White Paper

Indoor CRAC Unit Designed with
State-of-the-art Technologies
The Liebert
®
DSE™ indoor unit (DA080, DA085, DA125
or DA150) is equipped with several high-technology
components that are designed and controlled to work
together to provide a highly efcient and reliable DX system.
Key technologies serve the following functions to enhance
energy efciency and performance:
Digital scroll compressors match cooling to
IT load
Staged evaporator coil reduces compressor power and
optimizes economizer performance
Electronic expansion valve enables part-load and low
ambient efciency
Electronically commutated (EC) plug fans match
airow to server needs
To maximize efciency and control at full and partial
loads, the Liebert DSE is equipped with variable capacity
digital scroll compressor technology and direct-drive,
variable-speed EC fans, which are modulated to respond
to and match changes in room load. Varying the capacity
of the compressors enables them to run at a more efcient
operating point than at full capacity. A staged evaporator
coil inside of the unit enables each refrigerant circuit to
operate over large coil surface area, increasing system
efciency. Alternative coil lacing designs that circulate
refrigerant through only one coil slab can result in air passing
through dormant coils, resulting in lower circuit efciency and
uneven air distribution across the coils.
The CRAC’s variable-speed, direct-drive EC fans enable
air volume to be precisely adjusted to match the needs
of the server load. The Liebert DSE’s indoor unit also is
equipped with electronic expansion valves, which enable
compressors to modulate to a lower head pressure than
traditional mechanical expansion valves (TXVs), resulting in
lower operating costs during mild temperatures.
Highly efficient Micro-Channel
Condenser Design
The Liebert
®
MC™ condenser integrated into the Liebert
DSE system enables the system to achieve higher efciency,
reduced sound levels, reduced refrigerant charge and an
overall decreased footprint. As shown in Figure 1, micro-
channel condensers such as those found in the Liebert
DSE system are smaller, lighter (up to 40 percent) and
can require signicantly less refrigerant charge (nearly 73
percent) than a traditional n/tube design. This results in a
greener design, using less refrigerant and providing a more
favorable LEED calculation for refrigerant use.
Because the Liebert MC condenser is equipped with a coil
that is only about one 1 inch thick, the condenser is able
to achieve lower pressure drop on the air side, resulting in
reduced fan power. Micro-channel condenser coils allow
for the same heat transfer within a smaller footprint,
providing efciency gains as much as 52 percent compared
to traditional n/tube condensers. Even higher efciency
levels can be realized during low load or lower ambient
temperatures, when the fan speed can be reduced, utilizing
the condensers’ variable speed fans controlled by Liebert
iCOM™ controls.
Digital scroll compressors (a) and EC plug fans (b) optimize
the energy efciency of the Liebert DSE by matching cooling
and airow to the demands of the environment.
a.
b.
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