【正文】 塔的水中。 C(– 47176。 ASHRAE組制冷劑 (表 )根據(jù)它們的毒性和易燃性 (ASHRAE,1994)劃分的。 制冷劑 22 屬于 HCFC，在多數(shù)的相同設(shè)備中被用，也是在多數(shù)往復(fù)和螺旋式冷卻設(shè)備和小型商業(yè)和住宅的集中式設(shè)備中的首選制冷劑，它可以在一個(gè)更高的壓力下運(yùn)行，這一點(diǎn)要優(yōu)于 R11或 R12中的任何一個(gè)。 R410A系統(tǒng)利用特定的壓縮機(jī)，膨脹閥和熱交換器來(lái)利用該制 冷劑 . 氨廣泛地被在工業(yè)的冷卻設(shè)備和氨水吸收式制冷中用，它具有可燃性并且分毒性等級(jí)為 B，因此在商業(yè)建筑物中使用受到限制，除非冷卻設(shè)備的制造工廠獨(dú)立于被冷卻的建筑物之外。在商用建筑中普遍采 用五種型式的制冷機(jī)：往復(fù)式、螺桿式、旋渦式、離心式和吸收式。在這個(gè)過(guò)程中，冷水的溫度升高，然后必須回送到蒸發(fā)器中。在美國(guó)，出售的大部分制冷機(jī)組是用電的，利用蒸汽壓縮制冷循環(huán)來(lái)制得冷凍水。每種制冷機(jī)以所使用的壓縮機(jī)類型來(lái)命名 。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(cè) 得滿負(fù)荷時(shí)的效率，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(jī)，而這些設(shè)備可以增加 ～ 制冷機(jī)組在大部分時(shí)候是在部分負(fù)荷下運(yùn)行的。知道制冷機(jī)在部分負(fù)荷下效率是怎樣變化的，這是很重要的。制冷機(jī)可使用 HCFCs（ R22， R123） 或 HFCs（ R－ 134a）制冷劑。一小部分的離心式制冷機(jī)利用內(nèi)燃機(jī)或蒸汽機(jī)代替電來(lái)啟動(dòng)壓縮機(jī)。水通過(guò)每個(gè)機(jī)組的冷凝器循環(huán)，在冷凝器中，水吸收了來(lái)自高壓制冷劑的熱量。它們的不同主要在于使用的壓縮機(jī)種類的不同。 天然制冷劑的使用 , 例如二氧化碳 (R744) 和碳化氫在空調(diào)和制冷系統(tǒng)中的使用正在研究之中，二氧化碳能在高于傳統(tǒng)的 HCFCs或 HFCs的壓力下 工作和在超過(guò)臨界點(diǎn)的典型的空調(diào)設(shè)備中工作。在 15 2020年， R22不能在新的空調(diào)設(shè)備中被使用。因?yàn)樗麄兪菬o(wú)毒的和不燃燒的 , 所以在 A1組中制冷劑通常作為理想的制冷劑能基本滿足舒適性空調(diào)的需求。C(– 35176。 F)的廢熱可以減少建筑物中采暖的費(fèi)用。壓縮機(jī)提升制冷劑的蒸汽壓力以便使制冷劑的飽和溫度微高于在冷凝器中冷卻介質(zhì)溫度，使用的壓縮機(jī)類型和系統(tǒng)的設(shè)備有關(guān)，比較大的電冷卻設(shè)備使用一個(gè) 離心式的壓縮機(jī)而小的住宅設(shè)備使用的是一種往復(fù)或漩渦式壓縮機(jī)。 建筑物中的空氣調(diào)節(jié)通常是利用機(jī)械設(shè)備或熱交換設(shè)備完成 .在大多數(shù)應(yīng)用中，建筑物中的空調(diào)器為維持舒適要求必須既能制冷又能除濕，空調(diào)系統(tǒng)也用于其他的場(chǎng)所，例如汽車、卡車、飛機(jī)、船和工業(yè)設(shè)備，然而，在本章中，僅說(shuō)明空調(diào)在商業(yè)和住宅建筑中的應(yīng)用。C) (39 to 45176。F) and a condensation (dew) point of –37176。 2 Vapor Compression Cycle Even though there is a large range in sizes and variety of air conditioning systems used in buildings, most systems utilize the vapor pression cycle to produce the desired cooling and dehumidification. This cycle is also used for refrigerating and freezing foods and for automotive air conditioning. The first patent on a mechanically driven refrigeration system was issued to Jacob Perkins in 1834 in London, and the first viable mercial system was produced in 1857 by James Harrison and . vapor pression, there are two less mon methods used to produce cooling in buildings: the absorption cycle and evaporative cooling. These are described later in the chapter. With the vapor pression cycle, a working fluid, which is called the refrigerant, evaporates and condenses at suitable pressures for practical equipment designs. The four basic ponents in every vapor pression refrigeration system are the pressor, condenser, expansion device, and evaporator. The pressor raises the pressure of the refrigerant vapor so that the refrigerant saturation temperature is slightly above the temperature of the cooling medium used in the condenser. The type of pressor used depends on the application of the system. Large electric chillers typically use a centrifugal pressor while small residential equipment uses a reciprocating or scroll pressor. The condenser is a heat exchanger used to reject heat from the refrigerant to a cooling medium. The refrigerant enters the condenser and usually leaves as a subcooled liquid. Typical cooling mediums used in condensers are air and water. Most residentialsized equipment uses air as the cooling medium in the condenser, while many larger chillers use water. After leaving the condenser, the liquid refrigerant expands to a lower pressure in the expansion valve. The expansion valve can be a passive device, such as a capillary tube or short tube orifice, or an active device, such as a thermal expansion valve or electronic expansion valve. The purpose of the valve is toregulate the flow of refrigerant to the evaporator so that the refrigerant is superheated when it reaches the suction of the pressor. At the exit of the expansion valve, the refrigerant is at a temperature below that of the medium (air or water) to be cooled. The refrigerant travels through a heat exchanger called the evaporator. It absorbs energy from the air or water circulated through the evaporator. If air 3 is circulated through the evaporator, the system is called a direct expansion system. If water is circulated through the evaporator, it is called a chiller. In either case, the refrigerant does not make direct contact with the air or water in the evaporator. The refrigerant is converted from a low quality, twophase fluid to a superheated vapor under normal operating conditions in the evaporator. The vapor formed must be removed by the pressor at a sufficient rate to maintain the low pressure in the evaporator and keep the cycle operating. All mechanical cooling results in the production of heat energy that must be rejected through the condenser. In many instances, this heat energy is rejected to the environment directly to the air in the condenser or indirectly to water where it is rejected in a cooling tower. With some applications, it is possible to utilize this waste heat energy to provide simultaneous heating to the building. Recovery of this waste heat at temperatures up to 65176。C (12176。 5000 tons).Chillers can utilize either an HCFC (R22 and R123) or HFC (R134a) refrigerant. The steady state efficiency 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 kW or 12,000 btu/h. With this measure of efficiency, the smaller number is better. centrifugal chillers are the most efficient。居住的建筑物（即研究對(duì)象）被劃分成單獨(dú)的家庭或共有式公寓，應(yīng)用于這些建筑物的冷卻設(shè)備通常都是標(biāo)準(zhǔn)化組裝的，由空調(diào)廠家進(jìn)行設(shè)計(jì)尺寸和安裝。膨脹閥是一個(gè)節(jié)流的裝置，例如毛細(xì)管或有孔的短管，或一個(gè)活動(dòng)的裝置，例如熱力膨脹閥或電子膨脹閥，膨脹閥的作用是到蒸發(fā)器中分流制冷劑以便當(dāng)它到壓縮物吸入口的時(shí)候 , 制冷劑處于過(guò)熱狀 態(tài)，在膨脹閥的出口，制冷劑的溫度在介質(zhì) (空氣或水 ) 的溫度以下。 美國(guó)社會(huì)的供暖、制冷和空調(diào)工程師學(xué)會(huì) (ASHRAE)有一個(gè)標(biāo)準(zhǔn)的限制系統(tǒng) (表 )用來(lái)區(qū)分制冷劑，許多流行的氟氯碳化物，氟氯碳?xì)浠锖头蓟锏闹评鋭┦窃诩淄楹鸵彝榈闹评鋭┫盗兄?，因?yàn)辂u素元素的存在他們被叫作碳化鹵或鹵化的碳化氫，例如氟或氯。 F)，一個(gè) azeotropic 混合物的性能像單獨(dú)成份制冷劑那樣，它在不變的壓力下蒸發(fā)或冷凝它們的飽和溫度不會(huì)有少許變化。在對(duì)氟氯碳化物的制造的禁令頒布之前 , R11和 R12已經(jīng)是冷卻設(shè)備的首選制冷劑，在已存在的系統(tǒng)維護(hù)中，現(xiàn)在這兩種制冷劑的使用已經(jīng)被限制，現(xiàn)在， R123 和 R134a都廣泛的用在新的冷卻設(shè)備中。然而，用R407C來(lái)替換 R22應(yīng)該在和設(shè)備制造者商議之后才能進(jìn)行，至少潤(rùn)滑油和膨脹裝置將需要更換。目前，在美國(guó)沒(méi)有用二氧化碳或可燃的制冷劑的商業(yè)系統(tǒng)用于建筑部門。在冷凍水系統(tǒng)中，建筑物的回水通過(guò)每個(gè)蒸發(fā)器循環(huán)流動(dòng)，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℉）。冷凝器也可以是空冷式的。在所需制冷量小于 1000kw（ 280tons）時(shí)，使用往復(fù)式或螺桿式制冷機(jī)組較合適。用這種方法衡量效率，其數(shù)值越小越好。相反地，帶葉片控制的離心式的效率在負(fù) 荷為額定負(fù)荷的 60％以后是基本不變的 ,它的 kw/ton值隨百分