Vertiv Liebert Xtreme Density Series Guide

Liebert® Xtreme Density™
System Design Manual

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TABLE OF CONTENTS
1 System Description 7
1.1 European Union Fluorinated Greenhouse Gas Requirements 7
1.2 Generic Piping Layouts 8
1.3 Liebert XDA—Air Flow Enhancer 9
1.4 Liebert XDCF—Liebert XD CoolFrame 10
1.5 Liebert XDH—Horizontal Cooling Module 10
1.6 Liebert XDO—Overhead Cooling Module 11
1.7 Liebert XDR—Rear Cooling Module 13
1.8 Liebert XDV—Vertical, Above-Cabinet Cooling Module 13
1.9 Liebert XDC—Refrigerant Chiller 15
1.9.1 Liebert XDC Minimum Load 15
1.10 Liebert XDP—Pumping Unit 15
1.10.1 Liebert XDP Minimum Load 16
1.11 Liebert XD Piping 16
1.11.1 Liebert XD Field Piping 16
2 Starting a New Equipment Cooling Project 19
2.1 Determining Cooling Equipment Needs 19
2.2 Implementing a Hot-Aisle/Cold Aisle Design 19
3 Designing a Liebert XD Solution 21
3.1 Determine Cooling Requirements and Select Liebert XD System 21
3.2 Calculate the Heat Load to be Handled by Liebert XD System 21
3.3 Selecting Liebert XD Cooling Modules 22
3.4 Configuring a Liebert XD System 24
3.4.1 Number of Modules Supported by a Liebert XDP or Liebert XDC 24
3.4.2 System Connection Configuration 25
3.5 Airflow Requirements for Liebert XD Solutions 26
3.6 Liebert XDCF Placement 26
3.7 Liebert XDH Placement 27
3.8 Liebert XDO Placement 28
3.8.1 Determining Spacing of Liebert XDOs in an Aisle 28
3.8.2 Determining Vertical Placement of Liebert XDOs Above the Cold Aisle 29
3.9 Liebert XDR Module Placement 30
3.9.1 Airflow 31
3.10 Liebert XDV Module Placement 32
3.11 Liebert XDP/Liebert XDC Placement 33
3.12 Examples of Expansion and Interlaced Connection of Liebert XD Cooling Modules 34
3.13 Liebert XD Piping System Design 38
3.14 Liebert XD Piping Slope 40
3.15 Bypass Flow Controllers 40
3.16 Piping Details—Shutoff/Isolation Valves 42
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3.17 Piping Details—Shutoff/Isolation Valves 43
3.18 Piping Details—Return Header Port Orientation 44
3.19 Piping Details—Bull Heading Layout 46
3.20 Piping Installation Method Prefabricated Headers 47
3.21 Liebert XD Flex Pipe Kit 54
3.22 Liebert XD Refrigerant 55
3.23 Determining Refrigerant Volume 56
3.23.1 Liebert XDP/Liebert XDC Pumped R-134a Circuit Volume 56
3.23.2 Calculating Refrigerant R134a Charge—Example 57
3.24 Chilled Water Piping 58
3.25 Electrical 60
3.26 Temperature/Humidity Sensor Locations 60
3.27 Connecting Liebert XDP and Liebert XD Cooling Modules in a CANbus Network 60
3.27.1 CANbus Cables 60
3.27.2 CANbus Cable Length in a Network 61
3.27.3 Remote Sensor Placement Within the CANbus 62
4 Liebert XD Cooling Modules—LiebertXDCF, LiebertXDH, LiebertXDO, LiebertXDR and
LiebertXDV 65
4.1 Liebert XDCF Standard Features 65
4.2 Liebert XDCF Mechanical Considerations 65
4.3 Liebert XDCF Installation Considerations 67
4.4 Liebert XDCF Piping Connection Methods and Points 67
4.4.1 Header System—Liebert XDCF 68
4.5 Liebert XDH Standard Features 68
4.6 Optional Features—Liebert XDH 69
4.7 Connecting High-Voltage Wiring—Liebert XDH 71
4.8 Connecting Low-Voltage Wiring—Liebert XDH Smart Modules 72
4.9 Liebert XDO Standard Features 73
4.10 Optional Features Liebert XDO 73
4.11 Low-Voltage Wiring—Liebert XDO Smart Modules 80
4.12 Liebert XDR Standard Features 81
4.13 Optional Features—Liebert XDR 81
4.14 Liebert XDR Installation Considerations 82
4.15 Liebert XDV Standard Features 86
4.16 Optional Features—Liebert XDV 87
4.17 High-Voltage Cabling for Liebert XDV 93
4.18 Low-Voltage Wiring—Liebert XDV Smart Modules 97
5 Liebert XDC and Liebert XDP 99
5.1 Liebert XDC Standard Features 99
5.1.1 Liebert XDC Optional Features 99
5.2 Liebert XDP Standard Features 109
6 Heat Rejection 117
6.1 Liebert Lee-Temp™ Refrigerant Control Air-cooled Condensers 117
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6.1.1 Liebert Lee-Temp Refrigerant Control Air-Cooled Condenser 117
6.1.2 Standard Features-All Condensers 117
6.1.3 Condenser Coil 118
6.1.4 Housing 118
6.1.5 Propeller Fan 118
6.1.6 Fan Motor 118
6.1.7 Electrical Controls 118
6.2 Mechanical Considerations 119
6.2.1 Dimensions 119
6.3 Heat Rejection Piping 123
6.3.1 Piping for Direct Expansion (DX) Circuit—R-407C Air-Cooled Units 123
6.4 Install Double Discharge Risers 123
6.4.1 Air-Cooled Condenser with Liebert Lee-Temp “Flooded Condenser” Head Pressure
Control System—R-407C (DX) Circuit 133
6.5 Calculating Refrigerant Volume 133
6.5.1 Liebert XDC DX R-407c Circuit Volume 134
6.6 Liebert Drycoolers 135
6.6.1 Liebert Drycooler Fan Cycling Control 135
6.6.2 Pump Controls 135
6.7 Typical System configurations 135
6.8 Site Considerations 136
6.9 Dimensions and Weights 137
6.10 Mounting the Drycooler 140
6.11 Glycol Piping 140
6.11.1 Piping Guidelines 140
6.11.2 Expansion Tanks, Fluid Relief Valves, Air Management and Other Devices 141
6.12 Electrical Supply 141
6.12.1 Line Voltage Wiring 142
6.12.2 Low Voltage Control Wiring 143
6.13 Filling Instructions 145
6.13.1 Preparing the System for Filling 145
6.13.2 Glycol Solutions 145
6.13.3 Filling the System 147
6.14 Outdoor Control Enclosure 147
6.14.1 Electrical Connections 149
6.14.2 Hazardous Voltage Power Supply Wiring 149
6.14.3 Extra-Low Voltage Control Wiring 150
6.14.4 Dual Pump Package Flow Switch 151
6.14.5 Dual Pump Controls Sequence of Operation 151
7 Liebert iCOM 153
7.1 Liebert iCOM Display Layout 153
7.2 Cooling Module Overview 155
7.3 Graphical Data Record 156
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7.3.1 Liebert iCOM User Menu Icons and Legend 156
7.3.2 Liebert iCOM Service Menu Icons and Legend 157
7.4 Liebert XDC Alarms Descriptions 157
7.5 Warning Descriptions 161
7.6 Liebert XDP Alarms 161
7.7 Liebert XDP Warnings 164
7.8 CANbus Communications 164
7.9 Network Layout Options 165
7.9.1 Remote Temperature/Humidity Sensor Placement and Connection to the CANbus 165
7.9.2 CANbus Maximum Length 168
7.10 CANbus Cables 168
7.11 Connecting the CANbus Network 169
7.11.1 Connection to the Liebert XDP or Liebert XDC 169
7.11.2 Connecting to the Liebert XDV Smart Modules 171
7.11.3 Connecting to the Liebert XDH Smart Modules 172
7.11.4 Connecting to the Liebert XD Smart modules 175
7.12 CANbus Termination 175
7.12.1 Remote Temperature and Humidity Sensors Termination 175
7.12.2 Terminating a Smart Module 176
8 Monitoring 177
9 Specifications and Model Number Nomenclature 183
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1 SYSTEM DESCRIPTION
The Liebert XD™ family of cooling units delivers efficient, sensible cooling to high-heat environments.
Liebert XD systems are designed to cool computer racks and hot zones in a data center or computer room
without taking up expensive floor space for cooling components.
The Liebert XD family includes:
•Liebert XDC™—Liebert XD Chiller; cools and pumps refrigerant to cooling modules
•Liebert XDP™—Liebert XD Pumping unit; pumps refrigerant to cooling modules
•Liebert XDA™—mounts on the rear of the equipment cabinet
•Liebert XDCF™—Liebert XD CoolFrame; mounts on the rear of an Egenera BladeFrame EX
cabinet
•Liebert XDH™—Liebert XD Horizontal row cooler; integrated into hot aisle-cool aisle room
layout
•Liebert XDO™—Liebert XD Overhead module; suspended from the ceiling structure
•Liebert XDR™—Liebert XD Rear cooling module; mounts on the rear of equipment cabinets
that are 24" (600mm) wide and 42U high, approximately 79" (2000 mm)
•Liebert XDV™—Liebert XD Vertical module; mounted on top of the equipment cabinet or
suspended from the ceiling structure
Systems combining Liebert XDO, Liebert XDR and Liebert XDV modules can remove more than 20kW (5.7
tons) of heat per cabinet. A set of Liebert XDCF modules also can remove 20kW (5.7 tons) of heat from an
Egenera BladeFrame EX™ cabinet. A system with Liebert XDH modules can remove more than 30kW
(8.5tons) of heat per rack.
For minimum Liebert XDP and Liebert XDC load recommendations, see Liebert XDP Minimum Load on
page16; Liebert XDC Minimum Load on page15; and Table 9.13 on page193and Table 9.17 on page197.
The Liebert XD system also performs at high efficiency rates. Properly spaced cooling modules and the
Liebert XD system’s fluid phase change technology, combine to reduce a Liebert XD system’s energy
consumption to at least 27 percent less than a traditional cooling system.
The Liebert XD family maintains this energy efficiency by employing the heat absorption properties of a
liquid (pumped refrigerant) through a phase change. Refrigerant is pumped as a liquid, becomes a gas
within the heat exchangers of the cooling modules (either the Liebert XDCF, Liebert XDH, Liebert XDO,
Liebert XDR or Liebert XDV) and then is returned to either the Liebert XDP or Liebert XDC where it
condenses to a liquid. This eliminates the compression cycle required by traditional systems. And, if a leak
were to occur, the environmentally friendly refrigerant in the data center would escape as a gas, causing
no harm to critical equipment. Because no compressor is used in the pumped refrigerant circuit, no oil is
needed.
Liebert XD cooling modules further increase efficiency with optional control board that reduces fan use
when maximum cooling levels are not required. The control board is available on Liebert XDH, Liebert
XDO and Liebert XDV modules.
1.1 European Union Fluorinated Greenhouse Gas Requirements
Stationary air conditioning, refrigeration, heat pump equipment and stationary fire protection systems in
the European Community market and operating with fluorinated greenhouse gases (f-gas), such as
R407C, R134a, R410A, must comply with the F-Gas Regulation: (EC) No. 842/2006 (F-gas). The regulation
prohibits, among other actions, venting fluorinated greenhouse gases to the atmosphere.
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The F-Gas Regulation requires operators to use all measures that are technically feasible and do not
entail disproportionate cost to prevent leakage of these gases, to test for leakage regularly and to recover
f-gas before disposing of equipment, as well as during service and maintenance.
Refer to the full regulation for additional details.
1.2 Generic Piping Layouts
Liebert XD systems are available in two configurations—differentiated essentially by the method of heat
rejection (see Figure 1.1 below andFigure 1.2 below). The Liebert XDP is a pumping unit connected to a
building chilled water system to control and circulate the refrigerant. Liebert XDPs pump refrigerant to
Liebert XDCF, Liebert XDH, Liebert XDO, Liebert XDR or Liebert XDV modules, isolate refrigerant circuit
from building chilled water supply with an internal heat exchanger and maintains refrigerant temperature
above the actual dew point. The Liebert XDC incorporates the pumping functions with the chiller, which
must be connected to a separate heat rejection system. Pumping and refrigerant control are performed
by Liebert XDC.
Figure 1.1 Liebert XDP generic piping layout
Figure 1.2 Liebert XDC generic piping layout
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1.3 Liebert XDA—Air Flow Enhancer
The Liebert XDA is a fan unit that boosts the airflow through densely populated enclosures, removing hot
spots from within the racks. One or two units can be mounted on the rear of most rack enclosures.
Figure 1.3 Liebert XDA—air flow enhancer—on equipment enclosure
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1.4 Liebert XDCF—Liebert XD CoolFrame
The Liebert XDCF is a self-contained module designed to cool Egenera’s BladeFrame EX cabinets and
equipment without exhausting heat into the room. Two modules (top and bottom) may be mounted on
the rear of a BladeFrame cabinet. Liebert XDCF modules consist of a sheet-metal frame, coil and filter
dryer. It has no moving parts and needs no electricity.
The module is available with optional, Liebert XD Flex Pipes (flexible metal pipes) with quick-connect
couplings at each end for easy connection to the refrigerant distribution pipes.
Figure 1.4 Liebert XDCF modules on Egenera’s BladeFrame EX cabinets
1.5 Liebert XDH—Horizontal Cooling Module
The Liebert XDH is designed for placement within a row of computer cabinets in the data center in a hot-
aisle-cold-aisle arrangement to maximize the Liebert XDH’s cooling. The Liebert XDH, available in a half-
rack-width module (12" [305mm]), is intended for use with a Liebert XD pumped refrigerant cooling
system, supplied by either a Liebert XDP or Liebert XDC. The module takes in hot air through the rear
from the hot aisle, cools the air by air-to-fluid heat exchangers and discharges the air through the front of
the module into the cold aisle in a diffuse pattern. The cooling air is then drawn into the enclosures to cool
the equipment.
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Replaceable front panels on the Liebert XDH may be customized to match the appearance of various
computer manufacturer’s equipment, allowing the Liebert XDH to blend in with adjacent server
equipment and enclosures. Unidirectional and bidirectional diffusers are available to direct cooling air for
more efficient cooling, depending on the Liebert XDH’s positioning in a row or at the end of a row. Chilled
R-134a refrigerant is provided to the Liebert XDH by a Liebert XDP or by a Liebert XDC. The Liebert XDH
has dual refrigeration circuits, one in the upper half of the module and the other in the lower half. This
permits increasing and decreasing cooling levels in response to server room conditions. The dual
refrigeration circuits permits interlaced connection of two Liebert XD refrigerant sources to enhance
system reliability. The Liebert XDH may be installed in a Liebert XD piping system that includes other
Liebert XD cooling modules.
Controls on the front of the Liebert XDH permit independent operation of the two banks of fans. Dual
power connections ensure continued fan operation if one of two electrical sources fails. Optional smart
modules allow remote shutdown, fan failure alarms, condensate detection and switching fan per bank On
and Off. This saves energy by permitting the module to run with two fans per bank and switching on the
middle when the temperature requires all fans for cooling.
The Liebert XDH is available for hard-piped configurations and with flexible metal pipes with
quick-connect couplings (one-shot or removable) at each end for easy connection to the header system.
The Liebert XDH and Liebert XD Flex Pipes are also available for shipment with a pre-charge of R134a.
This option requires the use of the one-shot flexible pipes.
Figure 1.5 Liebert XDH—horizontal cooling module in hot aisle-cold aisle arrangement
1.6 Liebert XDO—Overhead Cooling Module
The Liebert XDO is an overhead cooling system designed for installation above heat-dissipating
equipment. A fan draws hot air exhausted from the equipment through two cooling coils and discharges
cool air back down to the equipment (see Figure 1.6 on the next page).
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A Liebert XDO smart module will allow remote monitoring, shutdown, fan failure alarms, condensate
detection and automatically cycling the fan On and Off as the heat load requires. The Liebert
XDP/Liebert XDC monitors room conditions and prevents coil condensation by maintaining the
temperature of the refrigerant pumped to the Liebert XDOs above the room dew point.
The Liebert XDO is available for hard-piped configurations or with Liebert XD Flex Pipes with quick-
connect couplings (one-shot) for easy connection to the header system. When the pre-charged option is
selected, the Liebert XDO and the one-shot flexible pipes contain R134a.
NOTE: The Liebert XDO is the most sensitive module to system load. The Liebert XDO’s air intake and
the discharge are not separated by a rack. This can lead to the Liebert XDO pulling in cold air rather
than hot air. The Liebert XDP and Liebert XDC minimum loads must be met to prevent this from
occurring.
Figure 1.6 Suspended Liebert XDO modules in hot aisle-cold aisle arrangement
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1.7 Liebert XDR—Rear Cooling Module
The Liebert XDR is a cooling system for high-density heat loads that mounts on the rear of a 24" (600mm)
x 42U rack (consult the factory for other rack sizes) and maintains access to the back of the server rack.
Room air is drawn in through the front of the rack and picks up heat from the servers. The coil captures
that heat, cooling the air, which is expelled through the rear of the rack.
The Liebert XDR relies on the rack equipment’s fans to move air across the microchannel coil. Captured
heat is carried away through pumped R-134a refrigerant supplied by either a Liebert XDPor Liebert XDC.
The Liebert XDR is available in hard-piped configurations or with Liebert XD Flex Pipes with
quick-connect couplings (one-shot or removable) for easy connection to the header system. The Liebert
XDR and flexible pipes are also available pre-charged with R134a refrigerant. This option requires the one-
shot connections.
Figure 1.7 Liebert XDR on cabinet
1.8 Liebert XDV—Vertical, Above-Cabinet Cooling Module
The Liebert XDV cooling system is designed to be attached to the top of a computer cabinet or rack
containing heat-dissipating equipment. Two fans draw hot air exhausted from the equipment or from the
hot aisle, pass it through a cooling coil and discharge cool air back down to the cold aisle, where the
equipment's air intake is located.
The Liebert XDV comes from the factory ready to draw heated air through a perforated grille on the back
of the module. The Liebert XDV is easily modified to draw hot air through the bottom of the module,
should that cooling method be better suited to your application.
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Liebert XDV smart modules allow remote shutdown, fan failure alarms and automatically switching the
second fan On and Off. This saves energy by permitting the module to run with one fan and switching on
a second fan when the temperature requires both fans for cooling.
The Liebert XDV is available for hard-piped configurations or with Liebert XD Flex Pipes with quick-
connect couplings (one-shot or removable) for easy connection to the header system. The Liebert XDV
and flexible pipes are also available for shipment with a pre-charge of R134a. This option requires the use
of the one-shot flexible pipes
Figure 1.8 Top-mounted Liebert XDV modules with hard piping in hot aisle-cold aisle arrangement
Figure 1.9 Top-mounted Liebert XDV modules with Liebert Flex Pipe in hot aisle-cold aisle
arrangement
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1.9 Liebert XDC—Refrigerant Chiller
The Liebert XDC is an indoor chiller that connects directly to the Liebert XD cooling modules and
provides refrigerant circulation and control. The Liebert XDC keeps the refrigerant temperature above
the room dew point at the sensors. The Liebert XDC contains a refrigerant to refrigerant heat exchanger
along with two tandem scroll compressor circuits. This allows heat rejection to the outdoor ambient air by
using either the air-cooled condensers or water/glycol shell-and-tube condensers much like a standard
computer room air conditioning unit. The Liebert XDC employs two remote sensors (for redundancy) to
determine the temperature and humidity in the air and instantly adjusts refrigerant supply temperature
to compensate for changing conditions.
The Liebert XDC uses the Liebert iCOM®. This advanced control enables the user to monitor essentially
all aspects of the Liebert XD Precision Cooling system, from operating status to maintenance
1.9.1 Liebert XDC Minimum Load
The Liebert XDC’s minimum recommended operating load is 40% of system nominal capacity. For
example, a Liebert XDC160 60Hz system’s minimum load would be 64 kW. Loading below this value can
unfavorably affect system operation.
Figure 1.10 Liebert XD Chiller
1.10 Liebert XDP—Pumping Unit
The Liebert XDP isolates the building’s chilled water circuit from the pumped refrigerant circuit. The
Liebert XDP circulates refrigerant to Liebert XD cooling modules while preventing condensation by
maintaining the refrigerant’s temperature above the room dew point at the sensors. The Liebert XDP
employs two sets (for redundancy) of remote sensors to determine the temperature and humidity in the
air and instantly adjusts refrigerant supply temperature to compensate for changing conditions.
The Liebert XDP uses the Liebert iCOM. This advanced control enables the user to monitor essentially all
aspects of the Liebert XD Precision Cooling system, from operating status to maintenance.
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1.10.1 Liebert XDP Minimum Load
The Liebert XDP’s minimum recommended operating load is 30% of system nominal capacity. For example,
a Liebert XDP160 60Hz system’s minimum load would be 48 kW. Loading below this value can unfavorably
affect system operation.
Figure 1.11 Liebert XDP
1.11 Liebert XD Piping
Liebert XD Piping is prefabricated distribution piping that is installed in anticipation of a growing system.
Liebert XD cooling modules are added as required and are quickly made operational with flexible
connection piping with threaded couplings. This unique system allows the room cooling capacity to
increase to more than 30kW per rack with no additional disruptive piping installation. The flexible
connection piping also allows the cooling modules to be re-positioned without interruption in operation.
1.11.1 Liebert XD Field Piping
Flexible Piping Kit
Flex pipe kits are available in lengths of 4, 6, 8 and 10 feet (1.2, 1.8, 2.4 and 3 meters). Connection style to
the module end may be straight or 90 degrees with one-shot style couplings or removable couplings. The
one-shot flexible pipes are charged at the factory with R134a. Connection to the prefabricated piping
assembly is a threaded coupler. For information on acquiring the correct kit for your installation refer to
DPN000780, available by calling 1-800-222-5877 and from your local Vertiv representative. Contact the
factory when ordering additional flex piping kits for Liebert XD systems installed before 2007.
Prefabricated Headers
Field piping kits are available in several versions
•10 ft. (3.05m) with 5 or 10 ports
•8 ft. (2.44m) with 2 or 4 ports
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Each version is available in two pipe sizes:
•Supply pipe: 1-1/8"; return pipe: 2-1/8"
•Supply pipe: 1-3/8"; return pipe: 2-5/8"
Each kit contains one (1) supply pipe and one (1) return pipe. Each port has a threaded coupling at the
end with automatic shutoff when disconnected. Each port also has a ball valve for manual shutoff. For
more information refer to section Liebert XD Piping System Design on page38.
Liebert XD Connection Port Kit
The connection ports in the Liebert XD Field Piping Kits are available as Liebert XD Connection Port Kit.
Each port has a threaded coupling, with automatic shutoff when disconnected, at the end. Each port also
has a ball valve for manual shutoff. Each kit contains one supply and one return port. Two kit sizes are
available:
•Supply pipe: 1-1/8"; return pipe: 2-1/8"
•Supply pipe: 1-3/8"; return pipe: 2-5/8"
Figure 1.12 Liebert XD connection port kit
Assembly P# Supply Header Diameter Return Header Diameter
183169G3 1-1/8" 2-1/8"
183169G4 1-3/8" 2-5/8"
Table 1.1 Liebert XD field-installed port kits header connection size
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2 STARTING A NEW EQUIPMENT COOLING PROJECT
2.1 Determining Cooling Equipment Needs
1. Is adequate space available for a Liebert XD installation? ____________
2. Is the hot aisle/cold aisle approach being utilized for this room design or can it be utilized in this room
design? ____________
3. Is redundant cooling equipment required? ____________
4. Are there access considerations for all components (possible rigging problems) ____________
5. What heat load growth is anticipated over the next few years? ____________
6. How are the cabinets going to be populated (density of heat generation)? ____________
7. What monitoring requirements are desired or needed? ____________
8. Who will be involved in this project (stakeholders)? ____________
9. Is there existing computer room environmental cooling systems for humidity control and filtration? ____________
10. Is the vapor barrier sufficient? ____________
11. Is a chilled water system available? ____________
•What is the system’s capacity? ____________
•What is the system’s chilled water supply temperature? ____________
•Does the chilled water supply temperature vary during the year or is the temperature constant? ____________
12. How much power is available for cooling equipment? ____________
13. What is the maximum distance between the Liebert XDP/Liebert XDC unit and the farthest Liebert XD
cooling module in the proposed layout? ____________
14. If an air-cooled Liebert XDC is used—is an area available for the remote condenser? ____________
15. Does the Liebert XD system refrigerant volume exceed 13 lb/1000ft3? If so, a refrigerant detection and
removal equipment may be required. Refer to Liebert XD Refrigerant on page55. ____________
2.2 Implementing a Hot-Aisle/Cold Aisle Design
A best practice is to place equipment racks in alternating rows of cold aisles and hot aisles. This is best
accomplished when the layout of the file-server farm area is being planned. It is more difficult to
accomplish when the computer room is already populated with operating hardware.
In the cold aisle, the equipment racks are arranged face-to-face so the cooling air from the computer room
cooling unit discharged up through the perforated floor tiles is drawn into the face of the computer
hardware and exhausted out the back of the equipment rack into the adjacent hot aisles.
Hot aisles are literally hot because the objective of the alternating cold and hot aisle design is to separate
the source of cooling air from hot air discharge, which returns to the computer-room cooling unit.
Therefore, no perforated tiles should be placed in the hot aisles. This would mix hot and cold air, lowering
the temperature of the air returning to the cooling units, reducing their usable capacity.
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