Performance and cost-benefit analysis of an integrated earth-air heat exchanger and air handling unit system

Earth-Air Heat Exchanger (EAHE) systems present a sustainable solution to reduce the energy consumption of HVAC systems by utilizing stable subsurface temperatures for passive air conditioning. This study investigates the performance of an EAHE integrated with a central air conditioning system, focusing on the effects of pipe geometry, burial depth, cross section of pipe and thickness on thermal efficiency and economic viability. Despite extensive studies on EAHE systems, gaps remain in understanding the combined impact of pipe cross-section, thickness, and burial depth on system performance and cost-effectiveness. This study addresses these gaps by evaluating four pipe cross-sections (circular, square, rectangular, hexagonal) at varying depths (1-4 m) and thicknesses (5-20 mm) using a validated transient thermal model. A comprehensive analytical model was developed and validated against experimental and computational data to assess energy savings and operational benefits. The study employed an integrated MATLAB/EES-based computational framework to conduct a continuous parametric and economic analysis. This analytical approach systematically evaluated the effects of pipe geometry, burial depth, and thickness on the system's thermal performance and financial viability. Results show that rectangular pipes (410 mm perimeter) achieve the highest cooling efficiency (85%), reducing outlet air temperature by up to 10.5 °C compared to ambient conditions. Burial depth significantly influences performance, with 4 m depth yielding 38.2% compressor power savings nearly double that of 1 m depth (19.9%). Pipe length optimization reveals diminishing returns beyond 15 m, where 34.2% power savings are achieved with a 3.8-year payback period. Economic analysis identifies the 15 m rectangular pipe at 3-4 m depth as the optimal configuration, balancing efficiency (38.2% savings) and cost (payback: 3.8 years). These findings provide actionable insights for designing energy-efficient EAHE systems in HVAC applications.