Energy savings techniques in ventilation processes with fans operating at variable load

Abstract

Ventilation is vital in various processes where dilution of dust and gases and removal of heat are some of the primary reasons. Millions of Dollars are annually spent on investments, electricity bill, maintenance and repair costs of the fan components. Energy consumption represents one of the biggest components of ownership costs and therefore many steps are taken in order to develop and implement Energy Conservation Measures (ECMs). Very little attention have been paid on critical elements and processes equipments in the case of variable loads when revolutionary ECM types are required to design and maintain energy (efficient) ventilation systems. In fluids movement, variable load is due to variable fluid power. This could appear as a result of air density variation (dust and gas content) but also as a result of impeller pitch variation. Variable impeller pitch mechanisms are used for big fan units (hundreds of kW of installed power) in order to minimize the energy consumption when no air movement is required. Classic methods of estimating energy savings by using VFDs are assuming constant pitch impellers and constant load (air power). These methods are not applicable for big fans yielding variable performances while working at variable load. This research focuses on techniques of obtaining energy savings by controlling the parameters of the power supply as a combination of variable frequency of the power supply with reduction of magnetic loading of the motor. This work present result of two years' activity in reviewing various techniques of obtaining energy savings with fans performing at variable loads by using various ECMs. A mathematical model has been created to estimate and maximize energy savings by using combined techniques (variable frequency and variable magnetic loading). Power/energy savings have been estimated for every ECM, including reliability indicators estimation of the system impeller. Proposed method is suitable for any application yielding variable performances concomitant with variable load factors: conveyors, escalators, saw mills, pumps, variable pitch fans.