The widespread use of heat pumps (HP) can be a major lever for reducing CO2 emissions linked to energy consumption in buildings. Besides, integrating an energy storage solution into the HP’s heating system helps to limit peaks in the electricity grid by storing energy for later use. This could also help to ensure greater penetration of electricity from renewable sources. A concept combining a HP and a latent heat storage device has been developed. Energy storage is achieved using a Phase Change Material (PCM) which is placed directly on the heat pump's refrigeration circuit, enabling direct heat transfer between the PCM and the refrigerant. This storage heat exchanger can also exchange heat with the heat transfer fluid used to meet the heating demand. A numerical model has been used to estimate the performance in various configurations and scenarios, in particular through the determination of its seasonal performance. The results show that the objectives of peak shaving may be achieved, with similar performance to a standard HP.