Mechanical structures for electrical and electronic equipment - Thermal management for cabinets in accordance with IEC 60297 and IEC 60917 Series - Part 6: Air recirculation and bypass of indoor cabinets (IEC 62610-6:2020)

IEC 62610-6 which deals with thermal management for cabinets in accordance withIEC 60297 and IEC 60917 series, provides compatible measurement methods of recirculationratio and bypass ratio which are indicators for defining quality of airflow in the forced air coolingthat can be commonly applied to indoor cabinets for mounting subrack and/or chassis-basedequipment.

Mechanische Bauweisen für elektrische und elektronische Einrichtungen - Wärmemanagement für Schränke nach den Reihen IEC 60297 und IEC 60917 - Teil 6: Luftrezirkulation und Verlustluftstrom von Innenschränken (IEC 62610-6:2020)

Structures mécaniques pour équipements électriques et électroniques - Gestion thermique pour les armoires conformes aux séries IEC 60297 et IEC 60917 - Partie 6 : Recyclage et dérivation de l'air des armoires intérieures (IEC 62610-6:2020)

IEC 62610-6:2020 traite de la gestion thermique pour les armoires conformément aux séries CEI 60297 et CEI 60917, fournit des méthodes de mesure compatibles du taux de recirculation et du taux de dérivation qui sont des indicateurs pour définir la qualité du flux d'air dans le refroidissement à air forcé qui peuvent être couramment appliquées aux armoires intérieures pour le montage des bacs et / ou des équipements sur châssis. Ce document contient les éléments suivants: a) la définition des débits de recirculation et de dérivation dans le refroidissement de l'armoire, b) les niveaux du taux de recirculation RC, c) la définition de la formule du taux de recirculation RCs du bac de refroidissement à air forcé et / ou des équipements sur châssis installés dans l'armoire, d) la formule de définition du taux de recirculation RCr et du taux de dérivation BPr de l'ensemble de l'armoire, e) les exigences de la méthode de mesure de chaque température nécessaire au calcul du taux de recirculation RCs, RCr et du taux de contournement BPr. Le but de ce document est de fournir: • pour l'intégrateur d'équipement et le concepteur de développement de l'armoire les critères pour déterminer efficacement et correctement la spécification, et • pour le fournisseur de l'armoire, la méthode de mesure et de classification du taux de recirculation du flux d'air d

Mehanske strukture za električno in elektronsko opremo - Uravnavanje toplote v omaricah v skladu s skupinama standardov IEC 60297 in IEC 60917 - 6. del: Recirkulacija zraka in obvod notranjih omaric (IEC 62610-6:2020)

General Information

Status
Published
Publication Date
28-May-2020
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
27-May-2020
Due Date
01-Aug-2020
Completion Date
29-May-2020

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SLOVENSKI STANDARD
SIST EN IEC 62610-6:2020
01-julij-2020
Mehanske strukture za električno in elektronsko opremo - Uravnavanje toplote v
omaricah v skladu s skupinama standardov IEC 60297 in IEC 60917 - 6. del:
Recirkulacija zraka in obvod notranjih omaric (IEC 62610-6:2020)

Mechanical structures for electrical and electronic equipment - Thermal management for

cabinets in accordance with IEC 60297 and IEC 60917 Series - Part 6: Air recirculation

and bypass of indoor cabinets (IEC 62610-6:2020)
Mechanische Bauweisen für elektrische und elektronische Einrichtungen -
Wärmemanagement für Schränke nach den Reihen IEC 60297 und IEC 60917 - Teil 6:
Luftrezirkulation und Verlustluftstrom von Innenschränken (IEC 62610-6:2020)
Structures mécaniques pour équipements électriques et électroniques - Gestion

thermique pour les armoires conformes aux séries IEC 60297 et IEC 60917 - Partie 6 :

Recyclage et dérivation de l'air des armoires intérieures (IEC 62610-6:2020)
Ta slovenski standard je istoveten z: EN IEC 62610-6:2020
ICS:
31.240 Mehanske konstrukcije za Mechanical structures for
elektronsko opremo electronic equipment
SIST EN IEC 62610-6:2020 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN IEC 62610-6:2020
---------------------- Page: 2 ----------------------
SIST EN IEC 62610-6:2020
EUROPEAN STANDARD EN IEC 62610-6
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2020
ICS 31.240
English Version
Mechanical structures for electrical and electronic equipment -
Thermal management for cabinets in accordance with IEC
60297 and IEC 60917 series - Part 6: Air recirculation and
bypass of indoor cabinets
(IEC 62610-6:2020)

Structures mécaniques pour équipements électriques et Mechanische Bauweisen für elektrische und elektronische

électroniques - Gestion thermique pour les armoires Einrichtungen - Wärmemanagement für Schränke nach den

conformes aux séries IEC 60297 et IEC 60917 - Partie 6 : Reihen IEC 60297 und IEC 60917 - Teil 6: Luftrezirkulation

Recyclage et dérivation de l'air des armoires intérieures und Verlustluftstrom von Innenschränken

(IEC 62610-6:2020) (IEC 62610-6:2020)

This European Standard was approved by CENELEC on 2020-04-29. CENELEC members are bound to comply with the CEN/CENELEC

Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC

Management Centre or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation

under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the

same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,

Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the

Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2020 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. EN IEC 62610-6:2020 E
---------------------- Page: 3 ----------------------
SIST EN IEC 62610-6:2020
EN IEC 62610-6:2020 (E)
European foreword

The text of document 48D/700/CDV, future edition 1 of IEC 62610-6, prepared by SC 48D

"Mechanical structures for electrical and electronic equipment" of IEC/TC 48 "Electrical connectors

and mechanical structures for electrical and electronic equipment" was submitted to the IEC-

CENELEC parallel vote and approved by CENELEC as EN IEC 62610-6:2020.
The following dates are fixed:

• latest date by which the document has to be implemented at national (dop) 2021-01-29

level by publication of an identical national standard or by endorsement

• latest date by which the national standards conflicting with the (dow) 2023-04-29

document have to be withdrawn

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.

Endorsement notice

The text of the International Standard IEC 62610-6:2020 was approved by CENELEC as a European

Standard without any modification.

In the official version, for Bibliography, the following notes have to be added for the standards

indicated:
IEC 60297-3-101 NOTE Harmonized as EN 60297-3-101
IEC 60917-2-1 NOTE Harmonized as EN 60917-2-1
IEC 60917-2-2 NOTE Harmonized as EN 60917-2-2
IEC 62610-2 NOTE Harmonized as EN IEC 62610-2
IEC 62610-5 NOTE Harmonized as EN 62610-5
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SIST EN IEC 62610-6:2020
EN IEC 62610-6:2020 (E)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments)

applies.

NOTE 1 Where an International Publication has been modified by common modifications, indicated by (mod), the relevant

EN/HD applies.

NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here:

www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60297-3-100 - Mechanical structures for electronic EN 60297-3-100 -
equipment - Dimensions of mechanical
structures of the 482,6 mm (19 in) series -
Part 3-100: Basic dimensions of front
panels, subracks, chassis, racks and
cabinets
IEC 60917-1 - Modular order for the development of EN IEC 60917-1 -
mechanical structures for electrical and
electronic equipment practices - Part 1:
Generic standard
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SIST EN IEC 62610-6:2020
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SIST EN IEC 62610-6:2020
IEC 62610-6
Edition 1.0 2020-03
INTERNATIONAL
STANDARD
Mechanical structures for electrical and electronic equipment – Thermal
management for cabinets in accordance with IEC 60297 and IEC 60917 series –
Part 6: Air recirculation and bypass of indoor cabinets
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.240 ISBN 978-2-8322-8006-5

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 7 ----------------------
SIST EN IEC 62610-6:2020
– 2 – IEC 62610-6:2020 © IEC 2020
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms and definitions ...................................................................................................... 8

4 Recirculation level ........................................................................................................... 8

5 Determination of recirculation and bypass ratio ............................................................... 9

5.1 Cooling airflow in a cabinet ..................................................................................... 9

5.2 Recirculation ratio of a subrack ............................................................................. 10

5.3 Recirculation ratio of a cabinet .............................................................................. 11

5.4 Bypass ratio of a cabinet ....................................................................................... 11

6 Measurement of recirculation and bypass ...................................................................... 11

6.1 Measurement of recirculation of a subrack ............................................................ 11

6.2 Measurement of recirculation of a cabinet ............................................................. 12

6.3 Measurement of bypass of a cabinet ..................................................................... 12

6.4 Measurement methods of temperature .................................................................. 12

6.4.1 Intake air temperature of a subrack ............................................................... 12

6.4.2 Intake air temperature of a subrack group ...................................................... 13

6.4.3 Exhaust air temperature of a subrack ............................................................ 13

6.4.4 Exhaust air temperature of a subrack group ................................................... 13

6.4.5 Intake air temperature of a cabinet ................................................................ 13

6.4.6 Exhaust air temperature of a cabinet ............................................................. 13

6.5 Measurement method of recirculation for an empty cabinet ................................... 14

Annex A (normative) Measurement method of recirculation with dummy thermal loads ........ 15

A.1 Purpose ................................................................................................................ 15

A.2 Specifications ....................................................................................................... 15

A.2.1 DTL ............................................................................................................... 15

A.2.2 Cabinet specifications .................................................................................... 15

A.2.3 Measurement configurations .......................................................................... 16

A.3 Environmental conditions ...................................................................................... 16

A.4 Measurement positions ......................................................................................... 16

A.4.1 Intake air temperature of DTL ........................................................................ 16

A.4.2 Exhaust air temperature of DTL ..................................................................... 16

A.4.3 Intake air temperature of a cabinet ................................................................ 16

A.4.4 Exhaust air temperature of a cabinet ............................................................. 16

A.4.5 Evaluation of recirculation ratio of a subrack .................................................. 16

A.4.6 Evaluation of recirculation and bypass ratio of a cabinet ................................ 16

A.5 Case study ............................................................................................................ 16

A.6 Relationship between recirculation ratio and intake temperature rise .................... 19

Annex B (normative) Derivation of recirculation and bypass in a cabinet .............................. 21

B.1 General ................................................................................................................. 21

B.2 Derivation of recirculation and bypass ................................................................... 21

Annex C (informative) Application of recirculation and bypass to outdoor cabinets ............... 22

C.1 General ................................................................................................................. 22

C.2 Application example .............................................................................................. 22

Bibliography .......................................................................................................................... 24

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SIST EN IEC 62610-6:2020
IEC 62610-6:2020 © IEC 2020 – 3 –

Figure 1 – Airflow in a cabinet ................................................................................................. 9

Figure 2 – Diagram of cabinet airflows .................................................................................. 10

Figure A.1 – Outline drawings of DTL ................................................................................... 17

Figure A.2 – Experimental setup of a cabinet and DTL .......................................................... 17

Figure A.3 – Measurement points of intake air temperature of DTL ....................................... 18

Figure A.4 – Measurement points of exhaust air temperature of DTL .................................... 18

Figure A.5 – Measurement points of intake air temperature of a cabinet ............................... 18

Figure A.6 – Measurement points of exhaust air temperature of a cabinet ............................. 18

Figure A.7 – Recirculation ratio vs intake air temperature rise............................................... 20

Figure C.1 – Outdoor cabinet airflow schematic .................................................................... 23

Figure C.2 – Airflow diagram and air temperature in outdoor cabinet .................................... 23

Table 1 – Recirculation level ................................................................................................... 9

Table A.1 – Specifications of DTL ......................................................................................... 15

Table A.2 – Specifications of DTL ......................................................................................... 17

Table A.3 – Test result .......................................................................................................... 19

Table A.4 – Recirculation and bypass ratio of a cabinet ........................................................ 19

Table C.1 – A case study of an outdoor cabinet .................................................................... 23

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SIST EN IEC 62610-6:2020
– 4 – IEC 62610-6:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MECHANICAL STRUCTURES FOR ELECTRICAL AND ELECTRONIC
EQUIPMENT – THERMAL MANAGEMENT FOR CABINETS IN
ACCORDANCE WITH IEC 60297 AND IEC 60917 SERIES –
Part 6: Air recirculation and bypass of indoor cabinets
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international

co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and

in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,

Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their

preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with

may participate in this preparatory work. International, governmental and non-governmental organizations liaising

with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for

Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence between

any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent

rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 62610-6 has been prepared by subcommittee 48D: Mechanical

structures for electrical and electronic equipment, of IEC technical committee 48: Electrical

connectors and mechanical structures for electrical and electronic equipment.
The text of this International Standard is based on the following documents:
CDV Report on voting
48D/700/CDV 48D/715/RVC

Full information on the voting for the approval of this International Standard can be found in the

report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

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SIST EN IEC 62610-6:2020
IEC 62610-6:2020 © IEC 2020 – 5 –

A list of all parts in the IEC 62610 series, published under the general title Mechanical structures

for electrical and electronic equipment – Thermal management for cabinets in accordance with

iec 60297 and iec 60917 series, can be found on the IEC website.

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
---------------------- Page: 11 ----------------------
SIST EN IEC 62610-6:2020
– 6 – IEC 62610-6:2020 © IEC 2020
INTRODUCTION

The signal speed and component density of electrical and electronic equipment in the ICT field

and the FA field, such as high performance servers, communications equipment, and electronic

control equipment have been steadily increasing. As a result, the heat generation density of the

integrated circuits, the power consumption of the equipment, and therefore the cooling task has

also been increasing. In a computer room common in the ICT field, where many cabinets for

mounting subrack and/or chassis-based equipment are installed and high availability is required,

it is necessary to pay attention so that the equipment does not experience high temperature

problems.

To prevent high temperature problems with the electronic equipment, it is important that the air

conditioning installed in a computer room effectively contributes to the cooling of the cabinet

for mounting subrack and/or chassis-based equipment. Indicators relating to airflow such as

recirculation and bypass, are used to judge the effectiveness of the air conditioning system.

Recirculation is the ratio at which the cabinets in the computer room suck in their own exhaust

air, which affects the thermal problems of the equipment as it raises the intake air temperature.

Bypass is the ratio at which the cooled supply air does not pass through the cabinets in the

computer room, and affects the energy efficiency as it increases the air conditioning energy. If

these ratios, especially the recirculation ratio, are kept low, the airflow of the computer room

can be regarded as effectively cooling the cabinets. Conversely, if air recirculation or bypass

occurs, the temperature of subracks and/or chassis-based equipment in the cabinet rises.

Therefore it is necessary to provide similar indices to measure the effectiveness of the cooling

airflow for the equipment in the cabinet.

The existing standard for forced air cooling, IEC 62610-2, introduces a method for determining

the ideal airflow for a forced air cooled cabinet assembled with associated subrack and/or

chassis-based equipment. The standard also defines qualitative guidelines for avoiding

recirculation in such cabinets and a server(computer) room. However, concrete numerical

values and the evaluation method of the recirculation have not been defined. It was impossible

to judge in advance whether the cabinet for mounting subrack and/or chassis-based equipment

satisfies the environmental conditions, or whether the empty cabinet has sufficient cooling when

subrack and/or chassis-based equipment are mounted.

This document defines a method for easily measuring the recirculation ratio (RC) and the

bypass ratio (BP) of the airflow in a cabinet and provides performance levels of recirculation on

effectiveness of the cooling airflow in such cabinets. This can be regarded as the degree of

conformity with respect to behaviour of the airflow in the cabinet in the computer room.

Alternatively, even for an outdoor cabinet including a heat exchanger and an air conditioner,

this method can be effectively utilized as an index for knowing the degree of airflow

appropriately contributing to cooling the internal space in which the equipment is mounted.

The purpose of this document is to provide:

• for the equipment integrator and development designer of the cabinet the criteria for

efficiently and correctly determining the specification, and

• for the supplier of the cabinet the measuring and classifying method for the airflow

recirculation rate of the subrack and/or chassis-based equipment installed in the cabinet.

This document is addressed to the mechanical structures in accordance with IEC 60297 and

IEC 60917 series.
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SIST EN IEC 62610-6:2020
IEC 62610-6:2020 © IEC 2020 – 7 –
MECHANICAL STRUCTURES FOR ELECTRICAL AND ELECTRONIC
EQUIPMENT – THERMAL MANAGEMENT FOR CABINETS IN
ACCORDANCE WITH IEC 60297 AND IEC 60917 SERIES –
Part 6: Air recirculation and bypass of indoor cabinets
1 Scope

This part of IEC 62610 which deals with thermal management for cabinets in accordance with

IEC 60297 and IEC 60917 series, provides compatible measurement methods of recirculation

ratio and bypass ratio which are indicators for defining quality of airflow in the forced air cooling

that can be commonly applied to indoor cabinets for mounting subrack and/or chassis-based

equipment.

NOTE 1 Both recirculation and bypass represent leakage airflows, i.e. detrimental phenomena in terms of cooling

efficiency; their measurement is obviously aimed at their mitigation.
This document contains the following:

a) the definition of recirculation and bypass flow rates in the cooling of the cabinet,

b) the levels of the recirculation ratio RC,
of forced air cooling subrack and/or
c) the definition of the formula for the recirculation ratio RC
chassis-based equipment installed in the cabinet,

d) the definition formula of recirculation ratio RC and bypass rate BP of the entire cabinet,

r r

e) the requirements of the measuring method of each temperature necessary for calculating

the recirculation ratio RC , RC and bypass ratio BP .
s r r

NOTE 2 This document includes the definition of measuring bypass ratio, but excludes the definition of levels of

bypass ratio.

The drawings used are not intended to indicate product design. They are only for explanatory

indications for defining forced air cooling airflows.

The recirculation and bypass measurement methods dealt with in this document are assumed

to be applied to a cabinet installed indoors. The cooling air inlet is at the front or the bottom of

the cabinet and the heated air is exhausted to the rear or the top. These methods are also

applicable to a cabinet that is installed outdoors and has a cooling device such as a heat

exchanger or an air conditioner on the front or the back (see Annex C).

The recirculation ratio of a subrack or a cabinet is defined for each individual subrack or chassis-

based equipment mounted in the cabinet or for the entire cabinet. The bypass ratio of a cabinet

is defined for the entire cabinet.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies.

For undated references, the latest edition of the referenced document (including any

amendments) applies.

IEC 60297-3-100, Mechanical structures for electronic equipment – Dimensions of mechanical

structures of the 482,6 mm (19 in) series – Part 3-100: Basic dimensions of front panels,

subracks, chassis, racks and cabinets
---------------------- Page: 13 ----------------------
SIST EN IEC 62610-6:2020
– 8 – IEC 62610-6:2020 © IEC 2020

IEC 60917-1, Modular order for the development of mechanical structures for electrical and

electronic equipment practices – Part 1: Generic standard
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
recirculation flow rate

flow rate of the air that returns directly from the exhaust of the equipment to be cooled to the

intake side of the equipment
3.2
bypass flow rate

flow rate of the air going through a cabinet without going through any of the equipment to be

cooled
3.3
recirculation ratio of a subrack

ratio of the recirculation flow rate of a subrack or a chassis-based equipment to the flow rate of

the equipment
3.4
recirculation ratio of a cabinet

ratio of the total recirculation flow rate of all of the subracks mounted in a cabinet to the total

flow rate of all of the subracks mounted in a cabinet
3.5
bypass ratio of a cabinet
ratio of the bypass flow rate of a cabinet to the airflow rate of a cabinet
3.6
dummy thermal load
DTL

simulator that reproduces thermal fluid behaviour such as heat dissipation and flow rate

generated by subrack and/or chassis-based equipment

Note 1 to entry: Generally, a heater and a fan mounted in a chassis are used, and the amount of heat dissipation

and the fan flow rate can be adjusted.
4 Recirculation level

The recirculation level RL indicates the degree of recirculation of a subrack or a chassis or a

cabinet and is represented by levels RL1 through RL4 according to the recirculation ratio of a

subrack RC or recirculation ratio of a cabinet RC . See Table 1.
s r
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SIST EN IEC 62610-6:2020
IEC 62610-6:2020 © IEC 2020 – 9 –
Table 1 – Recirculation level
Recirculation level Recirculation ratio of a subrack RC
or of a cabinet RC
RL1 more than 33
RL2 20 to 33
RL3 10 to 20
RL4 0 to 10

If the RC or RC value varies depending on the mounting condition or position of the subrack

s r

and/or chassis, or the conditions of cables and/or other mechanical parts, etc., the manufacturer

shall clearly indicate the configuration and the corresponding recirculation level in the data

sheet.
5 Determination of recirculation and bypass ratio
5.1 Cooling airflow in a cabinet

Figure 1 schematically shows the airflow in the cabinet in which the subrack is mounted, with

arrows by size and direction according to the flow balance. In the equipment cabinet, cooling

air is supplied from the front, enters from the inlet of the subrack into the interior, cools the

interior of the subrack, exhausts from the subrack, and is exhausted from the rear of the cabinet.

A part of the cabinet intake bypasses the s
...

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