Optimal Energy Production and Energy Density for ATES and Open-Loop Groundwater Heating and Cooling Systems

Aquifer Thermal Energy Storage (ATES) and open-loop unidirectional Groundwater Heating and Cooling (GWHC) systems can supply sustainable, low carbon heating and cooling. The technologies use similar numbers of borehole pairs and have similar installation and operational costs. However, the seasonal reversal of ATES systems allows for the capture and re-use of energy that is wasted in GWHC systems.

Here we establish a framework to simulate the impact of a wide range subsurface and design parameters on both ATES and GWHC system performance. We assume homogeneous aquifer properties and no groundwater flow, to establish a baseline for future investigation. Aquifer permeability anisotropy is considered as an uncertain aquifer property. The lateral spacing of boreholes, borehole screen length and vertical offsetting of screens are considered as key design decisions.

Results indicate that ATES systems in the absence of groundwater flow always produce more energy than equivalent GWHC systems. They also offer higher energy density, which is important in urban settings with high demand per unit area. The optimal combination of high energy and high energy density is obtained from ATES systems with long screen length and close borehole spacing that is slightly less than twice the thermal radius.