Abstract:
A filter module configured for exhaust application, and a method and apparatus for testing the same are provided. In one embodiment, the filter module includes a downstream sampling port configured to allow a technician to sample flow, downstream of the filter module, from the cleanroom side of a filter module. In another embodiment, a shroud adapted to sealing engage a filter module under test is provided and includes a tube, disposed in the shroud, that couples a port to a downstream sampling port of the filter module.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims benefit of U.S. Provisional Patent Application Ser. No. 60/663,833, filed Mar. 21, 2005, which is herein incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     Embodiments of the invention generally relate to a filter module configured for exhaust applications, and a method and apparatus for testing the same.  
         [0004]     2. Description of the Related Art  
         [0005]     In many cleanroom and contaminant applications, filter modules are often utilized in an exhaust configuration to remove air or other fluids from rooms or equipment. In many of these applications, regulations, certifications and/or process protocols require that the filter be tested for overall efficiency after installation into the module. However, testing a filter module in this manner is a difficult challenge. Particularly, the interstitial space defined between the housing and the filter disposed therein often cannot be readily accessed by a technician. Thus, downstream sampling of the installed exhaust filter often cannot be performed. Additionally, sampling within the interstitial space defined between the housing of the module and the filter may not be accurate due to poor mixing of air within the filter housing. Thus, testing of an installed exhaust filter is usually performed in the reverse flow direction to facilitate downstream sampling from the cleanroom side of the filter. This manner of testing is controversial, as many believe that some pinhole filter leaks are flow direction dependent, and as such, a filter passing an efficiency test with air flowing in a first direction, may fail when the flow through the filter is reversed to the direction used during operation of the filter of the cleanroom. As leaking filters may pose health hazards, allow downstream contamination and present regulatory issues or other undesirable problems, it is highly desirable to test filters in the same flow direction utilized during normal filter operation.  
         [0006]     Thus, there is a need for a method and apparatus for efficiency testing of a filter installed in an exhaust housing.  
       SUMMARY OF THE INVENTION  
       [0007]     A filter module configured for exhaust application, and a method and apparatus for testing the same are provided. In one embodiment, an exhaust filter module includes a downstream sampling port configured to allow a technician to sample flow, downstream of the filter module, from the cleanroom side of a filter module.  
         [0008]     In another embodiment, an apparatus for testing the filter module includes a shroud mounted to the cleanroom side of a filter module. The shroud includes a flange for sealing against the face of the filter module and a collar for coupling to a duct coupled to a blower. In one embodiment, two sample ports are formed through the shroud. A first port is configured to sample air in the volume defined between the shroud and the face of a filter element. The second port is coupled to a conduit which is routed through the shroud to a penetration of the filter module. The penetration couples the second port to a downstream sampling port which may be disposed downstream of the filter module, for example, within the duct work coupling the filter module to an exhaust blower. The shroud may optionally include an aerosol injection port. The aerosol injection port may be coupled to an aerosol dispersion device, such as a perforated tube. Baffles or other mixing elements may be disposed in the shroud to mix the aerosol so that a uniform challenge is provided to the face of the filter element. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0010]      FIG. 1  depicts one embodiment of an apparatus for efficiency testing engaged with an exhaust filter module disposed in a ceiling of a cleanroom; and  
         [0011]      FIGS. 2-3  is a partial sectional views of the filter module of  FIG. 1 . 
     
    
       [0012]     To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the figures. It is contemplated that some elements of one embodiment may be beneficially incorporated in other embodiments.  
       DETAILED DESCRIPTION  
       [0013]     The method and apparatus for testing a filter module configured for exhaust applications is provided. The filter module itself is designed and engineered to allow for “roomside” measurement of overall filter efficiency in exhaust applications. This is not possible with conventional wall and ceiling-mounted systems because overall efficiency measurements require samples to be taken from upstream and downstream of the filter. Downstream ductwork is generally not accessible from the roomside because it is located in interstitial spaces behind hard ceilings or walls. The filter module is designed to provide the necessary connections to allow for overall efficiency measurement from the room.  
         [0014]      FIG. 1  depicts one embodiment of a filter module  100  configured for room exhaust applications mounting in a structure, for example, a wall, floor or ceiling  102  of a cleanroom  104 . Additional partial sectional views of the filter modules  100  are depicted in  FIGS. 1-3 . One filter module that may be adapted to benefit from the invention is the PHARMASEAL® Hood, available from Camfil Farr, Inc., of Riverdale, N.J. It is contemplated that the filter module  100  may alternatively be mounting in the floor or wall of the cleanroom  104 , or other equipment or mini-environments.  
         [0015]     The filter module  100  includes a hood or housing  106  which holds a replaceable filter element  108 . The housing  106  has filter-housing sealing interface that sealingly engages the filter element  108  to prevent air leakage between the housing  106  and filter element  108 . In one embodiment, the filter-housing sealing interface is a knife-edge flange  114  extending from the housing  106  that sealingly engages a fluid seal  116  of the filter element  108 . It is contemplated that the filter element  108  and housing  106  may alternately be sealed by other methods, for example, by a gasket or other seal.  
         [0016]     A room-side downstream sampling port  112  is provided through the knife-edge flange  114 , and in one embodiment, is in the form of a quick-disconnect fitting  110 . The quick-disconnect fitting  110  is coupled to a ceiling-side downstream sampling port  118  located, in one embodiment, on the top of the filter module  100  by a tube  120 . The ceiling-side downstream sampling port  118  includes a compression or other suitable fitting disposed on the exterior of the housing  106 . Alternatively, the downstream sampling port  112  may be formed through a centerboard of the filter element  108 , be disposed in the ceiling  102  of the cleanroom  104 , or other suitable location.  
         [0017]     The tube  120  generally provides a conduit through the interior portion of the housing  106 , thereby allowing gases to pass between the interior of the cleanroom  104  and the area above the ceiling  102  via ports  112 , 118  while maintaining fluid isolation with the interior of the housing  106 . The tube  120  may be rigid or flexible. In one embodiment, the tube  120  is metal and sealed to the housing  106  at each end.  
         [0018]     A sampling port  122  is disposed in a ductwork  124  coupling the filter module  100  to an exhaust blower  126 . The port  122  is disposed at a location sufficiently downstream of the filter module  100  to ensure adequate mixing of fluid (i.e., air and/or other exhaust gases). In one embodiment, the port  122  is located about 10 duct diameters downstream of the filter module  100 . The sampling port  122  is connected to the compression fitting of the ceiling-side downstream sampling port  118  of the filter module  100  using tubing  128 . This enables technicians to obtain a downstream sample of fluid passing through the filter as shown from the room side of the filter element  108 .  
         [0019]     To facilitate challenging the filter element  108  installed in the housing  106  from the room side of the filter module  100 , a light-weight, removable shroud  130  is configured to attach to the filter module  100  from the room side. The shroud  130  may seal against the filter module  100  or the filter element  108 . In one embodiment, a gasket  140  is disposed between a flange  142  of the shroud  130  and the filter module  100 . The shroud  130  is compressed against the filter module  100  to form a seal. In the embodiment depicted in  FIG. 3 , a nut  144  is threaded on a stud  146  extending from the filter module  100  to urge the flange  142  against the filter module  100 , and thus, to compress the gasket  140 . An o-ring or other gasket  180  may be used to seal the nut  144  to the shroud  130 . It is contemplated that the shroud  130  may be sealed to the filter module  100 , filter element  108  and/or ceiling  102  using fluid seals, bladders, clamps, magnets or other suitable device.  
         [0020]     The shroud  130  includes a plurality of ports, and a collar  160  disposed opposite the flange  142 . The collar  160  may optionally be coupled to a blower  162  to provide a test flow through the shroud  130  and through the filter element  108  as shown by the arrows in  FIGS. 1-2 . In one embodiment, the collar  160  has a 12-inch (304.8 mm). Alternatively, the exhaust blower  126  may be utilized to provide the fluid flow through the filter module  100 . In the embodiment depicted  FIG. 1 , three ports  132 ,  134 ,  136  are formed through the shroud  108 . Each port  132 ,  134 ,  136  may be configured with a quick disconnect fitting or other suitable fitting to enable coupling of instruments, aerosol generators and the like to the ports. In one embodiment, each port  132 ,  134 ,  136  includes a ⅜-inch NPT chrome-plated brass quick disconnect.  
         [0021]     The first and second ports  132 ,  134  allow the shroud to be coupled to a measuring device  164 , such a photometer or particle counter, to enable efficiency testing of the filter element  108 . The first port  132  is configured to allow an upstream sample to be taken from the plenum defined between the shroud  130  and the filter module  100 . The shroud  130  may also include baffles or other mixing elements  150  (shown in phantom) to ensure the upstream sample is well mixed and representative of the concentration of particulate (e.g., aerosol challenge) present in the fluid directed through the shroud  130  and through the filter element  108 .  
         [0022]     The second port  134  is coupled to a small “patch cord” or tube  152  disposed in the interior of the shroud  130 . The tube  152  allows connection of the second port  134  to the downstream sampling port  112  located on the knife-edge flange  114 . This tube  152  is connected prior to sealing the shroud  130  to the filter module  100 . This allows a downstream measurement to be taken by the measuring device  164  through the port  122 .  
         [0023]     The third port  136  is configured as an aerosol injection port. The third port  136  is connected to an aerosol generator  156  to provide the aerosol challenge to the area within the shroud  130 . The port  136  may be coupled to an aerosol dispersion device, such as a perforated tube  158  (shown in phantom).  
         [0024]     After the shroud  130  is installed, the downstream and upstream sampling lines from the measuring device  164  and the aerosol generator  156  are connected. The upstream aerosol challenge concentration may be measured, as well as the overall filter efficiency, using the measuring device  164 .  
         [0025]     In one embodiment, the shroud  130  is constructed from 0.063″ thick aluminum and weighs approximately 18 lbs. (8.2 kg). This allows technicians to easily mount the shroud  130  to the filter module  100  when positioned overhead.  
         [0026]     A method for efficiency testing is also disclosed. In one embodiment the method begins from removing the grille (not shown) from the filter module  100 . Next, the flexible tube  152  extending from the second port  134  in the shroud  130  is coupled to the downstream aerosol sample port  112  of the filter module  100 . One the tube  152  is connected, the shroud  130  is sealingly secured to at least one of the filter module  100 , ceiling  102  and/or filter element  108  in a manner that ensures that the flow through the shroud  130  passes through the filter element  108  substantially without leakage.  
         [0027]     The measuring device  164  is coupled to the upstream aerosol sample (first) port  132  and the downstream aerosol sample (second) port  134 . The aerosol generator  156  is coupled to aerosol dispersion (third) port  136 .  
         [0028]     Flow is established through the filter element  108  using at least one of the blowers  126 ,  162 . The aerosol generator  156  is activated to challenge the filter element  108 . Upstream and downstream samples are taken using the measuring device  164  to establish the efficiency of the filter element  108 . The efficiency calculations may be made using industry standards, such as National Environmental Balance Bureau (NEBB), Institute of Environmental Sciences (IES) or other testing protocol.  
         [0029]     If the test result is acceptable, the test instruments (i.e., the generator  156  and measuring device  164 ) and the shroud  130  are removed. The grille is replace on the filter module  100  and the module is ready to resume normal operation.  
         [0030]     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof.