CT: An earth-to-air heat exchanger draws ventilation supply air through buried ducts or tubes. As the temperature of the ground below 3m is practically constant, it substantially reduces ambient air temperature fluctuations. It therefore provides space conditioning throughout the year, with the incoming air being heated in the winter and cooled in the summer by means of earth coupling.
S: http://www.designingbuildings.co.uk/wiki/Earth_to_air_heat_exchangers (last access: 26 February 2015)
N: 1. Systems can be driven by natural stack ventilation, but usually require mechanical ventilation. In some cases air is circulated via air handling units, allowing filtering and supplementary heating/cooling. A simple controller can be used to monitor inlet and outlet temperatures, as well as indoor air temperatures. Ground coupling ducts or tubes can be of plastic, concrete or clay – the material choice is of little consequence thermally due to the high thermal resistance of the ground.
2. Earth-to-air heat exchangers are suited to mechanically ventilated buildings with a moderate cooling demand, located in climates with a large temperature differential between summer and winter, and between day and night. Location of the ducts in sand or gravel below the water level, where there is moving ground water, gives the best performance, however, the presence of ground water involves extensive sealing precautions.
S: 1 & 2. http://www.designingbuildings.co.uk/wiki/Earth_to_air_heat_exchangers (last access: 26 February 2015).
SYN: EAHX, earth tube, ground-coupled heat exchanger, earth channel.