This project will develop high efficiency air-to-water heat pump technologies, and further develop low-cost, polymer water-to-air heat exchangers that have improved performance (effectiveness/pressure drop) at lower cost.  System will have a primary loop consisting of flammable low GWP refrigerants and secondary loop using water. Utilize primary secondary loops to isolate flammable refrigerants. Additional thermal storage capabilities to manage load shift as well as domestic hot water.