Abstract:
A combination direct/indirect liquid heating heater comprises a tower, a cold water inlet conduit causing water to fall in said tower, a hot water reservoir in communication with said tower, a gas burner, a hot gas inlet manifold encased in the reservoir and, by means of a vertical section, directing the gas into the tower. The hot gas manifold vertical section is capped by a cap impeding water flow into the manifold. Also, the vertical section comprises a baffle impeding gas flow from the tower into the reservoir.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to the field of water heaters and, more particularly, the present invention relates to high efficiency devices which heat water using thermal conduction and also via direct contact of the water with combustion gases.  
         [0003]     2. Description of the Prior Art  
         [0004]     Direct heating of water by combustion gases is known. U.S. Pat. No. 6,089,223 awarded to Jasper et al. on Jul. 18, 2000, and assigned to the instant assignee teaches a heater whereby falling water contacts hot combustion gases.  
         [0005]     While direct water heaters are more efficient than indirect-heating configurations, the costs of the former are formidable. For example, the fabrication of housings for the combustion chamber of such units is time consuming, and therefore costly. Also, water switches and additional spray nozzles are necessary to assure adequate cooling of the housings and also of the combustion gases, respectively.  
         [0006]     Indirect heating of water by combustion gases occurs when water contacts a heat transfer surface. The heat transfer surface can be defined by one or a plurality of conduits through which hot combustion gas (or some other hot fluid) circulates. Boilers heat water this way.  
         [0007]     The heating efficiency of indirect heating systems is low inasmuch as such systems loose heat through the egress of hot combustion gases.  
         [0008]     The heating efficiencies of direct systems also can be low in situations where either the combustion gas temperature or the incoming water temperature is too high to facilitate condensation of all the water vapor in the heating zone. Instead, water vapor exits the system, resulting in heat loss. Finally, water-storage tank configurations in typical direct heating systems result in a build-up of vapor pressure above the water level in the tank (i.e., the “head space”) resulting in operating instabilities and further heat losses.  
         [0009]     A need exists in the art for an industrial-grade water heater which combines direct with indirect heating functions to maximize heat transfer. The device should enhance the surface area of heat transfer surfaces so as to maximize the time of heat transfer in indirect heating scenarios. The device also should minimize the potential of the development of “hot spots” during operation so as to enhance safety and prolong equipment life.  
       SUMMARY OF THE INVENTION  
       [0010]     It is an object of the present invention to provide a high efficiency combination direct/indirect water heater that overcomes many of the disadvantages of the prior art.  
         [0011]     It is a further object of the present invention to provide a high efficiency combination direct/indirect water heater that enhances indirect heat transfer. A feature of an embodiment of the present invention is an extended gas-carrying manifold submerged in the water to be heated. In a specific embodiment of the present invention the gas-carrying manifold is encased in a sleeve of water to define a pre-configured annular space. Another feature of the present invention are radially protruding fins from the manifold. An advantage of the present invention is that it ensures that the water to be heated is in constant and close thermal contact with the heated gases during the initial water input mode and in the storage mode, thereby enhancing heat transfer efficiency.  
         [0012]     Another object of the present invention is to provide a high efficiency combination direct/indirect water heater that allows unimpeded escape of the heated gases from a heat exchange manifold. A feature of the present invention is that the manifold terminates with a cap structure which prevents water blockage of the heated gas at the egress point. An advantage of the present invention is that the means of egress facilitates unhindered venting of gas and prevents back pressure from occurring at the gas egress point.  
         [0013]     Yet another object of the present invention is to provide a high efficiency combination direct/indirect water heater having a water reservoir configuration which prevents combustion gas build-up. A feature of the present invention is the positioning of a combustion gas point of egress adjacent to a water surface point in a vertical riser. An advantage of the present invention is the elimination of any gas head spaces and therefore of the build-up of high gas pressure and the accumulation of high temperature gas between the water level and a solid surface of the heater.  
         [0014]     Briefly, the invention provides a water heater comprising: a tower with a cold water inlet conduit causing water to fall through the tower and into a hot water collection tank in communication with the tower; a hot gas manifold adapted to receive hot gases and positioned in the tank so as to be at least partially submerged below the water surface; and a means of gas egress attached to the hot gas manifold and positioned above the water surface, the gas egress means configured to prevent the water falling through the tower from blocking gas egress from the manifold. In an alternative embodiment, the water collection tank surrounding said gas manifold forms an annular space adapted to receive water, the annular space configured to maximize thermal exchange between the manifold and the water residing in the annular space. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0015]     The foregoing invention and its advantages may be readily appreciated from the following detailed description of the invention, when read in conjunction with the accompanying drawing in which:  
         [0016]      FIG. 1  is a cross-sectional view of a combination direct/indirect water heater, in accordance with features of the present invention;  
         [0017]      FIG. 2  is a perspective view of a combination direct/indirect water heater, without the tower, in accordance with features of the present invention;  
         [0018]      FIG. 3   a  is a view of  FIG. 1 , taken along line  3 - 3 , and shows a cross-sectional view of a heat-transfer manifold included in the water tank of a combination direct/indirect water heater, in accordance with features of the present invention;  
         [0019]      FIG. 3   b  is a plan view of  FIG. 1 , taken along line  3 - 3 , of an embodiment of a heat-transfer manifold included in the water tank of a combination direct/indirect water heater, in accordance with features of the present invention;  
         [0020]      FIG. 3   c  is plan a view of  FIG. 1 , taken along line  3 - 3 , of another heat-transfer manifold configuration, in accordance with features of the present invention;  
         [0021]      FIG. 4   a  is a perspective view of a cap over a gas-inlet pipe included in a combination direct/indirect water heater, in accordance with features of the present invention;  
         [0022]      FIG. 4   b  is a perspective view of an alternative embodiment of a means of egress of combustion gases from a manifold, in accordance with features of the present invention;  
         [0023]      FIG. 4   c  is a detailed perspective view of a cap over a gas-inlet pipe included in a combination direct/indirect water heater, in accordance with features of the present invention;  
         [0024]      FIG. 5  is a cross-sectional view of a specific embodiment of a combination direct/indirect water heater, in accordance with features of the present invention;  
         [0025]      FIG. 6   a  is a cross-sectional view of  FIG. 5 , taken along the line  6 - 6 , of a heat-transfer manifold incased in the water tank of a high efficiency combination direct/indirect water heater, in accordance with features of the present invention;  
         [0026]      FIG. 6   b  is a cross-sectional view of  FIG. 5 , taken along line  6 - 6 , of an alternative embodiment of a heat-transfer manifold included in the water tank of a high efficiency combination direct/indirect water heater, in accordance with features of the present invention;  
         [0027]      FIG. 6   c  is a cross-sectional view of  FIG. 5 , taken along line  6 - 6 , and shows a cross-sectional view of another alternative embodiment of a heat-transfer manifold included in the water tank of a high efficiency combination direct/indirect water heater, in accordance with features of the present invention; and  
         [0028]      FIG. 7  is a more complete schematic diagram of the invented heater, in accordance with features of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     The present invention provides a high efficiency combination direct/indirect heater that facilitates both direct and indirect heat transfer to a liquid. For the sake of simplicity, it will be assumed throughout this specification that the liquid being heated is water. A salient feature of the invention is the immersion of a heat transfer surface, such as a combustion gas manifold, in already heated water, thereby enhancing efficiencies.  
         [0030]     As shown in  FIG. 1 , the combination direct/indirect water heater, generally designated as numeral  10  is comprised of five main components: a vertical riser  20  (often called “tower”), a cold water supply inlet  30 , a hot water reservoir  40 , a fuel burner  50 , a hot gas inlet conduit or manifold  60  that is nearly fully submerged in the reservoir  40 , and a means for water egress  58 .  FIG. 2  is a perspective view of the invented combination direct/indirect water heater, without the tower.  
         [0031]     A water supply and distribution means  30  distributes water  31  so as to contact the water with hot combustion gases  71  emanating from the gas conduit  60 . At this juncture, which is approximately midway along the vertically extending space defined by the tower, heat is transferred from the gas to the water in a direct heating mode. To impart additional heat transfer to the incoming water, heat transferring materials  22  are positioned intermediate the water distribution means  30  and the gas egress means  63  of the conduit  60 . These transfer materials  22 , which typically comprise high surface area, relatively inert materials, are heated continuously by the upwardly traveling gas, thereby imparting heat to the falling water. The transfer materials  22  are supported by a perforated packing shelf  24 , (such as a rack) extending transversely to the tower.  
         [0032]     The tower  20 , the cold water inlet manifold  30 , and the gas burner  50  are similar to devices disclosed in U.S. Pat. No. 6,089,223, assigned to the instant assignee, and incorporated herein by reference.  
         [0033]     A unique feature of the invented device is that combustion gases produced by the gas burner  50  are released into the partially submerged gas conduit or manifold  60 . As depicted in  FIG. 1 , the manifold is submerged in the collection tank  40  so as to be in direct physical contact with the water previously subjected to direct heating.  
         [0034]     Intermediate the gas exit point  63  and the gas means of ingress  61  of the gas manifold  60  is positioned a vertical, upwardly extending conduit section  68 . The upwardly extending conduit section  68  terminates with the means of gas egress  63 . The means of gas egress is positioned so as to reside in the middle to lower half of the tower  20 .  
         [0035]     Manifold Configuration Detail  
         [0036]     To maximize heat transfer, the submerged combustion gas manifold can effect a circuitous path for the combustion gas to travel, as shown in  FIG. 3   a.  The manifold depicted in  FIG. 3   a  comprises a single conduit  64  between ingress point  61  and egress point  62  with a plurality of substantially rectilinear sections  65  serially connected by U-shaped pipe junctions  66 .  
         [0037]     Alternatively, and as shown in  FIG. 3   b,  the manifold  60  comprises a plurality of substantially parallel conduits  64  between points  61  and  62 . The parallel conduits are intersected at each end by main combustion conduits  53 . This design minimizes travel time of combustion gas through the conduit so as to eliminate back pressure to the combustion chamber.  
         [0038]     In yet another configuration of the manifold, a spiral design is utilized for the manifold, as depicted in  FIG. 3   c.    
         [0039]     Optionally, fins substantially radially protruding from the conduits may be added so as to enhance heat transfer from the hot gas to the water in the tank  40 . The planar surfaces of these are positioned anywhere between 0° and 90° to the direction of gas flow at the point where the fins are attached to the conduit. For example, as depicted in  FIGS. 3   a - 3   c,  fins  67  are attached so that their plane surfaces are perpendicular to the direction of gas flow. This is particularly advantageous for maximizing heat transfer to the water. Also depicted in  FIG. 3   a  are fins  59  directed along the direction of gas flow.  
         [0040]     A variety of materials are suitable for fabrication of the gas manifold  60 , as long as the material is impermeable to the liquid being heated, and tolerant to the gas temperatures emanating from the combustion chamber.  
         [0041]     Preventing Water from Entering The Gas Manifold.  
         [0042]     To prevent water from entering the means of gas egress, the combustion gas manifold terminates in a cap  70  positioned distal to the rim  69  of the vertical conduit  68 , thereby defining the means of gas egress  63 . Specific embodiments of the means of gas egress are depicted in  FIGS. 4   a,    4   b,  and  4   c.  In practice, other embodiments may be employed by combining features of two or three of the depicted embodiments. The cap  70  is so positioned as to allow streams  71  of the hot gas to circumvent it and to contact the downward falling water  31 . As shown in  FIG. 4   a,  a plurality of circumferentially spaced apertures  80  about the rim  69  can be provided so as to allow venting of the gas from the means of egress and inferior to the position of the cap  70 . Several methods can be used to support the cap. In  FIG. 4   a  the cap is mounted at some distance above the point of gas egress  63  by means of a plurality of supporting rods  73  attached to a ring  51  encircling the rim  69  of the gas conduit  68 . In  FIG. 4   b  the cap  70  is attached to the riser by means of a perforated plate  21 , but brackets or other means of support can be employed.  FIG. 4   c  depicts an alternative embodiment wherein the cap is attached to the gas conduit  68  by means of four plates  89  and wherein circumferentially spaced apertures  80  on a vertical portion  74  of the cap  70  are provided so as to allow venting of the gas.  
         [0043]     To prevent a laminar flow of water from fanning out from the top  81  of the cap  70 , (which would lead to the impedance of gas from the means of egress), the cap  70  is so contoured as to prevent formation of such laminar water flow. As shown in  FIGS. 2, 4   a,  and  4   c,  the cap  70  comprises a vertical cylindrical portion  74 , to which is attached a radially protruding conical brim or a series of conical flaps  75 . Formation of laminar water flow around such an irregularly shaped cap is substantially prevented by the conical brim  75  or flaps. As shown in  FIGS. 2 and 4   a,  the conical flaps also provide protection from water entry into the gas egress apertures  80 . A variety of other cap embodiments comprising irregular surfaces achieve the same anti-laminar-flow objective.  FIG. 4   b  depicts a cap with an hemispherical top  93  the inside surface  91  of which allows a smoother redirection of the combustion gas  71 . Optionally, as shown in  FIG. 4   c,  flaps  85  mounted above the apertures  80  prevent water from entering into the gas conduit.  
         [0044]     Also shown in  FIG. 4   b  is a cooling ring  56  positioned in the annular space  32  defined by the inwardly facing surface  82  of the riser and the outwardly facing surface of the conduit  68 . As depicted in  FIG. 4   b  this cooling ring  56  is a plate separated from the conduit  68  and the riser  40  by narrow gaps arranged along its inner and outer peripheries. The cooling ring is skip welded to the inward pointing surface  82  of the riser  40  at locations  57 . The cooling ring  56  allows water to collect at this point, but one or more overflow ports  54  ensure that the water does not reach the gas egress point  63 . The cooling ring facilitates impact of the falling water with the outwardly facing surface of the conduit  60  and the inwardly facing surface  82  of the riser.  
         [0045]     Preventing Gas from Entering The Water Reservoir.  
         [0046]     After cascading downwardly past the cap  70 , the falling water enters the collection and storage tank  40  where it forms a volume of hot water  41  having a water surface  42 . In as much as the cap  70  covering the gas inlet conduit  68  inevitably directs downward some of the hot gas to the water surface  42 , a provision is made to prevent the hot gas from becoming trapped in the head space  43  defined by an inside top surface  45  of the storage tank which opposes the water surface  42 .  
         [0047]     To prevent gas from being trapped in the head space  43 , a baffle  77  is provided to deflect downwardly-flowing gas away from the water surface  42  and head space  43 . As depicted in  FIG. 4   a,  the baffle comprises a substrate radially extending from the upwardly extending conduit section  68 . Typically, the baffle is positioned coaxial with the conduit  68  with the plane of the baffle parallel to and above the top of the collection tank  40 . The periphery of the baffle  77  opposes an interior surface  79  of the upwardly extending tower  20  so as to define an annular passageway  78  through which water cascades. The width of the passageway is dimensioned so as not to impede downward water passage while also preventing substantial gas volumes from passing downwardly through the passageway. Generally, the diameter of the baffle  77  is greater than the diameter of the cap  70 .  
         [0048]     In the embodiment depicted in  FIG. 4   b,  the cooling ring  56  serves the same function as the baffle  77  in  FIG. 4   a.    
         [0049]     A Sleeve-Shaped Reservoir  
         [0050]     A feature of a specific embodiment of the invented device is depicted in  FIG. 5 . In this embodiment the hot gases produced by the gas burner  50  are released into a gas conduit or manifold  160  which is substantially submerged in a reservoir  140 .  
         [0051]     To maximize heat transfer, a longitudinally extending exterior surface of the heated-gas manifold  160  is juxtaposed in spacial relation to interior surfaces  164  of the reservoir  140 . More specifically, an inwardly-facing surface  164  of the reservoir serves as a sleeve encasing the manifold and spaced from the manifold so as to maximize the ratio of manifold surface area to water volume as shown in  FIG. 5 .  
         [0052]     In cases where the cross section of the manifold and the cross section of the sleeve are both circular, an annular space  163  is defined by an inside surface  164  of the reservoir opposing a longitudinally extending exterior surface  165  of the manifold  160 . The distance Δ between the opposing surfaces is generally maintained to ensure maximum heat exchange from the manifold. In one embodiment, in order to minimize turbulence in the water flow, the distance Δ is kept constant, no matter what circuitous route the conduit takes.  
         [0053]     To further maximize heat transfer, the diameter of the manifold is typically 30 to 60% of the diameter of the enveloping sleeve and preferably 40 to 56% the diameter of the enveloping sleeve.  
         [0054]      FIGS. 6   a - 6   c  are cross-sectional views of  FIG. 5 , taken along the line  6 - 6 . The manifold depicted in cross-section in  FIG. 6   a  comprises a single cylindrical conduit  160  nested inside a sleeve  140 . The surface of the conduit defines a smooth uninterrupted surface to facilitate rapid laminar flow of water along the surface.  
         [0055]     The manifold depicted in cross-section in  FIG. 6   b  comprises a single conduit  160  with, optionally, a plurality of substantially radial protruding sections or fins welded or otherwise suitably thermally connected to the manifold  160 . These fins may be aligned along the direction of gas flow (fins  166 ) or orthogonal thereto (fins  167 ) or at any angle there-between. The fins enhance heat transfer from the hot gas to the water in the tank  140 . The radially protruding sections are utilized in situations where calcification build-up is not an issue.  FIG. 6   c  depicts a detail of an alternative embodiment wherein the hot gas manifold  160  has a corrugated cross-section. This corrugated manifold can also be used in conjunction with the embodiment depicted in  FIGS. 1-3   c.    
         [0056]      FIG. 7  provides a more complete schematic diagram of the invented device. Specifically,  FIG. 7  shows a high temperature shut down sensor  120  and high water sensors  130  located below the gas egress point  63 . The “high water” sensors allow shut off of the device when water threatens to flood the gas conduit  60 . The “low water” sensors  150  allow shut off of the device when it threatens to overheat. Also provided is a heater overflow pipe  140 . Also depicted are components of the device discussed supra: the fuel burner  50 , the firing chamber  60 , the water storage tank  40 , the cooling ring  56 , the protective cap  70 , the heat transfer rings  22 , and the inlet nozzles  31 .  
         [0057]     The foregoing description is for purposes of illustration only and is not intended to limit the scope of protection accorded this invention. The present invention may be presented in other specific embodiments without departing from the essential attributes of the present invention. It is apparent that many modifications, substitutions, and additions may be made to the preferred embodiment while remaining within the scope of the appended claims, which should be interpreted as broadly as possible.