Water heating unit with integral thermal energy storage

Abstract

A water heater is provided which includes a heat exchange unit including heat exchange pipes filled with a phase change material. The phase change material has a freezing/melting temperature from about 58° C. to about 62° C. The water heater provides significantly greater thermal energy storage than conventional water heaters, and the excess heating capacity may be used for residential heating applications by using the water heater in combination with a liquid to air heat exchanger.

1 . A water heater comprising:
 a shell,   a cold water inlet for receiving water in said shell, and a hot water outlet for transporting heated water from said shell;   at least one heating element in said shell for heating said water; and   a heat exchange unit in said shell comprising a plurality of heat exchange pipes positioned therein, said pipes containing a phase change material and being positioned such that the water heated by said at least one heating element flows around said pipes and heats said phase change material; and wherein the heat stored in said phase change material is transferred through said pipes to said water.   
     
     
         2 . The water heater of  claim 1  including first and second heating elements positioned at the top and bottom of said water heater. 
     
     
         3 . The water heater of  claim 1  wherein said phase change material comprises a linear crystalline alkyl hydrocarbon comprising about 85% by weight of a linear crystalline alkyl hydrocarbon having chain lengths from C 20  to C 24  and about 15% by weight of a linear crystalline alkyl hydrocarbon having a mixture of carbon chains having an odd number of carbons and an even number of carbons having lengths from C 22  to C 26 . 
     
     
         4 . The water heater of  claim 3  wherein said phase change material has a melting/freezing temperature between about 58° C. to 62° C. 
     
     
         5 . The water heater of  claim 1  wherein said phase change material includes from about 5 to 10% by weight low density polyethylene. 
     
     
         6 . The water heater of  claim 1  wherein said phase change material includes from about 1 to 30% by weight carbon black. 
     
     
         7 . The water heater of  claim 1  wherein said phase change material includes from about 0.05 to 0.5% by weight of a surfactant. 
     
     
         8 . The water heater of  claim 7  wherein said surfactant comprises polyethylene glycol monolaurate. 
     
     
         9 . The water heater of  claim 1  wherein said phase change material includes from about 0.05 to 0.5% by weight zinc stearate. 
     
     
         10 . The water heater of  claim 1  wherein said phase change material comprises stearyl alcohol. 
     
     
         11 . The water heater of  claim 10  wherein said phase change material has a melting/freezing temperature between about 58° C. to 60° C. 
     
     
         12 . The water heater of  claim 1  further including a layer of insulation on the exterior surface of said shell. 
     
     
         13 . The water heater of  claim 12  wherein said insulation is vacuum panel insulation having an R value of about 50 to 60 per inch of thickness. 
     
     
         14 . The water heater of  claim 1  wherein said phase change material is in the form of a molded cylinder. 
     
     
         15 . The water heater of  claim 1  wherein said heat exchange pipes comprise a metal selected from copper, stainless steel, and glass-coated steel. 
     
     
         16 . The water heater of  claim 1  wherein said heat exchange pipes have an outer diameter of from about 0.5 to about 2.5 inches. 
     
     
         17 . The water heater of  claim 1  wherein said heat exchange pipes include a cap at each end such that said phase change material is sealed therein. 
     
     
         18 . The water heater of  claim 1  further including a solenoid valve in conjunction with said water inlet or outlet to provide pulsatile flow of said water. 
     
     
         19 . The water heater of  claim 1  having a three-dimensional rectangular configuration. 
     
     
         20 . The water heater of  claim 1  having a cubic configuration. 
     
     
         21 . A home heating system comprising the water heater of  claim 1  and a liquid to air heat exchanger; said liquid to air heat exchanger including a hot water inlet for receiving heated water from said water heater, an air inlet and air outlet.