Patent Publication Number: US-2017363310-A1

Title: Method and apparatus for passively controlling airflow

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/075,514 filed Nov. 8, 2013, issued as U.S. Pat. No. 9,759,442, which is a continuation-in-part of U.S. patent application Ser. No. 12/783,826 filed May 20, 2010, issued as U.S. Pat. No. 9,201,428, which is a division of U.S. patent application Ser. No. 11/318,682 filed Dec. 27, 2005, now issued as U.S. Pat. No. 7,766,734, to which Applicant claims the benefit of the earlier filing date. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a method and apparatus for controlling airflow and, more particularly, a method and apparatus for controlling air distribution in fan assisted central exhaust and/or return air ventilating systems. 
     2. Description of the Related Art 
     Generally, central ventilation fans and ventilators used for the purpose of removing or exhausting air from areas in a building or structure, such as bathrooms, utility closets, kitchens in homes, offices, and other areas, will simultaneously remove air from fixed inlet terminals connected to the central ventilation fan whenever the fan is operating. Whether the fan operates intermittently or continuously, this results in excessive energy consumption as a result of removing heated and conditioned air from spaces that may not require ventilation simply because the demand for ventilation exists in one or more of the areas. 
     Previous attempts to limit a central fan or ventilation system to ventilating only occupied areas by opening and closing terminal devices, caused fluctuations in duct air pressure, and ultimately caused a shift in the amount of air removed or delivered to one or more of the areas or zones. This resulted in excessive ventilation rates and excessive energy usage in some areas and under-ventilating other areas, which in turn, caused poor indoor air quality related problems and a failure to meet minimum building code requirements in some instances. 
     Controlling the central fan speed or revolution per minute (RPM) to prevent the over or under-ventilation problem in zoned systems has been difficult, expensive and generally ineffective in the past. The typical fan control method involved monitoring either main duct pressure or the number of open zones to determine the total amount of airflow needed. However, a problem remained in that controlling the total system airflow does not ensure proper and/or constant airflow amounts at each zone branched duct. 
     Moreover, controlling airflow rates at each zone or branched duct in a supply air system has been accomplished using variable air volume (VAV) terminals. These VAV terminals were designed to vary the airflow rates in response to temperature needs. While VAV terminals have the capability to control airflow at constant levels, they typically utilized an electrically or pneumatically powered control device that monitors duct pressure through a pilot tube and sends a signal to a separate zone damper. These control devices required a separate power source, separate parts, and direct coupling to, among other things, a damper actuator to allow for responsive zoned airflow control. If the VAV control device loses power, it will also lose it ability to control airflow. 
     What is needed, therefore, is a system and method for controlling air distribution in both fan assisted central exhaust systems and/or return air ventilating systems that facilitates overcoming one or more of the problems of the prior art. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of one embodiment of the invention to provide a ventilation terminal system and device with an integral primary zone controlled damper that regulates airflow in response to a switch, dehumidistat, light sensor, motion sensor, CO 2  sensor or the like. 
     An object of another embodiment is to provide a ventilation terminal device and system with a pressure independent flow control device that is integral to the primary flow control, which in one embodiment may be a damper. 
     Another object of another embodiment of the invention is to provide a flow control device and system that regulates airflow to substantially constant levels when exposed to varying duct pressures. 
     Still another object of another embodiment of the invention is to provide a flow control device and system that is mechanically removed from an airflow stream when the primary control device is caused to permit airflow to a predetermined demand level. 
     Still another object of another embodiment of the invention is to provide a control device for situating in an airflow stream to regulate or control airflow to a substantially constant or predetermined maximum rate. 
     Yet another object of another embodiment is to provide a system and method having a first control device that controls or regulates flow to a first substantially constant or predetermined rate, while another flow control device controls or regulates flow to a second predetermined level or rate. 
     Still another object of another embodiment of the invention is to provide at least one or a plurality of flow control devices that require no direct electric or pneumatic power source, but rather, utilize only system duct pressure to regulate airflow to first and/or second predetermined levels, respectively. 
     Still another object of another embodiment of the invention is to provide a minimum flow control device that will continue to operate if a primary flow control device cannot be actuated to permit increasing airflow or it loses power. 
     Still another object of another embodiment of the invention is to provide a ventilation control assembly and system that can be easily maintained and/or removed from a terminal housing without disconnecting the terminal to which the assembly is attached from any duct or ventilation shaft. 
     Still another object of another embodiment of the invention is to provide a system that is small enough to be mounted between floors, and/or ceiling assemblies, such as assemblies constructed of nominal 10″ joists on 16″ centers. 
     Another object of another embodiment of the invention is to provide an assembly that utilizes a damper drive-motor powered by 120 volt, 24 volt, 12 volt, or 220 volt AC or other suitable electrical voltage supply. 
     Yet another object of another embodiment of the invention is to provide a device that reduces or eliminates the need for routine maintenance of the type that is required by mechanical or electrical systems of the past. 
     Still another object of another embodiment of the invention is to provide a device that can be easily mounted in a fire or non-fire rated ceiling or wall assembly. 
     Yet another object of another embodiment of the invention is to provide a device that will reduce the necessary central fan horsepower requirements and will facilitate saving on energy consumption by reducing the overall fan or ventilator requirements in the system. 
     In one aspect, an embodiment of the invention comprises a zone control exhaust terminal comprising a housing having a first opening coupled to a duct and a second opening associated with an area to be ventilated, the housing directing airflow from the inlet to the outlet along a predetermined path and a damper hingeably coupled to the housing for controlling airflow between the area and a fan or ventilator, a motor for driving the damper from a closed position at which the damper becomes situated in the predetermined path and an open position at which the damper permits airflow along the predetermined path in response to a motor control signal and an airflow regulator situated in the predetermined path, the airflow regulator regulating airflow along the predetermined path when the damper is in the closed position. 
     In another aspect, another embodiment of the invention comprises a zone control ventilation system for use in a building having a plurality of areas to be ventilated, the system comprising at least one fan unit for generating airflow, a plurality of ducts coupled to at least one fan unit; a plurality of zone control exhaust terminals coupled to each of the plurality of ducts, respectively, and operatively associated with each of the plurality of areas each of the plurality of zone control exhaust terminals comprising a housing having an inlet coupled to a duct and an outlet associated with at least one of the plurality of areas to be ventilated, a damper pivotally coupled to the housing, a motor for driving the damper between a closed position and an open position at which the damper permits airflow between at least one fan unit and at least one plurality of areas and into at least one of the plurality of areas to be ventilated in response to a motor control signal, and an airflow regulator situated in an airflow path, the airflow regulator for regulating an airflow rate along the airflow path between the room and at least one fan unit. 
     In another aspect, another embodiment of the invention comprises a method for maintaining a substantially constant airflow in a ventilation system having a plurality of ducts, the method comprising the steps of passively regulating airflow at a first rate through the plurality of ducts and causing airflow through at least one of the plurality of ducts at a second rate in response to a demand signal as the airflow through the other of the plurality of ducts continues to flow at the first rate. 
     In yet another aspect, another embodiment of the invention comprises a method for controlling airflow through a plurality of ducts coupled to a ventilator, comprising the steps of permitting airflow from the ventilator through at least one of the plurality of ducts at a substantially constant rate and permitting airflow through at least one of the plurality of ducts to an area at a demand rate that is greater than the substantially constant rate in response to a demand signal. 
     In still another aspect, another embodiment of the invention comprises a method for providing zone-by-zone airflow regulation for regulating airflow to substantially constant levels, comprising the steps of controlling airflow substantially constant through a plurality of terminals associated with areas where no ventilation airflow is demanded at a first rate and controlling airflow through said terminal at a second rate, which is higher than said first rate in areas where ventilation airflow is demanded in response to an airflow demand at a demand rate. 
     In yet another aspect, another embodiment of the invention is to provide a method for regulating airflow to a plurality of zones of a building having a fan, comprising the steps of situating a primary regulator in operative relationship with each of said plurality of zones to regulate airflow between each of said plurality of zones and said fan and situating at least one constant airflow regulator in operative relationship with each of said primary regulators in order to regulate airflow between each of said plurality of zones and said fan such that when said primary regulator permits a demand airflow between one of said plurality of zones and said fan, said at least one constant airflow regulators control or regulate airflow such that airflow to at least the other of said plurality of zones is substantially constant. 
     In still another aspect, another embodiment of the invention is to provide a method for regulating airflow to a substantially constant level in each of a plurality of zones in a structure, said structure comprising an airflow generator and at least one conduit for providing fluid communication between each of said plurality of zones and said airflow generator and said method comprising the steps of causing airflow to a demand level in any of said plurality of zones where airflow to said demand level is demanded and regulating airflow to a substantially constant level in the other of said plurality of zones where airflow to a demand level is not demanded. 
     In yet another aspect, another embodiment of the invention comprises a system for regulating airflow in a structure having a plurality of zones and said system comprising an airflow generator and a plurality of terminals associated with each of said plurality of zones, respectively a conduit for coupling said airflow generator to each of said plurality of terminals a plurality of primary regulators coupled to said plurality of terminals, respectively, for causing airflow to a demand level in one of said plurality of zones in response to a demand and a plurality of first constant airflow regulators situated between each of said plurality of zones, respectively, and said airflow generator to regulate airflow between said airflow generator and those other plurality of zones where demand airflow is not demanded to a first predetermined level. 
     In another aspect, another embodiment comprises a damper assembly for use in a ventilation system having an airflow generator, a terminal associated with an area to be ventilated, and a duct for coupling the airflow generator to the terminal, the damper assembly comprising: a support, a damper pivotally coupled to one support, a motor mounted on the support for driving said damper between a closed position and an open position and the damper assembly being detachably secured and removable from the system without dismantling or disconnecting either the duct or the terminal. 
     In yet another aspect, another embodiment of the invention comprises a zone control terminal for use in an air distribution system, the zone control terminal comprising a housing having an entry opening for receiving airflow and an exit opening, a damper hingeably coupled to the housing and situated between the entry opening and the exit opening, a motor for driving the damper between an open position and a closed position, at least one first airflow regulator that is not situated in series with the damper, at least one second airflow regulator situated in series with the damper, wherein the at least one first airflow regulator controls or permits a predetermined minimum amount of airflow through the housing when the damper is in the closed position and the at least one second airflow regulator cooperating with the at least one first airflow regulator to control or permit a predetermined maximum amount of airflow through the housing when the damper is in the open position, the predetermined maximum amount of airflow through the zone control terminal being a sum of a maximum airflow rate of the at least one first airflow regulator and a maximum airflow rate of the at least one second airflow regulator. 
     In still another aspect, another embodiment of the invention comprises a system for regulating airflow is a structure having a plurality of zones, the system comprising a plurality of terminals associated with each of the plurality of zones, respectively, at least one conduit for coupling an airflow generator to each of the plurality of terminals, each of the plurality of terminals comprising a housing having an entry opening for receiving airflow and an exit opening, a damper hingeably coupled to the housing and situated between the entry opening and the exit opening, a motor for driving the damper between an open position and a closed position, the motor being responsive to an airflow demand, at least one first airflow regulator situated in each of the plurality of terminals, at least one second airflow regulator situated in series with the damper, wherein the at least one first airflow regulator controls or permits a first predetermined amount of airflow and the damper and at least one second airflow regulator cooperating with the at least one first airflow regulator to control or permit a second predetermined amount of airflow through the housing when the damper is in the open position, the second predetermined amount of airflow through the plurality of terminals, the second predetermined amount of airflow being a sum of a maximum airflow rate of the at least one first airflow regulator and a maximum airflow rate of the at least one second airflow regulator. 
     In another aspect, another embodiment of the invention comprises a zone control system for use in a structure having a plurality of zones, the zone control system comprising a plurality of terminals associated with each of the plurality of zones, respectively, the plurality of terminals being adapted to receive airflow from an airflow generator, each of the plurality of terminals comprising a housing having an entry opening for receiving airflow and an exit opening, a damper hingeably coupled to the housing and situated between the entry opening and the exit opening, a motor for driving the damper between an open position and a closed position, the motor being responsive to a demand, at least one first airflow regulator situated in parallel with the damper, at least one second airflow regulator situated in series with the damper, wherein when the damper is in the closed position the at least one first airflow regulator permits airflow to a first predetermined level and when the damper is in the open position, the at least one first airflow regulator cooperates with the at least one second airflow regulator to permit airflow to a second predetermined level. 
     These are illustrative objects. Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS 
         FIG. 1  is a perspective view showing an embodiment of the invention, illustrating the use of a fan or ventilator in combination with a central shaft in combination with one or more terminals associated with each area or zone to be ventilated; 
         FIG. 2  is a fragmentary view of another embodiment of the invention showing a system utilizing a ventilator in combination with one or more terminals; 
         FIG. 3  is a fragmentary view of a variable fan ventilation or exhaust system in accordance with one embodiment of the invention; 
         FIG. 4  is an exploded view of an embodiment illustrating, among other things, a housing, the ventilation duct, and a plurality of constant air controllers or regulators; 
         FIG. 5  is a fragmentary and sectional view illustrating various features of the embodiment shown in  FIG. 4  and also illustrating a damper having an aperture for receiving an airflow controller or regulator and also showing the damper in phantom after the airflow controller or regulator has been received in the aperture and the damper has been actuated by the drive motor to an open position; 
         FIG. 6  is an assembled view of the embodiments illustrated in  FIGS. 4 and 5 ; 
         FIGS. 7A-7B  illustrate one embodiment of the invention and also illustrates a plurality of airflow versus pressure difference characteristic curves relative to the airflow in each of the ducts illustrated; 
         FIGS. 8A-8B  are views of another embodiment of the invention illustrating a airflow controller or regulator situated in the damper and associated curves, but with no airflow controller or regulator situated in any of the ducts; 
         FIGS. 9A-9B  illustrate another embodiment of the invention, illustrating a system having a plurality of solid dampers, each of which comprise an associated constant airflow controller or regulator situated in a duct associated with each damper; 
         FIGS. 10A-10B  show various characteristic curves of a prior art constant airflow regulator and a prior art bulb-type controller or regulator ( FIG. 10A ) and a vain-type controller or regulator ( FIG. 10B ); 
         FIG. 11  illustrates the use of a terminal of the type shown in  FIGS. 4 and 5  mounted in a central pressurized shaft and further illustrating an open duct associated with the housing of the terminal open to the pressure in the central shaft; 
         FIGS. 12A-12B  illustrate another embodiment of the invention where various combinations of features of a primary, secondary, and tertiary control or regulators may be used in various combinations, with the embodiment shown in  FIGS. 12A-12B  being a representative example; 
         FIGS. 13A-13D  illustrate another embodiment showing a plurality of sub-ducts in a terminal, with a damper associated with one of the sub-ducts and at least one airflow regulator in each sub-duct. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to  FIGS. 1-3 , a zone control ventilation system or passive flow control system  10  for use in the building  12 , such as a multi-story commercial building ( FIG. 1 ), multi-story condominium or apartment building ( FIG. 2 ), a residential building ( FIG. 3 ). The system  10  provides a system, apparatus and method for providing on-demand airflow at a demand airflow rate and a passive airflow at a passive airflow rate to a plurality of zones or areas  14  in the manner described later herein. 
     The system  10  comprises at least one fan  16  ( FIGS. 1 and 3 ), or the system  10  may comprise a ventilator  17 , such as one or more of the multi-port ventilator series (“MPV”) model series MPV ventilator provided by American Aides Ventilation Corporation located at 4521 19th Street Court E. in Sarasota, Fla. It should be understood that other suitable ventilators or fans may be used and the invention is not limited by these particular model types. 
     The system  10  further comprises a plurality of ducts  18  that are coupled directly to the at least one fan  16  or ventilator  17 , as illustrated in  FIGS. 2 and 3 , or coupled to a main ventilation duct or shaft  20  ( FIGS. 1 and 11 ) that is coupled to either the at least one fan  16  or ventilator  17 . The plurality of ducts  18  are each coupled to at least one or a plurality of zone control exhaust terminals  22 , at least one of which is operatively associated with each of the areas  14  to be ventilated. Although the embodiments illustrated in  FIGS. 1-3  show a single zone control exhaust terminal  22  associated with each of the areas  14 , it should be understood that more than one of the plurality of zone control exhaust terminals  22  may be associated with each of the areas  14 . Although not shown, not every area or zone  14  in the building, structure, residence or building  12  must have one or more of the plurality of zone control exhaust terminals  22 , although in a preferred embodiment at least one of the plurality of zone control exhaust terminals  22  is associated with each area  14 . 
     Also, while the illustration shown in  FIG. 2  shows a multi-port ventilator  17  coupled directly to each of the plurality of zone control exhaust terminals  22  via ducts  18 , the zone control exhaust terminals  22  may be coupled directly to the main ventilation shaft  20  or to artery ducts, such as ducts  18  ( FIG. 1 ), that extend from the main ventilation shaft  20 . Alternatively, as illustrated in  FIG. 11 , the terminal  22  may be situated interior of the shaft, with an open duct extension or collar  30 , which in one embodiment is at least 22 inches. Note that the duct extension or collar  30  has an end  30   a  coupled to the terminal  22  and an end  30   b  that is open to the interior area  20   c  of shaft  20 . It should be understood that the interior area  20   c  of shaft  20  has an interior pressure created or provided by the at least one fan  16  or ventilator  17 . 
     Referring to  FIGS. 4-6 , various details of one of the plurality of zone control exhaust terminals  22  will now be described. It should be understood that each of the plurality of zone exhaust terminals  22  comprise substantially the same parts, although they do not have to be identical to each other as will become apparent later herein. Each of the zone control exhaust terminals  22  comprises a box-shaped housing  24  having a plurality of flanges  26  and  28 . The flanges  26  and  28  provide means for mounting the housing  24  to a structure, such as between adjacent 10″ joists or trusses on 16″ or 22″ centers in a ceiling or roof of the building  12  or between adjacent studs (not shown) in a wall  29  ( FIG. 1 ) of the building  12 , or to a wall  23  ( FIG. 11 ) of shaft  20 . 
     As illustrated in  FIGS. 4 and 6 , the housing  24  is generally rectangular and comprises the duct extension or collar  30  for coupling the housing  24  to duct  18  and for communicating with an opening  32  into an area  34  defined by the housing  24 . The duct collar  30  is conventionally coupled to the duct  18  as illustrated in  FIG. 6 . As mentioned earlier, however, terminal  22  could be mounted to shaft  20  and the end  30   b  of duct collar  30  could be open to the interior area  20   c  of central shaft  20 . The housing  24  further comprises a grille or cover  36  for covering a second opening  38  of the housing  24 . The second opening  38  is associated or in communication with the area or zone  14 . 
     The system  10  further comprises an air restrictor or damper assembly  40  which will now be described relative to  FIG. 5 . The assembly  40  comprises a generally U-shaped member or support  42  having an L-shaped bracket  44  welded or secured thereto. The apertures  46  and  48  typically support and receive a drive shaft  50  which is coupled to and pivotally driven by a motor  52  that is operatively coupled to a switch  54  as shown. The switch  54  may be a wall switch situated on, for example, the wall, such as a wall  29  in  FIG. 1 , associated with the area  14 . The switch  54  may be a manual wall switch actuated by a user, or the motor  52  may be coupled and respond to at least one of a motion sensor, manual control, timer mechanism, light sensor, occupancy sensor, CO 2  sensor or other indicators or sensors of presence when a user enters or exits one of the areas  14 . 
     The generally U-shaped member or support  42  is received in the area  34  ( FIG. 4 ) of housing  24  and secured between housing walls  24   a  and  24   b  with a plurality of screws  56  as shown. Note that the assembly  40  further comprises a primary flow control, which in the illustration is a damper  58  that is secured by a weld, screws or other suitable means to the drive shaft  50  of motor  52 . The damper  58  is pivotally driven by the motor  52  in response to a user actuating the switch  54 , for example, from an off position to an on position. It should be understood that the motor  52  is operatively coupled to a power source, an AC power source (not shown) in one embodiment, such as a 12V, 24V, 120V or 220V AC, but a DC power source may also be used. When the switch  54  is actuated by a user to the on position, the motor  52  becomes energized and pivotally drives the damper  58  from the closed position to the open position illustrated in phantom in  FIG. 5 . 
     It should be noted that the damper  58  is operatively associated with and situated adjacent to an opening  32  ( FIG. 4 ) in the surface  24   c  of housing  24 . A first side  58   a  of damper  58  may comprise a foam or other sealing material secured thereto by an adhesive for sealing the damper against the surface  24   c  of housing  24  when the damper  58  is in the closed position illustrated in  FIG. 6 . Note that the assembly  40  comprises a spring or plurality of springs  70  that act upon a joining portion  42   b  of the generally U-shaped member or support  42  and on the planar member or surface  58   b  of damper  58  to urge or bias the damper  58  in the direction of arrow A in  FIG. 5  so that the damper  58  is biased in the closed position illustrated in  FIG. 6 . The motor  52  retains the damper  58  in the open position during any demand period, which is the period in time that the motor  52  is being activated. 
     In one embodiment shown in  FIGS. 4, 5 and 9A-9B , the assembly  40  may further comprise a switch  62  that is mounted on a flat area or ledge  42   c  of generally U-shaped bracket  42  as illustrated in  FIGS. 4 and 5 . The switch  62  is operatively coupled to the at least one exhaust fan  16  or ventilator  17  such that when the damper  58  is actuated or driven from the closed position illustrated in  FIG. 6  to the open position (shown in phantom in  FIG. 5 ), a first side  58   a  of damper  58  actuates the lever or switch  62  coupled to the power source (not shown). When the switch  62  is triggered, the exhaust fan  16  or ventilator  17  becomes energized in response, thereby causing an increase of airflow in the ducts  18  or shaft  20 . When the damper  58  returns to the closed position, for example, when the user activates switch  54  to the off position, the damper  58  in the embodiment shown  FIGS. 9A and 9B  is driven or actuated to the closed position to close the opening  32  and release the switch  62  to cause at least one fan  16  or ventilator  17  to turn off. 
     One feature and advantage of this design illustrated in  FIGS. 4-5  is that it is easy to perform maintenance on or remove the assembly  40  after it is installed, although it is not believed that much maintenance will be required. 
     Returning to  FIGS. 9A-9B , an embodiment is illustrated where the ventilator  17  or at least one fan  16  is only on when the user actuates the switch  54  to the on position. In contrast, the embodiments illustrated in  FIGS. 7A-7B  and  FIGS. 8A-8B , described later herein, does not utilize switch  62  to activate at least one fan  16  or ventilator  17 . In these embodiments, at least one fan  16  or ventilator  17  provide a constant airflow in the ducts  18 ,  19  or shaft  20 . However, when a damper  58  in the system  10  is opened in these illustrative embodiments, at least one fan  16  or ventilator  17  responds to a decrease in duct system resistance or demand for increased airflow and automatically causes an increase in fan or ventilator speed, thereby causing a resultant increase in the airflow in the shaft  20  and ducts  18  in response and in a manner conventionally known. 
     Referring to  FIGS. 4-6 , the assembly  40  further comprises at least one or a plurality of airflow regulators  71  and  73  ( FIG. 6 ) and/or  72  and  74  ( FIGS. 1-5 ). In one embodiment, the airflow regulators  71  and  73  are integral constant dynamic airflow regulators, such as the constant airflow regulators CAR I and CAR II available from American Aides Ventilation Corporation, 4537 Northgate Court, Sarasota, Fla. 34234-2124. As illustrated in  FIGS. 4 and 5 , note that the damper  58  comprises an aperture or opening  59  defined by the interior area as shown. The diameter of the interior wall  58   d  in damper  58  is dimensioned to receive the airflow regulator  72  as shown. As illustrated, bulb-type constant airflow regulators, such as those regulators  71  and  73  illustrated in  FIG. 6 , may be used and these are also available from American Aides Ventilation Corporation. 
     It should be understood that the constant airflow regulators  72  and  74  may comprise different specifications in a preferred embodiment and they both provide constant airflow regulation. For example, the constant airflow regulators  72  and  74  provide constant airflow regulation by operation of the vane  72   a  ( FIG. 4 ), which acts to at least partially close the opening  59  ( FIG. 5 ) in a manner conventionally known. In contrast, the constant airflow regulators  71  and  73  ( FIG. 6 ) provide constant airflow regulation by the inflating action of the constant airflow regulator bulb  71   a  and  73   a , respectively, and in a manner that is conventionally known. As illustrated in  FIG. 6 , note that the bulbs  71   a  and  73   a  are generally hour-glass shaped. As a static pressure increases in the ducts  18 , the static pressure around the bulbs  71   a  and  73   a  increases, thereby causing the bulbs  71   a  and  73   a  to inflate and thereby decreasing the area around the bulbs  71   a  and  73   a . At substantially the same time, as the static pressure around the bulbs  71   a  and  73   a  increases, an air velocity also increases thereby resulting in constant airflow. The constant airflow regulators  71 ,  72 ,  73  and  74  thereby provide a generally or substantially constant airflow regardless of pressure differences in the system  10 .  FIGS. 10A and 10B  graphically illustrate the operative characteristics of the airflow regulators  71 ,  72 ,  73  and  74 . It should be understood that the associated specifications will change depending upon the specifications selected by the user. The operation of the system  10  will now be described relative to several illustrative examples shown in  FIGS. 7A-9B . For ease of illustration, the embodiment of  FIGS. 7A-7B  will be illustrated or used in the embodiment of  FIG. 1 ,  FIGS. 8A-8B  will be illustrated as used in the embodiment of  FIG. 2 , and  FIGS. 9A-9B  will be illustrated as used in the embodiment of  FIG. 3 . 
     In the embodiments shown in  FIGS. 7A-9B , the damper  58  provides primary airflow regulation or control. The damper  58  is used in combination with at least one of either the first or second regulator  72  or  74  as illustrated in  FIGS. 7A-9B . In embodiments shown in  FIGS. 9A-9B , the constant airflow regulator  74  permits a predetermined amount of airflow and provides substantially constant airflow regulation to a predetermined or maximum airflow rate. In contrast, the airflow regulator  72  in the illustration of  FIGS. 8A-8B  provides substantially constant airflow regulation at a predetermined amount or a minimum amount of airflow. When the regulators  72  and  74  are used together as illustrated in  FIGS. 7A-7B , they control or regulate airflow to both a minimum and maximum level, respectively, while the damper  58  controls or regulates airflow to a primary demand level, such as an airflow level required to provide increased ventilation to a room in response to a demand signal from a user. 
     Typical airflow versus pressure difference characteristics are graphically illustrated by the graphs under each terminal  22  in  FIGS. 7A-9B . It should be understood that the minimum amount of airflow rate and maximum of airflow rate will be dependent upon the size and specifications of the airflow regulators  71 ,  72 ,  73 , and  74 , respectively, selected. The user&#39;s selection of the appropriate constant airflow regulator  71 - 74  will depend on the environment or application in which the system  10  is being used. In one illustrative embodiment shown in  FIGS. 7A-7B , the minimum airflow rate may be on the order of at least 10 cubic feet per minute (“CFM”) and the maximum amount of airflow rate may be less than or equal to approximately 400 CFM, but this will be different depending on the application. 
     Returning to  FIG. 5 , note that the damper  58  is comprised of a generally circular planar member  58   b  lying in a first plane P 1  when the damper  58  is in the closed position illustrated in  FIG. 6 . After the constant airflow regulator  72  is received in the opening  59  defined by wall  58   d  ( FIG. 4 ) of the planar member  58   b , the constant airflow regulator  72  lies in the first plane P 1  or directly in the airflow path of air flowing into the opening  32  ( FIG. 4 ) of housing  24 . When the damper  58  is in the closed position shown in  FIGS. 5 and 6 , the constant airflow regulator  72  regulates, permits or controls the airflow to the constant rate as dictated by the specifications for the constant airflow regulator  72  selected by the user. Thus, it should be understood that when the damper  58  is actuated from the closed position to the open position (illustrated in phantom in  FIG. 5  and in the illustration of  FIGS. 7A-7B and 8A-8B ), the airflow regulator  72  is removed from the airflow path, thereby removing the minimum or constant airflow regulator from the opening  32  and from the airflow path between the zone or area  14  and the duct  18 . 
     It should be understood that one or both of the constant airflow regulators  72  and  74  may be used in various combinations, such as the illustrative combinations that will now be described relative to  FIGS. 7A-9B . It should be understood that the illustrations in  FIGS. 7A-9B  show the damper assembly  40  ( FIG. 4 ) and generally U-shaped member or support  42  removed from the housing  24  for ease of illustration. 
     In the embodiment shown in  FIGS. 7A-7B , the constant airflow regulator  72  is situated in each damper  58  associated with each of the zones or areas  14 . The constant airflow regulator  74  is situated in each duct  18  as shown. In the illustration in  FIGS. 7A-7B , the fan  16  runs continuously at a first fan speed to provide constant ventilation airflow at a first rate. As illustrated in  FIG. 7A , as air flows from the zones or areas  14  into the ducts  18 , the air flows both through the constant airflow regulator  72  and constant airflow regulator  74 . As exhaust air from fan  16 , for example, is pulled from each zone or area  14  through the duct  18 , the constant airflow regulator  72  provides constant airflow regulation to the first predetermined or minimum level. When there is a call or demand for increased ventilation in a remote area  14 , such as when the user in one area  14  actuates the switch  54  to the on position as illustrated in  FIG. 7B , the damper  58  in the demand area  14  is driven by motor  52  to the open position. The fan  16  senses the demand and causes increase in speed to a second fan speed. The dampers  58  in the other remote areas  14  remain closed, as shown by the two leftmost airflow regulators  72  shown in  FIG. 7B . These regulators  72  provide constant airflow control or regulation to the first predetermined or minimum level dictated by the specifications of those constant airflow regulators  72 . Notice that the increase in airflow through those constant airflow regulators  72  causes vanes  72   a  ( FIG. 4 ) to partially close as shown in  FIG. 7B , thereby controlling or regulating airflow to the desired rate. Substantially simultaneously, notice in the right-hand portion of  FIG. 7B  that the constant airflow regulator  72  in the damper  58  has been actuated to the open position and removed from the airflow path, thereby permitting increased airflow into and through the duct  18  from the area  14  as shown. The second constant airflow regulator  74  controls or regulates airflow to the second predetermined maximum level, while the constant airflow regulators  72  associated with the other zones or areas  14  control or regulate airflow to the first or minimum level. 
     Thus, the system  10  in the embodiments in  FIGS. 7A-7B  provides means for regulating or controlling airflow to the first predetermined or minimum flow rate in non-demand areas or zones  14  and between the first predetermined or minimum rate and the second predetermined or maximum rate during demand periods in demand zones or areas  14 . In other words, the constant airflow regulator  72  in  FIGS. 7A-7B  facilitate controlling or regulating airflow to a substantially constant predetermined or minimum rate through each of the ducts  18 . During ventilation demand periods in those demand areas  14  where there is a demand for increased ventilation, such as when a user activates switch  54 , the damper  58  has been actuated to the open position. As illustrated by the rightmost assembly in  FIG. 7B , at least one fan  16  or ventilator  17  responds to the pressure drop and increases fan speed, causing increased airflow at the increased or demand rate in response thereto. This causes increased ventilation from the area  14  where increased ventilation is demanded and through duct  18  and, ultimately, to the exhaust duct  19  associated with the building  12 . Substantially simultaneously, the constant airflow regulator  72  in the two leftmost ducts (when viewed from left to right in  FIG. 7B ) regulate and control the airflow through the ducts  18  and so that airflow continues at substantially the constant rate up to the minimum airflow rate which is dictated by the constant airflow regulator  72  selected. The airflow in the system  10  is graphically illustrated by the graph under each of the regulators  72  and  74 . 
     When the damper  58  in  FIGS. 7A-7B  is closed, the constant airflow regulators  72  or  74  that have the lowest maximum airflow specification will limit or regulate the maximum airflow to that specification. For example, if the constant airflow regulator  72  in  FIG. 7A  permits a maximum 10 CFM, while constant airflow regulator  74  permits a maximum airflow of 50 CFM, the airflow will be regulated to 10 CFM in the illustration shown in  FIG. 7A  when the damper  58  is in the closed position. When one of the dampers  58  in the system  10  is opened, the constant airflow regulator  72 , mounted in the damper, is removed from the airflow path into opening  32  ( FIG. 4 ), thereby permitting airflow at greater than 10 CFM. As the fan  16  or ventilator  17  cause airflow to increase, the regulator  74  regulates airflow through the duct  18  up to the maximum 50 CFM rate mentioned earlier. The airflow versus pressure characteristic is graphically illustrated by the graphs associated with the dampers  58  shown in  FIGS. 7A-7B . 
     Referring back to  FIGS. 9A and 9B , another illustrative embodiment is shown. In this embodiment, the regulator  74  is situated in the duct  18 , but regulator  72  is not in the damper  58 . In this embodiment the damper  58  and wall  58   d  are solid and only regulator  74  is used. During normal operation when there is no call or demand for ventilation or exhaust the dampers  58  are solid, remain closed and no ventilation through the ducts  18 , for example, is permitted. The fan  16  or ventilator  17  provide airflow or turn on in response to the user actuating switch  54  which causes motor  52  to drive damper  58  from the closed position to the open position. When there is a call or demand for exhaust, the user activates the switch  54  and damper  58  activates switch  62 , as described earlier, to turn on the fan  16  or ventilator  17  to cause an increased airflow to a demand rate. The airflow in the two leftmost ducts shown in  FIG. 9B  are continued to be blocked by solid damper  58  in this embodiment. The rightmost open damper  58  in  FIG. 9B  is open, but regulator  74  controls or regulates airflow to the second predetermined or maximum rate mentioned earlier. The graphs associated with the dampers  58  illustrate the airflow versus pressure difference for this embodiment. 
       FIGS. 8A and 8B  show another embodiment. In this illustration, the constant airflow regulator  74  has been removed from the system  10 . The regulators  72  permit minimum flow rate into the ducts  18  when the dampers  58  are in the closed position. When one damper  58  is driven by motor  52  to the open position, as illustrated by the rightmost damper  58  in  FIG. 8B , then unregulated airflow is permitted in the duct  18  associated with the open damper  58 . The constant airflow regulators  72  in the other dampers  58  provide airflow control and regulation to the first predetermined or minimum level, as illustrated by the airflow versus pressure graphs in  FIGS. 8A and 8B . 
     Comparing the embodiment of  FIGS. 7A and 7B  to the embodiment of  FIGS. 8A and 8B , notice that the constant airflow regulator  72  associated with the rightmost duct  18  shown in  FIG. 7B  has been removed from the direct airflow path between the zone or area  14  into the duct  18 , thereby permitting an increased airflow through the duct  18 . The second constant airflow regulator  74  in  FIG. 7B  limits the maximum amount of airflow through the duct  18  to the second predetermined amount or the maximum rate specified by that constant airflow regulator  74 . Substantially simultaneously, the constant airflow regulator  72  associated with the two leftmost ducts  18  (as viewed in  FIG. 7B ) in the areas or zones  14  where ventilation is not demanded continue to limit the amount of airflow to the minimum level amount. In this regard, notice that the vanes  72   a  associated with the two leftmost ducts have closed slightly, thereby limiting the airflow to the specification of those constant airflow regulators  72 . 
     In contrast, the embodiment in  FIGS. 8A and 8B  does not utilize the regulators  74 . Therefore, air flows unregulated into and through the duct  18  associated with the damper  58  in the area or zone  14  where ventilation is demanded. No maximum airflow control or regulation is provided in the duct  18  associated with that open damper  58 . 
     Thus, it should be understood that the system  10  may be provided with one or more constant airflow regulators  72  and  74  in various combinations and arrangements with damper  58  that is solid or that has a regulator  72  mounted therein to regulate or control airflow to a substantially constant minimum and/or maximum level in the areas  14 . On demand, the damper  58  may be actuated from the closed to the open position when the user desires to have increased airflow, such as ventilation airflow, in the zone or area  14 , such as a bathroom. 
     It should be understood that the regulators  71 - 74  and features of the various embodiments in  FIGS. 7A-9B  may be mixed or interchanged and provided in a single system. One illustrative combination is shown in  FIGS. 12A-12B . For example, a system  10  may have dampers  58  with regulators  71  or  72 , with or without regulators  73  and  74 . Some dampers  58  may be provided with the solid planar member  58   b  and without an opening  59  similar to the dampers in  FIG. 9B , while other dampers  58  and regulators  72  and  74  may be provided as in the illustrations shown in  FIGS. 7A-8B . 
     As mentioned earlier, it should be understood that while the system  10  and method have been shown utilizing the switch  54  that may be actuated by the user, other means for energizing and actuating the motor  52  to drive the damper  58  from the closed position to the open position may be used. For example, the system  10  may utilize any suitable means for providing a motor control signal for controlling the motor  52 , such as the switch  54 , a dehumidistat or occupancy sensor that senses when an occupant has entered or left a room, a timer, a CO 2  sensor, or any combination of the aforementioned means. 
     Advantageously, one feature of the embodiments illustrated is that it provides ventilation airflow regulation or control from the zones or areas  14  through at least one or a plurality of the ducts  18  to a maximum airflow rate or less or between minimum and maximum airflow rates. Note that the step of permitting airflow from the fan  16  or ventilator  17  is performed passively utilizing one or more of the constant airflow regulators  72  or  74 . 
     Advantageously, the aforementioned embodiments provide a primary flow controller or regulator in the form of the damper  58  and at least one or a plurality of other flow controllers or regulators, such as the constant airflow regulators  71  and  72 . These airflow regulators may be used alone or in combination with another constant airflow regulator  73  or  74 . 
     As mentioned earlier, one advantage of the embodiment of  FIGS. 4-6  is that maintenance is much improved over prior art systems because the assembly  40  can be completely removed from the housing  24  without having to disconnect the housing  24  or terminal  22  from any ducts or shafts. It should also be understood that the constant airflow regulators  71 - 74  require little or no routine maintenance, unlike the electrical and mechanical systems of the past. 
     The housing  24  does not have to be disconnected from the duct  18  if it is necessary to make any repairs or maintenance. The flow control device, such as regulators  72  and  74 , require no direct electrical or pneumatic power source, and can regulate and control the airflow by utilizing only system duct pressure. Thus, even if there is no power to switch  54  or motor  52 , the regulators  72  and/or  74  will continue to regulate airflow. 
     Another feature of one embodiment is the small size of the terminal  22 , which has dimensions of 10″×10″× 8 ″. The terminal  22  is capable of being mounted between floor, and ceiling assemblies, such as those constructed of standard joists on 16″ centers. 
     Because the system  10  is capable of regulating and controlling airflow in the various zones or areas  14  on an as needed basis, the overall capacity requirements of the central fan  16  and/or ventilator  17  can be reduced because the system  10  is capable of providing constant airflow in non-demand areas  14  and airflow at a demand rate in those areas where increased airflow or ventilation is demanded. This enables a smaller fan  16  or ventilator to be utilized in the system  10 . 
     The system  10  advantageously provides a flow control device that regulates airflow to constant levels when exposed to varying duct pressure. 
     Referring now to  FIGS. 13A-130 , another embodiment of the invention is shown. In these embodiments, like parts are identified with the same part number except that an apostrophe (“′”) has been added to the part numbers in  FIGS. 13A-13D . 
     The embodiment of  FIGS. 13A-13D  provides a zone control system  100  for use in air distribution systems, exhaust or ventilation systems and for use in buildings  12 , such as multi-story commercial buildings ( FIG. 1 ), multi-story condominiums or apartment buildings ( FIG. 2 ), a residential building ( FIG. 3 ) or the like. The system  100  provides a system, apparatus and method for providing on-demand airflow at a demand airflow rate in the manner described herein. As with the prior embodiments, the system  100  of this embodiment may comprise or utilize the at least one fan  16 ′ or may comprise the ventilator  17 ′, such as the one or more of the multi-port ventilator series (MPV) mentioned earlier herein. 
     Referring now to  FIGS. 13A-13D , in this embodiment a zone control terminal  102  is adapted for use in an air distribution system of the type mentioned earlier herein relative to the other embodiments. For example, the zone control terminal  102  is adapted for use in or connected to an existing duct  104 , which is shown in phantom in  FIG. 13A  as a generally rectangular conventional duct. Note that the zone control terminal  102  is generally rectangular and comprises a housing  103  having a first wall  106 , a generally opposing second wall  108 , a third wall  110  and a fourth wall or cover  112  as illustrated in  FIGS. 13A-13D . The housing  103  defines a housing area  103   a . As is shown, the walls  106 - 112  cooperate to define the generally rectangular housing  103  and housing area  103   a . In the illustration being described, the fourth wall  112  is pivotally secured to the first walls  106  and second wall with, for example, rivets or screws. The fourth wall  112  defines an access cover that pivots between an open position shown in  FIGS. 13A and 13D  to a closed position (not shown). The fourth wall or access cover  112  may comprise a latch (not shown) or may be secured into the closed position by suitable fasteners, such as sheet metal screws. In the illustration being described, the fourth wall or access cover  112 , when in the open position illustrated in  FIG. 13A , provides access to the components of the zone control terminal  102 . Note that the wall or cover  112  is pivotably coupled between the walls  106  and  108  and can pivot about the axis PA between the open position shown in  FIG. 13A  and the closed position (not shown). 
     As with prior embodiments, the ducts  18 ′ may be coupled to at least one or a plurality of zone control terminals  102 , at least one of which is operatively associated with each of the areas  14 ′ to be ventilated. As with prior embodiments, a single zone control terminal  102  may be associated with each of the areas  14 ′, but it should be understood that more than one of the plurality of zone control terminals  102  may be associated with each of the areas  14 ′. Also, and as mentioned earlier herein, not every zone or area  14 ′ in the building, structure or residence  12 ′ must have one or more of the plurality of zone control terminals  102 , although in a preferred embodiment at least one of the plurality of control terminals  102  is associated with each of the areas  14 ′. In the illustration shown in  FIGS. 13A-13B , note that the zone control terminal  102  is situated and exists in the existing duct work  104  of the building, structure or residence  12 ′. The zone control terminals  102  may be coupled directly to the main ventilator shaft  20 ′ mentioned earlier herein or to artery ducts, such as the ducts  18 ′, that extend from the main ventilation shaft  20 ′. As with one or more of the prior embodiments, the zone control terminal  102  may be situated interior of a ventilation shaft, with an open duct extension of the type mentioned and described earlier herein relative to  FIG. 11 . 
     The zone control terminal  102  comprises the first or upstream end  102   a  and the second or downstream end  102   b . Note that an inner surface  106   a  of wall  106 , inner surface  110   a  of wall  110 , inner surface  108   a  of wall  108  and an inner surface  116   a  of a flange or projection  116  cooperates with the wall or access cover  112  to provide a generally closed zone control terminal  102  when the wall or access cover  112  is in the closed position, but that is open at the downstream end  102   b . An internal wall  114  having a first side  114   a  and opposing second side  114   b  is conventionally secured, such as by a weld, fasteners (not shown) or adhesive, to the inner surfaces  106   a ,  108   a  and  110   a . Note that portions of ends  106   b  ( FIG. 13C ),  108   b  and  110   b  of walls  106 ,  108  and  110 , respectively, extend beyond the wall  114  to provide or define a flange extension  118  that extends beyond the wall  114  to provide or define a coupling surface that is adapted to be received inside the duct  104 , as illustrated in  FIGS. 13A and 13D , and conventionally secured thereto. 
     A downward extending support rib or flange  120  ( FIGS. 13A and 13B ) is conventionally fixed to walls  106  and  108  and situated at the end  102   b  and provides a support for supporting the wall or access cover  112  when it is in the closed position. Although not shown, each of the walls  106 ,  108  and  110  and the flange  118  may be generally L-shaped in cross section and have portion (not shown) that extends laterally sideways (as viewed in  FIG. 13A ) from a top edge  108   c , respectively, either interiorly or exteriorly laterally to provide additional support or a seat for the wall or access cover  112 . 
     In the illustration being described, a first cut out  114   a  ( FIG. 13B ) and a second cut out  114   b  define a first aperture  126  and a second aperture  128 , respectively. The first and second apertures  126  and  128  are generally circular and are adapted, dimensioned and sized to receive generally cylindrical sub-ducts or duct extensions  130  and  132 , respectively. Note in  FIG. 13A  that the sub-ducts or duct extensions  130  and  132  are shown in fragmentary view so that the internal components thereof may be more easily seen and understood. The sub-ducts or duct extensions  130  and  132  comprise a radial flange  130   a  and  132   a  integrally formed in a generally elongated cylindrical portion  130   b ,  132   b , respectively, as best illustrated in  FIG. 13C . After the elongated cylindrical portions  130   b ,  132   b  of the sub-ducts or duct extensions  130  and  132  are received in the apertures  126  and  128 , respectively, the flanges  130   a  and  132   a  engage and seat against the wall  114  as illustrated in  FIG. 13C . At least one or a plurality of conventional fasteners  136  may be used to secure the sub-ducts or duct extensions flanges  130   a  and  132   a  to the wall  114 . Other means for fastening, such as a weld, adhesive or the like may also be used. After mounting, note that the sub-ducts or duct extensions  130  and  132  extend generally parallel and inside the zone control terminal  102 . 
     Advantageously, the embodiment being described shows the housing  103  that defines a duct that houses a plurality of ducts, namely, the sub-ducts or duct extensions  130  and  132 . As mentioned later herein, the sub-ducts or duct extensions  130  and  132  could be the same size, shape or dimension, but as shown, it should be understood that they could be adapted to be different sizes, areas, shapes or dimensions. For example, they could be different lengths, diameter, size or the like. 
     In the illustration being described, the generally elongated cylindrical portions  130   b  and  132   b  of sub-ducts or duct extensions  130  and  132  each house and comprise at least one or a plurality of air regulators, such as a constant airflow regulator of the type mentioned earlier herein. In this regard, note that the sub-ducts or duct extensions  130  and  132  comprises at least one constant airflow regulators  140  and  146 , respectively, which operate substantially as described earlier herein relative to the constant airflow regulators of the embodiments previously described. 
     In the illustration being described, the sub-duct or duct extension  130  also comprises at least one damper  142  comprises a securing bracket  142   a  ( FIG. 13C ) that couples a drive shaft  54   a ′ of the drive motor  52 ′ to the damper  142  which is under the control of the switch  54 ′ and actuates the damper  142  between the closed position illustrated in  FIG. 13A  to the open position illustrated in  FIG. 13D . The function and operation of the damper  142  will be described later herein. 
     Note that the sub-duct or duct extension  130  also comprises the at least one second airflow regulator  146 . The operation and function of the sub-duct or duct extension  130  and the damper  142  and at least one second airflow regulator  146  is similar to that described earlier herein relative to the illustrative example shown in  FIG. 9B . When the damper  142  is actuated by the motor  52 ′ from the closed position ( FIG. 13A ) to the open position ( FIG. 13D ), airflow is free to pass through the first sub-duct or duct extension  130 , with the airflow being regulated by the at least one second airflow regulator  146 . Thus, it should be understood that the damper  142  and at least one second airflow regulator  146  are in series and cooperate to provide a CFM to pressure difference similar to that shown in  FIG. 9B . 
     The sub-duct or duct extension  132  also comprises at least one first airflow regulator  140  and functions to control a minimum and maximum amount of airflow through the zone control terminal  102 , even when the damper  142  is in the closed position shown in  FIG. 13A . In contrast, note that when the damper  142  is in the open position shown in  FIG. 13D , air is also permitted to flow through the sub-duct or duct extension  130  with the maximum airflow rate or CFM through the sub-duct or duct extension  130  being dictated or controlled by the at least one second airflow regulator  146 . Thus, the at least one first airflow regulator  140  controls or permits a predetermined or minimum amount of airflow through the zone control terminal  102  when the damper  142  is in the closed position. The at least one second airflow regulator  146  cooperates with the at least one first airflow regulator  140  to control or permit airflow through the zone control terminal  102  when the damper  142  is in the open position ( FIG. 13D ), the at least one first and second airflow regulators  140  and  146  cooperate to allow a predetermined maximum amount of airflow through the zone control terminal  102 . Thus, it should be understood that the predetermined maximum amount of airflow through the zone control terminal  102  is, therefore, a sum of a maximum airflow rate of the at least first airflow regulator  140  and the at least one second airflow regulator  146 . The preceding is summarized for ease of understanding in the following Table I: 
     
       
         
           
               
               
               
             
               
                 TABLE I 
               
               
                   
               
               
                 Damper 
                   
                   
               
               
                 142 
                 Predetermined Minimum 
                 Predetermined Maximum 
               
               
                 Position 
                 Airflow Rate 
                 Airflow Rate 
               
               
                   
               
             
            
               
                 Damper 
                 minimum airflow rate through 
                 maximum airflow rate through 
               
               
                 142 in 
                 zone control terminal 102 and 
                 zone control terminal 102 and 
               
               
                 Closed 
                 duct 104 equal to the 
                 duct 104 equal to the 
               
               
                 Position 
                 minimum airflow rate of the 
                 maximum airflow rate of the 
               
               
                   
                 at least one first airflow 
                 at least one first airflow 
               
               
                   
                 regulator 140 
                 regulator 140 
               
               
                 Damper 
                 minimum airflow rate through 
                 maximum airflow rate through 
               
               
                 142 in 
                 zone control terminal 102 and 
                 zone control terminal 102 and 
               
               
                 Open 
                 duct 104 equals the sum of the 
                 duct 104 equals the sum of the 
               
               
                 Position 
                 minimum airflows of the at 
                 maximum airflows of the at 
               
               
                   
                 least one first airflow 
                 least one first airflow 
               
               
                   
                 regulator 140 and the 
                 regulator 140 and the 
               
               
                   
                 minimum airflow rate of the 
                 maximum airflow rate of the 
               
               
                   
                 at least one second airflow 
                 at least one second airflow 
               
               
                   
                 regulator 146 
                 regulator 146 
               
               
                   
               
            
           
         
       
     
     Thus, it should be understood that the at least one second airflow regulator  146  is always in series with the damper  142  and in parallel with the at least one first airflow regulator  140  when the damper  142  is open, and the maximum airflow rate permitted to flow through the zone control terminal  102  is the maximum airflow rate of the sum of the at least one first airflow regulator  140  and the at least one second airflow regulator  146 . For example, if each of the at least one first and second airflow regulators  140  and  146  had specifications of permitting airflow between 10-175 CFM, then when the damper  142  is in the closed position illustrated in  FIG. 13A , the maximum airflow through the zone control terminal  102  is controlled by the at least one first airflow regulator  140  and becomes 175 CFM. However, if the damper  142  has been actuated to the open position in response to a need in a particular zone or area  14 ′, then the maximum airflow through the zone control terminal  102  becomes 350 CFM (the maximum airflow of the at least one first airflow regulator  140  of 175 CFM added to the maximum airflow of 175 CFM of the at least one second airflow regulator  146 ). In contrast, note that in the prior embodiments described herein, the airflow regulators were situated in series, and in one embodiment the minimum airflow regulator was actually situated in the damper  142 . The maximum airflow rate in such embodiments was limited to the highest maximum airflow rate of the airflow regulators in the series. 
     Advantageously, the airflow regulators  140 ,  146  may have the same specifications, but more typically, they have different minimum and maximum airflow rate specifications may be utilized in this embodiment. This may be advantageous for customizing or adapting the zone control terminal  102  to particular environments or structures. For example, in an environment or room (e.g., an auditorium in a building) that is normally unused, but suddenly becomes filled with people, it may be desired to provide a high maximum airflow rate that permits a large airflow through the zone control terminal  102 . 
     It should also be understood that one or more features of the embodiments described earlier herein may be utilized with the embodiment shown in  FIGS. 13A-13D . For example, at least one third airflow regulator may be placed in the damper  142  as illustrated similar to the embodiment shown and described relative to  FIG. 6 . It should also be understood that one or more other airflow regulators may be situated in the wall  114  or in other sub-ducts or duct extensions (not shown) that are mounted either in or to the wall  114  in a similar manner as the sub-ducts or duct extensions  130  and  132 . In other words, the wall  114  may be utilized to support more sub-ducts or duct extensions than the two sub-ducts or duct extensions  130 ,  132  illustrated in  FIGS. 13A-13D . When the damper  142  is actuated to the open position, the damper  142  may actuate a damper switch as described earlier herein. 
     It should also be understood that the sub-ducts or duct extensions  130 ,  132  can take other shapes and forms and can be the same or different sizes. In the illustration shown in  FIGS. 13A-13D , the first sub-duct or duct extension  130  is larger in length and diameter than the second sub-duct or duct extension  132 . The bigger diameter permits the at least one second airflow regulator  146  to be larger than the at least one first airflow regulator  140 . Alternatively, the sub-ducts or duct extensions may be of the same size, or again, of different sizes. In the illustration being described, the at least one first airflow regulator  140  is smaller and has a lower maximum airflow rate than the at least one second airflow regulator  146 . 
     Referring back to  FIG. 13D , note that the sub-duct or duct extension  130  comprises a first foam seal  156  and a second foam seal  158 , both of which are conventional adhered in opposed relation to an interior surface or wall  130   a  of the sub-duct or duct extension  130 . Note that when the damper  142  is in the closed position, a first surface  142   a  ( FIG. 13C ) of the damper  142  engages the first foam seal  156  ( FIG. 13B ) and the generally opposing second surface  142   b  ( FIG. 13A ) engages the second foam seal  158  as illustrated in  FIGS. 13A-13D . It should be understood that the first and second foam seals  156  and  158  are slightly longitudinally offset from each other along the longitudinal axis of the sub-duct or duct extension  130  to enable the damper  142  to move between the open and closed positions. 
     During use, the damper  142  may be normally closed ( FIG. 13A ), in which case the first airflow regulator  140  controls airflow through the zone control terminal  102 . A corresponding airflow graph is shown in  FIG. 13A . For example, if the at least one or a plurality of first airflow regulators  140  have specifications of regulating airflow between 10 and 175 CFM. When there is a call for additional airflow resulting from the switch  54 ′ as described earlier herein, the switch  54 ′ causes the motor  52 ′ to be energized and actuate the damper  142  from the closed position illustrated in  FIG. 13A  to the open position illustrated in  FIG. 13D . Once in the open position, the at least one second airflow regulator  146  becomes active. The resulting airflow through the zone control terminal  102  is illustrated in the CFM to pressure difference graph shown in  FIG. 13D  and will be the sum of the airflow permitted through the at least one first airflow regulator  140  and the at least one second airflow regulator  146  as mentioned and described earlier herein relative to the Table I. 
     Advantageously, the system and method of the embodiment of  FIGS. 13A-13D  permit an increased amount of maximum airflow when desired. Features of the previous embodiments may be used in at least one or both of the sub-ducts or duct extensions  130  and  132 . For example, although not shown, the sub-duct or duct extension  132  may also comprise a damper in series with the airflow regulator  140  and may also comprise one or more of the other features of the embodiments described earlier herein. 
     As mentioned earlier, it should be understood that the zone control terminal  102  could be provided with more sub-ducts or duct extensions if desired and those sub-ducts or duct extensions may comprise airflow regulators and dampers as described herein relative to the embodiment of  FIGS. 13A-13D  or as described relative to the prior embodiments. For example, the additional sub-ducts or duct extensions (not shown) may comprise at least one or a plurality of constant airflow regulators situated in series and used with or without a damper. 
     While the system, apparatus and method herein described constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to this precise system, apparatus and method, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.