When using groundwater as a primary energy source in combination with heat pumps, the groundwater is pumped from the groundwater zone, cooled in the heat exchanger of the heat pump, and then reinjected into the groundwater zone.The design of traditional groundwater heat pump plants is based on the use of a separate pumping and reinjection well. An alternative design is to use a single-well for both pumping and reinjection. However a minimum distance between well screens is required in order to prevent break-through, caused by short-circuiting of the cooled groundwater.The present paper describes a simplified mathematical model to be used to analyze steady-state operational temperature conditions for a single-well groundwater heat pump plant. The model is based on a finite element solution of the temperature distribution in the pumping and reinjection zones of the groundwater reservoir.Furthermore, a model for the calculation of the ratio of the vertical to the horizontal permeability is presented in the paper. This ratio is one of the important parameters in the design of a single-well groundwater heat pump plant.Both models have been tested against data from a full-scale experimental plant on the campus of the Technical University, where the hydrogeological conditions are familiar. The results of a comparison between model predictions and experimental field data are included in the paper.