IMPACT of SOIL SURFACE FINISHING on HORIZONTAL GROUND HEAT EXCHANGERS

Unlike deep and vertical boreholes heat exchangers, shallow and horizontal ground heat exchangers (GHXs) exploit mainly the temporary underground thermal energy storage of the solar radiation. So, the soil surface finishing could play an important role for the energy balance and the performance of the GHXs. To evaluate the relevance, a numerical approach was pursued to assess the energy performance of a shallow GHX. A novel type of exchanger was analyzed, consisting of a flat-panel installed horizontally and edgeways at shallow depth. A 2D finite elements domain was composed for solving the heat transfer problem for two different soil surface finishing: lawn and asphalt pavement. The energy balance at the soil surface and the GHX energy requirement were introduced at monthly scale, taking into account the solar radiation and the natural convection. The results showed that no relevant differences were evident between the maximum and minimum temperatures achieved by the GHX and only a different thermal field was achieved. The asphalt pavement operated like an insulating layer and its shallow underground temperatures were slightly cooler on average. The underground thermal field only showed a time shift and some minimal differences, that did not affect the GHX’s working fluid temperature.