Abstract:
A radiant heater including a burner having an inlet for receiving an air and gas mixture and an exhaust for emitting exhaust gases generated by combustion of the air and gas mixture within the burner, an elongated radiant heating tube having an inlet for receiving the exhaust gases emitted by the burner, a gas flow control assembly for controlling the flow of gas to the burner, and a blower for controlling the flow of air to the burner. The blower comprises a two-stage blower including a motor having a low winding corresponding to a low blower speed and a high winding corresponding to a high blower speed. The gas flow control assembly comprises a two-stage regulator or two stage two-stage valve having a low setting for delivering a low gas flow to the burner and a high setting for delivering a high gas flow to the burner.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to an apparatus and method for heating an enclosed space with a variable low intensity infrared heater.  
       BACKGROUND OF THE INVENTION  
       [0002]     Gas fired infrared heaters typically are used in large industrial settings. A gas heater burns natural gas, propane, or similar combustible gases and the combustion by-products or exhaust gases are passed through a radiant heating tube which becomes hot and radiates energy waves therefrom Reflectors are often used to reflect the energy waves toward the desired location usually toward the floor where the infrared energy waves are converted into heat. These low intensity infrared heaters generally operate at full capacity when not in an off condition with the result that the burner constantly cycles between its on condition and its off condition, thus making it difficult to control heating levels.  
         [0003]     There have been some attempts to create a two-stage heater by utilizing a single gas flow control assembly with two pressure settings with a single speed blower. The problem with this system is that even though the gas pressure, and therefore the gas volume, is varied between the two stages, the blower speed is constant. As a result at both high and low stages the volume of air is the same. Therefore there is either too much air for a low stage or too little air for the high stage resulting in low efficiency combustion. Practically, since these systems idle most of the time at low stage, the excess air results in low efficiency operation and a great amount of wasted energy. Further, since a single gas flow control assembly valve is utilized, it is difficult to achieve an accurate setting for either the high or low level operation.  
       SUMMARY OF THE INVENTION  
       [0004]     This invention is directed to the provision of improved, more efficient radiant heater.  
         [0005]     The radiant heater of the invention is of the type including a burner having an inlet for receiving an air and gas mixture and an exhaust for emitting exhaust gases generated by combustion of the air and gas mixture within the burner; an elongated radiant heating tube having an inlet for receiving the exhaust gases emitted by the burner; a gas valve for controlling the flow of gas to the burner; and a blower for controlling the flow of air to the burner. According to the invention, the blower comprises a two-stage blower having a low speed for delivering a low air flow to the burner and a high speed for delivering a high air flow to the burner. This arrangement allows for a proper and fixed air/gas ratio for both high- and low-stage operation of the burner.  
         [0006]     According to a further feature of the invention, the blower includes an electric motor having a low winding corresponding to the blower low speed and a high winding corresponding to the blower high speed. This arrangement provides a ready and efficient means of providing the two levels of blower operation.  
         [0007]     According to a further feature of the invention, the gas flow control assembly includes a two-regulator assembly or a two-valve assembly, each having a different setting, one a low setting for delivering a low gas flow to the burner and the other having a high setting for delivering a high gas flow to the burner. This arrangement, utilizing a two-stage blower in combination with a two-stage gas flow control assembly, allows for precise control of the desired air/gas ratio for both high- and low-level operation.  
         [0008]     According to a further feature of the invention, the valve assembly includes two valves for independently controlling gas flow from a source to the burner. This arrangement allows for precise control of the gas flow volumes provided in the high and low level operational stages.  
         [0009]     The invention also provides a method of heating a room with an infrared heater of the type including a burner having an inlet for receiving an air and gas mixture and an exhaust for emitting exhaust gases generated by combustion within the burner; and an elongated radiant heating tube having an inlet for receiving the exhaust gases emitted by the burner.  
         [0010]     According to the invention methodology, a two-stage gas valve is provided having a low setting for delivering a low gas flow to the burner and a high setting for delivering a high gas flow to the burner. A two stage blower is provided having a low speed for delivering a low air flow to the burner and a high speed for delivering a high air flow to the burner; and the blower is operated at the low speed when the gas flow control assembly is operating at the low setting and at the high speed when the regulator is operating at the high setting. This methodology allows precise air/gas ratios to be provided at both the high- and low-level operational stages of the burner.  
         [0011]     According to a further feature of the invention methodology, a temperature set point is defined for the room, a programmed temperature differential is defined, the temperature of the room is monitored, and the burner is ignited when the room temperature is less than the temperature set point. A temperature threshold is defined as the temperature set point minus the temperature differential. The blower is operated at the high level when the room temperature is equal to or below the temperature threshold, and the blower is operated at the low level when the room temperature is greater than the temperature threshold and lower than the set point temperature. This arrangement provides a ready and convenient means of providing high level operation when the room is relatively cold relative to the set point temperature and providing low level operations when the room temperature is close to the set point temperature.  
         [0012]     According to a further feature of the invention methodology, the regulator is a two-stage regulator and the method includes the further step of operating the regulator at a high level when the blower is operating at the high level and operating the regulator at a low level when the blower is operating at the low level. This methodology allows precise air/gas ratios to be provided at both the high and low level operational stages of the burner.  
         [0013]     According to a further feature of the invention methodology the gas flow control assembly has either of two valves or two regulators operating in parallel and the method includes the step of opening one valve or regulator and closing one valve or regulator when the regulator is operating at the low level and opening both valves or regulators when the gas flow control assembly is operating at the high level. It is understood that also one valve or regulator could provide a higher flow such that one valve or regulator is used for the low setting and the other for a high setting. This methodology allows for precise control of the volume of gas delivered at both the low level and the high level operational stages. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:  
         [0015]      FIG. 1  is a perspective view of a radiant heater according to the invention;  
         [0016]      FIG. 2  is a cross section of the heater schematically showing reflected energy waves;  
         [0017]      FIG. 3  is a side elevational view of the heater;  
         [0018]      FIG. 4  is a fragmentary, cross-sectional, somewhat schematic view of the heater;  
         [0019]      FIG. 5  is a cross-sectional view taken on line  5 - 5  of  FIG. 4 ;  
         [0020]      FIG. 6  is a detail cross-sectional view of a gas flow control assembly utilized in the heater;  
         [0021]      FIG. 6A  is a detail cross-sectional view of an alternate gas flow control assembly utilized in the heater; and  
         [0022]      FIG. 7  is a flow chart showing the operation of the heater. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0023]     The infrared heater  10  of the invention, broadly considered, includes a housing  12 , a radiant tube  14 , a reflector  16 , a burner  18  (shown only in  FIG. 4 ), a blower  20 , a gas flow control assembly  22 , and a controller  24  (shown only in  FIG. 3 ).  
         [0024]     Housing  12  has a box like sheet metal configuration.  
         [0025]     Radiant tube  14  is elongated and includes an inlet end  14   a  secured to a front wall  12   a  of housing  12 , in communication with a wall aperture  12   b  as shown in detail in  FIG. 4 . Radiant tube  14  also includes an exhaust end  14   b  as shown in  FIG. 3 .  
         [0026]     Reflector  16  has an inverted U configuration in cross-section, is suitably supported in spaced overlying relation to tube  14 , and is generally coextensive with tube  14 .  
         [0027]     As shown in  FIGS. 4 and 5 , burner  18  is elongated and generally tubular, has a venturi configuration, and includes an inlet end  18   a  positioned in housing  12  proximate wall  12   a  and an outlet end  18   b  positioned in the inlet end  14   a  of tube  14  and centered concentrically within the tube by a plurality of circumferentially spaced spokes or vanes  18   c.    
         [0028]     Blower  20  is a centrifugal blower and includes a housing  26  and an electric motor  28  mounted on a side wall  26   c  of the housing and driving the blower scroll or impeller in a known manner. Housing  26  includes an air inlet  26   a  and an air exhaust  26   b  communicating with an aperture  12   c  in housing rear wall  12   d  whereby actuation of the blower discharges pressurized air into the interior of the housing  12 .  
         [0029]     Motor  28  is a two-speed motor having a high winding and a low winding so that the blower comprises a two-stage blower having a low speed for delivering a low air flow to housing  12  and burner  18  and a high speed for delivering a high air flow to housing  12  and burner  18 . Motor  28  may for example comprise a 1/25 HP, 110 V AC single phase 60 hz motor and may be operative to deliver a low air flow of 25 CFH and a high air flow of 50 CFH.  
         [0030]     Gas flow control assembly  22  may be supported within housing  12  on housing lower wall  12   e  and comprises either a two-stage regulator or a two-stage valve with the two stages achieved by the use of two independent valves  30  and  32  as shown in  FIGS. 4 and 6  or two regulators  202  and  204  arranged in parallel within a common housing as shown in  FIG. 6A .  
         [0031]     Valve  30  includes a gas inlet  30   a , a redundant solenoid valve  30   b , a main valve  30   c  controlled by a spring  30   d  and a diaphragm  30   e , a gas outlet  30   f , a cap screw  30   g , an adjustment screw  30   h , and a vent  30   i.    
         [0032]     Valve  32  is identical to valve  30  as indicated by the like reference numbers  32   a - 32   i.    
         [0033]     Main valves  30   c  and  32   c  are controlled in known manner by solenoids and each valve is moveable between first and second positions corresponding to the valve being 100% closed and 100% open respectively.  
         [0034]     In the assembled burner package shown in  FIG. 4 , blower  20  is mounted on rear housing wall  12   d  with the blower outlet  26   b  aligned with housing wall aperture  12   c . The regulator assembly  22  is mounted on housing lower wall  12   e  within housing  12 . A gas inlet line  34  passes through housing rear wall  12   d  and thereafter bifurcates to form a first branch  34   a  communicating with the inlet  30   a  of valve  30  and a second branch  34   b  communicating with the inlet  32   a  of valve  32 . Branch gas outlet lines  36   a  and  36   b  communicate respectively with the outlet  30   f  of valve  30  and the outlet  32   f  of valve  32  and thereafter converge to form gas outlet line  36 , which extends within housing  12  to a free end  36   c  fixedly and centrally secured to an annular disk  38   a  positioned at the inlet end  18   a  of burner  18  and defining a plurality of perforations  38   a  shown in  FIG. 5 .  
         [0035]     Controller  24 , shown in  FIG. 3 , may be mounted on housing  12  and is connected by a lead  40  to a two-stage thermostatic probe  42  carried by housing  12 . The controller  24  provides a reading of room temperature from the probe  42  to regulator  22  by a lead  44  and to the high and low windings of motor  28  of blower  20  by a lead  46 .  
         [0036]     With respect to the general overall operation of the heater, gas is supplied to the interior of burner  18  via line  36 , and air is supplied to the burner  18  via blower  20  with the air from the blower  20  entering into the interior of the venturi through the perforations  38   a  for mixture with the gas. Air also passes into tube inlet end  14   a  outwardly of the venturi for passage through vanes  18   c , which act to impart a swirl to the air to facilitate the air/gas nixing. It will be understood that ignition is accomplished in a known manner by a pilotless direct spark utilizing an ignition module (not shown) and that burner operation is monitored and controlled in a known manner by an ignition detection control (not shown).  
         [0037]     The specific operation of the invention heater is best understood with reference to  FIG. 7 . The flow sequence for the invention heater begins by defining a set point temperature T s  and a programmed differential d t  and comparing these values to the room temperature T r  as determined by the thermostatic probe  42  and as recognized by controller  24 . This comparison is shown at step  100  in  FIG. 7 . If the room temperature T r  is less than the set point temperature T s  the thermostat calls for heat in step  102 . If the room temperature T r  is greater than or equal to the set point temperature T s  the controller will turn the unit off as shown in step  104 . Once the thermostat calls for heat in step  102 , the controller calculates whether the room temperature T r  is less than or equal to the temperature set point T s  minus the programmed differential d t , or whether the room temperature T r  is greater than the temperature set point T s  minus the programmed differential d t . This calculation is shown as step  106 .  
         [0038]     If the room temperature T r  is less than or equal to the temperature set point T s  minus the programmed differential d t , the controller, as shown in step  108 , commands a high gas flow rate from the gas regulator by energizing solenoids to move both valves  30   c  and  32   c  to their second, fully-opened positions, and commands a high air flow rate from the blower by energizing a relay  109  (shown in  FIG. 3 ) in a sense to power the high winding of blower motor  28 . The heater  10  is now in a high output mode as shown in step  110  and then loops back to step  100  to continuously monitor the room temperature T r  relative to the set point temperature T s .  
         [0039]     If the room temperature T r  is greater than the set point temperature T s  minus the programmed differential d t  in step  106 , the controller, as shown in step  112 , commands a low gas flow rate from the gas regulator by energizing solenoids to move valve  30   c  to the second, open position and move valve  32   c  to the first, closed position, and commands a low air flow rate from the blower by energizing the relay  109  in a sense to power the low winding of the blower motor  28 . The heater  10  is now in a low output mode as shown in step  114  and then loops back to step  100  to continuously monitor the room temperature T r  for comparison with the temperature set point T s . It will be understood that if the heater is initially operated at the high output level, when the room temperature T r  reaches the set point temperature T s  minus the temperature differential d t , the controller will operate to place the heater in the low output mode by switching the blower motor  28  to the low winding and closing valve  32   c . When the room temperature eventually reaches the set point temperature T s , the controller shuts off the heater and allows the blower to stay on for a few minutes to purge any flue gases left in the system.  
         [0040]     With reference to  FIG. 6A , another preferred two-stage gas regulator  200  is illustrated. Gas flow control assembly  200  may for example be of the type available from White Rogers of St. Louis, Mo. sold under the brand name Two Stage Gemini. As shown, the gas flow control assembly includes a low-fire regulator  202  and a high-fire regulator  204 . Low-fire and high-fire regulators  202  and  204  work in combination with main valve  206  to provide two-stage gas control. The regulator body includes an inlet  208  and associated inlet pressure tap  210  and inlet screen  212 . Gas exits the assembly  200  at outlet  214 . Outlet  214  includes an associated outlet pressure tap  218  and outlet screen  216 . The assembly  200  includes a control gas orifice  220  and associated orifice opening  222 . Main valve  206  is biased by diaphragm  224  in a manner known to those of skill in the art. The assembly  200  includes a vent  226  and redundant solenoid  228 .  
         [0041]     It is understood by those of skill in the art that the assembly illustrated in  FIG. 6A  could be substituted for the assembly illustrated in  FIG. 6 . In particular, where  FIG. 6  illustrates an assembly in which valves  30   c  and  32   c  selectively cooperate to provide two levels of gas flow,  FIG. 6A  illustrates an assembly in which low-fire regulator  202  and high-fire regulator  204  operate to deliver two gas flows.  
         [0042]     When the temperature drops below the set point, yet still stays above the set point temperature minus the programmed differential, the low stage of the heater comes back on until the thermostat is satisfied. The system idles around the set point on the low stage, on and off, preventing any overshoot effect with otherwise a high heating inertia However, if there is a sudden drop in the room temperature for any reason the heater comes on with high stage allowing a fast recovery.  
         [0043]     The invention, by utilizing a two-stage blower and a two-stage gas flow control assembly, allows for a proper and fixed air/gas ratio for both the high and low output levels. This arrangement has the advantages of saving energy by operating with optimum gas/air ratios at all times; saving energy by reducing the temperature overshoots due to the high heat inertia; reducing wear and tear on the components by eliminating unnecessary cycling of the unit on high heat; providing accurate constant rate for each stage due to the two independent valves or regulators; allowing for a higher differential between the two stages due to the independent regulator adjustment; and reducing the cost of the heater by eliminating the need for an expensive, continuously variable blower motor providing a continuously variable blower speed.  
         [0044]     The gas flow control assemblies disclosed in the present embodiments provide a much more accurate two-stage flow control as compared to the gas flow control assemblies of the prior art.  
         [0045]     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.