Characteristics, design, and optimization of earth-air heat exchangers: A review

The Earth-Air Heat Exchanger (EAHE), also known as a Ground Source Heat Exchanger (GSHE) or Ground-Air Heat Exchanger (GAHE), is used to condition air in buildings and store thermal energy in a soil volume. Heat transfer within an EAHE system consists primarily of convection between air within buried pipes and conduction within adjacent soil volumes. EAHEs are most commonly employed for cooling in warm areas, with horizontal configurations being more common than vertical ones; however, they are also used for heating and in other configurations. Parameters affecting EAHE performance and cost include pipe diameter, length, and air velocity, as well as pipe material and soil type. The impact of these variables on heat transfer performance is explored. The metrics used to quantify thermal performance are reviewed. The most common are the coefficient of performance (COP) and thermal efficiency. The thermal performance of EAHE systems has been modeled at various levels of complexity. Instances of one-, two-, and three-dimensional modeling approaches, as well as transient and steady-state simulations, are reviewed. Simulation tools such as ANSYS Fluent, COMSOL, and TRNSYS are frequently used, while some studies implement model equations directly in various programming languages. A range of optimization strategies for EAHE design and operation is reviewed. Experimental and numerical studies in the literature are reviewed, highlighting key examples and those that present relevant data suitable for validating future modeling studies. Finally, current research gaps are identified, and focus areas for future EAHE research are presented. • A comprehensive review of EAHE design layouts and configurations is presented. • Key design parameters influencing thermal performance and cost are identified. • Energy modeling techniques and simulation tools used for EAHE analysis are examined. • Design and operational optimization strategies for enhancing EAHE performance are reviewed. • Energy performance metrics for technical and economic evaluation of EAHEs are summarized.