ASHRAE Journal - July 2022 - 86

Better Ceiling Containment Yields Best Effi ciency
Airfl ow Management and
Containment
In a typical air-cooled data center, airfl ow
management is about delivering cool air to
the IT equipment and returning warm air
to the computer room air handler (CRAH).
Cooling is most e cient when hot and cold
airstreams are separated to prevent mixing,
thereby improving predictability and
control. Recognized in modern design, the
containment of hot and cold air is one of the
most promising energy-e ciency measures
available to both new and legacy data centers.
Hot Aisle Containment (HAC) is a popular
strategy where cold air is supplied to the
room and passed through the IT equipment
before returning to the CRAH. Ideally, the
air supplied by the CRAH is in balance with
the air demanded by the IT equipment so that
conditioned air passes once through the racks.
In the real world, some amount of air bypasses
the IT equipment or recirculates through due
to leakage in containment structures. The
result is elevated fan power and reduced
chiller e ciency.
Containment Aisles,
Raised Floors... Do Not
Forget the Ceilings
Much attention is given to reduce leakage
in containment aisles and raised fl oors.
These components are known sources of
fugitive leaks and distributed leaks that
contribute to bypass losses. Raised fl oors
form a supply plenum and help to direct
airfl ow to the IT equipment.
The discipline given to sealing raised fl oors
and racks should also be applied to ceilings.
Ceilings form a return air plenum and, more
importantly, separate the warm return air
from the conditioned room. Gaps around
the tiles and drop rod penetrations allow
conditioned air to bypass the IT equipment.
The bypassed air must be made up by
increasing cool air supply from the CRAH,
thereby consuming more energy.
Typical ceiling systems have leakage rates
far larger than raised fl oor systems. At a
di erential pressure of 0.02 in WC, a raised
fl oor system may leak about 0.05 to 0.30 cfm/
SF. A non-gasketed ceiling with typical drop
rod penetrations will leak about 1.44 cfm/SF.
When AirAssure™
DynaMax®
about 0.19 cfm/SF and becomes comparable
to raised fl oor and containment wall systems.
AirAssure Tile + DynaMax Grid:
The Best Solution
AirAssure Ceiling Tiles with DynaMax
structural grid is an engineered solution
designed for data centers. AirAssure tiles
feature a factory-applied gasket that reduces
ceiling leakage at the tile edges. DynaMax
structural grid eliminates drop rod ceiling
penetrations. Paired together, the system
reduces bypass leakage down to levels of
the best raised fl oor systems. The Armstrong
ceiling solution delivers accessibility and
containment that improves cooling e ciency
and saves fan energy.
ceiling tile is combined with
structural grid, leakage reduces to
Typical high leakage suspended ceilings may have bypass
leakage rates of 0.4 to 2.0% for total HVAC system fl ow
(right distribution). Low leakage AirAssure with DynaMax
ceilings reduce that bypass leakage to below 0.5% of total
HVAC system fl ow (left distribution).
Typical non-gasketed tile with tee-bar grid and drop
rod penetrations. Leakage rate may be 1.44 cfm/SF
at 0.02 in WC.
Depending on operating conditions and local electricity costs,
fan energy savings can range from 0.42 $/SF (median)
to 1.30 $/SF (maximum) in this 25,600 SF example.
AirAssure gasketed tile with DynaMax grid reduces leakage
at the tile perimeter and eliminates leakage around drop rods.
Leakage rate may be 0.19 cfm/SF at 0.02 in WC.
Leakage resistance curves for typical raised fl oors (dashed)
and AirAssure™
ceiling tile with DynaMax®
grid (solid green).
suspension
Controlling Costs Means
Controlling Leakage
To illustrate the impact of ceiling leakage and
its e ect on operating energy, one-dimensional
calculations were made for a 25,600 SF data
hall. This used on-slab, hot aisle containment
and included an IT cooling load of 13.2 MW.
Supply air temperature was fi xed at 65 F and
hot aisle temperature was fi xed at 82 F.
System static pressure across the fan was varied
from 1 to 4 in WC. The pressure di erence
across the ceiling plane was varied from 0.01
to 0.08 in WC. The cost of electricity was
varied from 0.08 to 0.17 $/kWh.
Heat balance and airfl ow calculations were
solved to satisfy the governing equations for
4000 random combinations of parameters.
The resulting charts clearly show the e ects
of changing from a typical (high leakage)
ceiling to the (low leakage) AirAssure with
DynaMax system.
Summary
Ceiling and grid systems form return air
plenums in data centers and separate cold
supply air from warm return air. Leaks across
this containment plane contribute to bypass
losses, increased fan energy, and increased
operating cost. The use of AirAssure gasketed
ceiling tiles with DynaMax structural grid
reduces leakage rates equal to the best sealed
raised fl oor systems.
William Frantz, Senior Principal Scientist,
ASHRAE Member
Jason Cavanaugh, Research Engineer,
ASHRAE Member
Armstrong World Industries
2500 Columbia Ave
Lancaster, PA
1-877-276-7876 | techline@armstrongceilings.com | armstrongceilings.com/airassure
http://www.armstrongceilings.com/airassure
ASHRAE Journal - July 2022

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