Abstract:
A method for controlling the motor of an air handling system to provide a desired output of flowing air therefrom while minimizing the power used by the motor, including operationally connecting a switched reluctance electric motor to a blower, operationally connecting an electronic controller to the switched reluctance electric motor, operationally connected at least one sensor to the electronic controller, measuring at least one environmental parameter with the at least one sensor, inputting the desired air flow into the electronic controller, calculating the minimum motor speed necessary to provide the desired air flow, and sending a control signal from the electronic controller to the motor to control the motor to the minimum motor speed necessary to provide the desired air flow.

Description:
TECHNICAL FIELD 
       [0001]    The present novel technology relates generally to air flow control in air handling systems, and, more particularly, to at a method and apparatus for optimizing the efficiency of the air handling system while maintaining constant air flow by a blower operationally connected to the system. 
       BACKGROUND 
       [0002]    Air handling systems, whether residential, commercial, or municipal, typically use a blower to urge air of a predetermined temperature through a duct system to control and maintain the temperature of an enclosure. The blower typically includes a fan operationally connected to a motor. The motor is typically electric. The air handling system is typically required to provide air flow under a variety of conditions, including variable enclosure volume, the temperature of the enclosure, the temperature of the air delivered, the duct geometry, and the like. 
         [0003]    Typically, an air handling system is required to provide air at a constant flow rate. A constant flow rate is generally achieved by controlling the speed of the driver motor in response to detected changes in the air flow rate and/or related variables. A number of control paradigms have been developed to control air flow rate by controlling motor speed, the specifics of each tailored to the characteristics of the hardware, desired output, and building environment of the particular air handling system in question. 
         [0004]    Typically, the electric motor driving the blower fan is a synchronous and operating at fixed increments of speed, such as 600 RPM, 900 RPM, 1800 RPM, 3600 RPM and the like. In order to effectively operate synchronous motors at speeds other than their incremental options, the motors must be connected to the blower fan via an adaptor, such as a V-belt or the like, whereby the motor speed may be relatively smoothly stepped up or down as desired. The drawback of this approach is that such adaptor systems are somewhat inefficient, costing the system extra energy. Further, such systems contribute to increased noise output and the requirement of sound insulation, more powerful electronic controller capability, and additional control and feedback modules. 
         [0005]    Further, the standard electric motors and blowers of existing air handling systems are designed to more or less efficiently operate around a narrow plateau of operating speeds and are typically designed to most efficiently operate around the speeds correlating to the standard and most common air flow demand. When demand spikes, it becomes very inefficient and even stressful to the system to ramp up to meet the sudden increase in demand for air flow, if the motor can even accommodate the demand at all. Thus, it is often necessary to have several independent and redundant air handling systems in place to handle acute, unusually heavy demands. For example, water treatment plants have two, and sometimes three, separate air handling systems in place to handle increased water demand due to heavy rainstorms or morning and evening heavy load times. The drawback of this configuration is that energizing the redundant blower unit often supplies more air flow than is required for the process, resulting in unneeded power consumption. Alternatively, an induction motor and VFD can be used, to adjust the blower airflow and meet process demands However, induction motors operate at less than their optimum efficiency when run at less than full motor load. Also, these motors have a relatively steep efficiency drop as motor speed moves away from the optimal. Finally, there is an added cost to supplying and maintaining several independent blower units for one job. 
         [0006]    Thus, there is a need for an air handling system having a motor capable of directly providing variable output speeds and a method and apparatus for controlling the same to optimize the efficiency of the air handling system while providing a constant air flow output. The present novel technology addresses these needs. 
       SUMMARY 
       [0007]    The present novel technology relates to an improved air handling control system. It is an object of the present novel technology to overcome the drawbacks associated with the conventional air handling delivery and control methods. The present novel technology relates generally to an improved air handling control system. 
         [0008]    One object of the present novel technology is to provide an improved method of air handling delivery and control. Further objects, features, and advantages will become apparent from a consideration of the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    For a better understanding of the nature and objects of the present novel technology, reference should be made to the following drawings, in which: 
           [0010]      FIG. 1  is a block diagram illustrating a first embodiment of the present novel technology, an apparatus for controlling the operation of a blower to yield increased efficiency. 
           [0011]      FIG. 2  is a block diagram illustrating the embodiment of  FIG. 1  used to provide flowing air in a waste water treatment application. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    For the purposes of promoting an understanding of the principles of the novel technology, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the novel technology is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the novel technology as illustrated therein being contemplated as would normally occur to one skilled in the art to which the novel technology relates. 
         [0013]    A first embodiment of the present novel technology is illustrated in  FIG. 1 , and relates to an air handling system  10  that includes an electric motor  20  operationally connected to a blower  25  and connected in electric communication to an electronic controller or microprocessor  30 . In some embodiments, the microprocessor  30  is connected to the motor  20  through switch  33 , which is typically connected to a power source (not shown). The electric motor  20  is more typically a switched reluctance motor. One or more sensors  35  are arrayed throughout the system  10  and also electrically connected to the microprocessor  30 . The system  10  is typically a ‘middle pressure’ system, operating to provide an output pressure of between about 4 and about 20 psig. 
         [0014]    The sensor array  35  typically may include an air flow sensor  40  positioned to measure the flow rate of the air as urged by the blower  25 . Also, the sensors  35  may include a barometric pressure sensor  45  and/or ambient air relative humidity sensor  50  and/or an ambient air temperature sensor  55  and/or a dissolved oxygen sensor  60  and/or the like, each positioned to measure respective properties of the fluid into which the system  10  outputs its flowing air (i.e., ambient air in a building or enclosure, water in a water treatment reservoir, or the like). 
         [0015]    The sensor array  35  typically includes a blower speed sensor  70  and/or a blower discharge temperature sensor  75  and/or a blower discharge pressure sensor  80  and/or a blower inlet pressure sensor  85  the like, each positioned to measure respective properties associated with the blower. Likewise, the sensor array  35  typically includes a motor voltage sensor  90  and/or a motor amperage sensor  95  and/or the like, each positioned to measure properties associated with the electric motor  20 . 
         [0016]    While the system  10  may include an air flow sensor  40  positioned upstream or downstream of the blower  25  for providing a control feedback signal to the microprocessor  30 , air flow sensors typically have an error margin of +/−5% or greater. A more precise method of determining air flow is to calculate from the blower motor speed and air parameters that are measureable with greater precision. For example, in one particular embodiment system  10 , the motor  20  is a switched reluctance drive motor provided by Switched Reluctance Drives, Ltd., East Park House, Otley Road, Harrogate, UK, HG3 1PR, and the following inputs are received by the microprocessor  30  from the sensor array  35 : 
         [0000]                                    Relative Humidity (Φ)   %       Atmospheric Pressure (P atm )   PSIA       Pressure drop across inlet filter (P in )   Inches Water Column       Inlet Pressure at blower flange (P 1 )   PSIG       Inlet Temperature at air inlet (T 1 )   Degrees Rankine       Discharge pressure at blower flange (P 2 )   PSIG       Discharge temperature at blower flange (T 2 )   Degrees Rankine       Motor/Blower Speed (v)   RPM       and       Standard Pressure (P std )   14.7 PSIA       Standard Temperature (T std )   528 Degrees Rankine       Standard Relative Humidity (Φ std )   36%                    
are given as predetermined values. From these data, ICFM (Inlet Cubic Feet per Minute) may be calculated for the system  10 , typically based on proprietary equations provided by the blower manufacturer. These proprietary equations are programmed into the microprocessor  30  and, using these, ICFM is determined. From the ICFM value a conversion to SCFM (Standard Cubic Feet per Minute) is made; the ICFM is essentially a volumetric value while the SCFM is an air mass (or oxygen mass) value. The equation used for the conversion is as follows:
 
         [0000]    
       
         
           
             SCFM 
             = 
             
               ICFM 
               * 
               
                 T 
                 std 
               
               * 
               
                 ( 
                 
                   
                     
                       P 
                       atm 
                     
                     - 
                     
                       
                         P 
                         sat 
                       
                       * 
                       φ 
                     
                   
                   
                     
                       T 
                       1 
                     
                     * 
                     
                       P 
                       std 
                     
                   
                 
                 ) 
               
             
           
         
       
     
         [0000]    where P sat  is determined from published tables for air based on T 1 . 
         [0017]    In general, for rotary lobe positive displacement blowers the ICFM can be determined using the variables listed above along with a value for the Cubic Feet per Revolution (CFR) and the Slip RPM for a particular blower. Slip RPM is the speed at which 1 PSI of discharge pressure is developed with the discharge. ICFM may thus be expressed as: 
         [0000]    
       
         
           
             
               I 
                
               
                   
               
                
               C 
                
               
                   
               
                
               F 
                
               
                   
               
                
               M 
             
             = 
             
               C 
                
               
                   
               
                
               F 
                
               
                   
               
                
               R 
               * 
               
                 [ 
                 
                   
                     Blower 
                      
                     
                         
                     
                      
                     Speed 
                   
                   - 
                   
                     Slip 
                      
                     
                         
                     
                      
                     R 
                      
                     
                         
                     
                      
                     P 
                      
                     
                         
                     
                      
                     M 
                     * 
                     
                       
                         
                           ( 
                           
                             
                               P 
                               2 
                             
                             - 
                             
                               P 
                               1 
                             
                           
                           ) 
                         
                         * 
                         
                           
                             T 
                             1 
                           
                           
                             T 
                             std 
                           
                         
                         * 
                         
                           
                             G 
                             s 
                           
                           
                             G 
                             a 
                           
                         
                       
                     
                   
                 
                 ] 
               
             
           
         
       
     
         [0000]    Where G s  and G a  are standard specific gravity of air and the actual specific gravity of the process gas, respectively. G s  is given as 1.0. G a  is determined by the following relation: 
         [0000]    
       
         
           
             
               G 
               a 
             
             = 
             
               
                 
                   ( 
                   
                     
                       
                         P 
                         1 
                       
                       - 
                       
                         
                           P 
                           sat 
                         
                         * 
                         φ 
                       
                     
                     
                       P 
                       1 
                     
                   
                   ) 
                 
                 * 
                 
                   MW 
                   dry 
                 
               
               + 
               
                 
                   ( 
                   
                     
                       
                         P 
                         sat 
                       
                       * 
                       φ 
                     
                     
                       P 
                       1 
                     
                   
                   ) 
                 
                 * 
                 
                   MW 
                   wv 
                 
               
             
           
         
       
     
         [0000]    where the MW terms are the molecular weights of the components of the process gas, which consists of dry air and water vapor. Their values are as follows:
   MW dry =28.964 lbm/lb mol   MW wv =18.02 lbm/lb mol   
 
         [0020]    An alternate method for calculating SCFM from ICFM follows as: 
         [0000]    
       
         
           
             
               S 
                
               
                   
               
                
               C 
                
               
                   
               
                
               F 
                
               
                   
               
                
               M 
             
             = 
             
               I 
                
               
                   
               
                
               C 
                
               
                   
               
                
               F 
                
               
                   
               
                
               M 
               * 
               
                 ( 
                 
                   
                     P 
                     1 
                   
                   
                     P 
                     std 
                   
                 
                 ) 
               
                
               
                 ( 
                 
                   
                     T 
                     std 
                   
                   
                     T 
                     1 
                   
                 
                 ) 
               
                
               
                 ( 
                 
                   
                     1 
                     + 
                     
                       ω 
                       std 
                     
                   
                   
                     1 
                     + 
                     
                       ω 
                       1 
                     
                   
                 
                 ) 
               
                
               
                 ( 
                 
                   
                     MW 
                     1 
                   
                   
                     MW 
                     std 
                   
                 
                 ) 
               
             
           
         
       
     
         [0000]    where ω std  is standard humidity ratio and may be expressed as: 
         [0000]    
       
         
           
             
               ω 
               std 
             
             = 
             
               
                 ( 
                 
                   
                     
                       φ 
                       std 
                     
                     * 
                     
                       P 
                       
                         
                           v 
                           1 
                         
                          
                         
                           sat 
                           std 
                         
                       
                     
                   
                   
                     
                       P 
                       std 
                     
                     - 
                     
                       
                         φ 
                         std 
                       
                       * 
                       
                         P 
                         
                           
                             v 
                             1 
                           
                            
                           
                             sat 
                             std 
                           
                         
                       
                     
                   
                 
                 ) 
               
                
               
                 ( 
                 
                   
                     MW 
                     wv 
                   
                   
                     MW 
                     dry 
                   
                 
                 ) 
               
             
           
         
       
     
         [0000]    and ω 1  is inlet humidity ratio and may be expressed as: 
         [0000]    
       
         
           
             
               ω 
               1 
             
             = 
             
               
                 ( 
                 
                   
                     
                       φ 
                       1 
                     
                     * 
                     
                       P 
                       
                         
                           v 
                           1 
                         
                          
                         
                           sat 
                           1 
                         
                       
                     
                   
                   
                     
                       P 
                       1 
                     
                     - 
                     
                       
                         φ 
                         1 
                       
                       * 
                       
                         P 
                         
                           
                             v 
                             1 
                           
                            
                           
                             sat 
                             1 
                           
                         
                       
                     
                   
                 
                 ) 
               
                
               
                 ( 
                 
                   
                     MW 
                     wv 
                   
                   
                     MW 
                     dry 
                   
                 
                 ) 
               
             
           
         
       
     
         [0000]    with MW 1  equivalent to G a  above. 
         [0021]    In operation, the motor  20  is typically run to provide a constant speed, constant air flow, or varied speed based on a predetermined parameter, such as dissolved oxygen demand. The electronic controller  30  monitors the input from the sensor array  35 , calculates the optimum motor speed to provide the required output at a minimum energy use, and automatically controls the motor speed to maximize system efficiency. 
       Water Treatment Applications 
       [0022]    Dissolved oxygen in water treatment is required for the aerobic microorganisms that are used to convert unwanted organic wastes to inert inorganic byproducts. In order for these microorganisms to thrive, the dissolved oxygen content of the water is desired to be maintained above a certain threshold level, typically around 2 mg per liter of water. The actual value in any specific case is predetermined by the treatment facility and is typically measured and verified manually by a laboratory technician. Typically, the technician will go to an aeration basin, remove a water sample, determine the dissolved oxygen content and then determine whether more or less air is being supplied to the tank than is needed to maintain the dissolved oxygen content at an acceptable level. 
         [0023]    For water treatment, the system  10  is typically utilized to provide air flow for scouring and backwashing water filters. Scouring and backwashing are typically constant flow applications, wherein pressure may sharply increase or spike upon startup of the air directing ductwork leading from the blower  20  into the water reservoir, until water clears the discharge line. The system  10  may also be connected as part of a pneumatic conveying system for dry chemicals. This configuration would likewise typically be a constant flow application. 
         [0024]    For wastewater treatment applications, the system  10  may be connected to provide air for pre-aeration, secondary aeration, more scour and backwash, and mixing. The system  10  is suited for use in applications requiring varying flow and aeration, the blower(s)  25  provides air through a duct or conduit  110  to the bottom of a tank or basin  120 , typically through one or more diffusers  125 . The diffusers  125  portion the air into small diameter bubbles  130  in order to maximize the surface area of the air volume so introduced into the waste water  135 . Diffusion of oxygen into the mixture occurs as the bubbles  130  rise through the waste water  135 . The oxygen is used by bacteria in a biological process to break down solid organic wastes and contaminants. Oxygen demand by the process fluctuates regularly due to changes in the amount of influent waste, composition of the influent, and environmental conditions. If oxygen demand drops, less airflow can be provided to the system and operating cost is reduced. Typically the feedback is provided by a dissolved oxygen probe or sensor  60 . These are typically constant pressure, variable volume applications. 
         [0025]    Typically, mixing applications require a set airflow for a given volume of waste water  135 . Air is provided again through diffusers  125 , however, these diffusers  125  are configured to produce larger bubbles  130  in order to induce greater fluid displacement and, thus, more thorough mixing. Some oxygen transfer is still required, as there is a biological process occurring, but the main concern is maintaining a homogenous fluid mixture. Effective water volume does fluctuate with the amount of influent, therefore the application is variable volume and variable pressure. 
         [0026]    Treatment water  135  having a dissolved oxygen content above the value required for the waste-reducing microorganisms to proliferate provides no benefit, and represents an added and unnecessary expense. The system  10  measures the dissolved oxygen content with one or more oxygen sensors  60  positioned in the water reservoir or basin  120  to provide real-time feedback to the microprocessor  30 , as well as to system operators, to indicate what adjustments, if any, should be made to provide sufficient, but not excessive, airflow to the water reservoir  120  to maintain the dissolved oxygen concentration at the desired, predetermined level. The system  10  typically receives a signal from the sensor  60  and automatically adjusts the speed of the blower  25  to provide increased or decreased air flow into the water reservoir  120  as indicated by the sensor  60  and determined by the microprocessor  30  to yield sufficient, but not excessive, dissolved oxygen for the waste reducing microorganisms to live in the water reservoir  120 . The signal from the sensor  60  is typically a low current signal, more typically in the 4 mA to 20 mA range. This blower  25  may be energized by the motor  20  to run faster or slower to provide increased or decreased air flow depending upon feedback from the dissolved oxygen probe  60  and/or other sensors in the sensor array  35  while maintaining substantially optimum efficiency, without the need of one or more redundant backup blower systems on line. The system efficiency curve plotted as a function of blower speed for various loads is given as  FIG. 3 . 
       Other Applications 
       [0027]    In a dilute phase pneumatic conveying application, the air handling system  10  is engaged to maintain a minimum airflow velocity for the highest density particle stream. Where particles of lesser density or varying physical characteristics are introduced into the stream, the additional airflow velocity is not required in order to maintain the minimum flow velocity. Energy can be conserved by measuring particle velocity with the sensor array  35 , such as via radar or the like, and communicating the particle velocity measurement signal to the microprocessor  30 , which then automatically calculates the minimum blower  20  speed necessary to yield the minimum airflow velocity required to maintain the required conveyance speeds. This would be defined as a variable flow and pressure application. 
         [0028]    While the novel technology has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It is understood that the embodiments have been shown and described in the foregoing specification in satisfaction of the best mode and enablement requirements. It is understood that one of ordinary skill in the art could readily make a nigh-infinite number of insubstantial changes and modifications to the above-described embodiments and that it would be impractical to attempt to describe all such embodiment variations in the present specification. Accordingly, it is understood that all changes and modifications that come within the spirit of the novel technology are desired to be protected.