Performance analysis of high temperature cascade organic Rankine cycle coupled with water heating system

Abstract

This paper presents performance analysis of a high temperature cascade organic Rankine cycle coupled with water heating system capable of providing maximum power output of 542 kW and hot water at 35 °C for household purposes. The analysis makes use of monthly ambient air and water temperature data of the city of Busan, South Korea as input parameters of the system. The working fluid at the exit of turbine 1 is split into two mass fractions, one providing heat to the bottom cycle (ORC II) and the other used to heat water in the water heating system. These mass fractions are adjusted according to the expected seasonal demand of hot water. Among three high critical temperature working fluids, m-xylene has been selected for the top cycle whereas R245fa has been selected for the bottom cycle among five low critical temperature working fluids. A comprehensive thermal and exergy efficiency analysis shows the performance of the system during the different months of the year. The analysis show the comparison of the winter season (when demand for hot water is high) with the summer season (when demand for hot water is low).