SIST-TP ETSI/TR 102 489 V1.4.1:2016

TECHNICAL REPORT
Environmental Engineering (EE);
European telecommunications standard for
equipment practice;
Thermal management guidance for
equipment and its deployment
2 ETSI TR 102 489 V1.4.1 (2015-10)

Reference
RTR/EE-0164
Keywords
Energy Efficiency, environment, equipment
practice, rack
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3 ETSI TR 102 489 V1.4.1 (2015-10)
Contents
Intellectual Property Rights . 5
Foreword . 5
Modal verbs terminology . 5
Abstract . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 Informative references . 6
3 Definitions and abbreviations . 7
3.1 Definitions . 7
3.2 Abbreviations . 7
4 ARCM integration overview . 8
5 Subrack integration in the same ARCM . 8
5.1 Configuring equipment in an ARCM . 8
5.1.0 Introduction. 8
5.1.1 Subrack location . 8
5.1.2 Cabling . 9
5.2 Mechanical structure of ARCM . 9
5.2.0 Introduction. 9
5.2.1 Opening geometry for the airflow . 9
5.2.2 Equipment fastening in the ARCM . 10
5.2.3 Doors . 10
5.3 ARCM cooling issues . 10
5.3.0 Introduction. 10
5.3.1 Cooling equipment including fans . 10
5.3.2 Air Cooling techniques . 10
5.3.3 Air filtering . 11
5.4 Impact of the implementation of subracks in an ARCM . 11
5.5 Impact of the temperature on equipment reliability . 12
6 ARCM integration in the same telecommunications equipment or Data centre room . 12
6.1 Positioning the ARCM in a room . 12
6.1.0 Introduction. 12
6.1.1 Room layout. 13
6.1.2 Cabling . 13
6.1.3 Cooling systems . 14
6.2 Mechanical structure of ARCMs in the rows . 15
6.2.1 Opening geometry for the airflow . 15
6.3 Cooling systems for a room . 15
6.3.1 General design considerations . 15
6.3.2 Cooling techniques . 15
6.3.2.0 Introduction . 15
6.3.2.1 Passive cooling . 15
6.3.2.2 Warm air extraction (without cool air) . 16
6.3.2.3 Fresh air supply with natural release via pressure relief ventilators . 17
6.3.2.4 Cool air blowing (with or without relative humidity control) . 18
6.3.3 Room air paths . 20
6.3.3.1 Room air supply . 20
6.3.3.1.0 Introduction . 20
6.3.3.1.1 Free blow . 20
6.3.3.1.2 Overhead distribution . 20
6.3.3.1.3 Raised floor distribution . 20
6.3.3.2 Return air path . 21
6.3.3.2.1 Direct return to side walls at side/end of room . 21
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4 ETSI TR 102 489 V1.4.1 (2015-10)
6.3.3.2.2 Overhead return . 21
7 Thermal evaluation of the equipment/room architecture . 21
8 Temperature reference point . 22
8.0 Introduction . 22
8.1 Temperature measurement point for rack . 23
8.2 Temperature measurement point for aisle . 23
Annex A: Examples of cooling systems in an ARCM in use prior to ETSI EN 300 119-5 . 24
A.0 General . 24
A.1 Single subrack cooling . 24
A.1.0 Introduction . 24
A.1.1 Air outlet located at the top of the ARCM . 24
A.1.2 Air outlet located at the front of the ARCM . 25
A.2 Multiple subrack cooling . 26
A.2.0 Introduction . 26
A.2.1 Serial cooling . 26
A.2.2 Parallel airflow with air inlet located at the front or the bottom of the ARCM . 27
A.2.3 Parallel airflow with air inlet located at the sides of the rack . 29
A.3 300 mm cabinet ARCM thermal solution . 30
A.3.0 Introduction . 30
A.3.1 Current 300 mm ARCM thermal solutions . 30
A.3.2 Alternative 300 mm cabinet solution. 31
A.3.3 Simulation test result about proposed thermal solution . 32
A.3.3.1 Mock-up configuration . 32
A.3.3.2 Component test result . 33
A.3.4 Air deflector design . 33
A.3.4.1 Key factors in air deflector design . 33
A.3.4.2 Different air deflector mock-up test . 33
Annex B: Example of ARCM cooling systems in a room . 36
B.1 Room - serial cooling . 36
B.2 Room - parallel cooling . 36
B.3 ETSI 300 mm ARCM in Central Office . 37
B.3.0 Introduction . 37
B.3.1 ETSI 300 mm ARCM solution . 37
B.3.2 ETSI 300 mm ARCM in CO . 38
B.3.3 Alternative ETSI 300 mm ARCM instalment in CO . 39
B.3.3.0 Introduction. 39
B.3.3.1 Simulation equipment configuration . 40
B.3.3.2 Simulation results . 40
B.3.3.3 Proposed CO arrangement . 41
B.3.3.4 300 mm ARCM in CO simulation . 42
Annex C: Bibliography . 44
History . 45

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5 ETSI TR 102 489 V1.4.1 (2015-10)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (http://ipr.etsi.org).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This Technical Report (TR) has been produced by ETSI Technical Committee Environmental Engineering (EE).
The present document applies to all telecommunications racks/cabinets, miscellaneous racks/cabinets and subracks
forming part of the public telecommunications network and defined in ETSI EN 300 119-1 [i.3], ETSI
EN 300 119-2 [i.4], ETSI EN 300 119-3 [i.5], ETSI EN 300 119-4 [i.6] and ETSI EN 300 119-5 [i.7]
The present document applies also to telecom and data centre room installations.
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Abstract
It is often necessary to integrate different subracks into the same rack/cabinet and different racks/cabinets into a
common equipment room sharing the common room environment. The integration between equipment and the room is
increasingly more important. The present document is intended to provide assistance in integration of equipment and
room environment to ensure that the equipment has the required environment and that each equipment rack/cabinet is
not detrimental to the other equipment in the locality.
It should be an aid for all integrators and designers with their different elementary knowledge to integrate.
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6 ETSI TR 102 489 V1.4.1 (2015-10)
1 Scope
The present document is an aid for all integrators of Information and Communication Technologies (ICT) equipment to
minimize thermal problems. It establishes recommendations for the thermal management of racks/cabinets,
miscellaneous racks/cabinets and locations.
The present document considers telecommunication Central Office (CO) and Data Centers (DC) locations.
The present document considers only the thermal factors. The integrator should consider the thermal factors in
conjunction with the ETSI EN 300 019-1-3 [i.1] and other non-thermal factors.
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
reference document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
http://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are necessary for the application of the present document.
Not applicable.
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
reference document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] ETSI EN 300 019-1-3: "Environmental Engineering (EE); Environmental conditions and
environmental tests for telecommunications equipment; Part 1-3: Classification of environmental
conditions; Stationary use at weatherprotected locations".
[i.2] CENELEC EN 60950-1 (2006): "Information technology equipment - Safety - Part 1: General
requirements".
[i.3] ETSI EN 300 119-1: "Environmental Engineering (EE); European telecommunication standard for
equipment practice; Part 1: Introduction and terminology".
[i.4] ETSI EN 300 119-2: "Environmental Engineering (EE); European telecommunication standard for
equipment practice; Part 2: Engineering requirements for racks and cabinets".
[i.5] ETSI EN 300 119-3: "Environmental Engineering (EE); European telecommunication standard for
equipment practice; Part 3: Engineering requirements for miscellaneous racks and cabinets".
[i.6] ETSI EN 300 119-4: "Environmental Engineering (EE); European telecommunication standard for
equipment practice; Part 4: Engineering requirements for subracks in miscellaneous racks and
cabinets".
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7 ETSI TR 102 489 V1.4.1 (2015-10)
[i.7] ETSI EN 300 119-5: "Environmental Engineering (EE); European telecommunication standard for
equipment practice; Part 5: Thermal management".
[i.8] ETSI EN 300 386: "Electromagnetic compatibility and Radio spectrum Matters (ERM);
Telecommunication network equipment; ElectroMagnetic Compatibility (EMC) requirements".
[i.9] IEC TR 62380: "Reliability data handbook - Universal model for reliability prediction of
electronics components, PCBs and equipment".
[i.10] Recommendation ITU-T L.1300: "Best practices for green data centers".
[i.11] ASHRAE TC9.9.
NOTE: Available at http://tc99.ashraetcs.org/.
[i.12] ETSI ES 202 336-12: "Environmental Engineering (EE); Monitoring and control interface for
infrastructure equipment (power, cooling and building environment systems used in
telecommunication networks); Part 12: ICT equipment power, energy and environmental
parameters monitoring information model".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
ambient: spatial maximal temperature of the air entering the rack/cabinet
NOTE: As defined in ETSI EN 300 019-1-3 [i.1].
cabinet: free-standing and self-supporting enclosure for housing electrical and/or electronic equipment
NOTE: It is usually fitted with doors and/or panels which may or may not be removable.
equipment: equipped subracks, racks/cabinets and miscellaneous racks/cabinets
integrator: end user/operator of telecommunication or IT equipment or their agent
NOTE: For example, an equipment manufacturer could be an operator's agent.
micro-climate: conditions found within the rack/cabinet/miscellaneous rack/cabinet creating a local ambient for the
subrack
NOTE: In practice this will typically result in elevated temperatures and reduced relative humidities to those
quoted in ETSI EN 300 019-1-3 [i.1].
Miscellaneous Rack/Cabinet (MRC): cabinet that accommodates subracks of several different types of equipment and
suppliers
NOTE: It is freely configurable by the Integrator.
rack: free-standing or fixed structure for housing electrical and/or electronic equipment
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
AC Air Cooling
AHU Air Handling Unit
ARCM Any Rack, Cabinet and Miscellaneous rack/cabinet
ASHRAE American Society of Heating, Refrigeration and Air-conditioning Engineers
CFM Cubic Feet to Minute
CO Central Office
CRAC Computer Room Air Conditioner
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8 ETSI TR 102 489 V1.4.1 (2015-10)
DC Data Centre
DT Data Temperature
EMC Electro Magnetic Compatibility
HVAC Heating, Ventilation & Air Conditioning
ICT Information and Communication Technology
MRC Miscellaneous Rack/Cabinet
PDU Poer Distribution Unit
4 ARCM integration overview
The integration can be broken down into:
• Positioning equipment in ARCMs including routing the cables.
• Analysing the possible impact of thermal issues on the configuration of racks/cabinets (e.g. location of
racks/cabinets) and MRCs (e.g. location, openings, placement of baffles).
• Providing the cooling solutions.
During the integration the following parameters have to be taken into account:
• The available volume.
• The maximum ambient temperature/micro-climate.
• The provision of coherent air flow to avoid hot spots.
• The functional thermal limits of equipment.
• The cabling space.
The overall cooling effectiveness needed depends in principle on the type of equipment to be cooled and thermal
requirements to be complied with.
Special attention should be taken to check the impact of the installation of different equipment in the same ARCM on
their functional thermal limits.
It is often very helpful to check, by suitable hand calculation, thermal simulation and measurement, whether the
integration is applicable for the purpose.
5 Subrack integration in the same ARCM
5.1 Configuring equipment in an ARCM
5.1.0 Introduction
This activity consists of choosing how to combine the different subracks and the cabling in the ARCM.
5.1.1 Subrack location
This phase consists of positioning the different subracks in the ARCM.
The distribution of subracks should take into account the following parameters:
• Maximum power dissipated by the equipment for the maximum traffic load or its intended operational state.
For instance, knowledge of the maximum power dissipated will allow the integrator to locate the highest
dissipating subracks at the top of the ARCM in order to minimize the increase of temperature experienced by
the other subracks.
• Subracks working maximum temperature: For example, subracks which withstand high temperature can be
installed at upper part of the ARCM (where generally the temperature is the highest).
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9 ETSI TR 102 489 V1.4.1 (2015-10)
• Thermal restrictions of each subrack. If possible, place the most restrictive subrack in an area not heated by
other subracks, for example, at the bottom in an ARCM with natural convection cooling system, or in an area
receiving fresh air with as high an air velocity as necessary.
• The position and area of air inlet and air outlet for the different subracks. The porosity of the surface and the
obstacles to the airflow in front of the ventilation surface should also be taken into account.
• Air inlet velocity, air outlet velocity of different subracks and estimated air outlet velocity of the ARCM.
• Air velocity inside the ARCM: This should be enhanced as much as possible, by means of subrack distribution
or additional subracks, e.g. fans, baffles, etc.
• Environmental class according to ETSI EN 300 019-1-3 [i.1] (for instance maximum air ambient temperature).
• Estimated direction of the airflow inside the ARCM. It is not recommended to have in the same ARCM two
subrack types which blow the air in the opposite direction.
• Recirculation of the air. Where possible, the recirculation of a-9ir between subracks should be avoided, unless
the design is specifically for serial cooling of the subrack. The risk of recirculation is higher when subracks
with different airflow paths are installed together in the ARCM. For instance, where the increase of
temperature is significant, the hot air exhausted by a subrack should be prevented from being reused to "cool"
another one. Check also the possibility of introducing additional elements to enhance the airflow, such as
baffles (to guide the air flows), vertical covers (to improve the performance of the convection, natural or
forced), plates (to separate flows and minimize re-circulation).
It is sometimes necessary to assign some space between two adjacent subracks to accommodate the location of the air
inlets or the air outlets. This information is generally provided by the manufacturers and detailed in the user's guides.
5.1.2 Cabling
It is recommended that cables within the ARCM are routed in order to minimize the impact on the airflow, without
restricting access to other subracks and making best use of the side cable access channels.
Cables and cable bundles can represent a significant obstruction to airflow. When undertaking an analysis of thermal
performance accounting for airflow in an ARCM it is important that the analysis takes into account the location of
significant amounts of cabling (or wave guides) along with the significance of their obstruction.
5.2 Mechanical structure of ARCM
5.2.0 Introduction
The thermal issues may have an impact on the mechanical structure of the ARCM, i.e.:
• Opening geometry definition.
• Equipment fastening in the rack.
• Definition of the doors and side panels.
This may lead to the choice of a new kind of ARCM (well adapted to the specific application) or to reuse an existing
product (generally, in this case, a compromise has to be found between requirements and performance of the ARCM).
5.2.1 Opening geometry for the airflow
To dissipate the power from the equipment the following parameters have to be considered:
• Position of openings.
• Shape of openings.
• Area and porosity of openings.
• Airflow direction due to the shape of the grid (with or without deflector of air inlet or outlet).
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10 ETSI TR 102 489 V1.4.1 (2015-10)
• Air inlet and air outlet temperature.
NOTE: In case of shielded racks, the openings may be well adapted to equipment frequencies.
5.2.2 Equipment fastening in the ARCM
The fastening elements should not obstruct the air circulation. For instance, in the case of transversal cooling, the
mounting brackets should be well designed to allow the subrack to be cooled. For ETSI compliant equipment this
should already be the case.
5.2.3 Doors
When it is necessary to cool the subracks, cabinet doors, when present, can be punched with a lot of small holes or a
grid may be placed at lower part of the door, allowing air access to a front ventilation channel. The degree of
perforation may be determined using any of the assessment techniques identified in clause 4.
5.3 ARCM cooling issues
5.3.0 Introduction
It is a primary requirement for all equipment to be cooled by natural convection. The mechanical architecture of the
ARCM should be designed to promote natural convection. Assisted cooling methods should be employed only when
natural convection methods are unable to deal with the relevant heat dissipation.
While defining the cooling issues of ARCM the integrator may check the different cooling possibilities:
• What types of cooling techniques have to be used?
• Is natural convection sufficient to provide enough cooling for the equipment and to ensure that the temperature
of the issuing air does not exceed 75 ºC (in accordance with EN 60950-1 [i.2]) in worst-case conditions
(specified in the ETSI EN 300 019-1-3 [i.1])?
• Are additional fan trays necessary to supply/extract the air to/from the ARCM?
• Is air filtration necessary?
5.3.1 Cooling equipment including fans
During the configuration of the cooling equipment, the following issues have to be taken into account:
• Power supply interface requirements.
• EMC performance (e.g. voltage dips and spikes generated into the power network).
• Acoustic noise.
• Safety requirements (including fire protection).
5.3.2 Air Cooling techniques
Many cooling solutions already exist but they fall into two main categories:
• Serial cooling.
• Parallel cooling.
Annex A presents cooling system examples. Other approaches are possible. The present document helps the integrator
to mix different equipment in an ARCM.
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11 ETSI TR 102 489 V1.4.1 (2015-10)
5.3.3 Air filtering
In some instances (see ETSI EN 300 019-1-3 [i.1]) air filters (normally provided at the room level) could be required at
the equipment inlets. Where air filters are used, precautions should be taken in order to clean or replace them
periodically. If the filter is not cleaned or replaced, the micro-climate air inlet temperature for the subracks can increase
dramatically, or the air volume through the equipment be reduced and these changes in ventilation performance can lead
to equipment malfunction.
5.4 Impact of the implementation of subracks in an ARCM
When integrating a subrack in an ARCM, the integrator should implement subracks that fulfil environmental classes of
ETSI EN 300 019-1-3 [i.1]. The environmental class applied to the ARCM should be the lowest environmental class of
the subracks in the ARCM. For example if in the ARCM are integrated 1 subrack complying with class 3.1 of
ETSI EN 300 019-1-3 [i.1] and 3 subracks complying with class 3.2 of ETSI EN 300 019-1-3 [i.1], the environmental
class of the ARCM will be the class 3.1 of ETSI EN 300 019-1-3 [i.1].
The subracks installed in an ARCM maybe subject to highest temperatures depending on the adopted cooling technique.
For instance with the serial cooling technique as shown in figure 5.4a the subracks in the upper positions of the ARCM
are subjected to temperatures that may exceed the maximum temperature specified for the environmental class, as
defined in ETSI EN 300 019-1-3 [i.1] standard, for which the subrack has been designed. If one of the subracks in the
ARCM can be subject to a temperature higher than the maximum temperature of the environmental class for which the
subracks have been designed, then the ARCM will not be considered to be compliant with the specified environmental
class of ETSI EN 300 019-1-3 [i.1]. In this case the ARCM configuration has to be modified (for example installing in
the upper positions the subracks that comply with higher environmental classes) or the cooling technique has to be
changed (use the parallel cooling instead of the serial cooling).
EXAMPLES:
• Case 1: An ARCM with 3 subracks designed to operate in temperature conditions according class 3.1 of
ETSI EN 300 019-1-3 [i.1] and intended to be used in telecom centres where the maximum temperature is set
to 25 °C.
Using the serial cooling technique as shown in figure 5.4a, the upper equipment in the MRC is not operating at
temperature conditions of class 3.1 of ETSI EN 300 019-1-3 [i.1]. In this case it needs to use the parallel
cooling techniques with the air deflectors between the subracks as shown in figure 5.4b.
• Case 2: An ARCM with 1 subrack designed to operate in temperature conditions according class 3.1 of
ETSI EN 300 019-1-3 [i.1] and 1 subrack designed for class 3.2 of EN 300-019-1-3 [i.1] intended to be used in
telecom centres.
Where the maximum temperature is set to 25 °C. In this case the serial cooling technique can be used as shown
in figure 5.4c and the upper equipment in the MRC is then operating at temperature conditions within the
range of the class for which this subrack was designed. However in this case it needs to consider the impact on
the equipment reliability because the upper shelf is operating permanently at high temperature conditions; see
clause 5.5.
• Case 3: An ARCM with 2 subracks designed to operate in temperature conditions according class 3.1 of
ETSI EN 300 019-1-3 [i.1] intended to be used in telecom centres where the maximum temperature can be up
to 30 °C.
The serial cooling technique, as shown in figure 5.4d, cannot be used.
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12 ETSI TR 102 489 V1.4.1 (2015-10)

Figure 5.4a  Figure 5.4b   Figure 5.4c  Figure 5.4d
In practice, the room will not deliver the cool air from the fresh air or mechanically cooled supply without some degree
of mixing. Furthermore the room temperature is not the same in any point of the room and can increase during failure of
the cooling system. It is good practice therefore, to design the cooling system for a normal high air temperature lower
than the highest temperature specified by the reference environmental class (see ETSI EN 300 019-1-3 [i.1]) so that the
temperature of the air entering all subracks in the ARCMs remains within the maximum temperature defined for the
applicable environmental classes of ETSI EN 300 019-1-3 [i.1]. For telecom centres where the cooling system is
without redundancy, it is not recommended to use the serial cooling technique. Where more space is required for
increased airflow then a larger rack/cabinet could be used by the integrator, for example 900 mm width. In this case the
900 mm width racks offers the possibility of introducing equipment according to the ETSI EN 300 119-4 [i.6] leaving
an increased space for airflow. In this case it is necessary to verify that this size is acceptable to the operator for their
room layout.
5.5 Impact of the temperature on equipment reliability
It should be considered that the failure rate of an electronic circuit depends on the working temperature conditions. The
IEC TR 62380 [i.9] provides a model for the reliability prediction of electronic components. The standard assumptions
for the reliability prediction are an average room temperature of 20 °C and an average temperature surrounding the
components of 40 °C. Then, if the room temperature is higher than 20 °C a higher failure rate can be expected for
certain components that have the failure rate with high dependence on the temperature.
In the serial cooling the upper subracks in the ARCM are exposed to highest temperatures and then a higher failure rate
may occur.
In order to get the reliability prediction in line with the ARCM configuration, it is recommended to perform the
reliability prediction at the temperature condition of each subrack in the ARCM when the serial cooling technique is
used (e.g. at or at the expected room temperature when the parallel cooling technique is used). The reliability data at the
different room temperatures can be requested to the equipment supplier.
6 ARCM integration in the same telecommunications
equipment or Data centre room
6.1 Positioning the ARCM in a room
6.1.0 Introduction
This involves positioning the different racks and the cabling in the room.
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13 ETSI TR 102 489 V1.4.1 (2015-10)
6.1.1 Room layout
In a room, it is recommended to line up the ARCM in rows, which will be separated by aisles as stated in
ETSI EN 300 119-2 [i.4]. As an example see the room layout shown in figure 6.1.1.
Space for cooling equipment is determined by the operator's requirement.
The minimum aisle width is 750 mm as stated in ETSI EN 300 119-2 [i.4], but any aisle width can be larger as
determined by the operator's requirement or as required to satisfy health and safety requirements.
300 mm deep equipment is normally placed back to back (or to a wall) as stated in ETSI EN 300 119-2 [i.4]. In this
case all aisles are to the front of the equipment and therefore will require cool air supply so that they are cold aisles.
Where 600 mm equipment is used then a cold aisle is normally created with cool air being supplied in front of the
equipment with a hot aisle to the rear of the equipment. For this approach to be effective it is important that alternate
rows or equipment face opposite directions so that they are all "front to front" (cold aisle) or "back to back" (hot aisle).
Two types of ARCM installation can be encountered:
• ARCMs installed on a raised floor. In this case the cool air may be introduced from the floor void directly into
the room to create a room environment compliant with ETSI EN 300 019-1-3 [i.1]. Cool air can also be
introduced directly into the ARCM. However this can lead to air distribution problems, e.g. some equipment
has too much air while others have insufficient air. This is not preferred unless the integrator can guarantee the
correct balancing of the cool air distribution at the raised floor outlets whenever new equipment is installed or
equipment is removed. External connections are via the bottom or top of the ARCM.
• ARCMs installed directly on the ground (without raised floor), external connections are via the top of the
ARCM and cooling is normally provided via the room.

Figure 6.1.1: Room Layout
When determining the layout of ARCMs in a room, the thermal effects of one ARCM on another or of one ARCM row
to another need to be considered. ARCMs are positioned in the rows in order to facilitate the inter-rack wiring and to
make a complete EMC enclosure for the entire system.
6.1.2 Cabling
The cables are generally routed either over a cable support structure or under a raised floor.
In both cases the cables and the cable support structure should be placed in a way that minimizes the effect on air flow.
Placing cables parallel to the ventilation airflow in the main room, or floor void, generally minimizes the effect on
airflow. Cables placed perpendicular to the supply airflow into the room (or floor void) are best placed at the opposite
end of the room to the ventilation air supply.
ETSI
14 ETSI TR 102 489 V1.4.1 (2015-10)

Figure 6.1.2a: Cable position in a floor void
It is important that the cable depth be carefully considered when the cables are in the main air path. Cables in the
perimeter zone could be allowed to virtually fill the depth of the air path. However, cables in the air path from the Air
Handling Units (AHUs) to the equipment may significantly restrict cooling effectiveness if the proportion of the air path
blocked is not controlled. In general cable obstructions can be greater when the cable routes are parallel to the air paths
rather than perpendicular.
NOTE: Where possible wave guides should be treated in a similar manner to cables.
The cabling can be arranged over the ceiling or under the floor (as shown in figures 6.1.2b and 6.1.2c), it is important to
arrange the cabling to prevent air blockage.

Figure 6.1.2b: Ceiling cabling Figure 6.1.2c: Underground cabling
6.1.3 Cooling systems
Two cases can be encountered:
• Cooling system exists: in this case, the room layout of the ARCMs has to take into account the existing
situation.
• Cooling system does not exist: therefore, the cooling system should be co-ordinated with the room layout. Due
to the increase of power dissipated in the equipment, the provision of cooling should be taken into account.
• Consideration should be given in the room cooling design to allow for cooling system component failure. This
does not necessarily mean allowing totally redundant s
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