物和氟氯碳?xì)浠镌谝恍﹫?chǎng)合依然被使用，對(duì)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(guān)于為特定的設(shè)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(shè)備和標(biāo)準(zhǔn)。 液體制冷劑在離開冷凝器之后，在膨脹閥中節(jié)流到一個(gè)更低的壓力。這些系統(tǒng)的正確設(shè)計(jì)需要一個(gè)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(xiàn) 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