Energy conservation improvement and ON–OFF switch times reduction for an existing VFD-fan-based cooling tower. (15th September 2015) - Chang, Chun-Cheng
Highlights: Achieve energy saving and reduce the ON/OFF switching frequency at the same time. Propose a PI feedback controller with a temperature zone setting. Implement hybrid operations of rule-based and equation-based feedback control. Introduce larger approach for the setting of the outlet cooling water temperature. Abstract: The increasing economic advantage of replacing traditional two-speed fans with variable-frequency drive (VFD) fans has been gaining popularity in the industry. However, concerns regarding frequent ON/OFF switching and the lack of a well-devised controller have discouraged widespread adoption. In this study, a temperature zone method is proposed to replace the set-point method of fan control. Additionally, the highest output water temperature allowed in the process is set as the upper limit of a zone in order to further conserve energy. Both strategies are comprehensively analyzed for a virtual cooling tower that uses operational data from an existing VFD-fan-based cooling tower system in Taiwan. The results show energy savings of 38% for a 0.75 °C zone without increasing the ON/OFF switching frequency. The proposed strategies were further verified via an on-line field experiment. The proposed methods can be universally and easily applied to any existing cooling tower, and have significant implications for energy conservation if adopted globally.