Impact of groundwater heat pump systems on subsurface temperature under variable advection, conduction and dispersion

Abstract

The number of worldwide installed groundwater heat pump (GWHP) systems is approaching one million units. This increase in GWHP systems creates an increasing competition for groundwater use. Thus, we have simulated the long-term thermal impacts of such open-loop geothermal systems with numerical heat transport models, by studying the role of flow and heat transport parameters. The focus is set on transient conditions evolving over decades of seasonally imbalanced heat injections in aquifers with differing ambient flow regimes. The results demonstrate the existence of plume length peaking in moderate groundwater flow velocities (0.5–1.0 m d−1). The longitudinal and transverse dispersivity coefficients have a strong influence on the plume extension and on transient development. Reducing the injected temperature difference allows the control of the maximum temperature reached in the plume but implies a considerable hydraulic influence. Comparisons with numerical simulations, using an average of the thermal load, shows that the flow velocity and dispersity coefficients strongly condition the relevance of such simplified approaches. In addition, if satisfactory results are obtained for seasonal or long-term estimations, those for intermediate lengths of time are insufficient. This study contributes to improving the overall understanding of key elements involved in the thermal impact and the development of GWHP systems.