Lifecycle assessment and multi- criteria performance evaluation of hollow-finned versus conventional circular borehole heat exchangers: numerical simulation and experimental validation for GSHP systems

Ground source heat pumps (GSHPs) are widely recognized for their potential as sustainable, climate-resilient systems for heating and cooling applications; however, their overall performance and impacts are highly dependent on the design of borehole heat exchangers (BHEs), where effective optimization can lead to substantial performance improvements and significant reductions in lifecycle costs and CO₂ emissions. This study presents a comprehensive analysis of BHEs, integrating a 3-D numerical model, validated by lab-scale experiments, combined with a pulse load finite line source model to conduct multi-criteria performance evaluation and seasonal lifecycle assessments. Innovative hollow-finned BHE designs are compared with conventional circular configurations within the GSHPs to evaluate the system lifecycle thermal performance, economic viability, and environmental impacts. An innovative multi-criteria performance evaluation framework is implemented, targeting two key objectives: minimizing the number of BHEs ( n BHE, min ) and reducing the total BHE length ( L BHE, min ), considering the lifecycle energy consumption (LCEC), lifecycle costs (LCC), and lifecycle CO₂ emissions (LCCO) as key evaluation metrics. The results revealed that the hollow-finned BHE consistently outperforms the typical circular BHE across all cases, especially with hollow-finned BHE with a fin length ratio of 0.4 and the hollow-finned BHE featuring mid-placed plates. It is indicated that, adopting n BHE, min optimization objective: hollow-finned BHE with a fin length ratio of 0.4 reduces the required n BHE , LCEC, LCC, and LCCO₂ emissions by up to 12.50%, 6.96%, 6.88%, and 6.96%, compared to traditional circular BHE, respectively, while hollow-finned BHE featuring mid-placed plates yield reduction rates of 17.50%, 7.68%, 6.51%, and 7.66%, respectively. Furthermore, adopting L BHE, min optimization objective: hollow-finned BHE with a fin length ratio of 0.4 reduces the required L BHE , LCEC, LCC, and LCCO₂ emissions by up to 20.00%, 18.22%, 16.70%, and 18.19%, compared to traditional circular BHEs, respectively, whereas hollow-finned BHE featuring mid-placed plates demonstrates the best reduction percentages as 24.00%, 18.53%, 16.29%, and 18.47%, respectively. These findings highlight the potential of hollow-finned BHEs to enhance GSHP efficiency and sustainability.