KEY POINTS OF
INTEREST:
CASE STUDY
A A O N
C A S E
S T U D Y
x A LEED Platinum
Certified building
project
x Underfloor air
distribution
x Seven patentable
claims
x AAON patented
design promoting
energy savings of 20—
40% over comparable
air-cooled models
x Challenge of
condensation and
dehumidification
x Partnering to reduce
millions of dollars by
reducing absenteeism
and increasing
productivity
x Optional individual
comfort control
capabaility
Can you say...
C S 3 . 6 . 2 0 0 7
Greenist?
Signature Centre—Denver, CO
The Signature Centre is a
186,000 SF office building
developed by Aardex
Corporation, and designed by
the world renowned architect
Binh Vinh. Located at Denver
West, Jefferson County, the
Signature Centre has opened
the door to what may be
considered Denver’s ‘Greenist’
office building, and one of
America’s top LEED buildings.
Aardex Corporation is known
for their development of usereffective buildings, a
harmonious environment on
the interior and the exterior of
the structure. With an exterior
complete with high-efficiency
glazing, the Signature Centre
has panoramic views of
downtown Denver and the
surrounding foothills of Golden
Colorado. Volker Hartkopf,
director of the Center for
Building Performance and
Diagnostics at Carnegie Mellon
University said, “...I’m
impressed by what Aardex is
doing. This is breaking the
mold in development.”
The building’s mechanical
system consists of highefficiency heating and cooling
systems comprised of four
AAON evaporative-condensed
rooftop units and one AAON
evaporative-condensed chiller.
This equipment efficiently
provides the air and water
required for the underfloor air
distribution system and chilled
beam technology, respectively.
AAON’S unique evaporative
condenser operates with a
refrigerant desuperheater located
in the evaporative condenser
section.
SEVEN PATENTABLE
DECLARATIONS
AAON gives direct benefit to the
customer when comparing the
AAON evaporative-condensed
design to other evaporative
condensers in the industry.
x 22-100% less water usage
x 22-100% less chemical usage
x Reduced tendency to form
scale with all water
chemistry—refrigerant tube
temperature is lowered by the
desuperheater before the
refrigerant tube comes in
contact with the water
x Lower energy consumption
due to reduced fouling and
more efficient heat transfer
x Longer condenser fan motor
life—the desuperheater allows the
motor to operate in a maximum
70% RH ambient versus 100% RH
for models without a
desuperheater
x 100% total heat rejection
achievable at 33°F DB with no
water flow—desuperheater
functions as an air-cooled
condenser at low ambient
temperature conditions
x 50% of total heat rejection at 70°F
DB with no water flow achievable
through desuperheater models
(part load conditions)
“This building is the
wave of the future…
[a] leading-edge kind
of building.”
Preston Gibson, President/CEO
Jefferson Economic Council
PAGE
2
“A chill[ed] beam
technology used
mostly in Europe
is designed to
mitigate heat gain
through outside
windows, and a
high-grade
commercial tinted
glass window
exterior also helps
with energy
efficiency.”
- Ben Weeks,
Executive Principal
over project
Beams Chilled Via AAON Chiller
Chilled beams operate by
pumping chilled water through
cooling elements in the ceiling.
Heat-generated from solar loads,
building occupants
and office
equipment rises
to the ceiling. This
hot air is then
cooled by the
chilled beams and
falls, creating a
natural
convection
process of hot air
rising and cold air
falling. Additional
radiant cooling
from the chilled beam supports
the convection process.
A roof-mounted AAON
evaporative-condensed chiller
with a factory-installed
distribution pumping package
serves the chilled beams. The
water is blended and delivered
to the chilled beams at 64 °F.
the need to house the chiller or
pumps in an internal mechanical
equipment room, because the
pumps, chiller and condenser are
packaged together and
installed on the roof—
saving valuable square
footage that can be used by
the owner or rented by
tenants.
The water temperature is
elevated approximately 2 °F
above dewpoint to prevent
condensation. Usable building
space is maximized by eliminating
Patented Evaporative Condenser
VFD Controlled Fans
From Compressor
Air-Cooled Desuperheater
Moisture Eliminators
Spray Misters
R410A Evaporative Condensing Coil
To Cooling Coil/
Heat Exchanger
Reservoir
CAN
YOU
SAY...
GREENIST?
Pump
A A O N
C A S E
S T U D Y
PAGE
C S 3 . 6 . 2 0 0 7
3
Annual Water Usage Comparison (Evaporative Condensers)
Water Usage
Conventional
Gallons
PB
Albq, NM
100
8760
12.1
1,604,683
804,617
49.9%
Dallas, TX
100
8760
14.7
1,478,941
914,909
38.1%
Tampa, FL
100
8760
14.7
1,481,039
1,052,485
28.9%
Location
Water Usage
AAON Gallons
Water
Savings %
Chiller (Tons)
Hours of
Operation
Underfloor Air Distribution
Underfloor Air Distribution, known as UFAD,
is a system of supplying conditioned air from
a pressurized plenum that is created between
the floor slab and a raised floor system.
diffusers utilized in a traditional underfloor air
distribution system are generally higher to
provide a ‘mixed’ condition within a few feet
above the floor.
The concept behind an underfloor air distribution system is to create a stratified condition from floor to ceiling, as opposed to a
mixed condition, thus relying on the natural
buoyancy of the air to remove heat and contaminants away from the occupants. Cool
conditioned air (typically between 62 °F and
68°F) is supplied by a central air handling unit
to the underfloor plenum, entering the conditioned zone through floor diffusers—or as
part of workspace furniture or partitions. The
air velocity from the diffusers, in a true displacement ventilation system, are extremely
low and do not typically induce any mixing
within the occupied zone. However, the discharge velocity from either passive or active
With adjustable outlets, occupants have moderate control over thermal comfort conditions in their environment. [Automatic diffusers are used primarily to serve conference
rooms or zones with varying interior loads.]
SYSTEM DIFFERENCES
UFAD is different from a conventional overhead air system in multiple ways:
1. Air moves from a bottom to top manner
because it is supplied at low levels directly
into the occupied portion of the space.
This also means that conditioned air and
outside/fresh air is provided much closer to
occupants.
2. Air is supplied at low level and removed at
high level.
3. Air can be supplied at
a warmer temperature (63°F to 65°F)
than it can with an
overhead system
(55°F to 57°F). Additionally, it’s a lowpressure system,
which means the air
isn’t forced through
branching supply
ducts.
Raised floors
enable delivery
of a continuous
source of fresh
air to employees
and allow
maximum
flexibility for
electrical, phone
and data systems.
Dehumidification
A challenge that UFAD systems pose is condensation problems and dehumidification
needs. In humid climates, outside air must be
properly dehumidified before delivering supply air to the underfloor plenum where condensation may occur on cool structural slab
surfaces. In most climates, the outside air
must be cooled 10 °F to 15 °F cooler than
the desired supply air temperature in order
to dehumidify the air. The problem is, air this
cold can not be supplied to the space without
significant comfort concerns.
AAON modulating hot gas reheat uses energy
that would have been rejected in the
condenser to reheat the supply air to the
desired discharge air temperature. AAON’S
Modulating hot gas reheat offers enhanced
temperature and comfort control over on/off
reheat systems by providing the exact amount
of reheat needed.
Conventional systems cycle on and off, creating
uncomfortable temperature swings for the
tenant. The on/off system is unable to maintain
as an exact temperature setpoint as the
modulating reheat seem is able to maintain.
(AAON offers multiple methods of humiidty control,
including modulating hot gas reheat, two-stage hot
gas reheat, return air bypass, and mixed air
bypass.)
Getting Green with R-410A
The Signature Centre’s mechanical system
operates using the environmentally-friendly
and LEED-preferred R-410A refrigerant.
Most air-conditioners and heat pumps sold
around the world use a refrigerant called R22. Emissions of R-22 are considered by some
experts to be a significant factor in depleting
the ozone layer.
R-410A air conditioners and heat pumps are
today’s “state of the art” systems, and utilize
the most current technology available for
efficient and reliable operation. The heart of
every air conditioner or heat pump is the
compressor, and newer systems are
specifically designed to use R-410A
refrigerant. Since R-410A can absorb and
release heat more efficiently than R-22 ever
could, compressors with R-410A run cooler
than R-22 systems, reducing the risk of
burnout due to overheating.
mechanical system—as R-22 is to be phased
out by the year 2010.
This environmental approach meant more
costs up-front, but Aardex built-in ‘enormous
efficiencies’ and has been able to present a
cost-benefit analysis illustrating annual cost
savings per square foot, said Steve Grund,
Chief Marketing Officer for Aardex.
Aardex estimates the average tenant will
recoup any additional leasing costs in about
three years.
AAON and Engineered Mechanical Systems
would like to thank Aardex for the fortunate
opportunity to be part of this spectacular
creation, ‘LEEDING’ the way to an
environmentally-safe and economically sound
future—for which we all ultimately strive.
“The complete
mechanical system
will be a livingbreathing entity—
adapting to the
environmental
changes inside and
outside of the
building.”
Randy Rinker
Professional Engineer
E3MS
Increased efficiency is obtained and probable
future costs are avoided by using R-410A
refrigerant in the Signature Centre’s
AAON LL Chiller
AAON Incorporated
2425 South Yukon Avenue
Tulsa, Oklahoma 74107
Phone: 918-583-2266
Fax: 918-583-6094
E-mail: marketing@aaon.com
AAON RL Rooftop Unit
We’re on the Web!
www.aaon.com