Comparison of model-based flow rate estimation methods in frequency-converter-driven pumps and fans

Fluid handling systems such as pump and fan systems are found to have a significant potential for energy efficiency improvements. To determine the energy-saving potential, there is a need for easily implementable methods to monitor the system output. This essential information provides an opportunity to identify inefficient operation of the fluid handling system and to control the output of the pumping system according to process needs. Model-based pump or fan monitoring methods implemented in variable-speed drives have proven to be able to give information on the system output without additional metering; however, the present model-based methods may not be usable or sufficiently accurate in the whole operation range of the fluid handling device. To apply model-based system monitoring in a wider selection of systems and to improve the accuracy of the monitoring, this paper proposes a new method for pump and fan output monitoring with variable-speed drives. The method uses a combination of already known operating point estimation methods. Laboratory measurements are used to verify the benefits and applicability of the improved estimation method, and the new method is compared with five previously introduced model-based estimation methods. According to the laboratory measurements, the new estimation method is the most accurate and reliable of the model-based estimation methods.