應用壓力差於中央空調系統流量判讀之探討

中央空調的冰水與冷卻水流量控制，對系統的節能操作策略有直接而密切的關聯。然而流量計的安裝並不容易，大多數需配合水管工程的施作，預先以焊接或牙接的方式安裝於管路內部，不當的安裝將會讓流量的判讀產生誤差，安裝後如需更改位置將極為不便。另一方面，流量計的器具費用偏高，簡略的流量計需數千元，精密型的超音波流量計至少需數萬元，對於需求量較大的建築空調系統，偏高的器具費用將對建置成本形成負擔。本研究主要目的在於應用迴歸分析法，透過實驗數據建模完成流量與壓力差之間的關係，並將此種關係具體應用於空調水系統流量判讀，以建立一種成本更低、資訊取得更便利的流量判讀替代方案。實驗方式是以一小型的空調系統，在冰水主機冷凝器側、空調箱及泵浦的進出口端，分別安裝壓力傳送器與蹼輪式流量計，並記錄泵浦、空調箱、冷凝器等設備在單一泵浦運轉、多台泵浦並聯運轉、多台泵浦變頻運轉等不同使用狀況下之數值，以實際運轉數據進行壓力差與流量關係的建模並分析結果。從實驗結果可知，空調箱與冷凝器端所獲得的建模程式，在單一泵浦運轉、多台泵浦並聯運轉與多台泵浦變頻運轉時，皆能適用，所獲得的壓力差用以判讀流量有極高的準確度，誤差值在2%以內。泵浦設備因為管路阻抗效應的因素，並聯運轉與單一泵浦運轉時不會有相同的建模程式，但以變頻方式分別建模後的壓力差來判讀流量，亦有極高的準確度。根據本實驗的研究成果，可大幅提升流量判讀的便利性，有利空調節能策略擬定與增進水系統平衡調整的便利性，在經濟成效上，則可降低建造成本，讓節能工程達到更佳的成效。

關鍵字

壓力差；流量；流量計；迴歸分析

並列摘要

The chilled water and cooling water flow rate control for the Central Air Conditioning System is directly and mutually related to the energy conservation operating strategies of the System. In spite of this, the installation of the Flow Meter is not an easy task, as most of them would require the coordination of the plumbing work for mounting inside the pipeline by welding or threading method. Improper installation would result in errors when determining the flow rate, and it would not be very convenient to modify the position after being installed. In addition, higher expenses are also required for the components of Flow Meter, which may roughly require several thousand dollars for the Flow Meter and it may even run up to several thousand dollars if adopting precision-type Ultrasonic Flow Meter. As such, higher facility costs would become a burden to the implementation cost for the building’s A/C System enjoying bigger demand. In this Research, the Regression Analysis Method is selected to verify the relationship between flow rate and differential pressure through the experimental figures. Such relationship will then be applied in determining the flow rate of A/C water system for establishing a flow rate determining alternative which is much lower in cost and more convenient in information acquisition. The experiment was conducted with a Mini-sized A/C System for which, the Pressure Transmitter and the Paddle Wheel Flow Meter are mounted next to the Condenser of the Chiller as well as at the inlet/outlet ends of the A/C Case and the Pump respectively. In the meantime, a record is also maintained for the values when the pump, A/C Case and Condenser are operated under varied servicing conditions such as single pump operation, multi-pump tie-up operation and multi-pump varied-frequency operation, etc. Consequentially, actual figures are based to develop the model for investigating the relationship between differential pressure and flow rate and for analyzing the result. The experiment result indicated that the model program obtained from the A/C Case and Condenser ends can be applied to the single pump operation, multi-pump tie-up operation and multi-pump varied-frequency operation and that pretty high accuracy can also be achieved when determining the flow rate with the resulted differential pressure while maintaining error within 2%. As fixed curve relationship exists between the flow rate and the pressure dropping, the property curve of the pump will change as long as the flow rate fluctuates. On this basis, the model developing programs will differ between the tie-up operation and single pump operation; however both have exhibited pretty high accuracy when determining the flow rate with the differential pressure after developing the model for the Balance Valve. According to the research result of the experiment, it will significantly enhance the convenience of determining the flow rate, facilitate the preparation of A/C energy conservation strategies, and improve the convenience of water system balance adjustment. On the cost-efficiency aspect, it can also reduce the construction cost to achieve a much better effect for the energy conservation project.