Abstract:
A radiant heater system of the type having an radiant energy emitter conduit, the radiant heater system comprising an emitter extending at least partly through the area to be heated. The radiant heater system further including a burner for burning fuel thereby forming combustion products, said burner connected to an inlet end of the emitter to inject thermal energy into the emitter and an exhaust end of the emitter serving to exhaust combustion products. The radiant heating system further including an air intake sleeve for controlling the amount of combustion air available to said burner, and a blower sized to provide dilution air communicating with said burner wherein the dilution air cools the combustion products proximate said inlet end thereby reduces the emitter temperature proximate said inlet end.

Description:
This application claims benefit to U.S. provisional application No. 60/139,432, filed Jun. 8, 1999. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to indoor heating systems and specifically to a radiant heater system. 
     BACKGROUND OF THE INVENTION 
     Tube fired radiant energy heater systems are frequently used in industrial and commercial buildings which are difficult to heat. In such applications, radiant energy heating systems are regarded as superior to forced air systems from the stand points of the economy and comfort in minimizing the stratification of heat from top to bottom in a building and in fuel savings. Tube fired radiant heaters radiate heat downwards towards the floor thereby heating the floor and taking advantage of the natural convection of heat from the bottom to the top of the interior of the building. 
     Tube fired radiant heating systems normally include a burner mounted at the inlet end of an emitter tube which radiates heat along its length to the exhaust and of the emitter tube wherein the combustion products are naturally vented away into the atmosphere. The temperature of the emitter tube naturally varies from the inlet end to the exhaust end, the hottest end being nearest the combustion flame of the burner at the inlet end and the coolest area of the emitter tube normally being the exhaust end where the exhaust gases are vented to the atmosphere. This results in an undesirable temperature profile (or temperature drop) along the emitter tube, the inlet being the hottest end of the emitter tube and the exhaust end being the coldest part of the emitter tube. Most indoor heating systems strive to produce as uniform as possible, temperature distribution throughout the building that is being heated. Unfortunately the temperature profile that is present in most radiant tube emitters creates non uniform heating along the length of the emitter tube and therefore, non uniform temperatures throughout the building that is being heated. 
     The problem is further exacerbated the longer the emitter tube being supplied with heat from a single burner. Therefore, building configurations which are long and narrow requiring long emitter tubes are particularly susceptible to a larger temperature profile from the inlet end to the exhaust end in a radiant tube heater system. 
     Some attempts have been made to minimize this problem and in particular U.S. Pat. No. 4,529,123 filed by Arthur C. W. Johnson on Sep. 2, 1983 and issued on Jul. 16, 1985 and assigned to the Combustion Research Corporation describes an attempt to minimize the temperature profile along a radiant heater emitter tube. U.S. Pat. No. 4,529,123 utilizes an insulated sleeve along the inlet portion of the emitter tube in order to reduce the amount of heat transferred to the emitter tube along the first portion of the emitter tube. The Patent discusses insulating materials such as magnesium oxide, aluminum oxide, ceramic materials, solid materials, glomerate fired and/or laminated sheets. Preferably the use of a ceramic insulator material is recommended which is manufactured by Carborundum Corporation under the Trademark Fiberfrax™. The patent disclosures that a more uniform temperature distribution along the emitter tube is achieved by using insulated sleeves however, a number of drawbacks have been experienced using this type of insulation method. In commercial practice the insulating material within the emitter tube tends to erode preferentially in certain areas due to direct impingement of the burner flame onto the insulating material and/or local hot spots caused by either small imperfections within the insulating material and/or in and around areas where connections in the insulating material have been made. Where a local hot spot develops in the insulating material, the emitter tube quickly heats to temperatures far beyond normal which it is capable of handling and often emitter tube failure will occur quickly thereafter. 
     In U.S. Pat. 4,044,751 by Arthur C. W. Johnson, filed May 19, 1975 and issued May 30, 1977 and assigned to the Combustion Research Corporation, the inventor describes a radiant energy heating system with power exhaust and excess air inlet. The object of the invention was to reduce the inlet and emitter tube temperature in order to reduce oxidation of the emitter tube and also to ensure that structural integrity was maintained of the emitter tube and also to be able to use lighter strength and thinner gauge emitter tubes in order to reduce the cost of radiant tube heaters. The patent does not discuss the possibility of using this technique for producing a more uniform temperature profile along the length of the emitter tube, but rather is essentially concerned with reducing the emitter end temperature in order to avoid material breakdowns. 
     It is desirable to have a radiant heater system having a more uniform emitter tube, temperature profile along its length in order to provide for more uniform heating particularly in spaces requiring very long emitter tubes. The more uniform the temperature profile along the emitter tube the more uniform heating can be achieved. In some instances, uniformity of temperature is highly critical, as for example in animal confinement and/or other applications. 
     SUMMARY OF THE INVENTION 
     The present invention a radiant heater system of the type having an radiant energy emitting emitter conduit, the radiant heater system comprises 
     a) an emitter extending at least partly through the area to be heated; 
     b) a burner means for burning fuel thereby forming combustion products, said burner connected to an inlet end of the emitter to inject thermal energy into the emitter; 
     c) an exhaust end of the emitter serving to exhaust combustion products from the burner; and, 
     d) a means for supplying dilution air to combustion products released by said burner means, wherein the dilution means cools the combustion products proximate said inlet end thereby reducing the emitter temperature proximate said inlet end. 
     Preferably the radiant heater system further comprises a means for lining the interior of said emitter, such that the liner means reduces the heat transferred to the emitter adjacent said liner. 
     Preferably the radiant heater system comprises an emissivity means for varying the emissivity of said emitter along the length of the emitter such that the emissivity means is employed to control the amount of radiant heat emitted by the emitter as a function of the distance along the emitter. 
     Preferably the radiant heater system wherein said dilution means includes an air intake sleeve for controlling the amount of combustion air available to said burner. 
     Preferably said air intake sleeve also providing for a dilution air passageway directing dilution air for mixing with said combustion products. 
     Preferably said lining means includes a liner adapted to lie adjacent a portion of the inner periphery of said emitter. 
     Preferably said lining means includes a sheet metal liner formed to lie adjacent a portion of the inner periphery of said emitter. 
     Preferably said emitter being tubular and said lining means including an emitter liner gap along the bottom of the emitter inner periphery for minimizing heat distortion of the emitter and promoting a more uniform vertical temperature distribution within said emitter. 
     Preferably said emissivity means includes said emitter being constructed of numerous emitter lengths wherein each emitter length having a preselected emissivity, wherein emitter length emissivities are preselected in order to maximize the temperature uniformity of the emitter along the emitter length. 
     Preferably the radiant heater system comprises a baffle inserted into the interior of said emitter proximate the exhaust end for promoting increases heat transfer to said emitter proximate said exhaust end and thereby providing a more uniform emitter temperature profile along the length of the emitter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described by way of example only, with references to the following drawings in which: 
     FIG. 1 is a schematic top plan view of the burner housing showing the top mounted blower and a portion of the emitter; 
     FIG. 2 is a side elevational view of the burner housing showing the blower mounted on top and viewing into the end of the emitter, showing a portion of the burner cup; 
     FIG. 3 is a side elevational view with the side panel removed exposing the contents of the burner housing including the gas regulator, the top mounted blower, a portion of the emitter as well as a portion of the air intake sleeve; 
     FIG. 4 is a schematic side elevational view of the radiant heater system with the side panel removed from the burner housing, showing the burner unit together with the emitters and a coupling; 
     FIG. 5 is a schematic side cross-sectional view of the radiant heater system shown in FIG. 4, showing in cross-section the emitter detail along its length; 
     FIG. 6 is a schematic graphical representation of the floor temperature as a function of the distance along the emitter reflecting the temperature profile along the emitter; 
     FIG. 7 is a perspective view showing a portion of the burner including the fuel supply line, a portion of the air intake sleeve, as well as a portion of the emitter tube; 
     FIG. 8 is a schematic perspective partial cut away view of the burner assembly showing details of the air intake sleeve, the burner, the dilution air passageway as well as the emitter tube and the emitter liner; 
     FIG. 9 is a front elevational view showing the emitter, the emitter liner, the burner, the burner cup as well as the dilution air passageway; 
     FIG. 10 is a schematic side partial cross-sectional view of the burner together with a portion of the emitter showing the details of the air flow through the burner as well as the emitter and details of the dilution air and the dilution air passageways; 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention, radiant heater system, shown generally as  20  is shown in schematic fashion in FIGS. 5 and 8. The major components of radiant heater system  20  include burner housing  22 , blower,  24 , air inlet compartment  26 , air intake sleeve  42 , control compartment  27  having gas regulator  44 , burner  90 , emitter  30  having inlet end  32  and exhaust end  34  and optionally emitter liner  36  and exhaust baffle  38  and coupling  120 . In addition emitter  30  has an emitter inner periphery  200 , emitter outer periphery  206 , liner outer periphery  202 , and liner inner periphery  204 . The emitter has a length extending from the inlet end  32  to the exhaust end  34 . 
     Referring now to FIG. 6, which is a schematic representation of the floor temperature shown as a function of the distance along the emitter tube, the prior art or the normal temperature distribution is shown in the dashed line, whereas the present invention which is shown in the solid line provides for a more uniform temperature distribution along the distance of the emitter. 
     The invention will now be described in more detail as to how it provides for a more uniform temperature profile along the length of the emitter. Still referring to FIG. 6, the dashed line  50  shows the prior art exhibiting a fairly steep temperature increase adjacent burner  90  followed by a substantial decrease in temperature moving away from inlet end  32  towards exhaust end  34  of emitter  30 . In contrast the solid line  52  which schematically represents the current invention, provides for a relatively flatter temperature profile along the distance of the emitter. Therefore the total temperature fluctuation exhibited by prior art devices dashed line  50  is much greater than the total temperature fluctuation provided for by the current invention solid line  52 . 
     Dilution Air 
     Referring now to FIG. 10 which is a schematic partial cross-sectional view of radiant heater system  20  including burner housing  22  as well as a portion of emitter  30 . 
     Burner housing  22  includes a control compartment  27  having disposed therein an electrical control  92 , a gas regulator  44 , a fuel supply line  60  communicating fuel  62  to burner  90 . 
     Burner housing  22  further includes air inlet compartment  26  having mounted thereon a blower  24  having an air intake  66  for receiving ambient air into blower  24  and communicating air  100  into air control compartment  68 . Air control compartment  68  includes an air baffle  64  having an opening  102  for communicating air  100  from air control compartment  68  into air inlet compartment  26 . Air  100  within air inlet compartment  26  is divided into two main streams; the air passing through air intake sleeve  42  providing combustion air  71  for a burner  90  and secondly, dilution air  76  passing through dilution air passageway  74 . 
     Fuel  62  passing through fuel supply line  60  is ejected at burner  90  and is mixed with primary combustion air  70  producing a combustion flame  80  and combustion products  104  which travel along emitter  30 . 
     Dilution air  76  passing through dilution air passageway  74  intermixes with combustion products  104  from combustion flame  80  thereby reducing the temperature of combustion products  104  and the ambient temperature within emitter  30  nearest inlet end  32 . 
     Air intake sleeve  42  acts as an air choke controlling the amount of combustion air  71  entering through and into air intake sleeve  42  and thereby controlling the amount of combustion air  71  available for burning of fuel  62 . Burner cup  78  houses ignition devices for lighting combustion flame  80  as well for providing a stabilized combustion area for combustion flame  80 . Secondary combustion air  72  passes between burner cup  78  and air intake sleeve  42  thereby providing further combustion air for ensuring that complete combustion of fuel  62  takes place in combustion flame  80 . 
     Primary combustion air  70  and secondary combustion air  72  ensure that a stoichiometric amount of air is provided and mixed with fuel  62  to ensure for substantially complete combustion of fuel  62 . In practice, a slightly excessive (usually  10  to 50% above stoichiometric) amount of secondary combustion air  72  and primary combustion air  70  is supplied to fuel  62  to ensure complete and thorough burning of fuel  62 . In other words, total combustion air supplied in normal practice ranges from 1.1 to 1.5 times stoichiometrically required air for complete combustion. 
     Dilution air  76  passing through dilution passageway  74  is cool unmixed air which mixes with combustion products  104  when these combustion products leave air intake sleeve  42  and burner cup  78 . The mixing of combustion products  104  with dilution air  76  results in the lowering of the combustion products temperature and ultimately the temperature of emitter  30  relative to the temperature that would be observable had no dilution air been introduced. 
     In practice, dilution air  76  can be one to 10 times the amount of stoichiometric air required for combustion of fuel  62  preferably, however, the dilution air  76  is proximately two to five times the stoichiometric air required for combustion of fuel  62 . 
     It will be apparent to a person skilled in the art that blower  24  must be sized accordingly to provide the excess dilution air  76  required over and above the combustion of air  71  required for the combustion of fuel  62 . 
     Referring now to FIG. 9 which is a cross-sectional view taken through emitter  30  and looking into burner  90 , it includes air intake sleeve  42 , emitter liner  36 , emitter  30 , burner  90 , burner cup  78 , dilution air passageway  76 , and support flanges  84 . One can see that air intake sleeve  42  which is roughly concentric with burner cup  78  and burner  90 , is not mounted concentrically within emitter tube  30 . Burner cup  78  along with air intake sleeve  42  is mounted off centre purposely and proximate the bottom portion of emitter  30  in order to offset the natural tenancy for hot air to rise and heat the top portion of emitter  30  in preference to the bottom portion of emitter  30 . Support flanges  84  position air intake sleeve  42  within emitter  30  providing the desired position. 
     Referring now to FIG. 7, which shows the separation of air  100  into two main streams, the first one being combustion air  71  which flows into air intake sleeve  42  through air inlets  110  for the purpose of mixing with fuel  62  and providing for combustion flame  80 . As already stated before, combustion air  71  is further divided into secondary combustion air  72  and primary combustion air  70  which together in practice normally provide for a slightly greater amount of air than stoichiometrically required to bum fuel  62 . The amount of excess air required to bum fuel  62  is known in the art and depends upon the burner design and the type of fuel used and generally speaking ranges anywhere from 10% to 50% excess air above the stoichiometric amount required to just burn fuel  62 . 
     Still Referring to FIG. 7, the second stream of air  100  is dilution air  76  which flows through dilution air passageway  74  which passageway is defined as the area between intake sleeve  42  and the inner wall of emitter  30 . 
     FIG. 8 in similar fashion shows in cross-sectional view the details of air intake sleeve  42 , fuel supply line  60 , fuel  62 , combustion flame  80 , combustion air  71 , primary combustion air  70 , secondary combustion air  72 , dilution air  76 , dilution air passageway  74 , and emitter  30 . 
     Emitter Liner 
     Referring now to FIG. 5 which shows in schematic fashion the lengths of emitter  30  which are joined together by coupling  120 . FIGS. 4 and 5, show two emitter lengths  31  however, in practice there may be 2. 3, 4, 5 and more emitter sections joined together by couplings  120  to create a total emitter length of anywhere between 10 and 100 feet. In order to reduce the temperature of emitter  30  near inlet end  32 , emitter  30  is fitted with an emitter liner  36  which preferably extends from the inlet end  32  to approximately 20 to 50% of the entire emitter length  30 . 
     Emitter liner  36  preferably is made of metallic materials such as aluminum and/or steel and preferably is made of stainless steel and preferably utilizes ASTM 304 stainless steel sheet Material. As shown in FIG. 9, emitter liner  36  extends partway around the inner periphery of emitter tube  30 , thereby leaving an emitter liner gap  37  along the bottom portion of emitter  30 . The purpose of emitter liner gap  37  is to create a more uniform temperature distribution between the upper and lower portions of emitter  30 . Emitter liner gap  37  tends to offset the natural temperature gradient which is observed in the interior of emitter  30  between the top portion and the bottom portion of the emitter tube. Naturally rising hot gases tend to create a hotter surface on the top side of emitter  30  than on the bottom side of emitter  30 . Therefore, the emitter liner gap  37  allows greater heat transfer along the bottom of emitter  30  whereas, where the emitter liner  36  is positioned, less heat is transferred to emitter  30 . Emitter  30  may warp and/or bow should the natural temperature gradient between the top of emitter  30  and the bottom of emitter  30  become to great. Therefore, in order to avoid heat distortion of emitter  30 , emitter liner gap  37  provides for a more uniform temperature distribution between the upper and lower surfaces herein referred to as (the vertical temperature distribution) of emitter  30  and thereby helps to minimize heat distortion of emitter  30 . 
     Preferably the inside of emitter liner  36  is a smooth and/or mirror finish in order to reflect heat back in towards the centre of emitter  30  thereby minimizing the amount of heat transferred to emitter  30 . In addition in order to maximize the contact resistance between the outer surface of emitter liner  36  and the inner surface of emitter  30 , preferably emitter liner  36 , has an outer smooth surface and emitter  30  has a rougher inner surface, thereby maximizing the contact resistance. 
     Preferably emitter liner  36  is a stainless sheet steal which is formed into a tubular section having a diameter slightly larger than the inner diameter of emitter  30 . Therefore, when emitter liner  36  is placed within emitter  30  it is held in place by friction as well as by spring contact of the emitter liner  36  naturally wanting to expand to a large diameter than the inner diameter of emitter  30 . 
     Variable Emissivity Emitters 
     Referring to FIGS. 4 and 5, which shows schematically emitter  30  comprised of a number of emitter lengths  31  joined together with couplings  120 . Preferably, to flatten out the temperature profile shown in FIG. 6 as much as possible, (ie. reduce the temperature gradient) materials are selected for the emitter having a low emissivity proximate the inlet end and moving along the emitter toward the exhaust end, higher and higher, emissivity materials would be selected in order to increase the heat transfer of the emitter as one approaches the exhaust end  34 . Therefore, the heat released from burner  90  would be more uniformly released along the length of emitter  30  thereby radiating more evenly the heat along the length of emitter  30 . 
     By way of example only and not to limit the concept of using variable emissivity emitters, looking to FIG. 5 which shows two emitter lengths  31  of emitter  30 , one could for example use a low emissivity emitter  122  for the emitter length  31  closest to inlet end  32 . Low emissivity emitter  122  may have an emissivity of approximately 0.2 to 0.5 which is obtainable from a mild steel which is either aluminized or zinc aluminum coated. For the second emitter length  31  one would use a high emissivity emitter section  124  having an emissivity of approximately 0.7 to 0.8 which is obtainable using a mild steel which is either oxidized from the hot rolling process (commonly termed hot rolled steel) and/or aluminized and heat treated in order to produce a higher emissivity emitter section  124 . 
     As a result the low emissivity emitter  122  would radiate less heat proximate the inlet end  34  and high emissivity emitter  124  would radiate more heat near the exhaust end  34 . 
     Persons skilled in the art would recognize that various combinations of emissivities could be used and a gradual gradient from a low emissivity emitter from inlet end  32  to a higher emissivity emitter near the exhaust end  34  could be employed depending upon the number of sections of emitter  30  along the entire emitter  36  length, and/or the result one wishes to achieve. 
     Exhaust Baffle 
     In addition to using the dilution air  76 , the emitter liner  36 , the low emissivity emitter  122  and the high emissivity emitter  124  (ie. the variable emissivity emitters) one can additional improve the heat transfer to the emitter  30  near the exhaust end  34  by using a exhaust baffles  38  as shown schematically in FIG.  5 . Exhaust baffles  38 , well known in the art can aid the heat transfer of heat from the exhaust gases to the emitter  30  in the section of the emitter they are deployed thereby increasing the radiation emitted from the emitter  30  and exhaust end of emitter  30 . A person skilled in the art of radiant tube heating recognizes that most baffles commercially available currently could be used in order to obtain the necessary function of exhaust baffle  38 . 
     In Use 
     In order to provide for a more uniform temperature profile along the length of the emitter, first of all the radiant heater system  20  would be fitted with the capability of introducing dilution air  76  which would mix with the combustion products  104  of the combustion flame  80  in order to cool down the temperature of combustion products  104  thereby lowering the temperature of the products  104  proximate the inlet end  32 . Referring to FIG. 6, this would decrease the temperature increase one observes near the inlet end  32 . Depending upon the burner size and the emitter configuration, the amount of dilution air is selected in order to provide as uniform as possible temperature profile which is shown in solid line  52  in FIG.  6 . 
     Secondly, one can also provide a emitter liner  36  proximate the inlet end  32  which again has the effect of reducing the temperature of emitter  30  proximate the inlet end  32  of emitter  30 . The length of emitter liner  36  and the thickness of emitter liner  36  and the materials from which emitter liner  36  are made from are selected depending upon the amount of temperature decrease that is required near the inlet end  32  of emitter  30 . It is obvious to those skilled in the art that the longer the liner, the thicker the emitter liner, the greater will be the effectiveness of emitter liner  36  in preventing the heat transferred to emitter  30 . In addition, preferably as already discussed above, emitter liner  36  has an interior mirrored or very smooth surface for reflecting heat back into the centre of emitter  30  and by controlling the surface roughness of the emitter liner and also the inner surface of the emitter itself, one can control the contact resistance between the emitter liner  36  and emitter  30 , thereby additionally controlling the amount of heat transfer between the emitter liner  36  and emitter  30 . In practice stainless steel ASTM 304 grade has been found to be a suitable material for emitter liner  36 . 
     Thirdly, in addition, one can select portions of emitter  30  namely emitter lengths  31  of varying emissivity ranging from a very low emissivity of approximately 0.2 to a very high emissivity ranging to approximately 0.9. This can be accomplished by selecting various materials known in the art for their various emissivities which are well known and measured. The emissivities of emitter lengths  31  can also be varied by altering the surface finish on the materials by for example aluminizing the materials and heat treating the materials and/or selecting differently coated and/or heat treated metal or other material. Depending on the number of emitter lengths  31 , which make up the entire length of emitter  30 , one can gradually increase the emissivity of emitter lengths  31  as one moves from the inlet end  32  to the exhaust end  34 . The emissivity value selected will depend to a large extent on the result one wishes to achieve as well as cost considerations and availability of materials. However the purpose of varying the emissivities of the emitters is to reduce the temperature variations along the length of emitter  30 . 
     Fourthly, one can increase the temperature transferred to the emitter near the exhaust end  34  by introducing exhaust baffle  38 , proximate the exhaust end  34 . This technique, well known in the art, however has never been used in association with the other technologies discussed in this patent application. 
     It will be apparent to persons skilled in the art that by using the combination of the dilution air  76  and the emitter liner  36 , the variable emissivity emitters and the exhaust baffle  38 , one has a great amount of control over the temperature transfer to emitter  30  and thereby one is able to provide as uniform as possible a temperature profile along the length of emitter  30 . 
     The selection of one type of technology over the other will depend upon the total length of emitter tube  30 , the materials that are available at the time, the cost involved, the sizes of the emitter tubes as well as the burners and the configuration or the geometry of the area that is to be heated. 
     It will be apparent to persons skilled in the art, various modifications and adaptations of the structure described above are possible without departure from the spirit of the invention, the scope of which is defined in the appended claims.