Experimental and numerical exergoeconomic evaluation of soil depth and pipe material effects in an earth to air heat exchanger assisted heat pump for cooling and heating applications

Abstract

Earth air heat exchanger (EAHX) systems utilize the thermal inertia of the soil to improve the heating and cooling performance of building energy systems. Although previous studies have mainly focused on isolated EAHX performance or purely numerical analyses, comprehensive experimental-numerical and exergoeconomic evaluations of EAHX-assisted air source heat pump (ASHP) systems under hot-arid climatic conditions remain limited. This study presents an integrated experimental and numerical investigation of an EAHX-assisted ASHP operating in S & cedil;anl & imath;urfa, T & uuml;rkiye, considering both summer cooling and winter heating modes. Four EAHX configurations, installed at soil depths of 2 m and 3 m, with identical pipe diameters and different pipe materials, were experimentally evaluated to examine the effects of soil depth and pipe material on system performance. Field measurements were conducted for both seasons, and the optimal configuration was subsequently integrated with an ASHP. Detailed energy, exergy, and exergoeconomic analyses were performed using Engineering Equation Solver (EES). For the cooling mode, a constant cooling load of 15 kW was considered. Condenser-side EAHX integration, providing a 10 degrees C pre-cooling of the inlet air, increased the refrigeration coefficient of performance (COPR) from 3.12 to 4.24 (35.6% improvement) while reducing compressor power consumption by approximately 26%. Accordingly, the unit cooling cost decreased from 0.0688 $/kWh to 0.0569 $/kWh, yielding a 17.3% reduction. For the heating mode, a constant heating load of 20 kW was analyzed. EAHX-assisted operation increased the heat pump coefficient of performance (COPHP) from 3.76 to 4.65 (23.7% improvement), while the unit heating cost decreased from 0.0519 $/kWh to 0.0460 $/kWh. Exergy analysis revealed notable reductions in irreversibilities, particularly in the compressor and condenser, for both operating modes. The results further indicate that a soil depth of 3 m provides superior thermal and economic performance. Overall, the study demonstrates that EAHX-assisted ASHP systems offer significant efficiency gains and cost savings for year-round heating and cooling applications in hot-arid climates, providing practical design guidance for sustainable building energy systems.