Buildings account for 70% of U.S. electricity consumption, of which the major electricity consumer is space heating and cooling. Therefore, grid-interactive efficient buildings (GEBs) have potential to provide the electricity grid with significant demand flexibility necessary for further adoption of the intermittent renewable electricity generation from solar and wind. Heat pumps are the key technology for buildings to respond to grid demand with their high efficiency and flexibility to provide both heating and cooling. Furthermore, when integrated with energy storage such as phase change materials (PCM), the heat pump – thermal energy storage (HP-TES) systems have the potential to provide significant capability of responding to the grid operation status by shifting the electricity load. To properly design and operate HP-TESEIR systems for providing grid demand response services, the characteristics of the different HPTES systems with different HP heat sources and ES materials need to be systematically evaluated and analyzed. However, such a holistic understanding is lacking in the literature. Therefore, this study is aimed to provide a comparative evaluation of the demand flexibility potential provided by different HPTES systems for residential buildings.

In this study, we first developed simulation models for HP-TES systems of various configurations in Modelica coupling the water-air heat pump with sensible and phase-change-material (PCM) energy storage. Then a virtual testbed is implemented by combining the Modelica HP-TES models with DOE residential prototype building models in EnergyPlus under the framework of Spawn of EnergyPlus. The demand flexibility for each HP-TES system is evaluated in the virtual testbed with a rule-based controller. Finally, a comparison across the included HP-TES systems and the simulation results revealed that how much flexibility the HP-TES systems could achieve and to provide reference and guidance for future research and development of HP-TES systems for GEB applications.