Heat pump using phase change materials

Abstract

The present invention is directed toward compositions of phase change materials derived from fats and oils, and the utilization of such phase change materials in heating, venting, and air conditioning (HVAC) systems. More particularly, the utilization of such phase change materials in a heat pump or air conditioner to significantly increase the efficiency of heat exchange with the surrounding environment. Various embodiments are disclosed including energy storage devices having phase change materials encapsulated between sheets of material to reduce stresses associated with freezing and thawing of the phase change material. A preferred heat pump apparatus utilizes the phase change material in the evaporator, and a smart fan mode of operation to circulate outside air through the evaporator based on approach temperature rather than compressor operation.

I claim:  
     
         1 . A heat pump apparatus utilizing a phase change material chemical for heating a building, comprising: 
 a condenser that functionally releases thermal energy into a building;    a compressor that compresses a working fluid;    an evaporator that takes in thermal energy, and    a fan that directs air through the evaporator;    said evaporator having at least one conduit for flow of the working fluid through the evaporator, at least one sealed cavity containing a phase change material chemical, and at least one air path through which surrounding air can flow and transfer heat to said evaporator.    
     
     
         2 . The heat pump apparatus according to  claim 1 , wherein 
 said at least one conduit has an outer perimeter with a cumulative area, at least 10% of which is in direct contact with said phase change material chemical.    
     
     
         3 . The heat pump apparatus according to  claim 1 , wherein 
 the mass of phase change material chemical contained in said sealed cavity of said evaporator is at least 10 times greater than the mass of working fluid flowing through said evaporator.    
     
     
         4 . The heat pump apparatus according to  claim 1 , wherein 
 said at least one conduit has a mean internal hydraulic radius of from about 0.02 inches to about 1 inch that is defined by the conduit wall; and    heat flows from outside the conduit wall to said working fluid inside said conduit, and the ratio of the cumulative thermal resistance between said working fluid and said phase change material chemical is from about 0.1 to about 10 times the cumulative thermal resistance between said working fluid and the air in said air path.    
     
     
         5 . The heat pump apparatus according to  claim 1 , wherein 
 said at least one conduit has an outer perimeter with a cumulative area, at least 20% of which is in direct contact with said phase change material chemical; and    at least 10% of which is in direct contact with the air in said air path.    
     
     
         6 . The heat pump apparatus according to  claim 1 , further comprising: 
 a housing that contains and connects said evaporator and fan;    said housing having an outer surface with a surface area, at least 50% of which functions to provide insulation resistant to heat flow, and as a sealing surface resistant to air flow.    
     
     
         7 . The heat pump apparatus according to  claim 6 , wherein 
 said fan directs air through said housing; and further comprising: 
 shutter means for blocking air from flowing through said housing when said fan is not running.  
   
     
     
         8 . An apparatus utilizing a phase change material chemical for exchanging heat between a fluid and the phase change material chemical, comprising: 
 a phase change material chemical encapsulated between sheets of thermally conductive material.    
     
     
         9 . The apparatus according to  claim 8 , wherein 
 said sheets are laminated to seal said phase change material chemical therebetween.    
     
     
         10 . The apparatus according to  claim 8 , wherein 
 said phase change material chemical comprises multiple pouches of said phase change material chemical.    
     
     
         11 . The apparatus according to  claim 8 , further comprising: 
 a container having an entrance and exit for fluid flow; and    said sheets having said phase change material chemical encapsulated therebetween are suspended in said container the path of fluid flowing between said entrance and said exit.    
     
     
         12 . The apparatus according to  claim 11 , wherein 
 said sheets are suspended from an upper end thereof in said container and disposed vertically therein.    
     
     
         13 . The apparatus according to  claim 11 , wherein 
 said fluid flowing through said container is air.    
     
     
         14 . The apparatus according to  claim 8 , further comprising: 
 a sheet of porous material disposed between said sheets to facilitate even fluid flow and improved heat transfer between the fluid and said phase change material chemical.    
     
     
         15 . The apparatus according to  claim 8 , further comprising: 
 at least one conduit disposed between said sheets for conducting a working fluid therethrough having an exterior surface in contact with said phase change material chemical in heat exchanging relation to function as an evaporator.    
     
     
         16 . A method of exchanging heat with outside air in an outdoor heat pump unit having an evaporator/condenser and at least one conduit for conducting a flow of working fluid through the evaporator/condenser, and a fan that directs air through the evaporator/condenser, comprising the steps of: 
 providing a mass of material having a heat capacity greater than 30 kJ/° C. in contact with the working fluid conduit in thermal exchange relation, said mass of material absorbs heat and releases heat; and    operating said fan based on the temperature difference between the average temperature of said at least one conduit and the outside ambient temperature; whereby    said evaporator/condenser serves as an evaporator in a heating mode of operation, and as a condenser in a cooling mode of operation.    
     
     
         17 . The method according to  claim 16 , wherein 
 in said cooling mode, said fan is switched on when the outside ambient temperature is at least 3° F. cooler than the average temperature of said at least one conduit.