Improvement to the Design of Vertical Geothermal Heat Exchangers Through Parameter Optimization

This study proposes the use of optimization algorithms to improve the design of vertical borehole geothermal heat exchangers (GHE). The designs are optimized to improve the temperature difference across the GHE, thus improving the efficiency of the ground-source heat pump. The finite line-source model is utilized as an accurate, straightforward model for geothermal heat transfer. This model was demonstrated to be accurate for both single-borehole and multi-borehole GHEs; however, in order to optimize the multi-borehole heat exchangers, the traditional model was modified. This modification allows for each borehole to be simulated individually, allowing for effective optimization. The GHEs were optimized using the MATLAB fmincon optimization function, utilizing an interior-point algorithm. This method yielded improved performance for both single-borehole and multi-borehole GHEs, although the results for multi-borehole GHEs are shown to be more useful. For multi-borehole GHEs, optimization resulted in a 26% increase in heat transfer with the ground and a 10% increase in heat pump COP. Overall, GHE optimization using the finite line-source method and MATLAB’s fmincon is shown to be an effective way to improve the efficiency of ground-source heat pumps.