Variable speed drives for fans in small and medium-size ventilation systems with a constant design air flow, including a regenerative filter for dust separation, are evaluated in this paper. In the past, variable speed drives were considered for systems with varying air flow. It was found that this is also an appropriate measure to reduce the operating costs of such systems. With the chosen approach the calculated payback period based on 24h operation is between 0.7 and 1.7 years, depending on the size of the system. For systems in a two-shift operation the payback periods are still in the range of 1.4-3.4 years. The profitability of the installation of fan speed-control based on 12,000 service hours is in the range of 80-150%. A new operation mode, in which the filter cleaning is triggered at a fixed pressure drop of the filter cake, would further reduce the payback period and improve profitability. Systems with automatic damper flow control are much less economical. However, for the assumed conditions such systems are still better than uncontrolled systems. The installation of speed-control for fans in ventilation systems with a constant design air flow is therefore highly recommended for an-economical design. (C) 2016 Elsevier B.V. All rights reserved.