【正文】 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。 EPA 1993b) and international agreements (UNEP, 1987) have placed restrictions on the production and use of CFCs and HCFCs. Hydrofluorocarbons (HFCs) are now being used in some applications where CFCs and HCFCs were used. Having an understanding of refrigerants can help a building owner or engineer make a more informed decision about the best choice of refrigerants for specific applications. This section discusses the different refrigerants used in or proposed for building air conditioning applications and the regulations 4 affecting their use. The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) has a standard numbering system,for identifying refrigerants (ASHRAE, 1992). Many popular CFC, HCFC, and HFC refrigerants are in the methane and ethane series of refrigerants. They are called halocarbons, or halogenated hydrocarbons, because of the presence of halogen elements such as fluorine or chlorine (King, 1986). Zeotropes and azeotropes are mixtures of two or more different refrigerants. A zeotropic mixture changes saturation temperatures as it evaporates (or condenses) at constant pressure. The phenomena is called temperature glide. At atmospheric pressure, R407C has a boiling (bubble) point of –44176。F), which gives it a temperature glide of 7176。F) that it is considered a nearazeotropic refrigerant mixture. ASHRAE groups refrigerants by their toxicity and flammability (ASHRAE, 1994).Group A1 is nonflammable and least toxic, while Group B3 is flammable and most toxic. Toxicity is based on the upper safety limit for airborne exposure to the refrigerant. If the refrigerant is nontoxic in quantities less than 400 parts per million, it is a Class A refrigerant. If exposure to less than 400 parts per million is toxic, then the substance is given the B designation. The numerical designations refer to the flammability of the refrigerant. The last column of Table shows the toxicity and flammability rating of mon refrigerants. Refrigerant 22 is an HCFC, is used in many of the same applications, and is still the refrigerant of choice in many reciprocating and screw chillers as well as small mercial and residential packaged equipment. It operates at a much higher pressure than either R11 or R12. Restrictions on the production of HCFCs will start in 2020. In 2020, R22 cannot be used in new air conditioning equipment. R22 cannot be produced after 2020 (EPA, 1993b). R407C and R410A are both mixtures of HFCs. Both are considered replacements for R22. R407C is expected to be a dropin replacement refrigerant for R22. Its evaporating and condensing pressures for air conditioning applications are close to those of R22 (Table ). However, replacement of R22 with R407C should be done only after consulting with 5 the equipment manufacturer. At a minimum, the lubricant and expansion device will need to be replaced. The first residentialsized air conditioning equipment using R410A was introduced in the . in 1998. Systems using R410A operate at approximately 50% higher pressure than R22 (Table )。 8 tons) to the largest centrifugal (18,000 kW。在 1998年， 83%的新建住宅安裝了中央空調(diào) ( 人口普查局 , 1999)。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。對(duì)于蒸汽壓縮制冷循環(huán)，有一種叫制冷劑的工作液體，它能在適當(dāng)?shù)墓に囋O(shè)備設(shè)計(jì)壓力下蒸發(fā)和冷凝。 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。 所有在生產(chǎn)中的機(jī)械冷卻產(chǎn)生的熱量必須經(jīng)過(guò)冷凝器散發(fā)，在許多例子中，在冷凝器中這個(gè)熱能被直接散發(fā)到環(huán)境的空氣中或間接地散發(fā)到一個(gè)冷卻塔的水中。 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(wèn)題，因?yàn)樵谥评鋭┑氖褂蒙线€沒(méi)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铮掖蠖鄶?shù)的制冷劑是無(wú)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)。 C(– 47176。 C的溫度移動(dòng) (12176。 ASHRAE組制冷劑 (表 )根據(jù)它們的毒性和易燃性 (ASHRAE,1994)劃分的。 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。 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)。 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 )。 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。 R290, 丙烷 , 都有接近 R22的工作壓力，并被推薦來(lái)替代 R22 (Kramer, 1991)。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。 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）。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。冷卻塔將在后一部分講述。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。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)。每種制冷機(jī)以所使用的壓縮機(jī)類型來(lái)命名 。 1tons 的制冷量等于 或 1200btu／ h。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。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。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。離心式制冷機(jī)的效率最高。制冷機(jī)可使用 HCFCs（ R22， R123） 或 HFCs（ R－ 134a）制冷劑。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。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)。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(lái)自高壓制冷劑的熱量。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。然后，冷凍水通過(guò)各設(shè)備 16 傳送到水－空 氣換熱器。它們的不同主要在于使用的壓縮機(jī)種類的不同。 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。 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)