Abstract:
A method of controlling a blower motor including: receiving a requested airflow from a thermostat; accessing an airflow table and determining an airflow closest to the requested airflow; using a location of the airflow closest to the requested airflow in the airflow table to access a control signal value in a control signal table; and using the control signal value to control the blower motor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a non-provisional application of U.S. Provisional Patent Application No. 61/389,901 filed Oct. 5, 2010, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The subject matter disclosed herein generally relates to air blowers, and in particular to a method and system for controlling an air blower motor. 
         [0003]    Heating, ventilation and air conditioning (HVAC) systems typically use a blower driven by a blower motor to supply air through ducts. Systems are typically designed to provide an amount of airflow expressed as cubic feet per minute (CFM) in certain modes. For example, low heat, high heat, cooling and continuous fan may all utilize different airflows. There is a need to simply and efficiently control the blower motor through different modes of operation. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    An embodiment is a method of controlling a blower motor including: receiving a requested airflow from a thermostat; accessing an airflow table and determining an airflow closest to the requested airflow; using a location of the airflow closest to the requested airflow in the airflow table to access a control signal value in a control signal table; and using the control signal value to control the blower motor. 
         [0005]    Another embodiment is a system for handling air including: a blower; a blower motor; a controller for controlling the blower motor, the controller: receiving a requested airflow from a thermostat; accessing an airflow table and determining an airflow closest to the requested airflow; using a location of the airflow closest to the requested airflow in the airflow table to access a control signal value in a control signal table; and using the control signal value to control the blower motor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    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: 
           [0007]      FIG. 1  depicts an exemplary furnace having an evaporator coil; 
           [0008]      FIG. 2  depicts an exemplary airflow table and control signal table; and 
           [0009]      FIG. 3  is a flowchart of a control process. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0010]    Referring to  FIG. 1 , the numeral  10  generally designates a gas-fired condensing furnace employing the blower motor control of the present invention. Condensing furnace  10  includes a steel cabinet  12  housing therein burner assembly  14 , combination gas control  16 , heat exchanger assembly  18 , inducer housing  20  supporting, inducer motor  22  and inducer wheel  24 , and circulating air blower  26 . Combination gas control  16  includes a hot surface igniter (not shown) to ignite the fuel gas. 
         [0011]    Burner assembly  14  includes at least one inshot burner  28  for at least one primary heat exchanger  30 . Burner  28  receives a flow of combustible gas from gas regulator  16  and injects the fuel gas into primary heat exchanger  30 . A part of the injection process includes drawing air into heat exchanger assembly  18  so that the fuel gas and air mixture may be combusted therein. A flow of combustion air is delivered through combustion air inlet  32  to be mixed with the gas delivered to burner assembly  14 . 
         [0012]    Primary heat exchanger  30  includes an outlet  34  opening into chamber  36 . Connected to chamber  36  and in fluid communication therewith are at least four condensing heat exchangers  38  having an inlet  40  and an outlet  42 . Outlet  42  opens into chamber  44  for venting exhaust flue gases and condensate. 
         [0013]    Inducer housing  20  is connected to chamber  44  and has mounted thereon an inducer motor  22  together with inducer wheel  24  for drawing the combusted fuel air mixture from burner assembly  14  through heat exchanger assembly  18 . Air blower  26  is driven by a variable speed blower motor  25  and delivers air to be heated in a counterflow arrangement upwardly through air passage  52  and over heat exchanger assembly  18 . The cool air passing over condensing heat exchanger  38  lowers the heat exchanger wall temperature below the dew point of the combusted fuel air mixture causing a portion of the water vapor in the combusted fuel air mixture to condense, thereby recovering a portion of the sensible and latent heat energy. The condensate formed within heat exchanger  38  flows through chamber  44  into drain tube  46  to condensate trap assembly  48 . As air blower  26  continues to urge a flow of air, upwardly through heat exchanger assembly  18 , heat energy is transferred from the combusted fuel air mixture flowing through heat exchangers  30  and  38  to heat the air circulated by blower  26 . Finally, the combusted fuel air mixture that flows through heat exchangers  30  and  38  exits through outlet  42  and is then delivered by inducer motor  22  through exhaust gas outlet  50  and thence to a vent pipe (not illustrated). 
         [0014]    Cabinet  12  also houses a controller  54  and a display  56 . Controller  54  may be implemented using a microprocessor-based controller executing computer program code stored on a computer readable storage medium. A thermostat  55  communicates with controller  54  to designate operational modes and temperature. Thermostat  55  may be an intelligent device that communicates requested air flow rates as described in further detail herein. A pressure tap  58  is located at primary heat exchanger inlet  60 , a pressure tap  62  is located at condensing heat exchanger outlet  42  and a limit switch  64  is disposed in air passage  52 . In a non-condensing furnace, pressure tap  62  would be disposed at primary heat exchanger outlet  34 , since there would be no condensing heat exchanger  38 . 
         [0015]    A cooling coil  82  is located in housing  80  on top of furnace cabinet  10  and is the evaporator of air conditioning system. The cooling coil  82  has an inlet  84 , where subcooled refrigerant enters, and an outlet  86 , where superheated refrigerant leaves, as is conventional. In response to an input from heating/cooling thermostat, air blower  26  urges air flow upwardly through cooling coil  82  where heat exchange takes place. As a result of this heat exchange, cool air is delivered to the conditioned space and superheated refrigerant is returned to the outdoor condensing section (not illustrated) via outlet  86 . In the outdoor condensing section the refrigerant is subcooled and returned to inlet  84 . This cycle continues until the thermostat is satisfied. 
         [0016]    In operation, the controller  54  controls blower motor  25  by providing a control signal to the motor. The control signal may be a pulse width modulated (PWM) signal indicating a duty cycle for blower motor  25 . In exemplary embodiments, the control signal is a 12-bit PWM control signal. It is understood that analog control signals may be used, or different types of digital codes may be used to provide the control signal. Controller  54  maintains tables to map the requested CFM to a control signal, as represented in  FIG. 2 . 
         [0017]    The CFM airflow table  100  in  FIG. 2  includes airflow values for four different operating modes, shown as columns  1 - 4 . Column  1  may be standard mode (e.g., 350 CFM/ton), column  2  may be a dehumidifying mode (e.g., 275 CFM/ton), column  3  may be a super dehumidifying mode (e.g., 200 CFM/ton) and column  4  may be a maximum mode (400 CFM/ton). When communicating thermostat  55  requests a certain airflow and a certain mode, controller  54  accesses the CFM airflow table  100  and locates the closest airflow value to the requested airflow. The controller  54  records the row and column of the airflow value closest to the requested airflow. 
         [0018]    Controller  54  then accesses the control signal table, a PWM and Multiplier table  102 , to find the appropriate control signal value. The table location (i.e., row and column) from the CFM airflow table is used to map to a cell in the PWM and Multiplier table  102  to retrieve a control signal value (e.g., a PWM value) and a multiplier, which varies depending upon the mode selected. As shown in the embodiment of  FIG. 2 , eight PWM values are used along with three multipliers. This allows  32  control signals to be generated by storing only eight PWM values. 
         [0019]    Thermostat  55  allows a user to also specify a restriction multiplier that is used to adjust the control signal. During initial installation or maintenance, as user (e.g., installer) can access a menu through thermostat  55  to set a restriction multiplier for one or more modes of operation. The restriction multiplier is used to compensate for varying degrees of duct restriction. In an exemplary embodiment, the restriction multiplier ranges from 1 to 1.5. The user specifies the restriction multiplier using a slide bar on thermostat  55 . Controller  54  then applies the restriction multiplier as described herein. 
         [0020]      FIG. 3  is a flowchart of an exemplary process executed by controller  54  to control the blower motor  25 . The process begins at  200  where the controller  54  receives a requested airflow (e.g., in CFM) from the thermostat  55 . At  202 , the controller  54  accesses the CFM airflow table  100  and locates the airflow value in the table closest to the requested airflow. At  204 , the controller  54  records the table location (e.g., row and column) of the airflow value closest to the requested airflow. At  206  the controller  54  accesses PWM table  102  at the same table location to retrieve a control signal value in the form of a PWM signal and multiplier. At  208 , the controller applies the optional restriction multiplier. At  210 , the controller applies a control signal to the blower motor  25  in response to the control signal value, the multiplier (if any) and the restriction multiplier (if any). The controller  54  multiplies the control signal value by the multiplier (if any) from the control signal table and by the restriction multiplier (if any). The result is used to generate a control signal for the blower motor  25 . 
         [0021]    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.