冷卻水塔濕氣回流率影響參數及節能控制策略之研究

Parametric Study of Wet Air Return Ratio and Energy Saving Control Strategy for Cooling Tower

劉家瑋(Chia-Wei Liu)

指導教授 ： 蔡尤溪

國立臺北科技大學/機電學院/機電科技研究所/博士(2011年)

摘要

本文以解析、模擬及部分量測方式，針對冷卻水塔濕氣回流率影響參數及節能控制策略作深入之研究探討。本文分為四大研究主題，即：(1)冷卻水溫節能控制研究、(2)冷卻水流量節能控制研究、(3)冷卻水塔設計容量耦合研究、(4)冷卻水塔排之濕氣回流率影響參數研究。
本文制訂系統性能因子(SPF)，在冷卻水溫節能控制研究部分，本研究發展最佳冷卻水溫(OCT)運算搜尋計畫維持主機與水塔系統於最大SPF下運作，以數學迴歸方程式制訂OCT控制策略，進行多項控制參數解析，如：外氣濕球溫度、主機負載率及冷卻水塔因子等，結果發現OCT控制策略在相同建築案例下，相較於基本冷卻水溫控制方式，台灣台北地區可達4.35∼5.74％節能，高雄地區可達3.46∼4.2％節能，以外氣濕球溫度變化較廣之氣候區，特別適用於OCT控制策略。
在冷卻水流量節能控制研究部分，本研究發展最佳冷卻水流量(OFR)運算搜尋計畫，維持整體冷卻水系統於最大SPF下運作，亦以數學迴歸方程式制訂OFR控制策略，基於OFR控制策略下，增加水泵因子為控制參數，結果發現OFR控制策略較OCT在台灣台北地區多出1.13∼9.71％節能，台灣高雄地區部分達0.59∼4.03％節能，OFR雖優於OCT控制策略，但應用時必須詳加注意冰水主機在變冷卻水流量下之耗能特性。
另本文特別探討過去尚未有文獻所注意之冷卻水塔設計容量耦合問題，在水塔容量增大下，OCT及OFR控制策略皆可再提升其節能效果，以台灣台北地區為例，以OCT控制策略及原水塔設計容量作為比較基準，OCT在1.1∼1.6倍水塔容量下之節能幅度為0.59∼2.67％、OFR為5.3∼7.08％，回收年限OCT在8∼10.7年間，OFR則在0.9∼4年間，然水塔容量不可貿然無限增大，因節能率受限於水塔最終效率、及最低冷卻水量與水溫限制，而提高回收年限。
最後在冷卻水塔排之濕氣回流率影響參數研究部分，特別分析過去尚未有文獻所注意之平行塔排列，考慮全年負載及氣候變化，針對塔排長度與間距，及水塔排風性質及外界風速作相互影響參數分析，以各影響參數建立兩種風向(垂直及平行於塔排)下之總平均濕氣回流率影響迴歸方程式。同時本研究也發展以濕氣回流率計算等效濕球度之評估模式，可計算出濕氣回流率對於系統之耗能影響幅度。本研究之結果可作為未來水塔設計與設置時參考，並提供增進系統節能之新思維。

關鍵字

冷卻水塔 ； 冰水主機 ； 冷卻水溫控制 ； 冷卻水流量控制 ； 濕球溫度 ； 濕氣回流

並列摘要

Parameters of wet air return and energy saving control strategies for cooling towers are analyzed by theoretical modeling and partly field measurements. There are four major topics in this thesis, namely, the energy saving control of condensing water temperature, the condensing water flow rate control, the capacity coupling of cooling towers, and the parameters that affect the wet air return.
A system performance factor (SPF) is used in the study of condensing water temperature control. A computation scheme is developed to seek the optimum condensing water temperature (OCT) so to maintain the maximum SPF for the chillers and the cooling towers as a system. A mathematical regression for the control of OCT is presented that include multi-control parameters such as outdoor wet bulb, chiller load ratio, cooling tower factors, etc. It was found that for a typical building case with a baseline condensing water temperature control, the OCT control strategy would give the energy saving rate of 4.35∼5.74％ for Taipei, and 3.46∼4.2％ for kaohsiung. This control strategy is applicable to regions with wide variation of annual wet bulb temperature.
For the control of condensing water flow rate, an optimal flow rate (OFR) scheme is presented that to achieve the maximum SPF for the condensing water system. A regression function is presented for the OFR control strategy. However as water pump control is added in the control, additional energy saving of 1.13∼9.71％ is possible for Taipei, and 0.59∼4.03％ for Kaohsiung. For OFR control, the effects to the chiller efficiency have to be taken into consideration.
A subject often neglected in the research literature is the capacity coupling of cooling towers, relative to the chiller capacity. For the system as a whole, the increase in the cooling tower capacity would further increase the system performance either for OCT and OFR controls. For Taipei and the OCT control as compared to the base case, 1.1∼1.6 times of cooling tower capacity would further allow energy saving of 0.59∼2.67％. For OFR the further energy saving is 5.3∼7.08％. The payback return is calculated and for OCT is between 8∼10.7 years. However for OFR the payback is between 0.9∼4 years. There is a limit to the capacity coupling due to cooling tower efficiency and the minimum flow rate and temperature requirement for the condensing water. Otherwise the payback years would be longer.
Lastly the influencing parameters for the wet air return to the cooling towers are studied. It is a subject of practical importance but not found in the literature. Parellel arrangement of two banks of cooling towers is used in the studied. This study considers the annual tower load, weather variation, the length of tower bank, the spacing of the two banks of towers, and the flow characteristics of towers. The interactions of these factors are also considered. Two ambient wind directions, parallel and normal to the tower banks, are also considered in the analysis of total wet air return ratio. This study also considers the effects of wet air return on the system performance of the cooling towers and the chillers. A regression function is presented to predict the wet air return ratio. The research results of this study can be used in the design and installation of cooling towers, in order to increase the operating energy efficiency.

並列關鍵字

Cooling tower ； Water chiller ； condensing water temperature control ； condensing water flow rate control ； Wet bulb temperature ； Wet air return

參考文獻

[43]柏斯成，冷卻水塔氣流模擬之實例分析，碩士論文，國立臺北科技大學能源與冷凍空調工程系碩士班，台北，2010。

[45]王啟川，「冷卻水塔的熱流設計」，冷凍與空調雜誌，2001年10月，第53-63頁。

[54]陳東煒，應用於預測變冰水量冰水機耗能經驗模式適用性之研究，碩士論文，國立臺北科技大學能源與冷凍空調工程系碩士班，台北，2006。

[58]許庭嘉，空調負荷計算輻射時間序列計算法(RTS)程式開發及降低空調負荷研究，碩士論文，國立臺北科技大學能源與冷凍空調工程系碩士班，台北，2009。

[2]陳森煌，以現場實用測量結果作冰水主機部分負載性能分析，碩士論文，國立臺北科技大學能源與冷凍空調工程系碩士班，台北，2001。