低GWP冷媒應用於高溫熱泵之設計與分析

Abstract

本研究主要為開發一利用電力驅動而產生高溫蒸汽的系統，以取代傳統鍋爐，系統架構主要包含低溫熱泵系統、高溫熱泵系統以及機械式蒸汽再壓縮系統。低溫熱泵可採用一般熱泵或使用廢熱進行替代，而高溫熱泵則自低溫熱泵取得熱量後，進而產生80 ~ 90°C的熱水，再經由閃蒸桶與MVR系統進行再壓縮，產生高溫之蒸汽。除此之外，亦探討低GWP冷媒在高溫熱泵中的應用及可行性，透過系統性能的分析與設計，解決現有技術應用中面臨的挑戰，從而推動高溫熱泵技術的綠色發展。 高溫熱泵系統配置對於其性能有相當之影響力，若使用單級系統，亦造成壓縮機壓縮比過大而功耗上升，因而降低COP，因此本研究除了進行單級系統的分析外，亦比較雙級與級聯系統性能，結果顯示使用雙級與級聯的配置可明顯提升COP，在較低熱源溫度下COP都可達到3以上，而HFO-1234ze(Z)、HCFO-1224yd(Z)、HCFO-1233zd(E)、HC-601、HC-601a及HFO-1336mzz(Z)更是相比HFC-245fa有所提升，而在蒸發溫度35°C時，雙級系統使用HC-601的COP可達4.64、級聯系統使用HC-601也可達4.35。在本研究中，同時探討評估熱泵的重要指標參數-體積加熱能力(VHC)，此參數對於選用壓縮機有著直接關聯性，而結果指出，雖然HC-601、HC-601a與HFO-1336mzz(Z)在性能上有優異的表現，但其VHC過小為致命缺點，這會導致選用壓縮機尺寸過大，亦同時造成成本提升，建置意願降低，因此在評估性能時，同時也需兼顧VHC，以達到雙贏的局面。 另外，若利用冷凝器出口作廢熱回收，利用廢熱進行補給水的預熱，可提升整體COP，在單級系統中，平均可提升4.0%，若在雙級系統平均可提升3.0%，在級聯系統平均可提升1.7%，而若將過冷度提高，整體COP提升幅度會增加更多。

This study primarily focuses on developing a system that generates high-temperature steam using electric power to replace traditional boilers. The system architecture mainly includes a low-temperature heat pump system, a high-temperature heat pump system, and a mechanical vapor recompression (MVR) system. The low-temperature heat pump can use either a conventional heat pump or utilize waste heat as a substitute, while the high-temperature heat pump obtains heat from the low-temperature heat pump to produce hot water at 80-90°C. This hot water is then compressed again through a flash tank and the MVR system to produce high-temperature steam. In addition, the study explores the application and feasibility of low-GWP (Global Warming Potential) refrigerants in high-temperature heat pumps. Through the analysis and design of system performance, the study addresses challenges in the application of current technologies, thereby promoting the green development of high-temperature heat pump technology. The configuration of the high-temperature heat pump system significantly impacts its performance. If a single-stage system is used, it results in an excessive compression ratio for the compressor, which increases power consumption and reduces the Coefficient of Performance (COP). Therefore, this study not only analyzes the single-stage system but also compares the performance of two-stage and cascade systems. The results show that using two-stage and cascade configurations can significantly improve the COP, achieving a COP of over 3 even at lower heat source temperatures. Furthermore, refrigerants such as HFO-1234ze(Z), HCFO-1224yd(Z), HCFO-1233zd(E), HC-601, HC-601a, and HFO-1336mzz(Z) perform better compared to HFC-245fa. At an evaporation temperature of 35°C, the two stage system using HC-601 achieves a COP of 4.64, and the cascade system using HC-601 also achieves a COP of 4.35. This study also evaluates an important performance indicator for heat pumps: Volumetric Heating Capacity (VHC). This parameter is directly related to the selection of the compressor. The results indicate that although HC-601, HC-601a, and HFO-1336mzz(Z) exhibit excellent performance, their low VHC is a critical drawback, leading to the selection of larger compressor sizes, which in turn increases costs and reduces the willingness to implement the system. Therefore, when evaluating performance, it is necessary to consider VHC to achieve a win-win scenario. Furthermore, if waste heat recovery is employed at the condenser outlet to preheat the feed-water using waste heat, the overall COP can be improved. In a single-stage system, this can result in an average improvement of 4.0%. In a two-stage system, the average improvement can be 3.0%, while in a cascade system, it can be 1.7%. Moreover, if the subcooling degree is increased, the overall improvement in COP will be even greater.