Patent Publication Number: US-9897340-B2

Title: Economizer having source-specific damper blade assemblies and heating, ventilation and air conditioning unit employing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 13/332,740, filed on Dec. 21, 2011. U.S. patent application Ser. No. 13/332,740 claims the benefit of U.S. Provisional Patent Application No. 61/523,005, filed by Douglas on Aug. 12, 2011, entitled “Economizer for Precise Ventilation Control,” commonly assigned with this application and incorporated herein by reference. U.S. patent application Ser. No. 13/332,740 and U.S. Provisional Patent Application No. 61/523,005 are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This application is directed, in general, to heating, ventilation and air conditioning (HVAC) systems and, more specifically, to an economizer having improved air blending characteristics. 
     BACKGROUND 
     An air-side economizer is an accessory to an HVAC system that enables it to run more economically. Economizers proportionally blend return air drawn from the indoor space of a building and outdoor air drawn from outside the building to make the overall enthalpy of the blended air as low as reasonably possible and to comply with building ventilation codes that exist in virtually every jurisdiction. Economizers have two damper assemblies: a return air damper for the return air and an outdoor air damper for the outdoor air. When the return air damper is fully closed, the outdoor air damper is fully open. 
     As the return air damper is opened, the outdoor air damper is closed. When the return air damper is fully open, the outdoor air damper is fully closed. As the outdoor air damper is opened, the return air damper is closed. 
     Each damper is an assembly having a plurality of elongated damper blades that rotate about their major axis as the damper is opened and closed. Conventional economizers come in two varieties: those in which all of the damper blades of both damper assemblies move in parallel and those in which adjacent damper blades of both damper assemblies move in opposition. Conventional economizers work reasonably well and are becoming ever more popular as energy costs rise and customers look for ways to decrease costs and help the environment. 
     SUMMARY 
     One aspect provides an economizer having a first air inlet, a second air inlet and an air outlet. In one embodiment, the economizer includes: (1) a first damper blade assembly in fluid communication with the first air inlet and the air outlet and having a first plurality of damper blades configured to move in parallel and (2) a second damper blade assembly in fluid communication with the second air inlet and the air outlet and having a second plurality of damper blades configured to move in opposition. 
     Another aspect provides a method of operating an economizer having source-specific damper blade assemblies. In one embodiment, the method includes: (1) determining an enthalpy of first and second air sources, (2) determining a blend of the first and second air sources having an optimal enthalpy, (3) determining damper settings needed to achieve the blend, (4) moving a first plurality of damper blades in parallel in accordance with the damper settings and (5) moving a second plurality of damper blades in opposition in accordance with the damper settings. 
     Yet another aspect provides an HVAC system. In one embodiment, the HVAC system includes an economizer having a return air inlet, an outdoor air inlet and a blended air outlet. In one embodiment, the economizer includes: (1) a frame, (2) a first damper blade assembly mounted in the frame, in fluid communication with the return air inlet and the blended air outlet and having a first plurality of damper blades configured to move in parallel and (3) a second damper blade assembly mounted in the frame, in fluid communication with the outdoor air inlet and the blended air outlet and having a second plurality of damper blades configured to move in opposition. 
    
    
     
       BRIEF DESCRIPTION 
       Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a high-level schematic diagram of one embodiment of an HVAC system having an economizer; 
         FIG. 2A  is a front elevational view of one embodiment of source-specific damper blade assemblies of an economizer; 
         FIG. 2B  is a right side elevational, sectional view of the source-specific damper blade assemblies of  FIG. 2A , taken along lines  2 B- 2 B, in a first example configuration blade position in which a first damper blade assembly is in a fully closed position and a second damper blade assembly is in a fully open position; 
         FIG. 2C  is a right side elevational, sectional view of the source-specific damper blade assemblies of  FIG. 2A , taken along lines  2 B- 2 B, in a second example configuration in which both the first and second damper blade assemblies are in partially open positions; 
         FIG. 3  is a partial right side elevational view of one embodiment of the source-specific damper blade assemblies including a linkage that may be employed to interconnect damper blades thereof; and 
         FIG. 4  is a flow diagram of one embodiment of a method of operating an economizer having source-specific damper blade assemblies. 
     
    
    
     DETAILED DESCRIPTION 
     As stated above, conventional economizers come in two varieties: those in which all of the damper blades of both damper assemblies move in parallel and those in which adjacent damper blades of both damper assemblies move in opposition. In other words, conventional economizers employ either damper blades moving in parallel or damper blades moving in opposition. 
     It has been discovered herein that different aerodynamic effects result from damper blades moving in parallel than from damper blades moving in opposition. Damper blades moving in parallel exhibit a lower pressure drop than damper blades moving in opposition. However, damper blades moving in opposition provide more precise volume control than damper blades moving in parallel. Therefore, the conventional economizers either opted for either a lower pressure drop for both the return air and the outdoor air or more precise volume control for both the return air and the outdoor air. 
     It has also been discovered herein that a reduced pressure drop is more important for return air than it is for outdoor air and that the precision of volume control is more important for outdoor air than it is for return air. To elaborate, it is generally important to keep the pressure drop through an HVAC system as low as reasonably possible to keep its efficiency as high as reasonably possible. Being adjunct to the HVAC system, the economizer is no exception. However, it is also important to ensure that the proper amount of outside air is admitted into the HVAC system. Underventilating violates applicable building ventilation codes. Overventilating reduces HVAC efficiency. Both of these considerations prevail throughout the full range of motion of the damper blades—from fully closed to fully open and all positions in between. 
     Accordingly, introduced herein are various embodiments of a novel economizer having “source-specific” damper blade assemblies, that is, damper blade assemblies that differ in terms of, the manner in which they move depending upon whether they are damping return air or outdoor air. The various embodiments introduced herein include a damper blade assembly that is “source-specific” for return air in that its damper blades move in parallel and further include a damper blade assembly that is “source-specific” for outdoor air in that its damper blades move in opposition. 
     Also introduced herein are various embodiments of a novel method of operating an economizer having source-specific damper blade assemblies and an HVAC system that includes the novel economizer. 
       FIG. 1  is a high-level schematic diagram of one embodiment of an HVAC system having an economizer. A building  110  has an HVAC system  120  configured to condition the air in the building  110 . In the illustrated embodiment, the HVAC system  120  is a rooftop unit (RTU). However, the HVAC system  110  may be of any conventional or later-developed configuration. 
     The HVAC system  120  has an economizer  130 . The economizer  130  is coupled to the HVAC system  120  and is configured to receive return air drawn from the building  110  into a return air inlet  131  thereof. The economizer  130  is further configured to receive outdoor air drawn from outside the building  110  into an outside air inlet  132  thereof. In the illustrated embodiment, the return air inlet  131  and the outdoor air inlet  132  are substantially separate; they are not in substantial fluid communication with one another when the economizer  130  is in operation. 
     The economizer  130  further includes a return air damper assembly  133  in fluid communication with the return air inlet  131 . The economizer  134  still further includes an outdoor air damper assembly  134  in fluid communication with the outdoor air. When the return air damper assembly  133  is fully closed, the outdoor air damper assembly  134  is fully open. As the return air damper assembly  133  is opened, the outdoor air damper assembly  134  is closed. When the return air damper assembly  133  is fully open, the outdoor air damper assembly  134  is fully closed. As the outdoor air damper assembly  134  is opened, the return air damper assembly  133  is closed. 
     Return air and outdoor air passing respectively through the return air damper assembly  133  and the outdoor air damper assembly  134  enter a common outlet  135  where they are blended and thereafter enter the HVAC system  120  for conditioning. In the illustrated embodiment, the common outlet  135  is in substantially unidirectional fluid communication with the return air inlet  131  and the outdoor air inlet  132  when the economizer  130  is in operation. Due to suction from the HVAC system  120 , air flows from the return air inlet  131  and the outdoor air inlet  132  into the common outlet  135 , but not generally the opposite way. 
       FIG. 2A  is a front elevational view of one embodiment of source-specific damper blade assemblies of an economizer having a frame  210  and an elongated member  220  configured, among other things to allow multiple source-specific damper blade assemblies to be mounted in the frame  210 . The economizer of  FIG. 2A  may be the economizer  130  of  FIG. 1 . The elongated member  220  may be advantageously coupled to other structures and therefore assist in substantially separating air inlets, perhaps the return air inlet  131  and the outdoor air inlet  132  of  FIG. 1 , from one another. 
     The embodiment of  FIG. 2A  includes a first damper blade assembly  133  and a second damper blade assembly  134 . The first damper blade assembly  133  includes a first plurality of damper blades, one of which being referenced as  230 . In the embodiment of  FIG. 2A , each of the first plurality of damper blades  230  is elongated and rotatably coupled to the frame  210  at ends thereof such that the each of the first plurality of damper blades  230  can rotate about a major axis thereof between a fully open position and a fully closed position. Each of the first plurality of damper blades  230  is shown in  FIG. 2A  in a fully closed position in which the first plurality of damper blades  230  cooperate to allow minimal air flow through the first damper blade assembly  133 . 
     The second damper blade assembly  134  includes a second plurality of damper blades, one of which being referenced as  240 . In the embodiment of  FIG. 2A , each of the second plurality of damper blades  240  is elongated and rotatably coupled to the frame  210  at ends thereof such that the each of the second plurality of damper blades  240  can rotate about a major axis thereof between a fully open position and a fully closed position. Each of the second plurality of damper blades  240  is shown in  FIG. 2A  in a fully open position in which the second plurality of damper blades  240  are feathered to allow maximal air flow through interstices  250  separating the second plurality of damper blades  240  of the second damper blade assembly  134 . 
     As stated above, the economizer may be the economizer  130  of  FIG. 1 . As such, the first damper blade assembly  133  may be the return air damper assembly  133 , and the second damper blade assembly  134  may be the outdoor air damper assembly  134 . However, those skilled in the pertinent art will realize that the first and second damper blade assemblies  133 ,  134  may be specific to other sources, such as conditioned air and exhaust air. Further, those skilled in the pertinent art will realize that the first and second damper blade assemblies  133 ,  134  may be employed, perhaps with further damper blade assemblies, in an apparatus other than an economizer. 
       FIG. 2B  is a right side elevational, sectional view of the source-specific damper blade assemblies of  FIG. 2A , taken along lines  2 B- 2 B. The source-specific damper blade assemblies are in a first example configuration blade position in which the first damper blade assembly  133  is in a fully closed position and the second damper blade assembly  134  is in a fully open position. If the first damper blade assembly  133  is the return air damper assembly  133  and the second damper blade assembly  134  is the outdoor air damper assembly  134 , the configuration of  FIG. 2B  represents a configuration called “free cooling,” in which outdoor air is more efficient to condition than return air. As in  FIG. 2A , each of the first plurality of damper blades  230  is shown in  FIG. 2B  in a fully closed position in which the first plurality of damper blades  230  cooperate to allow minimal air flow through the first damper blade assembly  133 . Further as in  FIG. 2A , each of the second plurality of damper blades  240  is shown in  FIG. 2B  in a fully open position in which the second plurality of damper blades  240  are feathered to allow maximal air flow through the interstices  250  separating the second plurality of damper blades  240  of the second damper blade assembly  134 . 
       FIG. 2C  is a right side elevational, sectional view of the source-specific damper blade assemblies of  FIG. 2A , taken along lines  2 B- 2 B. The source-specific damper blade assemblies are in a second example configuration in which both the first and second damper blade assemblies  133 ,  134  are in partially open positions. This partially open configuration is typical when building ventilation codes require at least some outside air be admitted into the building—the objective becomes one of meeting the code while maintaining HVAC efficiency as high as possible. 
     Each of the first plurality of damper blades  230  is shown in  FIG. 2B  in a partially open position in which the first plurality of damper blades  230  cooperate to allow less-than-maximal (i.e., more than minimal) air flow through interstices  260  separating the first plurality of damper blades  230  of the first damper blade assembly  133 . Each of the second plurality of damper blades  240  is likewise shown in  FIG. 2B  in a partially open position in which the second plurality of damper blades  240  cooperate to allow less-than-maximal (i.e., more than minimal) air flow through the interstices  250  separating the second plurality of damper blades  240  of the second damper blade assembly  134 . In the embodiment of  FIG. 2C , the elongated member  220  extends from the frame  210  in a direction that allows it to assist in substantially separating air inlets (e.g., the return air inlet  131  and the outdoor air inlet  132  of  FIG. 1 ).  FIG. 2C  shows particularly well the fact that the first plurality of damper blades  230  move in parallel and the second plurality of damper blades  240  move in opposition. 
       FIG. 3  is a partial right side elevational view of one embodiment of the source-specific damper blade assemblies including a linkage that may be employed to interconnect damper blades thereof.  FIG. 3  shows the first and second damper blade assemblies  133 ,  134 . One damper blade of the first plurality of damper blades ( 230  of  FIGS. 2A, 2B, 2C ) is referenced as  230   a . Two damper blades of the second plurality of damper blades ( 240  of  FIGS. 2A, 2B, 2C ) are referenced as  240   a ,  240   b . The linkage of  FIG. 3 , which is only one embodiment by which the blades of the first and second damper blade assemblies  133 ,  134  may be interconnected, includes a plurality of links rotatably coupled to the damper blades (i.e., one link  310  couples an unshown damper blade adjacent the damper blade  230   a , another link  320  couples the damper blade  230   a  to the damper blade  240   a , yet another link  330  couples the damper blade  230   a  to the damper blade  240   b , and still another link  340  couples the damper blade  240   b  to an unshown damper blade adjacent the damper blade  240   b ). When, for example, the link  310  is urged downward as shown, the damper blade  230   a  rotates clockwise as arrows indicate. The downward urging of the link  310  also causes the link  320  to be urged downward, and the damper blade  240   a  rotates counterclockwise as arrows indicate. The downward urging of the link  310  further causes the link  330  to be urged downward, and the damper blade  240   b  rotates clockwise as arrows indicate. The link  340  is also urged downward as a result. 
     As stated above, the linkage of  FIG. 3  is but one embodiment that may be employed to interconnect damper blades thereof. Gears coupled to the ends of the first and second pluralities of damper blades  230 ,  240  may mesh with each other, intermediate gears a rack or any combination of these to effect parallel movement of the first plurality of damper blades  230  and opposing movement of the second plurality of damper blades  240 . 
       FIG. 4  is a flow diagram of one embodiment of a method of operating an economizer having source-specific damper blade assemblies. The method begins in a start step  410 . In a step  420 , the enthalpy of first and second air sources is determined. In one embodiment, the first air source is return air drawn from the indoor space of a building. In a related embodiment, the second air source is outdoor air drawn from outside a building. In a step  430 , the blend of the first and second air sources having the optimal enthalpy is determined. In one embodiment, the blend is expressed in terms of percentage (e.g., 40% return air and 60% outdoor air). In a step  440 , the damper settings needed to achieve the blend of the first and second air sources having the optimal enthalpy is then determined. In a step  450 , a first plurality of damper blades is moved in parallel in accordance with the damper settings determined in the step  440 . In a step  460 , a second plurality of damper blades is moved in opposition in accordance with the damper settings determined in the step  440 . The method ends in an end step  470 . 
     Those skilled in the art to which this application relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described embodiments.