Variable-speed-drive-based method for the cost optimization of air filter replacement timing

Abstract

The flow resistance of air filters accounts for a significant share of the electric energy consumed by fan systems. Due to their inevitable fouling, filters must be replaced periodically. This paper presents a novel variable-speed-drive-based method for online determination of the cost-optimal time to replace the filter of a fan system. The total cost of filtering per filtered volume of air is continuously calculated and when its minimum is reached, filter replacement is recommended. As part of the calculation, the energy cost related to the pressure drop of the filter is estimated using a variable-speed-drive-based filter pressure drop soft sensor. In addition to a variable-speed-drive and manufacturers’ specifications for the fan and filter, no extra equipment is required. As such, the method can be implemented as a programmed feature in a variable-speed drive or in a remote control and monitoring system. Feasibility of the method is verified with simulations and laboratory measurements, and the results suggest that it can realize a lower life-cycle cost of air filtering than the so far prevalent practices of filter replacement timing.