ISO 15138:2018
(Main)Petroleum and natural gas industries — Offshore production installations — Heating, ventilation and air-conditioning
Petroleum and natural gas industries — Offshore production installations — Heating, ventilation and air-conditioning
This document specifies requirements and provides guidance for the design, testing, installation and commissioning of heating, ventilation, air-conditioning and pressurization systems, and equipment on all offshore production installations for the petroleum and natural gas industries that are — new or existing, — normally occupied by personnel or not normally occupied by personnel, and — fixed or floating but registered as an offshore production installation. This document is normally applicable to the overall facilities. For installations that can be subject to "Class" or "IMO/MODU Codes & Resolutions", the user is referred to HVAC requirements under these rules and resolutions. When these requirements are less stringent than those being considered for a fixed installation, then it is necessary that this document, i.e. requirements for fixed installations, be utilized.
Industries du pétrole et du gaz naturel — Plates-formes de production en mer — Chauffage, ventilation et climatisation
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 15138
Third edition
2018-06
Petroleum and natural gas
industries — Offshore production
installations — Heating, ventilation
and air-conditioning
Industries du pétrole et du gaz naturel — Plates-formes de production
en mer — Chauffage, ventilation et climatisation
Reference number
©
ISO 2018
© ISO 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 2018 – All rights reserved
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Abbreviated terms . 3
5 Design . 4
5.1 General . 4
5.2 Development of design basis . 6
5.2.1 Orientation and layout . 6
5.2.2 Hazardous area classification and the role of HVAC. 8
5.2.3 Environmental conditions . 9
5.2.4 Natural/mechanical ventilation .12
5.2.5 Selection of controls philosophy .14
5.2.6 Operating and maintenance philosophy .17
5.2.7 Materials and corrosion .19
5.2.8 Design margins and calculations .20
5.2.9 Wind-tunnel and computational fluid dynamics modelling .21
5.2.10 Performance standards .26
5.3 System design — General .27
5.3.1 Natural ventilation .27
5.3.2 Mechanical ventilation .28
5.3.3 Secondary ventilation systems .30
5.3.4 Black start .31
5.4 Area-specific system design .31
5.4.1 Process and utility areas .31
5.4.2 Living quarters .32
5.4.3 Temporary refuge.35
5.4.4 Drilling and drilling utility areas .35
5.4.5 Gas turbine .37
5.4.6 Emergency plant ventilation .38
5.4.7 Battery and charger rooms .39
5.4.8 Laboratories .39
5.4.9 Purge air systems .40
5.4.10 Rooms protected by gaseous extinguishing agents .40
5.4.11 Engine-room ventilation .40
5.4.12 Watertight compartments .41
5.4.13 Air locks .41
5.4.14 Stairs and escape routes .41
5.5 Equipment and bulk selection .42
5.6 Installation and commissioning .42
5.7 Operation and maintenance .42
Annex A (normative) Equipment and bulk selection .43
Annex B (normative) Installation and commissioning .64
Annex C (informative) Operation and maintenance .69
Annex D (informative) Datasheets .72
Annex E (normative) Standard data for flanges.136
Bibliography .139
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
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 ISO documents 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 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/TC 67, Materials, equipment and offshore
structures for petroleum, petrochemical and natural gas industries, SC 6, Processing equipment and
systems.
This third edition cancels and replaces the second edition (ISO 15138:2007), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— minimum and maximum temperatures have been added to 5.2.3.3.4 below Table 2 for clarification;
— a requirement for black start has been added to 5.3;
— requirements for the specific areas stairways/escape routes and air locks have been added to 5.4;
— phase-down and phase-out of high and medium global warming potential (GWP) refrigerants are
addressed in 5.4;
— a reference to new filtration standard and note for chemical filtration have been added to Table A.1;
— fail safe criteria for fire damper for safety critical areas have been added to Clause A.9;
— requirements for duct earthing have been added to B.1.1;
— the datasheet for DX cooling coil has been updated with electronic expansion valve;
— the datasheet for heating coils has been updated with data for self-generated noise.
iv © ISO 2018 – All rights reserved
INTERNATIONAL STANDARD ISO 15138:2018(E)
Petroleum and natural gas industries — Offshore
production installations — Heating, ventilation and air-
conditioning
1 Scope
This document specifies requirements and provides guidance for the design, testing, installation and
commissioning of heating, ventilation, air-conditioning and pressurization systems, and equipment on
all offshore production installations for the petroleum and natural gas industries that are
— new or existing,
— normally occupied by personnel or not normally occupied by personnel, and
— fixed or floating but registered as an offshore production installation.
This document is normally applicable to the overall facilities. For installations that can be subject to
“Class” or “IMO/MODU Codes & Resolutions”, the user is referred to HVAC requirements under these
rules and resolutions. When these requirements are less stringent than those being considered for a
fixed installation, then it is necessary that this document, i.e. requirements for fixed installations, be
utilized.
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 7235, Acoustics — Laboratory measurement procedures for ducted silencers and air-terminal units —
Insertion loss, flow noise and total pressure loss
ISO 8861, Shipbuilding — Engine-room ventilation in diesel-engined ships — Design requirements and basis
of calculations
ISO 12241, Thermal insulation for building equipment and industrial installations — Calculation rules
ISO 12499, Industrial fans — Mechanical safety of fans — Guarding
ISO 14694:2003, Industrial fans — Specifications for balance quality and vibration levels
ISO 21789, Gas turbine applications — Safety
IEC 60079-0, Electrical apparatus for explosive gas atmospheres — Part 0: General requirements
IEC 60079-10, Electrical apparatus for explosive gas atmospheres — Part 10: Classification of
hazardous areas
IEC 60079-13, Electrical apparatus for explosive gas atmospheres — Part 13: Construction and use of
rooms or buildings protected by pressurization
IEC 61892-7, Mobile and fixed offshore units — Electrical installations — Part 7: Hazardous Areas
EN 1751, Ventilation for buildings — Air terminal devices — Aerodynamic testing of dampers and valves
EN 1886, Ventilation for buildings — Air handling units — Mechanical performance
EN 50272-2, Safety requirements for secondary batteries and battery installations — Part 2: Stationary
batteries
API RP 505, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum
Facilities Classified as Class 1, Zone 0, Zone 1 and Zone 2
IMO Resolution MSC 61(67): Annex 1, Part 5 — Test for Surface Flammability
IMO Resolution MSC 61(67): Annex 1, Part 2 — Smoke and Toxicity Test
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:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at https: //www .electropedia .org/
3.1
active system
system that relies on energized components
3.2
air-displacement unit
supply device to achieve movement of air within a space in piston- or plug-type motion
Note 1 to entry: No mixing of room air occurs in ideal displacement flow, which is desirable for removing
pollutants generated within a space.
3.3
fugitive emission
continuous emission on a molecular scale from all potential leak sources in a plant under normal
operating conditions
Note 1 to entry: As a practical interpretation, a fugitive emission is one which cannot be detected by sight,
hearing or touch but can be detected using bubble-test techniques or tests of a similar sensitivity.
3.4
open area
area in an open-air situation where vapours are readily dispersed by wind
Note 1 to entry: Typical air velocities in such areas are rarely less than 0,5 m/s and frequently above 2 m/s.
3.5
passive system
system that does not rely on energized components
3.6
temporary refuge
TR
place where personnel can take refuge for a predetermined period while investigations, emergency
response and evacuation pre-planning are undertaken
3.7
stagnant area
area where the ventilation rate is less than adequate
2 © ISO 2018 – All rights reserved
4 Abbreviated terms
AC/h air changes per hour
AHU air-handling unit
AMCA Air Movement and Control Association Inc.
API American Petroleum Institute
ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers
BS British Standard
CCR central control room
CFD computational fluid dynamics
CIBSE Chartered Institution of Building Services Engineers
CVU constant-volume unit
D&ID duct and instrumentation diagram
DX direct expansion
EN European Standard
ESD emergency shutdown
F&G fire and gas
GWP global warming potential
HSE health, safety and environment
HVAC heating, ventilation and air conditioning
HVCA Heating and Ventilating Contractors' Association
IACS International Association of Classification Societies
IEC International Electrotechnical Commission
IMO International Maritime Organization
IP Institute of Petroleum
LQ living quarters
MODU mobile offshore drilling unit
NFPA National Fire Protection Association
NS Norsk Standard (Norwegian Standard)
TR temporary refuge
5 Design
5.1 General
This clause provides requirements on all aspects of the design of heating, ventilation and air-
conditioning (HVAC) systems for offshore installations for the petroleum and natural gas industries.
For requirements and guidance on air change rates and pressurization requirements, reference is made
to classification codes for the specific project.
The HVAC systems form part of the safety services of the installation. The key functional requirements
for HVAC systems applicable to all areas of the installation are as follows:
a) sufficient ventilation, heating and cooling capacity in all adverse weather conditions;
b) acceptable air quality in all adverse weather conditions;
c) reliable performance through concept selection, the design having the following features in
decreasing order of importance:
1) simplicity, with a preference for passive systems;
2) inherent robustness by providing design margins for systems and equipment;
3) fault/status indication and self diagnostics;
4) sparing of systems and equipment;
5) maintainability through testability, inspectability and ease of access.
The following additional requirements apply to specific areas in the installation to ensure their safety
goals are met:
— maintain survivability in the TR by preventing ingress of potentially flammable gas-air mixtures
through appropriate siting, isolation, pressurization, provision of multiple air-intake locations,
sufficient number of air changes, gas detection and emergency power supply;
— prevent the formation of potentially hazardous concentrations of flammable gaseous mixtures
in hazardous areas by the provision of sufficient ventilation and air distribution for the dilution,
dispersion and removal of such mixtures, and contain such mixtures, once formed, through
maintaining relative pressures, avoiding cross-contamination and providing dedicated systems for
hazardous areas;
— prevent, through pressurization, the ingress of potentially flammable gas-air mixtures into all
designated non-hazardous areas;
— maintain ventilation to all equipment and areas/rooms that are required to be operational during
an emergency when the main source of power is unavailable;
— provide a humidity- and temperature-controlled environment as required in which personnel, plant
and systems can operate effectively, free from odours, dust and contaminants, including smoke
control.
These high-level goals are supported by the lower-level functional requirements that are stated later in
the appropriate subclauses of this document.
Functional requirements for the development of a design basis for either a new project or major
modification to an existing installation are the focus of 5.2. These requirements are related to the
following:
— platform orientation and layout (5.2.1);
4 © ISO 2018 – All rights reserved
— hazard identification and hazardous-area classification (5.2.2);
— environmental conditions (5.2.3);
— choice of natural or mechanical ventilation systems (5.2.4);
— development of the controls philosophy (5.2.5);
— operating and maintenance philosophy (5.2.6);
— materials selection (5.2.7);
— design margins and calculations (5.2.8);
— design development and validation using wind-tunnel testing or computational fluid dynamics
(CFD) (5.2.9).
Ventilation may be natural (i.e. the wind) or mechanical or a combination of both. Throughout this
document, the use of the term “ventilation” should be taken to include either natural or mechanical
ventilation, as appropriate.
Natural ventilation is preferred over mechanical ventilation, where practical, since it is available
throughout gas emergencies, does not rely on active equipment and reduces effort required for HVAC
maintenance.
For new designs, the development of a design basis shall be progressed using the practices that
are identified in this document, though it should be recognized that the design involves a process
of iteration as it matures and does not happen as a sequential series of steps as is presented in this
document for simplicity. The processes outlined here are equally applicable to major redevelopments
of existing installations, but it can be necessary to make some compromise as a result of historical
decisions regarding layout, equipment selection and the prevailing level of knowledge at the time. The
challenge of providing cost-effective solutions in redevelopment can be significantly greater than for a
new design.
The finalized basis of design may be recorded on datasheets such as those provided in Annex D.
The completed design shall be subject to hazard-assessment review. The hazard and operability
(HAZOP) study technique may be used for this.
In 5.2, objectives are identified which establish the goals. Detailed requirements that enable the
objectives to be achieved are outlined.
In 5.3, the fundamental choice in system design, i.e. between natural and mechanical methods of
ventilation, is addressed.
In 5.4, the functional requirements associated with the design of HVAC systems for different areas of a
typical offshore installation that require particular technical considerations due to their location and/
or their function are given.
Figure 1 is intended to illustrate the processes undertaken at various stages of the installation life cycle
and to identify reference documents and the appropriate subclauses of this document that provide the
necessary requirements.
Figure 1 — Application of this document to a project life cycle
5.2 Development of design basis
5.2.1 Orientation and layout
5.2.1.1 Objective
The objective is to provide input into the early stages of design development so that areas and equipment
that can have a requirement for HVAC, or be affected by its provision, are sited in an optimum location,
so far as is reasonably practicable.
5.2.1.2 Functional requirements
Installation layout requires a great deal of coordination between the engineers involved during design
and the operation, maintenance and safety specialists. Attention shall also be paid to the minimization
of construction, offshore hook-up and commissioning. It is not the intention of this document to detail
a platform-layout philosophy, but to identify areas where considerations of the role of HVAC, and
requirements for it, can have an impact in the decision making surrounding installation orientation
and layout.
Installations can have a temporary refuge (TR). The TR is in almost all cases the living quarters (LQ),
where they are provided. The survivability of the TR, which is directly related to the air leakage rate,
6 © ISO 2018 – All rights reserved
can introduce consideration of active HVAC systems for pressurization of the TR or enclosed escape
and evacuation routes. Active systems require detailed risk-assessment exercises to be undertaken as
part of the design verification, and passive systems are generally preferred since they do not rely on
equipment functioning under conditions of emergency.
Hazardous areas, particularly those containing pressurized hydrocarbon systems, should be located as
far as practicable from the TR, so that any gas leaks are naturally dispersed.
The layout shall include correct positioning of ventilation inlets and outlets, engine inlets and exhausts,
vents and flares to allow for safe operation, particularly of the TR. Hot exhausts shall not interfere
with crane, helicopter, production or drilling operations or the LQ, and shall be directed so as not to be
drawn into gas-turbine air intakes.
Air intakes to hazardous and non-hazardous areas shall be located as far as is reasonably practicable
from the perimeter of a hazardous envelope and not less than the minimum distance specified in the
prevailing area classification code. The location of the air inlet shall also be evaluated for availability in
emergency situations.
5.2.1.3 Detailed requirements
Results of wind-tunnel model tests or CFD calculations on the installations shall be used as a basis for
determining the external zone(s) of wind pressure in which to locate the intake(s) and outlet(s) for the
HVAC system(s). Particular care shall be taken in locating air intakes and discharges with regard to the
location's coefficient of pressure and its subsequent effect on fan-motor power.
The underside of a platform can be a convenient location for HVAC inlets and outlets because a large
proportion of the below-platform zone can be classified as non-hazardous and have stable wind
conditions. However, consideration shall be given to the effects of the wind and waves and the location
of items such as dry-powder dump chutes and cooling-water discharges when locating the outdoor air
intakes and extract discharges below the platform. The air inlets/outlets shall be protected against the
dynamic wind pressure.
Air intake and discharge from the same system on conventional installations shall, where reasonably
practical, be located on the same face of the installation or in external zones of equal wind pressure.
Particular care shall be taken in orienting air intakes and discharges on systems serving adjacent
hazardous and non-hazardous areas, such that while the wind can affect the absolute values of
pressurization in each area, the differential pressure requirements between them does not vary to a
significant degree. For floating production systems (FPS), however, the downwind area can provide an
appropriate intake location but it shall be positioned to avoid ingestion of smoke or contaminants and
capable of operation in adverse weather (reference is also made to 5.3.2).
Air intakes shall be located to avoid cross-contamination from
— exhausts from fuel-burning equipment,
— lubricating oil vents, drain vents and process reliefs,
— dust discharge from drilling dry powders,
— helicopter engine exhaust,
— flares,
— other ventilation systems, and
— supply and support vessels.
The positioning of the air intake and exhaust of gas turbines and generators requires careful consideration.
They shall be located in a non-hazardous area and with consideration of the following points.
a) The air intake shall be located at the maximum possible distance from hazardous areas and as high
above sea level as possible to avoid water ingress (an absolute minimum of at least 3 m above the
100 year storm wave level). If enclosed, the intakes shall be located such that powder and dust are
not ingested. Since most particulate matter in the air is generated on the platform from drilling
operations and grit blasting, the preferred arrangement is for air intakes to be located above the
upper-deck level.
b) Recirculation from the exhaust back to the inlet shall be avoided and may be demonstrated by wind-
tunnel tests or CFD. These tests shall also show that exhaust flue gas emissions do not interfere
with helicopter, production, drilling and crane operations.
The party that initiates the project shall establish a maximum allowable air temperature rise above the
surface of the helideck for helicopter operation.
Computer models are available to simulate hot- and cold-plume dispersion patterns and may be used to
establish outlet positions.
5.2.2 Hazardous area classification and the role of HVAC
5.2.2.1 Objective
The objective is to adopt in the design and operation processes a consistent philosophy for the
separation of hazardous and non-hazardous areas and the performance of ventilation in those areas.
5.2.2.2 Functional requirements
IEC 60079-10 shall be used for classification of a hazardous area. The choice of hazardous-area code
determines the choice of equipment for use in particular areas of the installation and also provides
input to the performance standards for HVAC systems in those areas.
5.2.2.3 Detailed requirements
The application of a recognized hazard identification and assessment process can identify a requirement
for the separation and segregation of inventories on an installation. Area classification codes specify
separation distances between hazardous and non-hazardous areas in order to avoid ignition of those
releases that inevitably occur from time to time in the operation of facilities handling flammable liquids
and vapours.
All area classification codes should be interpreted in a practical manner. They offer only best guidance
and often the particular circumstances require a safety and consequence review and the subsequent
application of the “as safe as is reasonably practicable” approach to the location of classified area
boundaries and potential ignition sources nearby. In order to correctly and consistently establish area
zoning, historical data from similar plant operating conditions may be used as a basis for assessment.
Ventilation impacts upon hazardous-area classification and provides a vital safety function on offshore
installations by
— diluting local airborne concentrations of flammable gas due to fugitive emissions;
— reducing the risk of ignition following a leak by quickly removing accumulations of flammable gas.
The quantity of ventilation air to maintain a non-flammable condition in areas with fugitive emissions
[14]
may be calculated from data in API 4589, using the methodology given in API RP 505.
Areas shall be classified using the general guidance of IEC 60079-10. Specific guidance for classifying
[33]
petroleum facilities can be found in documents such as EI 15 (2015) 4th version and API RP 505.
It shall be recognized that a level of ventilation higher than the default lower limit of acceptable
ventilation given in the hazardous area codes can be required to
— provide a suitable atmosphere for personnel and equipment,
8 © ISO 2018 – All rights reserved
— remove excess heat, and
— provide an enhanced rate of ventilation to mitigate against the creation of a potentially explosive
atmosphere.
5.2.3 Environmental conditions
5.2.3.1 Objective
The objective is to determine an environmental basis for the design of HVAC systems in order to meet
the objectives for HVAC.
5.2.3.2 Functional requirements
External and internal environmental bases suitable for the location of the installation shall be
established for the design.
5.2.3.3 Detailed requirements
5.2.3.3.1 External meteorological conditions
The requirement for shelter shall be evaluated, which can reveal a subsequent need for an HVAC system.
The design of the HVAC systems shall take design codes into consideration. Conservative selection of
criteria can carry a cost, mass and power penalty.
Seasonal extremes of temperature, humidity and wind speed vary widely throughout the world, and
local regulations governing working conditions can also dictate the allowable extremes in occupied or
unoccupied spaces. Local environmental information shall be specified in the basis of a design. This
should not require the installation of additional capacity to accommodate the small proportion of the
time during which meteorological extremes are encountered.
Sub-local effects on the external environmental conditions shall be considered for design purposes in
case they have any influence on the design, such as heating of the air before the air reaches the intakes,
intake contamination, shading of solar radiation, reflection of solar radiation from the sea surface,
changes in wind speed and direction and, consequently, wind pressure.
Effective temperatures, resulting from wind chill or heat loading, shall be determined to establish
the effects on personnel operating efficiency (where personnel are required to work in thermally
uncontrolled areas) and equipment, and, consequently, the extent of any required protection. In
determining operating efficiency, consideration shall be given to the nature of the work (sedentary or
physical) being undertaken.
The selected data source shall be acceptable to the party that initiates the project.
The following provides typical data that may be used to establish an environmental basis of design in
an area where microclimate is not an important factor and variations in any month follow a normal
distribution:
— maximum temperature: 2 % probability of being exceeded;
— minimum temperature: 98 % probability of being exceeded;
— design wind speed: 1/12th year — 1 h mean velocity at a reference height of 10 m;
— maximum wind speed: maximum 1/12th year — average 3 s gusts at the height of equipment.
NOTE The 1/12th year mean condition is that which, on average, is exceeded 12 times a year.
Wind velocity data are usually reported at a standard 10 m height, but can be recorded at a different
height on an installation. The correction factors in Table 1 shall be applied to the commonly reported
1 h mean wind velocities.
Table 1 — Wind correction factors
Height above mean
Duration of gust Sustained mean wind duration
sea level
m 3 s 15 s 1 min 10 min 1 h
10 1,33 1,26 1,18 1,08 1,00
20 1,43 1,36 1,28 1,17 1,09
30 1,49 1,42 1,34 1,23 1,15
50 1,57 1,50 1,42 1,31 1,22
60 1,59 1,52 1,44 1,34 1,25
80 1,64 1,57 1,49 1,39 1,30
100 1,67 1,60 1,52 1,42 1,33
120 1,70 1,63 1,55 1,46 1,36
150 1,73 1,66 1,58 1,49 1,40
Exponent (n) 0,100 0,100 0,113 0,120 0,125
EXAMPLE 1 Given a 1 h mean wind velocity of 24 m/s at 10 m height, the maximum 1 min sustained wind
velocity at a height of 50 m is estimated to be 24 m/s × 1,42 = 34 m/s.
The wind-velocity factor, v , at another height, h, expressed in metres above sea level, can be obtained
h
from the reference value at 10 m using the power law profile as given in Formula (1):
n
h
vv=× (1)
h 10 ()
where
v is the velocity at height h above sea level;
h
n is the power law exponent (see Table 1).
EXAMPLE 2 The velocity, v , at the 10 m base of a wind with an average velocity of 7 m/s (1 h mean velocity)
at a deck level 50 m above mean sea level can be calculated as
v = 7 m/s × (100/122) = 5,378 m/s
In areas where there are high seasonal fluctuations from an average, such as in monsoon, typhoon and
tropical regions, consideration may be given to setting design criteria based on the number of days or
hours of exceedance if data are available for analysis in this form.
Where there is a significant microclimate, data may be analysed under additional criteria for which the
following guidance is appropriate.
5.2.3.3.2 Maximum sea temperature
The maximum sea temperature is the maximum monthly average water temperature during the
warmest month at the depth of abstraction, which may be extrapolated from surface temperature
measurements.
5.2.3.3.3 Direct and diffuse solar radiation intensities
For detailed design calculation, hourly radiation data for a period of clear days in the warmest month
is necessary. The period is considered to coincide with a period in which the maximum temperature
10 © ISO 2018 – All rights reserved
occurs, taking into account the associated relative humidity. The traditional method of designing
structures assumes that the maximum room-cooling loads and the maximum refrigeration load for air-
conditioning occur simultaneously, but it is noted that maxima of room-cooling loads can actually occur
in a period which is not coincident with maximum outside temperature.
In the absence of solar radiation data for the location, data may be taken from a similar locality at the
[15]
same latitude. In the absence of collected data, calculated values may be applied from ASHRAE or a
similar reference.
The reflection from the sea surface may be taken as 20 % of the total radiation intensity.
Radiation heat gains from flare stacks shall also be considered.
5.2.3.3.4 Internal environmental conditions
Two approaches may be used for the specification of internal environmental conditions. The traditional
approach relies on the specification of absolute values established by experience or local regulations.
[5]
An alternative approach based on a measurement of population acceptance is given in ISO 7730 . The
ISO 7730 method applies only to manned areas. Table 2 gives guidance that may be used if the approach
outlined in ISO 7730 is not adopted.
Table 2 — Recommended indoor environmental conditions
Description Examples Minimum Maximum HVAC Comments
temperature temperature noise
(winter) (summer) limit
°C °C dBA
Manned areas — Control room 19 24 40
sedentary work Radio room
Living quarter Recreation areas 19 24 40
areas Cabins
Dining room 19 24 50
Corridors/toilets 16 25 50
Laundry
Stores/galley
Switch room 10 35 65
Plant room 10 35 65 Noise level up to 85 dBA can
be acceptable, if measures are
taken to avoid unacceptable
noise levels in adjacent areas.
Offices 19 24 40
Dry store 16 24 50
Gymnasium
Sick bay 21 25 40 A room controller should
allow adjustment of room
temperature to a maximum
of 25 °C when outside min./
max. design temperature are
prevalent.
Light manual Laboratories 18 24 50
work Stores 16 24 60
Workshops
Unmanned Utilities module 5 35 80
without electrical
equipment
Table 2 (continued)
Description Examples Minimum Maximum HVAC Comments
temperature temperature noise
(winter) (summer) limit
°C °C dBA
Unmanned with Switch rooms 5 35 70 As an option to cooling, heat
electrical may be provided to limit hu-
equipment midity to 80 %.
Equipment Battery rooms 15 25 70 35 °C maximum may be
rooms with accepted for certain types of
temperature- batteries.
critical
instruments
Unmanned Production mod- 5 35 80
ules
The HVAC plant shall as minimum have the following capacity:
a) heating to achieve the minimum temperature during winter conditions;
b) cooling to achieve the maximum temperature during summer conditions.
It is also recommended that the relative humidity be kept between 30 % and 70 %. These limits are set
in order to decrease the risk of unpleasant wet or dry skin, eye irritation, static electricity, microbial
growth and respiratory diseases.
Sound attenuators shall be located at points in the HVAC systems where they can control both break-out
and break-in of noise. Typical positions are at plant-room walls prior to the ductwork leaving the room,
and at duct entry into control rooms and other areas requiring low noise levels. Care shall be taken
when designing the HVAC systems to allow for the poor sound absorption characteristics of many of the
areas served. As all spaces except the cabins and public areas are acoustically “live”, little attenuation of
HVAC noise by the space is likely to occur.
Consideration shall be given to reducing the noise levels at source in the first instance.
Outdoor air inlets and outlets shall be attenuated to a value where they do not exceed the local predicted
background level by 5 dB or exceed 80 dBA (or national standards) at a distance of 3 m from the outlet,
whichever is the more stringent.
Permissible noise limits shall not be exceeded as a result of sound power generated by, or transmitted
through, the HVAC systems. See also guidance given in Table 2. An analysis shall be performed to
demonstrate the noise and vibration contribution from the HVAC system.
Where sound attenuators are required in the LQ and laundry extract systems, they shall be suitably
designed to reduce the risk of lint accumulation and subsequent fire hazards.
Sound attenuators are not permitted in galley extract systems, unless sufficient measures are taken to
eliminate grease.
Sound attenuators are not recommended in the shale shaker or mud tank extract systems, where
excessive airborne dirt would nullify their effectiveness.
5.2.4 Natural/mechanical ventilation
5.2.4.1 Objective
The objective is to select a means of providing ventilation to any hazardous or non-hazardous area of an
installation.
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5.2.4.2 Functional requirements
Provide ventilation to any area that requires it, giving consideration to the following:
a) meteorological conditions, particularly prevailing wind and its strength, external temperature,
and precipitation;
b) risk-driven segregation of hazardous areas;
c) heating and cooling design loads;
d) life cycle costs of the purchase and maintenance of mechanical HVAC and associated emergency
shutdown (ESD) systems;
e) environmental considerations, such as personnel comfort, particulate control, and noise;
f) weather integrity of instrumentation and controls;
g) need for structural integrity;
h) control and recovery from hydrocarbon loss of containment;
i) process heat conservation.
5.2.4.3 Detailed requirements
The major consideration in installation layout and ventilation philosophy is likely to be risk, whether
it is measured in terms of potential harm to the individual, asset or the environment. Quantitative risk
analysis (QRA) may be undertaken to evaluate the risk benefits of alternative layout arrangements
during the option-selection phase, and HVAC engineers can be expected to contribute to the modelling
of smoke and gas releases as part of the decision-making process.
The requirements for heat-tracing, insulation, corrosion protection and maintenance cost shall also be
considered when evaluating natural ventilation versus enclosed mechanically ventilated areas.
Production areas generally shall be ventilated by natural means, where possible, as this is the least
complex and most reliable method. However, effective temperatures, result
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