Abstract:
A radiant heating system having a housing for holding a plurality of gas burners with a ceramic burner element that emits infrared rays after becoming hot. A controller is used for selectively controlling at least one valve to restrict the gas flow to the individual burners. A method is shown for radiating heat from a gas burner in response to a thermostat by controlling the gas flow to individual burners with electronic valves located in a gas supply line and selectively shutting off the gas flow to each burner.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to an apparatus and method for heating an enclosed space with a variable high intensity infrared heater.  
         BACKGROUND OF THE INVENTION  
         [0002]    High intensity gas-fired infrared heaters are typically used in large commercial or industrial settings. A gas heater burns natural gas, propane or other similar combustible gases to heat a porous ceramic plate. The ceramic plate turns red hot and emits infrared energy waves. Such heaters often include reflectors to broadly reflect the energy waves. Such high intensity infrared heaters generally operate at full capacity when not in an off condition. This operating condition results in the burner constantly cycling between its on condition and its off condition thus making it difficult to control heating levels.  
         SUMMARY OF THE INVENTION  
         [0003]    A radiant heating system having a housing for holding a plurality of gas burners. The fuel used in these burners is typically natural gas or propane gas. The gas burners each have a plenum for mixing the gas with combustion air, a ceramic burner element that emits infrared rays after becoming hot, a controller for selectively controlling the gas burners, a common rail gas line for supplying the gas from an inlet line to the plurality of burners, and at least one valve positioned in the common rail gas line to prevent gas from flowing to burners located downstream from the valve. The valves for controlling the gas flow to the individual burners are positioned downstream of the first burner and prior to the inlet of each succeeding burner so that the downstream burners can be individually turned on and off by the controller. A controller for the gas heater provides a room temperature set by a thermostat. The controller controls the temperature between a lower threshold temperature and an upper threshold temperature by controlling the numbers of individual gas burners operating. A control algorithm is designed to heat up a space as quickly as possible by turning all the burners on, while minimizing the overshoot and undershoot of the set point temperature by selectively reducing the number of burners operating as the room temperature fluctuates between the lower threshold and the set point temperature. The gas burner has a 100 percent safety shut-off feature and is powered by a 24-volt electrical source. Direct spark ignition with a spark electrode is used to ignite the fuel. The burner does not require a pilot to be lit continually for operation. The burner uses a flame sensing electrode for determining if the burner is operational.  
           [0004]    A method for radiating heat comprising operating a gas burner in response to a thermostat, controlling the gas flow to individual burners with electronic valves located in a gas supply line by selectively shutting off the gas flow delivered to individual burners, generating infrared rays from a hot ceramic burner surface, and reflecting the radiated infrared rays from a reflector in a desired direction.  
           [0005]    Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:  
         [0007]    [0007]FIG. 1 shows a front view of a variable high intensity infrared heater;  
         [0008]    [0008]FIG. 2 shows a rear view of the variable high intensity infrared heater;  
         [0009]    [0009]FIG. 3 is a control diagram of the variable intensity infrared heater; and  
         [0010]    [0010]FIG. 4 is a graph of temperature versus time showing less wasted energy with a multi-stage system than with a single stage system.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]    High intensity gas-fired infrared heaters are typically either controlled in the on or off position so that the burner elements are either all firing or all off. An improvement to the heater allows one or more burner elements to be selectively shut off so that a set point temperature can be controlled more precisely by minimizing overshoot and undershoot of the desired temperature.  
         [0012]    With reference to FIGS. 1 and 2, there is shown a high-intensity radiant heating system  10  having a housing  12  for holding a first burner  16  and a second burner  18 . This preferred embodiment shows two burners, but it should be understood that there is no limit as to the maximum number of burners in this apparatus, e.g., 3, 4, 5, 6, . . . Ceramic burner elements  17 ,  19  are heated until they are red hot so that infrared energy waves are generated therefrom. A reflector  14  reflects the infrared rays emitted from burners  16 ,  18  in a desired direction to provide heat. A spark electrode ignitor  27  is used to initiate combustion of the fuel. A combination power supply and controller  28  includes logic for ignition detection control and operational control over the various components on the heating system  10 . After power is applied to an ignition detection controller (IDC)  31 , a delay of preferably fifteen seconds occurs before a spark is developed at the electrode  27  and a gas regulator valve  22  opens allowing gas to flow to the burners  16 ,  18 . A flame sensing electrode  29  is used to determine when combustion has begun and to signal the IDC  31  to power down the spark electrode ignitor  27 . The flame sensing electrode  29  will signal the IDC  31  to power up the spark electrode ignitor  27  when a flameout condition is detected. The spark electrode ignitor  27  generally begins firing within 0.8 seconds of a flameout condition.  
         [0013]    Heater  10  has a gas inlet line  20  for providing gas from an external source to the burners  16 , 18 . Gas, preferably natural gas or propane, passes through a regulator valve  22 . Regulator valve  22  is capable of shutting off the gas flow to burners  16 ,  18  and providing a fixed amount of gas to burners  16  and  18 . After passing through regulator valve  22 , the gas enters a common rail gas line  24  for distribution to individual burners  16 ,  18 . A trunk line  30  tees into common rail  24  to deliver gas to burner  16  while a second trunk line  32  provides gas from common rail  24  to burner  18 . It is understood that if more than two burners are provided, each would be provided gas by a trunk line connected to the common rail  24 . A solenoid valve  26  can be installed in common rail  24  or in trunk line  32  downstream of burner  16 . Solenoid valve  26  prevents gas from traveling downstream therefrom thus preventing gas from flowing to burner  18 .  
         [0014]    Spark electrode ignitor  27  provides a spark to start combustion in burner  16  which, if gas is flowing to burner  18 , causes burner  18  to ignite by a flame transfer from burner  16 . A combination power supply and controller  28  controls power to the solenoid valve  26 , spark ignitor electrode  27 , regulator valve  22 , and the flame sensing electrode  29 . Solenoid valve  26  is operable to selectively prevent gas from flowing downstream to burner  18  thus selectively allowing only burner  16  to operate.  
         [0015]    Referring now to FIG. 3, a schematic diagram illustrates a method for controlling the variable high intensity infrared heater  10 . The control sequence starts with determining if the thermostat set point temperature is below a first (lowest) threshold in query  52 . If the answer to query  52  is yes, then the controller turns all the burners on in  54 . Power is applied to the IDC  31  and, fifteen seconds after power is applied, a spark is developed at the spark electrode ignitor  27  and the regulator valve  22  opens allowing gas to flow to the burners  16 ,  18 . The spark electrode ignitor  27  begins ignition and an electrical current begins flowing from the flame sensing electrode  29  through the flame to a ground to determine when to shut off the spark. The IDC  31  senses the current and turns off the spark once the flame has taken hold and the gas continues to flow through the regulator valve  22 . If the burners  16 ,  18  have a flame outage detected by the flame sensing electrode  29 , the IDC  31  responds by initiating sparking within preferably 0.8 seconds. A preferred fifteen second ignition period initiates the attempt to relight the burners  16 ,  18 . If the flame is reestablished, then normal operation resumes. If the burners  16 ,  18  do not light after the first try, an interpurge sequence preferably occurs between trials before attempting to relight the burners  16 ,  18 . If the burners  16 ,  18  fail to light after the third trial, the IDC  31  will de-energize the regulator valve  22  and go into lock-out mode. Lock-out recovery requires the thermostat  40  to be reset below ambient temperature or the electrical power supply to be shut off for five seconds. If the answer to query  52  is no, then the controller checks the thermostat to see if the temperature is below a second (lower) threshold in query  56 . If the answer to query  56  is yes, then the controller  28  turns one burner on in  58 . If the answer to query  56  is no, then the controller loops back to  50  and turns all the burners off. The controller loops back to query  52  after turning all burners on in  54  or turning one burner on in  58  to determine if the temperature is below a first (lowest) threshold. The controller  28  will continue looping through the algorithm until heater  10  is manually turned off.  
         [0016]    The controller  28  allows the heater  10  to operate with a variable number of burners to control the room temperature within a second (lower) threshold temperature and the set point temperature while minimizing the on and off fluctuations of the heater system  10 . The control system is designed to heat a location as quickly as possible while minimizing overshoot and undershoot of the set point temperature by varying the number of burners firing. For example, starting in the query  52 , if set point temperature is 72° F., the first (lowest) threshold could be 60° F., and a room temperature is 50° F., then all the burners will be turned on at  54 . As the room temperature begins to warm up, the controller  28  continues to measure the room temperature via the thermostat  40  to determine if the temperature is below the first threshold temperature. If the answer is no, then the controller will check whether the temperature is below a second (lower) threshold in  56 , for example 70° F. If the room temperature is above 70° F. in query  56 , then all of the burners are turned off in  50 . If the room temperature in query  56  is less than 70° F., but greater than 60° F., then the controller will turn one burner on in  58 . If the room temperature falls below the first threshold 60° F. in query  52  then all of the burners are turned on in  54 . The control algorithm will continue to loop through this method until the heating system  10  is manually shut off.  
         [0017]    Referring now to FIG. 4, a plot  80  of temperature versus time is shown comparing a single stage system  82  with a multi-stage system  84 . The plot  80  shows that with the multi-stage system  84  the overshoot and undershoot of the temperature set point is greatly reduced compared with that of the single stage system  82 . Overshoot peaks  86  show the amount of wasted energy that the single stage system  82  produces relative to the multi-stage system  84 . The multi-stage system  84  not only saves on energy usage, but, since the undershoot and overshoot of the temperature set point is minimized, the comfort level is improved for occupants in the room.  
         [0018]    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.