Nanotechnology Applied to Ground Heat Exchanger Pipes: A Review

Abstract

During the last decades, the use of Geothermal Source Heat Pumps (GSHP) has growth exponential around the world, since it has been considered as the best technology available for the air conditioning of residential or commercial spaces (Lund and Boyd, 2016). The GSHP offers important benefits, e.g. reduction of electricity consumption, efficiency in heat transfer and the reduction of CO2 emissions. A GSHP is composed of three important elements: the space to be conditioned, the Heat Pump (HP) and the Geothermal Heat Exchanger (GHE). The latter uses the subsoil as an energy source, which through the use of pipes buried under the subsoil (horizontal or vertical) and through the HP, can move the fluid to transfer heat into the space to be conditioned as a source (heating in winter) or heat sink (cooling in summer). The GHE is a process of high-energy efficiency because the soil temperature remains stable throughout the year. Over the last decade, research has been carried out to enhance heat transfer in heat pipes using traditional working fluids or developing new pipe materials. The aim of this review is to summarize recent research on the study of heat transfer using nanotechnology in the Geothermal Heat Exchangers pipes (GHEP). This work analyzes the development of new fluids (nanofluids) and new materials (nanoparticles and nanocomposites) which enhance heat transfer efficiency of heat pipes. As a result, the present review may generate a perspective for future research regarding the use of nanotechnology to reduce the costs involved in the Geothermal Heat Exchangers design by means heat transfer optimization.