Patent Publication Number: US-2023160585-A1

Title: Exhaust fan unit of a heating, ventilation, and/or air conditioning (hvac) system

Description:
This application is a continuation of U.S. Pat. Application No. 16/836,671, entitled “EXHAUST FAN UNIT OF A HEATING, VENTILATION, AND/OR AIR CONDITIONING (HVAC) SYSTEM,” filed Mar. 31, 2020, which claims priority from and the benefit of U.S. Provisional Application Serial No. 62/945,621, entitled “EXHAUST FAN UNIT OF A HEATING, VENTILATION, AND/OR AIR CONDITIONING (HVAC) SYSTEM,” filed Dec. 9, 2019, which are hereby incorporated by reference in their entireties for all purposes. 
    
    
     BACKGROUND 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     A wide range of applications exists for HVAC systems. For example, residential, light commercial, commercial, and industrial systems are used to control temperatures and air quality in residences and buildings. In certain HVAC systems, exhaust gases or fumes from a space being conditioned by the HVAC system are expelled to a surrounding environment via an exhaust fan unit, sometimes referred to as a laboratory exhaust unit. It is now recognized that traditional exhaust fan units may be inefficient in removing, diluting, and dispersing exhaust gas, and may be susceptible to environmental and other damage. For example, traditional exhaust fan units may not provide adequate protection against gas leakage, flow control, dilution of contaminants, and evacuation to reduce entrainment through other HVAC intake systems or direct contact. Furthermore, traditional exhaust systems may deposit contents of the exhaust gas in small, concentrated areas of the surrounding environment. 
     SUMMARY 
     A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of the disclosure. Indeed, this disclosure may encompass a variety of aspects that may be set forth below. 
     The present disclosure relates to an exhaust fan unit of a heating, ventilation, and/or air conditioning (HVAC) system. The exhaust fan unit includes an outer fluid path of a nozzle assembly of the exhaust fan unit defined by and between an outer wall of the nozzle assembly and an inner wall of the nozzle assembly. The exhaust fan unit also includes an inner fluid path of the nozzle assembly defined by and radially inward from the inner wall. The exhaust fan unit also includes multiple entrainment ports extending from the outer wall to the inner wall and configured to enable environmental air to pass to the inner fluid path. Each entrainment port includes a bottom surface that tapers downwardly from the inner wall to the outer wall. 
     The present disclosure also relates to an exhaust fan unit including an outer fluid path of a nozzle assembly of the exhaust fan unit defined by and between an outer wall of the nozzle assembly and an inner wall of the nozzle assembly. The exhaust fan unit also includes an inner fluid path of the nozzle assembly defined by and radially inward from the inner wall. The exhaust fan unit also includes a bottom surface extending radially across the inner fluid path and configured to collect liquids within the inner fluid path. The exhaust fan unit also includes entrainment ports extending from the outer wall to the inner wall and configured to enable environmental air to pass to the inner fluid path. The entrainment ports are configured to drain from the inner fluid path the liquids collected within the inner fluid path. 
     The present disclosure also relates to an exhaust fan unit having an outer fluid path of a nozzle assembly of the exhaust fan unit defined by and between an outer wall of the nozzle assembly and an inner wall of the nozzle assembly. The exhaust fan unit also includes an inner fluid path defined by and radially inward from the inner wall. The exhaust fan unit also includes dual-tapered shaped entrainment ports extending from the outer wall to the inner wall and configured to enable environmental air to pass to the inner fluid path. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic front view of an exhaust fan unit for a building, in accordance with an aspect of the present disclosure; 
         FIG.  2    is a perspective view of the exhaust fan unit of  FIG.  1   , in accordance with an aspect of the present disclosure; 
         FIG.  3    is a cross-sectional perspective view of portions of the exhaust fan unit of  FIG.  2   , in accordance with an aspect of the present disclosure; 
         FIG.  4    is a cross-sectional front view of portions of the exhaust fan unit of  FIG.  3   , in accordance with an aspect of the present disclosure; 
         FIG.  5    is a schematic front cutaway view of a nozzle assembly and wind band for use in the exhaust fan unit of  FIG.  1   , in accordance with an aspect of the present disclosure; 
         FIG.  6    is a perspective view of a nozzle assembly and wind band for use in the exhaust fan unit of  FIG.  1   , in accordance with an aspect of the present disclosure; 
         FIG.  7    is a cross-sectional perspective view of the nozzle assembly and wind band of  FIG.  6   , and a portion of a fan assembly, in accordance with an aspect of the present disclosure; 
         FIG.  8    is a cross-sectional top-down view of the nozzle assembly and wind band of  FIG.  6   , and a portion of a fan assembly, in accordance with an aspect of the present disclosure; 
         FIG.  9    is a perspective view of the nozzle assembly of  FIG.  6   , in accordance with an aspect of the present disclosure; 
         FIG.  10    is a cross-sectional perspective view of the nozzle assembly of  FIG.  9   , in accordance with an aspect of the present disclosure; 
         FIG.  11    is a cross-sectional front view of the nozzle assembly of  FIG.  9    with a wind band attached thereto, in accordance with an aspect of the present disclosure; 
         FIG.  12    is schematic view of an entrainment port for use in the exhaust fan unit of  FIG.  1   , in accordance with an aspect of the present disclosure; 
         FIG.  13    is a perspective view of a fan assembly and a mixing box for use in the exhaust fan unit of  FIG.  1   , in accordance with an aspect of the present disclosure; 
         FIG.  14    is a cross-sectional perspective view of the fan assembly and the mixing box of  FIG.  13   , in accordance with an aspect of the present disclosure; and 
         FIG.  15    is a perspective view of multiple exhaust fan units of a heating, ventilation, and/or air conditioning (HVAC) system, in accordance with an aspect of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present disclosure will be described below. These described embodiments are only examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation- specific decisions must be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     The present disclosure is directed toward heating, ventilation, and/or air conditioning (HVAC) systems and, more particularly, toward an induction scheme of an exhaust fan unit. 
     In accordance with present embodiments, an exhaust fan unit includes a mixing box, a fan assembly, a nozzle assembly, and a wind band. The mixing box may be configured to receive exhaust fumes from an internal space of a building. In some embodiments, the mixing box may also receive external air from a surrounding environment, drawn into the mixing box via the fan assembly of the exhaust fan unit, via a Venturi effect, or both. In conditions where the mixing box receives the external air, the mixing box may mix the exhaust fumes from the internal space and the external air from the external environment. In other embodiments or operating modes, the mixing box may only receive the exhaust air from the internal space. 
     The fan assembly may cause the exhaust air or the mixture of exhaust air and external air to pass to the nozzle assembly of the exhaust fan unit. The nozzle assembly may include an outer flow path, such as an annulus, defined between an outer wall of the nozzle assembly and an inner wall of the nozzle assembly, where the annulus is configured to receive the exhaust air or the mixture of exhaust air passed thereto from the mixing box (e.g., by way of the fan assembly). The nozzle assembly may also include an inner cavity (or flow path) radially inward from the inner wall of the nozzle assembly. That is, the inner cavity may be fluidly separated from the annulus by the inner wall of the nozzle assembly. Entrainment points may be positioned about the nozzle assembly, extending between the outer wall and the inner wall forming the annulus, fluidly separate from the annulus defined between the inner and outer walls of the nozzle assembly. Thus, the entrainment ports may fluidly couple the inner cavity of the nozzle assembly and an external environment surrounding the nozzle assembly, while maintaining fluid separation from the annulus of the nozzle assembly. As the exhaust air or the mixed air exits a top end of the annulus of the nozzle assembly, a flow of the exhaust air or the mixed air may cause a pressure drop in the inner cavity of the nozzle assembly. The pressure drop may cause external air, referred to herein as nozzle entrained air, to pass through the entrainment ports, into the inner cavity of the nozzle assembly, and upwardly through a top end of the inner cavity. The top end of the annulus and the top end of the inner cavity may be disposed at similar axial levels at an exit end of the nozzle assembly. 
     A wind band may be attached to the nozzle assembly near the exit end of the nozzle assembly. The wind band may extend circumferentially or otherwise about the exit end of the nozzle assembly. As the exhaust air or the mixed air passes through the top end of the annulus of the nozzle assembly and as the nozzle entrained air passes through the top end of the inner cavity of the nozzle assembly, a flow thereof may cause a pressure drop adjacent a gap between the wind band and the nozzle assembly. The pressure drop may cause external air, referred to herein as wind band entrained air, to pass through the gap between the wind band and the nozzle assembly. The exhaust air or mixed air, the nozzle entrained air, and the wind band entrained air may mix radially inward from the wind band and then be ejected from an upper end of the wind band and into the external environment. 
     In accordance with present embodiments, the inner wall of the nozzle assembly, described above as defining the inner cavity of the nozzle assembly, may include a frustoconical shape, which is herein defined to include a true frustoconical shape or a shape similar to a frustoconical shape. That is, the inner surface of the inner wall of the nozzle assembly may flare, slope, or taper outwardly from an entry side of the nozzle assembly toward the exit side of the nozzle assembly. The frustoconical shape may be defined by a diameter that increases non-linearly, meaning that the diameter of the inner wall of the nozzle may increase non-linearly along an axial direction of the nozzle assembly, from a bottom of the frustoconical shape (i.e., the entry side of the nozzle assembly) upwardly. The outer wall of the nozzle assembly may include a cylindrical shape. One or both of these shapes may contribute to improved air flow performance of the exhaust fan unit. For example, a flow path of the outer flow path (e.g., annulus) defined between the inner wall and the outer wall of the nozzle assembly may include a restricted cross-sectional area, which enables a pressure drop that causes acceleration of the fluid flow through the annulus. 
     Further, the frustoconical shape may include a bottom or lower surface (e.g. lower horizontal surface) defining a floor of the inner cavity. The floor defining the inner cavity, and a shape of the entrainment ports of the nozzle assembly, may contribute to improved rain/liquid drainage from the nozzle assembly, which improves air flow performance and protects electronic components, such as fan assembly components and/or damper components, from rain damage. For example, the entrainment ports of the nozzle assembly may include a tapered shape (e.g., a tear-drop or leaf shape) that includes a tapered bottom surface sloping downwardly from the inner surface of the nozzle assembly to the outer surface of the nozzle assembly, thereby enabling rain collected on the horizontal floor to drain through the entrainment ports and into the external environment. It should be noted that the floor of the inner cavity may be flat or curbed. For example, the floor may form a bowl shape. These and other features will be described in detail below. 
     Turning now to the drawings,  FIG.  1    is a schematic front view of an embodiment of an exhaust fan unit  10 , referred to in some instances as a laboratory exhaust unit, for a building  12 . In the illustrated embodiment, the building  12  includes an internal space  14  from which the exhaust fan unit  10  expels exhaust gases toward an external environment  16  surrounding the exhaust fan unit  10  and the building  12 . 
     The exhaust fan unit  10  includes a mixing box  18 , a fan assembly  20 , a nozzle assembly  22 , and a wind band  24 . The mixing box  18  may couple to a vent or vent system  26  extending from the internal space  14  of the building  12  toward a roof  28  of the building  12 . In some embodiments, a damper  30  may be positioned between the mixing box  18  and the vent system  26 , where the damper  30  is configured to open and close to enable and disable, respectively, a flow of exhaust gas to the mixing box  18 . The damper  30  may also include intermediate settings that enable a certain pre-determined amount of flow therethrough. The damper  30  may be a part of the exhaust fan unit  10 , or a separate component from the exhaust fan unit  10  (e.g., a part of the roof  28  or building  12  and interfaced with the exhaust fan unit  10 ). 
     The mixing box  18  also includes an outdoor air inlet  31  (e.g., hood or louver) and a damper  32  (e.g., “bypass damper”) configured to be opened and closed to enable a flow of outdoor air through the outdoor air inlet  31  and into the mixing box  18 . The damper  32  may include intermediate settings that enable a certain pre-determined amount of flow therethrough under certain conditions. As shown, the damper  32  may be positioned within the mixing box  18  downstream from the outdoor air inlet  31  (e.g., hood or louver). An additional damper  33  may be disposed between the mixing box  18  and the fan assembly  20 , and may be utilized to control a flow of fluid (e.g., air, exhaust gas or a mixed fluid of exhaust gas and air drawn into the mixing box  18  via the outdoor air inlet  31 ) from the mixing box  18  to the fan assembly  20 . 
     The fan assembly  20 , which sits above the mixing box  18  in the illustrated embodiment, may include an outer shell, such as a cylindrical outer shell, and a fan  21  disposed in the outer shell, where the fan  21  is configured to draw the flow of exhaust gases from the vent system  26  into the mixing box  18 , and the flow of outdoor air through the outdoor air inlet  31  and into the mixing box  18 . In some embodiments, the fan  21  may extend between the fan assembly  20  and the mixing box  18  (e.g., the fan  21  may extend partially into the mixing box  18 ). In certain operating conditions, the damper  32  may be closed to disable a flow of outdoor air through the outdoor air inlet  31 , in which case only the exhaust gas is drawn into the mixing box  18 . In other operating conditions, the damper  32  may be opened to enable a flow of outdoor air through the outdoor air inlet  31 , and the outdoor air may be mixed with the exhaust gas in the mixing box  18 . A combination of exhaust gas and outdoor air may be referred to herein as a “mixed fluid.” While other dampers may also be incorporated into the mixing box  18 , such dampers will be described in detail with reference to later drawings. 
     The fan assembly  20  may pass the exhaust gas or the mixed fluid from the fan mixing box  18 , through the fan assembly  20 , and to the nozzle assembly  22 . The nozzle assembly  22  may include an outer wall and an inner wall, an annulus positioned radially between the outer wall and the inner wall, and an inner cavity positioned radially inward from the inner wall. The annulus may be configured to receive the exhaust gas or the mixed fluid. The annulus, inner cavity, and corresponding features (e.g., outer wall and inner wall) will be illustrated and described in detail with reference to later drawings. The nozzle assembly  22  may also include multiple entrainment ports  34  extending from the outer wall of the nozzle assembly  22  to the inner wall of the nozzle assembly  22 . That is, the entrainment ports  34  may be defined by structural features of the nozzle assembly  22  extending between the outer and inner walls of the nozzle assembly  22 , and the entrainment ports  34  may be fluidly coupled to the inner cavity of the nozzle assembly  22 . Thus, the entrainment ports  34  may define openings that fluidly couple the inner cavity of the nozzle assembly  22  with the surrounding environment  16  around the exhaust fan unit  10 . Further, the entrainment ports  34  may be fluidly separated from the annulus defined radially between the inner and outer walls of the nozzle assembly  22 . 
     The above-described annulus of the nozzle assembly may be fluidly coupled with a space above the nozzle assembly  22 , defined by the wind band  24 . That is, the exhaust gas or mixed fluid may empty from the annulus of the nozzle assembly  22  into a flow path defined by the wind band  24 . The flow of the exhaust gas into the wind band  24  may cause a pressure drop within the inner cavity of the nozzle assembly  22 , and the pressure drop may cause a flow of outside air into the cavity of the nozzle assembly  22  via the entrainment ports  34 . The cavity of the nozzle assembly  22  may also empty into the flow path defined by the wind band  24 . Accordingly, the outside air drawn into the cavity of the nozzle assembly  22  may exit the nozzle assembly  22  and mix with the exhaust gas or mixed fluid that exits the annulus of the nozzle assembly  22  into the flow path defined by the wind band  24 . 
     Additionally, an entrainment gap  36  may be defined between an inner surface of the wind band  24  and the outer surface of the nozzle assembly  22 . The entrainment gap  36  may operate to fluidly couple the external environment  16  with the flow path defined inside the wind band  24 . Accordingly, additional outside air may be drawn into the flow path defined inside the wind band  24  via the entrainment gap  36 . The additional outside air may mix with the exhaust gas or mixed fluid, and the entrained air introduced via the entrainment ports  34  as described above. An outlet  38  of the wind band  24  may enable the exhaust fan unit  10  to expel the fluids passed therein and therethrough to the surrounding environment  16 . 
     In accordance with present embodiments, the inner wall of the nozzle assembly  22 , described above as defining the cavity of the nozzle assembly  22 , may include a frustoconical shape. Further, the frustoconical shape may be defined by a diameter that increases non-linearly, meaning that the diameter of the inner wall of the nozzle may increase non-linearly along an axial direction of the nozzle assembly, from a bottom of the frustoconical shape upwardly, in the illustrated embodiment. The outer wall of the nozzle assembly  22  may include a cylindrical shape or prismatic shape. These shapes, individually or together, may contribute to improved air flow performance of the exhaust fan unit  10  and corresponding fan assembly  20 . Further, the frustoconical shape may include a horizontal surface, such as a horizontal bottom surface, defining a floor of the inner cavity. The horizontal floor, and a shape of the above-describe entrainment ports  34  of the nozzle assembly  22 , may contribute to improved rain drainage from the nozzle assembly  22 , which improves air flow performance and protects electronic components, such as components of the fan assembly  20  and/or damper  30 ,  32  (or other damper) components, from water damage. For example, the entrainment ports  34  of the nozzle assembly  22  may include a tear-drop or leaf shape that includes a tapered bottom surface sloping downwardly from the inner surface of the nozzle assembly  22  to the outer surface of the nozzle assembly  22 , thereby enabling rain collected on the horizontal floor to drain through the entrainment ports  34  and into the external environment  16 . These and other features will be described in detail below. 
       FIG.  2    is a perspective view of an embodiment of the exhaust fan unit  10  of  FIG.  1   . As previously described, the exhaust fan unit  10  includes the mixing box  18  having the outdoor air inlet  31 , the fan assembly  20 , the nozzle assembly  22 , the entrainment ports  34 , and the wind band  24  including a flow path  40  and the outlet  38 . A longitudinal axis  41  is illustrated in  FIG.  2    extending axially from the wind band  24 . In the illustrated embodiment, the wind band  24  may axially overlap with the entrainment ports  34  along the longitudinal axis  41 . In other embodiments, the wind band  24  may not axially overlap with the entrainment ports  34  along the longitudinal axis  41 . 
       FIG.  3    is a perspective cross-sectional view of an embodiment of portions of the exhaust fan unit  10  of  FIG.  2   . As previously described, the exhaust fan unit  10  includes the mixing box  18 , the fan assembly  20 , the nozzle assembly  22 , the entrainment ports  34  of the nozzle assembly  22 , and the wind band  24  including a flow path  40  and the outlet  38 . As shown in  FIG.  3   , the nozzle assembly  22  includes an inner cavity  60  that may be exposed to environment  16  via the entrainment ports  34  of the nozzle assembly  22 . The inner cavity  60  may receive rain water or other liquids during certain conditions. A floor  61  may be included at a bottom of the inner cavity  60  to collect rain water thereon. The floor  62  may be adjacent to, or axially aligned with along the longitudinal axis  41 , a bottom surface  63  (e.g., an edge) of each entrainment port  34 . Thus, rain water may be drained from the floor  62  of the inner cavity  60  through the entrainment ports  34 . The floor  62  may be flat or curbed (e.g., bowl shaped). Further, the bottom surface  63  (e.g., edge) of each entrainment port may slope downwardly as the bottom surface  63  (e.g., edge) moves away from the floor  61 , thereby enabling rain or other water to be gravity fed out of the inner cavity  60 . 
       FIG.  4    is a front cross-sectional view of the portions of the exhaust fan unit of  FIG.  3   . Focusing on  FIG.  4   , the nozzle assembly  22  includes an inner wall  50 , an outer wall  52 , and an annulus  54  (e.g., outer flow path) defined between the inner wall  50  and the outer wall  52 . As previously described, the annulus  54  may receive a flow of exhaust fumes or mixed fluid (i.e., exhaust fumes and outside air), denoted be reference numeral  56 , from the fan assembly  20 . The inner wall  50  of the nozzle assembly  22  may taper, curve, or slope outwardly (i.e., away from the longitudinal axis 41) toward the outer wall  52 . That is, starting with an entry side  57  of the nozzle assembly  22  and moving toward an exit side  58  of the nozzle assembly  22 , the inner wall  50  of the nozzle assembly  22  may taper, curve, or slope outwardly toward the outer wall  52 . It should be noted that the exit side  58  is located closer to a distal end of the exhaust fan unit  10  than a base of the exhaust fan unit  10  (i.e., where the base of the exhaust fan unit  10  interfaces with the building or roof thereof). 
     In the illustrated embodiment, the inner wall  50  tapers outwardly non-linearly. In other embodiments, the inner wall  50  may include a linear taper. The shape of the inner surface of the inner wall  50  may form a frustoconical shape of the inner cavity  60 . The shape of the outer surface of the inner wall  50  may enable a restricted cross-sectional area of the annulus  54  (i.e., inner flow path) at the exit end  58  of the nozzle assembly  22  that causes acceleration of the exhaust fumes or mixed fluid through the annulus  54  and into the flow path  40  defined by the wind band  24 . 
     As previously described, the nozzle assembly  22  also includes the entrainment ports  34  fluidly coupling an inner cavity  60  defined radially inward from the inner wall  50  of the nozzle assembly  22 . The inner cavity  60  is fluidly separate from the annulus  54  by way of the inner wall  50 . As the exhaust fumes or mixed air are passed from the annulus  54  of the nozzle assembly  22  to the flow path  40  defined by the wind band  24 , a pressure drop may cause environmental air to pass through the entrainment ports  34  and into the inner cavity  60 . The environmental air passing through the entrainment ports  34  may be referred to as nozzle entrained air. The dual-tapered (e.g., leaf or tear-drop shape) of the entrainment ports  34  in the illustrated embodiment may improve an air flow of the nozzle entrained air therethrough. The environmental air (i.e., nozzle entrained air) may be drawn from the inner cavity  60 , through the exit side  58  of the nozzle assembly  22 , and into the flow path  40  defined by the wind band  24  via the above-described pressure drop. The environmental air (i.e., nozzle entrained air) may then mix with the fluid passed from the outer annulus  54  to the flow path  40  defined by the wind band  24 . 
     The wind band  24  may also draw environmental air through a gap between the wind band  24  and the outer wall  52  of the nozzle assembly  22 , referred to as the entrainment gap  36 . The environmental air drawn through the entrainment gap  36  may be referred to as wind band entrained air. The wind band entrained air may mix with the nozzle entrained air and the exhaust fumes or mixed fluid passed to the flow path  40  from the nozzle assembly  22 . 
       FIG.  5    is a schematic front cutaway view of an embodiment of the nozzle assembly  22  and the wind band  24  for use in the exhaust fan unit  10  of  FIG.  1   . In the illustrated embodiment, the outer wall  52  of the nozzle assembly  22  is partially cutaway.  FIG.  5    illustrates the fluid flow of environmental air (i.e., nozzle entrained air) through the entrainment ports  34  into the inner cavity  60 , the mixed air through the annulus  54 , and the environmental air (i.e., wind band entrained air) through the entrainment gap  36  defined between the wind band  24  and the nozzle assembly  22 . 
       FIG.  6    is a perspective view of an embodiment of the nozzle assembly  22  and the wind band  24  for use in the exhaust fan unit  10  of  FIG.  1   . As previously described, the entrainment ports  34  include a leaf or tear-drop shape that improves air flow performance and rain/water drainage from the inner cavity  60 . The entrainment ports  34  extend from the outer wall  52  of the nozzle assembly  22  toward the inner wall of the nozzle assembly  22 , and defined a flow path through which environmental air is drawn into the inner cavity  60 .  FIG.  7    is a cross-sectional perspective view of an embodiment of the nozzle assembly  22  and the wind band  24  of  FIG.  6   , and a portion of the fan assembly  20 . As shown in  FIG.  7   , the entrainment ports  34  include sloped bottom edges  63  that slope downwardly from the inner wall  50  toward the outer wall  52  (e.g., such that the surface  63  [or edge] includes a lower point relative to the longitudinal axis  41  at the outer wall  52  than at the inner wall  50 ). The floor  61  may then collect rain or other water and drain the rain or other water through the entrainment ports  34 .  FIG.  8    is a top-down cross-sectional view of an embodiment of the nozzle assembly  22  and the wind band  24  of  FIG.  6   , and a portion of the fan assembly  20  and the mixing box  18 .  FIGS.  9 ,  10 , and  11    illustrate the above-described entrainment ports  34  of the nozzle assembly  22 .  FIG.  8    also illustrates the entrainment ports  34  and the sloped bottom edges  63 . 
       FIG.  9    is a perspective view of an embodiment of the nozzle assembly  22  of  FIG.  6   .  FIG.  10    is a cross-sectional perspective view of an embodiment of the nozzle assembly  22  of  FIG.  9   .  FIG.  11    is a cross-sectional front view of an embodiment of the nozzle assembly  22  and the wind band  24  of  FIG.  9   .  FIGS.  9 - 11    illustrate various features of the nozzle assembly  22  in accordance with the present disclosure. For example,  FIG.  9    illustrates the entrainment ports  34  having the sloped bottom surface  63  (e.g., edge) configured to drain water from the floor  61  of the nozzle assembly  22 .  FIG.  10    illustrates the annulus  54  defined between the outer wall  52  of the nozzle assembly  22  and the inner wall  50  of the nozzle assembly  22 . The annulus  54  includes a restricted cross-sectional area toward the exit end  58  of the nozzle assembly  22 , as previously described. That is, the annulus  54  includes a larger width  67  adjacent the entry end  57  of the nozzle assembly  22  than a width  69  at the exit end  58  of the nozzle assembly  22 . Further,  FIG.  10    illustrates a juncture  70  between the sloped bottom surface  63  (e.g., edge) of the entrainment port  34  and the floor  61  of the nozzle assembly  22 . That is, in  FIG.  10   , the sloped bottom surface  63  (e.g., edge) extends from the floor  61  and toward the outer wall  52  of the nozzle assembly  22 . In other embodiments, the floor  61  may be disposed above the sloped bottom surface  63  (e.g., edge) or below the sloped bottom surface  63  (e.g., edge).  FIG.  11    illustrates the curvilinear nature of the inner wall  50  of the nozzle assembly  22 . For example, in  FIG.  11   , the inner wall  50  includes a non-linear curvature away from the longitudinal axis  41  working from the entry end  57  of the nozzle assembly  22  toward the exit end  58  of the nozzle assembly  22 . In other embodiments, the inner wall  50  may include a linear taper or may include a cylindrical surface. The illustrated curvature may improve air flow performance. In each of  FIGS.  9 - 11   , a flange  71  may extend radially outwardly from the outer wall  52  of the nozzle assembly  22 , and may be configured to couple to a component (e.g., fan assembly) of the exhaust fan unit. 
       FIG.  12    is schematic view of an embodiment of the entrainment port  34  for use in the exhaust fan unit of  FIG.  1   . The illustrated entrainment port  34  may be included in any of the preceding embodiments. As shown, the entrainment port may extend between the inner wall  50  of the nozzle assembly  22  and the outer wall  52  of the nozzle assembly  22 . The entrainment port  34  includes a bottom surface  63  (e.g., edge) that extends from the inner wall  50  to the outer wall  52 . In the illustrated embodiment, the bottom surface  63  (e.g., edge) extends from the floor  61  of the nozzle assembly  22 , where the floor  62  is disposed in the inner cavity  60  defined by the inner wall  50 . As previously described, the floor  61  may drain water or other liquids within the inner cavity  60  across the bottom surface  63  (e.g., edge) of the entrainment port  34  and into the environment  16 . The bottom surface  63  (e.g., edge) is sloped downwardly to gravity feed the water out of the inner cavity  60 . For example, as shown, the bottom surface  63  (e.g., edge) may include a higher axial position  80  adjacent the inner wall  50  than an axial position  82  of the bottom surface  63  (e.g., edge) adjacent the outer wall  52  (e.g., as measured along the longitudinal axis  41 . As shown, in some embodiments, the bottom surface  63  (e.g., edge) may extend directly from the floor  61 . In other embodiments, the floor  61  may include a different axial position. 
       FIG.  13    is a perspective view of an embodiment of the fan assembly  20  and the mixing box  18  for use in the exhaust fan unit  10  of  FIG.  1   .  FIG.  14    is a cross-sectional perspective view of an embodiment of the fan assembly  20  and the mixing box  18  of  FIG.  13   .  FIG.  15    is a perspective view of an embodiment of multiple of the above- described exhaust fan units  10  arranged in a ventilation system  100 . In  FIG.  13   , the outdoor air inlet  31  may be configured to enable outdoor air to enter the mixing box. The outdoor air inlet  31  may be equipped with a damper configured to open to enable flow of outdoor air and close to disable flow of outdoor air. In some embodiments, the damper may include intermediate settings that enable a particular amount of outdoor air flow. The mixing box  18  is shaped such that the outdoor air inlet  31  and the corresponding damper can be disposed on any of four sides  90 ,  91 ,  92 ,  93  of the mixing box  18 . This may enable versatile integration of the exhaust fan unit in the ventilation system  100 . For example, as shown in  FIG.  15   , the outdoor air inlets  31  of various exhaust fan units  10  may point in different directions. That is, the central exhaust fan unit  10  in the illustrated embodiment is directed away from the viewer, whereas the outer exhaust fan units  10  in the illustrated embodiment face the viewer. The versatility may improve air flow of environmental air into the various exhaust fan units  10  and improve efficiency of the system  100 . 
     In accordance with the present disclosure, an exhaust fan unit includes a nozzle assembly having an inner wall defining a cavity radially inward from the inner wall, and an outer wall that defines a flow annulus radially between the inner wall and the outer wall. Entrainment ports may also extend between the inner wall and the outer wall, defining a flow passage fluidly separate from the flow annulus and coupling the cavity of the nozzle assembly with a surrounding environment. The inner wall of the nozzle assembly, described above as defining the inner cavity of the nozzle assembly, may include a frustoconical shape. Further, the frustoconical shape may be defined by a diameter that increases non-linearly, meaning that the diameter of the inner wall of the nozzle may increase non-linearly along an axial direction of the nozzle assembly, from a bottom of the frustoconical shape upwardly. The outer wall of the nozzle assembly may include a cylindrical shape. One or both of these shapes may contribute to improved air flow performance of the exhaust fan unit. Further, the frustoconical shape may include a horizontal surface, such as a horizontal bottom surface, defining a floor of the inner cavity. The horizontal floor defining the inner cavity, and shape of the above-describe entrainment ports of the nozzle assembly, may contribute to improved rain drainage from the nozzle assembly, which improves air flow performance and protects electronic components, such as fan assembly components and/or damper components, from rain damage. For example, the entrainment ports of the nozzle assembly may include a tear-drop or leaf shape that includes a tapered bottom surface sloping downwardly from the inner surface of the nozzle assembly to the outer surface of the nozzle assembly, thereby enabling rain collected on the horizontal floor to drain through the entrainment ports and into the external environment. These and other features of the exhaust fan unit improves air flow performance of the exhaust fan unit, distribution of exhaust gas contents, rain drainage, and electronics protection. 
     While only certain features and embodiments have been illustrated and described, many modifications and changes may occur to those skilled in the art, such as variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, such as temperatures and pressures, mounting arrangements, use of materials, colors, orientations, and so forth, without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re- sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described, such as those unrelated to the presently contemplated best mode, or those unrelated to enablement. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.