Energetic and exergetic performance evaluation of natural circulation solar water heating systems

Abstract

This study deals with the energy and exergy analyses of natural circulation solar water heating (SWH) systems. The system comprises of a single glazed flat plate solar collector (FPSC) with absorber plate of 2 m2, and a separate insulated well-mixed vertical water storage tank (WST) of 125 liters. The variable heat transfer coefficients, water inlet and outlet temperatures of the FPSC; and temperature of heated water stored in the WST are predicted theoretically for each interval. The daily energy and exergy efficiency of the FPSC, WST and SWH system are estimated to be about 39 and 4.36%, 67 and 38.55%, 27 and 1.01%, respectively. It is found that the water inlet temperature, optical efficiency and the solar radiation strongly influence the performance of the FPSC both energetically and exergetically. It is observed that change in the mass flow rate of water improves the exergy efficiency of the FPSC significantly. FPSC has been identified as a critical component of the system where exergy destruction of 308 W/m2 takes place daily as compared to 24 W/m2 in the WST against available solar exergy of about 663 W/m2.