Numerical Optimization of Double Tube GHE for Ground Source Heat Pump

Abstract

In this paper, a two-dimensional axisymmetric numerical simulation model was developed for optimization of double (coaxial) tube vertical ground heat exchangers (GHEs) in cooling mode. Details of the heat transfer rates and pressure drops for each model are presented and analyzed. The results of the numerical study of optimization of double tube vertical GHEs have been done by considering heat transfer rates and pressure drops. The effect of different inlet and outlet tube diameters, and mass flow rates were numerically investigated. Effect of the different materials on heat transfer and longtime operation also discussed. The double tube vertical GHEs are more effective in laminar flow condition considering balance between heat transfer and pressure drop. The results indicate that since in laminar flow condition, pressure drop is not significantly high, it is possible to reduce the inlet and outlet diameter of double tube GHEs if double tube GHEs operate in laminar flow condition. The heat transfer rate decreased only 17% but diameter of the inlet tube can be reduced from 130 mm to 40 mm with fixed outlet diameter 20 mm. Heat transfer rate can also be enhanced by reducing the outlet tube diameter for a fixed inlet tube diameter. Long time operation suggested the possibility of installation of multiple double tube GHE at 2.0 m apart.