This article is about earth tubes. For the ground loop of a heat pump, see geothermal heat pump. They use the Earth’s near constant subterranean temperature to warm or cool air or other fluids for residential, agricultural or industrial uses. These systems are known by several other names, including: air-heat pipe heat exchanger pdf-soil heat exchanger, earth channels, earth canals, earth-air tunnel systems, ground tube heat exchanger, hypocausts, subsoil heat exchangers, thermal labyrinths, underground air pipes, and others.
Earth tubes are often a viable and economical alternative or supplement to conventional central heating or air conditioning systems since there are no compressors, chemicals or burners and only blowers are required to move the air. Their use can help buildings meet Passive House standards or LEED certification.
United States over the past several decades and have been used in conjunction with solar chimneys in hot arid areas for thousands of years, probably beginning in the Persian Empire. Implementation of these systems in Austria, Denmark, Germany, and India has become fairly common since the mid-1990s, and is slowly being adopted in North America.
Ground-coupled heat exchanger may also use water or antifreeze as a heat transfer fluid, often in conjunction with a geothermal heat pump. See, for example downhole heat exchangers. The rest of this article deals primarily with earth-air heat exchangers or earth tubes. Earth-air heat exchangers can be analyzed for performance with several software applications using weather gage data.