Variable flow controls of closed system pumps for energy savings in maritime power systems

Pumps are extensively used in maritime industries as marine vessels utilize a wide range of pumps and pumping techniques to transfer and distribute all types of air and fluids. The electrical energy consumed by the various motors accounts for about 70% of a vessel's total power consumption, and this presents a problem in unique marine environments. Such situations are especially conducive to energy-saving strategies using variable frequency drives (VFDs) in centrifugal load service. This paper presents the design and results of applying variable frequency constant pressure technology in closed system pumps on marine vessels. The existing problem of traditional control methods for closed system pumps is analyzed and a mathematical model for variable flow controls with the appropriate control settings is derived. The performance of the proposed method is demonstrated and verified through experimental and field tests of a practical auxiliary boiler feed water management system on a commercial vessel. It is proved that the proposed method can maintain constant water pressure for closed system pumps and provide an efficient way to measure energy savings and maintenance benefits. The results serve to highlight the significant energy-saving opportunities for retrofitted and new VFD installations in marine power applications.