Patent Publication Number: US-2023134766-A1

Title: Low-Profile In-Duct Air Sanitizer Using UV Emitter and Cooperating Wall-Mountable Reflectors

Description:
FIELD OF THE INVENTION 
     This application relates generally to UV-based sanitization of airflow in an HVAC system, and more particularly to in-duct UV-based air sanitizers that are mountable to the ductwork of such HVAC systems. 
     BACKGROUND 
     While UV-based devices for sanitizing airflow in HVAC systems are found in the prior art, the COVID-19 pandemic has particularly emphasized a greater need than eve for effective solutions in this field. Prior art in this field of endeavour includes UV-based air sanitizers designed for installation in ductwork of an HVAC system, examples of which can be seen in U.S. Pat. Nos. 5,894,130, 5,968,455, 6,797,966, 7,107,778, 7,238,326, 8,753,575, 8,772,744, US20040213703, US20050163652, US20050163668, US20080279733, US20140294666, and US20180361007. In contrast to in-duct equipment installed within sections of the HVAC ductwork, other prior art HVAC air sanitizers included combined filtration and UV sterilization devices, or specially fabricated sterilization chambers that are installed in-line with the HVAC ductwork, thus requiring a more complex installation process, especially when retrofitting into a pre-existing HVAC system. Examples of such designs can be seen in U.S. Pat. Nos. 5,523,057, 7,875,247 and US20120315184. Despite these prior endeavours, there remains room for improvement, and particularly a need for effective solutions that can be easily integrated into an existing HVAC system. 
     Disclosed herein is Applicant&#39;s unique in-duct air sanitization solution with a novel and inventive combination of features not heretofore seen in the prior art. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, there is provided an in-duct air sanitization apparatus comprising: 
     an air sanitizer comprising:
         a housing configured for mounting thereof to a wall of an HVAC duct inside of which a forced airflow is to be sanitized; and   a UV emitter mounted on a working side of the housing that faces into the HVAC duct when installed thereon and operable to irradiate an interior of said HVAC duct with UV light; and       

     one or more reflectors mountable on one or more interior wall surfaces of the HVAC duct to receive and reflect incident light from the UV emitter to create thorough UV coverage throughout a cross-sectional flow area of the duct. 
     According to another aspect of the invention, there is provided an in-duct air sanitization apparatus comprising: 
     an air sanitizer comprising:
         a housing configured for mounting thereof to a wall of an HVAC duct inside of which a forced airflow is to be sanitized, said housing containing electronic operating components of said air sanitizer; and   a UV emitter supported in said housing in a position residing externally of the housing at a working side thereof that faces into the HVAC duct when installed thereon, said UV emitter being operable by said electronic operating components to irradiate an interior of said HVAC duct with UV light, and said UV emitter comprising one or more UV bulbs each composed of one or more tubular segments having a longitudinal axis along which the tubular segment is elongated, and that lies in an orientation that is more parallel than perpendicular to said working side of housing such that said UV emitter lies more parallel than perpendicular to said wall of the HVAC duct.       

     According to yet another aspect of the invention, there is provided a method of installing an UV-based air sanitizer in an HVAC duct that has a plurality of duct walls delimiting an interior duct space having a cross-sectional flow area, said method comprising: 
     (a) to an interior wall surface of at least a subset of said duct walls, mounting one or more reflectors for the purpose of receiving and reflecting incident UV light from the air sanitizer to create thorough UV coverage throughout said cross-sectional flow area of the duct; and 
     (b) mounting said UV-based air sanitizer to one of said duct walls in an installed position in which a UV emitter of said air sanitizer is operable to irradiate the interior duct space, and the one or more reflectors mounted therein, with UV light, and thereby generate said thorough UV coverage throughout said cross-sectional flow area of the duct. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One embodiment of the invention will now be described in conjunction with the accompanying drawings in which: 
         FIG.  1    is a perspective view of an UV-based HVAC air sanitization apparatus of the present invention installed on a return air duct of a residential furnace. 
         FIG.  2    is another perspective view of the installed apparatus of  FIG.  1    from an opposing side of said furnace. 
         FIG.  3    is an overhead plan view of the installed apparatus of  FIG.  1   . 
         FIG.  4    is another overhead plan view of the installed apparatus of  FIG.  3   , schematically illustrating thorough UV irradiation of an interior of the air duct throughout a full cross-sectional flow area thereof. 
         FIG.  5    is a side elevational view of the installed apparatus of  FIG.  1   . 
         FIG.  5 A  is a partial closeup view of the return air duct of the furnace of  FIG.  5   , in isolation, at the area thereof denoted by detail circle A. 
         FIG.  6    is an isolated perspective view of an air sanitization unit of the apparatus of  FIG.  1   , from a rear working side thereof that faces into the duct when installed thereon. 
         FIG.  7    is an elevational rear view of the air sanitization unit of  FIG.  6    showing the rear working side thereof. 
         FIG.  8 A  is an elevational edge view of the air sanitization unit of  FIG.  6   . 
         FIG.  8 B  is another elevational edge view of the air sanitization unit of  FIG.  7    from an opposing viewpoint. 
         FIG.  9    is an elevational front view of the air sanitization unit of  FIG.  6    showing a front display side thereof that faces outwardly from duct when installed thereon. 
         FIG.  10    is an isolated plan view of a reflective working side of a singular wall-mountable reflector of the apparatus of  FIG.  1   , for installation an interior wall surface of the duct. 
         FIG.  11    is a plan view of an opposing magnetic mounting side of the wall-mountable reflector of  FIG.  10   . 
         FIG.  12    schematically illustrates provision of the apparatus of  FIG.  1    in the form of a kit composed of the air sanitization unit of  FIGS.  6  through  9    and an accompanying set of reflectors of the type shown in  FIGS.  10  and  11   . 
         FIG.  13    schematically illustrates daisy-chained installation of a plurality of the air sanitization units in networked connection to a control panel of a building automation system (BAS). 
     
    
    
     DETAILED DESCRIPTION 
     With initial reference to  FIG.  1   , illustrated therein is UV-based HVAC air sanitization apparatus of the present invention, installed in this non-limiting example on return air ductwork  100  of a residential furnace  102 . More particularly, the illustrated example is installed on a vertically upright return air duct  104  that feeds into a return air intake of the furnace  102  via an elbow boot  106  at the bottom of the upright return air duct  104 . In this example, the air duct  104  is a rectangular duct whose four walls include first and second narrow duct walls  108 A,  108 B of equal width and opposing positional relationship to one another, and third and fourth wide duct walls  108 C,  108 D of equal width and opposing positional relationship to one another. The wide duct walls  108 C,  108 D are wider than the narrow duct walls  108 A,  108 B and span therebetween in perpendicular relationship thereto. 
     The installed air sanitization apparatus is composed of an air sanitization unit  10  for installation on one of the duct walls  108 A- 108 D, and an accompanying set of wall-mountable reflectors  12 A- 12 F for installation on interior wall surfaces of the remainder of the duct walls for cooperation with the air sanitization unit  10  to ensure thorough distribution of UV light from the air sanitization unit  10  throughout an entirety of the air duct&#39;s internal cross-sectional flow area, thus ensuring thorough and effective UV-based sterilization of the airflow moving therethrough. In the non-limiting example of the illustrated embodiment, the air sanitization unit  10  is mounted on the narrow first duct wall  108 A of the air duct  104 , and the set of reflectors  12 A- 12 F are installed in distributed fashion among the narrow second duct wall  108 B and the wide third and fourth duct walls  108 C,  108 D. 
     In the illustrated embodiment, the air sanitization unit  10  is of elongated rectangular shape, whose overall width is no greater than that of the two narrow duct walls  108 A,  108 B, and whose length is no greater than that of the two wide duct walls  108 C,  108 D. The reflectors  12 A- 12 F of the illustrated embodiment are all identical to one another, and likewise are of elongated rectangular shape whose overall width is no greater than that of the two narrow duct walls  108 A,  108 B, and whose length is no greater than that of the two wide duct walls  108 C,  108 D. Advantageous sizing relationships between the air sanitization unit  10 , the reflectors  12 A- 12 F and the walls  108 A- 108 D of the ductwork  100  in preferred embodiments of the invention are described herein further below in more detail, but more detail concerning the preferred design of the air sanitization unit  10  itself is first set forth as follows. 
     The air sanitization unit  10  is shown in isolation in  FIGS.  6  through  9   , and features a housing  14  whose shape is that of a rectangular parallelopiped of greater length than width, and greater width than thickness. A facial front wall  14 A of the housing  14  is one of the two largest rectangular sides of the housing&#39;s parallelopiped shape, of which the other is a matching and opposing facial rear wall  14 B of equal size an shape to the facial front wall  14 A. A remaining four perimeter walls  14 C- 14 F of the housing  14  serve to interconnect the facial front and rear walls  14 A,  14 B to one another around the four perimeter boundaries thereof. These perimeter walls  14 C- 14 F include two lengthwise perimeter walls  14 C,  14 D that span the elongated length dimension of the housing, and two widthwise perimeter walls  14 E,  14 F that span the lesser width dimension of the housing. The distance between the facial front and rear walls  14 A,  14 B and spanned by the perimeter walls  14 C- 14 F denotes the even lesser thickness dimension of the housing. 
     The interior space of the housing  14  delimited between the housing walls  14 A- 14 F contains all of the working electronics of the air sanitization unit. The facial rear wall  14 B defines an interior working side of the housing that faces into the interior space of the air duct  104  when the unit  10  is installed on a duct wall  108 A thereof. 
     Mounted to the facial rear wall  14 B of the housing  14  is a UV-emission device  16  composed of one of more UV bulbs  18  operable to emit ultraviolet light, and more particularly, UV light in the UV-C wavelength range. In the non-limiting illustrated embodiment, the UV-emission device is composed of a singular UVC bulb having an O-shaped configuration composed of four tubular segments  18 A- 18 D of linear configuration that are connected together end-to-end in a closed loop of O-shaped appearance, when viewed straight on from the rear working side of the unit  10 . Of these four bulb segments  18 A- 18 D, two lengthwise bulb segments  18 A,  18 B lie parallel to one another and run in the lengthwise direction of the housing  14 . These lengthwisebulb segments  18 A,  18 B reside at respective positions closely neighbouring the planes of the housing&#39;s lengthwise perimeter walls  14 C,  14 D of the housing, and are both contained entirely within the space delimited between those planes. The two remaining widthwise bulb segments  18 C,  18 D lie parallel to one another and run in the widthwise direction of the housing  14  at respective positions closely neighbouring the planes of the widthwise perimeter walls  14 E,  14 F of the housing, and contained entirely within the space delimited between those planes. 
     The lengthwise bulb segments  18 A,  18 B are longer than the widthwise bulb segments  18 C,  18 D, and span a substantial majority or near entirety of the length dimension of the facial rear wall  14 B of the housing  14 . Respective linear axes  22 A- 22 D of the four bulb segments  18 A- 18 D are coplanar with one another in a plane residing parallel to the plane housing&#39;s facial rear wall  14 B. The bulb is held in slightly offset relation from the plane of the housing&#39;s facial rear wall  14 B by standoffs, for example a pair of such standoffs  20 A,  20 B that support the widthwise bulb segments  18 C,  18 D at opposite ends of the bulb  18 , and through which connection of the bulb to the lamp ballast, which is located within the housing  14  along with the other working electronics inside the housing  14 . In the illustrated example, the widthwise bulb segments  18 C,  18 D are offset more inwardly from the respective perimeter boundaries of the of the housing than their lengthwise counterparts  18 A,  18 B to accommodate adequate room for attachment of the standoffs  20 A,  20 B to the facial rear wall  14 B of the housing  14 . Accordingly, the O-shaped configuration of the bulb doesn&#39;t quite span the full housing length. 
     The longitudinal axis  22 A- 22 D of each tubular bulb segment  18 A- 18 D of the UV emitter  16  lies parallel to the inner working side of the housing  14 , which in turn lies parallel to the respective duct wall  108 A on which the housing  14  is mounted in the installed state of the unit  10 , whereby each tubular segment  18 A- 18 D of the UV emitter  16  of the installed unit  10  has its longitudinal axis  22 A- 22 D oriented parallel to the plane respective duct wall  108  on which the unit  10  is installed. The result is a low-profile air sanitization unit  10  of minimal invasiveness into the interior airflow space of the ductwork  100 , compared to prior art designs in which the longitudinal axes of tubular UV bulbs instead reside perpendicular to the plane of the duct wall on which they are mounted, and project across an entirety or near entirety of the duct&#39;s internal cross-section. This novel low-profile design of the unit  10  makes for easier handling thereof during the installation process. 
     The facial front wall  14 A of the housing  14  defines an outer display side of the unit  10  that faces outwardly from the air duct  104  in the unit&#39;s installed position thereon. At this display side of the housing  14 , the unit  10  includes one or more visual indicators  24 A- 24 B of the unit&#39;s operating status, for example preferably including both a power status indicator  24 A, and one or more lamp status indicators  24 B. The lamp status indicator(s) illuminate(s) in visually distinct states (e.g. different colours, and/or different continuous vs. blinking patterns, etc.) to reflect different statuses of the UV emitter  16 . The illustrated example employs a singular lamp status indicator  24 B that illuminates in different colours to reflect different possible operational states: for example illuminating in a first “lamp okay” state (e.g. in solid green) when the working electronics have determined that the UV emitter  16  is operating properly, illuminating in a second “lamp warning” state (e.g. in sold yellow) when the working electronics have determined that the bulb  18  of the UV emitter  16  is nearing an anticipated end of its expected useful operating life, and illuminating in a third “lamp expired” state (e.g. in solid red) when the working electronics identify that the bulb  18  has exceeded the anticipated end of its expected useful operating life. 
     In addition to detection of these different operating states, the working electronics are also operable to detect a “lamp failure” state of the UV emitter  16 , for example based on measured ballast current, in which case the lamp status indicator  24 B may illuminate in yet another visually distinct fashion (e.g. in flashing red). An audible alarm may be included for activation in the event of detected lamp failure, and optionally also in the event of the detected “lamp expired” state, in which case, two audibly distinct alarm sounds may optionally be employed for these different detected events. In embodiments that include the lamp life monitoring and indicating functions described above, a lamp life reset button  26  is also provided for manual depression thereof by service personnel when the bulb  18  is replaced so as to reinitiate countdown of a new expected lamp life period. 
     For mounting of the housing  14  to the duct wall  108 A, a mounting flange  28  spans around the full perimeter of the housing  14  in outwardly projecting relationship from the four perimeter walls  14 C- 14 F thereof at a plane residing intermediately between, and parallel to, the front and rear facial walls  14 A,  14 B of the housing  14 . The mounting flange  28  has fastening apertures  30  therein at spaced intervals around the perimeter of the housing  14  to enable fastening of the mounting flange  28  to the exterior of the duct wall  108 A using suitable fasteners, for example self-drilling screw fasteners. 
     Referring to  FIG.  8 B , a power connection port  32  is provided for connection of a power cord (not shown) by which the unit  10  is connectable to an AC mains power outlet for powering of the lamp ballast and other working electronics of the unit  10 . The illustrated embodiment also includes a wiring terminal  34  by which the unit  10  can be communicably connected to a control panel  200  of a building automation system (BAS), and to one more additional air sanitation units of the same or similar design installed in the same building. In one non-limiting example, schematically illustrated in  FIG.  13   , an eight-pin wiring configuration is used, in which a four-pin output group of terminal pins includes a bulb status output pin ( 1 ), a fault output pin ( 2 ), and positive and negative enablement output pins ( 3  &amp;  4 ), while a corresponding four-pin input group of terminal pins includes a bulb status input pin ( 5 ), a fault input pin ( 6 ), and positive and negative enablement input pins ( 7  &amp;  8 ). In the event of a detected “lamp failure” or “lamp expiration” state by a local on-board controller included among the working electronics of each unit  10 , the local controller changes an on/off state at the status output pin ( 5 ) from its default state to the opposite state, thus creating a detectable alarm signal sent onward to the connected BAS control panel  200 , via other daisy-chained air sanitization units if so installed. 
     Referring again to  FIG.  8 B , the illustrated embodiment has both the power connection port  32  and the wiring terminal  34  on the same perimeter wall  14 D of the housing, specifically on an outer fraction thereof that resides between the planes of the mounting flange  28  and the facial front wall  14 A, so that the power connection port  32  and the wiring terminal  34  both reside outside the air duct  106  in the unit&#39;s installed position. It will be appreciated however that either or both of these components may be relocated elsewhere on the housing. Likewise, though placement of the indicators  24 A,  24 B and lamp life reset button  26  on the facial front wall  14 A is optimal for the most convenient visual detection and access, they may be positioned elsewhere on the housing. 
     The enablement input pins ( 7  &amp;  8 ) allow a singular unit  10  to be remotely switched between active/inactive states by the BAS, and in combination with enablement output pins ( 3  &amp;  4 ), also allow a bank of daisy chained units  10  to be likewise switched between active/inactive states. To maximize lamp life, each unit  10  preferably includes a pressure switch that is installed at the working side of the unit  10  so as to reside inside the air duct, and is connected to the local onboard controller so that the UV emitter  16  is only activated in the presence of detected airflow inside the air duct. In daisy chained scenarios, the lamp activation/deactivation routine executed by the controller uses not only detected air pressure, but also detected presence/absence of an activation signal on the enablement input pins ( 7  &amp;  8 ) as a further input condition on the decision of whether to activate the UV emitter when airflow is detected. So, for example, the BAS can be used to activate a larger quantity of directly wired units  10 , or larger quantity of daisy chained banks of units  10 , during higher airflow periods, and a activate a lesser quantity of units/banks during lower airflow periods (e.g. higher airflow during daytime business hours, vs. lower airflow during overnight/weekend HVAC down-turn). 
       FIGS.  10  and  11    illustrate a singular one of the reflectors  12 A- 12 F, of which the other reflectors are identical in the illustrated embodiment. The reflector  12 A is of flat rectangular shape, and on a frontside  36  thereof, features a reflective surface  38 , preferably spanning the full rectangular area the reflector&#39;s frontside  36 . The opposing backside  40  is referred to as a mounting side of the reflector, which is to be attached to an interior wall surface of one of the duct walls  108 A- 108 D during installation. The preferred embodiment employs fastener-free magnetic mounting of the reflectors  12 A- 12 D to the metal walls of the air duct  106  via one or more magnets on each reflector. The illustrated reflector  12 A of  FIG.  11    thus features multiple magnets on the backside  40  thereof, for example embodied by four pieces of magnetic tape  42 A- 42 D each spanning a respective outer margin of the reflector&#39;s backside  40  along a respective perimeter edge thereof. As shown, each such length of magnetic tape  42 A- 42 D may span an entirety of the respective perimeter edge of the reflector, whereby the four pieces  42 A- 42 D collectively span the full perimeter of the reflector&#39;s backside  40 . 
     In the preferred embodiment shown in the figures, a length L R  of the reflector  12 A is roughly equal to a housing length L H  of the air sanitization unit  10 , which excludes the mounting flange  28  and is measured between the widthwise perimeter walls  14 E,  14 F of the housing  14 . Likewise, a width W R  of the reflector  12 A is preferably equal to a housing width W H  of the air sanitization unit  10 , which again excludes the mounting flange, and is measured between lengthwise perimeter walls  14 C,  14 D of the housing  14 .  FIG.  12    illustrates a preferred implementation of the invention in the form of a kit  44  composed of an air sanitization unit  10  accompanied by a plurality of identical reflectors  12 A- 12 G. Since each reflector  12 A- 12 G is dimensioned roughly equal to the front and rear facial walls  14 A,  14 B of the housing  14  of the air sanitization unit  10 , any one of the identical reflectors  12 A- 12 G can be used as a tracing template to mark off a suitable rectangular cut-out area on the duct wall  108 A, which is then cut-out from the duct wall  108 A to accommodate mounting of the air sanitization unit  10  in the cut-out opening.  FIG.  5 A  shows a rectangular opening  110  having been cut out from the duct wall  108 A in such fashion so that its size roughly matches the rear facial wall  14 B of the sanitizer unit&#39;s housing  14 . By roughly matching, it is meant that the opening  110  is at least as large as the housing&#39;s rectangular shape, and typically slightly larger if cut accurately to the traced outline of the equally dimensioned reflector.  FIG.  5 A  shows an array of fastening points  112  distributed around the cut-out opening  110  at matching intervals to the fastening apertures  30  in the flange  28  of the air sanitization unit  10 , though these fastening points  112  need not be marked and pre-drilled if self-drilling screw fasteners are used to install the unit  10 . 
     Before inserting the rear working side of the unit  10  into the opening  110  and fastening the mounting flange  28  of the housing  10  in place, the set of reflectors  12 A- 12 G are first inserted into the interior space of the duct  106  through the cut-out opening  110 , and are magnetically secured on the interior wall surfaces the second, third and fourth duct walls  108 B,  108 C,  108 D at elevations thereon matching the opening  110  into which the air sanitization unit  10  will then be mounted. The illustrated example represents a scenario in which the reflectors  12 A- 12 G and the rear facial wall  14 B of the housing all measure 8-inches by 23-inches, the rectangular duct  106  measures 10-inches by 24-inches (a common duct size), and the overall flanged width of the air sanitization unit measures no more than 10-inches, and preferably slightly less than 10-inches (e.g. between 9.0 and 9.9 inches). This way, the rought 8-inch opening  110  cut centrally in the 10-inch-wide duct wall  108 A leaves a 1-inch margin on each side of the opening  110  to accommodate the mounting flange  28  of the unit  10 , which is fastened to these intact margins of the duct wall on either side of the opening  110 , and preferably also above and below the opening. Meanwhile, placement of a singular reflector  12 A in a length-up orientation on the interior surface of the second duct wall  108 B in aligned relation across from the opening  110  in the first duct wall  108 A means that a substantial majority of the second duct wall&#39;s 10-inch width will be covered by the reflector&#39;s 8-inch wide reflective surface  38 , and owing to the reflector&#39;s equal length to that of the housing  14 , this reflective surface will also cover an entirety of the elevational range within which the entire bulb  18  of the air sanitizations unit  10  will reside, once the unit  10  is isntalled. 
     In addition to the first reflector  12 A placed on the second duct wall  108 B across from where the air sanitization unit will be mounted, at least one additional reflector is also magnetically mounted on the interior surface of each of the duct&#39;s remaining wider third and fourth walls  108 C,  10 D, once again at this same elevational range corresponding to the cut-out opening  110  in the first duct wall  108 A. In the illustrated example, where the duct  106  is 24-inches wide and the reflectors are each 23-inches long, three reflectors  12 B,  12 C,  12 D are shown mounted on the third duct wall  10 C in stacked relation one over the other, each in a width-up orientation placing the reflector&#39;s length in crosswise width-spanning relationship to the third duct wall  108 C. Another three reflectors  12 E,  12 F,  12 G are likewise mounted to the fourth duct wall  108 D in this same stacked, width-up orientation of width-spanning relationship to the duct wall  108 D. The respective 8-inch widths of the three reflectors on each wide wall  108 C,  108 D of the duct thus collectively span an entirety of the full 23-inch elevational span of the opening  110  in the first duct wall  108 A, while the 23-inch length of each such reflector  12 B- 12 G spans a substantial majority ( 23/24ths) of the duct wall on which it is mounted. Accordingly, a substantial entirety of interior wall surfaces of the second, third and fourth duct walls  108 B- 108 D, within the elevational span of the opening  110  in which the unit  10  will now be mounted, are lined by the magnetically installed reflectors  12 A- 12 G, whose reflective surfaces  38  face inwardly from the duct walls on which they are mounted. The multiple reflectors on the wide duct walls  108 C,  108 C may alternatively be placed side by side to one another in length-up orientations to accomplish the same effective full-width, full-elevation coverage, given suitable relative dimensions of the reflectors and duct walls. 
     The rear working side of the air sanitization unit  10  is then inserted into the opening  110  in the first duct wall  108 A, and the mounting flange  28  of the housing  14  is fastened in place to the exterior of the first duct wall  108 A on all four sides of the opening  110  therein. The UV emitter  16  is thereby placed into the duct&#39;s interior space, in a position residing close to, but offset a short distance inward from, the first duct wall  108 A. Since the bulb axes  22 A- 22 D are all parallel to the rear facial wall  14 B of the housing  14 , and likewise parallel to the first duct wall  108 A to which the housing is now mounted, the bulb  18  is of little protrusive relation to overall cross-sectional flow area of the duct, spanning only a minor fraction of the duct&#39;s interior width. Nonetheless, effective UV coverage of the duct&#39;s cross-sectional flow area is achieved by reflection of incident UV light from the bulb  18  off the installed reflectors that substantially cover the interior wall surfaces, as schematically illustrated by reflected light rays in  FIG.  4   . 
     While the illustrated example in  FIGS.  1  and  2    shows multiple reflectors being installed in stacked relation one over another on the wide duct walls to collectively cover the entire elevational range of the opening  110  and installed unit  10 , or to at least cover the entire elevational range of the bulb(s)  18  of the unit  10 , it will be appreciated that this may not be necessary, and the installed quantity of reflectors may be reduced, for example to as few as one reflector per duct wall, even at the wider walls of the duct, while still accomplishing a thorough sheet of incident and reflected light spanning an effective entirety of the duct&#39;s cross-sectional flow area. It will also be appreciated that while the illustrated embodiment employs a plurality of identically sized reflectors, differently sized reflectors in various combinations and quantities may alternatively be employed. For example, reflectors in a variety of dimensions chosen to match common duct sizes may be provisioned, and supplied to customers in user-specific kits specifically sized for their intended application. 
     It will also be appreciated that the invention is not limited to installation specifically on a return air duct, and for example may alternatively be used on a supply air duct, nor is the invention limited to use on an upright duct, use in a residential HVAC system, or use on a duct whose dimensions are such that a substantially full width of the supporting duct wall of the unit  10  is spanned by the installed unit. In instances where the unit  10  spans notably less than the width of the duct wall on it is installed, one or more additional reflectors may optionally be placed on the same wall as the unit  10 , in positions situated beside the opening  110  in that same duct wall. While the magnetic securement of the reflectors is ideal in terms of convenient tool-free installation thereof in a manner that maintains the integrity of the duct walls on which they are installed, it will be appreciated that other means of securing the reflectors in place may alternatively be employed. 
     Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.