« Stock-air 2 » project aims at developing and controlling a technical solution where an air-to-air heat pump is coupled to a thermal storage made of Phase Change Material (PCM) in order to erase the electricity demand during the peak hours between 6 p.m. and 8 p.m. This technical option is relevant for refurbishment of domestic heating by electrical resistance of the current installed base of buildings as well as for the future low-energy buildings. Indeed energy storage by solid-liquid phase change stabilizes the condensing temperature of the heat pump and leads to choose the temperature level leading to the maximization of the seasonal heat pump performance. On another hand the phase change allows steady operation of the thermodynamic system and limits drastically energy losses due to short operation cycles associated to low thermal loads. This project aims at developing upstream research on new materials and applied research on heating d systems including energy storage tested in real operating conditions. Developed PCMs will present phase change levels of temperature adapted to air heating systems i.e. 30 to 50°C. Those PCMs will be integrated in energy storage / delivery heat exchangers. Two main technical options will be studied in parallel: - PCM integration in heat pump condenser taking advantage of high heat exchange coefficients - PCM integration in the air circuit associated with enhance heat exchange surface with circulating air Stock – Air2 project is performed under a double approach: a systemic approach based on numerical simulation, and technologic approach for material and system development with an adapted speed for energy storage and delivery of the chosen heating system. One of the .project originalities is based on solving issues related to phase change delay and incomplete phase changes by integration of PCMs in high heat exchange coefficient surfaces (40 to 500 W/m2.K). One of the project work packages addresses PCM container design. The container required qualities are: a very low permeance to the active material, a good resistance to corrosion, sufficient fatigue strength, a good heat exchange performance. The program will lead to test Two physical demonstrators of storage / delivery heat exchangers: one integrated in a heat pump condenser (indoor unit) and the other integrated into ventilation ducts or plenum. Once those systems are validated by laboratory tests, they will be tested in individual houses with ordinary occupants. The energy performances as well as the comfort felt by occupants will be analyzed.