| If
you’re planning a new cleanroom or maintaining an existing
one, your choice of filters can be critical to product
quality, production yields and regulatory compliances. The
key to achieving contamination control, whether in the
hospital operating room or the semiconductor assembly area,
is the air filtration system, which is ultimately dependent
on the reliable performance of HEPA (and in some cases ULPA)
filters.
This includes cleanrooms
and mini clean filtration “environments” such as
biosafety cabinets, clean benches and fume hoods. While most
HEPA filters may look the same, they vary widely in quality
and highpurity performance. These filters also vary in
design, pressure resistance, frame construction, sealant and
temperature capabilities. Although cleanroom filtration
systems are certified to meet initial contamination
containment capabilities and regulatory requirements, the
effective lifespan of filters may be limited, requiring
premature replacement to avoid costly air quality problems
– that is, if the user is aware of the problem.
Examples of limiting
factors include filter design shortcomings, marginal quality
of filter material, incomplete or inappropriate filter
testing, and insufficient heat resistance in
high-temperature applications. “Inadequate filtration in
cleanrooms or clean spaces can result in lower production
yields and unsatisfactory conditions,” says Wayne
Copeland, president of CEPA Operations, Inc. (Ontario, CA) a
cleanroom certification service and HEPA filter specialist.
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“It can also
mean failure reports, downtime and frequent replacement or
maintenance – all of which can get very expensive.”
Given the pivotal impact HEPA filters have on cleanrooms and
other clean environments, here are five points that experts
say you should consider before replacing your filters or
specifying a new cleanroom system: Test according to
application Prior to purchasing any HEPA filters, Copeland
advises his customers to confirm that all HEPA (or ULPA)
filters are tested individually, because batch testing is
unacceptable.
“We have a
strict policy of individually testing every customer’s
filter according to the application and specification
requirements,” says Richard Braman, president and
co-founder of HEPA Corp (Anaheim, CA), one of the leading
manufacturers of HEPA and ULPA filters . “We also certify
the test results and performance characteristics of the
filters on an individual basis.” In addition to standard
flow and pressure testing, some industries require leak
testing. However, the standard oil-based aerosol DOP (dioctyl
phthalate) leak testing is not permitted in some sectors,
such as optics and semiconductors.
For those
ultra-sensitive applications Braman says his firm uses PSL
(polystyrene latex spheres) for leak testing. Use deep
pleats to save energy The lower a filter’s resistance to
air flow, the less air handler force is required to push the
required amount of air through a filter. Hence, the less
energy expended to move the required air via electric fan.
Copeland says the best way to lower resistance is with
deep-pleated HEPA filters, which are designed to give more
surface area and thus dramatically improve filter
efficiency. “We have used HEPA Corp’s deep-pleated
filter packs that more than doubled the filter media size,
and the energy savings were very substantial,” says
Copeland. “The original filter installation had a
resistance in the .6”-.7” Water Column (in inches)
range. By installing the deep-pleated filters we reduced the
pressure to the .3” W.C. range, which allowed the customer
to slow their air handlers by 50 percent and also shut down
a cooling tower.
While the
initial investment was higher than standard filters, the
savings in electric power consumption may have saved that
amount within the first year. Plus, they won’t have to
change the filters for years to come, which will save
substantial labor and material cost savings.” On the “green”
side of the picture, because deeppleated HEPA filters
promise a substantially longer lifespan, that means improved
sustainability and fewer products that end up in landfills.
Roomside systems are easiest Copeland points out the
difficulty of changing cleanroom filters is often overlooked
by cleanroom designers and engineers.
However, when
replacement service is required, the cost includes much more
than just the filters. “When it is time to change the HEPA
filters, the true cost includes downtime, labor and cleanup,”
Copeland says. “And those costs can really add up.”
Copeland adds that when you change out most individual
terminal type filters, which can be time-consuming because
they are commonly a difficult replacement, you can tie up a
cleanroom for an extended period of time.
This will be
very expensive in terms of production downtime. It also is a
dirty operation, causing contaminants to enter the clean
space, and that will require time and labor to clean
properly. To solve this situation Copeland recommends a “roomside
replaceable” filtration system, such as HEPA Corp’s
Perma-Hood® filter system or Q3-4000® Gridless® ceiling
filter system. Through the use of an innovative, patented
latching system, filters and lights are suspended in a “gridless”
double channel system.
The ceiling is
constructed and installed completely from the roomside.
Filters are self-aligning; there is no need to lift the
filters up into the plenum before putting in place, nor
time-consuming squaring of a T-bar grid. He says that with
these gridless and modular systems he can change filters
from 5-10 times faster
than individual panels. “Plus, with a roomside replaceable
you have a housing that stays permanently installed,”
explains Copeland. “So now you simply flip a couple of
levers to change the filter out, so you have a much faster
change with far fewer contaminants to deal with.” Copeland
adds that welldesigned roomside filtration systems can
improve the laminar flow of air in a cleanroom, making it
easier to provide cleanest “first” air to desired areas
within the room. Sourcing custom and odd sizes For one
reason or another, some cleanrooms and many mini clean
environments (biosafety cabinets, clean benches and fume
hoods) require custom, odd-size HEPA filters.
Many
distributors don’t stock odd-size filters simply because
there are so many shapes and sizes, and orders may be
difficult to predict. Some manufacturers evidently find odd
sizes difficult to deal with, so they wait for like-size
orders to accumulate before making the filters, which can
cause extensive delays in turnaround time. “Custom or odd
sizes are a fact of life that we have to deal with,” says
Copeland. “Our company avoids the backlog that results
from filter manufacturers who simply add these special size
orders together until they have what they consider a
sufficient number to run. In combination with required
testing, those orders can take months to fill.”
Copeland says
one reason his firm sources from HEPA Corporation is that it
is the only HEPA filter manufacturer he knows who will make
filters to custom specifications and test them as part of
the normal production flow. This means that custom shapes
and sizes will be tailor-made and delivered in weeks rather
than months. Spec’ing hightemperature filters In the case
of hightemperature applications, HEPA filters need to have
special materials for the frames and seals, allowing them to
handle temperatures of up to 750 degrees (F), and are
available with a choice of frames and seals. Applications
that are performed in high-temperature environments require
corresponding high-temperature ASHRAE, HEPA, or ULPA
filters. However, it is essential to specify
high-temperature filters according to appropriate filter
media, frame and sealant capabilities. For example, while
filters are readily available in various temperature ranges
up to 750 degrees (F), the sealant method will determine the
range, with urethane sealing appropriate for temperatures up
to 230 degrees (F), and glass pack required for the highest
temperature range. Some consideration must be given to
filter binders, also.
Since the
acrylic binder used in temperature ranges above 500 degrees
(F) will burn off and produce smoke, products should not be
introduced to the high-temperature environment until the
smoke is exhausted. Nevertheless, the variables governing
the correct choice of high-temperature filters suggest that
users confirm their choices. “Whenever in doubt about any
filter specification, it’s a good idea to talk to a filter
manufacturer,” Braman advises.
For more
info, contact HEPA Corporation, 3071 East Coronado Street,
Anaheim, CA 92806; Phone: (714) 630-5700; Fax: (714)
630-2894; Email: filters@ HEPA.com; Visit the web site:
www.HEPA.com
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