In-field performance of continuous flight auger (CFA) energy piles with different configurations

Abstract

In order to face the national energy crisis in Brazil, the use of geothermal energy piles (GEP) integrated with heat pumps is an attractive and cost-effective solution for the building cooling demand. On the other hand, there are very few field studies on the thermal performance of GEP systems in Brazilian soils and climate conditions, and for this reason, the implementation of this technology is still a challenge. Motivated by this need, continuous flight auger (CFA) energy piles were constructed to support a building in São Paulo city, and an experimental study, described in this paper, was carried out to provide useful data for the design of these GEPs. This work examined two key aspects of the design of GEP systems: (1) the influence of the heat exchange pipe configuration, and (2) the thermal response of GEPs and their effect on nearby piles installed in multi-layered ground. For this study, thermal response tests (TRTs) were conducted on four GEPs constructed with different pipe configurations, installed in a saturated sandy deposit intercalated by soft organic clay layers. The results obtained showed that: (i) the influence of pipe configuration on the GEP heat transfer is more significant during the first hours of pile heating process, and decreases with time due to the thermal interference between the pipe loops; (ii) the GEP temperature profile is impacted by the presence of soil layers of highly different thermal conductivities and groundwater flow velocities; and (iii) the temperature variation of nearby piles was also affected by the thermal characteristics of the soil layers, and therefore it should be considered for the structural design of GEPs.