Low-Charge R290 Modular Heat Pump System Using Thermal Storage

Two key challenges to transitioning heating processes to electricity are improving the efficiency of heat pump systems, especially at high temperature lift conditions, and using low-charge sustainable refrigerant. A modular cold-climate heat pump system (ccHP) with thermal storage, which can efficiently, and cost-effectively serve space heating, space cooling, and water heating has been designed. This heat pump system consists of a factory-charged propane (R290) modular outdoor unit, connected through secondary glycol loops to different end-use modules selected and tailored to the climate and requirements of the specific building. These modules are an auxiliary thermal energy storage (TES), a hot water tank (WT), and an indoor air handling unit (AHU). They can be installed using low-cost, low-tech equipment with low-skill labor. One innovation of this system lies in the development of a multiple segment heat exchanger (MSHX) composed of a de-superheater, a condenser, and a sub-cooler section in one component. The heat pump system works under different operating modes, including typical heating and cooling modes, but also modes th at use different sections of the MSHX to charge or discharge the thermal storage, or heat domestic hot water. This paper describes the simulation of this new MSHX and of the ccHP. The proposed system is first compared to a typical heat pump, then we simulated this ccHP model, including the TES and AHU modules , under various operating conditions and modes. It shows an increase in efficiency and lowers the peak demand by using thermal storage.