Abstract:
A dual fuel—gas fuel and electric heat pump—water heater is provided that captures waste heat from the exhaust flue of the gas fuel heating system and utilizes it in the evaporator of the electric heat pump. Multiple mechanisms are disclosed for the transfer of heat from the exhaust flue gases to the evaporator. Heat from the exhaust gas that would otherwise be lost is used to help heat refrigerant in the evaporator to improve the efficiency of the system. This heat can also be used to prevent or remove frozen condensate on the evaporator.

Description:
FIELD OF THE INVENTION 
       [0001]    The subject matter of the present disclosure relates generally to a dual fuel water heater designed to transfer waste heat from an exhaust flue of a gas fuel heating system to an evaporator of an electric heat pump. 
       BACKGROUND OF THE INVENTION 
       [0002]    Water heaters can provide for the heating and storage of water to be used in, e.g., a residential or commercial structure. While water heaters can be provided in a variety of shapes and sizes, a typical shape includes an elongated cylindrical tank. In some water heaters, the tank may be configured for a vertically upright position and be surrounded by insulation and an exterior wrapper or jacket. A heat source is provided for raising the temperature of water in the tank. The heat energy may be supplied by, e.g., gas burners, electrically-resistant coils, an electric heat pump using a refrigerant cycle, or a combination thereof. 
         [0003]    In one construction, a water heater may utilize both gas fuel burners and an electric heat pump using a refrigerant cycle to heat the water in the tank. The gas fuel heating system may place gas burners underneath the tank and provide thermal energy to the tank through combustion of the gas fuel. Additionally, the electric heat pump may wrap a plurality of coils around the cylindrically-shaped exterior wall of the water tank. In this configuration, the coils serve as a heat exchanger, also referred to as a condenser, through which hot refrigerant flows around the tank. This configuration enables heat transfer from the hot refrigerant, through the coils and the tank walls, and then to the water. 
         [0004]    Certain challenges exist with this construction, however. Such construction, for example, can have inefficiencies as significant heat loss can occur from the gas fuel heating system in form of exhaust gas exiting through the exhaust flue. Additionally, when a water heater of this construction is operated in conditions that are near or below freezing, the condensation on the evaporator of the heat pump may freeze, impeding air flow over the evaporator. As a result, some water heaters of this construction require a reversing flow valve for the heat pump, a defrost heater, or other similar device to melt the frozen condensate on the evaporator. However, utilizing these or similar devices may lead to an inefficient water heater system and adds complexity to the manufacture and operation of the water heater. 
         [0005]    Accordingly, a dual fuel—gas fuel and electric heat pump—water heater having one or more features that can improve the efficiency of the water heater would be useful. More particularly, such a water heater that can capture and utilize the waste heat from the exhaust flue of the gas fuel heating system would be beneficial. Such a water heater that could also remedy frozen condensate on the evaporator would also be useful. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    The present disclosure provides a dual fuel—gas fuel and electric heat Pump—water heater that captures waste heat from the exhaust flue of the gas fuel heating system and utilizes it in the evaporator of the electric heat pump. Multiple mechanisms are disclosed for the transfer of heat from the exhaust flue gases to the evaporator. Heat from the exhaust gas that would otherwise be lost is used to help heat refrigerant in the evaporator to improve the efficiency of the system. This heat can also be used to prevent or remove frozen condensate on the evaporator. Multiple features as described herein may be used to further improve heat transfer as well. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention. 
         [0007]    In one exemplary embodiment, the present disclosure provides a water heater that includes a tank for holding water. It may also include a gas fuel heating system configured for heating the water in the tank. The gas fuel heating system may include an exhaust flue, wherein the exhaust flue has an exterior surface. The water heater may also include a heat pump heating system, which may also be configured for heating the water in the tank. The heat pump heating system may include an evaporator. Additionally, the water heater may include a pipe. The pipe may be in thermal communication with the exhaust flue and the evaporator and configured for transferring heat from the exhaust flue to the evaporator. The water heater may also include a fan configured for causing the flow of air past the exhaust flue and over the evaporator. 
         [0008]    In another exemplary embodiment, the present disclosure provides a water heater that includes a tank for holding water. It may also include a gas fuel heating system configured for heating the water in the tank. The gas fuel heating system may include an exhaust flue. The water heater may also include a heat pump heating system, which may also be configured for heating the water in the tank. The heat pump heating system may include an evaporator. Additionally, the water tank may include a fan configured for causing an air flow over the evaporator and past the flue so as to provide for heat transfer from the flue to the evaporator. 
         [0009]    In yet another exemplary embodiment, the present disclosure provides a water heater that includes a tank for holding water. It may also include a gas fuel heating system configured for heating the water in the tank. The gas fuel heating system may include an exhaust flue that facilitates the flow of exhaust, wherein the exhaust includes heated gases from the gas fuel heating system. The water heater may also include a heat pump heating system, which may also be configured for heating the water in the tank. The heat pump heating system may include an evaporator. Additionally, a portion of the exhaust from the exhaust flue may flow over the evaporator. 
         [0010]    These and other features, aspects, and advantages of the present disclosure will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    A full and enabling disclosure of the present disclosure, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
           [0012]      FIG. 1  is a cross-sectional side view of an exemplary embodiment of a water heater of the present disclosure. 
           [0013]      FIGS. 2 and 3  are close-up side views of two exemplary embodiments of an exhaust flue and an evaporator of a water heater of the present disclosure. 
           [0014]      FIG. 4  is a close-up, cross-sectional top view of an exemplary embodiment of an exhaust flue of a water heater of the present disclosure. 
           [0015]      FIG. 5  is a close-up side view of an exemplary embodiment of an exhaust flue of a water heater of the present disclosure. 
           [0016]      FIGS. 6 and 7  are close-up side views of exemplary embodiments of an evaporator of a water heater of the present disclosure. 
           [0017]      FIGS. 8 ,  9 , and  10  are close-up side views of three exemplary embodiments of an exhaust flue and an evaporator of a water heater of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
         [0019]      FIG. 1  provides a cross-sectional side view of an exemplary embodiment of a vertically oriented water heater  100  of the present disclosure. In this embodiment, water heater  100  includes a tank  124  for storing water. Tank  124  defines a radial direction R and a vertical direction V. In  FIG. 1 , vertical direction V runs parallel to the axial direction of tank  124 . Notably, however, in other exemplary embodiments, tank  124  may be horizontally oriented, in which case radial direction R of tank  124  would be approximately parallel with the vertical direction, and the axial direction of tank  124  would be approximately parallel with the horizontal direction. 
         [0020]    Tank  124  may be positioned within an outer jacket  98  that surrounds tank  124  to create an annular space  146  between tank  124  and jacket  98 . Insulation  126  may be provided within annular space  146  to reduce the amount of heat transfer from tank  124  to the environment. Insulation  126  may be provided as foamed-in insulation, but other materials may be used as well. 
         [0021]    Tank  124  extends between a pair of end portions or, more particularly, between a bottom portion  170  and a top portion  172 . Top portion  172  may include a water outlet  122  with associated coupling  114  and a water inlet  120  with associated coupling  116 . Coupling  114  may connect with conduit  110 , and coupling  116  may connect with conduit  112 , and each may extend through housing  102 . In turn, conduits  110  and  112  can each be fitted with couplings  106  and  108 , respectively, for connection of water heater  100  to the piping or plumbing associated with a water supply system of, e.g., a commercial or residential structure. Coupling  108  may be connected with, e.g., a pipe delivering a pressurized water supply that flows into tank  124  using dip tube  118 . In turn, heated water may be returned to such piping system through the connection provided by coupling  106 . 
         [0022]    In an alternative embodiment of the present disclosure, however, water outlet  122  may include conduit  110  welded to tank  124  and water inlet  120  may include conduit  112  welded to tank  124 , each having no separate couplings for connection to tank  124 . Additionally, instead of couplings  106  and  108 , conduits  110  and  112  may include a threaded portion and pipe nipples for connection of water heater  100  to the piping or plumbing associated with a water supply system of, e.g., a commercial or residential structure. 
         [0023]    Bottom portion  170  of tank  124  may include a circular bottom edge  142  and a bottom wall  128 . Beneath bottom wall  128  is a gas fuel heating system  224 , which may include a combustion chamber  208 . Within combustion chamber  208  may be one or more gas burners  206 . Gas burner  206  may be constructed of a circular plate with a series of burner holes  222  positioned along an edge of the circular plate. Gas fuel and air may enter the burner through a burner inlet  220  positioned at a side of the gas plate or, alternatively, burner inlet may be positioned underneath the circular plate. Gas burners  206  heat the water in tank  124  by providing thermal energy to tank  124  through combustion of a gas fuel. A separate pilot light may be provided to ignite the gas fuel and air as it exits burner holes  222 , such that flames are provided that come up and around the circular plate. The gas fuel may be supplied by, e.g., a gas line from consumer&#39;s house supply  214 , which in turn may be connected to a gas control mechanism  216 , configured for providing the gas fuel to burners  206  through gas line  218 . Other constructions and configurations of gas fuel heating system  224 , as are well known in the art, are contemplated by the present disclosure as well. 
         [0024]    The exhaust air from the combustion of gas fuel in combustion chamber  208  exits through an exhaust flue  174 . Exhaust flue  174  may extend through the center of tank  124  and out through housing  102 , where it may then connect with a vent to, e.g., the consumer&#39;s chimney  204  using a draft hood  202 . Exhaust flue  174  may have a diameter that is approximately twice the size shown in  FIG. 1 , such as from between 3 inches and 5 inches. Additionally, exhaust flue  174  may include one or more restrictive baffles (not shown) to slow down and create turbulence in the exhaust gas. This may allow for increased heat transfer from exhaust flue  174  to the water in tank  124 . 
         [0025]    Mounted to top  172  is housing  102 , which houses an electric heat pump heating system  104  using a refrigerant cycle. Heat pump heating system  104  may be used to heat the water in tank  124  in conjunction with or in alternative to gas fuel heating system  224 . Heat pump heating system  104  employs coils  130  to circulate hot refrigerant around tank  124  and heat water in tank  124 . Coils  130  operate as a heat exchanger or, more particularly, as a condenser for heat pump heating system  104 . As will be understood by one of skill in the art, compressed refrigerant vapor flowing through coils  130  condenses to a liquid in coils  130  to provide heat to water in tank  124 . The refrigerant in coils  130  then flows through an expansion valve, wherein the refrigerant is depressurized and the temperature of the refrigerant drops. The refrigerant then flows through an evaporator  178 , wherein air may be moved past evaporator  178  to begin warming the refrigerant prior to the refrigerant being compressed and sent back around tank  124 . A fan  226 , configured for creating a flow of air over evaporator  178  in an air flow direction F, may be provided. Water heater  100  is provided by way of example only. Using the teachings disclosed herein it will be understood that other configurations, constructions, or shapes for water heater  100  with heat pump heating system  104  and gas fuel heating system  224  may be used as well. 
         [0026]    The configuration of water heater  100  is provided by way of example only. As will be understood by one of skill in the art using the teachings disclosed herein, the present invention includes water heaters of other constructions and configurations as well. 
         [0027]    For reasons previously stated, it is desirable to capture the waste heat from exhaust flue  174  of gas fuel heating system  224  and utilize it in evaporator  178  of heat pump heating system  104 . Such a configuration will provide a heat pump heating system having increased efficiency, as well as providing increased efficiency in water heater  100  as a whole. Additionally, the waste heat from exhaust flue  174  may be utilized to defrost evaporator  178 , or prevent evaporator  178  from accumulating frost. 
         [0028]      FIG. 2  provides an exemplary embodiment of the present disclosure, wherein water heater  100  includes a heat pipe  176  to transfer waste heat from exhaust flue  174  of gas fuel heating system  224  to evaporator  178  of heat pump heating system  104 . A fan  226  is configured for creating a flow of air past exhaust flue  174  and over evaporator  178 . In one exemplary embodiment, as shown in  FIG. 2 , pipe  176  may capture waste heat from exhaust flue  174  by extending in the vertical direction along exterior surface  196  of exhaust flue  174 . Further, pipe  176  may transfer the waste heat captured from exhaust flue  174  by also extending in the vertical direction adjacent to evaporator  178 , and by being positioned upstream from evaporator  178  in the air flow direction F created by fan  226 . A variety of configurations may be used for providing heat transfer between pipe  176 , exhaust flue  174 , and evaporator  178 . 
         [0029]    In one exemplary embodiment, pipe  176  may be comprised of a solid material for transferring heat by conduction, whereas in another exemplary embodiment pipe  176  may carry a heat transfer fluid for transferring heat using the sensible and/or latent heat of the fluid. As used herein with regard to pipe  176 , the term “pipe” is not limited to a circular shape in cross-section or to a tube and refers, instead, to a medium for conducting heat as described herein. 
         [0030]    In one exemplary embodiment the transfer fluid may be a single phase fluid. As used herein, a “single phase fluid” is a material that does not change phases as it passes through pipe  176  and is heated and cooled by exhaust flue  174  and evaporator  178 . 
         [0031]    When a single phase fluid is used, pipe  176  may be positioned along exhaust flue  174  and evaporator  178  so as to allow the fluid to act as a thermosyphon, where natural convection will move fluids in pipe  176  from exhaust flue  174  to evaporator  178 . More particularly, as shown in the exemplary embodiment of  FIG. 2 , pipe  176  may extend vertically upward along axial direction A of exhaust flue  174 . This allows fluid to move upward along vertical direction V in pipe  176  as it is heated while travelling next to exhaust flue  174 . Pipe  176  may also extend vertically downward along evaporator  178  so that as fluid in pipe  176  cools and becomes more dense, it can move vertically downward along evaporator  178  and return to exhaust flue  174 . For the exemplary embodiment shown, a leg  177  of heat pipe  176  extending between the exhaust flue  174  and evaporator  178  is angled upwardly therebetween so as to allow heated fluid to in pipe  176  to move towards evaporator  178 . Other configurations may be used as well. 
         [0032]    In yet another exemplary embodiment, pipe  176  may carry a phase change fluid. As used herein, a phase change fluid refers to a material that is capable of storing a relatively large amount of energy when it changes phase between, e.g., a gas and liquid or between a liquid and a solid. By way of example, for pipe  176  of the present disclosure, phase change fluids that may be used include dichlorodifluromethane, trichlorofluromethane, benzene, methanol, ammonia, water, mercury, and mixtures thereof. Other materials may be used as well. By way of example, where a phase change material is used, the configuration of pipe  176  can be similar to that shown in  FIGS. 2 . However, as is discussed below, other configurations of pipe  176  are contemplated as well. 
         [0033]    Referring now to  FIG. 3 , in one exemplary embodiment, pipe  176  may capture waste heat from the exhaust flue by wrapping around exterior surface  196  of exhaust flue  174  one or more times. Pipe  176  may then transfer the waste heat captured from exhaust flue  174  to evaporator  178  by extending adjacent to evaporator  178 , and by being positioned upstream from evaporator  178  in the air flow direction F created by fan  226 . Additionally, pipe  176  may extend across evaporator  178  one or more times. In another exemplary embodiment, as shown in  FIG. 3 , evaporator  178  may contain a plurality of grooves  190 , and pipe  176  may further be positioned within grooves  190 . This configuration may assist in holding pipe  176  in position and may increase the amount of heat transfer between pipe  176  and evaporator  178 . With each of the above exemplary embodiments, however, pipe  176  may be comprised of a solid material, a single phase fluid, or a phase change fluid, as previously discussed. 
         [0034]    In another exemplary embodiment, as shown in  FIGS. 4 and 5 , a portion of pipe  176  may extend around a portion of exhaust flue  174  to form a partial sleeve  192  around exhaust flue  174 . In this exemplary embodiment, exhaust flue  174  further defines a radial direction, R. As shown in the cross-sectional top view of  FIG. 4 , partial sleeve  192  may have an interior surface  194  that has a semi-circular shape as viewed in a plane containing radial direction R, which shape approximately matches the shape of exterior surface  196  of exhaust flue  174  in radial direction R. Further, as shown in the side view of  FIG. 5 , partial sleeve  192  may extend along exterior surface  196  of exhaust flue  174  in axial direction A for a defined length. 
         [0035]    Pipe  176  may be affixed to evaporator  178  in a number of ways. In one exemplary embodiment, pipe  176  may be welded to evaporator  178 . As previously discussed, in an alternative exemplary embodiment, pipe  176  may be fitted integrally to evaporator  178  by positioning pipe  176  within grooves  190  defined by evaporator  178 . This embodiment is illustrated in  FIG. 3 . In yet another exemplary embodiment, pipe  176  may be attached to evaporator  178  by a plurality of hooks  188 , as is shown in  FIG. 6 . In this exemplary embodiment, hooks  188  may be attached to pipe  176  and then hooked into evaporator  178  or vice versa. Hooks  188  may be comprised of a metal, which may assist in heat transfer by acting as a heat exchanger between pipe  176  and evaporator  178 . 
         [0036]    Referring now to  FIG. 7 , in one exemplary embodiment of the present disclosure, pipe  176  may run adjacent to evaporator  178 , without physically touching it. Additionally, pipe  176  may be positioned upstream from evaporator  178  in the air flow direction F created by fan  226 . Further, as is shown in  FIG. 7 , a portion of pipe  176  may comprise a plurality of fins  186 . Fins  186  may assist in transferring waste heat captured by pipe  176  to the air flow and then to evaporator  178 . The portion of pipe  176  with fins  186  may extend across the air flow path to evaporator  178  one or more times. 
         [0037]    Referring now to  FIG. 8 , in still another exemplary embodiment of the present disclosure, water heater  100  may transfer waste heat from exhaust flue  174  to evaporator  178  by having exhaust flue  174  define a plurality of branches  200  along axial direction A, wherein each branch is configured for carrying exhaust air. The branches  200  may also be configured for allowing air to pass between branches  200  and over evaporator  178 , and may be positioned upstream from evaporator  178  in the air flow direction F created by fan  226 . The addition of branches  200  to exhaust flue  174  exposes additional surface area of exhaust flue  174  to the air passing by exhaust flue  174  and over evaporator  178 . This may allow for an increased transfer of waste heat from exhaust flue  174  to evaporator  178 . Branches  200  may rejoin to form a single exhaust flue  174 , as shown in  FIG. 8 . 
         [0038]    In yet another exemplary embodiment of the present disclosure, shown in  FIG. 9 , water heater  100  may transfer exhaust heat from exhaust flue  174  to evaporator  178  by having exhaust flue  174  includes a plurality of fins  184 . In this exemplary embodiment, fan  226  is configured for causing a flow of air past fins  184  and over evaporator  178 , wherein exhaust flue  174  is positioned upstream from evaporator  178  in the air flow direction F created by fan  226 . This configuration may assist in the transfer of waste heat from exhaust flue  174  to evaporator  178 . 
         [0039]    In still another exemplary embodiment of the present disclosure, waste heat from exhaust flue  174  may be transferred to evaporator  178  by diverting a portion of the exhaust air, including heated gases from gas fuel heating system  224 , from exhaust flue  174  over evaporator  178 , as is shown in  FIG. 10 . In one exemplary embodiment, the amount of exhaust air that flows over evaporator  178  may be fixed. For example, a small portion of the exhaust air may be diverted to flow over evaporator  178 , or all of the exhaust air may be diverted to flow over evaporator  178 , or anywhere in between. In another exemplary embodiment, the amount of exhaust air that flows over evaporator  178  may be varied depending on the operating conditions of water heater  100 . For example, the entire stream of exhaust air from exhaust flue  174  may be diverted over evaporator  178  when gas fuel heating system  224  is not being operated, while only a portion of the exhaust air from exhaust flue  174  may be diverted over evaporator  178  when gas fuel heating system  224  is being operated. 
         [0040]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.