ASHRAE Journal - December 2021 - 86

Putting the Science Behind " Sealing the Ceiling "
PRESSURE AND FLOW
Creating pressure differences between
adjoining spaces in a building is a common
way to control the fl ow of air and possible
containments away from clean spaces and
toward less clean spaces. The amount of net
airfl ow required to control fl ow between
spaces is directly related to envelope
leakage: the greater the leakage, the more
airfl ow is needed. The most cost-effective
way to achieve pressure (and fl ow) control
is to make a room tighter (by better sealing)
which allows a smaller offset between
incoming (supply) and leaving (return
or exhaust) airfl ows.
AIRASSURE™
THE SOLUTION
Net airfl ow and resulting pressure differentials
NEW RELEVANCE IN
NON-TYPICAL APPLICATIONS
Critical environments like cleanrooms,
airborne infection isolation rooms, and
protective environment rooms have always
used room pressurization or depressurization
to achieve desired airfl ow directions and
minimize contamination from a less-clean
space into a more-clean space.
The pandemic has made the world rethink
how we control the fl ow of air between
spaces. Almost overnight, private quarters
in senior living facilities were converted
into negative pressure rooms. Typical
patient rooms were pressed into service as
Expedient Patient Isolation Rooms. Health
suites in schools and universities were
retrofi tted to create controlled fl ow rooms.
Suddenly, air leaks mattered, and these
spaces took on some design considerations
more typical of critical environments.
SOME LEAKAGE IS NECESSARY,
TOO MUCH IS COSTLY
Air within an interior space can leave that
space by many different parallel paths -
planned or not planned. Planned paths include
return air and transfer grilles. Unplanned
paths such as electrical outlets, wall
penetrations, light switches, light fi xtures,
fi re protection sprinklers, and ceilingmounted
sensors all represent potential
fugitive leak paths. Suspended ceilings
are also a signifi cant unplanned leak path.
FOR RETROFITTING THESE
NON-TYPICAL SPACES
Armstrong World Industries provides ceiling
tile and grid solutions for controlling fl ow
in critical environments like cleanrooms
and data centers.
As the pandemic unfolded in early 2020,
Armstrong responded with the AirAssure™
product line for use in these " new nontypical "
applications. Suspended ceilings
frequently form the " top of the box " in a
room and are often overlooked as leak points
or wrongly dismissed as impractical to make
tight. Armstrong's AirAssure ceilings make
it easy to address this design challenge.
AirAssure ceiling tiles include a factoryapplied
gasket seal between the tile and the
suspension grid. The gasket reduces leakage
rate across the ceiling plane by a factor of 4.
The system provides a fl exible way to control
this leak path without the use of tapes,
sealing compounds or hold-down clips. You
read that right, no hold-down clips. The tiles
control the leakage while also maintaining
complete accessibility to the MEP equipment
in the plenum above the ceiling.
Picture of test fi xture with four ceiling panels
in place
in measured fan energy compared to
a typical suspended ceiling system.
Retrofi t Airborne Isolation Infection
Room: The application of AirAssure
ceilings reduced leakage enough to eliminate
nuisance low pressure alarms. Replacing
the existing ceiling with AirAssure caused
room pressure to change from -0.018 to a
more robust -0.037 [in wc] using the existing
fan and controls. This brought the room into
compliance and freed medical staff to focus
attention on patients.
Employee Break Room: AirAssure ceilings
were used to retrofi t an 890 [ft2
] employee
breakroom. The leak controlling features
of the system allowed less net airfl ow to be
used to create a positive pressure difference
between the break room and manufacturing
area. Before the intervention, the room was
under a slight negative -0.015 [in wc] pressure
with no net airfl ow into the room. The
ceilings were replaced with AirAssure and
net airfl ow was adjusted to +670 [ft3
/min],
AirAssureª
tile with gasketing
PREDICTABLE AIRFLOW
RESISTANCE FOR RELIABLE
OUTCOMES
Armstrong uses ASTM testing guidance
to measure this new performance variable
of leakage resistance. Ceiling systems are
installed in a test frame and subjected to
pressure differences typically used for
contaminant fl ow control. Airfl ow rates
through the test assembly are measured
and fl ow resistance curves are generated
for all our systems.
SUCCESS IN YOUR BUILDINGS
AirAssure ceilings have been studied in the
laboratory and applied to real life buildings.
Laboratory Test Room: AirAssure ceilings
reduced the net airfl ow required to pressurize
a room by 40% resulting in a 78% reduction
1-877-27 -787 | techline@armstrongceilings.com | armstrongceilings.com/airassure
resulting in a positive pressure of +0.021
[in wc] in the room. With the room under
slight positive pressure, measured PM2.5
particulate levels decreased from (median)
28 [microgram/m3
5 [microgram/m3
] before renovation to
] after renovation.
SUMMARY
AirAssure ceiling tiles provide an easy
way to control a signifi cant air leak path
in rooms today. This simple retrofi t option
keeps project costs low by using the existing
ceiling grid. The factory-applied gasketing
provides a reliable fl ow restriction, making
it possible to pressurize or depressurize a
space with less net airfl ow while maintaining
accessibility without the use of hold-down
clips. This fl exible solution can be applied to
create surge capacity during a health crisis
or control the fl ow of air in health suites,
manufacturing control rooms, cleanrooms,
and data halls.
Armstrong World Industries
2500 Columbia Ave
Lancaster, PA
http://www.armstrongceilings.com/airassure
ASHRAE Journal - December 2021

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