Investigation of ship cooling system operation for improving energy efficiency

The application of recently introduced IMO regulations for reduction of CO2 gaseous emissions as well as the initiatives for greener shipping, rendered the efforts for improving on-board energy systems performance to be of high priority. This study focuses on the investigation of the on-board operation of the combined sea/fresh water cooling system of a merchant ship. The detailed model of a cooling system is presented based on energy and mass conservation laws. The simulation input data includes the system geometry and arrangement, the operational characteristics of cooling pumps, the control scenarios for the system valves as well as data for calculating the pipes friction and minor losses coefficients, wherefrom the system performance parameters can be calculated. The cooling system energy consumption was estimated considering a typical annual ship operational profile. Two cases were investigated; first, a conventional case of controlling the sea water and fresh water temperatures by using three-way valves and, second, a more sophisticated case of installing variable speed motors for driving the system pumps. The obtained results are compared in terms of annual power consumption leading to conclusions about the system performance. The developed models can be used as an assessment tool for improving shipboard power demand early in the design stage and, also, during operation