Influence of different types of pipes on the heat exchange performance of an earth-air heat exchanger

An earth-air heat exchanger (EAHE) is a green technology suitable for regulating the thermal environment of buildings; however it requires a large space and high construction costs. In this study, five types of pipes, such as aluminum, stainless steel, polyvinyl chloride, corrugated, and perforated corrugated pipes were selected as the heat exchange pipes to study the effects of pipe material, roughness of pipe, and bottom perforation on the performance of the EAHE under short-time, intermittent, and continuous operation conditions, and to identify the most suitable EAHE pipe. The results showed that the pipe material with thin wall had a negligible effect on EAHE performance, with a preference for cheaper pipes. Compared to smooth pipes, corrugated and perforated corrugated pipes significantly improved the heat transfer performance and reduced the pipe length by 28.33–33.33% and 22.67–29.33%, respectively. Although perforations in the bottom of the pipe could increase the heat exchange between the air inside the pipe and the lower soil layer, accelerate the recovery of the soil temperature, and increase the cooling time, it significantly reduced the heat exchange efficiency. Thus, the corrugated pipe with the best overall performance indicated that a pipe with rough surfaces was the most suitable pipe type for EAHE. This can significantly lower the amount of space and money needed for EAHE construction, making it suitable for a variety of building types and contributing to the solution to the issue of rising global temperatures brought on by the use of conventional energy in the construction sector.