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basis, as outlined in the
"Cleaning Procedures and Equipment"
Pay particular attention to the areas beneath the hardware and the access floor grid.
Contaminants near the air intakes of the hardware can more easily be transferred to
areas where they can do damage. Particulate accumulations on the access floor grid
can be forced airborne when floor tiles are lifted to gain access to the sub-floor.
The subfloor void in a downward-flow air conditioning system acts as the supply air
plenum. This area is pressurized by the air conditioners, and the conditioned air is
then introduced into the hardware spaces through perforated floor panels. Thus, all air
traveling from the air conditioners to the hardware must first pass through the
subfloor void. Inappropriate conditions in the supply air plenum can have a dramatic
effect on conditions in the hardware areas.
The subfloor void in a data center is often viewed solely as a convenient place to run
cables and pipes. It is important to remember that this is also a duct, and that
conditions below the false floor must be maintained at a high level of cleanliness.
Contaminant sources can include degrading building materials, operator activity or
infiltration from outside the controlled zone. Often particulate deposits are formed
where cables or other subfloor items form air dams that allow particulate to settle and
accumulate. When these items are moved, the particulate is re-introduced into the
supply airstream, where it can be carried directly to hardware.
Damaged or inappropriately protected building materials are often sources of subfloor
contamination. Unprotected concrete, masonry block, plaster or gypsum wall-board
will deteriorate over time, shedding fine particulate into the air. Corrosion on
post-filtration air conditioner surfaces or subfloor items can also be a concern. The
subfloor void must be thoroughly and appropriately decontaminated on a regular
basis to address these contaminants. Use vacuums equipped with only High Efficiency
Particulate Air (HEPA) filtration in any decontamination procedure. Inadequately
filtered vacuums will not arrest fine particles, passing them through the unit at high
speeds, and forcing them airborne.
Unsealed concrete, masonry or other similar materials are subject to continued
degradation. The sealants and hardeners normally used during construction are often
designed to protect the deck against heavy traffic, or to prepare the deck for the
application of flooring materials, and are not meant for the interior surfaces of a
supply air plenum. While regular decontaminations will help address loose
particulate, the surfaces will still be subject to deterioration over time, or as subfloor
activity causes wear. Ideally all of the subfloor surfaces will be appropriately sealed at
the time of construction. If this is not the case, special precautions will be necessary to
address the surfaces in an on-line room.
It is extremely important that only appropriate materials and methodology are used in
the encapsulation process. Inappropriate sealants or procedures can actually degrade
the conditions they are meant to improve, impacting hardware operations and
reliability. Take the following precautions when encapsulating the supply air plenum
in an on-line room:
Manually apply the encapsulant. Spray applications are totally inappropriate in an
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on-line data center. The spraying process forces the sealant airborne in the supply
airstream, and is more likely to encapsulate cables to the deck.
Use a pigmented encapsulant. The pigmentation makes the encapsulant visible in
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application, ensuring complete coverage, and helps in identifying areas that are
damaged or exposed over time.
It must have a high flexibility and low porosity to effectively cover the irregular
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textures of the subject area, and to minimize moisture migration and water
damage.
Room Conditions
on page F-8 section.
Controlling Contaminants F-5
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