Experimental Exergy Analysis of the Solar Thermal System in the Off-Grid Zero Emissions Building

This paper presents an experimental exergy analysis of the solar thermal system in the Off-Grid Zero Emissions Building (OGZEB) at the Florida State University in efforts to identify components with major irreversibilities, i.e., exergy destruction. The solar thermal system comprises a series of flat-plate solar thermal collectors and 250-gal sensible thermal energy storage tank, and it is an essential constituent of the OGZEB heating system. In this study, exergy flow and destruction rates throughout the solar thermal system were evaluated using the experimental data obtained on two different days. According to the analysis, the greatest exergy destruction rate was observed in the solar thermal collector as expected, and its average exergetic efficiencies were 7.9% and 6.5% on each respective day. In the thermal energy storage tank, most of the exergy destruction was attributed to the mixing of hot water from the collector with the reservoir. This work serves as an initial step to the integrative thermodynamic optimization of the HVAC system in an off-grid residential building, where most energy is consumed for air-conditioning and heating.