Heating and cooling of buildings are responsible for a large percentage of world energy consumption. Today, ground source heat pumps offer one of the most energy efficient technologies to provide heating and cooling by using the renewable heat source of the building's surrounding ground volume. Primarily in Northern Europe these systems are becoming a common heating/cooling technology. Some currently available building simulation programs like TRNSYS or EnergyPlus have the ability to model them. In this paper a parameter estimation study of a water-to-water heat pump model, implemented in IDA-ICE simulation environment, is presented and validated using experimental data. The model is based on performance maps: user-supplied data files containing catalogue data for the delivered energy and power absorbed are based on the entering load and source temperatures. The simulation results show that, if the input parameters (e.g. heat pump typology and control operation) are known, the simulated heat-pump model corresponds closely with the experimental operation. The maximum absolute mean deviation in the predicted values is equal to 5.09, 0.94, and 5.06%, respectively, for COP, condenser water temperature, and power delivered by the heat pump in heating operation. (C) 2012 Elsevier B.V. All rights reserved.