Performance characterization and optimization of thermally activated building systems with hybrid geothermal-solar energy technologies in net/nearly zero energy buildings

This study aims to characterize and optimize the thermal comfort, environmental impact, economic performance, and energy flexibility of a thermally activated building system (TABS) integrated net/nearly zero energy building (NZEB) equipped with ground source heat pump-air source heat pump-photovoltaic-battery (GSHP-ASHP-PV-battery) systems. The TABS parameters, including design variables, physical properties, and operating variables, were considered in the performance investigation. The developed TABS model was validated and exhibited acceptable performance based on two in-situ response experiments. The Taguchi method and Utility concept were used to design simulation cases and determine the optimal conditions. The simulation results from the Taguchi confirmation tests demonstrated improvements across all performance indicators in both heating and cooling operations through appropriate optimization. In particular, the Taguchi-optimal cases achieved reductions of up to 58.3% in the heating unmet-hour ratio and 28.4% in the heating imported electricity cost, compared with the best-performing cases in the design set. The performance of each Utility-optimal case was comparable to, or slightly lower than, that of the Taguchi-optimal cases. Nevertheless, the Utility-optimal cases for the unmet hour ratio, carbon dioxide emissions, imported electricity bill, and self-consumption ratio still outperformed the best-performing cases among the original Taguchi cases, with improvements ranging from 1.5% to 18.3% for cooling and from 9.0% to 38.9% for heating. Additionally, based on the Utility concept, the operating factors exhibited significant influence on various performance indicators, particularly the system start time and operating duration. The results can provide valuable information to facilitate the efficient design and operation of the integrated building energy systems.