Thermal analysis of a triple helix ground heat exchanger using numerical simulation and multiple linear regression

Abstract

Geothermal heat exchangers, one of the main components of shallow geothermal systems, have been investigated by many researchers in recent years to exploit clean and renewable energies. Most of the previous studies have mostly concentrated on the common types of ground heat exchangers including U-tube and helical ground heat exchangers. In the case of helical type, only two types of heat exchanger, with an inner outlet or with an outer outlet, have been examined. In order to increase the surface interaction between heat exchanger and backfill to improve the heat transfer rate, this study intends to present a new generation of helical ground heat exchangers called triple helix. Three helical branches are considered for both inlet and outlet of triple helix ground heat exchanger. The influences of geometric parameters such as helix pitch, helix diameter, helical coil length, the distance between centers of inner and outer helical coil branches, and the distance between centers of inner/outer helical coil branches on the efficacy of the heat transfer process are investigated by a numerical study. The results indicate that the most effective geometric parameter on the performance of the triple helix ground heat exchanger is the length of the helical coil, while the two parameters of the distance between centers of inner/outer helical coil branches, as well as the distance between centers of inner and outer helical coil branches, have the least effect. Along with the numerical results, multiple regression method accompanies with the artificial neural network are used to propose effective formulations to predict thermal properties of a triple helix ground heat exchanger.