Investigations on the influence of aquifers on the ground temperature in ground-source heat pump operation

The winter operation of ground-source heat pumps is expected to lead to temperature decrease in the zones surrounding the vertical ground heat exchangers. The following thermal drift phenomenon occurring over the years is still deeply studied from both the experimental and the theoretical viewpoint. A moving aquifer tends to oppose the thermal drift, due to the advection groundwater phenomena. For this purpose, a modelling study on the quantitative influence of the groundwater flow on the thermal drift is performed. Then, the analytical solution of the moving infinite line source is applied. Different forms (closed analytical, asymptotical or tabled one) are identified for this solution depending on the value range of the thermal physical parameters of the system. Referring to a particularly critical case study, an easy-to-use application of the model based on this analytical solution is then presented. An evaluation is carried out as well on the interaction between the existing borefield and a nearby one, being operated afterwards, in presence of either still or moving aquifer. Finally, the influence of the actually existing flow upon improving the effective operating conditions of the heat pump plant is assessed. Moreover, when groundwater flow is taken into account, the decrease of the total borehole length is evaluated. (C) 2013 Elsevier Ltd. All rights reserved.