Researchers in the Department of Mechanical Engineering and Mechanics at Drexel University have developed an energy-efficient, standalone, single heat pump water heater.  Electric heat pump water heaters use about half of the energy of conventional electric resistance or gas water heaters, but they lack widespread market adoption due to the higher initial equipment cost that results from having a backup electric heater.  The need for a backup heater precludes their use in cold locations, as the minimum environmental temperature for operation is above 45°F.  Lower temperatures impede effective heat transfer to the hot water tank from the heat pump water heater. 

In the proposed device by the Cho lab, the heat pump system can operate in a wider range of temperatures due to the addition of an electric heater that heats the environmental medium (i.e., inlet air) prior to contact with the evaporator coil, where the refrigerant is stored.  The system may include a plasma pulse-spark system to facilitate the removal of scale deposits on the surfaces of the condenser coil in the heat pump water heater.