Applications of earth-to-air heat exchangers: A holistic review

The building sector is responsible for 40% of primary energy consumption, with heating/cooling covering the most significant portion. Thus, passive heating/cooling applications have gained significant ground during the last three decades, with many research activities on the subject. Among passive cooling/heating applications, ground cooling (especially earth-to-air heat exchangers) has been highlighted as a remarkably attractive technological research subjects because of its significant contribution to the reduction of heating/cooling energy loads; the improvement of indoor thermal comfort conditions; and the amelioration of the urban environment. This paper presents a holistic review of state-of-the-art research, methodologies, and technologies of earth-to-air heat exchangers that help achieve energy conservation and thermal comfort in the built environment. The review covers the critical subject of the thermal performance of earth-to-air heat exchanger systems; experimental studies and applications; parametric studies for investigating the impact of their main characteristics on thermal efficiency; and recent advances and trends including hybrid technologies and systems. The models describing the thermal performance of earth-to-air heat exchangers systems were classified in numerical, analytical, and data-driven; their main theoretical principles were presented; and experimental validation was mentioned when carried out. System parameters were grouped into three categories: system design, soil types, and soil surface coverage. System design parameters, especially length and burial depth, bore the most important influence on the thermal efficiency of the system. The paper was rounded up with an economic assessment of system application, and the conclusions highlighted the need for more experimental work including laboratory simulators.