Optimization of energy pile conductance using finite element and fractional factorial design of experiment

In Ground Source Heat Pumps (GSHP), Energy Piles pose as heat exchangers that transfer the heat from the buildings to the shallow ground lower temperature in order to decrease the energy consumption whilst cooling the buildings. These piles are mainly designed for highest possible thermal conductance. In this paper, nine factors influencing the thermal conductance of the energy pile are defined and statistically evaluated. These nine factors are; number of tubes, pile diameter, tube diameter, tube thickness, tube location, pile conductivity, tube conductivity, soil conductivity, and water flow rate. The thermal conductance of the energy pile is calculated using finite element model. The significance of these factors is evaluated using fractional factorial uniform design of experiment. The results show significance increase in the pile thermal conductance with the increase of the tube diameter, number of tubes, water flow rate, and tube and pile thermal conductivities. Furthermore, the tubes location near the pile outer surface show significant increase in the pile thermal conductance. On the other hand, decreasing pile diameter slightly increases the pile thermal conductance. Nevertheless, the soil thermal conductivity has shown insignificant effects on the pile thermal conductance.