Cleanroom Ceilings
More than just a ceiling surface, ceiling
systems include the quality, the flow and the direction of the air, the lighting
of the room, the control of static. The surface must be cleanable, nonporous,
nonshedding and easily maintained. It should be smooth, water impermeable and
resistant to cleaning agents and disinfectants. It may have a vinyl or metal
face. The metal may be finished with epoxy enamel. It comes prefabricated or in
standard 2' x 4' lay-in panels and has a respectable fire rating.
Ceiling Systems
This system employs a grid system, usually
T Frame, specifically designed to suspend ceiling filter modules. The air flow
feeds into this plenum through one or more ducts, then through the filters and
into cleanrooms ranging from Class 1 to Class 1000. Major factors determining
these ratings include the distribution and balance of air and the sealing of the
filter modules.
The usual gridwork is in a T-frame system,
with a sealant to prevent leakage. Suppliers offer a dry gasket seal or, for a
dual seal, a liquid gel and dry gasket.
Most companies are getting away from using
silicone sealants in fabrication of the module. Silicone long has been suspected
of contributing to contamination problems in many microelectronics operations
due to its out-gassing properties.
The open-plenum system requires advance
planning when designing cleanroom space allotment and air systems. It's
preferred by those who don't want to run a lot of ductwork and can be cost
effective if maintenance, air supply and possible leakage are considered before
installation.
Ducted Supply
Modules
This is a system especially suitable for
cleanrooms slated for long-term operation. Each ceiling filter module has its
own ducted supply of air, which comes from a central air system. The air which
is distributed through each duct may yield a more balanced air dispersement than
an open-plenum system.
From the central air supply, air travels
through each duct, into a ceiling filter module and into the cleanroom. The
modules are designed to be used in a grid ceiling system.
Ceiling
Filter Modules
Several kinds of ceiling filter modules
are designed for ceiling grid systems. They are the major determinants of
cleanroom air quality, and make the area acceptable to pharmaceutical,
electronic, photo film manufacturing, food processing, health care and other
industries requiring a very high degree of clean air. The modules are designed
for use in laminar and non-laminar flow cleanrooms from Class 1 to Class
100,000.
They are designed to be an integral part
of the cleanroom ceiling and to filter the air at the point of entry into the
room. The CFM modules are separate, self-contained units, and the filtration
systems can be expanded by installation of additional modules to upgrade the
facility to a higher class of cleanliness at a later date. Modules may be moved
to different locations, as required, to fit changing needs. The final HEPA
filter element is 99.99 percent on 0.3 and larger micron size by DOP test
method. Available 3" or 6" deep, depending upon customer preference.
Usually, each module has an access port
with removable plug, located in the center divider of the HEPA filter element,
which functions both as testing access for dioctylphthalate (DOP) testing and
periodic static resistance tests. It also provides access for damper adjustment.
This adjustment is accomplished without use of special tools.
There are many varieties of the ceiling
filter modules:
Fully Encapsulated Ceiling Filters are a one-piece sealed-at-the-factory design.
Replaceable Filter Module Units permit
simple filter change in areas where filter changes are needed more often.
Disposable HEPA Filter Ceiling Modules
are used when filters must be replaced periodically. They can be used as
replacements for ceiling modules consisting of a permanent housing with a
replaceable HEPA filter, or for earlier vintage disposable modules made from a
HEPA filter cartridge with a transition attached. They are especially cost
effective compared to systems requiring proprietary filter cartridges and
sealing designs. Disposable modules are easier and faster to install because
of their light weight, low profile design and elimination of the
time-consuming task of removing and resealing the cartridge.
Self-Contained Ceiling Filter Modules.
Ceiling modules are independent, self-contained units which provide Class 100
vertical laminar air flow. They are widely used for microelectric component
manufacturing, aerospace, pharmaceutical and hospital laboratories. They are
designed to be suspended over the area which is to be kept clean. The units
can be coupled together on all four sides to expand the protected area. By
using a vinyl curtain, a Class 100 atmosphere can be created even within a
non- controlled environment. The modules use ambient air, which also serves to
make the surrounding air cleaner. Some manufacturers add duct inlets to
connect it to a facility air-handling system.