Abstract:
An apparatus for providing a condensing side-arm water heater with improved efficiency. The condensing side-arm element recirculates exhaust gases into heating the cooler part of a water heater tank by the thermosiphon (or buoyancy) effect in a counterflow configuration, thus increasing efficiency of the water heater.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority as a continuation application to PCT International Patent Application No. PCT/US2007/072160, filed Jun. 26, 2007, which in turn claims priority to U.S. Provisional Patent Application Ser. No. 60/805,811, filed Jun. 26, 2006, both of which are hereby incorporated in their entireties by reference. 
     
    
     STATEMENT REGARDING FEDERAL FUNDING 
       [0002]    This invention was made with U.S. Government support under Contract Number DE-AC02-05CH11231 between the U.S. Department of Energy and The Regents of the University of California for the management and operation of the Lawrence Berkeley National Laboratory. The U.S. Government has certain rights in this invention. 
     
    
     REFERENCE TO A COMPUTER PROGRAM 
       [0003]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of the Invention 
         [0005]    The present invention relates generally to water heating, and more specifically to high efficiency water heating, and most specifically to condensing side-arm water heaters. 
         [0006]    2. Description of the Relevant Art 
         [0007]    Both gas and electric water heaters are well known. It is believed that condensing side-arm gas-fired water heaters has not been done. Such a device dramatically increases the efficiency of water heating at low cost. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    In one embodiment, this invention provides for a condensing side-arm water heater, comprising: a) a tank; b) a recirculation pipe fluidly connected to an upper and lower aperture in the tank; c) a heat exchanger in thermal contact with the recirculation pipe; d) a burner for heating the water, that produces heated combustion products; e) an exhaust system that takes the heated combustion products from the burner, and transfers a fraction of the heat to the heat exchanger; i) the exhaust system comprising: (1) an exhaust fan blower; (2) a drip pipe; (3) and an air inlet; f) whereby the heated combustion products pass through the exhaust system, condensing water vapor from the combustion byproducts, and expelling the condensed water vapor through the drip pipe. It should be noted that the burner may burn anything that produces heat when oxidized in air, examples would include, oil, gas, LP gas, propane, etc. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]    The invention will be more fully understood by reference to the following drawings, which are for illustrative purposes: 
           [0010]      FIG. 1  is a traditional electric water heater schematic. 
           [0011]      FIG. 2  is a condensing side-arm gas-fired water heater. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Definitions 
       [0012]    “Side-arm” means external to a main reservoir tank, physically appears as an arm on the side. 
       Introduction 
       [0013]    In this application methods for increasing the efficiency of combusted water heating through use of the combustion byproduct heat. 
         [0014]    This invention would be a condensing sidearm heat exchanger synergistically attached to a water heater tank. The heated water would be transferred from a side-arm heat exchanger to the tank by thermosiphonic action, or through heat-induced density changes in the water acting as a driver. No mechanical pumps would be necessary. The water tank could be an electric resistance tank with the elements removed. 
         [0015]    To retrofit an existing gas water heater, the sidearm heater could be plumbed into the openings where the original elements had previously been placed. 
         [0016]    For highest efficiencies, the heat exchanger would have sufficient heat transfer so as to condense the water vapor present in the combustion products. The combustion products would be too cool to buoyantly self-vent, so an electric fan would be used to vent the combustion products. By using a fan, the combustion products could be pulled down through the heat exchanger. The bottom of the heat exchanger would be connected to the lower end of the tank. The combustion products would exit the heat exchanger at the lower end where they would be cooled by the coldest water in the tank. By using thermosiphon action to transfer heated water to the tank, the flow rate will be slow enough to preserve stratification in the tank. This keeps cold water in the bottom of the tank even as the rest of the water in the tank heats up. 
         [0017]    Because the combustion products exit the heat exchanger where the cold water enters, the heat transfer efficiency is high, as is usually the case in counterflow heat exchangers. This will maximally cool the combustion products and condense as much of the water vapor in the combustion products as possible. The combustion products are cool enough so they can be vented to the outdoors through an attached plastic pipe. Inlet air can be drawn in through plastic pipe from outdoors as well. This would be an isolated combustion system thereby removing accidental sources of ignition of flammable vapors. Flammable vapor ignition resistant designs will not have to be used on this water heater. If the burner is made small enough (perhaps as low as 15 kBtu/hr), the motor on the draft inducer fan can be powered with low-voltage electricity. This would enable installers to provide power to the water heater without needing the services of an electrician. 
         [0018]    Because combustion is fan assisted, it may be possible to use one of the low NO x  burners that Robert Cheng et al. of U.S. Pat. No. 5,879,148 have invented. Thus, not only would the water heater be much more efficient than current water heaters, it would also have much lower emissions. There would be two thermostatic controls on the water heater. One, near the top of the heat exchanger would decrease the resistance to water flow through the heat exchanger as the temperature rises. This control would allow water to move through the heat exchanger more quickly, so that it acquires less heat and enters the water heater at a temperature that is not quite so hot. Conversely, the thermostatic control would increase resistance to water flow as temperature drops. This control will keep the heated water in the top of the tank at a constant temperature. The other thermostatic control would be at the bottom of the heat exchanger. When the water temperature at this point rises above a setpoint, gas flow to the burner would be stopped, and then the draft inducer fan would be turned off. When the water temperature at this point gets cool enough, the fan, igniter and burner would all be started. 
         [0019]    This invention allows water to be heated much more efficiently (˜90% compared to current typical water heater efficiencies of 60%). 
         [0020]    The temperature of water in the heat exchanger does not increase until the tank is full of hot water. 
       Embodiments of the Condensing Side-Arm Water Heater 
       [0021]    Refer now to  FIG. 1 , which shows in a cut away view a few of the salient features of a prior art electrical water heater  100 . The electrical water heater  100  has an interior heated space  110  that is typically filled with water. The heated space  110  is substantially surrounded by insulation  120 . An upper electrical heating element  130  and lower electrical heating element  140  provide heat to the heated space  110 , and are inserted through and secured to the upper threaded aperture  150  for the upper element  130 , and the lower threaded aperture  160  for the lower heating element  140 . 
         [0022]    It should be noted that for optimal operation, the heat exchanger/burner assembly lower threaded aperture  160  should be mounted as low as possible on the tank, perhaps even extending below the bottom of the tank (which is not shown in  FIG. 1 ). Of course in the case if retrofitting an electrically heated tank, this is difficult or impossible to achieve. 
         [0023]    Although here we initially discuss retrofitting an electrical water heater, the invention disclosed here could be made from non-electrical water heater components, and suitably combined. 
         [0024]      FIG. 2  shows a side-arm condensing water heater  200  based on the retrofitting or new construction of the electrical water heater  100  of  FIG. 1 . In the side-arm system  200 , an interior space  205  is filled with water, which is insulated from external temperatures by insulation  210 . In this instance, the upper  130  and lower  140  electrical water heating elements have been removed. Instead, a recirculation line  215  forms a loop between the upper aperture  270  and the lower aperture  275 , which may have contained the upper  130  and lower  140  electrical water heating elements from  FIG. 1 , or may just be new apertures in a tank as built. 
         [0025]    The recirculation line  215  has surrounding it heat transfer elements  220  that are in good thermal contact with the recirculation line  215 . A supply of air enters through aperture  225 , to provide oxidizer to a burner  230 . Combustion byproducts are pulled down through the heat transfer elements  220 , and pulled through an exhaust pipe  235  that pumps the exhaust byproducts to an exit vent  250  by virtue of a fan blower  240 . One of the combustion byproducts is that of condensed water vapor, which drips onto a collection area  255  below the heat transfer elements  220 . The condensate is then exhausted through a drip pipe  260 . An insulated housing  265  surrounds the heat transfer elements  220 , and the burner  230 . The insulated housing  265  is attached to the insulation  210  of the interior space  205 . 
         [0026]    Power for the fan blower  240  may be supplied externally, though may better be provided by a thermopile supply  280  that would be mounted in close proximity to the burner  230 . Wires are not shown to the fan blower  240 , as such wiring would be obvious. 
         [0027]    Operation of the system is controlled by an upper thermostat at  270  and lower thermostat at  275 . 
         [0028]    This invention is intended as a replacement for currently existing residential gas water heaters. 
       CONCLUSION 
       [0029]    All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application were each specifically and individually indicated to be incorporated by reference. 
         [0030]    The description given here, and best modes of operation of the invention, are not intended to limit the scope of the invention. Many modifications, alternative constructions, and equivalents may be employed without departing from the scope and spirit of the invention.