Emerson 80-150kW White Paper download pdf (Page 5)

Liebert

iCOM™ Controls: The Industry’s

Most Advanced Control System

The Liebert DSE™ is managed by the latest Liebert

iCOM intelligent controls, which enable the system to

continuously adapt to the data center IT load and outdoor

conditions to take full advantage of economization while

providing consistent cooling to IT equipment. The controls

monitor all cooling system components as well as inlet rack

temperatures throughout the data center.

Monitoring inlet temperatures provides two primary

benets: rst, it enables the Liebert DSE system to adjust

cooling capacity to the exact amount of cooling needed.

Second, the inlet rack temperature may be reported back

to a building management system and recorded to ensure

service level agreements are met.

The Liebert iCOM controls scale the operation of the CRAC

to variably modulate the air volume and compressor

capacity to precisely match the data center’s IT load,

enabling the CRAC unit to deliver the right amount of air at

the right temperature. Liebert iCOM also monitors the load

and outdoor conditions to control the outdoor Liebert MC™

micro-channel condenser, and during cooler temperatures,

automatically activates the Liebert EconoPhase pumped

refrigerant economizer to provide economization when

conditions are optimal to do so.

The system’s integrated Liebert iCOM controls also monitor

several parameters within each sub-system and coordinate

operation to provide efcient and reliable cooling. The

Liebert iCOM control system provides hassle-free operation

by automatically transferring between mechanical cooling

and economizer operation modes. Built-in diagnostics

ensure that system reliability is maintained, and information

about system operation is reported.

Comparing Economizer Designs and

Efficiency Implications

Traditional direct expansion systems packaged with water-

side economizers utilize a direct expansion cooling coil

overlaid by a closed loop of water/glycol refrigerant solution.

When ambient temperatures are low enough, the system’s

pump moves the water/glycol solution from an outdoor uid

cooler (or drycooler) to the system’s indoor economizer coil.

While this type of system can provide economization and

reduce compressor operation, its efciency is hampered by

the energy required for the pump to move a highly viscous

water/glycol solution. In addition, the glycol solution itself—

especially a propylene glycol solution—signicantly reduces

heat transfer of the economizer coil, resulting in very low

ambient temperatures required to provide full cooling.

The Liebert EconoPhase requires much less power to pump

refrigerant than alternative systems that pump glycol.

The Liebert EconoPhase maintains full cooling capacity by

taking advantage of the two-phase properties of refrigerant.

Alternative glycol-based economizers can experience

capacity reduction as much as 40 percent compared to

full-DX operation resulting in a need to oversize the

economizer to reach system rated capacity. Water-side

economizers require extra fan power year-round, due to

the additional heat exchange that overlays the DX coil. The

Liebert DSE system requires no additional economizer coils,

keeping air-side pressure drop lower, resulting in lower

indoor fan energy consumption

Another option is to use chilled water air handlers

(CRAHs) in conjunction with a chiller plant and an air-side

economizer. In this conguration, the chiller plant produces

cold water during warmer times of the year, and outdoor

air is brought into the data center when conditions are

right. However, some end-users do not wish to change

According to ASHRAE 90.1-2010, data centers are now required to meet mandatory requirements for minimum SCOP (full-load,

design day) to achieve a satisfactory efciency rating per ASHRAE rating Standard 127. The ASHRAE 90.1 requirements also mandate

the utilization of economizers in many regions of the United States. This minimum efciency target for direct expansion cooling systems

ranges from 1.8 to 2.6, depending on the cooling capacity, condensing type, and airow conguration.

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