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1、<p>　　CENRTRAL COOLING AND HEATING</p><p>　　The energy used to heat and cool many buildings often comes from a central location in the facility. The energy input may be combination of electricity , oil

2、,gas , coal ,solar ,geothermal ,etc. This energy is typically converted into hot or chilled water or steam that is distributed throughout the facility for heating and air conditioning(cooling) . Centralizing this functio

3、n keeps the conversion equipment in one location and distributes the heating and cooling in a more readily usable form. Al</p><p>　　This lesson addresses the design alternatives that should be considered whe

4、n centralizing the cooling and heating sources in a facility.</p><p>　　The economics of these systems require extensive analysis. Boilers ,gas , steam ,and electric turbine-driven centrifugal refrigeration u

5、nits; and absorption chillers may be installed in combination in one plant . In large buildings with core areas that require cooling and perimeter areas require heating , one of several heat reclaim systems may heat the

6、perimeter to save energy .</p><p>　　The choice of equipment for a central heating and cooling plant depends on the following :</p><p>　　Required capacity and type of use</p><p>　　Co

7、st and types of energy available</p><p>　　Location and space for the equipment room</p><p>　　A stack for any exhaust gases and its environment impact\</p><p>　　Safety requirements f

8、or the mechanical room and surrounding areas </p><p>　　Type of air distribution system</p><p>　　Owning and operating costs </p><p>　　Many electric utilities impose very high charges

9、 for peak power use or ,alternatively ,offer incentives for off-peak use . This policy has renewed interest in both water and ice thermal storage .The storage capacity installed for summer load leveling may also be avail

10、able for use in the winter ,making heat reclaim a more viable option. With ice storage, the low-temperature ice water can provide colder air than that available from a conventional system that supplies air at 10 to 13℃.

11、The use of a</p><p>　　Refrigeration Equipment</p><p>　　The major types of refrigeration equipment in large systems use reciprocating compressors, helical rotary compressors, centrifugal compress

12、ors, and absorption chillers.</p><p>　　These large compressors are driven by electric motors, gas and diesel engines, and gas and steam turbines. The compressors may be purchased as part of a refrigeration c

13、hiller that includes the compressor, drive, chiller, condenser, and necessary safety and operating controls. Reciprocating and helical rotary compressor units are frequently field assembled, and include air-cooled or eva

14、porative condensers arranged for remote installation. Centrifugal compressors are usually included in packaged c</p><p>　　Absorption chillers are water-cooled. They use a lithium bromide/water or water/ammon

15、ia cycle and are generally available in the following four configurations(1) direct fired, (2) indirect generated by low-pressure steam of hot water, (3) indirect generated by high-pressure steam of hot water, and (4)ind

16、irect generated by hot exhaust gas. Small direct-fired chillers are single-effect machines with capacities of 12 to 90kW. Larger, direct-fired, double-effect chillers in the 350 to 7000kW range a</p><p>　　Lo

17、w-pressure steam at 100kPa of low temperature hot water heats the generator of single-effect absorption chillers with capacities from 180 to 5600kW. Double-effect machines use high-pressure steam up to 1000kPa or high-te

18、mperature ht water at an equivalent temperature. Absorption chillers of this type are available from 1200 to 7000kW.</p><p>　　In large installations the absorption chiller is sometimes combined with steam tu

19、rbine-driven centrifugal compressors. Steam from the noncondensing turbine is piped to the generator of the absorption machine. When a centrifugal unit is driven by a gas turbine of an engine, an absorption machine gener

20、ator may be fed with steam of hot water from the engine jacket. A heat exchanger that transfers the heat of the exhaust gases to a fluid medium may increase the cycle efficiency.</p><p>　　Cooling towers</

21、p><p>　　Water from condensers is usually cooled by the atmosphere. Either natural draft or mechanical draft cooling towers or spray ponds are used to reject the heat to the atmosphere. Of these, the mechanical

22、draft tower, which may be of the forced draft, induced draft, of ejector type, can be designed for most conditions because it does not depend on the wind. Air-conditioning systems use towers ranging from small package un

23、its of 20 to 1800kW to field-erected towers with multiple cells in unlimited s</p><p>　　If the cooling tower is on the ground, it should be at least 30m away from the building for two reasons: (1)to reduce t

24、ower noise in the building; and (2)to keep discharge air from fogging the building’ windows. Towers should be kept the same distance from parking lots to avoid staining car finishes with water treatment chemicals. When t

25、he tower is on the roof, its vibration and noise must be isolated from the building. Some towers are less noisy than others, and some have attenuation housings t</p><p>　　The bottom of many towers, especiall

26、y larger ones, must be set on a steel frame 1 to 1.5m above the roof to allow room for piping and proper tower and roof maintenance. Pumps below the tower should be designed for an adequate net positive suction pressure,

27、 but they must be installed to prevent draining the piping on shutdown.</p><p>　　The tower must be winterized if required for cooling at outdoor temperatures below 2℃. Winterizing includes the ability to byp

28、ass water directly into the tower basin or return line (either automatically of manually, depending on the installation) and to heat the tower pan water to a temperature above freezing. Heat may be added by steam of hot

29、water coils of by electric resistance heaters in the tower pan. Also, an electric heating cable on the condenser water and makeup water pipes and insulati</p><p>　　Careful attention must also be given to wat

30、er treatment to minimize the maintenance required by the cooling tower and refrigeration machine absorbers and /on condenser.</p><p>　　Cooling towers may also cool the building in off-seasons by filtering an

31、d directly circulating the condenser water through the chilled water circuit, by cooling the chilled water in a separate heat exchanger, or by using the heat exchangers in the refrigeration equipment to produce thermal c

32、ooling. Towers are usually selected in multiples so that they may be run at reduced capacity and shut down for maintenance in cool weather. Chapter 36 includes further design and application details.</p><p>

33、　　Air-Cooled Condensers</p><p>　　Air-cooled condensers pass outdoor air over a dry coil to condense the refrigerant. This process results in a higher condensing temperature and, thus, a larger power input at

34、 peak condition; however, over 24 hours this peak time may be relatively short. The air-cooled condenser is popular in small reciprocating systems because of its low maintenance requirements.</p><p>　　Evapor

35、ative Condensers</p><p>　　Evaporative condensers pass outdoor air over coils sprayed with water, thus taking advantage of adiabatic saturation to lower the condensing temperature. As with the cooling tower,

36、freeze prevention and close control of water treatment are required for successful operation. The lower power consumption of the refrigeration system and the much smaller footprint of the evaporative versus the air-coole

37、d condenser are gained at the expense of the cost of the water used and increased maintenance cost.</p><p>　　HEATING EQUIPMENT</p><p>　　A boiler is the most common device used to add heat to th

38、e working medium, which is then distributed throughout the facility. Although steam is an acceptance medium for transferring heat between buildings or within a building, low-temperature hot water provides the most common

39、 and more uniform means of perimeter and general space heating. The working medium may be either water of steam, which can further be classified by its temperature and pressure range. The term hot-water boiler applies to

40、 fu</p><p>　　Fuel Section</p><p>　　Functionally a boiler has two major sections. For all fuel burning boilers, that fuel must first be burned in the combustion section of the boiler. Control of

41、both the fuel and air greatly effect the efficiency of the combustion process. This is also the primary point at which the heating capacity of the boiler is regulated. On smaller boilers that only turn on or off, the air

42、/fuel ratio is fixed and is not actively controlled. A next step of regulation may have one of two intermediate steps of </p><p>　　Heat Transfer Section</p><p>　　The second major section of the

43、boiler is the heat transfer section where heat from the combustion process is transferred to the working medium that will distribute the heat. The effectiveness of these heat transfer surfaces depends on the temperature

44、difference between the fluid, water, or steam on one side and the gases on the other side, and on the circulation rate of both the water and the hot gases. Heating surfaces are classified as direct and indirect. Direct s

45、urfaces are those upon which</p><p>　　Working pressure</p><p>　　Pressures in the boiler also affect its classification. The combustion section can be regulated at a slightly negative pressure re

46、lative to the atmosphere to ensure that the combustion gases do not flow anywhere except up the stack. In a natural draft boiler, the chimney effect of the stack draws the combustion products up the stack. Alternatively,

47、 the boiler may use a fan to force air through the burner and boiler in a forced draft arrangement. In this case the combustion chamber and boiler its</p><p>　　The pressure of the working medium(steam or wat

48、er) can be low, medium, or high. For hot water boilers more so then steam boilers the location in the facility as well as its elevation relative to the rest of the facility impacts the working pressure. Pumping in or out

49、 of a water boiler can effect its operating/dynamic pressure; and the boiler’s location, either in a basement or on a roof, can effect its standby/static pressure. </p><p>　　DISTRIBUTION</p><p>

50、　　The steam or hot water is the working medium of the heating system that transfer the heat produced by the boiler to the areas where it will be used. Steam typically is distributed by its inherent pressure; but once it

51、is condensed, it must rely on gravity or pumps to return to the boiler. The issue of condensate traps and the return is one of the important design and operational concerns for steam. If water is the working medium, pump

52、s distribute it from the boiler.</p><p><b>　　Pumps </b></p><p>　　HAVC pumps are usually centrifugal pumps. Pumps for large, heavy-duty systems have a horizontal split case with a dou

53、ble-suction impeller for easier maintenance and higher efficiency. End suction pumps, either close coupled of flexible connected, may be used for smaller tasks. Pumps can be installed in-line of be base mounted.</p>

54、;<p>　　Pumps are used to distributed or circulate the following fluids:</p><p>　　Primary and secondary chilled water</p><p>　　Primary and secondary hot water</p><p>　　Condens

55、er water</p><p>　　Condensate</p><p>　　Boiler feed</p><p><b>　　Fuel oil</b></p><p>　　When pumps handle hot liquids of have a high inlet pressure drop, the re

56、quired net positive suction pressure must not exceed the net positive suction pressure available at the pump. It is common practice to provide spare pumps to maintain continuity in case of a pump failure. The chilled wat

57、er and condenser water system characteristics may permit using one spare pump for both systems, if they are properly valved and connected to both manifolds.</p><p>　　CENTRAL PLANT LOADS</p><p>　

58、　The design cooling and heating loads are determined by considering the entire portion of block of the building served by the air-and-water system at the same time. Because the load on the secondary water system depends

59、on the simultaneous demand of all spaces, the sum of the individual room or zone peaks is not considered.</p><p>　　The peak cooling load time is influenced by the ourdoor wet-bulb temperature, the period of

60、building occupancy, and the relative amounts of east, south, and west exposures. Where the magnitude of solar load is about equal for each of the above exposures, the building peak usually occurs on a midsummer afternoon

61、 when the west solar load and outdoor wet-bulb temperature are at or near concurrent maximums.</p><p>　　If the side exposed to the sun or interior zone loads require chilled water in cold weather, the use of

62、 condenser water with a water-to-water heat exchanger should be considered. Varying refrigeration loads require the water chiller to operate satisfactorily under all conditions.</p><p>　　If water supply temp

63、erature or quantities are to be reset at times other than at peak load, the adjusted settings must be adequate for the most heavily loaded space in the building. An analysis of individual room load variations is required

64、.</p><p>　　The peak heating load may occur when the facility must be warmed to occupancy conditions after an unoccupied weekend setback. The peak demand may also occur during unoccupied conditions when the a

65、mbient environment is at its harshest and there is little internal heat gain to assist the heating system. Another possible maximum may occur during occupied times if significant outdoor air must be preconditioned or som

66、e other process (maybe non-HVAC) requires significant heat. The designer must analyz</p><p>　　From:《Architecture Environment and Engineering Equipment》</p><p>　　China Architecture and Building P

67、ress</p><p><b>　　譯文：</b></p><p>　　在過去，許多建筑物供熱和制冷的能量常常來自于機房中的某一集中區(qū)域。輸入的能量可能是電、石油、 天然氣、煤、太陽能、地熱能等的任一混合物。這些能量主要被轉化成為熱水或冷凍水或者是供熱和制冷設備分流組織的蒸汽的熱能。這種功能的集中化可使得轉換設備在一個區(qū)域而且還能以一種更容易利用的形式來布置供熱和制

68、冷。另外，一個集中式制冷和供熱設備比一個分散式設備能提供更多的多樣性，整體運轉效率更高，所用的維護費用和勞務費用也更低。但是，集中式設備需要一個集中的區(qū)域和一個具有很大潛力的組織系統(tǒng)。</p><p>　　本課介紹了當把冷熱源集中設置在一個機房中時應該考慮的設計方法。</p><p>　　這些系統(tǒng)的經(jīng)濟性需要廣泛的分析。鍋爐、天然氣、蒸汽、以及電驅動的離心式制冷機組；吸收式冷水機可以以組合

69、的形式安裝在一個設備內(nèi)。在一些有內(nèi)區(qū)需要制冷，外區(qū)需要供熱的大型建筑中，幾種熱回收系統(tǒng)中的方法之一或許就是給外區(qū)供熱以此來節(jié)約能量。</p><p>　　對于一個集中供熱和制冷設備的選擇，取決于以下幾點：</p><p><b>　　所需容量和利用形式</b></p><p>　　可利用能量的耗費和種類</p><p>

70、　　設備室的位置和空間大小</p><p>　　任何廢氣的煙囪和環(huán)境影響</p><p>　　機械室和周圍地區(qū)的安全要求</p><p><b>　　氣流組織系統(tǒng)的形式</b></p><p><b>　　初投資和運行費用</b></p><p>　　很多電力公司都對高峰用電

71、采取高昂的收費，而鼓勵低谷用電。這項政策已經(jīng)引起對水和冰熱力蓄存技術的興趣。為夏季負荷調(diào)整配置的蓄存容量也可以在冬季使用，使得熱回收成為一個更為可行的選擇。有了冰蓄存技術，低溫的冰水可以提供比常規(guī)系統(tǒng)提供的10℃～13℃的空氣溫度還要低的空氣。高溫水和低溫空氣的溫差，降低了泵和風機（扇）能量的需求。另外，在一些情況下，也補償了由于制冰而需要的低溫所耗費的能量。</p><p><b>　　制冷設備<

72、;/b></p><p>　　在大型系統(tǒng)中所使用的制冷設備主要形式是：往復式壓縮機，螺桿式壓縮機，離心式壓縮機和吸收式冷水機。</p><p>　　這些大型的壓縮機由電機、燃氣和柴油發(fā)動機以及燃氣和蒸汽輪機所驅動。這些壓縮機可以作為一個包含壓縮機，驅動，冷卻器，冷凝器和必要的安全設施和運行控制的制冷機組的一部分來購買。往復式和螺桿式壓縮機組是應用的最廣泛的，還包括一些遠距離安裝時空冷

73、式和蒸發(fā)式冷凝器的使用。離心式壓縮機則常常包括在組裝式冷水機組中。</p><p>　　吸收式冷水機是水冷的。它們用溴化鋰-水或者水-氨來循環(huán)。在一下四種情況下經(jīng)常使用：（1）直燃式 （2）由低壓蒸汽或熱水間接驅動的 （3）高壓蒸汽或熱水間接驅動的 （4）由高溫廢氣間接驅動的 。具有12到90kw容量的小型直燃式冷水機是單效作用的機器。更大一點的，容量從350kw到1700kw的直燃式雙效冷水機也是可以應用的。&

74、lt;/p><p>　　容量從180kw到5600kw的單效吸收式冷水機組的電機是由100kpa時的低壓蒸汽或低溫熱水來驅動的。雙效式用的是壓力高達1000kpa的高壓蒸汽或具有當高溫度的熱水來驅動的。這種形式的吸收式冷水機應用范圍是從1200kw到7000kw。</p><p>　　在大型安裝中，吸收式冷水機有時和汽輪機驅動的離心式壓縮機組合在一起。來自于渦輪機的沒有冷凝的蒸汽被輸送到這個吸

75、收式機器的電機。當一個離心式制冷機組由燃氣輪機或發(fā)動機所驅動時，吸收式冷水機的發(fā)電機要由蒸汽或來自于發(fā)動機夾套的高溫熱歲來驅動。一個能夠把廢氣的熱能轉移到液體媒介中的熱交換器，可以提高循環(huán)效率。</p><p><b>　　冷卻塔</b></p><p>　　從冷凝器出來的水通常被大氣冷卻?？梢圆捎米匀煌L或機械通風式冷卻塔或用噴水池將熱量排到大氣中去。這當中的機械通

76、風式冷卻塔，可以是強制通風，誘導通風或噴射泵形式的。由于它不依賴于自然風，它可以適用于大多數(shù)情況?？諝庹{(diào)節(jié)系統(tǒng)所用的冷卻塔是從容量20kw到1800kw的小型組裝式機組到具有無尺寸限制的多個機組的室外直立式冷卻塔。</p><p>　　如果冷卻塔在地面上，由于以下兩個原因，它應該離建筑物30m遠：（1）為了減少建筑物內(nèi)冷卻塔產(chǎn)生的噪音；（2）為了防止排氣在建筑物的窗戶上結霧。塔也應該離停車場同樣的距離以防止帶有污

77、染化學物質的水使車漆褪色。當塔在屋頂時，它的振動和噪音必須與建筑物隔離。一些塔比其他的噪音低，還有一些設有減噪房來降低噪音。在選擇一個冷卻塔之前，這些選擇都應考慮。令人滿意感到舒適的房間應該能夠有合理的空氣流動以防止室內(nèi)空氣的再循環(huán)。</p><p>　　許多塔的底部，特別是較大型的，必須建在離屋頂1m到1.5m高的鋼架上，給水管及對塔和屋頂?shù)木S護留出合適的空間。比冷卻塔低的水泵應具有足夠的凈正吸入壓力，但是它們

78、必須安裝成能夠防止停機時排空管道。</p><p>　　如果在室外溫度低于2℃的條件下制冷，冷卻塔必須防凍。防凍包括使旁通水直接到塔盤或返回到水管（自動地或人工地，取決于安裝）和把塔底的水加熱到高于冷凍點之上的能力。熱量可以由蒸汽或熱水盤管或由塔底的熱電阻加熱器提供。另外，在冷凝器和水管上的電熱纜以及熱追蹤部分的隔熱措施是必不可少的來防止水管凍裂。當冷卻塔在接近冰凍條件下運行時，特殊的控制也是必須的。在冷凍的天氣

79、條件下，冷卻塔不能工作的地方，必須為排空冷卻塔和管道做一些準備。排空是防止冷卻塔和水管結凍最有效的形式。</p><p>　　為了減少冷卻塔、制冷設備的吸收器或冷凝器所需的維護費用，仔細的水處理也是必不可少的。</p><p>　　在過渡季，冷卻塔可以通過過濾直接使冷凝水在冷水環(huán)路中循環(huán)。通過在一個備用的熱交換器中冷卻冷水，或者是通過使用制冷設備中的熱交換器來產(chǎn)生冷卻熱這些方式來給建筑制冷

80、。選擇冷卻塔時通常是多類型的，這樣它們就可以在運行時節(jié)省能量，在冷天氣時，可以停機維護。36章包含了更詳細的設計和應用。</p><p><b>　　空冷式冷凝器</b></p><p>　　空冷式冷凝器使室外空氣通過干燥的盤管來使制冷劑冷凝。這個過程會產(chǎn)生一個較高的冷凝溫度，因此，在高峰時需要輸入更多的電；然而，超過24小時，這個高峰時段會相應縮短。這種空冷式冷凝器

81、，由于它的維護費用較低，在往復式制冷系統(tǒng)中得到的廣泛的應用。</p><p><b>　　蒸發(fā)式冷凝器</b></p><p>　　蒸發(fā)式冷凝器使室外空氣通過噴水的盤管，這樣可以利用飽和潛熱來降低冷凝溫度。和冷卻塔一樣，防凍措施和水處理的閉環(huán)控制是正常運行必不可少的，蒸發(fā)式冷凝器和空冷式冷凝器一對比，蒸發(fā)式冷凝器的制冷系統(tǒng)電力能耗更低，尺寸小，而空冷式冷凝器是以所使用

82、過的水的耗費為代價的，增加的維護費用。</p><p><b>　　供熱設備</b></p><p>　　鍋爐是最常見的用于給工作介質加熱的設備。這種介質被加熱后再通過鍋爐房被分配。盡管蒸汽對于建筑之間或一個建筑內(nèi)的換熱是一種可以利用的介質，但是，低溫熱水能夠提供對外區(qū)和一般空間的供熱最常見的和更均勻的方式。工作介質可能是水或蒸汽，這又可以通過它們的溫度和壓力范圍進一

83、步分類。熱水鍋爐適用于給供熱系統(tǒng)加熱水的燃料式機組。熱水鍋爐和蒸汽鍋爐的不同在于，熱水鍋爐在頂部沒有足夠的空間可以利用。但是在許多方面，對于同一形式的建筑，熱水鍋爐和蒸汽鍋爐是一樣的。如果布置、選型和安裝合理的話，許多蒸汽鍋爐也可以作為熱水鍋爐來使用。蒸汽鍋爐和熱水鍋爐用天然氣、石油、煤、電，有時還用垃圾作為燃料。</p><p><b>　　燃料部分</b></p><

84、p>　　一個正常運轉的鍋爐有兩個主要部分。對于所有燃燒燃料的鍋爐，燃料必須先在鍋爐的燃燒室中燃燒。燃料和空氣的控制在很大程度上影響著燃燒的效率。這也是控制鍋爐供熱能力的主要的一點。僅進行開關控制的小型鍋爐，空氣/燃料比是固定的，且不能主動控制。進一步的調(diào)節(jié)控制可以有一級或兩級燃料輸入的中間值，這樣的低火或高火，在每一燃料輸入級空氣/燃料比都固定。一種更大型或者比例調(diào)節(jié)的鍋爐可能具有調(diào)節(jié)到任何水平的燃料流量。為了確保燃料的充分燃燒而

85、不加熱過量的空氣或者產(chǎn)生有毒或污染性的化合物，一種正確的控制空氣的方法也是必須的。</p><p><b>　　傳熱部分</b></p><p>　　鍋爐的第二個主要部分是傳熱部分。在這里，熱量從燃燒過程轉移到分配熱量的工作介質。傳熱面的效率取決于流體、水或者是蒸汽側和燃氣側的溫差，還取決于水和熱燃氣的循環(huán)倍率。加熱面分為直接加熱面和間接加熱面。直接加熱面上可以看到火

86、光；它們把熱量轉移到爐水的效率是很高的，因為表面的高溫能夠促進輻射和對流。間接加熱面僅和燃氣接觸，隨著燃氣的冷卻，從傳熱點的傳熱效果要差很多。鍋爐制造廠家一般他這兩種傳熱面結合在一起。在煙管鍋爐中，燃燒產(chǎn)物在管內(nèi)流動，傳熱介質在管外流動。在水管鍋爐中，燃燒產(chǎn)物在管外流動，傳熱介質在管內(nèi)流動。鑄鐵斷絕鍋爐通過鑄鐵段把熱量從燃氣轉移到水中。</p><p><b>　　工作壓力</b></

87、p><p>　　鍋爐中的壓力也影響它的分類。燃燒部分相對于大氣來說可以有一點點的負壓，以此來保證燃燒氣體除了在煙囪中，不到處流動。在自然通風鍋爐中，煙囪的煙囪效應把燃燒產(chǎn)物從煙囪中抽走。另外，鍋爐還可以用鼓風機（風扇）來強制空氣通過燃燒器和一個強制通風的鍋爐。在這種情況下，燃燒室和爐體本身相對于周圍大氣來說處于正壓狀態(tài)。</p><p>　　工作介質（蒸汽或水）的壓力可以是低壓，中壓或高壓。鍋

88、爐在機房中的位置和它們相對于其他設施的高度會影響工作壓力，這種影響熱水鍋爐比蒸汽鍋爐要來的大。熱水鍋爐的泵進和抽出能夠影響其運行和動態(tài)壓力；鍋爐的位置—位于地下室或屋頂—可以影響其待機和靜態(tài)壓力。</p><p><b>　　氣流組織</b></p><p>　　蒸汽或熱水是供熱系統(tǒng)的工作介質，供熱系統(tǒng)把鍋爐產(chǎn)生的熱量轉移到利用這些熱量的地區(qū)。蒸汽主要是由它內(nèi)在的都壓

89、力來分配的，但是一旦蒸汽冷凝成水，它就必須依靠重力或者是泵來返回鍋爐。冷凝水的存水彎和返回問題是設計中很重要的一方面。對于蒸汽來說在運行中要考慮。如果工作介質是水，水泵會把它從鍋爐中分配。</p><p><b>　　水泵</b></p><p>　　供熱、 通風與空調(diào)使用的水泵通常是離心式的水泵。為便于維護和保持較高效率，大型的負荷大的系統(tǒng)的水泵具有臥式分開的機殼、

90、雙吸式葉輪。負荷較小的系統(tǒng)可以用單吸泵，或緊密對接，或柔性連接。水泵可以管道式安裝，或者裝在基座上。水泵用來分配或循環(huán)以下流體：</p><p>　　一次冷凍水和二次冷凍水</p><p><b>　　一次熱水和二次熱水</b></p><p><b>　　冷凝器中的水</b></p><p>&l

91、t;b>　　凝結水</b></p><p><b>　　鍋爐補水</b></p><p><b>　　燃料石油</b></p><p>　　當泵處理高溫流體或有一個高的入口壓力降時，所需的凈正吸入壓力不能超過水泵本身可利用的凈正吸入壓力。為了防止泵出現(xiàn)故障，使泵持續(xù)運行而配置備用泵是一種慣例。如果能夠合理

92、地配備安全閥和分支管連接，冷凍水系統(tǒng)和冷凝水系統(tǒng)就可以使用一臺備用泵。</p><p><b>　　中央設備的負荷</b></p><p>　　冷負荷的設計是由考慮到由空氣—水系統(tǒng)服務的整個建筑或建筑的一部分所決定的。因為二次水系統(tǒng)的負荷取決于所有空間同時的需求。單個房間的總量或區(qū)域的峰值不在考慮范圍之內(nèi)。</p><p>　　冷負荷的峰值時間

93、受室外濕球溫度、建筑物的居住時間和東、南以及西面受太陽照射的相對總量的影響。在太陽負荷的量級對以上各朝向（東、南、西）差不多的場合，建筑的峰值負荷往往發(fā)生在某一個仲夏的下午—西面的太陽和室外濕球溫度都同時處于或接近于最大值時。</p><p>　　在寒冷的季節(jié)，如果受太陽照射的一側或內(nèi)區(qū)負荷需要冷凍水時，應該考慮使用帶有水—水換熱器的冷凝器。變化的冷負荷需要冷水以滿足各種條件下的負荷的要求。</p>

94、<p>　　如果供水溫度或總量需要在除峰值負荷時刻以外的其他時間重新設置時，調(diào)整的設置必須能夠滿足建筑當中最大的負荷。單個房間負荷變化的分析也是必須的。</p><p>　　峰值供熱負荷可能發(fā)生在某一個無人的周末停機之后，整個設施都要被加熱到有人的狀態(tài)。當周圍的環(huán)境使人感到很不舒服時，而且?guī)缀鯖]有內(nèi)部熱量來加熱系統(tǒng)時，峰值負荷也可以在無人居住的條件下出現(xiàn)。如果大量的室外空氣需要預熱或有其他一些需要大量