Abstract:
A water heater is provided having a sorption based reactor that is integrated into a water tank. The water heater is operated between an adsorption cycle and a desorption cycle. During the endothermic desorption cycle, a primary heat exchanger is used to transfer heat from a condensing primary fluid that was vaporized from the sorbate to water in the tank. A charging heat transfer system supplies heat for the vaporization during endothermic desorption cycle. During the exothermic adsorption cycle, a secondary heat exchanger is used along with a secondary fluid to transfer heat generated by adsorption of the primary fluid to water in the tank. An evaporator provides for vaporization of the primary fluid during the adsorption cycle. Substantial improvements in energy efficiency can be achieved.

Description:
FIELD OF THE INVENTION 
       [0001]    The subject matter of the present disclosure relates generally to a water heater that uses a sorption based reactor for heating 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 source is commonly based on e.g., 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. 
         [0004]    While substantial improvements have been achieved, there is still a need for improvement in water heater efficiency. 
         [0005]    One technology that has been proposed for improving water heater efficiency is the use of sorption based water heaters. For such water heaters to be profitable, such need to be simple, robust, highly efficient, affordable and easy to integrate into water systems where conventional water heaters have previously been used. 
         [0006]    Many sorption based devices work according to a batch process, which means that they operate intermittently. These sorption based devices usually include two main components: a reactor and another component that acts as either a condenser or evaporator depending on the phase of the process. In these types of devices, during a charging phase, the reactor takes in heat at high temperature and the condenser releases heat at relatively low temperatures. During the discharging phase, the reactor releases heat at low relatively temperatures and the evaporator absorbs heat at much lower temperatures. In each of these two phases, the device needs to exchange heat with the environment or ambient conditions. To supply or release heat at different temperatures using the same component as both a heat exchanger and a condenser, prior sorption based devices often use a complex system of valves, pumps, and pipes that act as an auxiliary system for the sorption device. Thus, these prior devices are typically more complex and have moving parts that result in higher electricity consumption, greater risk of leakage, and increased risk of repair or maintenance. 
         [0007]    Accordingly, improvement is needed in sorption based devices and in water heaters using such devices. 
         [0008]    BRIEF DESCRIPTION OF THE INVENTION 
         [0009]    The present invention provides a water heater having a sorption based reactor that is integrated into a water tank. The water heater is operated between an adsorption cycle and a desorption cycle. During the endothermic desorption cycle, a primary heat exchanger is used to transfer heat from a condensing primary fluid that was vaporized from the sorbate to water in the tank. A charging heat transfer system supplies heat for the vaporization during endothermic desorption cycle. During the exothermic adsorption cycle, a secondary heat exchanger is used along with a secondary fluid to transfer heat generated by adsorption of the primary fluid to water in the tank. An evaporator provides for vaporization of the primary fluid during the adsorption cycle. Substantial improvements in energy efficiency can be achieved. Additional aspects and advantages of the invention will be set forth in part in the following description, may be apparent from the description, or may be learned through practice of the invention. 
         [0010]    In one exemplary embodiment, the present invention provides a water heater that includes a tank having a volume for storing water. The tanks also defines a cavity. A primary heat transfer system is included in which a primary fluid is recirculated. The primary heat transfer system includes a reactor located within the cavity and a sorbate located within the reactor. A primary heat exchanger is positioned within the volume of the tank and is in fluid communication with the reactor to receive vaporized primary fluid that is endothermically desorbed from the sorbate. An evaporator is in fluid communication with the primary heat exchanger to receive primary fluid condensed in the primary heat exchanger. The evaporator is in fluid communication with the reactor to provide primary fluid vaporized by the evaporator to the reactor. 
         [0011]    This exemplary water heater also includes a secondary heat transfer system in which a secondary heat transfer fluid is recirculated. The secondary heat transfer system includes an auxiliary heat exchanger positioned within the reactor and configured for transferring heat energy to the secondary fluid. A secondary heat exchanger is positioned within the volume of the tank and configured for transferring heat from the secondary fluid to the water in the tank. The secondary heat exchanger is in fluid communication with the auxiliary heat exchanger and is configured to receive liquid secondary fluid from the auxiliary heat exchanger that is heated by exothermic adsorption of primary fluid by the sorbate. The secondary heat exchanger is also configured to return to the auxiliary heat exchanger liquid secondary fluid that has transferred heat to the water in the tank. 
         [0012]    This exemplary water heater also includes a charging heat transfer system in which the charging fluid is recirculated. The charging heat transfer system includes a heater configured for vaporizing the charging fluid and a reactor heat exchanger positioned within the reactor and in fluid communication with the heater. The reactor heat exchanger is configured to receive vaporized charging fluid from the heater and to return condensed charging fluid to the heater. 
         [0013]    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 
         [0014]    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, in which: 
           [0015]      FIGS. 1, 2, 3, and 4  each provide a schematic view of an exemplary embodiment of a water heater of the present invention. Different aspects of operation of the exemplary water heater are depicted throughout these figures. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    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. 
         [0017]    Schematic representations of an exemplary embodiment of a water heater  100  of the present invention are set forth in the figures. Beginning with  FIG. 1 , water heater  100  includes a tank  102  having a volume  104  for water storage and heating. Tank  102  extends along vertical direction V between a top  110  and a bottom  112 . Tank  102  includes a recess or cavity  106  in bottom  112  that defines an inside surface  108 . An inlet  116  is provided for the inflow of water to be heated and an outlet  114  is provided for the outflow of heated water. Outlet  114  and inlet  116  can be connected with e.g., a residential or commercial water system in a home or other structure. 
         [0018]    For this exemplary embodiment, water heater  100  also includes a primary heat transfer system  200 , a charging heat transfer system  300 , an exhaust gas heat transfer system  400 , and a secondary heat transfer system  500 . Water heater  100  is operated by shifting between two cycles: 1) an adsorption cycle where heat is released from exothermic adsorption of a primary fluid onto a sorbate  206 , and 2) a desorption cycle requiring heat for the endothermic desorption of the primary fluid from sorbate  206 . A further description of each heat transfer system as well as the structure and operation of water heater  100  in these two cycles now follows. 
         [0019]    Continuing with  FIG. 1 , primary heat transfer system  200  is used to recirculate a primary fluid  216  between several components that are in fluid communication with each other. As used herein, “fluid” refers to vapor and/or liquid states unless otherwise specified as a vapor or as a liquid. As also used herein, components described as being in “fluid communication” means that a fluid can travel between such components that are either directly connected or may be connected through piping, tubing, flow channels, other components, and combinations thereof unless otherwise specified. 
         [0020]    Primary heat transfer system  200  includes an integrated sorption reactor  202 —i.e., reactor  202  is positioned within the cavity  106  of tank  102 . In one exemplary embodiment, reactor  202  is positioned with a slight gap  238  between reactor  202  and the inside surface  108  of cavity  106  defined by tank  102 . In other embodiments, reactor  202  may be formed integrally with tank  102  such that reactor  202  is embedded within cavity  106 . Either construction allows for thermal communication between reactor  202  and tank  102  such that heat can be transferred to water in the volume  104  of tank  102 . 
         [0021]    A sorbate  206  is located within reactor  202 . As used herein, “sorbate” refers to material that can be combined with the primary fluid  216  to create an exothermic reaction. Conversely, the sorbate can be heated to remove the primary fluid  216  in an endothermic reaction. By way of example, sorbate  206  may be a salt such as lithium chloride or lithium bromide while the primary fluid may be a relatively volatile liquid such as water. In still another embodiment, sorbate  206  is at least one metal salt selected from the group consisting of LiCl, LiBr, LiI, MgCl 2 , MgBr 2 , MgI 2 , CaCl 2 , CaBr 2 , CaI 2 , SrI 2 , KOH, NaOH, ZnCl 2 , ZnBr 2 , ZnI 2 , AlCl 3 , AlBr 3 , and AlI 3 . In another alternative embodiment, sorbate  206  is at least one metal salt selected from the group consisting of MgCl 2 , MgBr 2 , LiCl, CaCl 2 , CaBr 2 , ZnCl 2 , and NaOH. 
         [0022]    For the exemplary embodiment shown in the figures, sorbate  206  is provided in a plurality of plates  208  positioned in layers along vertical direction V in an alternating manner with a plurality of heat transfer plates  306  of a reactor heat exchanger  304  ( FIG. 2 ), which will be more fully described below. Plates  208  act as membranes that contain sorbate  206  while allowing primary fluid to pass in or out and thereby interact with sorbate  206 . The adsorption of primary fluid onto sorbate  206  (i.e., an adsorption cycle) is an exothermic event that generates heat. Conversely, the desorption of primary fluid from sorbate  206  (i.e., a desorption cycle) requires the addition of heat (from charging heat transfer system  300 ), which liberates primary fluid as a vapor  224  from sorbate  206 . 
         [0023]    During the desorption cycle, a flow  224  of vaporized primary fluid (i.e., steam) rises to bonnet  204  and exits through reactor outlet  236 . Primary heat transfer system  200  includes a primary heat exchanger  210  that is positioned within the volume  104  of tank  102 . Primary heat exchanger  210  is in fluid communication with reactor  202  by outlet  236  and thereby receives the flow  224  of vaporized primary fluid created by the endothermic desorption from sorbate  206 . The flow  224  of vaporized primary fluid travels through primary heat exchanger  210  and transfers heat to the water in tank  102  as it cools and condenses. The resulting flow  218  of condensed—i.e., liquid-primary fluid  216  flows under the force of gravity vertically down through primary heat exchanger  210 , through condensate return leg  214 , and into a primary storage vessel  226  where it is collected as a liquid volume of primary fluid  216 . 
         [0024]    During the desorption cycle, a primary valve  230  remains closed to prevent flow along vapor return leg  232  between reactor  202  and an evaporator  212  and primary storage vessel  226 . Both evaporator  212  and primary storage vessel  226  are in fluid communication with primary heat exchanger  210 . A primary pump  228  remains off during the desorption cycle. 
         [0025]    The desorption cycle is continued until all or a certain portion of primary fluid has been desorbed from sorbate  206 . Such determination can be made by monitoring the level PL of primary fluid  216  in primary storage vessel  226  and/or by monitoring the temperature at or near the sorbate  206  in reactor  202 . For example, the temperature at or near sorbate  206  would be substantially constant during desorption and then would begin to increase as desorption of the primary fluid is completed. 
         [0026]    During an adsorption cycle, primary valve  230  is opened to allow for fluid communication between evaporator  212  and reactor  202 . More particularly, opening of primary valve  230  allows a flow  222  of primary fluid in the form of vapor (from evaporator  212 ) into reactor  202  through reactor inlet  234 . Additionally, primary pump  228  is activated. As shown in  FIG. 1 , primary pump  228  has a primary pump inlet  228   a  that is in fluid communication with primary storage vessel  226  to draw condensed primary fluid  216  therefrom. By way of distribution manifold  240  and connector  242 , primary pump outlet  228   b  is in fluid communication the evaporator  212  to provide a flow  220  of liquid primary fluid thereto. 
         [0027]    Once pumped to evaporator  212 , at least a portion of flow  220  of primary fluid is vaporized. For example, in one embodiment, the primary fluid is water that is at or near a vacuum pressure condition within primary heat transfer system  200 —thereby increasing its volatility. For example, water might be used as a primary fluid at a pressure of less than about 2 millibars. Under such conditions, the surrounding atmosphere or ambient  50  can provide heat for the vaporization of primary liquid  216  in evaporator  212 . A fan  244  can be used to provide a forced air flow (arrows A) to improve heat transfer with the ambient  50 . Accordingly evaporator  212  provides a flow  222  of vaporized primary fluid along vapor return leg  232 , through an opened primary valve  230 , and into reactor  202 . 
         [0028]    Liquid that is not vaporized in evaporator  212  drains into primary storage vessel  226 . For this purpose, evaporator  212  may be elevated along vertical direction V higher than primary storage vessel  226  but lower than primary heat exchanger  210  so as to provide a gravity flow of liquid primary fluid  216  back into primary storage vessel  226 . Evaporator  212  may also be placed at non-zero angle θ ( FIG. 2 ) from the horizontal direction H as shown with the inlet  212   a  positioned higher than the outlet  212   b  to further facilitate the return of liquid primary fluid  216  back into primary storage vessel  226 . While activated, primary pump  228  will recycle this liquid primary fluid  216  back into evaporator  212 . 
         [0029]    As stated, evaporator  212  is in fluid communication with reactor  202  to provide vaporized primary fluid flow  222  back into reactor  202 . Therein, this vaporized primary fluid can undergo exothermic adsorption onto sorbate  206 , which generates heat that can be transferred to water in tank  102  by secondary heat transfer system  500  as further described below. Once sorbate  206  is substantially fully saturated by adsorption of the primary fluid, the adsorption cycle is ended by closing primary valve  230  and deactivating primary pump  228 . The desorption cycle can then be repeated as described above. The amount of saturation of the sorbate  206  during the adsorption cycle can be determined by monitoring the level PL of primary fluid  216  in primary storage vessel  226  and/or by monitoring the temperature at or near the sorbate  206  in reactor  202 . 
         [0030]    Turning now to  FIG. 2 , a charging heat transfer system  300  is used to recirculate a charging fluid  314  between several components that are in fluid communication with each other. During the desorption cycle, a heater  302  is positioned at the bottom of system  300  (i.e. vertically lower than reactor  202 ) and is used to vaporize the charging fluid that collects therein. More particularly, heater  302  uses a boiler  320  to provide a flow  308  of vaporized charging fluid to reactor heat exchanger  304 . Therein, heat is transferred to the sorbate  206  to endothermically desorb primary fluid from the sorbate  206  as previously described. Reactor heat exchanger  304  includes plates  306  alternating with plates  208  to improve such heat transfer. Upon releasing its latent heat, the charging fluid condenses and provides a return flow  312  to heater  302  by gravity feed through line  337 . 
         [0031]    Notably, as shown in the figures, primary fluid is recirculated within primary heat transfer system  200 , charging fluid is recirculated within charging heat transfer system  300 , and secondary fluid is recirculated within secondary heat transfers system  500 . Each system remains closed in that primary fluid, secondary fluid, and charging fluid are not mixed during the heat transfer operations described. Thus, reactor heat exchanger  304  is positioned with reactor  202  but provides a flow path for charging fluid that is separated from the flow path of primary fluid in reactor  202 . While water can be used for primary fluid, charging fluid, and secondary fluid, the pressures within the primary heat transfer system  200  and secondary heat transfer system can be much different so as to determine the level of volatility. 
         [0032]    Continuing with  FIG. 2 , plates  306  of reactor heat exchanger  304  extend between a first leg  310  and a second leg  318  of reactor heat exchanger  304 . First leg  310  has a top portion  310   t  and a bottom portion  310   b.  Bottom portion  310   b  is in fluid communication with heater  302  through heater outlet  303  to receive a flow  308  of vaporized charging fluid therefrom. Second leg  318  has a top portion  318   t  and a bottom portion  318   b.  Bottom portion  318   b  is in fluid communication with heater  302  through a heater inlet  305  and line  337 . Charging system  300  is activated during the desorption cycle and deactivated during the adsorption cycle. 
         [0033]    Referring now to  FIG. 3 , a secondary heat exchanger  528  is positioned within volume  104  of tank  102  so that heat can be exchanged with water in tank  102 . Secondary heat exchanger  528  is in fluid communication with an auxiliary heat exchanger  504  to receive secondary fluid heated by the exothermic adsorption of primary fluid onto sorbate  206  during the adsorption cycle. Secondary heat exchanger  528  is also in fluid communication with the auxiliary heat exchanger  504  to return liquid secondary fluid after the secondary fluid has transferred heat to water in tank  102 . 
         [0034]    During the desorption cycle, a secondary valve  524  remains closed and a secondary pump  526  remains off. Once the desorption cycle ends, secondary valve  524  is opened and secondary pump  526  is activated. Secondary pump  526  has a secondary pump inlet  526   a  that is in fluid communication with a secondary storage vessel  516  and a secondary pump outlet  526   b  that is in fluid communication with a secondary heat exchanger  528 . 
         [0035]    When activated during the adsorption cycle, secondary pump  526  causes a secondary fluid flow  530  from secondary storage vessel  516  to flow into secondary heat exchanger  528 . While travelling through second heat exchanger  528 , secondary fluid flow  530  transfers heat to water in tank  102 . After exiting secondary heat exchanger  528 , secondary fluid flows into a riser  532  of auxiliary heat exchanger  504  that extends upwardly along vertical direction V. Riser  532  provides fluid to a return  533  of auxiliary heat exchanger  504  that feeds secondary fluid back into secondary storage vessel  516 . 
         [0036]    While travelling through auxiliary heat exchanger  504 , heat is transferred to the secondary fluid from the exothermic adsorption of primary fluid onto sorbate  206 . Secondary fluid is then collected in secondary storage tank  516  for recirculation to secondary heat exchanger  528  to heat water in tank  102  as previously described. 
         [0037]    Accordingly, water heater  100  operates by shifting between a desorption cycle and an adsorption cycle. During the desorption cycle, valves  230  and  524  remain shut while pumps  228  and  526  remain off or inactive. During the adsorption cycle, valves  230  and  524  are both opened while pumps  228  and  526  are activated. In one exemplary embodiment, the operation of the valves and pumps of water heater  100  are controlled by one or more processors or controllers. Such 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  100 . 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  100 . The controller can also be used to activate heater  302  along with the previously described valves and pumps. The controller may also receive temperature information from one or more temperature sensors. Such temperature information may include e.g., the temperature of water in tank  102  and of the sorbate  106 . The controller may also receive fluid level information from storage vessels  226  and  516 . 
         [0038]    Returning to  FIG. 2 , heater  302  may utilize a fuel burner  338  to provide heat to a boiler  320  for vaporizing secondary fluid  314 . The combustion of such fuel creates an exhaust gas flow  402  that is used by an exhaust gas heat transfer system  400  to heat water in tank  102 . An exhaust gas heat exchanger  404  is positioned in the volume  104  of tank  102  for transferring heat to the water. A vent  406  receives exhaust gas flow  402  from fuel burner  338 /boiler  320  and supplies such exhaust into the exhaust gas heat exchanger  404 . Vent  406  extends vertically upward through exchanger  404  so that a counterflow is created therethrough as shown. After passing through exchanger  404 , the exhaust gas flow exits through outlet  408 . 
         [0039]    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.