Abstract:
A water heater that can be operated with improved efficiency is provided. The water heater uses a thermally activated sorption heat pump to heat water stored in a tank. A sorbate is endothermically desorbed from a refrigerant, which in turn is released as a gas or vapor. The latent heat of condensing this refrigerant vapor to a liquid is transferred directly to the water in the tank. Ambient air is then used to vaporize the refrigerant liquid. The vapor refrigerant is then exothermically absorbed by the sorbate. The heat released by this absorption is transferred to the water in the tank using a heat transfer fluid. The cycle can then be repeated by desorbing the sorbate again to release the refrigerant as vapor. A heat source is used to provide heat energy to endothermically desorb the sorbate

Description:
FIELD OF THE INVENTION 
       [0001]    The subject matter of the present disclosure relates generally to a water heater that uses a thermally activated sorption heat pump to provide heat to the water. 
       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. A typical construction includes a water tank that is surrounded by a jacket and is insulated. A heat source is provided for increasing the temperature of water in the tank. The heat energy is commonly supplied e.g., by gas burners or electrically-resistant coils. 
         [0003]    In such constructions, heat created from combustion or the resistance to a current flow is provided directly to the water tank. With gas burners, for example, the burner is located just below the bottom wall of the water tank. Combustion of a liquid or gaseous fuel provides heat that is conducted through the wall of the water tank. In the case of electrically-resistant coils, one or more such coils are typically inserted through a wall of the tank and into the water. Heat generated by the resistance to current flow is transferred to the water. While substantial improvements have been achieved, there is still a need for improvement in water heater efficiency. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    The present invention provides a water heater that can be operated with improved efficiency. The water heater uses a thermally activated sorption heat pump to heat water stored in a tank. A sorbate is endothermically desorbed from a refrigerant, which in turn is released as a gas or vapor. The latent heat of condensing this refrigerant vapor to a liquid is transferred directly to the water in the tank. Ambient air is then used to vaporize the refrigerant liquid. The vapor refrigerant is then exothermically absorbed by the sorbate. The heat released by this absorption is transferred to the water in the tank using a heat transfer fluid. The cycle can then be repeated by desorbing the sorbate again to release the refrigerant as vapor. A heat source is used to provide heat energy to endothermically desorb the sorbate. Features can be provided to further improve efficiency by capturing additional heat from the heat source. 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. 
         [0005]    In one exemplary embodiment, a water heater is provided that includes a tank for holding water and a sorption heat pump. The sorption heat pump includes a condensate collection chamber, a regenerator in fluid communication with the condensate collection chamber, a sorbate located in the regenerator, a condenser positioned in the tank that is in fluid communication with the condensate collection chamber and is also configured for exchanging heat with water in the tank, and an evaporator in fluid communication with the condensate collection chamber. A heat source is positioned proximate to the regenerator and is configured for selectively applying heat to the regenerator. A heat transfer loop is provided that includes a first heat exchanger positioned in the tank and configured for delivering heat energy to water in the tank. The loop also includes a second heat exchanger positioned proximate to the regenerator and the heat source and is configured for receiving heat energy from the regenerator, the heat source, or both. The loop also includes a pump for circulating a heat transfer fluid between the first and second heat exchangers. 
         [0006]    In another aspect, the present invention provides a method of operating a water heater, the water heater having a tank for holding water, a regenerator for a sorbate, and an evaporator. The method includes the steps of applying heat to the regenerator so as to heat a solution containing the sorbate and provide a refrigerant vapor; exchanging heat between the refrigerant vapor and water in the tank so as to increase the temperature of water in the tank; condensing the refrigerant vapor into a refrigerant liquid; draining the refrigerant liquid under force of gravity to the evaporator; vaporizing the refrigerant liquid in the evaporator to provide a refrigerant vapor by exchanging heat energy between the refrigerant liquid and ambient air; combining the refrigerant vapor from the step of vaporizing with the sorbate so as to regenerate the sorbate solution by an exothermic reaction; circulating a heat transfer fluid during between the regenerator and the water tank after the step of applying and during the step of combining; and terminating the step of circulating when the difference in temperature between the heat transfer fluid and the water in the tank is less than a predetermined temperature difference. 
         [0007]    These and other features, aspects and advantages of the present invention 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 invention and, together with the description, serve to explain the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    A full and enabling disclosure of the present invention, 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, each of which are schematic representations in which: 
           [0009]      FIG. 1  illustrates an exemplary embodiment of a water heater of the present invention in charging mode while  FIG. 2  illustrates a discharge mode. An exemplary system for heat pump is illustrated. Certain features are not shown until later figures for purposes of additional clarity in describing the invention. 
           [0010]      FIGS. 3 and 4  illustrate the exemplary embodiment of a water heater shown in  FIGS. 1 and 2  along with an exemplary heat transfer loop. 
           [0011]      FIGS. 5 and 6  illustrate the exemplary embodiment of a water heater shown in  FIGS. 1 and 2  along with an exemplary vent gas heat exchange system. 
           [0012]      FIG. 7  illustrates the exemplary embodiment of a water heater shown in  FIG. 1  and indicates exemplary positioning of various sensors as further described below. 
       
    
    
       [0013]    The use of the same reference numerals throughout the figures indicates the same features. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    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. 
         [0015]    An exemplary embodiment of a water heater  200  of the present invention is shown schematically in  FIGS. 1 through 7 . For purposes of clarity in describing the invention, certain features are illustrated in some drawings while not repeated in others. As will be understood using the description that follows, this exemplary embodiment of water heater  200  includes all of the features shown in  FIGS. 1 through 7 . 
         [0016]    Referring now to  FIGS. 1 and 2 , water heater  200  includes tank  202  for holding the water to be heated. Tank  202  can be provided with insulation and a protective jacket (not shown) to contain insulation between tank  202  and the jacket as will be understood by one of skill in the art. Additionally, a water inlet and water outlet (not shown) can be used to connect tank  202  with the piping system of e.g., a commercial or residential structure for the receipt of water to be heated and for the return delivery of water heated while in tank  202 . 
         [0017]    Water heater  200  includes a sorption heat pump  204 .  FIG. 1  shows heat pump  204  in charging mode while  FIG. 2  shows heat pump  204  in a discharge mode as will be further described. Heat pump  204  includes a regenerator  208  that includes a sorbate. As used herein, sorbate refers to material that can be combined with liquid or gas/vapor, referred to herein as a refrigerant, to create an exothermic reaction. Conversely, the sorbate can be heated to remove the refrigerant in an endothermic reaction. By way of example, the sorbate may be a salt such as lithium chloride or lithium bromide while the refrigerant may be water. Before the application of heat, heat pump  204  is at a near vacuum pressure condition. For example, the water and salt within heat pump  204  may be at a pressure of less than about 2 millibars. 
         [0018]    During operation of water heater  200 , a heat source is used to apply heat energy to regenerator  208 . For the exemplary embodiment of  FIG. 1 , the heat source is provided as gaseous fuel burner  216  that is located proximate to regenerator  208  so that flames  218  from the combustion of a gaseous fuel will apply heat to regenerator  208  when heater  200  is in charging mode as shown in  FIG. 1 . Heating sources other than gaseous fuels may also be used in other embodiments of the present invention. 
         [0019]    Gaseous fuel burner  216  can be selectively operated by e.g., a controller connected to an ignition mechanism and a valve (not shown) that controls the flow of gas to burner  216 . As used herein, the controller may include a memory and one or more microprocessors, CPUs or the like, such as general or special purpose microprocessors operable to execute programming instructions or micro-control code associated with operation of water heater  200 . The memory may represent random access memory such as DRAM, or read only memory such as ROM or FLASH. In one embodiment, the processor executes programming instructions stored in memory. The memory may be a separate component from the processor or may be included onboard within the processor. The controller may be positioned in a variety of locations throughout water heater  200 . Accordingly, the controller can be used to activate burner  216  when water heater  200  is in charging mode so as to provide heat for the endothermic reaction needed to drive refrigerant vapor from the sorbate in regenerator  208 . 
         [0020]    Sorption heat pump  204  also includes a condensate collection chamber  206  that is in fluid communication with regenerator  208  by vapor channel  230 . Heat pump  204  also includes a condenser  210  and an evaporator  214 , both of which are also in fluid communication with condensate collection chamber  206 . As shown by arrows V, during charging mode, refrigerant vapor desorbed from the sorbate travels to condensate collection chamber  206 . A first valve  224  is in the closed position during the charging mode so as to prevent refrigerant vapor from travelling into evaporator  214 . Instead, the refrigerant vapor travels into condenser  210  through a second valve  226  that is in an open position. 
         [0021]    For this exemplary embodiment, condenser  210  is shown as a helical coil elevated along vertical direction V relative to the condensate collection chamber  206 . A terminus  212  seals one end of condenser  210 . Gaseous refrigerant can travel upwardly within condenser  210  and transfer heat into water in tank  202  and thereby increase the temperature of the water. As the refrigerant vapor condenses and transfers latent heat to water in tank  202 , the vapor changes phase to a refrigerant liquid that travels under the force of gravity back to condensate collection chamber  206  as indicated by arrow C. The resulting refrigerant liquid or condensate is pooled in condensate collection chamber  206 . 
         [0022]      FIG. 7  provides another schematic view of water heater  200  and illustrates the placement of certain sensors. As shown, a first temperature sensor  232  is used to measure the temperature at regenerator  208 . During the charging stage when heat source  216  is applying heat to regenerator  208 , an increase in temperature as measured by first temperature sensor  232  is used to indicate that the sorbate has been substantially regenerated to remove all or a substantial portion of refrigerant. Returning to  FIG. 1 , the controller can then turn off the heat source i.e., burner  216 . Once the refrigerant vapor has been condensed, first valve  224  is then opened to allow condensate to drain under the force of gravity into evaporator  214 . 
         [0023]    Referring now to the discharge mode shown in  FIG. 2 , after condensate  228  has drained into evaporator  214 , second valve  226  is closed, first valve  224  remains open, and a fan  222  is activated to move ambient air over evaporator  214 . Fan  222  can be a blower or other air movement device configured to push or pull air over evaporator  214 . The ambient air provides thermal energy that is transferred to the refrigerant liquid to provide the latent heat energy required for vaporization. As shown in  FIG. 1  with arrow CV, the resulting vapor travels through the open first valve  224 , through vapor channel  230 , and back to regenerator  208  where is absorbed by the sorbate in an exothermic reaction. As shown in  FIG. 7 , a second temperature sensor  234  is positioned at evaporator  214  and is configured for measuring the temperature of evaporator  214 . An increase in this temperature can be used to determine that the refrigerant liquid has been substantially or completely vaporized so that water heater  200  can be recycled to the charge mode. 
         [0024]      FIG. 3  illustrates water heater  200  in a charging mode as discussed above with regard to  FIG. 1 , while  FIG. 4  illustrates water heater  200  in a discharging mode as discussed above with regard to  FIG. 2 . As shown, water heater  200  also includes a heat transfer loop  220  with a reservoir or holding tank  240  containing a heat transfer fluid  236  that can be circulated by pump  238 . During charging mode when gas burner  216  is operating to provide heat to regenerator  208 , pump  238  remains inactive and the heat transfer fluid remains in holding tank  240  under force of gravity. However, after gas burner  216  is deactivated, significant heat energy may still be present in or near regenerator  208  that can be used to provide heat to the water in tank  202 . 
         [0025]    Accordingly, referring to  FIG. 4 , pump  238  can be activated (by e.g., a controller) shortly after gas burner  216  is deactivated so as to capture and transfer this heat to water in tank  202 . More specifically, heat transfer loop  220  includes a first heat exchanger  242  (shown as coils) in tank  202  for delivering heat energy to water in tank  202 . A second heat exchanger  244  is positioned at regenerator  208  for receiving heat energy from regenerator  208 , gas burner  216 , or both. Pump  238  circulates heat transfer fluid  236  as shown by arrows F. Heat transfer fluid  236  may be e.g., water, oil, or another suitable medium. 
         [0026]    In addition, during discharge mode, heat is provided by the exothermic reaction between returned vapor and the sorbate in regenerator  208 . Heat transfer loop  220  is also used to capture this heat from regenerator  208  using second heat exchanger  244  and transfer the same to water in tank  202  using the first heat exchanger  242  and circulated heat transfer fluid  236  as previously described. Thus, heat transfer loop  220  can be used to capture and deliver residual heat remaining after burner  216  has been deactivated as well as heat from the exothermic reaction that occurs in regenerator  208  during discharge mode. 
         [0027]    Turning now to  FIG. 7 , water heater  200  includes a third temperature sensor  246  positioned at tank  202  to measure the temperature of water in tank  202 . A fourth temperature sensor  248  is positioned in heat transfer loop  220  at a position downstream of regenerator  208  and a fifth temperature is positioned at a position upstream of regenerator  208  at the inlet thereto. Temperature measurements provided by these temperature sensors can be used to determine when to activate and deactivate pump  238 . 
         [0028]    For example, by comparing the temperature measurements of water tank  202  from third temperature sensor  246  with measurements from fourth temperature sensor  248 , the controller can determine whether to continue operating pump  238 . If, for example, temperature of the heat transfer fluid  236  is cooler than the water in tank  202  by at least about 2° C., then pump  238  can be deactivated or remain in an off mode. Conversely, if the heat transfer fluid  236  is warmer than the water in tank  202  by about 2° C., then the controller can activate or continue operating pump  238  to heat water in tank  202 . A difference of 2° C. is provided by way of example only—other values or ranges may be used as well. Additionally, by comparing the temperature readings between fourth temperature sensor  248  and fifth temperature sensor  250 , the controller can determine whether the heat transfer fluid  236  is capturing heat energy from regenerator  208 . 
         [0029]    Water heater  200  is also provided with a vent gas heat exchange system  252  as shown in  FIG. 5  (charge mode) and  FIG. 6  (discharge mode). Where the heat source uses e.g., a combustible fuel to provide heat as with fuel burner  216 , a significant amount of heat is still present in the combustion gases. Accordingly, heat transfer system  252  includes an inlet  254  for the intake of combustion gases from fuel burner  216 , which are then fed (arrows G) to a vent gas heat exchanger  256  located in water tank  202 . Vent gas heat exchanger  256  transfers heat from the vent gas to the water to raise its temperature. A fan or blower  258  is used to assist the flow of vent gas through heat transfer loop  252 . A drain  260  allows water or other liquids L that condense as the vent gas is cooled to be removed. A flue or vent  264  provides for discharge of the vent gas after circulation through heat exchanger  256 . During discharge mode as shown in  FIG. 6 , blower  258  is likely not operated unless heat can be captured from the exothermic reaction occurring in regenerator  208 . 
         [0030]    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.