Earth-air heat exchangers in the Belgian climate: Analysis of the potential with a 3D modelling technique.

Earth-air heat exchangers can be used to reduce energy consumption in building ventilation systems. The idea is to pre-heat air in winter and pre-cool air in summer using the thermal capacity of the soil. To do this concrete and plastic tubes are put underground, through which the ventilation air is drawn. In this paper a 3D unstructured finite volume model is derived, which allows evaluating the earth-air heat exchanger. The model solves conduction through the soil and the convection from air to the tube wall. The air ground-surface heat transfer is described by the heat flux through convection and solar radiation. The model is used to study the performance of the earth-air heat exchanger in the Belgian climate. It is shown that in summer the air can be cooled with about 9 C at sufficient depth (3m) and tubes of about 50 m. In winter heating of 7 C can be realised. It is also shown that a good control strategy is important.