Patent ID: 8438864

Claim:
A method for increasing efficiency of a transcritical heat pump water heater system, comprising; compressing a transcritical refrigerant to a supercritical point and passing the refrigerant through a gas cooler that is wrapped at least partially around a water storage tank, wherein the refrigerant transfers heat to water stored in the tank; discharging hot water from the storage tank proximate to a top of the tank, and introducing cold water into the tank proximate to a bottom of the tank; wherein the refrigerant is directed to flow through the gas cooler from a top point to a lowermost point in a flow direction such that the refrigerant exits the gas cooler proximate to the bottom of the tank at a location of the coldest water within the storage tank; wrapping the gas cooler as a continuous member in a series of coils around and in contact with the storage tank; stratifying a pronounced temperature gradient of the water within the storage tank to maintain a relatively cold water layer proximate the bottom of the tank by wrapping a greater number of coils around the top portion as compared to bottom portion of the tank proximate to the refrigerant exit; wherein the top portion of the tank above a mid-level point has a high density section of coils of the gas cooler as compared to the bottom portion of the tank; defining a section of the tank below the high density section of coils in the top portion of the tank that is essentially void of coils of the gas cooler; and providing an additional section of coils of the continuous member below the void section of the tank proximate to the refrigerant exit.