ISO/IEC TS 22237-4:2018

Information technology - Data centre facilities and infrastructures - Part 4: Environmental control

ISO/IEC TS 22237-4:2018 addresses environmental control within data centres based upon the criteria and classifications for "availability", "security" and "energy efficiency enablement" within ISO/IEC TS 22237‑1. ISO/IEC TS 22237-4:2018 specifies requirements and recommendations for the following: a) temperature control; b) fluid movement control; c) relative humidity control; d) particulate control; e) vibration; f) floor layout and equipment locations; g) energy saving practices; h) physical security of environmental control systems. Issues related to electromagnetic environment can be found in ISO/IEC TS 22237‑6.

Technologie de l’information — Installation et infrastructures de centres de traitement de données — Partie 4: Contrôle environnemental

General Information

• Status: Withdrawn
• Publication Date: 26-Apr-2018
• Withdrawal Date: 26-Apr-2018
• ICS: 35.020 - Information technology (IT) in general
• Technical Committee: ISO/IEC JTC 1/SC 39 - Sustainability, IT and data centres
• Drafting Committee: ISO/IEC JTC 1/SC 39/WG 3 - Sustainable facilities and infrastructures
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 29-Oct-2021
• Completion Date: 30-Oct-2025

Relations

• Revised: ISO/IEC 22237-4:2021 - Information technology - Data centre facilities and infrastructures - Part 4: Environmental control
• Effective Date: 23-Apr-2020

Standards Content (Sample)

TECHNICAL ISO/IEC TS
SPECIFICATION 22237-4
First edition
2018-05
Information technology — Data centre
facilities and infrastructures —
Part 4:
Environmental control
Technologie de l’information — Installation et infrastructures de
centres de traitement de données —
Partie 4: Contrôle environnemental
Reference number
©
ISO/IEC 2018
© ISO/IEC 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
ii © ISO/IEC 2018 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 Abbreviated terms . 3
4 Conformance . 3
5 Environmental control within data centres . 3
5.1 General . 3
5.1.1 Functional elements . . 3
5.1.2 Requirements . 4
5.1.3 Recommendations . 4
5.2 Environmental control of data centre spaces . 5
5.2.1 Building entrance facilities . 5
5.2.2 Personnel entrance(s) . 5
5.2.3 Docking/loading bay(s) . 5
5.2.4 Generator space(s) including fuel storage . 5
5.2.5 Transformer space(s) . 5
5.2.6 Electrical distribution space(s) . 6
5.2.7 Telecommunication spaces(s) . 6
5.2.8 Main distributor spaces(s) . 6
5.2.9 Computer room space(s) and associated testing space(s) . 6
5.2.10 Electrical space(s) . . 7
5.2.11 Mechanical space(s) . 7
5.2.12 Control room space(s) . 7
5.2.13 Office space(s) . 7
5.2.14 Storage and holding space(s) . 7
5.2.15 Accommodation of UPS equipment . 7
6 Availability . 8
6.1 General . 8
6.2 Design options by space . 8
6.2.1 General. 8
6.2.2 Spaces excluded from the availability classification . 9
6.2.3 Main distributor space(s) . 9
6.2.4 Computer room space(s) and associated testing space(s) .10
6.2.5 UPS space .11
6.3 Environmental control system capacity planning with respect to expansion .12
6.4 Environmental control system capacity planning with respect to resilience .12
7 Physical security .12
7.1 General .12
7.2 Access .12
8 Energy efficiency enablement .12
8.1 General .12
8.2 Measurement of temperature .12
8.2.1 External temperature .12
8.2.2 Computer room temperature .13
8.3 Measurement of relative humidity .14
8.3.1 External relative humidity .14
8.3.2 Computer room relative humidity .14
8.4 Measurement of air pressure .15
© ISO/IEC 2018 – All rights reserved iii

8.5 Coolant flow rates .15
8.6 Heat removal .15
8.7 Outside air .15
8.8 Provision of alarms .15
8.9 Measurement requirements by Granularity Level .15
Annex A (normative) Distribution methodologies for temperature-controlled airin
computer room space .17
Annex B (informative) Control system concepts .20
Bibliography .21
iv © ISO/IEC 2018 – All rights reserved

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
members of ISO or IEC participate in the development of International Standards through technical
committees established by the respective organization to deal with particular fields of technical
activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other international
organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the
work. In the field of information technology, ISO and IEC have established a joint technical committee,
ISO/IEC JTC 1.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for
the different types of document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject
of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent
rights. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/IEC JTC 1, Information technology,
Subcommitte SC 39, Sustainability for and by Information Technology.
A list of all parts in the ISO/IEC TS 22237 series can be found on the ISO website.
© ISO/IEC 2018 – All rights reserved v

Introduction
The unrestricted access to internet-based information demanded by the information society has led to
an exponential growth of both internet traffic and the volume of stored/retrieved data. Data centres
are housing and supporting the information technology and network telecommunications equipment
for data processing, data storage and data transport. They are required both by network operators
(delivering those services to customer premises) and by enterprises within those customer premises.
Data centres need to provide modular, scalable and flexible facilities and infrastructures to easily
accommodate the rapidly changing requirements of the market. In addition, energy consumption of data
centres has become critical both from an environmental point of view (reduction of carbon footprint)
and with respect to economical considerations (cost of energy) for the data centre operator.
The implementation of data centres varies in terms of:
a) purpose (enterprise, co-location, co-hosting or network operator facilities);
b) security level;
c) physical size;
d) accommodation (mobile, temporary and permanent constructions).
The needs of data centres also vary in terms of availability of service, the provision of security and
the objectives for energy efficiency. These needs and objectives influence the design of data centres
in terms of building construction, power distribution, environmental control and physical security.
Effective management and operational information is required to monitor achievement of the defined
needs and objectives.
The ISO/IEC TS 22237 series specifies requirements and recommendations to support the various
parties involved in the design, planning, procurement, integration, installation, operation and
maintenance of facilities and infrastructures within data centres. These parties include:
1) owners, facility managers, ICT managers, project managers, main contractors;
2) architects, building designers and builders, system and installation designers;
3) facility and infrastructure integrators, suppliers of equipment;
4) installers, maintainers.
At the time of publication of this document, the ISO/IEC TS 22237 series will comprise the following
documents:
ISO/IEC TS 22237-1, Information technology — Data centre facilities and infrastructures — Part 1: General
concepts;
ISO/IEC TS 22237-2, Information technology — Data centre facilities and infrastructures — Part 2:
Building construction;
ISO/IEC TS 22237-3, Information technology — Data centre facilities and infrastructures — Part 3: Power
distribution;
ISO/IEC TS 22237-4, Information technology — Data centre facilities and infrastructures — Part 4:
Environmental control;
ISO/IEC TS 22237-5, Information technology — Data centre facilities and infrastructures — Part 5:
Telecommunications cabling infrastructure;
ISO/IEC TS 22237-6, Information technology — Data centre facilities and infrastructures — Part 6:
Security systems;
vi © ISO/IEC 2018 – All rights reserved

ISO/IEC TS 22237-7, Information technology — Data centre facilities and infrastructures — Part 7:
Management and operational information.
The inter-relationship of the specifications within the ISO/IEC TS 22237 series is shown in Figure 1.
Figure 1 — Schematic relationship between the ISO/IEC TS 22237 series of documents
ISO/IEC TS 22237-2 to ISO/IEC TS 22237-6 specify requirements and recommendations for particular
facilities and infrastructures to support the relevant classification for “availability”, “physical security”
and “energy efficiency enablement” selected from ISO/IEC TS 22237-1.
This document addresses the environmental control facilities and infrastructure within data centres
together with the interfaces for monitoring the performance of those facilities and infrastructures in
line with ISO/IEC TS 22237-7 (in accordance with the requirements of ISO/IEC TS 22237-1).
ISO/IEC TS 22237-7 addresses the operational and management information (in accordance with the
requirements of ISO/IEC TS 22237-1.
This document is intended for use by and collaboration between architects, building designers and
builders, system and installation designers.
The ISO/IEC TS 22237 series does not address the selection of information technology and network
telecommunications equipment, software and associated configuration issues.
© ISO/IEC 2018 – All rights reserved vii

TECHNICAL SPECIFICATION ISO/IEC TS 22237-4:2018(E)
Information technology — Data centre facilities and
infrastructures —
Part 4:
Environmental control
1 Scope
This document addresses environmental control within data centres based upon the criteria and
classifications for “availability”, “security” and “energy efficiency enablement” within ISO/IEC TS 22237-1.
This document specifies requirements and recommendations for the following:
a) temperature control;
b) fluid movement control;
c) relative humidity control;
d) particulate control;
e) vibration;
f) floor layout and equipment locations;
g) energy saving practices;
h) physical security of environmental control systems.
Issues related to electromagnetic environment can be found in ISO/IEC TS 22237-6.
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.
ISO/IEC TS 22237-1, Information technology — Data centre facilities and infrastructures — Part 1: General
concepts
ISO/IEC TS 22237-6, Information technology — Data centre facilities and infrastructures — Part 6:
Security systems
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions in ISO/IEC TS 22237-1 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http: //www .electropedia .org/
© ISO/IEC 2018 – All rights reserved 1

— ISO Online browsing platform: available at https: //www .iso .org/obp
3.1.1
adiabatic cooling
cooling system that uses the evaporative cooling principle to reduce the air temperature
3.1.2
absolute humidity
quantity of water vapour in a given volume of air
Note 1 to entry: Expressed by mass.
3.1.3
access floor
system consisting of completely removable and interchangeable floor panels that are supported on
adjustable pedestals connected by stringers to allow the area beneath the floor to be used by building
services
Note 1 to entry: Also known as “raised floor”.
[SOURCE: ISO/IEC TS 22237-2:2018, 3.1.1]
3.1.4
comfort environmental controls
controls which produce an environment which is appropriate for the effective performance of personnel
in a given space
3.1.5
dew point
temperature at which the water vapour in a gas begins to deposit as a liquid or ice, under standardized
conditions
[SOURCE: IEC 60050-212:2010, 212-18-11]
3.1.6
exhaust air temperature
temperature of the air leaving the data centre building or the temperature of the air leaving the heat load
3.1.7
fresh air cooling
cooling system that uses the external air to cool the data centre either directly or indirectly
3.1.8
heat load
thermal power that is produced
3.1.9
information technology equipment
equipment providing data storage, processing and transport services together with equipment
dedicated to providing direct connection to core and/or access networks
3.1.10
outdoor air temperature
temperature of the air measured outside of the data centre building
3.1.11
relative humidity
ratio, expressed as a percentage, of the vapour pressure of water vapour in moist air to the saturation
vapour pressure with respect to water or ice at the same temperature
[SOURCE: IEC 60050-705:1995, 705-05-09]
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3.1.12
return air temperature
temperature of the air re-entering the environmental control system, e.g. the air handling unit
3.1.13
supply air temperature
temperature of the air entering the IT equipment
3.1.14
ventilation
supply of air motion in a space by circulation or by moving air through the space
Note 1 to entry: Ventilation can be produced by any combination of natural or mechanical supply and exhaust.
Note 2 to entry: Such systems can include partial treatment such as heating, relative humidity control, filtering
or purification, and, in some cases, evaporative cooling.
3.2 Abbreviated terms
For the purposes of this document, the abbreviated terms given in ISO/IEC TS 22237-1 and the
following apply.
UPS Uninterruptible Power Supply
CRAC Computer Room Air Conditioning (Unit)
IT Information Technology
ITE Information Technology Equipment
4 Conformance
For a data centre to conform to this document:
a) it shall feature an environmental control solution that meets the requirements of Clauses 4 and 5;
b) it shall feature an approach to physical security in relation to the environmental control solution
that meets the requirements of Clause 6;
c) it shall feature an energy efficiency enablement solution that meets the requirements of the
relevant Granularity Level of Clause 7;
d) local regulations, including safety, shall be met.
5 Environmental control within data centres
5.1 General
5.1.1 Functional elements
The environmental control system is one of the most important parts of the data centre infrastructure.
Excessive variations of temperature or relative humidity can directly affect the functional capability of
the data centre and its infrastructures.
The functional elements of the environmental control system are divided into primary and secondary
elements.
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Primary elements relate to the mechanical generation of temperature controlled fluids. Secondary
elements relate to the distribution of fluids generated by the primary elements. See Table 1 for examples
of these elements.
Some environmental systems combine the function of primary and secondary elements.
Table 1 — Examples of primary and secondary functional elements
Area Fluid Functional element(s)
Water Water supply grid, chiller, pump(s)
Primary
Air Outside air intake, filter, heat exchanger
Water Pump(s), valve(s), pipe system, liquid cooled enclosures
Secondary
Air Duct system, computer room air conditioning unit
It should be noted that a Class 1 environmental control system does not necessarily contain any of these
elements.
5.1.2 Requirements
The approach taken for the design of the environmental control system shall take into account available
technology, physical security and data centre availability.
The design of the environmental control system and the selection and installation of functional
elements shall take into consideration the effect of vibration on the data centre spaces.
The design of the environmental control system and the selection and installation of functional elements
shall take into consideration the effect of friction and/or obstruction in the pathways for temperature
controlled fluids. Operational controls shall be provided to ensure no degradation of fluid flow due to
changes in the pathways.
During the design phase the requirement for the number of air changes per unit time and air pressure
shall be established.
In all data centre spaces the requirements for filtration shall be considered.
In all spaces where there is a risk of damage to static-sensitive equipment from electro-static discharge
the relative humidity shall be maintained in accordance with the instructions of the supplier of the
equipment to be accommodated. Where no information exists or where the equipment manufacturer is
not specified, a minimum dew point of 5,5 °C shall be maintained.
Where direct fresh air cooling solutions are chosen the requirements analysis and the resulting
methodology of monitoring and control is of prime importance. In these circumstances particular
consideration shall be given to the control of contaminants.
For guidance on the ventilation requirements of activated gaseous suppression systems see ISO/
IEC TS 22237-6.
5.1.3 Recommendations
Opportunities for reductions in energy consumption exist where wider tolerances of temperature and
relative humidity can be tolerated in defined data centre spaces. It is recommended to use cooling units
with integrated vibration decoupling for all rotating parts (e.g. fan, compressor) or low vibration parts.
If the cooling units or other external components with rotating parts are not equipped with integrated
vibration decoupling the whole unit should be decoupled.
4 © ISO/IEC 2018 – All rights reserved

5.2 Environmental control of data centre spaces
5.2.1 Building entrance facilities
No specific requirements.
5.2.2 Personnel entrance(s)
Comfort environmental controls shall be applied to this space.
5.2.3 Docking/loading bay(s)
No specific requirements.
5.2.4 Generator space(s) including fuel storage
5.2.4.1 Generator spaces
Temperature shall be maintained in accordance with the instructions of the supplier of the equipment to
be accommodated. Where no information exists or where the equipment manufacturer is not specified
the temperature shall be maintained above 0 °C and should be above 10 °C.
Adequate ventilation shall be provided for combustion and for radiator cooling.
Where the manufacturer is not known at the time of design the maximum temperature shall be 35 °C.
Anti-condensation heating shall be provided for alternators and switchgear.
Temperature and the presence of particulates (smoke, carbon monoxide and fuel) shall be monitored.
See ISO/IEC TS 22237-6 for further information regarding monitoring of smoke.
Heater elements in the generator engine may provide sufficient heat for this space, where this is not
possible thermostatically controlled heaters shall be applied.
5.2.4.2 Fuel storage systems
The fuel storage system shall be protected against continuous sub-zero ambient temperatures to avoid
fuel solidification.
The fuel storage systems shall be monitored for leakage.
NOTE The availability of generators can be adversely affected by cold (<10 °C) or poor quality fuel and can
be improved through the installation of crankcase heaters.
5.2.5 Transformer space(s)
Temperature shall be maintained in accordance with the instructions of the supplier of the equipment
to be accommodated unless the system has been de-rated for operation at higher ambient temperatures.
Where no information exists or where the equipment manufacturer is not specified the temperature
shall be maintained above 0 °C and should be above 10 °C.
The maximum ambient temperature shall not exceed the maximum temperature specified by the
equipment manufacturer unless the system has been de-rated for operation at higher ambient
temperatures. Where the manufacturer is not known at the time of design the maximum temperature
shall be 35 °C.
Filtration against dust shall be provided, if required, in accordance with the instructions of the supplier
of the equipment to be accommodated.
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Forced air cooling of the transformer should be considered at the design phase where this would
represent an improvement in transformer efficiency.
Anti-condensation heating shall be provided for switchgear.
Temperature and the presence of smoke particulates shall be monitored. See ISO/IEC TS 22237-6 for
further information regarding monitoring of smoke.
5.2.6 Electrical distribution space(s)
Temperature shall be maintained in accordance with the instructions of the supplier of the equipment to
be accommodated. Where no information exists or where the equipment manufacturer is not specified
the temperature shall be maintained above 0 °C and should be above 10 °C.
Natural ventilation shall be provided.
The maximum ambient temperature shall not exceed the maximum temperature specified by the
supplier of the equipment to be accommodated unless the system has been de-rated for operation at
higher ambient temperatures. Where the manufacturer is not known at the time of design the maximum
temperature shall be 40 °C.
Anti-condensation heating shall be provided.
Temperature controlled air extraction shall be provided, where the facility’s redundancy so requires
ventilation shall be by redundant fans each rated to the maximum load expected. Temperature and
relative humidity shall be monitored.
5.2.7 Telecommunication spaces(s)
Temperature and relative humidity shall be maintained in accordance with the instructions of the
supplier of the equipment to be accommodated. Where this is not known in advance temperature shall
be maintained between 10 °C and 30 °C with relative humidity maintained between 20 % and 70 %.
Temperature and relative humidity shall be monitored.
Where the data centre is supported by a single telecommunications space, or by multiple, non-resilient
telecommunications spaces, the space(s) shall have a single path resilient environmental control system
(for examples see 6.2.5.3).
5.2.8 Main distributor spaces(s)
If external to computer room space the requirements of 5.2.7 shall be applied; if contained within the
computer room space then the requirements of 5.2.9 shall be applied.
5.2.9 Computer room space(s) and associated testing space(s)
The computer room space is the most important space from an environmental control perspective.
An analysis examining the balance between tight environmental controls versus high performance
energy saving controls with reference to the type of IT equipment to be accommodated shall be
performed by the owner of the data centre. The results of this analysis shall be compared with the
business model for the data centre.
Environmental controls shall be applied that maintain the following parameters within limits defined
by the requirements of the analysis described above:
a) operating temperature;
b) relative humidity;
6 © ISO/IEC 2018 – All rights reserved

c) air quality:
1) particulate content;
2) bacterial content;
3) gaseous contaminants.
The designer of the environmental control system shall assess the impact of the failure of the system on
the data centre infrastructure.
5.2.10 Electrical space(s)
See 5.2.15, if the electrical space contains UPS equipment.
Temperature shall be maintained in accordance with the instructions of the supplier of the equipment to
be accommodated. Where no information exists or where the equipment manufacturer is not specified
the temperature shall be maintained above 0 °C and should be above 10 °C.
Natural ventilation shall be provided.
The maximum ambient temperature shall not exceed the maximum temperature specified by the
supplier of the equipment to be accommodated unless the system has been de-rated for operation at
higher ambient temperatures. Where the manufacturer is not known at the time of design the maximum
temperature shall be 40 °C.
Anti-condensation heating shall be provided.
Temperature and relative humidity shall be monitored.
5.2.11 Mechanical space(s)
Temperature and relative humidity shall be monitored.
If the mechanical space accommodates electrical equipment then the requirements of 5.2.10 apply.
5.2.12 Control room space(s)
Comfort environmental controls shall be applied to this space.
5.2.13 Office space(s)
Comfort environmental controls shall be applied to this space.
5.2.14 Storage and holding space(s)
Basic environmental controls shall be applied (temperature and relative humidity); temperature and
relative humidity shall be monitored.
5.2.15 Accommodation of UPS equipment
5.2.15.1 Static and rotary UPS
Temperature shall be maintained in accordance with the instructions of the supplier of the equipment
to be accommodated. Where no information exists or where the UPS equipment is not specified the
temperature shall be maintained between 15 °C and 35 °C (non-condensing); where storage batteries
are included in the UPS space the requirements of 5.2.15.3 shall be applied.
Air conditioning, rated for the maximum heat output of the UPS system, shall be provided if the external
ambient conditions preclude the use of filtered fresh air.
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Closed loop monitoring for temperature and relative humidity shall be provided.
Waste heat should be used to pre-heat standby generator plant of the UPS system where possible.
5.2.15.2 Diesel rotary UPS
The environmental controls required for the accommodation of diesel rotary UPS are as stated in 5.2.4.
5.2.15.3 Batteries
Where UPS storage batteries are located away from the UPS equipment that they serve, temperature
shall be controlled in accordance with the manufacturer’s instructions. Where no information exists or
where the UPS equipment is not specified the temperature shall be maintained at (20 ± 2) °C.
Ventilation shall be provided to avoid hydrogen accumulation. Where mechanical extraction is used the
fans shall be redundant and fed from separate secondary power supply points.
It is recommended that Hydrogen monitoring is provided.
See EN 50272-2 for further information.
6 Availability
6.1 General
The environmental control system shall be designed to support the Availability Class chosen following
the risk assessment undertaken in accordance with the availability classification defined ISO/
IEC TS 22237-1.
This standard defines four Classes of Environmental Control Systems of increasing availability (Class 2,
Class 3, Class 4 and Enhanced Class 4).
6.2 Design options by space
6.2.1 General
All systems in data centres utilize the concept of ‘N’ when planning the load and the redundancy, e.g.
N, N+1, 2N or 2(N+1), etc. where N is seldom equal to 1. To maximize the utilization of capital plant, and
so minimize energy standing losses, the designer shall take into account the increased redundancy for
running at partial load when choosing how to specify the configuration of ‘N’.
Four design options, of increasing availability are specified:
It should be noted that Class 1 as defined by ISO/IEC TS 22237-1 has no meaning within this standard
and no specific requirements exist.
a) Class 2: Single path (no resilience) - a single path system without resilience is suitable where it is
acceptable that a single fault in an element in the path will result in loss of functional capability and
where maintenance requires the load to be shut-down.
b) Class 3: Single path (resilience provided by redundancy of components) - a single path system with
resilience is suitable where it is required that a single fault in the path will not result in loss of
functional capability because sufficient redundant components in each sub-assembly are included
and where routine planned maintenance does not require the load to be shut-down. Major faults
may result in unplanned load shutdown and some maintenance routines may require planned load
shutdown.
c) Class 4: Multi-path resilience and concurrent repair/operate solution - an active/passive multi-path
system with resilience is suitable where it is required that a single fault in the path will not result
8 © ISO/IEC 2018 – All rights reserved

in loss of functional capability because sufficient redundant components in each sub-assembly
are included and where routine planned maintenance does not require the load to be shut-down.
Major faults may result in unplanned load shutdown but maintenance routines will not require
planned load shutdown. The passive path serves to act as the concurrent maintenance enabler as
well as reducing to the minimum the recovery of service time (minimising the mean downtime)
after a major fault. The designer should aim to have the least number of common-points-of-
failure possible between the active and passive paths, including segregated routing and physical
compartmentalisation.
d) Enhanced Class 4: Multi-path resilience, concurrent repair/operate, and fault tolerant solution -
an active/active multi-path system is suitable where it is required that no single fault in any path
will result in loss of functional capability and where planned maintenance does not require the
load to be shut-down. A major fault in one path will not result in unplanned load shutdown and no
maintenance routines will require planned load shutdown by use of the other active path. Each path
serves to act as the concurrent maintenance enabler as well as avoiding any recovery of service time
(mean downtime of zero) after a major fault. The designer should aim to have no common-point-of-
failure between the two paths, including segregated routing, physical compartmentalisation and
fire-rated enclosures. Each path does not require N+1 redundancy unless the client specifies that
during maintenance or repair (planned or unplanned) where one path is removed from service
the remaining path has to retain a higher degree of resilience than N. This is most valid when
each path is modular and contains more than three elements. It is assumed in this standard that
during system maintenance or repair, unless specified by the client, a degraded level of resilience is
permitted.
6.2.2 Spaces excluded from the availability classification
The following spaces are not subject to a classification for the design of environmental control systems
in relation to availability:
a) building entrances facilities;
b) personnel entrances;
c) docking/loading bays;
d) generator space(s);
e) transformer space;
f) electrical distribution space(s);
g) telecommunications space(s);
h) electrical space(s);
i) mechanical space(s);
j) control room space(s);
k) office space(s);
l) storage and holding space(s).
6.2.3 Main distributor space(s)
If external to computer room space there are no scalable design options for this space. If contained
within the computer room space the requirements of 6.2.4 shall be applied.
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6.2.4 Computer room space(s) and associated testing space(s)
6.2.4.1 General
The computer room space is the most important space from an environmental control perspective.
6.2.4.2 Class 2: Single path (no resilience)
An example of a chilled water cooling system would comprise a single (or N) compressor based chiller,
single primary pump and single (or N) air-conditioning modules in the critical space - all being fed from
a single path electrical power system that need not include redundancy.
An example of a fresh-air cooling system with adiabatic cooling would comprise a single (or N) inlet
fan, single (or N) supplementary cooling coil, single (or N) adiabatic cooling spray system and, where
required, powered louvres - all being fed from a single path electrical power system that need not
include redundancy. The supplementary cooling coils would feed N heat rejection systems.
6.2.4.3 Class 3: Single path (resilience provided by redundancy of components)
An example of a chilled water cooling system would comprise a redundant (N+1) compressor based
chiller system, redundant (N+1) primary pumps and redundant (N+1) air-conditioning modules in the
critical space - all being fed from a single path electrical power system that includes N+1 redundancy in
key components. Some passive and inherently reliable sub-systems (e.g. the chilled water piping) would
not have redundancy built-in and a failure in such an element would be considered major and would
usually result in a loss of cooling.
An example of a fresh-air cooling system with adiabatic cooling would comprise a redundant array
(N+1) of inlet fans, a redundant array (N+1) of supplementary cooling coils, single (or N) adiabatic
cooling spray system and, where required, powered louvres - all being fed from a single path electrical
power system that includes N+1 redundancy in key components.
Where water is used for humidification or adiabatic cooling then a redundant source, or on-site storage
of sufficient volume to meet the clients’ resilience requirements, shall be included in the design. All
pumps and water treatment plant (where required) shall have N+1 redundancy in key components.
6.2.4.4 Class 4: Multi-path resilience and concurrent repair/operate solution
An example of a chilled water cooling system would comprise a redundant (N+1) compressor based
chiller system, dual (N+1) primary pumps and redundant (N+1) air-conditioning modules in the critical
space - all being fed from a single path electrical power system that includes N+1 redundancy in key
components but also has a passive delivery path (with automatic or manual changeover switches).
All passive sub-systems (e.g. the chilled water piping) shall also have in-built path redundancy where
a failure in such an element would usually result in a loss of cooling albeit with a rapid (manual)
substitution of the active path with the passive path.
An example of a fresh-air cooling system with adiabatic cooling would comprise a redundant array
(N+1) of inlet fans, a redundant array (N+1) of supplementary cooling coils, a redundant array (N+1) of
adiabatic cooling spray systems and, where required, powered louvres - all being fed from a single path
electrical power system that includes N+1 redundancy in key components b
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