Abstract:
A method for operating a furnace system includes initiating a start sequence comprising starting an inducer fan operative to induce an air flow through a burner assembly, a heat exchanger portion and a collector portion, determining whether an air pressure in the collector portion is above a first threshold value, starting a furnace ignition sequence including providing fuel to the burner assembly, igniting a fuel and air mixture and starting an ignition timer responsive to determining that the air pressure in the collector portion is above the first threshold value, determining whether the ignition timer has expired, determining whether the air pressure in the collector portion is above a second threshold value responsive to determining that the ignition timer has expired, and stopping the provision of fuel to the burner assembly responsive to determining that the air pressure in the collector portion is not above the second threshold value.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Many furnace systems include a control system that includes sensors, relays and control valves that are used to safely start and operate the furnace system. In operation, the furnace receives a signal to start from a thermostat. The system starts an inducer blower that creates a negative pressure in a collector box of the furnace by drawing air from a combustion air inlet and outputting air through a flue outlet. The system senses the negative pressure and starts a burner assembly in a heat exchanger portion of the system by providing fuel to the burner assembly and igniting the fuel. A blower motor may then start, such that the blower motor receives air flow from a return air duct of a space and outputs the air to the heat exchanger portion of the system. The heated air is output via a supply air duct to heat the space. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0002]    According to one exemplary embodiment, a method for operating a furnace system includes receiving a start instruction at a controller, initiating a start sequence comprising starting an inducer fan operative to induce an air flow through a burner assembly, a heat exchanger portion and a collector portion, determining whether an air pressure in the collector portion is above a first threshold value, starting a furnace ignition sequence including providing fuel to the burner assembly, mixing the fuel with induced air, igniting the fuel and air mixture and starting an ignition timer responsive to determining that the air pressure in the collector portion is above the first threshold value, determining whether the ignition timer has expired, determining whether the air pressure in the collector portion is above a second threshold value responsive to determining that the ignition timer has expired, and stopping the provision of fuel to the burner assembly responsive to determining that the air pressure in the collector portion is not above the second threshold value. 
         [0003]    According to another exemplary embodiment, a furnace system includes an inlet duct communicatively connected to an air source and a burner assembly, a heat exchanger portion communicatively connected to an output of the burner assembly, a collector portion communicatively connected to an output of the heat exchanger assembly, an inducer portion communicatively connected to an output of the collector portion and an exhaust duct, a gas valve communicatively connected to a fuel source and the burner assembly, a first pressure sensor operative to sense a pressure in the collector portion, a second pressure sensor operative to sense a second pressure in the collector portion, and a controller operative to control the gas valve, and the inducer portion, the controller operative to receive a start instruction, initiating a start sequence comprising starting the inducer portion, receive a signal from the first pressure sensor and determine whether the sensed pressure is above a first threshold value, starting a furnace ignition sequence including controlling the gas valve to provide fuel to the burner assembly and starting an ignition timer responsive to determining that an air pressure in the collector portion is above the first threshold value, determining whether the air pressure in the collector portion is above a second threshold value responsive to determining that the ignition timer has expired, and stopping the provision of fuel to the burner assembly by controlling the gas valve responsive to determining that the air pressure in the collector portion is not above the second threshold value. 
         [0004]    According to yet another exemplary embodiment, a furnace system includes an inlet duct communicatively connected to an air source and a burner assembly, a heat exchanger portion communicatively connected to an output of the burner assembly, a collector portion communicatively connected to an output of the heat exchanger assembly, an inducer portion communicatively connected to an output of the collector portion and an exhaust duct, a gas valve communicatively connected to a fuel source and the burner assembly, a first pressure sensor operative to sense a pressure in the collector portion, a second pressure sensor operative to sense a pressure in the inducer portion, and a controller operative to control the gas valve, and the inducer portion, the controller operative to receive a start instruction, initiating a start sequence comprising starting the inducer portion, receive a signal from the first pressure sensor and determine whether the sensed pressure is above a first threshold value, starting a furnace ignition sequence including controlling the gas valve to provide fuel to the burner assembly and starting an ignition timer responsive to determining that an air pressure in the collector portion is above the first threshold value, determining whether the air pressure in the inducer portion is above a second threshold value, and stopping the provision of fuel to the burner assembly by controlling the gas valve responsive to determining that the air pressure in the inducer portion is not above the second threshold value. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0006]      FIG. 1  illustrates an exemplary embodiment of a furnace system. 
           [0007]      FIG. 2  illustrates an alternate exemplary embodiment of a furnace system. 
           [0008]      FIGS. 3A-3B  illustrate a block diagram of an exemplary method for controlling the systems of  FIGS. 1 and 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]      FIG. 1  illustrates an exemplary embodiment of a furnace system (system)  100 . The system  100  includes a return air duct  102  that receives air from a space such as, for example, a residential or commercial structure (not shown). The air is drawn through the return air duct  102  and driven through a heat exchanger portion  104  with a blower fan  107 . The air passes through the heat exchanger portion  104 , which is heated by a burner assembly  106 . The air exits the heat exchanger portion  104  and is output to a supply air duct  108  and sent to the space. 
         [0010]    A controller  110  receives power from a power source  111 , and controller  110  may receive signals from a device such as a thermostat  112 . The controller  110  includes a logic system that may include, for example, a processor, memory, counters, timers, input devices, output devices and indicators, or other similar electronic circuitry that provides control to the system  100 . The controller  110  is operative to control the blower fan  107  and send power and signals to a gas valve assembly  114 . The gas valve assembly  114  includes a valve  116  that controls fuel, such as natural gas, received from a fuel source  118  and output to the burner assembly  106 . The valve  116  may be controlled by, for example, a solenoid (not shown) that actuates to open the gas valve assembly  114  when power is provided to the solenoid. When the gas valve assembly  114  is opened, fuel is provided to the burner assembly  106 . 
         [0011]    The burner assembly  106  receives a flow of air via a burner inlet  119 . The air from the burner inlet  119  mixes with the fuel and is ignited by an igniter (not shown) in the burner assembly  106 . The product of the combustion exits the burner assembly  106  and is output to a heat exchanger portion  104 , which in turn, is output to a collector portion  120 . An inducer portion  122  induces a negative pressure in the collector portion  120  and draws the product of the combustion from the collector portion  120  and outputs the product of the combustion via an exhaust duct  124 . 
         [0012]    As discussed above, the gas valve assembly  114  opens the valve  116  by providing power to a solenoid. A variety of sensors or switches may be connected to the controller  110  that prevent power from being provided to the solenoid (thereby opening the valve  116  and providing fuel to the burner assembly  106 ) unless the sensors or switches are closed (or in a state that indicates that the sensors have sensed a parameter that is within a desired threshold). For example, prior to providing fuel to the burner assembly (i.e., opening the valve  116 ), the negative air pressure in the collector portion  120  should be above a threshold value that may range from, for example, 0.83 inches water column (“wc) to 0.93″wc to ensure that the burner assembly  106  is receiving air via the burner inlet  119  and that air is being output from the collector portion  120  via the exhaust duct  124 . A low pressure sensor  126  is disposed in the outlet portion of the collector portion  120 . The low pressure sensor  126  senses the pressure in the collector portion  120  and may close a switch (or output a signal) that indicates that the negative pressure in the collector portion  120  is above a first threshold value. The controller  110  does not send a signal to the gas valve assembly  114  to open the valve  116  unless the low pressure sensor  126  switch is closed (or a signal indicative of a pressure above the first threshold value is received). A high pressure sensor  128  may be located in the collector portion  120  (or the inducer portion  122  as described below in  FIG. 2 ). The high pressure sensor  128  senses the air pressure in the collector portion  120  or the inducer portion  122  and activates a switch (or outputs a signal) that indicates that the pressure in the collector portion  120  or inducer portion  122  is above a second pressure threshold value. The second threshold value may include, for example, a value of ranging between approximately 0.45″wc to 0.50″wc in embodiments where the high pressure sensor is located in the inducer portion  122 , and a value of approximately 1.00″wc to 1.40″wc where the high pressure sensor  128  is located in the collector portion  120 . If the pressure in the collector portion  120  or inducer portion  122  is below the threshold value, the controller  110  may tell the gas valve assembly  114  to close the valve  116  to stop the flow of fuel to the burner assembly  106 . Other sensors or switches, such as, for example, a flame sensor  130  and limit switches (not shown) may also provide signals to the controller  110  to facilitate safe operation of the system  100 . 
         [0013]    The arrangement of the low pressure sensor  126  and the high pressure sensor  128  facilitate the safe starting and operation of the system  100  when the pressure in the collector portion  120  or inducer portion  122  is not above a second threshold value prior to fuel ignition, while maintaining efficient operation of the inducer portion  122 . Using the low pressure sensor  126  and the high pressure sensor  128 , the system may be started while ensuring that the air pressure in the collector portion  120  is above a first threshold value. Once a timer has expired, the system may run while ensuring that the air pressure in the collector portion  120  or inducer portion  122  is above a second threshold value. 
         [0014]      FIG. 2  illustrates an alternate exemplary embodiment of a system  200 . The system  200  is similar to the system  100  (of  FIG. 1 ) described above, however the high pressure sensor  128  is disposed in the inducer portion  122 . In this regard, the high pressure sensor  128  detects or measures a negative pressure in a portion of the inducer portion  122 . In the illustrated embodiment, the inducer portion  122  includes a cavity  202  that defines a flow path and induces a negative pressure on the air from the collector portion using a fan or wheel assembly (not shown). The high pressure sensor  128  may measure the negative pressure in the cavity  202 . In the systems and methods described herein, the operation of the systems  100  and  200  are similar, however, the thresholds associated with the high pressure sensor  128  may differ to correspond to the location of the high pressure sensor  128  in the systems. 
         [0015]      FIGS. 3A-3B  illustrate a block diagram of an exemplary method for controlling the systems  100  and  200  (of  FIGS. 1 and 2 ). Referring to  FIG. 3A , in block  302 , the controller  110  receives a start instruction. The start instruction may be received from, for example, the thermostat  112 . In block  304  the controller sends power to the inducer portion  122 . In block  306 , once the negative pressure in the collector portion  120  is above a threshold value, the low pressure sensor  126  switch closes. If the low pressure sensor  126  switch does not close within a threshold time period, the controller  110  may output a fault indication in block  308 . If the low pressure sensor  126  switch closes, in block  310 , the ignition sequence starts and the burner assembly  106  is ignited. The ignition sequence includes, for example, the opening of the valve  116 , the actuation of an igniter (not shown) and the combustion of the fuel and air mixture in the burner assembly  106 . The ignition sequence may also include starting the blower fan  107  and the starting of an ignition timer. In block  312 , the controller  110  determines whether the ignition timer has expired. In the illustrated embodiment, the ignition timer is set to approximately one minute; however, the ignition timer in alternate embodiments may be set for any appropriate time period. In block  311 , the controller  110  monitors the low pressure sensor  126  prior to the ignition timer expiring. If the low pressure switch is no longer closed, the burners are turned off and a fault indication is output in block  315  (of  FIG. 3B ). Once the ignition timer has expired, the controller  110  determines whether the low pressure sensor  126  switch is still closed in block  313 . If yes, the controller  110  determines whether the high pressure sensor  128  switch has closed in block  314 . The high pressure sensor  128  senses the air pressure in the collector portion  120  (or the inducer portion  122 , in the system  200 ) to determine whether the pressure is above a second threshold value. If yes, the system continues operation in block  316 . Referring to  FIG. 3B , in block  318 , if the high pressure sensor  128  switch is open, the burners are turned off, a fault indication may be sent, and a fault counter is incremented. In block  320 , the controller  110  determines whether the fault counter has reached a threshold fault value. In the illustrated embodiment, the threshold fault value is three faults; however, alternate embodiments may include a threshold fault value of any appropriate number of faults. If no, the start sequence is restarted in block  322 . If yes, a fault timer is started in block  324 . In block  326 , the controller  110  determines whether the fault timer has expired. If yes, the startup sequence is restarted in block  322 . The fault timer may run for any desired time period, such as, for example 3-4 hours. In block  317 , the high pressure sensor  128  and the low pressure sensor  126  switches are closed, operation continues in block  319 . If either of the high pressure sensor  128  or the low pressure sensor  126  switches is open, the burner assembly  106  is extinguished, and a fault indication is output in box  315 . 
         [0016]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.