Patent Publication Number: US-7722449-B2

Title: Air channel grill for security institutions

Description:
RELATED APPLICATION 
   This application claims the benefit of priority of U.S. provisional application Ser. No. 60/620,530, filed Oct. 20, 2004, which is relied on and incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates generally to an improved air channel grill for security institutions. More particularly, the present invention relates to an air channel grill having design features that improve air delivery performance and efficiency without compromising the security requirements of the air grills for security institutions. 
   BACKGROUND OF THE INVENTION 
   The term “air grill” is used in reference to gratings used to cover openings in the ventilation system for the purpose of supplying or exhausting air to or from a given space. 
   The term “security institution” is used in reference to correctional facilities, penal facilities, mental health facilities and/or any other type of facility where the persons under the care of such facility are purposely and/or lawfully isolated from the public. 
   Air grills used in security applications must perform above and beyond the standard inlet/outlet air grills. Specifically, such a security grill must be incapable of being disassembled to create weapons or tools, the security grill must restrict access to the ductwork beyond the grill to prevent storage of contraband material, the security grill must prevent escape or entry into the ductwork, and the security grill must virtually eliminate the occupant&#39;s ability to thread items into the air channels or passages of the diffuser for the purpose of suicide attempts. 
   Conventional security grills for security institutions that meet the above mentioned requirements generally comprise a body having two opposed faces, where at least one passage extends through the body between the opposed faces creating an air channel. The passageway (air channel) has at least one change in direction creating a so-called “zigzag pattern.”  FIG. 1  illustrates such a conventional security grill. 
   The prior art security grill shown in  FIG. 1  consists of a body  10  having two opposed faces  11  and  12 , and a number of channels  13  extending through the body between the opposed faces. Each channel  13  has at least one change in direction defining a zigzag pattern. The zigzag pattern of each channel forms segments S 1 , S 2 , S 3 , and S 4  which have a rectangular cross-sectional shape. The problem with conventional security grill designs is the notion that very little can be done to improve the air delivery performance and efficiency of the security grill without compromising the requirements of the air grills for security institutions as stated above. 
   What is required is an air grill for security institutions that would provide the security institutions with a more efficient and cost effective method of ventilating space without compromising the safety of the occupants. 
   SUMMARY OF THE INVENTION 
   According to the present invention, an air grill for security institutions comprises two opposing faces, with passages or channels extending between the faces in a zigzag course. The channels are elongated zigzag slots consisting of segments. The zigzag slots formed by the segments have a rectangular cross-sectional shape. The channels are defined by slats that are bent at least twice in alternating directions. 
   The first segment of each zigzag channel adjacent the air outlet has a smaller cross-sectional width than any of the other segments. This is done in order to limit the size of the slot at the air outlet, and therefore restrict the size and shape of the objects that could be possibly inserted in the slot. The following segments of each zigzag channel have at least one segment with an enlarged cross-sectional width. Increasing the cross-sectional width of at least one segment creates an area through which the air can move more freely, therefore reducing static pressure drop across that segment. Because the grill for security institutions can be comprised of more than one segment with an enlarged cross-sectional width, even more significant reductions in static pressure drop can be realized. Any reduction in static pressure drop across the entire grill improves efficiency of the ventilation system and therefore can reduce annual operating costs for ventilating systems in security institutions. 
   The slats are bent at certain angles which are larger than those of conventional security grills. Increasing the angle at which the slats are bent reduces the build-up of air molecules as they change direction while traveling through the zigzag channels. Therefore the static pressure drop across the security grill is reduced and the efficiency of the ventilation system is improved. 
   Corners are created along each slat as a result of bending the slats in alternating directions. In accordance with the present invention, the corners are rounded. By eliminating the sharp corner which exists in conventional security grill designs, the build-up of air molecules that travel through the channels is reduced and the efficiency of the system is improved. 
   Therefore, it is an object of the present invention to provide a security grill with zigzag channels having the segment of each channel adjacent the outlet with reduced cross-sectional area compared to segments upstream from the outlet. 
   Another object of the present invention is to provide a security grill with slats that are bent at larger angles to improve air flow through the zigzag channels. 
   Yet another object of the present invention is to provide a security grill where the corners created along the slats are rounded to improve air flow through the zigzag channels. 
   Further objects, features and advantages will become apparent upon consideration of the following detailed description of the invention when taken in conjunction with the drawings and the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional perspective view of the prior art security grill. 
       FIG. 2  is a cross-sectional perspective view of a security grill in accordance with the present invention. 
       FIG. 3  is a cross-sectional side view of a security grill in accordance with the present invention. 
       FIG. 4  is a side view of a slat for a security grill in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With reference to  FIGS. 2 and 3 , a security grill  20  in accordance with the present invention is illustrated. The grill  20  comprises two opposing faces  21  and  22 . The first face  21  comprises an air outlet, and the second face  22  comprises an air inlet. Multiple channels  23  extending from a point adjacent the first face  21  toward the second face  22  have at least two changes in direction forming a zigzag pattern. The channels  23  are elongated zigzag slots consisting of segments  24 ,  25 ,  26 , and, in the described embodiment the channels have three changes in direction. The slots formed by the segments  24 ,  25 ,  26 , and  27  have a rectangular cross-sectional shape. Multiple slats  30  are used to define the zigzag channels  23 . Each slat  30  extends from a point adjacent the first face  21  toward the second face  22  and is bent at least twice in alternating directions. It will be appreciated that the slats  30  may, but need not, extend exactly from the first face  21  and/or exactly to the second face  22 . In the described embodiment, at least one slat extends from the first face  21  to the second face  22  and defines an exterior wall  35 , thereby reducing the cost of materials needed to construct the grill  20 . The slats  30  may be constructed of aluminum, steel, or any other conformable material. 
   With reference to  FIG. 3 , each segment  24 ,  25 ,  26 , and  27  of each channel  23  has a cross-sectional width W 1 , W 2 , W 3 , and W 4 . In one embodiment of the present invention, for each channel  23 , the cross-sectional width W 2 , W 3 , and W 4  of each segment  25 ,  26 , and  27  upstream from the segment  24  adjacent the air outlet  21  is larger than the cross-sectional width W 1  of the outlet segment  24 . Particularly, the first segment  24  of each zigzag channel  23  at the air outlet  21  has the smallest cross-sectional width W 1 . The segments  25 ,  26 , and  27 , formed along the zigzag channels  23  upstream from the segment  24  nearest the air outlet  21 , have at least one segment with an enlarged cross-sectional width. 
   In the described embodiment, the cross-sectional width W 1  of the segment  24  adjacent the air outlet  21  is about 0.340 inches. In order to fit inside different sized ventilation ducts, the security grill  20  of the present invention may be constructed of various sizes, e.g., (in inches) 6×6, 9×9, 12×12, 15×15, or 18×18. Because each size grill  20  will require a different number of slats  30  to be appropriately spaced within the grill  20  for defining the air channels  23 , it will be appreciated that the cross-sectional width W 1  of the air outlet segment  21  may vary accordingly. 
   As shown in  FIG. 4 , each slat  30  is bent at least twice in alternating directions. Each bend of each slat  30  forms an angle A 1 , A 2 , and, in the described embodiment wherein the slats are bent three times, A 3 . The angles A 1 , A 2 , and A 3  are larger than those of conventional air grills and may be between about 84 degrees and about 100 degrees. In the described embodiment, the first angle A 1  is about 85 degrees, the second angle A 2  is about 95 degrees, and the third angle A 3  is about 93 degrees. In another embodiment, the first angle A 1 , the second angle A 2 , and the third angle A 3  are each about 84 degrees. Because each size grill  20  will require a different number of slats  30  to be appropriately spaced within the grill  20  between the opposing faces  21  and  22 , it will be appreciated that the size of the angles A 1 , A 2 , and/or A 3  may vary accordingly. 
   Each bend of each slat  30  also forms corner C 1 , C 2 , and C 3 , in the described embodiment wherein the slats are bent three times. The corners C 1 , C 2 , and, C 3  are rounded as opposed to being sharp, and thereby have radii, R 1 , R 2 , and R 3 , respectively. The radii R 1 , R 2 , and R 3  may be between about 0.093 inches and about 0.2 inches. In the described embodiment, the first radius R 1 , the second radius R 2 , and the third radius R 3 , are each about 0.2 inches. Because each size grill  20  will require a different number of slats  30  to be appropriately spaced within the grill  20  between the opposing faces  21  and  22 , it will be appreciated that the size of the radii R 1 , R 2 , and/or R 3  may vary accordingly. 
   With reference to  FIGS. 3 and 4 , the operation of a grille grill  20  in accordance with the present invention will now be described. 
   The cross-sectional width W 1  of the air outlet segment  24  is kept at a minimum to restrict the size and shape of the objects that could be possibly inserted in the slot. 
   Increasing the cross-sectional width of at least one segment  25 ,  26 , or  27 , upstream from the outlet segment  24 , creates an area with greater wall separation through which the air can move more freely in comparison to the outlet segment  24 , therefore reducing static pressure drop across that segment  25 ,  26 , or  27 . Because the grill  20  for security institutions can be comprised of more than one segment with enlarged cross-sectional width, even more significant reductions in static pressure drop can be realized. Any reduction in static pressure drop across the entire grill  20  improves efficiency of the ventilation system and therefore can reduce annual operating costs for ventilating systems in security institutions. 
   Increasing the angles A 1 , A 2 , and A 3  at which the slats  30  are bent creates a more gradual change in direction through which air molecules must travel when passing through the channels  23  of the grill  20 . A more gradual change in direction reduces the build-up of air molecules at each turn and allows the molecules to flow more quickly and freely through the grill  20 . Therefore the static pressure drop across the security grill  20  is reduced, and the efficiency of the ventilation system is improved. By limiting the size of the angles to an appropriate maximum, the security requirements of the grill  20  are not compromised as occupants remain unable to thread items through the air channels  23 . 
   Rounding the corners C 1 , C 2 , and C 3  along each slat  30  creates more space for air molecules to pass through as they change direction through the channels  23  and results in less build-up of air molecules. Thus, the static pressure drop across the security grill  20  is reduced and the efficiency of the ventilation system is improved. By limiting the size of the radii to an appropriate maximum, the security requirements of the grill  20  are not compromised as occupants remain unable to thread items through the air channels  23 . 
   Accordingly, by using a grill  20  in accordance with the present invention, one can derive significant air delivery performance improvements and therefore reduce annual operating costs of the ventilation system without compromising the security requirements of the grill  20  for security institutions. 
   With reference to Tables 1, 2, 3, and 4, the air delivery performance improvements of the present invention over the prior art ( FIG. 1 ) with sharp corners and sharp bend angles will be described. 
   
     
       
         
             
           
             
               TABLE 1 
             
           
          
             
                 
             
             
               Prior Art. 
             
          
         
         
             
             
             
          
             
                 
               Octave Band, PWL 
                 
             
          
         
         
             
             
             
             
             
             
             
             
             
             
          
             
               Run No. 
               CFM 
               ISP 
               2 
               3 
               4 
               5 
               6 
               7 
               NC 
             
             
                 
             
             
               10 
               238 
               0.359 
               51.4 
               50.7 
               47.4 
               46.5 
               40.3 
               31.1 
               35 
             
             
               11 
               271 
               0.435 
               52.0 
               52.5 
               50.5 
               49.5 
               43.6 
               36.0 
               38 
             
             
               12 
               306 
               0.546 
               54.1 
               55.0 
               53.7 
               52.7 
               47.6 
               41.5 
               41 
             
             
               13 
               342 
               0.657 
               55.1 
               56.7 
               55.9 
               55.4 
               50.4 
               45.5 
               44 
             
             
                 
             
          
         
       
     
   
   
     
       
         
             
           
             
               TABLE 2 
             
           
          
             
                 
             
             
               The Present Invention. 
             
          
         
         
             
             
             
          
             
                 
               Octave Band, PWL 
                 
             
          
         
         
             
             
             
             
             
             
             
             
             
             
          
             
               Run No. 
               CFM 
               ISP 
               2 
               3 
               4 
               5 
               6 
               7 
               NC 
             
             
                 
             
             
               1 
               241 
               0.192 
               45.3 
               38.6 
               42.1 
               44.8 
               38.5 
               — 
               33 
             
             
               2 
               270 
               0.240 
               46.8 
               41.5 
               44.2 
               47.8 
               42.2 
               30.9 
               36 
             
             
               3 
               305 
               0.309 
               49.3 
               43.9 
               45.7 
               50.7 
               45.9 
               35.8 
               39 
             
             
               4 
               342 
               0.381 
               50.7 
               46.8 
               47.6 
               53.2 
               49.2 
               39.9 
               42 
             
             
                 
             
          
         
       
     
   
   Table 1 shows internal static pressure (“ISP”) and noise level performance data which was gathered for a conventional air channel grill ( FIG. 1 ) having sharp corners, i.e., radii of about 0.062 inches, and small angles, i.e., angles that are about 80.5 degrees to 82.5 degrees. Particularly, four testing runs were performed, Run Nos. 10, 11, 12, and 13, each at a different airflow rate, expressed in cubic feet per minute (“CFM”). For each testing run, the internal static pressure (expressed in inches of water) and the sound power level (“PWL”) (expressed in decibels) in several octave bands were measured and the Noise Criteria (“NC”) was calculated. 
   Table 2 shows internal static pressure (“ISP”) and noise level performance data which was gathered for an air channel grill in accordance with an embodiment of the present invention wherein the cross-sectional width W 1  of the segment  24  adjacent the air outlet  21  is about 0.340 inches, the first angle A 1  is about 85 degrees, the second angle A 2  is about 95 degrees, the third angle A 3  is about 93 degrees, and the first radius R 1 , the second radius R 2 , and the third radius R 3  are each about 0.2 inches. Specifically, four testing runs were performed, Run Nos. 1, 2, 3, and 4, each at an airflow rate corresponding to the airflow rate used for Run Nos. 10, 11, 12, and 13, respectively, for the conventional air channel grill. For each testing run, the internal static pressure (expressed in inches of water) and the sound power level (“PWL”) (expressed in decibels) in several octave bands were measured and the Noise Criteria (“NC”) was calculated. 
   A comparison of the performance data shown in Table 1 with the performance data shown in Table 2 demonstrates that constructing an air channel grill in accordance with the present invention results in significantly lower internal static pressure and level of noise than conventional air channel grills. By providing a reduction in static pressure drop across the grill, the present invention improves the efficiency of the ventilation system and therefore can reduce annual operating costs for ventilating systems in security institutions. 
   
     
       
         
             
           
             
               TABLE 3 
             
           
          
             
                 
             
             
               Prior Art. 
             
          
         
         
             
             
             
             
             
          
             
                 
               Run No. 
               CFM 
               ISP 
               NC 
             
             
                 
                 
             
             
                 
               1 
               174 
               0.17 
               27 
             
             
                 
               2 
               193 
               0.21 
               31 
             
             
                 
               3 
               220 
               0.28 
               34 
             
             
                 
               4 
               238 
               0.36 
               35 
             
             
                 
                 
             
          
         
       
     
   
   
     
       
         
             
           
             
               TABLE 4 
             
           
          
             
                 
             
             
               The Present Invention. 
             
          
         
         
             
             
             
             
             
          
             
                 
               Run No. 
               CFM 
               ISP 
               NC 
             
             
                 
                 
             
             
                 
               5 
               173 
               0.16 
               23 
             
             
                 
               6 
               197 
               0.21 
               28 
             
             
                 
               7 
               222 
               0.26 
               31 
             
             
                 
               8 
               247 
               0.32 
               34 
             
             
                 
                 
             
          
         
       
     
   
   Table 3 shows internal static pressure (“ISP”) and noise level performance data which was gathered for a conventional air channel grill ( FIG. 1 ) having sharp corners, i.e., radii of about 0.062 inches, and small angles, i.e., angles that are about 80.5 degrees to 82.5 degrees. Particularly, four testing runs were performed, Run Nos. 1, 2, 3, and 4, each at a different airflow rate, expressed in cubic feet per minute (“CFM”). For each testing run, the internal static pressure (expressed in inches of water) was measured and the Noise Criteria (“NC”) was calculated. 
   Table 4 shows internal static pressure (“ISP”) and noise level performance data which was gathered for an air channel grill in accordance with another embodiment of the present invention wherein the first angle A 1 , the second angle A 2 , and the third angle A 3  are each about 84 degrees. Specifically, four testing runs were performed, Run Nos. 5, 6, 7, and 8, each at an airflow rate corresponding to the airflow rate used for Run Nos. 1, 2, 3, and 4, respectively, for the conventional air channel grill. For each testing run, the internal static pressure (expressed in inches of water) was measured and the Noise Criteria (“NC”) was calculated. 
   A comparison of the performance data shown in Table 3 with the performance data shown in Table 4 demonstrates that constructing an air channel grill in accordance with the present invention results in significantly lower internal static pressure and level of noise than conventional air channel grills. By providing a reduction in static pressure drop across the grill, the present invention improves the efficiency of the ventilation system and therefore can reduce annual operating costs for ventilating systems in security institutions. 
   While this invention has been described with reference to preferred embodiments thereof, it is to be understood that variations and modifications can be affected within the spirit and scope of the invention as described herein and as described in the appended claims.