太陽能輔助噴射式製冷系統性能最佳化研究

Optimum Performance Study for Solar-Assisted Ejector Cooling System

吳承駿(Chen-Chun Wu)

指導教授 ： 黃秉鈞

國立臺灣大學/工學院/機械工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.02962

摘要

傳統的噴射式製冷系統在熱源不穩定時會喪失製冷能力而無法符合商品化的需求。為提供穩定的空調製冷能力，往往會以加裝電熱器方式彌補熱能的不足，因而導致成本提高並喪失熱驅動製冷系統以太陽能驅動的優點。
本研究的太陽能輔助噴射式製冷系統，整合太陽能集熱系統、噴射式製冷系統與變頻空調系統。變頻空調獨立運轉可使系統穩定提供空調冷能，並以串聯方式連結噴射式製冷系統與變頻空調系統冷凝器，在太陽能的輔助下驅動噴射式製冷系統降低變頻空調系統冷凝溫度，提升空調性能並減少耗電達到節能的目的。
太陽能是個不穩定的熱源，因此產生器的液位控制系統必須要具備有隨時反應太陽輻射量變化的能力來維持固定的產生器液位高度，才能使噴射式製冷系統穩定的運轉，實驗結果顯示在輻射量劇烈變化下噴射式製冷系統的產生器液位仍可維持設定液位高度12cm的±3%之間。
太陽輻射量的變化也會造成產生器溫度的改變，容易造成噴射式製冷系統操作於偏離原設計點導致噴射器失效無法維持製冷效果。本研究根據前人的研究結果加以改良，建立一膨脹閥回饋系統，並以實驗的方式證明可以在不穩定的太陽能熱源中維持噴射式製冷系統正常運轉。
太陽能輔助噴射式製冷系統的週邊設備耗電相當大，本研究在維持噴射式製冷系統正常運轉的前提下，針對耗電量較大的太陽能集熱系統循環泵浦與水簾片冷卻水塔風扇進行節能控制，實驗結果證明太陽能集熱循環泵浦在輻射量大且穩定的情況下與全速運轉時的泵浦相比可降低70%的耗電量、水簾片冷卻水塔風扇與全速運轉的風扇相比可降低75~80%的耗電量。
本研究建立一套中央監控系統可量測噴射式製冷系統與變頻空調系統運轉時的溫度、壓力、冷媒質量流率及耗電量。由實驗結果分析變頻空調單獨運轉時性能係數(COP)在2.94~3.24之間，當噴射式製冷系統開啟後太陽能輔助噴射式製冷系統的性能係數則在3.93~4.32之間， 提升24.3~42.4%。噴射式製冷系統的運轉性能係數在0.22~0.32之間，遠低於一維模擬出來的噴射器性能預測。藉由過冷卻度與過冷卻所增加的冷媒質量流率之間的關係來分析探討串聯型噴射式製冷系統與變頻空調的熱負載匹配。分析結果顯示以本研究的噴射式製冷系統為基準，在高溫的環境中(如沙漠)變頻空調冷凝溫度為50℃以上，其冷媒質量流率要在0.045kg/s以上(相當於2冷凍噸以上的變頻空調機全速運轉時的冷媒質量流率)；若以台灣的氣候條件變頻空調冷凝溫度約為40℃左右，則其冷媒質量流率要在0.07kg/s以上(相當於3冷凍噸以上的變頻空調機全速運轉時的冷媒質量流率)。

關鍵字

太陽能 ； 噴射器 ； 噴射式製冷系統 ； 太陽能製冷

並列摘要

In order to provide steady cooling effect, conventional ejector cooling system use auxiliary heater to make up for insufficient thermal energy while thermal energy is unstable and therefore result in the rise of cost in installation.
Solar-assisted ejector cooling system (SACH-k2) combines solar heating system, ejector cooling system (ECS) and inverter-type air-conditioner (IAC) and is developed in the present study. In SACH-k2, IAC independently operates to provide steady cooling effect for the cooling room. ECS is connected with IAC’s condenser in series type and the cooling effect of ECS generated by solar heat is used to reduce the condensing temperature of the IAC, then increase IAC’s COP and reduce the power consumption of the compressor.
To utilize solar energy in ECS, the generator level control system should maintain a fixed liquid level during variation solar irradiation so that ECS could operate stably. Experiment result shows ECS is controlled between 11.6cm to 12.4cm for the level setting 12cm, representing ±3% error.
Solar irradiation changes abruptly could lead to fluctuation of generator temperature. Therefore ECS operation deviates from the design point and failed to maintain the cooling effect. In SACH-k2, ECS expansion valve feedback control system has been developed and proves it could maintain the cooling effect of ECS during variable solar energy.
The power consumption of peripheral device in SACH-k2 is too high to commercialization. This study reduces the power consumption of solar collector pump and cooling tower fan which accounts for the most of power in peripheral device under the premise that ejector cooling system operates stably. The experiment result shows that solar collector pump could save 70% pumping power under high and stable irradiation compared to full speed running pump; cooling tower fan could save 75%~80% power consumption compared to full speed running fan.
This study builds up a central control system measure the temperature, pressure, refrigerant flow rate and power consumption of ECS and IAC. According to the analysis of experiment results, the performance coefficient (COP) when IAC operates alone is between 2.94~3.24 and the COP is 3.93~4.32 raised 24.3~42.4% after ECS combines with IAC. The performance coefficient of ECS (COPECS) is between 0.22~0.32 which is far low than one-dimensional simulation in ejector performance predicted. Therefore, this study analyzes the effect of overcooling and increasing refrigerant flow rate due to overcooling in IAC for studying the heat load matching between ECS and IAC. The analysis result shows that the best match between ejector and IAC based on the ejector in this study requires over 0.045kg/s (equivalent 2RT IAC running at full speed) refrigerant flow rate in high temperature surrounding (IAC condenser temperature over 50℃) such as desert and requires over 0.07kg/s (equivalent 3RT IAC running at full speed) refrigerant flow rate in medium temperature surrounding (IAC condenser temperature over 40℃) such as Taiwan’s climate.

並列關鍵字

Solar energy ； Ejector ； Ejector cooling system ； Solar cooling

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