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 secondary heat transfer system uses a secondary fluid to supply heat for such vaporization during the endothermic desorption cycle. During the exothermic adsorption cycle, a secondary heat exchanger is used along with the 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 relatively low 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. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0008]    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 vaporized from the sorbate to water in the tank. A secondary heat transfer system uses a secondary fluid to supply heat for such vaporization during the endothermic desorption cycle. During the exothermic adsorption cycle, a secondary heat exchanger is used along with the 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. 
         [0009]    In one exemplary embodiment, the present invention provides a water heater that includes a tank having a volume for storing water. The tank also defines a cavity. The water heater includes a primary heat transfer system in which a primary fluid is recirculated. The primary heat transfer system includes a reactor that is located within the cavity of the tank; a sorbate that is located within the reactor; and a primary heat exchanger that is positioned within the volume of the tank. The primary heat exchanger is in fluid communication with the reactor to receive vaporized primary fluid that is endothermically desorbed from the sorbate. 
         [0010]    The primary heat transfer system also includes an evaporator that is in fluid communication with the primary heat exchanger to receive primary fluid condensed in the primary heat exchanger. The evaporator also is in fluid communication with the reactor to provide primary fluid vaporized by the evaporator back to the reactor. 
         [0011]    The water heater also includes a secondary heat transfer system in which a secondary fluid is recirculated. The secondary heat transfer system includes a heater configured for vaporizing the secondary fluid, a reactor heat exchanger positioned within the reactor and in fluid communication with the heater to receive vaporized secondary fluid from the heater, and a secondary heat exchanger positioned within the volume of the tank for transferring heat to the water in the tank. 
         [0012]    The secondary heat exchanger is in fluid communication with the reactor heat exchanger for receiving liquid secondary fluid that is heated by exothermic adsorption of primary fluid by the sorbate. The secondary heat exchanger is also in fluid communication with the reactor heat exchanger to return liquid secondary fluid to the reactor heat exchanger after liquid secondary fluid has transferred heat to the water in the tank. 
         [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 secondary heat transfer system  300 , and an exhaust gas heat transfer system  400 . 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 secondary 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  300  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 , secondary heat transfer system  300  is used to recirculate a secondary fluid  314  between several components that are in fluid communication with each other. During the desorption cycle, a heater  302  positioned at the bottom of system  300  (i.e. vertically lower than reactor  202 ) is used to vaporize secondary fluid provided by a gravity flow  325  through line  336  that collects in a boiler  320 . More particularly, heater  302  uses boiler  320  to provide a flow  308  of vaporized secondary 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, secondary fluid condenses and can travel to a secondary storage vessel  316 . 
         [0031]    Notably, as shown in the figures, primary fluid is recirculated within primary heat transfer system  200  while secondary fluid is recirculated within secondary heat transfer system  300 . Each system remains closed in that primary fluid and secondary fluid are not mixed during the heat transfer operations described. Thus, reactor heat exchanger  304  is positioned within reactor  202  but provides a flow path for secondary fluid that is separated from the flow path of primary fluid in reactor  202 . While water can be used for both primary 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  to receive vaporized secondary fluid flow  308  therefrom during desorption. Second leg  318  has a top portion  318   t  and a bottom portion  318   b . Bottom portion  318   b  is in fluid communication with a secondary storage vessel  316  to provide condensed primary fluid  314  thereto. 
         [0033]    More specifically, as heat is transferred from the vaporized secondary fluid  308  to the sorbate  206 , the secondary fluid condenses to provide a flow  312  of condensed—i.e. liquid—secondary fluid  314  into a secondary storage vessel  316 . As this process continues, the amount of secondary fluid  314  in boiler  320  of heater  302  will decrease as the liquid secondary fluid  314  is vaporized to create flow  308 . At the same time, the level SL of secondary fluid  314  in secondary storage vessel  316  will increase as secondary fluid  314  condenses in reactor heat exchanger  304  and flows out under the influence of gravity to vessel  316 . 
         [0034]    As shown in  FIG. 3 , eventually the level SL will rise vertically to a crossover  322  connecting or extending between first leg  310  and second leg  318 . Upon reaching crossover  322 , secondary fluid  314  will flow over from second leg  318  to first leg  310  to provide a gravity flow  325  of condensed secondary fluid through line  336  and back into boiler  320  of heater  302 . Once back in heater  302 , secondary fluid can be vaporized again until the desorption cycle ends. Thus, at certain times during the desorption cycle, there are counter flows ( 308  and  325 ) of vaporized secondary fluid and liquid secondary fluid in line  336 . 
         [0035]    The vertical level (along vertical direction V) of crossover  322  can be predetermined to control the amount of condensed secondary fluid  314  that will be collected before it flows through crossover  322 . By way of example, crossover  322  may be a pipe, tube, or other channel connected between first leg  310  and second leg  310 . In certain embodiments, the diameter of crossover  322  is relatively small so as to limit the flow of secondary fluid therethrough. 
         [0036]    During the desorption cycle, a secondary valve  324  remains closed and a secondary pump  326  remains off. Once the desorption cycle ends, secondary valve  324  is opened and secondary pump  326  is activated. Referring now to  FIG. 4 , secondary pump  326  has a secondary pump inlet  326   a  that is in fluid communication with the secondary storage vessel  316  and a secondary pump outlet  326   b  that is in fluid communication with a secondary heat exchanger  328 . 
         [0037]    Secondary heat exchanger  328  is positioned within volume  104  of tank  102  so that heat can be transferred to water in tank  102 . Secondary heat exchanger  328  is in fluid communication with the reactor heat exchanger  304  to receive liquid secondary fluid heated by the exothermic adsorption of primary fluid onto sorbate  206  during the adsorption cycle. Secondary heat exchanger  328  is also in fluid communication with the reactor heat exchanger  304  to return liquid secondary fluid after the secondary fluid has transferred heat to the water in tank  102 . 
         [0038]    More particularly, secondary pump  326  causes a secondary fluid flow  330  from secondary tank  316  to flow through secondary valve  324  and into secondary heat exchanger  328 . While travelling through second heat exchanger  328 , secondary fluid flow  330  transfers heat to water in tank  102 . After exiting secondary heat exchanger  328 , secondary fluid flows into a riser  332  that extends upwardly along vertical direction V within first leg  310 . The fluid riser has a fluid outlet  334  near the top portion  310   t  of first leg  310 . From fluid outlet  334 , the secondary fluid can flow downwardly (gravity flow) through reactor heat exchanger  304  and flood each of the plates  306 . While travelling through plates  306 , 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  316  for recirculation to secondary heat exchanger to heat water in tank  102  as previously described. 
         [0039]    Accordingly, water heater  100  operates by shifting between a desorption cycle and an adsorption cycle. During the desorption cycle, valves  230  and  324  are closed while pumps  228  and  326  are off. During the adsorption cycle, valves  230  and  324  are both open while pumps  228  and  326  are on. 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  206 . The controller may also receive fluid level information from storage vessels  226  and  316 . 
         [0040]    Returning to  FIG. 3 , 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 . 
         [0041]    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 language of the claims.