Buildings space conditioning is a key sector with a high potential for cost effective energy and carbon savings, in which high efficient heat pumps can have a significant contribution. Besides consuming electricity increasingly produced by renewable energies, heat pumps can also have an important role to balance supply and demand, allowing the integration of intermittent renewable generation in smart grids. The aim of this paper is to demonstrate that ground source heat pumps are a very high efficiency technology for buildings space conditioning, and present a high potential for electric load management as a flexible load, when combined with the thermal storage capacity of the building. The very high efficiency of an advanced ground source heat pump system, which integrates state of art components in an optimal manner, was assessed considering the seasonal performance factors for one complete heating season and one complete cooling season, calculated based on the monitored data of an experimental site installed in a service building in Portugal. Innovative load management strategies to control the heat pump coupled with the thermal mass of the building were tested and its associated benefits, including integration for intermittent generation, were evaluated. The thermal response of the building was analyzed applying a model based on the lumped capacitance method, and it was validated with experimental data. A load shifting strategy by preheating the building and avoiding peak periods is proposed to allow the use of lower electricity rates leading to a reduction of electricity costs of 34%. Additionally preheating the buildings also contributes a larger integration of the renewable generation surplus (19-30% of the surplus generation). The implementation of Demand Response actions by switching off heating loads, during some periods of time, to compensate the variations and forecasting errors of wind power is also evaluated with positive impacts. (C) 2015 Elsevier Ltd. All rights reserved.