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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. [ABSTRACT FROM AUTHOR]

Highlights: [•] Introducing an adaptive soft sensor in the cooling tower process. [•] Proposing and implementing an optimal fan operation strategy. [•] Demonstrating significant energy saving in the studied cooling tower. [ABSTRACT FROM AUTHOR]

Highlights: [•] We introduce an index to describe the cooling capability of a cooling tower. [•] The effect of ambient air on cooling capability is studied by statistics analysis. [•] Physical-meaningful and precise-enough model is built by actual operation data. [•] The application to a real cooling tower is promising for energy conservation. [ABSTRACT FROM AUTHOR]