暖通空調(diào)專業(yè)畢業(yè)設(shè)計外文翻譯

1、<p><b>　　英文翻譯</b></p><p>　　Chilled Water Systems</p><p>　　Chilled water systems were used in less than 4% of commercial buildings in the U.S. in 1995. However, because chillers

2、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 chillers are commonly applied to commercial buildings: reciprocati

3、ng, screw, scroll, centrifugal, and absorption. The first four utilize the vapor compression cycle to produce chilled water. They differ primarily in the type of</p><p>　　Overall System</p><p>　

4、　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 applied in multiple chiller arrangements like that shown in the figure (B

5、itondo 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 7°C) (39 to 45°F).

6、 The chilled water is then distributed to water-to-air heat exchangers </p><p>　　The chillers shown in Figure 4.2.2 are water-cooled chillers. Water is circulated through the condenser of each chiller where

7、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. C

8、hillers can also be air cooled. In this configuration, the condenserwould be a refrigerant-to-air heat exchanger with air absorbing the heat energy reject</p><p>　　Chillers nominally range in capacities from

9、 30 to 18,000 kW (8 to 5100 ton). Most chillers sold in the U.S. are electric and utilize vapor compression refrigeration to produce chilled water. Compressors for these systems are either reciprocating, screw, scroll, o

10、r centrifugal in design. A small number of centrifugal chillers are sold that use either an internal combustion engine or steam drive instead of an electric motor to drive the compressor.</p><p>　　FIGURE 4.2

11、.2 A dual chiller application with major auxiliary systems (courtesy of Carrier Corporation).</p><p>　　The type of chiller used in a building depends on the application. For large office buildings or in chil

12、ler plants serving multiple buildings, centrifugal compressors are often used. In applications under 1000 kW (280 tons) cooling capacities, reciprocating or screw chillers may be more appropriate. In smaller applications

13、, below 100 kW (30 tons), reciprocating or scroll chillers are typically used.</p><p>　　Vapor Compression Chillers</p><p>　　Table 4.2.5 shows the nominal capacity ranges for the four types of el

14、ectrically driven vapor compression chillers. Each chiller 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 centrif

15、ugal (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 of chillers is often stated as a ratio of the power input (in kW) to the</p>

16、<p>　　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 ef

17、ficiency of the chiller varies with part load capacity. Figure 4.2.3 shows a representative data for the efficiency (in kW/ton) as a function of percentage full load capacity for a reciprocating, screw, and scroll chille

18、r plus a centrifugal chiller with inlet vane control and one with variabl</p><p>　　load falls to about 60% of its rated capacity and its kW/ton increases to almost twice its fully loaded value.</p>&l

19、t;p>　　FIGURE 4.2.3 Chiller efficiency as a function of percentage of full load capacity.</p><p>　　In 1998, the Air Conditioning and Refrigeration Institute (ARI) developed a new standard that incorporates

20、 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 4.2.3 an

21、d weights it at the 25%, 50%, 75%, and 100% loads to produce a single integrated efficiency number. The weighting factors at these loads are 0.12, 0.45, 0.42, and 0.01, respe</p><p>　　Most of the IPLV is det

22、ermined by the efficiency at the 50% and 75% part load values. Manufacturers will provide, on request, IPLVs as well as part load efficiencies such as those shown in Figure 4.2.3.</p><p>　　FIGURE 4.2.4 Volum

23、e-pressure relationships for a reciprocating compressor.</p><p>　　The four compressors used in vapor compression chillers are each briefly described below. While centrifugal and screw compressors are primari

24、ly used in chiller applications, reciprocating and scroll compressors are also used in smaller unitary packaged air conditioners and heat pumps.</p><p>　　Reciprocating Compressors</p><p>　　The r

25、eciprocating compressor is a positive displacement compressor. On the intake stroke of the piston, a fixed amount of gas is pulled into the cylinder. On the compression stroke, the gas is compressed until the discharge v

26、alve opens. The quantity of gas compressed on each stroke is equal to the displacement of the cylinder. Compressors used in chillers have multiple cylinders, depending on the capacity of the compressor. Reciprocating com

27、pressors use refrigerants with low specific volumes and</p><p>　　Modern high-speed reciprocating compressors are generally limited to a pressure ratio of approximately nine. The reciprocating compressor is b

28、asically a constant-volume variable-head machine. It handles various</p><p>　　discharge pressures with relatively small changes in inlet-volume flow rate as shown by the heavy line (labeled 16 cylinders) in

29、Figure 4.2.4. Condenser operation in many chillers is related to ambient conditions, for example, through cooling towers, so that on cooler days the condenser pressure can be reduced. When the air conditioning load is lo

30、wered, less refrigerant circulation is required. The resulting load characteristic is represented by the solid line that runs from the upper right to l</p><p>　　The compressor must be capable of matching the

31、 pressure and flow requirements imposed by the system. The reciprocating compressor matches the imposed discharge pressure at any level up to its limiting pressure ratio. Varying capacity requirements can be met by provi

32、ding devices that unload</p><p>　　individual or multiple cylinders. This unloading is accomplished by blocking the suction or discharge valves that open either manually or automatically. Capacity can also be

33、 controlled through the use of variable speed or multi-speed motors. When capacity control is implemented on a compressor, other factors at part-load conditions need to considered, such as (a) effect on compressor vibra

34、tion and sound when unloaders are used, (b) the need for good oil return because of lower refrigerant veloc</p><p>　　With most reciprocating compressors, oil is pumped into the refrigeration system from the

35、compressor during normal operation. Systems must be designed carefully to return oil to the compressor crankcase to provide for continuous lubrication and also to avoid contaminating heat-exchanger surfaces. </p>

36、<p>　　Reciprocating compressors usually are arranged to start unloaded so that normal torque motors are adequate for starting. When gas engines are used for reciprocating compressor drives, careful matching of the t

37、orque requirements of the compressor and engine must be considered.</p><p>　　FIGURE 4.2.5 Illustration of a twin-screw compressor design (courtesy of Carrier Corporation).</p><p>　　Screw Compres

38、sors</p><p>　　Screw compressors, first introduced in 1958 (Thevenot, 1979), are positive displacement compressors. They are available in the capacity ranges that overlap with reciprocating compressors and s

39、mall centrifugal compressors. Both twin-screw and single-screw compressors are used in chillers. The twin-screw compressor is also called the helical rotary compressor. Figure 4.2.5 shows a cutaway of a twin-screw compre

40、ssor design. There are two main rotors (screws). One is designated male (4 in the figur</p><p>　　The compression process is accomplished by reducing the volume of the refrigerant with the rotary motion of sc

41、rews. At the low pressure side of the compressor, a void is created when the rotors begin to unmesh. Low pressure gas is drawn into the void between the rotors. As the rotors continue to turn, the gas is progressively co

42、mpressed as it moves toward the discharge port. Once reaching a predetermined volume ratio, the discharge port is uncovered and the gas is discharged into the high pressu</p><p>　　Fixed suction and discharge

43、 ports are used with screw compressors instead of valves, as used in reciprocating compressors. These set the built-in volume ratio — the ratio of the volume of fluid space in the meshing rotors at the beginning of the c

44、ompression process to the volume in the rotors as the discharge port is first exposed. Associated with the built-in volume ratio is a pressure ratio that depends on the properties of the refrigerant being compressed. Scr

45、ew compressors have the capabilit</p><p>　　Capacity modulation is accomplished by slide valves that provide a variable suction bypass or delayed suction port closing, reducing the volume of refrigerant compr

46、essed. Continuously variable capacity control is most common, but stepped capacity control is offered in some manufacturers’ machines. Variable discharge porting is available on some machines to allow control of the buil

47、t-in volume ratio during operation.</p><p>　　Oil is used in screw compressors to seal the extensive clearance spaces between the rotors, to cool the machines, to provide lubrication, and to serve as hydrauli

48、c fluid for the capacity controls. An oil separator is required for the compressor discharge flow to remove the oil from the high-pressure refrigerant so that performance of system heat exchangers will not be penalized a

49、nd the oil can be returned for reinjection in the compressor.</p><p>　　Screw compressors can be direct driven at two-pole motor speeds (50 or 60 Hz). Their rotary motion makes these machines smooth running a

50、nd quiet. Reliability is high when the machines are applied properly. Screw compressors are compact so they can be changed out readily for replacement or maintenance. The efficiency of the best screw compressors matches

51、or exceeds that of the best reciprocating compressors at full load. High isentropic and volumetric efficiencies can be achieved with screw compr</p><p><b>　　譯 文</b></p><p><b>

52、　　冷水機組</b></p><p>　　1995年，在美國，冷水機組應(yīng)用在至少4％的商用建筑中。而且，由于制冷機組通常安裝在較大的建筑中，在同一年里，制冷機組冷卻了多于28％的商用建筑的地板空間（DOE，1998）。在商用建筑中普遍采用五種型式的制冷機：往復(fù)式、螺桿式、旋渦式、離心式和吸收式。前四種利用蒸汽壓縮式循環(huán)來制得冷凍水。它們的不同主要在于使用的壓縮機種類的不同。吸收式制冷機在吸收循環(huán)中利用

53、熱能（典型的是來自蒸汽或燃料燃燒）并利用氨－水或水－鋰溴化物制得冷凍水。</p><p><b>　　總的系統(tǒng)</b></p><p>　　圖4.2.2 兩臺制冷機同時作用的系統(tǒng)圖及輔助設(shè)備（格力有限公司）</p><p>　　圖4.2.2給出了包括主要輔助設(shè)備在內(nèi)的復(fù)式制冷機的簡圖。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（Bit

54、ondo和Tozzi，1999）。在冷凍水系統(tǒng)中，建筑物的回水通過每個蒸發(fā)器循環(huán)流動，在蒸發(fā)器中，回水被冷卻到合意的溫度（典型的為4～7℃－）（39～45℉）。然后，冷凍水通過各設(shè)備傳送到水－空氣換熱器。在換熱器中，空氣被冷凍水冷卻和加濕。在這個過程中，冷水的溫度升高，然后必須回送到蒸發(fā)器中。</p><p>　　圖4.2.2所示的制冷機組是冷水機組。水通過每個機組的冷凝器循環(huán)，在冷凝器中，水吸收了來自高壓制冷劑

55、的熱量。接著，水用水泵打到冷卻塔中，水通過蒸發(fā)而降溫。冷卻塔將在后一部分講述。冷凝器也可以是空冷式的。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。</p><p>　　制冷機組名義制冷量為30～18000kw（8～5100tons）。在美國，出售的大部分制冷機組是用電的，利用蒸汽壓縮制冷循環(huán)來制得冷凍水。在設(shè)計中，這種系統(tǒng)所使用的壓縮機也有往復(fù)式、螺桿式、旋渦式和離心式。一小部分的

56、離心式制冷機利用內(nèi)燃機或蒸汽機代替電來啟動壓縮機。</p><p>　　在建筑中所使用的制冷機組類型根據(jù)應(yīng)用場所來確定。對于大的辦公室建筑或制冷機組需服務(wù)于多個建筑時，通常使用離心式壓縮機。在所需制冷量小于1000kw（280tons）時，使用往復(fù)式或螺桿式制冷機組較合適。在小的應(yīng)用場合，若低于100kw（30tons）時，使用往復(fù)式或旋渦式制冷機組。</p><p><b>　

57、　蒸汽壓縮式制冷機</b></p><p>　　圖4.2.3 制冷機在各種不同滿負荷百分數(shù)時的效率</p><p>　　表4.2.5表示了四種電啟動的蒸汽壓縮式制冷機組的名義制冷量范圍。每種制冷機以所使用的壓縮機類型來命名。各種系統(tǒng)的制冷能力范圍從最小的旋渦式（30kw，8tons）到最大的離心式（18000kw，5000tons）。制冷機可使用HCFCs（R22，R123）&

58、lt;/p><p>　　或HFCs（R－134a）制冷劑。制冷機的效率通常用輸入功（用kw表示）與制冷量（用tons表示）的比值表示。1tons的制冷量等于3.52kw或1200btu／h。用這種方法衡量效率，其數(shù)值越小越好。從表4.2.5可以看出，離心式制冷機的效率最高。而往復(fù)式是這四種類型中效率最低的。表中所提供的效率是根據(jù)ASHRAE Standard30（ASHRAE，1995）在穩(wěn)定狀態(tài)下測得滿負荷時的效率

59、，這些效率中不包括輔助設(shè)備的能耗，比如泵，冷卻塔的風(fēng)機，而這些設(shè)備可以增加0.06～0.31kw/ton（Smit　et　al..，1996）。</p><p>　　制冷機組在大部分時候是在部分負荷下運行的。只有在建筑物的最高熱負荷時，制冷機才在額定制冷量附近運行。知道制冷機在部分負荷下效率是怎樣變化的，這是很重要的。圖4.2.3給出了往復(fù)式、螺桿式、旋渦式、帶葉片控制的離心式制冷機組、壓縮機頻繁啟動的制冷機組在

60、滿負荷時的百分比下相應(yīng)的效率（用kw/ton表示）。往復(fù)式制冷機在占滿負荷較小的百分比運行時，效率增加。相反地，帶葉片控制的離心式的效率在負荷為額定負荷的60％以后是基本不變的,它的kw/ton值隨百分數(shù)的減小而增加到滿負荷時的兩倍. </p><p>　　1998年，空調(diào)制冷學(xué)會提出了一項新的標準，用來劃歸在部分負荷下制冷機組的運行情況。部分負荷時的效率用綜合部分負荷值（IPLV）這個簡單的數(shù)值來表示。IPLV

61、在數(shù)值上和圖4.2.3相似。用25%，50%，75%，100%負荷時的效率來計算這個簡單的綜合效率。在這些負荷下的度量值分別為0.12，0.45，0.42，0.01。IPLV的計算公式為</p><p>　　IPLV=1/（0.01/A+0.42/B+0.45/C+0.12/D）</p><p>　　其中A——100%負荷時的效率</p><p>　　B——75%負

62、荷時的效率</p><p>　　C——50%負荷時的效率</p><p>　　D——25 %負荷時的效率</p><p>　　大多數(shù)的IPLV由滿負荷的50%，75%時的效率決定的，根據(jù)要求，制造商除了提供如圖4.2.3所示部分負荷時的效率，還會提供IPLV值。</p><p>　　以下對使用在蒸汽壓縮式制冷機中的四種壓縮機做簡要的講述。離心

63、式和螺桿式壓縮機主要應(yīng)用在制冷機組上。往復(fù)式和旋渦式壓縮機應(yīng)用在整體式空調(diào)和熱泵中。</p><p><b>　　往復(fù)式壓縮機</b></p><p>　　圖4.2.4 往復(fù)式壓縮機容積-壓力的關(guān)系</p><p>　　往復(fù)式壓縮機是一種有確定排量的壓縮機。在活塞的進氣沖程時，一定量的氣體被吸進氣缸。在壓縮沖程時，氣體被壓縮直到排氣閥打開。在每

64、個沖程被壓縮的氣體數(shù)量等于氣缸的體積。在制冷機中使用的壓縮機根據(jù)壓縮機制冷能力不同有不同個氣缸的。往復(fù)式壓縮機使用的制冷劑具有較小體積和相對較高的壓力。使用在建筑上的往復(fù)式制冷機組目前大多采用R22。</p><p>　　現(xiàn)在高速往復(fù)式壓縮機所限制的壓力比大約為9。往復(fù)式壓縮機基本上是具有固定容積可變壓力的機器。從圖4.2.4所示的最粗的一條線（16個氣缸）可以看出：內(nèi)容積流量發(fā)生較小的變化，壓縮機的排氣壓力會發(fā)

65、生各種變化。在一些制冷機中的冷凝器的運行情況與周圍環(huán)境有關(guān)。比如，在制冷時，通過冷卻塔后，冷凝壓力會降低。當(dāng)空調(diào)負荷降低時，所需的循環(huán)制冷劑流量會減少，這種結(jié)果—負荷特性在圖4.2.4中用實線表示了，從右上角指向左下角。</p><p>　　壓縮機必須要和系統(tǒng)壓力和所需的流量相匹配。往復(fù)式壓縮機在任何水平時會讓排氣壓力達到它限定的壓力比。不同制冷能力的需求可以通過卸載一個或多個氣缸來實現(xiàn)。這種卸載又可通過阻止手動

66、或自動開啟的吸氣和排氣閥門來完成。制冷能力也可通過使用變速或多速電動機來控制。當(dāng)控制好了壓縮機的制冷能力，在部分負荷時的其他影響因素也應(yīng)考慮，比如（a）壓縮機震動的影響和卸載裝置運行時的噪聲；（b）較低的制冷劑流速需要較好的回油；（c）在較低制冷能力時膨脹裝置正確的使用。</p><p>　　在大多數(shù)往復(fù)式壓縮機中，在正常運行時油從壓縮機被打到制冷系統(tǒng)中。系統(tǒng)必須仔細設(shè)計使油能回到壓縮機曲軸箱，以便連續(xù)潤滑，同時

67、也能避免對熱交換器表面的污染。</p><p>　　往復(fù)式壓縮機通常是輕載啟動的。一般轉(zhuǎn)矩的電動機也能適用于啟動。當(dāng)蒸汽機用于往復(fù)式壓縮機啟動時，壓縮機所需的轉(zhuǎn)矩和蒸汽機的匹配問題必須仔細考慮。</p><p><b>　　螺桿式壓縮機</b></p><p>　　螺桿式壓縮機，在1958年（Thevenot，1979年）第一次被提出，是一種有

68、固定容積的壓縮機。它的制冷能力是可變的，其范圍與部分的往復(fù)式壓縮機及較小的離心式壓縮機一致。雙螺桿和單螺桿這兩種都有在制冷機中使用。雙螺桿制冷壓縮機也叫螺旋式壓縮機。圖4.2.5所示為雙螺桿壓縮機剖面圖。它有兩個轉(zhuǎn)子（即螺桿），一個叫陽轉(zhuǎn)子（圖中的4），另一個叫陰轉(zhuǎn)子（圖中的6）。</p><p>　　壓縮過程是通過螺桿的旋轉(zhuǎn)運動減少制冷劑的體積來完成的。在壓縮機的低壓一側(cè)，當(dāng)轉(zhuǎn)子開始不嚙合時，形成一個空間。低壓

69、氣體進入轉(zhuǎn)子間的這個空間。隨著轉(zhuǎn)子繼續(xù)旋轉(zhuǎn)，氣體被逐漸地壓縮直到移向排氣口。一旦達到預(yù)定的體積比，排氣口打開，氣體被排到系統(tǒng)的高壓側(cè)。在3600rpm的旋轉(zhuǎn)速度下，螺桿式壓縮機有每分鐘多于14000的排量（ASHRAE，1996）。</p><p>　　在螺桿式壓縮機中，用吸氣口、排氣口來代替使用在往復(fù)式壓縮機上的閥門。它有一個內(nèi)容積比---指在開始壓縮前嚙合轉(zhuǎn)子間的液體空間的體積和排氣口第一次打開時轉(zhuǎn)子間的體積

70、之比。內(nèi)容積比與由被壓縮的制冷劑的特性而定的壓力比相聯(lián)系的。螺桿式壓縮機能夠在大于20：1的壓力比下運行（ASHRAE，1996）。假如系統(tǒng)的排氣壓力和排氣口打開時轉(zhuǎn)子間的壓力相匹配時，可以達到最高的效率。當(dāng)內(nèi)部壓力大于或小于排氣壓力時，就會產(chǎn)生能量的損失，但這對壓縮機沒有害處。</p><p>　　制冷量的調(diào)節(jié)靠接有各種變化的吸氣旁通管的滑板閥門或延遲吸氣口的關(guān)閉來減少被壓縮的制冷劑的體積來實現(xiàn)。連續(xù)可變的制冷

71、量控制是最普遍的。但是階梯式制冷量的控制在一些制造商的機器中也被提供。各種形狀的排氣口適用在一些機器中，用來控制運行時的內(nèi)容積比。</p><p>　　油在螺桿式壓縮機上可解決轉(zhuǎn)子間寬大的間隙、冷卻機器、潤滑和充當(dāng)制冷量控制時水力上的液體。在壓縮機的排氣口需安裝一個油分離器，以分離高壓制冷劑中的油，這樣不會對系統(tǒng)中的熱交換器的運行造成不利的影響，而且油能回流到壓縮機中。</p><p>