為因應國內外對臭氧層保護及重視永續能源策略之趨勢，冷凍系統在設計上採用環保冷媒並儘可能的提高空調機組之性能已然勢在必行。在各種被接受的HFC新冷媒中，冷媒R-134a屬純冷媒且工作壓力較低(與R-22系統相比較)因而被廣為接受應用，目前各設備廠家大型空調機組（包含離心式與螺旋式）的開發設計大都是以R-134a冷媒機種為主要對象。

　　透過理想冷凍循環分析得知，R-134a冷媒系統採用雙段壓縮設計時之能源效率較單段壓縮約高10~15%左右。因此吾人可利用兩段壓縮技術進行系統之性能改善，不過在單機兩段壓縮系統中，中壓段冷媒閃氣分離狀態、節流系統設計之優劣及冷媒質量流率的控制都明顯地影響整個系統性能及效率。本論文建立雙段壓縮系統之模擬程式，並

　　進行實機測試，利用實驗量測數據來驗證系統模擬程式之可靠度，再利用已驗證之程式作系統計算，來預測系統經改造後之結果。
經本研究所實際開發以R-134a為冷媒的兩段壓縮螺旋主機之系統，機構簡單，製造成本低廉，而性能則較同條件單段壓縮約可提高6%，達到了兼顧經濟環保與耗能節省的雙重目的。

　　In order to comply with ozone-lager protection policy and the concern of energy sustaiuability, a new refrigeration system is usually designed to use HFC (hydrofloro carbon) refrigerant and posses a high energy efficiency rate (EER). Among a few HFC refrigerants, R-134a has a relatively low working pressure range (compare to the system using R-22) and has thus been accepted as the refrigerant for many large chillers (including centrifugal chillers and screw chillers).

　　From the thermodynamic cycle analysis for the refrigeration system using R-134a, a two-stage compression process may consume 10~15% less energy then that used by a single-stage compression under the same pressure range. An exiting screw type chiller is actually converted from the two-stage compression by adding a pressure reducing orifice and a flash tank. Since the flow rate and the intermediate pressure are closely related to the detailed designs of both orifice and flsh tank. Therefor a computer code is also developed and validated in this study to assist in the design and analysis processes.

　　The conversion from a single-stage compression to a two-stage compression was sucessfully completed at minimum alternation and relatively low cost, and about 6% improvement in performance was realized. From the environmental protection and energy conservation point of views, this conversion project is simple and meaningful.

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