Heat Pump Water Heater, Wrapped-Coil Tank, Low GWP Refrigerants, Insulation, Thermal Stratification
Domestic water heating accounts for 18% of all residential and commercial building site energy used in the United States. Heat pump water heater is one of the most efficient water heating technologies compared to other conventional electric resistance or gas based water heating technologies. For heat pump water heaters, the water in the storage tank absorbs heat rejected by the condenser of the heat pump system. To accomplish this indirect heat transfer, condenser in form of a coil is wrapped around the water tank and the whole assembly is covered with thermal insulation. Tank insulation plays an important role in controlling the amount of heat loss from the tank and from the condenser coil and consequently the thermal stratification inside the tank is continuously impacted by the heat loss to the environment. The thermal stratification is critical to achieve improved Unified Energy Factor (a performance parameter often used to characterize the water heater efficiency). This current study is focused on the impact of thermal insulation over the wrapped tank coil water heater on the water stratification inside the storage tank. The various thermal-physical properties of the insulation material and thickness will be studied and their potential effect on water heating process will be determined using CFD techniques. The boundary conditions will be established based on the refrigerants’ (R32, R1234ze and R1234yf) behavior inside the condenser tube as it goes through super-heated, two-phase flow and sub-cooled phased.