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Development of a virtual pump water flow meter using power derived from comprehensive energy loss analysis

Water flow rates are key controlled variables in chilled and hot water systems. The water flow rate through a pump can be virtually determined using a measured pump head and input power. Available input power can be either motor input power obtained from the connected variable-frequency drive or variable-frequency drive input power measured by a power meter. The harmonics created by the variable-frequency drive induce additional energy loss in the motor and consequently degrade the motor efficiency. The objective of this article is to evaluate a virtual pump water flow meter using either the variable-frequency drive input power or motor input power with calibrated pump, motor and variable-frequency drive efficiencies along with the consideration of additional harmonic energy loss. First, the water flow correlation with the measured pump head and available power input is discussed, then the calibration procedure is introduced to identify three efficiencies, and finally the experiment is conducted to develop and validate a virtual pump water flow meter on a pump motor variable-frequency drive system. The experimental results show that the water flow rates determined by the virtual water flow meter agrees well with the results measured by a physical water flow meter with the coefficient of determination of 0.91and 0.97, respectively.