The building sector is one of the key consumers of energy in Europe today with an overall rising trend over the past 20 years. In order to achieve the current EU 20-20-20 goals or the targets set in the EU Energy Roadmap 2050, it is essential to renovate and retrofit these buildings and to replace inefficient heating systems based on fossil fuels or direct electric heating. The proposed heat pump technology offers a solution to both present and future challenges.The goal of the GreenHP project is to investigate and develop a new highly efficient heating system based on high-capacity air/water heat pumps for retrofitting multi-family houses and commercial buildings. This high power heat pump system will use an alternative refrigerant and will interact with large (renewable) energy systems, like the smart grids in particular, and integrate other renewable energy sources, like photovoltaic and solar thermal, as well as energy storage.In order to tackle the relevant scientific challenges, the consortium will employ a holistic approach covering research topics on the system integration level, heat pump unit and component level. This will representatively be done for high-capacity air/water heat pumps for retrofitting applications in cities. The technological solutions generated will reinforce the technological leadership of the European industry and strengthen the position in the increasingly strong and global competition in the market place.The integral approach of the GreenHP project requires a special consortium structure with project partners able to cooperate and exploit the project results on a common basis. The consortium, which includes Originals Equipment Manufacturers and research institutes only, will offer the Know-how on the unit design and the system integration in the public domain, available to all European Heat Pump manufacturers. By this, the GreenHP project will trigger competition to find the best solutions for the market and make a larger impact possible. The consortium is aware that this requires a strong dissemination to heat pump manufacturers but also to architects, urban planners, installers and end users.At the end of the project, a 30 kW lab scale pilot with a new unit design using alternative refrigerant and innovative components will be developed. In addition, it will be shown how this heat pump integrates into buildings and interacts with the smart electric grid. This will be the basis for many different applications for room heating and cooling as well as sanitary hot water production, as any solution between 30 kW and 100 kW will be possible. The consortium is confident that the implementation of the proposed concept will have a fundamental impact on the European Building sector by providing a new technical solution. Thus it will substantially contribute towards a sustainable European energy system.