Earth tubes

An earth tube is a tube that is buried in the ground which heats or cools air moving inside it. Earth tubes may a be a closed circuit where they take air from inside a structure, circulate it in an underground loop before returning it to the structure, or an open circuit which takes air from outside and brings it into the structure, or counterflow open circuit when air is brought in and indoor air is taken out in sepearate earth tubes. The air can be moved passively with convection or actively with fans (air blowers). Whether the air is heated or cooled depends on the outside air temperature relative to the indoor temperature, and importantly the temperature of the soil at the edepth the tube is buried. This article focuses mainly on open systems.

Synonyms

Earth-to-air heat exchangers (EAHX / EAHE),^[1] Ground-coupled heat exchangers,^[1] Earth channels,^[1]

Problems

Moisture and mold

Moisture and mold may be encountered in earth tube systems. While some state that this is due to poorly designed, installed, operated and maintained systems;^[1] others conclude that the risk of deterioration of indoor air quality is significant and the technique cannot be justified given the limited energy savings provided.^[2]

Rainwater may pool inside earth tubes,^[2] if designed poorly. However moisture in the air can also be deposited on the iside of the tube as air moves through. Earth cooling tubes may benefit from dehimidification, particularly in warm and humid climates.^[3] Moisture can lead to growth of mold inside the tube.^[3] This mold releases spores which are carried on the air into the home. This can lead to a musty smell, and even cause health problems.^[3] Airborne spores of penicilium, aspergillus fumigatus, aspergillus versicolor and aspergillus niger were detected indoors in a PassivHaus with earth tubes in Belgium.^[2] The occupants had to move out due to chronic health problems which then resolved.^[2]

References

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