Abstract:
A heater comprises an enhanced-surface area heat transfer vessel which is situated co-axially in a hot flue gas plenum. The plenum is formed by dual-wall heating jacket. Liquid flowing through the jacket is heated co-currently by the flue gas before the preheated liquid is conducted to the top of the vessel for countercurrent heat exchange therein before discharge from the bottom of the vessel. Hot flue gas flowing through the plenum is directed circumferentially by one or more spaced and perforated ring plates placed across the plenum annulus between the jacket and the vessel. Aluminum construction of the vessel and jacket with protective coatings contribute to a lightweight heater for either floor or even wall mounting. The heater is conveniently implemented in a hydronic heating system, a potable hot water system or a combination of both.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to liquid heaters having a burner to dispense hot combustion or flue gases which heat a finned heat exchange vessel filled with fluid, the flue gas being diverted about and through baffles to increase efficiency. More particularly the liquid is first preheated in a first stage in an outer jacket which is also exposed to the flue gases. Such a heater is applicable to hydronic heating systems and domestic water heating.  
         BACKGROUND OF THE INVENTION  
         [0002]    Hydronic heating systems circulate hot water in a closed system comprising a water heater and a plurality of radiators. Sometimes consumable hot water is also obtained through heat exchange with the closed hydronic system.  
           [0003]    Today, the most common of domestic water heaters comprise a pressure vessel having a cylindrical wall, a hemispherical top and a concave, hemispherical bottom which is directly exposed to a gas or oil burner. The effective heat exchange surface is substantially limited to the hemispherical base. The vessel also has a central flue for discharge of flue gases and some recapture of the heat from the hot flue gases. A cool water inlet is located near the base of the vessel. The water in the vessel is heated and the resulting hot water rises to the top of the vessel for extraction on demand. The vessel is insulated along its cylindrical portion to reduce heat loss during standby periods. The efficiency of such a hot water vessel is not particularly high.  
           [0004]    In systems having a larger heat demand, such as those used for heating living space, it is conventional to use boilers and heat exchanger furnaces which utilize large surface heat transfer areas by providing a plurality of tubes either through which or around which combustion gases pass for delivering up their heat to the heat transfer fluid on the opposing side of the tubes. Tubes are often linearly extending between opposing heads or are coiled to minimize space and maximize surface area. There are many connective joints, relatively fragile materials of construction and many opportunities for failure and resulting expensive repairs.  
           [0005]    In the past and out of favor today due to low efficiencies, a water heater was introduced which utilized a ribbed, inverted cone-shaped water reservoir which was enclosed in an outer cylindrical casing. Such a heater is specifically set forth in Canadian patents 405,431 in 1942 and CA 473,394 in 1952, both to Wenger. An annular plenum having an upwardly diminishing cross-sectional area was formed between the conical reservoir and the casing through which flue gases were conducted for heating the reservoir. As in typical hot water heaters, cool water was introduced at the base of the reservoir and hot water was removed from the top of the reservoir. The reservoir was ribbed and heat transfer occurred substantially through conduction of heat to the reservoir from the hot flue gases passing in a co-current flow upwardly through the plenum to the reservoir&#39;s sidewall. Hot flue gases were vented from the plenum. While successful due to their simplicity and reliability, their efficiencies became unacceptable, and eventually their use diminished.  
           [0006]    The used of coiled tubing boilers is associated with high cost and expensive repairs but have relatively high efficiencies. The cone type heaters of Wenger were inexpensive, associated with low maintenance but have only low efficiencies. These disadvantages of the prior art systems are believed to be resolved by the water heater of the present invention.  
         SUMMARY OF THE INVENTION  
         [0007]    In one aspect of the present invention, a heater is provided for supplying hot water in a heating system. The heater comprises a combination of a low-maintenance, enhanced-surface area heat transfer vessel which is situated in an annular hot flue gas plenum. In a preferred arrangement using a supplemental and first stage dual-wall heating jacket, efficiency is increased so as to be comparable to more sophisticated, expensive and higher maintenance systems of the prior art. Hot flue gas flowing through the plenum is directed circumferentially by one or more perforated ring plates for enhanced convective heat transfer about the vessel.  
           [0008]    In a broad aspect of the invention, the heater comprises: a housing having a base and an upper exhaust end for forming a plenum which conducts a flow of hot flue gas from a burner positioned adjacent the housing&#39;s base; a heat transfer vessel having a substantially conical body with a closed tip and a closed top, the body residing substantially coaxially within the plenum so as to form an annular space therebetween through which hot flue gases upwardly flow to the exhaust end, the tip of the body being oriented closest to the burner and having side walls diverging upwardly towards the plenum&#39;s exhaust end; an inlet adjacent the vessel top and a vessel outlet adjacent the vessel tip so that the liquid flows downwardly and countercurrent to the hot flue gas and is heated before being discharged from the vessel; and one or more annular plates located transverse across the annular space for at least partially distributing the hot flue gas about the vessel as they pass upwardly by the one or more annular plates. It is preferred to insulate the housing for this embodiment, the housing quickly achieving flue gas temperatures.  
           [0009]    Preferably, the annular plates contain a plurality of openings therethrough, at least some of which are louvered forming baffles for urging the flue gas to circulate about the vessel. Where two or more plates are used, the baffles can be oriented in the same circumferential direction or in alternately opposite directions.  
           [0010]    More preferably, the heater can be fitted with a preheating jacket containing the liquid for preheating it before directing to the vessel.. The jacket accepts even more heat from the hot flue gas and results serendipitously in a lower outside jacket temperature which may not even require thermal insulation in when the feed liquid enters the heater at ambient temperatures. The annular jacket comprises inner and outer walls which are closed at a lower and an upper end and forming an annular cross-sectional space therebetween, the inner wall forming the housing and which is in heat conductive communication with the hot flue gases in the plenum; an inlet at the jacket&#39;s lower end and an outlet at the jacket&#39;s upper end so that liquid can flow from the inlet to the outlet and be preheated before discharge into the vessel&#39;s inlet.  
           [0011]    In another broad aspect, the preheater jacket can be combined with any of a variety of heat exchanger for convenient and more effective use of the hot flue gases. Further improvement in efficiency can be obtained by adding one or more annular plates.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a schematic view of a combined space heating and potable water heating system integrating a heater of the present invention;  
         [0013]    [0013]FIG. 2 is an isometric view of a conical vessel positioned in a plenum according to one embodiment of the invention;  
         [0014]    [0014]FIGS. 3 a  and  3   b  are two styles of annular plates having a plurality of baffles formed therein, about 36 baffles in the top plate of FIG. 3 a , and about 55 baffles and an additional 9 non-baffled openings in FIG. 3 b;    
         [0015]    [0015]FIG. 4 is a side cross-sectional view of a portion of a side wall of the vessel and a radial portion of an annular plate with a representation of the flow of hot flue gas through a plurality of baffles;  
         [0016]    [0016]FIG. 5 a  and  5   b  are schematic views illustrating a vessel in its plenum and having a pair of annular plates and baffles which induce circumferential flow of the hot flue gas about the vessel. FIG. 5 a  illustrates each annular plate inducing the same direction of flow and FIG. 5 b  illustrates inducing of alternating directions of flow;  
         [0017]    [0017]FIG. 6 is a side, cross-section view of the heating vessel and water jacket and illustrating a schematic of a preferred flow of liquid through the heater which includes a preheating jacket;  
         [0018]    [0018]FIGS. 7 a  and  7   b  are partial cross-sectional side and plan views of the vessel&#39;s top and the inlet and liquid discharge to the vessel;  
         [0019]    [0019]FIGS. 8 a - 8   c  are charts illustrating the improvement in heating efficiency by applying various embodiments of the present invention; and  
         [0020]    [0020]FIG. 9 is a top perspective view of a hydronic system implementing a heater of the present invention suitable for integration with the loop of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    With reference to FIG. 1, a heater  10  is provided in a system for heating liquids. Herein, several embodiments are described one of which includes a closed system such as a hydronic heating system which heats a first liquid in the heater which is usually recirculated as hot liquid in a domestic water heating system. In another embodiment. the heater heats a first fluid in a closed system for indirect heating of a second liquid. An example of such a system comprises heating liquid, glycol or water for instance, in the heater and passing this heated liquid through a heat exchanger for heating potable water as the second liquid.  
         [0022]    The heater can be part of a heating system or can used independently for heating the designated liquid.  
         [0023]    As shown in FIG. 1, in a typical hydronic domestic heating situation, an embodiment of the heater  10  of the present invention is part of a closed heating loop  11  which circulates a liquid such as water and the heat transfer medium. The heater comprises a heat exchanger portion  30  (described in detail below) and a burner  12  which bums a mixture of fuel  13  and air  14  and emits a hot flue gas  35 . The heater accepts cooled water and produces hot water for reintroduction to the closed heating loop  11 . The loop has a make-up water source  19 . The loop also comprises an expansion tank  15  and a circulation pump  16 . The loop  11  delivers hot water to a plurality of heating devices or radiators such as convectors, fan coils and floor heating tubing  17  or room radiators  18  as depicted in FIG. 1.  
         [0024]    A potable water heating loop circuit is also illustrated. Potable water  20  is directed through a conventional liquid to liquid heat exchanger  21  for transferring heat from the loop  11  to the potable water  20 . The heat exchange  21  has two chambers in thermal communication, a first in liquid communication with the hot water in the loop  11  and a second in communication with a supply of potable water  20 .  
         [0025]    In greater detail, and with reference to FIG. 2, in a first standalone embodiment, the heater  10  comprises a cylindrical housing  31  having a base  32  and an upper exhaust end  33 . One or more burners  12  are positioned in the base  32  of the housing  31 . The housing  31  forms a plenum  34  for conducting products of combustion, or hot flue gas  35 , to the exhaust end  33 .  
         [0026]    A suitable burner is a naturally aspirated, low pressure gas burner. As shown in FIG. 1, the burner comprises one or more annular burner heads having a multiplicity of ports for emitting a combustible gas/air mixture. Those of skill in the art are knowledgeable and capable of providing the associated combination of the type of gas, the gas pressure, the size of orifice and number and size of burner head ports required to effect efficient combustion. The top exhaust also produces enough draft to draw the hot flue gases and prevent burn back. The burner heads are spaced beneath from the body&#39;s tip end. By spacing the burners  12  below the vessel  40  so that the air and fuel mix before reaching the vessel heat exchanger, the flue gases are not dissuaded from intimate contact with the vessel.  
         [0027]    A heat transfer vessel  40  is suspended in the housing  31  for receiving heat from the burners  12  and hot flue gas  35 .  
         [0028]    There are a variety of heat transfer vessels which can be applied. Use of an enhanced surface unitary body vessel has simplicity as an advantage. Coiled heat exchangers have the advantage of greater surface area. Use of a coiled heat exchanger in combination with a preheater jacket is described in greater detail below.  
         [0029]    In one embodiment, the vessel  40  has a substantially conical body  41  with a closed tip  42  and a closed top  43 . The vessel  40  is located substantially coaxially within the plenum  34  so as to being in contact with hot flue gases  35  across the surface of the vessel  40 . The body&#39;s tip  42  is oriented closest to the base  32 . Accordingly, the body has side walls  46  that diverge upwardly towards the plenum&#39;s exhaust end  33 . The body&#39;s side walls  46  are fitted with a plurality of heat transfer fins  47 . The fins  47  are shown extending axially along the body&#39;s side walls. While they can be more challenging to manufacture, the fins  47  can also be formed in other orientations such as circumferentially or helically about the vessel&#39;s body  41 .  
         [0030]    An annular space  48  is formed between the vessel&#39;s body  41  and the housing  31  for enabling the hot flue gases  35  to flow from the burners  12 , past the vessel  40  and to the housing&#39;s exhaust end  33 . The housing can be cylindrical and the cross-section of the annular space diminishes upwardly to a minimum at about the body&#39;s top end  43 . A constriction between the vessel&#39;s top end  43  and the housing  31  at the top of the annular space  48  has been found to assist in creating a draft for the flue gas, aiding in combustion.  
         [0031]    The vessel  40  has an inlet  50  adjacent the top  43  of the conical body  41  for the entry of relatively cool liquid the vessel. An outlet  51  is located adjacent the tip  42  of the conical body  41  for the discharge of heated liquid from the vessel. Accordingly, and in contradistinction to conventional water heaters, the liquid flows in the inlet  50 , downwardly through the vessel  40  and out of the outlet  51 , while the flue gas  35  rises and flows upwardly past the vessel  40 ; the ;liquid and gases establishing a countercurrent heat exchange.  
         [0032]    Having reference to FIGS. 2, 3 a  and  3   b , one or more annular plates  60  are located transversely across the annular space  48 . Each plate  60  has a plurality of openings  61  formed therein for enabling hot flue gases  35  to pass therethrough.  
         [0033]    With reference to FIGS. 3 a - 5   b , in an alternate embodiment, at least some of the openings  61  are fitted with louvers or baffles  62  for diverting the flue gas  35  laterally. As shown in FIGS. 3 and 4, the baffles  62  extend laterally across the openings. By orienting all of the baffles circumferentially, and in the same direction, the flue gases can be induced to move somewhat circumferentially and thus swirl about the vessel  40  as they flow up the plenum  34  to the top exhaust  33 . The plates  60  have an inner periphery  60   i  and an outer periphery  60   o , each of which is sized to the body  41  and housing  31  respectively so that flue gas  35  is urged to flow through the plate&#39;s openings  61  and in the case of baffles  62 , to be urged to spiral up the annular space  48 .  
         [0034]    The plate&#39;s openings  61  are generally uniformly arranged circumferentially about the plates  60  so that hot flue gases  35  are substantially evenly distributed about the plenum.  
         [0035]    With reference to FIGS. 5 a  and  5   b , use of more than one plate  60  having baffles  62 , permits control over the movement of the hot flue gas. The plates are spaced vertically apart and successive plates with baffles having the same orientation can re-induce the flue gas to move in the same direction (FIG. 5 a ). Successive plates with baffles having alternating and opposing orientation will induce the flue gas to move in opposing directions (FIG. 5 b ).  
         [0036]    The one or more annular plates  60  are spaced vertically along the vessel  40 . The lowest of the plates  60  is positioned sufficiently above the burner so as to minimally impinge on the burner&#39;s combustion process.  
         [0037]    Cooler water enters the vessel at the upper inlet  50 , is heated by conduction through the body side walls and flows as hot water out of the lower outlet  51 . Additional heating is possible using the housing itself to recover heat from the burner and hot flue gas.  
         [0038]    When used as a single stage of heating, the housing is preferably insulated for safety and heat conservations purposes.  
         [0039]    In another embodiment, the housing  31  itself formed into an annular water jacket  70 . The jacket is a preheater stage for the liquid. It is conceivable that the jacket may not even require insulation as the incoming feed water, though the liquid therein is undergoing a heating process, may not require insulation on its periphery. Applicant is not aware of a heater provided with such a preheater jacket, regardless of the form of the main boiler or heat exchanger portion.  
         [0040]    The jacket has a cylindrical inner wall  71  which forms the housing  31  for the vessel  40  and which is in heat conductive communication with the hot flue gases  35  in the plenum  34 . A cylindrical outer wall  72  is positioned concentrically around the inner wall for forming an annular cross-sectional space  73  therebetween. The annular space  73  is closed at a lower end  74  and at an upper end  75  for forming a water chamber  76 .  
         [0041]    A liquid inlet  77  is formed at the outer wall  72  of jacket&#39;s lower end  74  for admitting feed liquid and an outlet  78  is formed at the inner wall  71  at the jacket&#39;s upper end  75  for conducting preheated liquid to the vessel&#39;s inlet  50 . Optionally, to better distribute the incoming feed water from the inlet  77  and circumferentially about the jacket  70 , , it may be advantageous to utilize means such as an annular baffle  79  situated in the annular space between the inner and outer walls  71 , 72 .  
         [0042]    With reference to FIG. 7, vessel inlet  50  is fitted with a discharge  80  into the interior  81  of the vessel&#39;s body  41 . The discharge  80  is oriented slightly downward (FIG. 7 a ) and at an angle to the side wall (FIG. 7 b ) so as to induce a spiraling and preferably turbulent movement of the water as it flows downwardly through the vessel  40 . The inlet  50  is located adjacent a side wall  46 .  
         [0043]    As shown in FIG. 1 the heater  10  is part of a space heating system. The system is fitted with safety features such as thermocouple auto shutoff and pressure relief valves.  
         [0044]    With reference to FIG. 9, a heater is incorporated in a package which includes the expansion tank  15 , the pump  16 . A potable hot water heater  21  is also tied into the loop  11  immediately adjacent to the pump  16 . Accordingly, the heater package can be applied for heating a product liquid such as for heating potable hot water directly. In a more versatile system, the heat heats a primary liquid such as water or glycol which is supplied to one or more radiators and to a heat exchanger for a secondary liquid such as for heating potable water  
       EXAMPLE  
       [0045]    A lightweight heater according to an embodiment of the invention as show in FIG. 6, was constructed and various performance tests were conducted thereon. The body&#39;s side walls were formed of nominally {fraction (3/16)}″ thick cast alloy aluminum with vertically oriented fins incorporated into the side walls; the fins alternating between ¾″ tall and ½″. The vessel  40  was 14″ tall with a top end  43  formed of a cast aluminum plate about 8″ in diameter. The jacket  70  was constructed of rolled aluminum with the inner wall and housing  71 , 31  being about 8½″ in diameter forming an annular gap around between the vessel&#39;s top end  43  and the inner wall  71  of about ¼″.  
         [0046]    The vessel&#39;s inlet  50  was fitted with a ¾″ pipe discharge angled downwardly at about 15° and angled from the side wall  46  at about 45°. As shown in FIG. 7 a , the vessel&#39;s top end  43  was sealed using a gasket  83  and secured to the body  41  with a plurality of fasteners. Nominal operating pressure rating for the vessel was about 18 psig.  
         [0047]    The vessel&#39;s cast components were treated inside and out. A smooth and non-reactive coating of high temperature single-part epoxy paint was added to the inside of the vessel for exposure to the heat transfer fluid; in the example case the fluid was water. Various epoxy formulations are possible and persons skilled in the art are aware of those enhanced for heat transfer such as composition and color. The outside was first treated with sodium meta-silicate under vacuum (cleaning and reduction of casing porosity) prior to applying a high temperature resistant and anti-corrosive mica-zinc coating (available from Corning). The liquid side of the jacket inner and outer walls were also coated with the epoxy paint. The cylindrical jacket components can be manufactured of rolled aluminum.  
         [0048]    The burners produced nominal heat output of 35000-55000 Btu/hr as natural gas burners operating on 3-5″ water column gas source and combustion air being naturally aspirated. Aluminum burner heats aid in maintaining an exceptionally light overall heater weight.  
         [0049]    The annular plates were stainless steel. Tests were performed with and without the plates and with one or two plates installed.  
         [0050]    Tests were performed, only some of which are illustrated herein. Objectives for the particular heater  10  were to achieve efficiencies greater that 80% with carbon monoxide levels below 200 ppm and flue gas exhaust temperatures of less than about 200-250° C. Different heaters and burners can alter the objectives and particularly the flue gas temperatures which could still higher yet while still achieving high efficiencies.  
         [0051]    Tests presented herein illustrate a large improvement in efficiency from the prior art co-current conical vessel and once the objectives were obtained, further variation only resulted in minimal changes in performance between the various embodiments. Water flow rates ranged from 1.8-2.2. Combustion was tested with a Bacharach Model 300 analyzer. The tests were conducted at 1200 m above sea level. A thermal load was placed across the hot outlet and cool inlet to the heater to form a differential temperature.  
         [0052]    As shown in Table 1 and FIGS. 8 a - 8   c , the results included:  
                                                                                                         Water                   Flue               flow   Load       Efficiency   CO   T               Gpm   ΔT ° C.   BTU/hr   %   ppm   ° C.   Status                                    A   1.8   40   46150   60   25   398   No Plates       B   2.2   30   42000   80   6   198   Single Plate       E   2.2   40   48000   82.6   201   178   Single Plate       F   2.2   35   55000   83.1   104   149   Two Plates       G   2.2   33   45000   83.2   72   169   Two Plates       H   2.2   30   42000   81   17   184   Two Plates                  
 
         [0053]    In the case of a single plate, the annular plate was located about 5″ from the top  43  of the 14″ vessel  40 . In the case of two plates, the second annular plate was spaced about 9″ from the top of the vessel, or 4 more inches from the first baffle and about 12 inches above the burners to minimize flame impingement and ensure substantially complete combustion was achieved. Typical temperatures for a test were about 140° C. at the jacket inlet  77 , 160° C. at the jacket outlet  78  to the vessel inlet  50 , and about 180° C. exiting at the vessel outlet  51  with the thermal load taking out about 40° C.  
         [0054]    The heater can be used as a new installation or as a retrofit. While the light, small and maintenance free operation is particularly appreciated in domestic service, the heat is just as adaptable to commercial operations. The vessel and jacket are less sensitive to hard water operations than are the coil-type boilers.  
         [0055]    Whereas a preferred embodiment of the invention has been shown and described herein, it will be apparent that many modifications, alterations and variations may be made within the intended broad scope of the invention as defined in the appended claims. For example, whereas the cylindrical shape of the housing or of the conical shape of the vessel is preferred, other shapes or cross-sections can be implemented.