Abstract:
In the specification and drawings a window fan control system and a method of controlling a fan unit are described and shown. The window fan control system may comprise an electronic controller, an indoor sensor responsive to at least one characteristic of interior air, and an outdoor sensor responsive to at least one characteristic of exterior air. The electronic controller may cause at least one fan of a window fan to be activated when the interior air meets certain criteria relative to a set point and the exterior air meets certain preselected criteria relative to the interior air. The method of controlling a fan unit may comprise the steps of measuring at least one characteristic of exterior air, measuring at least one characteristic of interior air, and activating an intake fan of the fan unit when the interior air meets certain criteria relative to a set point and the exterior air meets certain preselected criteria relative to the interior air.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     None. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     None. 
     REFERENCE TO SEQUENTIAL LISTING, ETC. 
     None. 
     BACKGROUND 
     1. Field of the Invention 
     This invention relates to a window fan control system and a method of controlling a fan unit. 
     2. Description of the Related Art 
     Prior art window fans are utilized to move stagnant air, cool internal building areas or rooms when air conditioning is not available. There are various known problems however, with prior art fan structures. First, as depicted in  FIG. 15 , prior art fans in many cases only pull air into a room and fail to exhaust air which causes poor circulation within the room and therefore hinders cooling. Alternatively, other fan systems pull air into a room and exhaust air in the same vertical plane or elevation. Therefore these fan systems fail to eliminate temperature stratification and reduce cooling effectiveness. 
     Another problem related to prior art fans is that fan units do no inhibit water passing through a housing and into a room when the fan is operated while a rain event is occurring. Consequently, during rain events, many window fans may not be operated without drawing water into the building. 
     Another problem with prior art window units is the limited control of fan operation. Most prior art units are manually operated, meaning a user must turn the fan on and off as desired. It would be desirable to use a window fan when specific outside air criteria are met, so that the air conditioning system in the building or home is not needed when the outside air is cool and of a saturation or humidity level which would be comfortable to an occupant of the building or room. 
     Additionally, the use of the dew point and humidity controls would allow for increased comfort and energy savings by limiting the use of air conditioning in the building or home. Such limited use of natural resources is desirable. 
     It would be desirable to create a window fan unit which overcomes these and other deficiencies in order to decrease energy consumption, more efficiently cool interior areas of a building, commercial, residential or other, and improve occupant comfort while ultimately saving money on cooling by using outside air where applicable. 
     SUMMARY 
     A control system for a window fan is disclosed. In some embodiments the window fan may have a fan for communicating air between an interior area having interior air and an exterior area having exterior air. In some embodiments the control system may include an electronic controller in electrical communication with the fan. The control system may also include a control panel having a user selectable set point input that is in electrical communication with the electronic controller and provides a user selected set point to the electronic controller. The control system may also include an indoor sensor located so as to be responsive to at least one characteristic of the interior air. The indoor sensor may be in electrical communication with the electronic controller and communicate the at least one characteristic of the interior air to the electronic controller. The control system may also include an outdoor sensor located so as to be responsive to at least one characteristic of the exterior air. The outdoor sensor may be in electrical communication with the electronic controller and communicate the at least one characteristic of the exterior air to the electronic controller. The window fan may be operable in an automatic mode, wherein in the automatic mode the electronic controller causes the fan to be activated when: the at least one characteristic of the interior air indicates a dry bulb temperature of the interior air is greater than the set point; the at least one characteristic of the exterior air indicates a dry bulb temperature of the exterior air is less than the dry bulb temperature of the interior air; and the at least one characteristic of the exterior air indicates a dew point of the exterior air is less than a dew point of the interior air as indicated by the at least one characteristic of the exterior air. 
     The fan of the control system may be driven at variable speeds. The speed of the fan may correspond to a differential between the set point and the indoor dry bulb temperature. The control system may further comprise a second fan, wherein the second fan is an exhaust fan for expelling the interior air into an exterior area and wherein the fan is an intake fan for drawing exterior air into an interior area, and wherein the speed of the second fan corresponds to a differential between the set point and the indoor dry bulb temperature. The control system fan and the second fan may be driven at low, medium, and high speeds. The electronic controller may cause the fan and the second fan to be operated at the low speed when the differential between the set point and the indoor dry bulb temperature is within a first range, the fan and the second fan to be operated at the medium speed when the differential between the set point and the indoor dry bulb temperature is within a second range greater than the first range, and the fan and the second fan to be operated at the high speed when the differential between the set point and the indoor dry bulb temperature is within a third range greater than the second range. The second fan may be disposed vertically above the fan when the window fan is installed. 
     A method of controlling a fan unit installable in an opening between an interior area and an exterior area is also disclosed. In some embodiments the fan unit may have an intake fan for drawing exterior air into a building interior. In some embodiments the method may include the steps of: providing an input device to allow a user to select a set point indicative of a minimum desired temperature of interior air; measuring at least one characteristic of the exterior air; measuring at least one characteristic of the interior air; and activating the intake fan when: the at least one characteristic of the interior air indicates a dry bulb temperature of the interior air is above the set point, the at least one characteristic of the exterior air indicates a dry bulb temperature of the exterior air is less than the dry bulb temperature of the interior air, and the at least one characteristic of the exterior air indicates a dew point of the exterior air is less than a dew point of the interior air as indicated by the at least one characteristic of the interior air. 
     In the method of controlling a fan unit at least one characteristic of the interior air may include an interior relative humidity measurement and at least one characteristic of the exterior air may include an exterior relative humidity measurement. In the method of controlling a fan unit the intake fan may be a variable speed fan and the step of activating the intake fan may further include determining a difference between the set point and the indoor dry bulb temperature and activating the intake fan at a first speed when the difference between the set point and the indoor dry bulb temperature is within a first range of numbers and activating the intake fan at a second speed greater than the first speed when the difference between the set point and the indoor dry bulb temperature is within a second range of numbers, wherein the second range of numbers contains numbers larger than the first range of numbers. The method may further comprise the step of deactivating the intake fan when the at least one characteristic of the interior air indicates a dry bulb temperature of the interior air is less than or equal to the set point. The method may further comprise the step of deactivating the intake fan when the at least one characteristic of the interior air indicates a dry bulb temperature of the interior air is less than the set point. 
     In the method the fan unit may be an air conditioning unit that includes a housing having an exterior side for positioning in the exterior area and an interior side for positioning in the interior area. The air conditioning unit may further include a compressor and the method may comprise the step of deactivating the compressor when: the at least one characteristic of the interior air indicates a dry bulb temperature of the interior air is above the set point, the at least one characteristic of the exterior air indicates a dry bulb temperature of the exterior air is less than the dry bulb temperature of the interior air, and the at least one characteristic of the exterior air indicates a dew point of the exterior air is less than a dew point of the interior air as indicated by the at least one characteristic of the interior air. 
     In some embodiments of the method of controlling a fan unit, the fan unit may have an intake fan for drawing exterior air through the fan unit into a building interior, an exhaust fan for expelling interior air through the fan unit into an exterior, and at least one louver assembly for selectively inhibiting airflow through the fan unit. In some embodiments the method may include the steps of: allowing a user to select a set point indicative of a minimum desired temperature of interior air; measuring at least one characteristic of the exterior air; measuring at least one characteristic of the interior air; activating the intake fan, activating the exhaust fan, and opening the at least one louver assembly to allow airflow through the fan unit when: the at least one characteristic of the interior air indicates a dry bulb temperature of the interior air is above the set point, the at least one characteristic of the exterior air indicates a dry bulb temperature of the exterior air is less than the dry bulb temperature of the interior air, and the at least one characteristic of the exterior air indicates a dew point of the exterior air is less than a dew point of the interior air as indicated by the at least one characteristic of the interior air. 
     In the method of controlling a fan unit the intake fan and the exhaust fan may be variable speed fans. In the method, the step of activating the intake fan and the exhaust fan may further include determining a difference between the set point and the indoor dry bulb temperature and activating the intake fan and the exhaust fan at a first speed when the difference between the set point and the indoor dry bulb temperature is within a first range of numbers and activating the intake fan and the exhaust fan at a second speed greater than the first speed when the difference between the set point and the indoor dry bulb temperature is within a second range of numbers, wherein the second range of numbers contains numbers larger than the first range of numbers. The method may further comprise the step of deactivating the intake fan, deactivating the exhaust fan, and closing the at least one louver when the at least one characteristic of the interior air indicate a dry bulb temperature of the interior air is less than the set point. The method may further comprise the step of deactivating the intake fan when the at least one characteristic of the interior air indicate a dry bulb temperature of the interior air is less than the set point. 
     In the method the fan unit may be an air conditioning unit that includes a housing having an exterior side for positioning in the exterior area and an interior side for positioning in the interior area. The air conditioning unit may further include a compressor and the method may further comprise the step of deactivating the compressor when: the at least one characteristic of the interior air indicates a dry bulb temperature of the interior air is above the set point, the at least one characteristic of the exterior air indicates a dry bulb temperature of the exterior air is less than the dry bulb temperature of the interior air, and the at least one characteristic of the exterior air indicates a dew point of the exterior air is less than a dew point of the interior air as indicated by the at least one characteristic of the interior air. 
     In the method the at least one characteristic of the interior air may include an interior relative humidity measurement and the at least one characteristic of the exterior air may include an exterior relative humidity measurement. The at least one characteristic of the interior air may include an interior dry bulb temperature measurement and the at least one characteristic of the exterior air may include an exterior dry bulb temperature measurement; an interior dew point may be calculated from the interior dry bulb temperature measurement and the interior relative humidity measurement; an exterior dew point may be calculated from the exterior dry bulb temperature measurement and the exterior relative humidity measurement; and the interior dew point may be compared to the exterior dew point to thereby determine if the dew point of the exterior air is less than the dew point of the interior air. The at least one characteristic of the interior air may include an interior dry bulb temperature measurement and the at least one characteristic of the exterior air may include an exterior dry bulb temperature measurement; an interior specific humidity level may be calculated from the interior dry bulb temperature measurement and the interior relative humidity measurement; an exterior specific humidity level may be calculated from the exterior dry bulb temperature measurement and the exterior relative humidity measurement; and the exterior specific humidity level may be compared to the specific humidity level to thereby indirectly determine if the dew point of the exterior air is less than the dew point of the interior air. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a window fan system positioned in a window sill for use; 
         FIG. 2  is a side schematic view of a room circulation pattern showing both intake into and exhaust from the room; 
         FIG. 3  is a rear perspective view of the window fan system with the housing structure removed; 
         FIG. 4  is a perspective view of the housing of the window fan system with much of the internal structure removed; 
         FIG. 5  is a partially sectioned perspective view of the window fan system; 
         FIG. 6  is a side section view of the window fan system; 
         FIG. 7  is a partially sectioned lower perspective view of the window fan system; 
         FIG. 8  is a front perspective view of the window fan unit with the housing structure removed; 
         FIG. 9  is a rear perspective of the room air exhaust and room air intake including linkage removed from the window fan system; 
         FIG. 10  is a second rear perspective view of the structure shown in  FIG. 9 ; 
         FIG. 11  is a perspective view of the linkage and louvers for the room air intake with the louvers in a first position; 
         FIG. 12  is a perspective view of the linkage and louvers for the room air intake in a second position; 
         FIG. 13  is a perspective view of the linkage and louvers for the outside air exhaust with the louvers in a first position; 
         FIG. 14  is a perspective view of the linkage and louvers for the outside air exhaust with the louvers in a second position; 
         FIG. 15  is a side schematic of a prior art window fan having limited air movement; 
         FIG. 16  is a top view of an embodiment of a control panel for use with the window fan system; 
         FIG. 17  is a schematic representation of an embodiment of a control system for a window fan system; 
         FIG. 18  is a flow diagram of an embodiment of the generalized logic of a control when a fan button of the window fan system is actuated by a user; 
         FIG. 19  is a flow diagram of an embodiment of the generalized logic of a control when a set point adjustment button of the window fan system is actuated by a user; and 
         FIG. 20  is a flow diagram of an embodiment of the generalized logic of a control when automatically operating the window fan system. 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. In addition, the terms “connected” and “coupled” and variations thereof are not restricted to physical or mechanical connections or couplings. 
     Furthermore, and as described in subsequent paragraphs, the specific mechanical configurations illustrated in the drawings are intended to exemplify embodiments of the invention and that other alternative mechanical configurations are possible. 
     Referring now to the drawings wherein like numerals indicate like elements throughout the several views that are shown in  FIGS. 1-20  various aspects of a window fan system. The window fan system inhibits rain passage through the housing and dispels the rain without the water content entering the interior area of the building. The window fan unit also comprises a damper or louver system to open and close vents to limit heat transfer through the system when the fans are turned off. Additionally, the fan unit has a ducting arrangement which pulls air into a room and exhausts air from the room to improve circulation and utilizes a fan arrangement to aid with the circulation. The fan system also utilizes a control system to utilize outside air having desirable characteristics which cools the room and may be also used with existing air conditioning, therefore decreasing the reliance on an air conditioning system, and saving energy and costs associated with air conditioning operation. 
     Referring now to  FIG. 1 , a perspective view of a window fan system  10  is depicted on a window sill and with a window sash (both shown in broken line) engaging an upper surface of the window fan system  10 . Positioned about the lower portion of the fan system  10  is a lower housing  12  which wraps around the front and sides of the fan system  10  and may be formed of metal, plastic or other resilient material and which has aesthetically pleasing qualities. A power cord  14  is shown extending from a side of the lower housing  12  and may extend to a power supply such as an in-wall power outlet (not shown). Adjacent to power cord  14  is a sill bracket  16  which allows for adjustable connection to the window sill wherein the window fan system  10  is positioned. Although a sash type window is depicted, it should be understood that use of the window fan system  10  may be used with slider type window which slides in a horizontal direction rather than a vertical direction. 
     Within the lower housing  12  is an outside air exhaust  18 . When outside air is entrained into the fan system  10  and passes through at least one fan within the window fan system  10 , the outside air is exhausted into the building or room through the outside air exhaust  18 . The outside air exhaust  18  is positioned on the lower area of the housing so that an upper intake  30  can remove hotter air from the room. The outside air exhaust  18  may be opened or closed to allow or inhibit airflow into the room or area being cooled. 
     Above the lower housing  12  is an upper housing  20  which may also be formed of metal, plastic or other resilient material like the lower housing  12  and may be matching. The upper and lower housings  20 ,  12  of the exemplary embodiment are depicted as separate housing pieces, however, such housing elements  12 ,  20  may be combined into a single one-piece housing. Additionally, the upper housing  20  comprises a control panel  22  having a display  24  and at least one control button  26 . Adjacent to the control panel  22  is a room exhaust intake  30 . The window fan system  10  also exhausts air from inside the building to outside in order to improve circulation within the room or building. Thus, cooler air comes into the building through the outside air exhaust  18  and hotter air is withdrawn from the room through the upper room exhaust intake  30 . With the room exhaust intake  30  on the upper surface of the window fan system  10 , the room exhaust intake  30  can better draw warm air from the room and move it outside. Conversely, the outside air exhaust  18  is at a lower position, as this air is cooler than the warmer air being exhausted by the room exhaust intake  30 . This configuration aids circulation since warm air rises and cooler air descends. 
     The surrounding window structure is shown in broken line to provide environmental understanding of how the window fan system  10  is placed in the window and when the sash is closed against the upper surface of the upper housing  20 . Positioned on the upper housing  20  is an adjustable sash bracket  28 . This bracket provides an adjustable width to fit various sizes of window sash. The bracket  28  also provides adjustability to compensate for the position the window fan  10  is inwardly or outwardly relative to the window sill beneath the system  10 . For example, some windows will require further positioning of the system  10  toward the interior of the building than other windows. The sash bracket  28  also aids to compensate for such adjustments. 
     Referring now to  FIG. 2 , a side schematic view of a room is depicted. A window fan system  10  is depicted in a sidewall of the room. A lower fan draws air into the room which circulates across the room, up an opposite wall, along the ceiling and down the wall in which the window fan unit  10  is positioned. Additionally, it will be understood that the air moving into the room may move along the walls toward the window fan system  10 . As the air moves along the walls toward the system  10 , any rising temperature of the air will cause the air to rise nearer the fan system  10 . A second upper fan draws air from within the room and out to atmosphere. As previously indicated, the upper fan is utilized to draw air from the room since warmer air will be higher in the room. In comparison with  FIG. 15 , one of skill in the art will recognize that where the prior art device fails by not removing air from the interior, the instant embodiment removes warmer air increasing circulation, which ultimately aids in cooling the room. The vertical circulation pattern created by the fan system  10  eliminates temperature stratification of prior art devices with air intake and air exhaust both in the same vertical elevation 
     Referring now to  FIG. 3 , a rear perspective view of the window fan system  10  is depicted. The rear side of the window fan system  10  is positioned on the outside of the building being cooled both drawing air into the room and exhausting air out of the room. With the upper housing  20 , the lower housing  12  and the rear louver  32  all removed, a frame  40  is revealed. The frame  40  comprises a first side member  41  and a second opposed side member  43 . Both the first side member  41  and the second side member  43  are vertical members and substantially parallel to one another in the exemplary embodiment although such design should not be considered limiting. Along the upper side of the frame  40  and connecting the first side member and second side member  41 , 43  is an upper frame member  42 . The upper frame member  42  is substantially horizontal and opposite to an opening  44  which is defined by a first strut  45  and an opposed second strut  46 . Around the mid-portion of the frame  40 , in a vertical direction is a partition  38  which separates the upper exhaust portion  50  from the lower intake portion  52  of the window fan system  10 . On the upper side of the fan partition  38 , is an upper fan housing  54 . Beneath the partition  38  in the lower intake portion  52  is a lower fan housing  56 . Each of the housings  54 ,  56  may be formed of one or more housing portions which are connected in various manners or alternatively may be formed integrally. 
     Referring now to  FIG. 4 , a perspective view of a window fan system  10  is depicted with the internal components of the system  10  removed. Through the openings of the upper housing  20 , the rear louver  32  may be seen which is positioned on the outwardly facing side of the window fan system  10 . The rear louver  32  covers the upper exhaust portion  50  and the lower intake portion  52  ( FIG. 3 ). These portions  50 , 52  are separated by the partition  38  ( FIG. 2 ) so as to create two separate air pathways. The lower intake portion  52  pulls outside air into the system  10  directs the air into the building or home through the outside air exhaust  18 . The upper exhaust portion  50  pulls air from the room or building interior through the room exhaust intake  30  and directs this warmer air out of the upper half of the rear louver  32 . 
     Within the lower area of the system  10 , a dam  60  may be seen adjacent the rear louver  32 . The dam  60  is located generally between the first and second struts  45 ,  46  ( FIG. 2 ). The dam  60  may be separately formed and positioned between the struts  45 , 46  or, alternatively the dam  60  may be integrally formed with lower housing portion  12 , frame  40 , or other portions of the fan system  10 . In either formation, the dam  60  inhibits water passage through the fan system  10 . Water passing through the lower portion of rear louver  32  encounters the dam  60  as it moves into or toward the lower intake portion  52 . The dam inhibits the water droplet from passing though the housing and into the room. The dam  60  performs this function by creating a reservoir for water droplets which fall out of the airstream being pulled into the housing. In other words, the dam  60  effectuates removal from the entrained water droplets from the airflow. Afterward, the fallen water droplets are gravity fed to a well  62  ( FIG. 6 ) where the water may drain through the housing and out of the system  10  and may be aided by the lower fan at the bottom of the fan blade. 
     Referring now to  FIGS. 5 and 6 , a partially sectioned rear perspective view and side sectioned view of the window fan unit  10  are depicted. The rear louver  32  comprises a plurality of vertical fins  32   a  and a plurality of horizontally extending fins  32   b . The horizontally extending fins  32   b  are tilted at an angle which slopes downward from the inside of the system  10  to the outside. The fins  32   a ,  32   b  are fixed and are sloped in order to deflect rain which might otherwise be pulled into the lower half of the louver  32  and into the lower intake portion  52 . According to the exemplary embodiment, the slope of the horizontal fins is 5%, although such slope should not be considered limiting as other slopes may be utilized. Additionally, an aspect ratio of the rear louver  32  is defined as being about two-to-one (2:1). The term aspect ratio means that, as measured between vertical fins  32   a , the width of the horizontal fin  32   b  is twice the vertical distance between louvers. Again this aspect ratio is merely exemplary, as other ratios may be utilized. The illustrative aspect ratio is utilized also for its ability to deflect rain which may be entrained near the lower intake portion  52  of the louver  32 . 
     From this view, one skilled in the art will realize that the upper exhaust portion  50  ( FIG. 2 ) which blows air outwardly through the upper portion of the louver  32  also aids to clear the airspace immediately above the lower intake portion  52  ( FIG. 2 ) of louver  32  of rain and other contaminants which may be otherwise pulled into the lower intake portion  52  by the lower fan. For purpose of this description, the term contaminants should be understood to mean rain, snow or other weather elements in addition to other elements which may be found in the outside air. Thus, the present embodiment utilizes a louver  32  having fin characteristics which aid to inhibit rain from entering the window fan system  10 . The arrangement of an upper fan system  80  blowing outwardly and a lower fan  74  pulling air inwardly aids to blow rain away from the lower portion of louver  32  inhibiting rainwater from entering the window fan system  10  during use. Additionally, any rainwater which passes through the rear louver  32  may be impinged on the dam  60  adjacent the lower intake fan  74  or alternatively slowed by the dam  60  causing the water to fall or drain into the well  62 . 
     As shown near the bottom of the window fan system  10 , and between the first and second struts  45 , 46 , the dam  60  has an upper surface  61  which generally slopes from an upper point closer to fan  74  to a lower point near the louver  32 . The dam  60  receives some water which passes through the louver  32 . Typically, the flow path of the water may be interrupted by the louvers  32  and this disruption in velocity causes the water droplets to fall onto the upper surface onto the dam  60 . The slope of dam  60 , in combination with gravity, causes water to drain down this dam slope into a well  62  ( FIG. 6 ). 
     Moving away from the louver  32 , beyond the dam  60 , an intake fan assembly  70  is depicted. The fan assembly  70  includes a motor  72  which may be a 120 Volt motor having a high speed of approximately 1425 RPM, a medium speed of approximately 1322 RPM, and a low speed of approximately 1184 RPM. Connected to the fan motor  72  is a blower or fan  74 . The blower or fan  74  may be a centripetal fan which draws air into the top portion beneath the partition  38 . Alternatively, various types of fans may be used, for example centrifugal, tangential or cross-flow fans. The blower  74  is generally cylindrical in shape having a plurality of horizontal fins which may be slightly curved and connected by a plurality of axially aligned ribs. The blower  74  is operably connected to the fan motor  72  and spins about a central axis with the motor  72 . In the views shown in  FIGS. 5 and 6 , the motor  72  rotates in a substantially counterclockwise direction which pulls air inwardly through the lower portion of louver  32  and moves the air upwardly through the blower housing  56  and expels the accelerated air through the room air exhaust  18 . The blower housing  56  is connected to the partition  38  which separates the lower intake portion  52  ( FIG. 2 ) from the upper exhaust portion  50  ( FIG. 2 ). 
     Still referring to  FIGS. 5 ,  6  and  7 , the partition  38  includes a sloped portion closest to the rear louver  32 . The sloped portion of the partition  38  also utilizes gravity to remove any water which may gather in this area of the fan and drains this water to the dam  60  or the well  62 . At the downhill side of the dam  60  is a well  62 . The function of the well  62  is to receive water which runs off the slope surface of the dam  60  and remove the water from the fan system  10 . A plurality of apertures  64  are seen at a lower surface of the window fan unit  10 . These apertures  64  function as drain holes and are located generally in the bottom of the well  62 . A plurality of ribs  66  are positioned on the lower surface of the dam  60  which eliminates the need to make a solid dam  60  and saves weight while strengthening the part. As previously described the dam  60  may be separately formed or integrally formed with the housing  12 , frame  40 , or other parts. 
     Above the partition  38 , an upper exhaust fan assembly  80  is positioned. Similar to the lower fan assembly  70 , the upper exhaust fan assembly  80  comprises a fan motor  82  and a centripetal fan or blower  84 . The upper fan assembly  80  removes air from the building interior through the room exhaust intake  30 , through the blower  74  and out to atmosphere through the upper portion of the rear louver  32 . 
     Referring now to  FIG. 8 , the window fan unit  10  is depicted with the lower housing  12  and upper housing  20  removed. Extending from the frame  40  is a room exhaust intake  30  having a plurality of louvers  34  which are pivotally positioned within a louver frame  36 . The louver frame  36  functions as a duct through which air passes from the room, through the room exhaust intake  30 , louvers  34  and into the upper fan assembly  80 . Beneath the louver frame  36  is the upper fan cowling  56  which is curved to proximate the curvature of the blower  84  and includes a plurality of stiffening ribs along the outer surface thereof. 
     Beneath the room exhaust intake  30 , is the outside air exhaust  18 , which also comprises a louver housing  90  and a plurality of pivotable louvers  92 . The louver housing  90  also functions as a duct adjacent to the lower fan assembly  70  and allows air passage through the outside air exhaust  18  into the room or building where the window fan unit  10  is positioned. 
     Referring now to  FIG. 9 , a perspective view of the room exhaust intake  30  and the outside air exhaust  18  is shown in a rear perspective view through which air passes from a building interior to the outside of the building. The upper louver frame  36  includes a plurality of louvers  34  positioned therein. The louvers  34  may be pivoted open to allow air flow when the system  10  is in operation. Alternatively, when the window system  10  is not operating, the louvers  34  may be closed to inhibit flow of air from the interior of the room to the outside or vice versa depending on the temperature difference between the outside ambient air and the inside air temperature. The louver frame  36  includes a plurality of moldings and fastening apertures for connection to the frame  40  ( FIG. 7 ) or other components of the system  10 . 
     Beneath the room exhaust intake  30  is the outside air exhaust  18 . The louver housing  90  defines a duct area through which air passes from the fan system  80  to the room interior. Within the lower housing  90  are a plurality of pivotally connected louvers  92  which also open and close depending on the state of the window fan system  10 . The lower housing  90  also includes a plurality of moldings and apertures for connecting the lower housing  90  to the frame  40  or adjacent structure. As best seen in  FIG. 8 , positioned about the front area of the housings  36 ,  90  and louvers  34 ,  92  are trim elements which define portions of the outer housings  12 ,  20 . 
     The louvers  34 , 92  may, according to one embodiment, move independently of one another. Alternatively, in the exemplary embodiment depicted, and described hereinafter, a linkage system  100  is utilized to open and close the louvers  34 , 92  simultaneously. The linkage system  100  comprises an actuated motor  102 . An actuator arm  104  is operably connected to the motor with a pivot point  106  and first and second linkage connections  108 , 109 . 
     Referring now to  FIG. 10 , a perspective view of the linkage system  100  is depicted. Connected to the arm  104  at pivot point  109  ( FIG. 9 ) is a lower linkage  110 . The lower linkage  110  connects to a lower louver pivot mechanism  112 . This mechanism  112  includes at least one arm  114 , connected to lower linkage  110 . The upper linkage  120  extends to an upper pivot mechanism  122  having an arm  124 . Both arms  114 , 124  pivot to move the corresponding louvers  92 , 34 . 
     Referring now to  FIGS. 11 and 12 , perspective views of the pivot mechanism  122  are depicted with the louvers  34  in first and second positions. Arm  124  is generally v-shaped and pivotally connected to the louver frame  36 . A slide member  126  is connected to the arm  124  and slides along a surface of the louver frame  136  as the arm  124  rotates with movement of linkage arm  120 . Each of the louvers  34  are operably connected to the slide  126  so that movement of the arm  124  causes movement of the slide  126 , and therefore movement of the louvers  34 . In sum, according to the exemplary embodiment, the actuator motor  102  pivots each of the louvers  34  with a single motion via the arm  124  and slide member  126 . As shown in  FIG. 11 , the louvers  34  are in an open position. As the arm  124  is rotated and the slide member  126  moves, the louvers  34  rotate to a closed position. 
     Referring now to  FIGS. 13 and 14 , perspective views of the lower pivot mechanism  112  are depicted with the louvers in first and second positions. Depending from the actuator motor  102  is the lower linkage  110  which engages an arm  134 . Extending from the lower housing  90  is a pivot structure about which the arm  134  rotates. Also connected to the arm  134  is a lower slide member  136 . The plurality of louvers  92  are each pivotally connected to the slide member  136  so that rotation of the arm  134  causes pivotal movement, opening or closing, of the louvers  92 . 
     Referring now to  FIG. 16 , a top view of a second embodiment of a control panel  122  is depicted. Both control panels  22 ,  122  may be in electronic communication with the fan systems  70 ,  80  as well as linkage system  100  for controlling the window fan system  10 . Control panel  122  may be located, for example, in a similar location as control panel  22  on window fan system  10 . Control panel  122  includes a display  124  that provides an area for displaying a current dry bulb temperature of the room or interior air and an area for displaying the current set point temperature that has been selected by a user. A power push button  126   a  is provided to enable a user to selectively power window fan system  10  and a fan push button  126   b  is provided to enable a user to cause lower fan  74  and upper fan  84  to be set to a low, medium, high, or automatic setting. AUTO LED  125   a , HIGH LED  125   b , MED LED  125   c , and LOW LED  125   d  are selectively illuminated to convey to a user which setting is selected for lower fan  74  and upper fan  84 . Similarly, ON LED  125   e  is illuminated when the window fan system  10  is powered on to convey to a user that it is powered. A set point “+” button  126   c  and a set point “−” button  126   d  are provided to enable a user to increment the set point upwardly or downwardly, respectively. The area of display  124  for displaying the current set point temperature conveys to a user the currently selected set point. 
     Referring now to  FIG. 17 , a schematic representation of an embodiment of a control system for a window fan is depicted. Power button  126   a , fan button  126   b , set point “+” button  126   c , and set point “−” button  126   d  of control panel  122  are in selective electrical communication with controller  210 , causing one or more signals to be sent to controller  210  when they are actuated. Controller  210  is also in electrical communication with AUTO LED  125   a , HIGH LED  125   b , MED LED  125   c , LOW LED  125   d , and ON LED  125   e  of control panel  122  and is programmed to selectively illuminate the LEDs based on input received from a user via power button  126   a , fan button  126   b , set point “+” button  126   c , and/or set point “−” button  126   d . Outdoor sensor  96  and indoor sensor  98  are also in electrical communication with controller  210  and may communicate one or more signals to controller  210  that are indicative of one or more characteristics of exterior air and interior air, respectively. Such characteristics include, without limitation, dry bulb temperature, wet bulb temperature, absolute humidity, specific humidity, relative humidity, pressure, and/or dew point temperature. Controller  210  is also in electrical communication with relays  214  for lower fan motor  72  and upper fan motor  82  and drivers  218  for actuated motor  102 . The relays  214  are in electrical communication with lower fan motor  72  and upper fan motor  82  and can be selectively activated to cause lower fan motor  72  and upper fan motor  82  to be driven at a desired speed of a plurality of speeds. In some embodiments three relays are provided and may be selectively activated to drive lower fan motor  72  and upper fan motor  82  at either a low, medium, or high speed. The drivers  218  are in electrical communication with actuated motor  102  and may be selectively activated to accurately control actuated motor  102  and, resultantly, louvers  34  and  92 . In some embodiments four driver channels may be provided in electrical communication with actuated motor  102  and may be selectively activated to provide full stepping or half stepping of the actuated motor  102 . 
     In some embodiments Power button  126   a , fan button  126   b , set point “+” button  126   c  and set point “−” button  126   d  may be membrane type buttons that engage a corresponding switch on a circuit board adjacent the control panel  122  when actuated. The circuit board may also include the controller  210 , AUTO LED  125   a , HIGH LED  125   b , MED LED  125   c , LOW LED  125   d , ON LED  125   e , display  124 , relays  214  for lower fan motor  72  and upper fan motor  82 , and/or drivers  218  for the actuated motor  102 . The control may be a PIC microcontroller model number PIC 18LF4331-1/PT, the actuator motor  102  may be a PM Step Motor 24BYJ model manufactured by Best Electronics Industrials Co., Ltd., and outdoor sensor  96  and indoor sensor  98  may be Relative Humidity and Temperature Modules HTG3500 Series manufactured by Measurement Specialties. Referring briefly to  FIGS. 5-7 , outdoor sensor  96  may be located just inside louver  32  near the base of louver  32  and strut  45 . The outdoor sensor  96  is located near lower intake portion  52  so as to be appropriately exposed to exterior air. Referring briefly to  FIG. 8  where a portion of control panel  22  is shown cut away, and to  FIGS. 5 and 6 , indoor sensor  98  may be located on a circuit board  205  adjacent the control panel  22  in a position so as to be exposed to the interior air and be relatively unaffected by any heat generated by other components attached to the circuit board  205 . In  FIGS. 1 and 5  apertures  23  are shown that extend through control panel  22  to enable indoor sensor  98  to be appropriately exposed to indoor air. Outdoor sensor  96  and indoor sensor  98  may be located elsewhere on window fan system  10  or may be located remote from window fan system  10 , so long as they are located to be responsive to one or more characteristics of the exterior air and interior air, respectively. Outdoor sensor  96  and indoor sensor  98  may be in wired or wireless electronic communication with electronic controller  210 . 
     Referring now to  FIG. 18 , a flow diagram shows an embodiment of the generalized logic of controller  210  when fan button  126   b  is actuated by a user. If it is the first time fan button  126   b  has been pressed, the controller  210  causes AUTO LED  125   a  to be illuminated and controller  210  automatically operates the window fan system  10 . An embodiment of the automatic operation of the window fan system is shown in detail in  FIG. 20  and described in detail hereinafter. If it is the second time fan button  126   b  has been pressed, the controller  210  causes HIGH LED  125   b  to be illuminated, communicates with relays  214  to cause them to all be activated, causing lower fan motor  72  and upper fan motor  82  to operate at a high speed. Controller  210  also communicates with drivers  218  to ensure actuated motor  102  is appropriately stepped to place louvers  34  and  92  in an open position to allow airflow through window fan system  10 . If it is the third time fan button  126   b  has been pressed, the controller  210  causes MED LED  125   c  to be illuminated, communicates with relays  214  to cause two relays to be activated, causing lower fan motor  72  and upper fan motor  82  to operate at a medium speed. Controller  210  also communicates with drivers  218  to ensure actuated motor  102  is appropriately stepped to place louvers  34  and  92  in an open position to allow airflow through window fan system  10 . If it is the fourth time fan button  126   b  has been pressed, the controller  210  causes LOW LED  125   d  to be illuminated, communicates with relays  214  to cause a single relay to be activated, causing lower fan motor  72  and upper fan motor  82  to operate at a low speed. Controller  210  also communicates with drivers  218  to ensure actuator motor  102  is appropriately stepped to place louvers  34  and  92  in an open position to allow airflow through window fan system  10 . 
     Referring now to  FIG. 19 , a flow diagram shows an embodiment of the generalized logic of controller  210  when set point “+” button  126   c  is actuated by a user and when set point “−” button  126   d  is actuated by a user. If the set point “+” button  126   c  is actuated controller  210  increments the currently stored set point up by one degree. The controller  210  also causes the area of display  124  that displays the current set point temperature to be updated to reflect the current set point temperature selected. If the set point “−” button  126   d  is actuated controller  210  increments the currently stored set point down by one degree. The controller  210  also causes the area of display  124  that displays the current set point temperature to be updated to reflect the current set point temperature selected. In alternative embodiments increments smaller or larger than one degree may be used. 
     Referring now to  FIG. 20 , a flow diagram shows an embodiment of the generalized logic of controller  210  automatically operating the window fan system  10 . In the flow diagram of  FIG. 20  interior dry bulb temperature (I. D. B.), exterior dry bulb temperature (E. D. B.), interior dew point (I. D. P), and exterior dew point (E.D.P.) are analyzed by controller  210 . In some embodiments indoor sensor  98  and outdoor sensor  96  supply signals to controller  210  that are indicative of measured interior and exterior dry bulb temperatures and relative humidity levels and controller  210  calculates an interior and exterior dew point that correspond to the measured interior and exterior dry bulb temperatures and relative humidity levels. In some embodiments controller  210  could calculate dew points by referencing a table, such as a table containing dry bulb temperatures, relative humidity levels, and dew point temperatures to determine a dew point temperature that corresponds to the measured dry bulb temperature and relative humidity level. In some embodiments controller  210  could calculate dew points by using one or more formulas. For example, the dew point could be calculated using the formula: Dew Point Temperature=[(17.271*Dry Bulb Temperature)/(237.7+Dry Bulb Temperature)]+ln(Relative Humidity/100), where the temperatures are in degrees Celsius and “ln” refers to the natural logarithm. 
     In other embodiments indoor sensor  98  and outdoor sensor  96  could measure alternative or additional characteristics of the interior and exterior air and supply signals to controller  210  indicative of such characteristics. Such characteristics include, without limitation, dry bulb temperature, wet bulb temperature, absolute humidity, specific humidity, relative humidity, pressure, and/or dew point temperature. Controller  210  could then use these alternative or additional characteristics to compare, either directly or indirectly, exterior and interior dry bulb temperatures and exterior and interior dew points for use in the automatic operation of the window fan system  10 . For example, instead of measuring interior and exterior relative humidity, determining the interior and exterior dew point from the relative humidity measurements, and directly comparing the interior and exterior dew point, interior and exterior relative humidity could be measured, interior and exterior specific relative humidity determined from the relative humidity measurements, and interior and exterior specific relative humidity directly compared. Comparison of the exterior specific humidity and interior specific humidity may indirectly indicate the exterior dew point is less than the interior dew point. For example, if the exterior specific humidity is less than the interior specific humidity it may indirectly indicate that the exterior dew point is less than the interior dew point. Other characteristics of exterior and/or interior air may be measured and analyzed to directly or indirectly determine if the exterior dew point is less than an interior dew point. Temperatures can be set, measured, calculated, and/or displayed in Celsius and/or Fahrenheit as desired. 
     If automatic operation of the window fan system  10  has been chosen by a user, at step  252  controller  210  determines if the interior dry bulb temperature as indicated by indoor sensor  98  is greater than the current set point temperature plus one degree. Comparing the interior dry bulb temperature to the current set point temperature plus one degree at this point in the flow diagram prevents excessive cycling of the lower fan motor  72  and upper fan motor  82 . If at step  252  the interior dry bulb temperature is determined to be greater than the current set point temperature plus one degree, at step  254  controller  210  determines if the interior dry bulb temperature is greater than the current set point. If the interior dry bulb temperature is greater than the current set point, at step  256  controller  210  determines if the exterior dry bulb temperature is less than the interior dry bulb temperature. If the exterior dry bulb temperature is less than the interior dry bulb temperature, at step  258  controller  210  determines if the exterior dew point minus five tenths is less than the interior dew point. If so, at step  260  then the controller  210  turns the motor flag on and opens louvers  34  and  92 . 
     The controller  210  then determines at step  262  if the difference between the interior dry bulb temperature and the current set point temperature (ΔD.B.) is less than or equal to two. If so, at step  266  the controller  210  activates the necessary relays to drive the lower fan motor  72  and upper fan motor  82  at low speed. If the difference between the interior dry bulb temperature and the current set point temperature is not less than or equal to two, the controller  210  determines at step  264  if the difference between the interior dry bulb temperature and the current set point temperature is greater than two and less than or equal to three. If so, at step  268  the controller  210  activates the necessary relays to drive the lower fan motor  72  and upper fan motor  82  at medium speed. If the difference between the interior dry bulb temperature and the current set point temperature is not greater than two and less than or equal to three, then at step  270  the controller  210  activates the necessary relays to drive the lower fan motor  72  and upper fan motor  82  at high speed. 
     Once the controller  210  has activated the necessary controls to drive the lower fan motor  72  and upper fan motor  82  at low speed in step  266 , medium speed in step  268 , or high speed in step  270 , a two minute countdown timer is started in step  274 . After the two minute timer is completed the controller  210  checks to see if the motor flag is on in step  276  (the motor flag will be on if the conditions of steps  254 ,  256 , and  258  were met in the previous loop). If the motor flag is on then controller  210  will proceed to determine if the conditions of steps  254 ,  256 , and  258  continue to be met. If the conditions of steps  254 ,  256 , and  258  are met, controller  210  will again check the difference between the interior dry bulb temperature and the current set point temperature at steps  262  and  264  to determine if the speed at which the lower fan motor  72  and upper fan motor  82  are being driven needs to be adjusted. If the conditions of steps  254 ,  256 , or  258  are not met than at step  272  the motor flag will be turned off if it is on, lower fan motor  72  and upper fan motor  82  will also be turned off, and then the two minute timer of step  274  executed. Following execution of the two minute timer, the process will proceed to step  252  (since the motor flag is no longer on) to determine if the indoor dry bulb temperature is greater than the current set point temperature plus one degree. If the interior dry bulb temperature is not greater than the current set point temperature plus one degree, controller  210  again executes a two minute timer at step  274  and after the timer has run again proceeds to step  252  to determine if the indoor dry bulb temperature is greater than the current set point plus one degree. 
     Automatic operation of the window fan system  10  will continue until a user chooses a different fan setting through actuation of fan button  126   b  or powers the window fan system down through actuation of power button  126   a . Automatic operation of the window fan system  10  brings exterior air into an interior area and exhausts interior air to an exterior area when doing so would be advantageous in cooling the interior area as desired by a user. Automatic operation of the window fan system  10  may result in energy savings without requiring consistent monitoring by a user and without the need to sync the window fan system  10  with an air conditioner or other device. 
     The methods and control systems described herein, as well as variations thereof, may be implemented in an air conditioning unit that includes a compressor and one or more fans that draw exterior air into an interior area. Such an air conditioning unit may also include one or more fans that exhaust interior air to an exterior area. The compressor of the air conditioning unit may be selectively deactivated when bringing exterior air into an interior area and/or exhausting interior air to an exterior area would be advantageous in cooling the interior area. For example, a hotel room air conditioning unit or a window room air conditioner unit may be installed in a wall or window and extend between a room and the outside. The air conditioning unit may include an interior sensor that monitors one or more characteristics of the air in the hotel room and an outside sensor that monitors one or more characteristics of the outside air. The air conditioning unit may include a fan that draws air from the outside and into the hotel room. Such a fan may be the same as, or distinct from, a primary air conditioning fan that blows air into the hotel room that has first been cooled through an evaporator or other device. The air conditioning unit may be programmed to utilize the compressor to cool air being blown from the air conditioning unit into a room interior when the desired set point is less than the current room interior temperature and bringing exterior air into the room interior would not be advantageous in cooling the interior area. The hotel room air conditioning unit may further be programmed to deactivate the compressor and provide exterior air into the room interior when the desired cooling temperature is less than the current room interior temperature and bringing exterior air into the room interior would be advantageous in cooling the interior area. 
     The foregoing description of structures and methods has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise steps and/or forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.