建環(huán)畢業(yè)設計外文翻譯--關于先進的低能耗的超市制冷系統(tǒng)的分析

1、<p><b>　　中文4830字</b></p><p>　　畢業(yè)設計（論文）譯文</p><p>　　題目名稱：關于先進的低能耗的超市制冷系統(tǒng)的分析 </p><p>　　學院名稱：能源與環(huán)境學院 </p><p>　　班 級：XXX <

2、/p><p>　　學 號：XXX </p><p>　　學生姓名：XXX </p><p>　　指導教師：XXX </p><p><b>　　X年 X月X日</b></p><p>　　關于先進的低能耗的超市制冷系統(tǒng)的分析<

3、/p><p>　　大衛(wèi)·沃克博士ASHRAE成員</p><p>　　范D·巴克斯特博士ASHRAE成員</p><p><b>　　摘要</b></p><p>　　目前，超市制冷系統(tǒng)的運行需要花費非常大的制冷劑費用，每年可以消耗掉高達1至1.5萬千瓦時。幾項新的措施，如分布式、二次循環(huán)、及先進的獨立式

4、制冷系統(tǒng)的使用，可以顯著地減少制冷劑使用量，同時相應降低制冷劑的泄漏損失。新的冷凝器控制多重制冷系統(tǒng)也得到了發(fā)展，使制冷劑充注接近于臨界操作水平，且允許在非常低的水頭壓力下運行。通過適當?shù)脑O計和實施，這些先進的系統(tǒng)，每年可以減少高達11.9％的能源消耗。可以通過水源熱泵機組，通過設在該散熱循環(huán)熱泵可利用的存儲空間來實現(xiàn)制冷、散熱，以不增加冷凝溫度制冷來整合暖通空調(diào)制冷和存儲操作。這種集成方法表明，可以減少12.6％的制冷和空調(diào)系統(tǒng)綜合經(jīng)

5、營成本。</p><p>　　關鍵詞 制冷系統(tǒng) 分布式 二次循環(huán) 獨立式</p><p><b>　　引言</b></p><p>　　在商業(yè)部門中，超市是最大的能源用戶。一個銷售面積約40000英尺的典型的超市，每年總儲存能量消耗約2萬千瓦時。許多大型超市和超級購物中心還存在消耗高達3至5萬千瓦時/年的情況。</p><p

6、>　　超級市場所出售的大多是易腐爛產(chǎn)品，在展示和存儲期間必須冷藏，其能量消耗最大的用途之一是制冷。典型超市制冷系統(tǒng)的能源消耗是對應超市能耗總數(shù)的一半。超市的能源消耗總量中，壓縮機和冷凝器占30％至35％，其余是消耗在：展示和存儲冷卻器風扇，顯示器外殼照明，防汗加熱器和用于防止冷凝水形成的門和外表面的展示柜。</p><p>　　圖1顯示了一家超市展示柜典型的冷藏布局。超市的空調(diào)制冷系統(tǒng)在所有的冷藏裝置中直接

7、采用膨脹線圈。為了降低噪聲和控制散熱，壓縮機和冷凝器保存在遠程機房背面或在超市的屋頂，由管道提供制冷劑，并返回設備。</p><p>　　圖1，一個典型的超市冷藏布局</p><p><b>　　圖2，多重制冷系統(tǒng)</b></p><p>　　圖2顯示了多重制冷系統(tǒng)的主要成分，這是在超市最常用的組態(tài)。在多個壓縮機運行時，飽和吸氣溫度都安裝在同一

8、線，并由共同管道吸入和排出制冷劑。多個壓縮機并聯(lián)使用提供了一種控制手段的能力，因為壓縮機可根據(jù)需要選擇循環(huán)，以滿足制冷負載。制冷系統(tǒng)經(jīng)常采用空氣冷卻冷凝器用以散熱。</p><p>　　由于使用此布局，造成超市制冷系統(tǒng)需要大量制冷劑。一個典型的超市將需要3000到5000磅的制冷劑。超市制冷系統(tǒng)大量使用配管及管接頭也會導致制冷劑泄漏的增加，其中每年總費用損失可達30％至50％（【W(wǎng)alker】2001年）。<

9、;/p><p>　　隨著人們對制冷劑的泄漏對全球變暖的影響的不斷關注，新的超市制冷系統(tǒng)配置正在考慮要求大大減少制冷劑。例如低能耗制冷劑系統(tǒng)包括分布式，二次循環(huán)和高性能獨立的配置。復合式制冷系統(tǒng)也取得了改進，以減少其運作所需的電荷量。關于這些低能耗能源消耗系統(tǒng)的運營幾乎沒有人了解。如果沒有適當?shù)脑O計和操作，通過降低制冷劑充注和泄漏減緩全球變暖很可能會由于電能源消耗的增加造成二次全球變暖而被否定（如由TEWI概念測量[S

10、andetal.1997]）。</p><p>　　基于這些原因，美國能源部啟動一項關于低能耗超市制冷系統(tǒng)的調(diào)查工程。這個制冷調(diào)查，包括分析分布式和二次循環(huán)制冷系統(tǒng)和多了一項能源的TEWI復合式系統(tǒng)。分析得到的結果刊登在【W(wǎng)alker】（2000年）。關于這項調(diào)查的工作仍在繼續(xù)，其中包括一個涉及兩家超市的現(xiàn)場試驗：一家配備分布式系統(tǒng)，另一家配備復合式的系統(tǒng)。分析內(nèi)容擴大到包括低能耗復合式和高性能的獨立系統(tǒng)。<

11、;/p><p>　　本文提出了關于這一點的所有分析結果，以前的結果可列入完整。</p><p><b>　　1.分布式制冷系統(tǒng)</b></p><p>　　圖3是一個顯示了分布式制冷系統(tǒng)主要部件的圖表。</p><p>　　圖3，分布式制冷系統(tǒng)</p><p>　　多級壓縮機位于柜子上或放置在附近的銷

12、售層。櫥柜接近耦合到展示柜，從櫥柜散熱，是通過在位于上方的櫥柜屋頂使用空氣冷卻冷凝器或乙二醇循環(huán)連接液體冷卻到一個柜子來完成的。</p><p>　　制冷系統(tǒng)采用的分布式滾動壓縮機是由于這種類型的壓縮機具有低噪音和振動水平。如果壓縮機柜位于銷售區(qū)或在銷售區(qū)域附近，那么這些特征是必要的。渦旋式壓縮機沒有閥，而且，在一般情況下，沒有像往復式那么高的效率。滾動式壓縮機的無閥功能允許它們在明顯低的冷凝溫度下運行。最低的冷

13、凝溫度可能發(fā)生在吸力對放電壓力比為2的情況下，其中，對于超市系統(tǒng)，是指凝結的最低溫度真實可能是在55℉到60℉，對于中型制冷系統(tǒng)溫度為40℉。這里不認為由于有兩個乙二醇循環(huán)存在而有必要在40℉的最低冷凝溫度下使用，它可能會或可能不切合實際安裝。因此，冷凝溫度最低為60華氏度，僅限于本評估。</p><p>　　渦旋壓縮機也有可能通過制冷劑蒸氣中期滾動注入提供過冷。這種特殊的方法尚未得到最優(yōu)化，壓縮機制造商并沒有為

14、這部分提供分析。</p><p>　　對于能源消費，具有緊密耦合的分布式冷藏柜顯示有其他后果。較短的吸力線表示，壓力落案之間的蒸發(fā)器和壓縮機吸氣流形比多重系統(tǒng)看到的少，意味著飽和吸力溫度（SST）的內(nèi)閣將接近陳列柜蒸發(fā)器的溫度。較短的吸力線也意味著更少的熱量增益到返回氣中是可行的。較冷的回氣有高密度，結果導致更高的壓縮機質(zhì)量流量利率，這意味著為滿足制冷負荷在時間上需要較少的壓縮機。</p><

15、p>　　當分別在900或1500英鎊的指令下時，無論水或空氣冷卻的冷凝被應用，制冷劑負載要求是一個分布式制冷系統(tǒng)。當水冷式冷凝器被應用時，從水冷式冷凝器散熱，經(jīng)由乙二醇循環(huán)和流體冷卻器完成，水冷式冷凝器通常位于超市的屋頂。該乙二醇循環(huán)使用的能源消耗增加在制冷過程中，根源于泵的能源需要和由于流體循環(huán)上升導致溫度升高帶來了較高的冷凝溫度。這種能量罰款的一大部分可以消除，如果一個蒸發(fā)閉式冷卻塔是應用在一個區(qū)域，在接近該區(qū)域周圍環(huán)境的濕球

16、溫度條件下熱排斥反應可以發(fā)生。</p><p>　　2.二次循環(huán)制冷系統(tǒng)</p><p>　　圖4顯示了一所中學的制冷系統(tǒng)循環(huán)管路圖。</p><p>　　圖4，二次循環(huán)制冷系統(tǒng)</p><p>　　鹽水在陳列柜和中央制冷系統(tǒng)之間循環(huán)運行。在冷水機組中，鹽水是被冷卻介質(zhì)，然后通過陳列柜中的散發(fā)線圈，它應用于寒冷的空氣中。</p>

17、<p>　　陳列柜蒸發(fā)器專門為鹽水的使用而設計，使得鹽水和空氣之間的溫度差異降至最低，此時二次回路系統(tǒng)獲得最低能源消耗。鹽水選擇也很重要，因為泵的能源消耗對于綜合能耗而言是一個大的組成部分。鹽水的使用，比如那些鉀酸鹽，高的熱容量和低的粘度在低溫下是可取的。</p><p>　　鹽水循環(huán)的數(shù)量也會影響能源消耗。通常情況下，應使用兩個循環(huán)溫度，例如-20℉和+20℉。如果制冷負荷重要的部分可以由較高的循環(huán)

18、溫度解決，就可以得到節(jié)約能源。例如，在10℉或15℉下的制冷負荷可以在0℉的環(huán)境下取得，而不是在-20℉下取得包括這個部分的負荷。對于這里給出的分析，被認為是四個回路，分別在-20℉，10℉，20℉和30℉的環(huán)境溫度下運行。</p><p>　　中央供冷系統(tǒng)的構造相似于多重平行架，使用多個并行壓縮機來控制能力。高效率壓縮機的應用，如往復式或滾動式對于幫助抵銷有關鹽水抽水而增加的能源消費是非常必要的。由于蒸發(fā)器位于

19、冷水機組上，為二次回路系統(tǒng)的壓縮機被認為是緊耦合的蒸發(fā)器。壓力下降和回氣熱量增加在這個組態(tài)上達到最小化。這兩個因素有助于減少壓縮機的能量消耗。這些機組系統(tǒng)也配備熱鹽水除霜，其中鹽水是由過冷冷水機組制冷劑加熱。</p><p>　　通過空氣冷卻，水冷，或風冷冷凝器可以完成散熱。通過蒸發(fā)冷凝器實現(xiàn)最低冷凝溫度，這有助于降低能源消耗，特別是當冷凝溫度被設置得越低時越好。該系統(tǒng)制冷劑的耗費將會是500至700磅（空氣冷卻

20、或蒸發(fā)冷凝），或200鎊（當應用水冷卻冷凝器和流體循環(huán)時）。一般推薦分布式制冷，蒸發(fā)使用熱流體循環(huán)，以減少能源消耗。</p><p>　　3.低能耗多重制冷系統(tǒng)</p><p>　　幾種制冷系統(tǒng)制造商現(xiàn)在提供冷凝器控制系統(tǒng)，限制多重制冷機的運行所需制冷劑額定量。圖5顯示了這種控制方法的一個例子。控制閥是用于操作冷凝器的旁路，使液體線之間保持恒定，用以鑒別該系統(tǒng)的高低壓力。制冷劑液體負載僅限

21、于所需要提供的所有顯示蒸發(fā)器。接收器不需要添加額外的液體，這些已經(jīng)包含在系統(tǒng)中，主要用于抽空運行。所有的制冷劑液體，通過多種放電形式的熱交換擴大和冷凝。由此產(chǎn)生的蒸汽通過管道輸送到吸氣支管加壓并返回到冷凝器。這種控制方法的應用減少了約占系統(tǒng)制冷機所需的三分之一的電荷。</p><p>　　圖5，低能耗系統(tǒng)的管路圖</p><p>　　液體的電荷控制可以用這種方法提供一些節(jié)能潛力，因為已經(jīng)發(fā)

22、現(xiàn)當應用這種控制方法時，壓縮機可在非常低的水頭壓力下運行。這種低能耗系統(tǒng)的最低冷凝溫度值建議為40℉和60℉，分別應用于低溫和中溫制冷。</p><p>　　結果表明，風扇控制策略對于以實現(xiàn)能源儲蓄為這個特定系統(tǒng)的目的是非常關鍵的，因為消耗所有壓縮機的能量儲存以維持低水頭壓力，這對于冷凝器風機是可能的。有一項控制策略，例如變速冷凝器風機往往導致最低的風機能源消耗，同時達到預期的低水頭壓力值。</p>

23、<p>　　有這樣的例子，為進行空氣冷卻和蒸發(fā)冷凝而運行低能耗復合式制冷系統(tǒng)。這需要大大減少蒸發(fā)冷凝風機功率達到預期的低水頭壓力值（【W(wǎng)alker】1997年）。</p><p>　　4.高性能獨立制冷系統(tǒng)</p><p>　　高性能的獨立系統(tǒng)是一種低能耗制冷劑配置，其中制冷壓縮機和水冷式冷凝器位于展示柜。乙二醇循環(huán)用來抑制來自超市陳列柜外部的熱量。先前有幾個問題阻礙了這種配置

24、的實施。滾動壓縮機在一個足夠低的噪音水平下運行，這要求它們安置在銷售區(qū)域。然而直到最近，渦旋壓縮機只能夠在一個垂直的配置中，這不適合于展示柜的位置?，F(xiàn)在，可應用于上述目的的水平滾動壓縮機已經(jīng)出臺。</p><p>　　對于一種獨立系統(tǒng)的能源效率操作，壓縮機容量控制是必要的。有了一個固定的壓縮能力，獨立系統(tǒng)的冷凝溫度必須維持一個有限的范圍內(nèi)以確保其能力不會大大超過所需制冷負荷。否則，會產(chǎn)生過多的壓縮機循環(huán)，將導致外

25、殼溫度很難控制。該壓縮機允許使用的卸載冷凝溫度實際上要隨環(huán)境溫度變化，這是由于卸載會降低壓縮機的能力，并有助于同制冷負荷相匹配。</p><p>　　圖6，容量控制和壓縮機電力需求之間的關系</p><p>　　典型的渦旋壓縮機包括卸載容量控制以保持吸氣壓力的設定值。卸載是以一個持續(xù)的過程為藍本，壓縮機功率是以與電能功率改變和壓縮機卸載相關的使用標準為藍本的。圖6顯示了容量控制和壓縮機電力

26、需求之間的關系。</p><p>　　分析表明，冷凝溫度最低定于40℉和60℉，分別應用于低溫和中溫制冷。這可能切合實際也可能不切合實際，因為為了獲得兩個不同的最低冷凝溫度值，采用兩個乙二醇循環(huán)是有必要的。</p><p>　　在蒸發(fā)情況下出現(xiàn)在自我封閉系統(tǒng)的壓縮機緊密耦合的情況，降低了壓縮機吸入口處的壓降，也最大限度地減少了吸入氣體的熱量增益。這些影響都將導致更多的有效運作，并納入分析。

27、</p><p><b>　　結論</b></p><p>　　這項分析的結果表明，一家超市最大的制冷節(jié)能是通過一個采用風冷冷凝蒸發(fā)器的分布式制冷系統(tǒng)、一個蒸發(fā)式冷凝的低能耗復合式系統(tǒng)和一個同樣應用蒸發(fā)式冷凝的輔助循環(huán)三者組合而獲得的。相比于復合式基線系統(tǒng)，一個高性能的自閉系統(tǒng)具有較高的能量消耗。伴隨著乙二醇循環(huán)泵的能源需求，促成了與壓縮機卸載相關的罰款權利的增長。&

28、lt;/p><p>　　這家超市制冷系統(tǒng)表明最低TEWI是采用乙二醇循環(huán)和蒸發(fā)散熱的分布式壓縮機和二次回路系統(tǒng)。高性能的自閉系統(tǒng)證明了氣候變暖的最低直接影響，但這些損耗被由于能源使用增加而引起較高的間接影響所抵消了。</p><p>　　制冷系統(tǒng)采用乙二醇循環(huán)用以散熱，人們發(fā)現(xiàn)制冷和空調(diào)相結合，應用水源熱泵可節(jié)省當前的經(jīng)營成本。在此配置中，分布式和二次回路系統(tǒng)，相比那些具有熱回收的復合式制冷系

29、統(tǒng)，均呈現(xiàn)出明顯高的節(jié)能。</p><p>　　如果過冷裝置中采用渦旋注射，可以通過在制冷系統(tǒng)中采用渦旋式壓縮機來實現(xiàn)進一步的節(jié)能。不幸的是，由于缺乏可用的設計或者缺乏這種類型壓縮機的操作數(shù)據(jù)，在這里節(jié)能可不能進行量化。</p><p>　　由于低能耗制冷系統(tǒng)有能源和成本的節(jié)約潛力，在本次調(diào)查美國能源部已加大努力，包括對分散式制冷系統(tǒng)采用乙二醇循環(huán)和暖通空調(diào)采用WSHP循環(huán)的現(xiàn)場測試?，F(xiàn)在

30、這套特殊的系統(tǒng)已經(jīng)安裝在伍斯特市，馬薩諸塞州郊區(qū)的一家運營超市。這家超市被設置成為了制冷和熱泵系統(tǒng)收集能源和運營數(shù)據(jù)。在同一時間，附近的第二家分店也設置了分布式存儲系統(tǒng)。第二個存儲系統(tǒng)采用了最先進的設備，使用復合式制冷系統(tǒng)和傳統(tǒng)的天臺暖通空調(diào)。這兩個網(wǎng)點目前正在監(jiān)測中。</p><p>　　此外，在洛杉磯、加利福尼亞州區(qū)域，美國加州能源委員會的第二場測試已經(jīng)開始，它將包括一個二次循環(huán)制冷系統(tǒng)的設計和現(xiàn)場測試。試驗

31、從美國能源部低冷媒系統(tǒng)這一領域的現(xiàn)場測試取得一些示范補充。</p><p><b>　　致謝</b></p><p>　　筆者要感謝由美國能源部的Esher Kweller博士提供的指引和支持。根據(jù)UT-Battelle有限責任公司的DE - AC05-00OR22725合同，這項工作由美國能源部辦事處，建筑技術辦公室和國家及社區(qū)署聯(lián)合主辦。</p>&

32、lt;p>　　本文摘譯自ASHRAE STD CH -03 -1-1 -2003。</p><p><b>　　參考文獻</b></p><p>　　[1]Sand, J.R., S.K. Fisher,和 V.D. Baxter，1997?！蛾P于HFC制冷劑和新興技術的能源和全球變暖的影響》——橡樹嶺，田納西州的橡樹嶺國家實驗室，由美國能源部和AFEAS贊助。

33、</p><p>　　[2]Walker,D.H.2000。《超市低能耗制冷》——斯塔德，荷蘭的國際能源署熱泵中心通訊18卷第1期。</p><p>　　[3]Walker,D.H.1997?！蛾P于北方氣候的蒸發(fā)冷凝器的發(fā)展》。由尼亞加拉鼓風機公司，紐約州能源研究和發(fā)展管理局（NYSERDA）和總部位于馬薩諸塞州，沃爾瑟姆的福斯特-米勒公司準備。</p><p>　

34、　[4]Walker,DavidH.2001?！兑豁椄咝阅艿牡某兄评?空調(diào)系統(tǒng)的開發(fā)與示范》——最后分析報告，橡樹嶺國家實驗室分包合同編號62X-SX363C，馬薩諸塞州沃爾瑟姆，福斯特-米勒公司合同編號02451。</p><p>　　Analysis of Advanced, Low-Charge Refrigeration for Supermarkets</p><p>　　Da

35、vid H. Walker, Ph.D. Member ASHRAE</p><p>　　Van D. Baxter, Ph.D. Member ASHRAE</p><p><b>　　ABSTRACT</b></p><p>　　Present supermarket refrigeration systems require very l

36、arge refrigerant charges for their operation and can consume as much 1 to 1.5 million kWh annually. Several new approaches, such as distributed, secondary loop, and advanced self-contained refrigeration systems, are avai

37、lable that utilize significantly less refrigerant and with correspondingly lower refrigerant losses through leakage. New condenser controls have also been developed for multiplex refrigeration systems that allow operatio

38、n wi</p><p>　　KeyWords: Distributed; Secondary loop; Advanced self-contained</p><p>　　INTRODUCTION</p><p>　　Supermarkets are the largest users of energy in the commercial sector. A

39、typical supermarket with approximately 40,000 ft2 of sales area consumes on the order of 2 million kWh annually for total store energy use. Many larger superstores and supercenters also exist that can consume as much as

40、3 to 5 million kWh/yr.</p><p>　　One of the largest uses of energy in supermarkets is for refrigeration. Most of the product sold is perishable and must be kept refrigerated during display and for storage. Ty

41、pical energy consumption for supermarket refrigeration is on the order of half of the store’s total. Compressors and condensers account for 30% to 35% of total store energy consumption. The remainder is consumed by the d

42、isplay and storage cooler fans, display case lighting, and for anti-sweat heaters used to prevent condens</p><p>　　Figure 1 shows the typical layout of the refrigerated display cases in a supermarket. All re

43、frigerated fixtures in a supermarket employ direct expansion air-refrigerant coils. To reduce noise and control heat rejection, compressors and condensers are kept in a remote machine room located in the back or on the r

44、oof of the store. Piping is provided to supply and return refrigerant to the case fixtures. </p><p>　　Figure 1 Layout of a typical supermarket.</p><p>　　Figure 2 shows the major elements of a mu

45、ltiplex refrigeration system, which is the most commonly used configuration in supermarkets. Multiple compressors operating at the same saturated suction temperature are mounted on a skid, or rack, and are piped with com

46、mon suction and discharge refrigeration lines. The use of multiple compressors in parallel provides a means of capacity control, since the compressors can be selected and cycled as needed to meet the refrigeration load.

47、An air-cooled conde</p><p>　　As a result of using this layout, the amount of refrigerant needed to charge a supermarket refrigeration system is very large. A typical store will require 3,000 to 5,000 lb of r

48、efrigerant. The large amount of piping and pipe joints used in supermarket refrigeration also causes increased leakage, which can amount to a loss of 30% to 50% of the total charge annually (Walker 2001).</p><

49、p>　　Figure 2 Multiplex refrigeration system.</p><p>　　With increased concern about the impact of refrigerant leakage on global warming, new supermarket refrigeration system configurations requiring signif

50、icantly less refrigerant charge are being considered. Examples of low-charge refrigeration systems include distributed, secondary loop, and advanced self-contained configurations. Modifications have also been made to mul

51、tiplex refrigeration systems to reduce the amount of charge needed for their operation. Little is known about the operating or ene</p><p>　　For these reasons, the U.S. Department of Energy initiated an engin

52、eering investigation of low-charge supermarket refrigeration. The initial work on this investigation involved analysis of distributed and secondary loop refrigeration systems and gave an energy and TEWI comparison with m

53、ultiplex. The results obtained for this analysis were presented in Walker (2000). Work has continued on this investigation including a field test involving two supermarkets with one equipped with distributed and t</p&

54、gt;<p>　　This paper presents all analytical results obtained to this point. Previous results are included for completeness.</p><p>　　1. DISTRIBUTED REFRIGERATION</p><p>　　Figure 3 is a di

55、agram showing the major components of a distributed refrigeration system.</p><p>　　Figure 3 Distributed refrigeration system.</p><p>　　Multiple compressors are located in cabinets placed on or n

56、ear the sales floor. The cabinets are close-coupled to the display cases and heat rejection from the cabinets is accomplished through the use of either air-cooled condensers located on the roof above the cabinets or by a

57、 glycol loop that connects the cabinets to a fluid cooler. </p><p>　　The distributed refrigeration system employs scroll compressors because of the very low noise and vibration levels encountered with this t

58、ype of compressor. These characteristics are necessary if the compressor cabinets are located in or near the sales area. The scroll compressors have no valves and, in general, do not have as high an efficiency as recipro

59、cating units. The no-valve feature of the scroll compressors allows them to operate at a significantly lower condensing temperature. The lowes</p><p>　　Scroll compressors also have the potential of providing

60、 subcooling through mid-scroll injection of refrigerant vapor. This particular method has not yet been optimized by the compressor manufacturers and was not included as part of this analysis. </p><p>　　The c

61、lose-coupling of the display cases to the distributed refrigeration cabinets has other ramifications to energy consumption. The shorter suction lines mean that the pressure drop between the case evaporator and the compre

62、ssor suction manifold is less than that seen with multiplex systems, which means that the saturated suction temperature (SST) of the cabinet will be close to the display case evaporator temperature. The shorter suction l

63、ines also mean that less heat gain to the return gas is</p><p>　　The refrigerant charge required for a distributed refrigeration system will be on the order of 900 or 1500 lb when either water- or air-cooled

64、 condensing is employed, respectively. When water-cooled condensers are employed, heat rejection from the water-cooled condensers is done by a glycol loop and a fluid cooler, usually located on the roof of the supermarke

65、t. The use of the glycol loop increases the energy consumption of the refrigeration process due to the pump energy needed and higher conde</p><p>　　2. SECONDARY LOOP REFRIGERATION</p><p>　　Figur

66、e 4 shows a piping diagram of a secondary loop refrigeration system.</p><p>　　Brine loops are run between the display cases and central chiller systems. The brine is refrigerated at the chiller and is then c

67、irculated through coils in the display cases where it is used to chill the air in the case. </p><p>　　Figure 4 Secondary loop refrigeration system.</p><p>　　Lowest energy consumption for seconda

68、ry loop systems is achieved when the display case evaporators are designed specifically for the use of brine, so that the temperature difference between the brine and air is minimized. Brine selection is also of importan

69、ce, because energy consumption for pumping is a large component of overall energy consumption. The use of brines, such as those employing potassium formate, with high heat capacity and low viscosity at low temperature is

70、 desirable. </p><p>　　The number of brine loops employed can also impact energy consumption. Typically, two loop temperatures are used, such as –20°F and +20°F. If significant portions of the refri

71、geration load can be addressed by higher temperature loops, energy savings can be obtained. For example, refrigeration loads at 10°F or 15°F could be addressed by a loop at 0°F, rather than including this

72、portion of the load with the –20°F. For the analysis given here, four loops are considered, operating at temperatures of</p><p>　　Central chiller systems are constructed similarly to the multiplex paral

73、lel racks, using multiple parallel compressors for capacity control. The use of high-efficiency compressors, such as reciprocating or scroll units is highly desirable to help offset some of the added energy consumption a

74、ssociated with brine pumping. Because of the location of the evaporator on the chiller skid, the compressors for the secondary loop system are considered close-coupled to the evaporator. The pressure drop and</p>

75、<p>　　Heat rejection can be accomplished with air-cooled, water-cooled, or evaporatively cooled condensers. Lowest condensing temperatures are achieved with evaporative condensers, which help reduce energy consumpti

76、on, particularly when the minimum condensing temperature is set as low as possible. The system refrigerant charge will be on the order of 500 to 700 lb with either air-cooled or evaporative condensers and 200 lb when wat

77、er-cooled condensers and a fluid loop are used. Like distributed refrig</p><p>　　3. LOW-CHARGE MULTIPLEX REFRIGERATION</p><p>　　Several refrigeration system manufacturers now offer control syste

78、ms for condensers that limit the amount of refrigerant charge needed for the operation of multiplex refrigeration. Figure 5 shows an example of such a control approach. A control valve is used to operate a bypass from th

79、e condenser liquid line in order to maintain a constant differential between the high and low pressures of the system. The refrigerant liquid charge is limited to that needed to supply all display case evaporators.</p

80、><p>　　The control of the liquid charge by this method offers some energy-saving potential because it has been found that compressors can be operated at very low head pressures when this control method is emplo

81、yed. The minimum condensing temperature values suggested for this low-charge system are 40°F and 60°F for low- and medium-temperature refrigeration, respectively. </p><p>　　Figure 5 Piping diagram

82、for the low-charge multiplex system.</p><p>　　It was found that the fan control strategy is very significant to the energy savings achieved for this particular system, since it is possible for the condenser

83、fans to consume all compressor energy saved in order to maintain the low head pressure. A control strategy such as variable-speed condenser fans tends to result in the lowest fan energy consumption while achieving the de

84、sired low head pressure values. </p><p>　　Modeling of low-charge multiplex refrigeration was performed for both air-cooled and evaporative condensing. Evaporative condensing requires significantly less fan p

85、ower to achieve the desired low head pressure values (Walker 1997). </p><p>　　4. ADVANCED SELF-CONTAINED REFRIGERATION</p><p>　　An advanced self-contained system is a low refrigerant charge con

86、figuration in which the refrigeration compressors and water-cooled condensers are located in the display cases. A glycol loop is used to reject heat from the display cases to the exterior of the store. Several problems h

87、ad prevented the implementation of this configuration previously. Scroll compressors operate at a low enough noise level to allow their placement in the sales area. Until recently, scroll compressors were available </

88、p><p>　　For energy-efficient operation of a self-contained system, capacity control of the compressor is needed. With a fixed compressor capacity, the condensing temperature of the selfcontained system must be

89、maintained within a limited range to ensure that the capacity does not greatly exceed the required refrigeration load. Otherwise, excessive compressor cycling will occur, making it difficult to control case temperature.

90、The use of compressor unloading allows the condensing temperature to vary with</p><p>　　Modeling of the scroll compressor included unloading for capacity control in order to maintain the suction pressure set

91、point. The unloading is modeled as a continuous process, and the compressor power is modeled using the standard relationship for power change with compressor unloading. Figure 6 shows the relation between capacity contro

92、l and compressor power required. </p><p>　　Figure 6 Relation between capacity and power used for modeling unloading scroll compressors.</p><p>　　For analysis the minimum condensing temperature w

93、as set at 40°F and 60°F for low- and medium-temperature refrigeration, respectively. This may or may not be practical, since two glycol loops are needed in order to have two different minimum condensing tempera

94、ture values. </p><p>　　The close coupling of the compressor to the case evaporator seen in self-contained systems reduces the pressure drop at the compressor suction and also minimizes the heat gain to the s

95、uction gas. Both of these effects will result in more efficient operation and were included in the analysis. </p><p>　　CONCLUSIONS</p><p>　　The results of this analysis showed that the greatest

96、 refrigeration energy savings for a supermarket application were achieved by a distributed refrigeration system with air-cooled condensing, a low-charge multiplex system with evaporative condensing, and a secondary loop

97、also with evaporative condensing. An advanced self-contained system approach showed higher energy consumption than the baseline multiplex system. The power penalty associated with compressor unloading along with energy r

98、equired</p><p>　　The supermarket refrigeration systems showing lowest TEWI were the distributed compressor and secondary loop systems employing the glycol loop and evaporative heat rejection. The lowest dire

99、ct warming impact was demonstrated by the advanced self-contained system, but these reductions were offset by the higher indirect impact due to increased energy use. </p><p>　　The use of water-source heat pu

100、mps with refrigeration systems employing glycol loops for heat rejection was found to produce operating cost savings due to combined savings for refrigeration and HVAC. Distributed and secondary loop systems in this conf