Drainwater heat recovery system

Abstract

A fluid-to-fluid heat exchanger for use where two fluid streams may be of indeterminate composition, temperature, and flow rate, and, where the two fluid streams may flow at different rates and at different times. Such conditions are found, for example, in the flow patterns of a building's hotwater, cold feed water for a water heater, and drainwater. As defined for heat recovery from drainwater, the present invention comprises a first, central, straight-through heat exchanger tube for cooling flowing drainwater, a second heat exchanger to heat cold water encircling and spaced from the first, and a non-pressurized reservoir between first and second heat exchangers permanently filled with water in thermal contact with first and second heat exchangers. Submerged in the reservoir water there is at least one insulated convection chamber, of small volume, enclosing first heat exchanger with a convection opening uppermost. Opening allows upward convection and therefore heat transfer when drainwater heats convection chamber water making it lighter. Convection and heat transfer ceases when drainwater cools convection chamber water making it heavier, blanketing drainwater heat exchanger in a small volume of cold water. This one-way heat transfer prevents heat loss from remaining reservoir water to cold drainwater. With convection chambers inverted to have convection opening bottommost, the device serves to make coldwater, for drinking, as cold as possible by transferring unwanted heat to colder drainwater. Used in series, heat recovery and fresh water cooling can both be accomplished. Units for horizontal and vertical installation are disclosed.

I claim:  
     
         1 . In a plumbing system for a building, the plumbing system including a cold water supply and a water disposal conduit, the improvement comprising an apparatus to transfer heat from waste water in said water disposal conduit to said cold water, said apparatus comprising a reservoir; 
 a heat transfer fluid substantially filling said reservoir;    a first heat exchanger for drainwater in thermal contact with said fluid;    a second heat exchanger having cold water from said cold water supply in thermal contact with said fluid;    convection chamber means partially surrounding said first heat exchanger, said convection chamber means having an opening therein allowing convection movement of said heat transfer fluid into and out of said convection chamber, said opening being located only at an upper portion of said convection chamber means,    the arrangement being such to heat said cold feed water by permitting convection of said fluid into and out of said convection chamber when said drainwater is hotter than said fluid, and, minimizing flow of said heat transfer fluid out of said convection chamber when said drainwater is colder than said heat transfer fluid.    
     
     
         2 . The improvement of    claim 1    wherein said plumbing system includes means for heating said cold water, said apparatus being connected such that cold water passes through said first heat exchange means prior to entering said means for heating said cold water.  
     
     
         3 . The improvement of    claim 1    wherein said second heat exchange means is connected to a water disposal conduit from a heat generating appliance.  
     
     
         4 . The improvement of    claim 1    wherein said first heat exchange means is connected to a toilet.  
     
     
         5 . The improvement of    claim 1    wherein said first heat exchange means is connected to a washing machine.  
     
     
         6 . The improvement of    claim 1    wherein said building is a residential house.  
     
     
         7 . The improvement of    claim 1    wherein said heat transfer fluid is water.  
     
     
         8 . The improvement of    claim 1    further including means to disturb the boundary layer of liquid about at least one of said first and second heat exchange means.  
     
     
         9 . The improvement of    claim 1    wherein at least one of said first and second heat exchange means comprise at least one tube having a plurality of inwardly directed dimples to thereby create turbulence in liquid flowing therethrough, said dimples being spaced sufficiently close together to provide continuous turbulence in said liquid passing therethrough.  
     
     
         10 . The improvement of    claim 1    further including a plurality of said apparatuses connected in a plumbing system, said apparatuses being connected in series or in parallel or in series-parallel.  
     
     
         11 . A heat transfer system suitable for recovering heat from waste water comprising: 
 a reservoir having a heat transfer fluid therein;    a first heat exchanger for receiving said waste water within said reservoir; said first heat exchanger having a first heat exchanger inlet and a first heat exchanger outlet;    a second heat exchanger within said reservoir in thermal contact with said heat transfer fluid, said second heat exchanger having a first heat exchanger inlet and a second heat exchanger outlet;    convection chamber means at least partially surrounding said first heat exchanger, said convection chamber means permitting convective movement of said heat transfer fluid from adjacent said first heat exchanger when said waste water flowing therethrough is warmer than said heat transfer fluid, said convection chamber means being arranged such that convective movement of said heat transfer fluid from adjacent said first heat exchanger is impeded when said waste water flowing therethrough is colder than said heat transfer fluid.    
     
     
         12 . The heat transfer system of    claim 11    wherein said first heat exchanger includes a first heat exchanger conduit extending in a generally horizontal direction, said second heat exchanger including a second heat exchanger conduit also extending in a generally horizontal direction, said first heat exchanger conduit being located below said second heat exchanger conduit in said reservoir.  
     
     
         13 . The heat transfer system of    claim 12    wherein said convection chamber means comprises a horizontally extending convection chamber encircling at least an upper portion of said horizontally extending first heat exchanger conduit.  
     
     
         14 . The heat transfer system of    claim 13    further including spacers spacing said convection chamber from said first heat exchanger conduit.  
     
     
         15 . The heat transfer system of    claim 13    wherein said convection chamber has a plurality of longitudinally extending slots formed therein.  
     
     
         16 . The heat transfer system of    claim 11    wherein said first heat exchanger comprises a vertically extending conduit within said reservoir, said second heat exchanger comprising a coiled conduit coiled about said first heat exchanger conduit and spaced therefrom.  
     
     
         17 . The heat transfer system of    claim 16    wherein said convection chamber means comprises a plurality of upwardly and outwardly extending flanges secured to said first heat exchanger conduit.  
     
     
         18 . In a plumbing system for a building, the plumbing system including a cold water supply and a water disposal conduit, the improvement comprising an apparatus to transfer heat from said cold water to said waste water in said water disposal conduit, said apparatus comprising a reservoir; 
 a heat transfer fluid substantially filling said reservoir;    a first heat exchanger for drainwater in thermal contact with said fluid;    a second heat exchanger having cold water from said cold water supply in thermal contact with said fluid;    convection chamber means partially surrounding said first heat exchanger, said convection chamber means having an opening therein allowing convection movement of said heat transfer fluid into and out of said convection chamber, said opening being located only at a lower portion of said convection chamber means,    the arrangement being such to cool said cold feed water by permitting convection of said fluid into and out of said convection chamber when said drainwater is colder than said fluid, and, minimizing flow of said heat transfer fluid out of said convection chamber when said drainwater is hotter than said heat transfer fluid.    
     
     
         19 . An apparatus for exchanging heat between drainwater and freshwater comprising, 
 a first heat exchanger comprising, 
 tube means having central portion for heat transfer and having end portions for connection to a supply of drainwater,  
   a second heat exchanger comprising tube means having central portion for heat transfer and having end portions for connection to a supply of freshwater,    reservoir means separating said first and second heat exchangers, 
 said reservoir means substantially filled with a fluid in thermal contact with said first and second heat exchangers,  
   at least one convection chamber submerged in said fluid comprising, 
 wall means,  
 said wall means being thermally insulative,  
 said wall means enclosing at least a portion said central portion said first heat exchanger,  
 said wall means including at least one convection opening,  
   the whole arranged to control the direction of heat transfer between drainwater and freshwater by orienting said convection opening upwardly or downwardly.