RECOVERY TIME OF GROUND TEMPERATURE AFTER HEATING TESTS ON ENERGY PILES IN UNSATURATED AND SATURATED BRAZILIAN SOILS

Energy piles are deep foundation structures which have been used as ground heat exchangers for air heating and cooling of buildings in different countries. However, the performance of these systems in Brazil is not known yet. Because of its tropical and subtropical climate, the consumption of electrical energy for air-cooling systems in Brazil is very high. Therefore, the use of ground source heat pump (GSHP) systems with energy piles seems to be an interesting alternative to address this problem.

Due to the climatic conditions, the heat exchange operations in Brazil are likely to result in the progressive heating of the ground. On the other hand, the groundwater flow rate are fundamental to permit the ground temperature recovery around the heat exchanger piles after periods of heat rejection in the ground.

Therefore, to investigate the effect of some local peculiarities of the use of energy foundations in Brazil, as the use of this system only for air cooling (no heat extraction, as normally occurs in temperate and cold climate countries) and higher ground temperatures, an experimental study have been carried out at two different sites in the State of Sao Paulo.

In the first site, an energy pile was installed in an unsaturated soil, which is the most critical condition of ground temperature recovery after the continuous use of GSHP systems. In the second site, an energy pile will be installed in a saturated sand soil, with high groundwater flow rate, which should be the most favorable condition for the ground temperature recovery, and consequently in this case the efficiency of energy piles may be better compared to the case of unsaturated soil.

The current work presents the first results of the ground temperature recovery around the energy pile in the unsaturated soil site, and a detailed description of the experimental programme designed to study the effect of groundwater flow rate on the ground temperature recovery of the case in the saturated sand site.