Heat transfer for heat pump water heater

Abstract

A water heater is provided that improves heat transfer between the coils of the heat exchanger of a refrigerant-based heating system and the water in the heater's water tank. Grooves can be added to the exterior of the water tank. The coils of the heat exchanger are positioned within the grooves on the exterior surface of the water tank. Additional features may also be used to further improve heat transfer. Methods for constructing such water heater are also provided.

What is claimed is: 
     
         1 . A water heater, comprising:
 a tank for holding water, said tank comprising a cylindrically-shaped wall connected between a pair of end portions, said tank defining axial, circumferential, and radial directions, the cylindrically-shaped wall having an exterior surface defining a plurality of circumferentially-extending grooves spaced-apart along the axial direction; and   a refrigerant-based heating system configured for heating water in said tank, said heating system comprising a heat exchanger that includes a plurality of coils for the flow of heated refrigerant, the coils extend around said tank and are positioned within the plurality of grooves defined by the exterior surface of the cylindrically-shaped wall.   
     
     
         2 . A water heater as in  claim 1 , further comprising a thermal paste that affixes the coils to the grooves and enhances heat transfer. 
     
     
         3 . A water heater as in  claim 1 , wherein the coils are affixed to the grooves by welding the coils to said tank. 
     
     
         4 . A water heater as in  claim 1 , wherein the coils extend around said tank in a helical manner. 
     
     
         5 . A water heater as in  claim 1 , wherein said refrigerant based heating system is mounted to one of the pair of end portions of said tank. 
     
     
         6 . A water heater as in  claim 1 , wherein the grooves have a depth along the radial direction that is less than the diameter of the coils, so that the coils extend above the external surface of said tank. 
     
     
         7 . A water heater as in  claim 1 , wherein the grooves have a width along the axial direction approximately equal to the diameter of the coils. 
     
     
         8 . A water heater as in  claim 1 , wherein the coils are comprised of a metal. 
     
     
         9 . A water heater as in  claim 1 , wherein the coils are comprised of copper. 
     
     
         10 . A water heater as in  claim 1 , wherein said tank is comprised of a metal. 
     
     
         11 . A water heater as in  claim 1 , further comprising an outer jacket that surrounds the cylindrically-shaped wall of said tank and defines an annular space between the exterior surface of the cylindrically-shaped wall and said outer jacket. 
     
     
         12 . A water heater as in  claim 11 , further comprising insulation positioned in the annular space. 
     
     
         13 . A water heater as in  claim 12 , wherein the insulation comprises a foamed-in insulation. 
     
     
         14 . A water heater as in  claim 1 , a plurality of heat transfer features projecting along the radial direction from an interior surface of said tank, said heat transfer features extending longitudinally along the axial direction of the tank and providing additional surface area for heat transfer with water contained in said tank. 
     
     
         15 . A method for making a tank with grooves, comprising:
 providing a metal sheet having a desired thickness, the metal sheet having a flat outer surface, the metal sheet defining lengthwise and widthwise directions, and the metal sheet beginning with a first edge and ending with a second edge, each approximately perpendicular to the lengthwise direction;   creating a plurality of grooves in the flat outer surface of the metal sheet, the grooves running in the lengthwise direction of the metal sheet, the grooves spaced apart in the widthwise direction, and the grooves beginning at the first edge of the metal sheet and ending at the second edge of the metal sheet;   rolling up the metal sheet in such a manner so as to form a cylindrically-shaped wall of a tank, wherein the grooves are on the outer surface of the cylindrically-shaped wall;   joining together said metal sheet in the form of the cylindrically-shaped wall of the tank; and   adding a pair of end portions to complete the formation of the tank.   
     
     
         16 . A method for making a tank with grooves as in  claim 15 , further comprising the step of aligning the grooves of the first edge of the metal sheet with the grooves of the second edge of the metal sheet so as to form continuous grooves that extend along the outside of the cylindrical wall in a helical manner. 
     
     
         17 . A method for making a tank with grooves, comprising:
 providing a tank having a cylindrically-shaped wall connected between a pair of end portions, the tank defining axial and radial directions, the cylindrically-shaped wall having an exterior surface and an interior surface; and   creating a plurality of grooves along the cylindrically-shaped wall of the tank, spaced apart along the axial direction, and providing grooves along the interior surface and exterior surface of the tank.   
     
     
         18 . A method for making a tank with grooves as in  claim 17 , wherein the grooves wrap around the cylindrically-shaped wall of the tank in a helical manner and have a rounded or semi-circular shape. 
     
     
         19 . A method for making a tank with grooves as in  claim 17 , wherein the metal sheet is comprised of steel. 
     
     
         20 . A water heater, comprising:
 a tank for holding water, said tank comprising a cylindrically-shaped wall connected between a pair of end portions, said tank defining axial, circumferential, and radial directions;   a plurality of heat transfer features projecting along the radial direction from an interior surface of said tank, said heat transfer features extending longitudinally along the axial direction of the tank and spaced apart about the circumferential direction; said heat transfer features providing additional surface area for heat transfer with water contained in said tank; and   a refrigerant-based heating system configured for heating water in said tank, said heating system comprising a heat exchanger that includes a plurality of coils for the flow of heated refrigerant, the coils extend around said tank on the cylindrically-shaped wall.