A numerical analysis for the dynamic performance of a multi-purpose solar thermal system for residential applications

Abstract

This paper presents results of a multi-purpose solar thermal system that provides hot service water, space heating and space cooling for residential use during all seasons in Pretoria, South Africa. A pressurized system using evacuated tube solar collectors with internal heat pipes to provide the required hot water and a micro single-effect LiBr -H2O absorption chiller to provide the required space heating and cooling was considered. For the solar field, collectors consisting of 25-tubes (3.266 m2 each) are connected in parallel in a 3, 4 and 5 array field. In this study, the focus was on determining the hourly performance trends of the considered system using typical meteorological year weather conditions. The performance of the system was obtained by developing the system’s mathematical model whose solution was obtained using Engineering Equation Solver (EES). The model was validated using available experimental data and good agreement was obtained. The absorption chiller model was validated using data from ASHRAE and was shown to be valid within ±2.2%. From the analysis, results show that the 25-tube collector with a 5 array field could operate without interruption throughout the seasons, yielding tank temperatures at 111.75°C and 95.18 °C for the summer and winter seasons, respectively. However, the recommended system, with the lowest scalding hazard risk, is that of the 25-tube collectors with a 4 array field. This system produced a cooling capacity of 5.94-7.3 kW at a cooling coefficient of performance (COP) of 0.78-0.8 in winter and 4.24-5.94 kW at a cooling COP of 0.77-0.73 in summer.