GB2054134A - Air mixing damper assembly - Google Patents

Abstract

A damper assembly for use in air conditioning apparatus wherein the volume flow of two distinct air streams, usually outside air and return air, must be controlled and the resulting mixture thereof passed over air treatment means such as filters and heat exchange coils comprises first and second groups (18, 19) of rotatably-supported damper blades for controlling the aforementioned air streams, and actuator means for positioning the damper blades such that, when one of the groups (e.g. 18) permits minimum air flow therethrough, the other group (19) permits a maximum air flow while further serving to direct a portion of the air flowing therethrough into the outlet volume lying immediately downstream of said one group (18) of damper blades, thereby improving in use air distribution over the particular air treatment means immediately downstream from the damper assembly. <IMAGE>

Description

SPECIFICATION Damper assembly providing improved air distribution Technical Field The present invention relates generally to air conditioning apparatus of the type utilized in heating or cooling air to be supplied to a particular structure or building, and wherein a portion of the air from the building is recirculated through the air conditioning apparatus where it is combined with an amount of fresh, or outside, air with the resulting air mixture being passed over air treatment means such as filters and heat exchange coils prior to being supplied to the building.

Background Art Air conditioning apparatus of the general type to which the present invention has application are well known in the art and generally comprise a housing containing suitable heating and/or cooling apparatus, which housing may suitably be located on the roof of the building or structure being served; alternately, such apparatus may be located in a central machinery room of the building. The housing receives both return air from the building and outside air which are mixed and suitably conditioned by the heating and/or cooling apparatus for recirculation to the building.

Conventionally, a damper assembly has been provided for controlling the relative quantities of return air and outside air passing through the apparatus, depending upon the particular air conditioning requirements of the building and the condition of the outside air. Air conditioning apparatus representative of this general type is disclosed in U.S. Patent No. 3,324,782; wherein first and second groups of damper blades are provided immediately adjacent each other for controlling the relative quantities of outside air and return air through the apparatus.

A problem existing with respect to this type apparatus is that of proper air distribution of the resultant mixed air stream over air treatment means such as filters, coils, and the like which are disposed downstream of the aforementioned damper assembly. Obviously, during those times when one of the groups of damper blades is in its minimum flow position, with the other being in its maximum flow position, the mixed air stream leaving the damper assembly will be disposed predominantly downstream from the group of damper blades which is in its maximum flow position. This problem is aggravated in air conditioning apparatus wherein the aforementioned air treatment means are disposed in close proximity downstream of the damper assembly in the interests of providing as compact an air conditioning apparatus as possible.

It is the above-described problem which is addressed by the present invention.

Disclosure of the Invention The damper assembly of the present invention includes frame means which define first and second adjacent air flow passages, each said passage having associated therewith respective first and second air inlet volumes lying immediately upstream therefrom and first and second air outlet volumes lying immediately downstream. First and second groups of damper blades are rotatably supported by the frame means and extend across the respective first and second adjacent air flow passages described above, with suitable actuator means being provided for rotating the damper blades between first and second positions.When in a first position, the damper blades of the first group permit minimum air flow therethrough while the damper blades of the second group permit maximum airflow and, in addition, serve to direct a portion of the air flowing therethrough into the aforementioned first outlet volume immediately downstream from the first group of damper blades. Similarly, the damper blades may be rotated by the actuator means to a second position wherein minimum airflow is provided through the damper blades of the second group while maximum flow is permitted through the damper blades of the first group and, in addition, a portion of the air flow therethrough is directed into the aforementioned second outlet volume immediately downstream from the second group of damper blades.

In the preferred embodiment, each group of damper blades comprises a plurality of damper blades rotatable about spaced, substantially parallel axes and disposed generally in a plane extending transverse to its respective airflow passage, said groups being disposed adjacent each other along respective first edge portions thereof which lie parallel to the axes of rotation of the damper blades. In this embodiment, the actuator means are operative to rotate the damper blades such that, when one of said groups is in its minimum air flow position, selected damper blades of the other group are maintained in positions transverse to air flow through its associated air passage in a sense to direct a portion of the air into the outlet volume of said one group of damper blades.Preferably, the selected damper blades are maintained in positions progressively less transverse to air flow in a direction away from the adjacent edge portions of the groups of damper blades.

Accordingly, it is a primary object of the present invention to provide a damper assembly for use in air conditioning apparatus for controlling the flow of two distinct air streams and for providing improved distribution of the resulting mixed air stream over air treatment means disposed downstream of the damper assembly.

It is a further object of the present invention to provide such a damper assembly which includes first and second groups of rotatable damper blades which are controlled by novel actuator means in order to bring about the desired result.

These and further objects of the present invention will become apparent from the following description of the preferred and alternate embodiments and by reference to the accompanying drawings.

Brief Description of the Drawings Figure 1 is a cross-sectional view of air conditioning apparatus embodying applicant's invention.

Figure 2 is a cross-sectional view taken along the line 2-2 of Figure 1.

Figures 3A, 3B, and 3C are a series of crosssectional views taken along the line 3-3 of Figure 2 illustrating various positions of the damper assembly comprising a first embodiment of the present invention.

Figures 4A, 4B and 4C are cross-sectional views similar to those of Figures 3A, 3B, and 3C illustrating an alternate embodiment of the present invention.

Best Mode for carrying out the Invention Turning to Figure 1 of the drawings, air conditioning apparatus are indicated by reference numeral 2 and include a housing 3 of generally rectangular configuration and constructed of sheet metal, which housing enclosed components of the air conditioning apparatus. Typically, apparatus of the type illustrated would be mounted on the roof of the structure or building being served, and the cross-sectional view of Figure 1 is one looking down from above the apparatus.

Housing 3 includes a fresh air inlet opening 4 which piaces chamber 5 in communication with the outdoor ambient, while a return air opening 6 in the bottom wall of the housing places chamber 7 in communication with return air from the structure or building being served. As is apparent from Figure 1, fresh air chamber 5 and return air chamber 7 are separated by an imperforate partition member 8. As is conventional, exhaust fans 9a and 9b, operated by an electric motor 10, are provided in return air chamber 7 and are selectively operated when required to exhaust large amounts of return air to the ambient from the building being served.

The flow of outside air and return air through air conditioning apparatus 2 is controlled by a damper assembly indicated generally by reference numeral 1, which will be described in detail hereinbelow, with the resulting mixed air stream passing through air treatment means disposed downstream therefrom such as-filter means 11 and a heat exchange coil indicated generally by reference numeral 12. In practice, heat exchange coil 12 may comprise any of the well known types, such as steam, heated or chilled water, the evaporator of a direct expansion refrigeration system, or the indoor coil of a vapor-compression type heat pump system. Alternately, combinations of the foregoing could be provided, with or without the addition of a fuel-fired heat exchanger for providing heating of the structure.

The thus-conditioned air, after passing over the air treatment means, is directed by fans 1 3a and 1 3b, driven by electric motor 14, to the space being conditioned.

Since the general theory of operation of air conditioning apparatus of this type is well known to those skilled in the art, no further description thereof is believed warranted, and the discussion will now turn to a description of the novel damper assembly comprising applicant's invention.

As seen in Figure 2, which comprises a frontal view of the damper assembly 1 taken along the line 2-2 of Figure 1, it may be seen that frame means 1 5 are provided of generally rectangular configuration, constructed of a material such as heavy gauge sheet metal. Frame means 1 5 further include a centrally located partition member 1 5a which defines within frame means 1 5 a first air flow passage 1 6 and a second air flow passage 17, such passages lying in adjacent relationship.

As best seen in Figure 3, air flow passages 16 and 1 7 have associated therewith respective first and second air inlet volumes 1 6a and 1 7a lying immediately upstream therefrom and first and second air outlet volumes 1 6b and 1 7b lying immediately downstream therefrom.

A first group of damper blades 1 8a through 18n are rotatably supported by frame means 15 and extend across first air flow passages 1 6, while a second group of damper blades 1 9a through 19n, also rotatably supported by frame means 16, extend across second second air flow passage 1 7.

As is apparent from Figures 2 and 3A, the damper blades of each of first and second groups 1 8 and 1 9 are rotatable about spaced, substantially parallel axes and are disposed generally in a plane which extends transverse to its respective air flow passage. Further, the first and second groups of damper blades are disposed adjacent each other along respective first edge portions thereof as defined by respective damper blades 1 8a and 19a, the axes of rotation of the damper blades of each group being parallel. In the preferred embodiment, the aforesaid planes defined by each respective group of damper blades define a common plane as best illustrated in Figures 3A, 3B, and 3C.

As best illustrated by a comparison of Figures 3A, 3B, and 3C, the damper blades of the first and second groups are rotatable between a first position, as illustrated in Figure 3A, and a second position as illustrated by Figure 3C. When in the first position of Figure 3A, damper blades 1 8a through 1 8n of the first group permit minimum air flow through the first air flow passage 1 6 between inlet volume 1 6a and outlet volume 16b, while damper blades 1 9a through 1 9n of the second group permit maximum air flow through second air flow passage 17 between inlet volume 1 7a and outlet volume 17b. It should be expressly noted from Figure 3A, that damper blades 1 9a through 1 9n of the second group further serve to direct a portion of the air flowing therethrough into first outlet volume 1 6b due to the fact that selected ones thereof are maintained in positions transverse to air flow through second air flow passage 1 7 in a sense to direct a portion of said air flowing therethrough into first outlet volume 16b.

As used herein, the terms "minimum air flow" and "maximum air flow" are used to refer to the relative volumes of air flow which are permitted through the first and second air flow passages 1 6 and 1 7 when the damper blades are in either of two extreme positions, denoted the first position and second position. It should be appreciated, however, that these terms are relative and are not intended to denote absolute limits. For example, while in the preferred embodiment, the minimum air flow position comprises a substantially shutoff condition of that set of damper blades, it is possible that, in a given installation, it may be desirable to always maintain a predetermined mimimum air flow through one or both of the flow passages.Similarly, it may be desirable in certain installations to place limits upon the maximum flow permitted through one or both of flow passages 16 and 17.

Turning then to Figure 3C of the drawings, the damper blades of the first and second groups are shown in a second position wherein damper blades 1 9a through 1 9n of the second group permit minimum airflow through second airflow passage 17 between second air inlet volume 1 7a and second air outlet volume 17b, while damper blades 1 8a through 1 8n of the first group permit maximum air flow through first air flow passage 16 between first air inlet volume 1 6a and first air outlet volume 16b.In the second position, damper blades 18a through 1 8n further serve to direct a portion of the air flowing therethrough into second air outlet volume 1 7b due to the positioning of selected ones of damper blades 1 8a through 1 8n in positions transverse to air flow through first air flow passage 16, in a sense to direct such air into outlet air volume 1 7b.

In order to rotate the damper blades of the first and second groups between the above-described first and second positions, actuator means are provided which will now be described with reference to Figure 3A. As illustrated, first linkage means comprising an elongated linkage member 24a are provided interconnecting damper blades 1 8a through 1 8n of the first group, and second linkage means comprising an elongated linkage member 24b are provided interconnecting damper blades 1 9a through 1 9n of the second group. In the preferred embodiment illustrated, wherein the planes defined by the first and second groups of damper blades define a common plane, first and second linkage members 24a and 24b comprise a single elongated member.Thus, movement thereof results in the simultaneous moving of the damper blades of the first and second groups between the respective first and second positions.

As best seen in Figure 3A, damper blades 1 8a through 1 8n of the first group include connection means comprising crank members 20a through 20n connected thereto and extending therefrom in a direction transverse to their axes of rotation. The crank members further include crank pins 21 a through 21 n affixed thereto and extending therefrom in a direction generally parallel to the axes of rotation of the damper blades. In a like manner, damper blades 1 9a through 1 9n of the second group each include connection means comprising crank members 22a through 22n connected thereto and extending in a direction transverse to their axes of rotation, such crank members further including crank pins 23a through 23n affixed thereto and extending a direction generally parallel to the axes of rotation of the damper blades.

In the embodiment illustrated in Figures 3A through 3C, crank pins 21 n and 23n are engaged by respective linkage members 24a and 24b so as to provide pure rotational movement therebetween, while the remaining damper blades of the first and second groups, hereinafter referred to as "selected" damper blades, have their crank pins engaged by slot means formed within the linkage members, for reasons which will be discussed immediately below.

For a proper understanding of the operation of application's invention, it may be useful to trace the movement of a single damper blade, such as damper blade 1 8a, as it moves from its first position illustrated in Figure 3A to its second position illustrated in Figure 3C, Figure 3B illustrating an intermediate position thereof.

Reference numerals have been omitted in Figures 3B and 3C for the sake of clarity. In Figure 3A, damper blade 1 spa is in its minimum flow position, substantially shutting off flow through first air flow passage 16, and its crank pin 21 a is engaged by a first portion of elongated slot means 25a formed in first linkage member 24a. As linkage member 24a is moved to the left (as viewed in Figure 3) damper blade 1 8a is initially caused to rotate in a clockwise direction, as seen in an intermediate position in Figure 3B, until such time as the arcuate path described by crank pin 21 a becomes tangent to elongated slot means 25a. At this point, damper blade 1 8a will actually be permitted to rotate in a counter-clockwise direction (as viewed in Figures 3A through 3C), finally reaching its second position of Figure 3C.

In the preferred embodiment, the damper blades have a configuration such that air flow passing thereover urges them toward a closed position, thereby providing the force necessary to achieve the aforementioned counterclockwise rotation. It will be appreciated, however, that such force could also be provided through the provision of suitable biasing means such as torsion springs acting upon the damper blades.

From an examination of Figure 3C, it is apparent that elongated slot means 25b, 25c, et.

seq. are of progressively decreasing length and disposed at progressively greater angles with respect to the plane defined by the first group of damper blades. This results in a series of selected adjacent damper blades, 1 8a up to but not including 1 8n, which, when in the second position of Figure 3C, are maintained in positions progressively less transverse to air flow through air flow passage 1 6, thereby progressively decreasing the amount of air directed thereby into second air outlet volume 1 7b.

Movement of linkage members 24a and 24b from the second position illustrated in Figure 3C to the first position illustrated in Figure 3A results in analogous movement of damper blades 1 9a through 1 9n of the second group and no detailed explanation thereof is believed warranted.

As is conventional in air conditioning apparatus of the type under consideration, drive means such as an electric motor or a pneumatic cylinder are provided to impart motion to linkage means 24a, b; preferably by rotating one of damper blades 18n or 19n.

Turning next to Figures 4A through 4C of the drawings, an alternate embodiment of the invention is illustrated which is similar in most respects to that of Figures 3A through 3C and, accordingly, like reference numerals have been utilized to identify like elements thereof.

The primary distinction between these two embodiments lies in the provision of arcuate slot means 27a through 27f and 28a through 28f for engaging the crank pins of the respective damper blades of the first and second groups. Specifically, arcuate slot means 27a through 27f and 28a through 28f have a radius of curvature which is equal to the radius defined between the axis of rotation of its associated damper blade and its respective crank pin. As in the embodiment of Figures 3A through 3C, the arcuate slot means are of progressively decreasing length in a direction away from respective slot means 27a and 28a, and are disposed at progressively increasing angles with respect to the plane defined by its respective group of damper blades.

The damper blade action provided by this arrangement may once again be illustrated by following the movement of damper blade 1 spa between its first position of Figure 4A and its second position of Figure 4C. As linkage member 24a, b moves from right to left (as viewed in Figures 4A through 4C), arcuate slot 27a acts to rotate damper blade 1 spa in the clockwise direction until it reaches a predetermined open position, following which its associated crank pin simply slides within slot 27a with no opening force being exerted thereon. Once again, it is preferable that the damper blades be configured such that air flow passing thereover urges them in a closing direction.

As in the previous embodiment, damper blades 1 spa up to but not including damper blade 1 8n comprise a series of selected, adjacent damper blades which, when in the second position, are maintained in positions progressively less transverse to air flow through first air flow passage 1 6 in a direction away from damper blade 18a.

Since, as in the previous embodiment, movement of linkage members 24a and 24b, from their second position of Figure 4C to its first position of Figure 4A results in analogous movement of the second set of damper blade 1 9a through 1 9n, no detailed description thereof is believed warranted.

It should thus be apparent from the above description that the damper assembly of applicant's invention, when utilized in air conditioning apparatus of the type illustrated in Figure 1, serves to provide improved air distribution over air treatment means such as filter 11 and heat exchange coil 12 when one of the first or second groups of damper blades is in its minimum flow position, in that a substantial portion of the air flowing through the other group of damper blades is directed into the outlet volume associated with the other group of damper blades.

It will be appreciated by those skilled in the art, that applicant's invention is not limited to a damper assembly having the precise number of damper blades illustrated in the preferred embodiments; similarly, it may be desirable that more than one damper blade from each group be engaged for pure rotational movement by linkage members 24a and 24b, depending upon the particular size of the damper assembly.

Conversely, in the event that blades 18n or 1 9n are not used in order to drive linkage means 24a, b as described above, they too could be engaged by slots as described with respect to the other damper blades. It will further be appreciated that the damper blades of the first and second groups need not define a single common plane as illustrated, but may each define a separate plane, in which case linkage members 24a and 24b would necessarily comprise separate elements having suitable means interconnecting them for simultaneous movement.

It is contemplated that the damper assembly of the present invention may be used in all types of air conditioning apparatus wherein two distinct air streams must be controlled and mixed, including both single zone and multizone units of either unitary or central station design, and adapted for heating, cooling, or heating and cooling.

While the invention has been described with respect to the preferred embodiment, it is to be understood that modifications thereto will be apparent to those skilled in the art within the scope of the invention, as defined in the claims which follow.

Claims (19)

1. A damper assembly for use in air conditioning apparatus comprising a. frame means defining first and second adjacent air flow passages, said first and second passages having associated therewith respective first and second air inlet volumes lying immediately upstream therefrom and first and second air outlet volumes lying immediately downstream therefrom;; b. first and second groups of damper blades rotatably supported by said frame means and extending across said respective first and second adjacent air flow passages for controlling air flow therethrough, each said group comprising a plurality of damper blades rotatable about spaced, substantially parallel axes and disposed generally in a plane extending transverse to its respective air flow passage, said groups being disposed adjacent each other along respective first edge portions thereof which lie parallel to the axes of rotation of said damper blades; c. actuator means for rotating the damper blades of said first and second groups between at least:: i. a first position wherein the damper blades of said first group permit minimum air flow through said first passage between said first air inlet and outlet volumes, and the damper blades of said second group permit maximum air flow through said second passage between said second air inlet and outlet volumes, selected damper blades of said second group being maintained in positions transverse to air flow through said second air flow passage in a sense to direct a portion of the air flowing therethrough into said first outlet volume; and ii. a second position wherein the damper blades of said second group permit minimum airflow through said second passage between said second air inlet and outlet volumes, and the damper blades of said first group permit maximum air flow through said first passage between said first air inlet and outlet volumes, selected damper blades of said first group being maintained in positions transverse to air flow through said first air flow passage in a sense to direct a portion of the air flowing therethrough into said second outlet volume.

2. The damper assembly of claim 1 wherein a. the selected damper blades of said second group comprise a series of adjacent damper blades, starting with one in relatively close proximity to the aforesaid first edge portion of said second group, and including adjacent damper blades in a direction away therefrom; said actuator means being operative to maintain said selected damper blades in positions progressively less transverse, in a direction away from said first edge portion, to air flow through said second air flow passage when in said first position, whereby air flow through said second air flow passage is directed into said first outlet volume by progressively lesser degrees in a direction away from said first edge portion; and b. the selected damper blades of said first group comprise a series of adjacent damper blades, starting with one in relatively close proximity to the aforesaid first edge portion of said first group, and including adjacent damper blades in a direction away therefrom; said actuator means being operative to maintain said selected damper blades in positions progressively less transverse, in a direction away from said first edge portion, to air flow through said first air flow passage when in said second position, whereby air flow through said first air flow passage is directed into said second outlet volume by progressively lesser degrees in a direction away from said first edge portion.

3. The damper assembly of claim 2 wherein said series of selected, adjacent damper blades of said second group includes the damper blade disposed adjacent the first edge portion of said second group, and all but the damper blade furthest removed therefrom; and wherein said series of selected, adjacent damper blades of said first group includes the damper blade disposed adjacent the first edge portion of said first group, and all but the damper blade furthest removed therefrom.

4. The damper assembly of claim 1, 2 or 3 wherein said actuator means comprise a. first linkage means interconnecting the damper blades of said first group and movable between first and second positions corresponding to the aforesaid first and second positions of said damper blades, said selected damper blades of said first group and said first linkage means including connection means therebetween for accommodating full movement of said first linkage means between said first and second positions while permitting said selected damper blades of said first group to remain in the aforesaid positions transverse to air flow through said first air flow passage when in said second position; and b. second linkage means interconnecting the damper blades of said second group and movable between first and second positions corresponding to the aforesaid first and second positions of said damper blades, said selected damper blades of said second group and said second linkage means including connection means therebetween for accommodating full movement of said second linkage means between said first and second positions while permitting said selected damper blades of said second group to remain in the aforesaid positions transverse to air flow through said second air flow passage when in said first position; and c. means for simultaneously moving said first and second linkage means between said first and second positions.

5. The damper assembly of claim 4 wherein the connection means between said selected damper blades of said first and second groups and the respective first and second linkage means comprise a. a crank member connected to each of said selected damper blades and extending therefrom in a direction transverse to its axis of rotation; b. a crank pin affixed to one of said selected damper blade and said linkage means; and c. slot means associated with the other of said selected damper blade and said linkage member, said slot means and crank pins being in interengaging relationship; the configuration of said slot means effecting predetermined movement of its associated damper blade in response to movement of said linkage means while permitting the selected damper blades of said first and second groups to remain in the aforesaid positions transverse to air flow through the respective first and second air flow passages when in said respective second and first positions.

6. The damper assembly of claim 5 wherein said crank pins are affixed to said respective crank members, and said slot means are associated with said respective linkage means.

7. The damper assembly of claim 6 wherein each of said first and second linkage means comprise an elongated member spaced transversely from its respective group of damper blades and extending in a direction generally parallel thereto.

8. The damper assembly of claim 6 wherein the planes defined by said first and second groups of damper blades define a common plane, and wherein said means for simultaneously moving said first and second linkage means between said first and second positions include said first and second linkage means comprising a single elongated member disposed generally parallel to the common plane defined by said groups of damper blades.

9. The damper assembly of claim 1 wherein the planes defined by said first and second groups of damper blades define a common plane.

10. A damper assembly for use in air conditioning apparatus comprising a. frame means defining first and second adjacent air flow passages having associated therewith respective first and second air inlet volumes lying immediately upstream therefrom and first and second air outlet volumes lying immediately downstream therefrom; b. first and second groups of damper blades rotatably supported by said frame means and extending across said respective first and second adjacent air flow passages for controlling air flow therethrough, each said group comprising a plurality of damper blades rotatable about spaced, substantially parallel axes and disposed generally in a plane extending transverse to its respective air flow passage, said groups being disposed adjacent each other along respective first edge portions thereof which lie parallel to the axes of rotation of said damper blades;; c. actuator means for rotating the damper blades of said first and second groups between first and second positions comprising i. a crank member connected to each damper blade of said first and second groups and extending therefrom in a direction transverse to its axis of rotation, further comprising a crank pin affixed to each crank member and extending therefrom in a direction generally parallel to the axes of rotation of said damper blades; ii. a first elongated linkage member disposed generally parallel to the plane defined by said first group of damper blades, interconnecting the crank pins thereof, and movable between first and second positions corresponding to the aforesaid first and second positions of said damper blades; the crank pins of selected ones of said first group of damper blades being engaged by elongated slot means formed in said first linkage member, each said slot means including a first portion for engaging its respective crank pin and maintaining its respective damper blade in said first position permitting minimum air flow through said first air flow passage, said slot means extending from said first portion to a second portion for engaging its respective crank pin and maintaining its respective damper blade in a position transverse to air flow through said first air flow passage in a sense to direct a portion of the air flowing therethrough into said second outlet volume, while permitting maximum air flow therethrough;; iii. a second elongated linkage member disposed generally parallel to the plane defined by said second group of damper blades, interconnecting the crank pins thereof, and movable between first and second positions corresponding to the aforesaid first and second positions of said damper blades; the crank pins of selected ones of said second group of damper blades being engaged by elongated slot means formed in said second linkage member, each said slot means including a first portion for engaging its respective crank pin and maintaining its respective damper blade in said second position permitting minimum air flow through said second air flow passage, said slot means extending from said first portion to a second portion for engaging its respective crank pin and maintaining its respective damper blade in a position transverse to air flow through said second air flow passage in a sense to direct a portion of the air flowing therethrough into said first outlet volume while permitting maximum air flow therethrough; and iv. means for simultaneously moving said first and second linkage members between said first and second positions.

11. The damper assembly of claim 10 wherein a. the selected damper blades of said first group comprise a series of damper blades, starting with one in relatively close proximity to the aforesaid first edge portion of said first group, and including adjacent damper blades in a direction away therefrom; the elongated slot means of said first linkage member being of progressively decreasing length in said direction, whereby the series of selected damper blades of said first group are maintained in positions progressively less transverse to air flow through said first air flow passage when in said second position; and b. the selected damper blades of said second group comprise a series of damper blades, starting with one in relatively close proximity to the aforesaid first edge portion of said second group, and including adjacent damper blades in a direction away therefrom; the elongated slot means of said second linkage means being of progressively decreasing length in said direction, whereby the series of selected damper blades of said second group are maintained in position progressively less transverse to air flow through said second air flow passage when in said first position.

12. The damper assembly of claims 10 or 11 wherein the crank pins of non-selected damper blades of said first and second groups are rotatably engaged by said respective first and second linkage members.

13. The damper assembly of claims 10 or 11 wherein the planes defined by said first and second groups of damper blades define a common plane, and wherein said means for simultaneously moving said first and second linkage members between said first and second positions include said first and second linkage members comprising a single, elongated member disposed generally parallel to the common plane defined by said groups of damper blades.

14. The damper assembly of claim 10 or 11 wherein the elongated slot means of said first and second linkage members extend from the first portions thereof angularly away from the planes defined by said first and second groups of damper blades.

15. The damper assembly of claim 14 wherein the elongated slot means of said first and second linkage members are substantially straight.

16. The damper assembly of claim t5 wherein the damper blades of said first group are configured such that air flow passing thereover urges them toward said first position, and wherein the damper blades of said second group are configured such that air flow passing thereover urges them toward said second position.

17. The damper assembly of claim 14 wherein the elongated slot means of said first and second linkage'members are arcuate and have a radius of curvature equal to the radius defined between the axis of rotation of the damper blade and its respective crank pin.

18. A damper assembly substantially as hereinbefore described with reference to Figures 1 to 3C of the accompanying drawings.

19. A damper assembly substantially as hereinbefore described with reference to Figures 4A to 4C of the accompanying drawings.