Sensorless frequency-converter-based methods for realizing life-cycle cost efficient pumping and fan systems

Frequency converters provide means for the energy efficient flow and pressure control in pumping and fan systems by varying the motor speed. Besides speed variation, a modern frequency converter can estimate the state and performance of system operation without additional measurement sensors. This ability provides several possibilities to optimize pumping or fan system operation and the resulting life-cycle costs (LCC) that mainly consist of energy and maintenance costs. First, information on the present operating state directly informs that how energy efficiently the system is driven, and does the system fulfill the given process requirements. Estimation of the pump or fan operating state can be further applied to determine the surrounding process characteristics, which is essential information for energy audits. This information can also be used for the optimization of the system operation with energy-efficiency-based speed control schemes that are a key factor to LCC efficient pumping and fan systems. Another, a less studied topic is the detection of lifetime reducing operating states with the frequency converter: it is shown that the occurrence of high flow cavitation, fluid recirculation and fan stalling have an effect on the frequency converter estimates for the motor rotational speed and shaft torque. Correspondingly, mass increase in the fan impeller caused by the contamination build-up can be detected with the converter estimates before the occurrence of impeller imbalance. In both cases, the successful detection of adverse operating state can provide notable cost savings, if the resulting production losses and their effect on the system LCC can be avoided. This article presents frequency-converter-based monitoring and optimization methods that can be used to optimize pumping and fan system life-cycle costs. The study is done both for commercially available products and for ideas that are verified with laboratory or pilot tests.