Handbook of Industrial Air Technology
Applications
VENTILATION AND AIRCONDITIONING OF ELECTRICAL
EQUIPMENT ROOMS
Second, revised edition
Kim Hagström
Jorma Railio
Esko Tähti
February 2003
PREFACE
This document is the revised version of the first pilot Application booklet for the Handbook of
Industrial Air Technology.
This text is based on INVENT project "Design Criteria for Ventilation in Electrical Equipment
Rooms", done in Finland in 1991-94, reported in Finnish as INVENT Reports 36 to 39. It has
been re-structured to follow the basic structure of the Design Methodology for industrial
ventilation, also in order to test the methodology in practice.
After being published as a draft manuscript in 1996 (INVENT Report 52), the text has been
reviewed by Mr Martti Lagus (Nokia Telecommunications, Finland) and by Mr Peter Kiff
(British Telecom). In addition, the described design methodology has been validated by several
Finnish companies who actively apply the results of the INVENT project, either as end users of
equipment rooms, or as suppliers of air-conditioning systems and equipment.
The text has been revised after review by Mr Jan Gustavsson (Camfil, Sweden), Dr Paolo
Tronville (Politecnico di Torino, Italy) and Dr David Shao (Ericsson Radio Access, Sweden). The
English language of the revision has been checked and corrected by Mr Eric Curd (U.K.)
Helsinki, December 2002
2
VENTILATION AND AIR-CONDITIONING OF ELECTRICAL EQUIPMENT
ROOMS
CONTENTS
PREFACE.......................................................................................................................... 2
CONTENTS....................................................................................................................... 3
SUMMARY ....................................................................................................................... 4
1. INTRODUCTION......................................................................................................... 5
1.1. Classification of environmental parameters for electrical equipment.............. 5
1.2 Typical environments of electrical equipment located in ventilated indoor
facilities .......................................................................................................................... 5
1.3 Application scope .................................................................................................... 6
2 DESIGN CRITERIA ..................................................................................................... 8
2.1 Given data................................................................................................................ 8
2.2 Process description.................................................................................................. 9
2.3 Building layout and structures ............................................................................ 11
2.4 Target level assessment......................................................................................... 20
2.5 Source description................................................................................................. 36
2.6 Load calculations .................................................................................................. 39
3 SYSTEM PERFORMANCE....................................................................................... 41
3.1 Selection of system ................................................................................................ 41
3.2 Selection of equipment.......................................................................................... 53
3.3 Implementation design ......................................................................................... 62
4 COMMISSIONING..................................................................................................... 66
4.1 The construction schedule.................................................................................... 66
4.2 Checks .................................................................................................................... 67
4.3 Spare parts............................................................................................................. 67
4.4 Documentation ...................................................................................................... 68
APPENDIX 1 - BASIS FOR DESIGN FOR VENTILATION IN ELECTRICAL
EQUIPMENT ROOMS, CLIMATIC CONDITIONS ................................................ 76
APPENDIX 2 - THE MEASURING PRECONDITIONS OF GASES...................... 77
APPENDIX 3 - REFERENCES..................................................................................... 79
3
SUMMARY
There has been a lack of "common language" for the design, construction and operation of
air-conditioning of industrial electric-, electrotechnical- and control rooms. Requirements
for the equipment and its environmental conditions are presented in different standards and
guidelines in such a way that many interpretations are possible. For example, a given
temperature limit can have been regarded by the end user as an absolute maximum, while
the equipment supplier could allow it to be exceeded (within another range) for a short
period.
As a result of this,
• in some rooms the environment is too severe, resulting in operational errors and
equipment failures, which really can be worth more than the whole equipment
• some rooms are conditioned unnecessarily well in relation to the actual
environmental requirements, resulting in high investment costs, due to oversized (or
unnecessarily double) air-conditioning equipment, or in high operation costs.
An INVENT project was done in 1991-94 to tackle this problem area.
The participants in the project represented different supplier and user groups such as: HVAC
equipment manufacturers and suppliers, HVAC consulting engineers, electrical equipment
manufacturers, process automation- and -control system manufacturers, and end-users from
different trades of process-industry: pulp and paper, chemical industry, metal industry. A
service product was also developed, in order to analyze the state of existing equipment
rooms. This work was done in 1995, and the results can be utilized in commercial basis
now, and several project references already exist. The knowledge gained in these actions has
been the basis of this application.
Modern electrical equipment containing electronics is very sensitive to their environmental
conditions: temperature and humidity, chemically and mechanically active substances etc.
In highly automated process industry a failure in process control equipment may cause
losses in production that are many times worth of the equipment itself. Just to mention one
example: a paper machine breakdown can cost up to 30.000 € or USD/hour.
Minor improvements can be also done with low costs. Very often the tightness of the room
can be improved so that the ventilation rate for maintaining over-pressure can be adjusted to
a much lower level. A typical pay-back time for sealing the room properly is 0,5-0,7 years
and investment less than 1000 € or USD/room respectively.
The benefits from proper design, construction and use can be summarized as follows:
• better operating conditions
• prolonged lifetime for electrical equipment
• improved reliability of the systems
• efficient use of the systems
• improved knowledge of the condition of the systems
• improved skills of he maintenance personnel
4
1. INTRODUCTION
1.1. Classification of environmental parameters for electrical equipment
The basis of the environmental classification for electrical equipment is covered in EN
60721-3-0 standard. International recommendations for environmental conditions in
electrical equipment rooms are covered by the European standard EN 60721-3-3.
To standardise design practice the above should be used in ventilation systems design.
Environmental factors covered in EN 60721-3-3 have been divided in the following groups.
•
•
•
•
•
•
Climatic conditions (K)
Climatic special conditions (Z)
Biological conditions (B)
Chemically active substances (C)
Mechanically active substances (S)
Mechanical conditions (M)
The environmental conditions in EN 60721-3-3 for electrical equipment room are covered
in various classes.
Electrical equipment manufacturers define the special requirements of each device
according to EN 60721-3-3 in the following manner:
A definition such as the following 3K1/3Z1/3Z4/3B1/3C1/3S1/3M1:
The code
-3K1
-3Z1
-3Z4
-3B1
-3C1
-3S1
Defines climatic conditions.
In class 3K1, the target temperature value is 20 - 25o C in the range 18 27o C.
The relative humidity target value is 30-60 % in the range 20-75 % and
the absolute humidity ranges from 3,5 - 15 g.kg –1
Z-class describes the special climatic conditions, including the
surroundings thermal radiation.
shows the permitted air velocity if different from the K-class value. In this
case it is 5 m.s-1. With special condition classes, it considers how a device
reacts to water.
describes biological conditions. Organisms or animals are not accepted in
the 3B1 class.
A demand that covers chemically active substances. This defines the
permissible concentrations of corrosive gases in the space.
Mechanically active substances. Defines the permissible concentration of
particle contaminants e.g. dust, sand etc in the space.
1.2 Typical environments of electrical equipment located in ventilated indoor facilities
Table 1.1.1 provides a general idea of the "environmental tolerance" of equipment in
different spaces. A nomenclature of electrical equipment rooms has not yet been
5
determined; Rooms of similar names in different industrial plants can contain very diverse
equipment. Therefore, the environmental requirements for each room have to be checked
individually during the various project stages.
1.3 Application scope
The environmental classification for electrical equipment and the design basis for
ventilation represented here, consider all indoor spaces where electrical equipment is
located.
Chapters 3 (System Performance) and 2.3 (Building Layout and Structures) emphasize
ventilation of electrical equipment rooms (computer-, tele-, automation and current supply
rooms).
6
Table 1.1.1 Operating Environments of Electrical and Electronic Equipment, Ventilated
Indoor Spaces
TYPICAL ENVIRONMENT
THE ENVIRONMENT
CLASS OF THE
EQUIPMENT ROOM
according to the standard
EN 60721-3-3. See 1.1 for
explanation of
classification
A Control- and automation rooms
a1) workspaces separated from the process
a2) automation rooms
a3) cross-connection rooms (measuring equipment,
monitors and connections)
Computer rooms
3K2 / 3Z2 / 3Z4 /
3B1 / 3C1 / 3S1 /
B Electrical equipment rooms
-rooms that are separated from outdoor spaces and the
process
b1) tele cross-connection and device rooms:
b2) electrical equipment rooms of the production:
(motor use, MCC)
b3) electrical exchange rooms:(main distribution centres,
sub-main distribution centers)
b4) transformer rooms (internal)
3K3 / 3Z2 / 3Z4 /
3B1 / 3C1 / 3S1 /
C Assembling halls in the electronics industry
-circuit card production, assembling of micro electronic
components testing and adjustments, assembling of fine
mechanisms and fibre optics
3K2 / 3B1 / 3C1 /
3S1 / 3M1 /
D Production spaces in the metal industry
-engineering workshops, light metal industry, bulk
assembling: (motors, robots, control devices)
-cable spaces
3K4 / 3Z2 / 3Z4 / 3Z7 /
3B2 / 3C2 / 3S2 /
E Production spaces in the process industry
-spaces where contaminants and corrosive gases are
typical:(instrumentation with protective cover, motors,
control device)
3K5 / 3Z2 / 3Z4 / 3Z7 /
3B2 / 3C2+C3 when
necessary/3S2 /
F An open, dirty industrial space
-dusty spaces in direct contact with outdoor air, foundries,
ore mills, waste treatment plants:(equipment with
protective cover, suitable for outdoor use)
-outdoor transformers
3K6 / 3Z2 / 3Z4 / 3Z7 3B2 /
3C2 / 3S2 /
G Movable containers -control cabinets and electrical
rooms that are movable during use (for example military
purposes)
3K2 / 3Z2 / 3B1 / 3C1 3S1 /
(As above, except 3K1)
7
2 DESIGN CRITERIA
2.1 Given data
2.1.1 Meteorological data
Consideration of external temperature, humidity, wind forces and solar radiation are
necessary in order to determine the cooling, heating and moisture loads.
The design criteria shown in 2.5 have been compiled to meet the requirements of the
standard EN 60721-3-3. If the maximum temperature 99% value is used i.e. (the
temperature for 99% of the time below the design value). However, if a customer wishes to
use higher design temperature for operational reliability the design parameters have to be
agreed with the customer.
2.1.2 Air contaminants.
2.1.2.1 Chemically active substances (corrosive gases).
In certain areas of the process industry (such as the pulp, chemical and petrochemical
industries) and in cities, the concentrations of corrosive gases may be higher than the
permissible concentrations for electrical equipment. In a corrosive environment, electrical
equipment is easily damaged shortening the operating life.
It is difficult to obtain information on the exact environmental air purity since:
Outdoor air purity is a complex matter: the concentrations measured in the same place can
vary within 1:100. This variation depends on wind direction air pressure and on process
malfunctions
In recent years air purity is constantly improving due to various environmental protection
acts. For these reasons, details that could easily be used in defining the outside air on a
design basis cannot be developed.
The following approaches can be used to define the contaminant concentration of the intake
air
1. Accurate concentration measurements.
This however is not often practical, as:
The measurements have to be carried out over a long time period (minimum 6
months) if exact initial values are required.
To obtain accurate information measurements have to be obtained close to the area
of concern. Attention has to be paid to the fact that a new building will create
changes in airflows, which can influence standard design requirements.
2. Estimating the concentration beforehand. This can be done by the copper-strip
method.
8
If the measuring period is long enough, and the concentration is measured at the air
intake, provided the copper-strip is in a warm location. The contaminant ratio can
be 1:4 within a few meters of the air inlet.
3. General measurements of the air conditions.
For example in Finland, these results can be obtained from the following sources:
- The Environment Department of the company.
- Measurements carried out by the county, city or town authorities.
- Meteorological Institute data
4. By rough estimations. For example tables provided by the equipment manufacturers
can be used.
5. Experience. This is probably the most important way knowledge is gained; it
depends on experience, regarding filters life and equipment corrosion. This is
accomplished by comparing practical experiences with similar plants in the
organization or in other factories.
While dimensioning filters the possible sudden pressure changes caused by
malfunctions in the process have to be considered as these changes can cause the
gas concentrations to momentarily rise up to 10-100 times the average
concentrations.
Measuring preconditions are described in Appendix 1.
2.1.2.2 Mechanically active substances (sand, dust)
The outdoor air data, relating to dust will not normally provide a base for selecting particle
filters. In 3.2.3 consideration is given on how to select a filter for electrical equipment
rooms.
The surrounding dust concentration can be defined by similar principles as gases.
2.2 Process description
2.2.1 Introduction
Regardless of the electrical equipment installed, there are usually no other emission sources
in electrical equipment rooms. In control- and automation rooms however, employees may
occupy the space for long periods of time.
Internal loads in electrical equipment rooms are:
• the heat developed by the equipment
• the emissions from humans
• (control cabinets and automation rooms)
9
•
In battery rooms hydrogen is liberated into the air, and care has to be taken
regarding explosion hazards.
The role of the ventilation in electrical equipment rooms is to: • remove the heat developed by electrical equipment
• keep the room clean of contaminants from the surroundings.
2.2.2 Typical electrical equipment room
A typical electrical equipment room has equipment cabinets positioned in several rows.
Many different-sized cables are fed to and from these cabinets either from below or above.
In the process industry the cable space is usually separated in its own compartment. Due to
fire safety reasons the cable space is confined by a raised floor forming its own fire cell
(compartment). Figures 2.2.1 and 2.2.2 show two alternative typical cross-sections of
electrical equipment rooms.
Figure 2.2.1. The recommended minimum dimensions of aisles for an equipment room
10
Figure 2.2.2. A cable space
2.3 Building layout and structures
2.3.1 Location of electrical equipment rooms
2.3.1.1 Introduction
The room shall be over-pressurised to reduce air infiltration from surrounding areas. The
air tightness of electrical equipment rooms has to be sound, and the degree of overpressurization has to be sufficient to neutralize the influence of wind forces, temperature
differences and surrounding process spaces, which may be operating under negative
pressure.
2.3.1.2 Effect of wind forces
If an electrical equipment room has external wall it can be greatly influenced by wind
forces. These may, over-pressure on the wind-exposed wall resulting in polluted outdoor
air entering the room. This effect has to be considered in the design process.
The electrical equipment room if possible should be positioned, so that wind forces do not
influence it. In spaces which rely on high air flows for cooling, the structural tightness and
exhaust air openings sizes should be dimensioned so that the internal overpressure is kept
to a reasonable level, e.g. not more than 20 Pa.
Figure 2.3.1 shows graphically the wind pressure on the outer wall of a building with the
wind velocity in the 0, 5 and 10 m.s-1 range against the wall.
11
The example results have been calculated by using the formula: ∆p=K*0.5 *ρ*v2
(1)
where
K= a pressure coefficient depending on building shape and the wind direction
ρ= air density = 1,2,kg.m-3
v= the wind velocity [m.s-1]
For air of standard density the above equation becomes ∆p = K 0.6 v2
Figure 2.3.1. The wind pressure on the outer wall of a building with wind velocities of 0, 5
and 10 m/s on the wall.
2.3.1.3 Vertical position in building
A temperature difference between indoor and outdoor air causes a pressure difference on
the outer wall. An internal neutral plane is formed at some height above the building floor.
The actual position of the neutral plane changes due to the influence of wind forces and
openings (crackage) in the structure. Above the neutral plane the inner parts of the building
are over-pressurized with respect to the outdoor air and below this point it has a negative
pressure when outdoor air is colder than the indoor air. This causes problems to the
resulting pressure ratios, especially when the room is located on the outer wall of a high
quality process space.
Figure 2.3.2 shows graphically the pressure difference on the outer wall created by
temperature difference, as a function of the distance from the neutral plane with different
temperatures, for a room temperature of 20o C.
12
Figure 2.3.2. Pressure difference created by the temperature difference between the indoor
and outdoor air, on the outer wall of the building with different outdoor air temperatures.
The interaction of the wind and temperature differences on the pressure difference of the
outer wall is shown in figure 2.3.3.
Problems of resulting pressure ratios will be created when the electrical equipment rooms
are connected to both indoor and outdoor areas.
If the room outlet is at a high position, the airflow will be outward from the space and if the
outlet is at low level the flow will be reversed.
Figure 2.3.3. The interaction of wind and temperature on the outer wall of a building when
θ = -20 C.
2.3.1.4 Surrounding rooms
The external heat loads on electrical equipment rooms vary considerably. The external heat
loads are due to open cable spaces, and adjacent process areas. The positioning of electrical
equipment rooms close to hot process should be avoided.
The pressure ratios in surrounding rooms will influence the design pressure conditions.
A typical example is that a strongly negative-pressurized cable space will reduce the overpressure in an electrical equipment room. Cable spaces should be designed to have evenpressures. If located beside, under or over an electrical equipment room. Process spaces
may be held at positive and negative pressure.
13
2.3.2 Tightness of the structure
2.3.2.1 Introduction
The air tightness of the structure is a critical factor when considering the influence the
contaminant loads have on electrical equipment. It also influences the design of the
ventilation system, as well as investment and operating costs. The design of the ventilation
supply is related to the structural air tightness. The required over-pressure necessary to
avoid infiltration will not be achieved if air leakage through the room structure is greater
than that calculated.
The tighter the structure, the less outdoor air flow is needed to provide the desired room
over-pressure, the operating costs will also be reduced. The worst leakage areas are service
holes and crackage in the structure, and it is essential that these be kept to a minimum.
The structure of an electrical equipment room is usually brick, concrete or sheet metalmineral wool-sheet metal elements. Untreated tile and concrete surfaces and porous, and air
flows through them. The structural leakage paths can be reduced by the use of special
paints.
If the electrical equipment room is built of sheet metal-mineral wool-sheet metal elements,
the joints between the elements and connections to other structures have to be sealed to
reduce external and internal air transfer. Partition walls also require sealing.
2.3.2.2 Estimation of the room tightness
The general formula (Olander 1982) that describes the leakage air flow through walls, is
following:
QVL= C * (dp)0,65 [m3s-1m-2, Pa0,65]
(2)
Factor C varies according to the tightness of the wall, typical values being
A tight wall
An average wall
A leaky wall
0,0003
0,0005
0,0007
With the above formula (2) the air tightness of electrical equipment rooms can be
determined.
The required air volume flow for the room pressurization depends not only on the room
volume but also on the room shape and size. Therefore the correct design criteria must be
based on room wall area. In normal cases the floor and ceiling can be considered as being
airtight due to the coatings on them. Measurement of the make-up airflow according to new
design criteria can be made using the diagram shown in Figure 2.3.4.
In properly sealed rooms the required make-up airflow, to maintain a 20 Pa overpressure in
the room, is 2,1 l.s –1, per m2 of wall.
14
Figure 2.3.4. Dimensioning diagram for pressurization airflow in electrical equipment
rooms
After the electrical equipment room has been completed, it should be tested to ensure that
the required over-pressure in the room is achieved with the designed outdoor airflow. In
normal cases it is aimed to reach the over-pressure of 20 Pa with an outdoor airflow of 2,1
l/(s m2) of wall.
For checking the actual over-pressure, a pressure difference meter should be installed
outside the door. The measurements recorded should logged and used for all future service
checks.
If the required over-pressure is not reached, or if it reduces during use, leakages may be the
cause, and extra sealing is required.
Fan problems also cause a pressure drop and fan airflow should be checked for design
conditions. If the over-pressure is greater than the required design energy costs will
increase.
2.3.2.3 Effect of openings on the room tightness
DOORS: The number of doors must be kept to a minimum. Doors not in everyday use, like
hauling and trap doors, should be securely sealed. It is recommended to use only one door
in the room and carefully seal other exits.
Doors in everyday use should have air locks to reduce uncontrollable airflow. Doors should
be self-closing, essential fire doors must be fitted with tight seals.
WINDOWS: These should be avoided in electrical equipment rooms. It is difficult to seal
window frames. In addition solar radiation through the windows increases the external heat
gain to the room.
STRUCTURAL PENETRATIONS FOR CABLES AND PIPES: The holes for cables and
pipes in the walls of the room should be sealed carefully with an incombustible airtight
material. Gypsum can be used for sealing, but it can break down with movement.
15
Leaks through penetrations must not unduly impair the air tightness of the wall. This
concerns the normal use, as not all of the so-called expanding sealants are suitable for
stopping penetrations.
When old building stock is being rebuilt, it is essential that an asbestos study be carried out
before work commences. Asbestos was in the past frequently used in structural firebreaks.
ELEMENT JOINTS: All the element joints have to be carefully sealed airtight before
painting the walls. The expansion joints shall not be placed on the roof of an electrical
equipment room. If an expansion joint has to be located in the room, it has to be carefully
tightened Figures 2.3.5 give examples of expansion joint construction.
2.3.3 Effect of the structural mass on the heat dynamics of the room
Over a short time period, say, less than 10 minutes, the structural mass will not have a
major influence on the decrement and the resulting thermal transmission.
Obviously for a longer time period a heavy structure will balance out the room temperature
changes.
In the approach used, thermally lightweight structure rooms are formed when the mean
surface areas are covered with timber panels or other similar materials. Structures made of
light concrete are graded as medium structures. Spaces classed as heavy structures have at
least a half of their surfaces of uncovered concrete.
Figures 2.3.6 - 2.3.8 show calculated warming curves with the help of two time-constants
model for a 1000 m3 type room during the period of time of eight hours. Figures indicate
the effect of different parameters (heat load, initial temperature and weight of structure) to
the warming of the room. Temperature of the environment was held at 25˚C.
16
Figure 2.3.5. Tightening the expansion joint, examples.
17
Figure 2.3.6. Warming curves of a middle-heavy construction room with 4 different heat
loads, when the initial temperature is 25 ºC.
With heat loads less than 100 W.m –2 the room temperature will not rise above 40 ºC
regardless of the nature of the structure when the outdoor temperature is +25º C.
With heat loads of 200 W.m –2 the temperature of the room will rapidly rise over +40 ºC
when the initial temperature is 35 ºC.
With an initial temperature of 30 oC warming up to 40 ºC will take 3-8 hours regardless of
the nature of the structure.
In rooms of heavy structure, with heat loads over 300 W.m -2 the temperature will rise
above 40 ºC regardless of the initial temperature.
The temperature of an electrical equipment room cannot be controlled by structural means
alone. As in the case of air conditioning plant failure with high heat gains, it is impossible
to maintain the design temperature. In order to control the temperature the space must be
provided with back up air-conditioning.
Figure 2.3.7. Warming curves of a light construction room with 4 different heat loads, with
initial temperature 25 ºC.
18
Figure 2.3.8. Warming curves of a medium heavy weight construction room with four
different heat loads, with initial temperature at 30ºC.
2.3.4 Materials
2.3.4.1 Construction materials
Untreated tile and concrete surfaces liberate dust, causing electrical equipment problems.
For this reason the walls of electrical equipment rooms have to be covered with a dustbinding coat of paint. Precoated sheet metal-mineral wool-sheet metal elements are also
used
Ceilings should not have mineral wool panels or other dust producing materials included in
them. Alternatives for mineral wool are bag wool with a fabric top. Closed suspended
ceilings, however, should be avoided in electrical equipment rooms.
2.3.4.2. Material emissions
Materials that liberate gases due to aging, which are harmful to equipment, should not be
used in electrical equipment rooms. After applying a surface coating, adequate time should
be allowed for drying before the electrical equipment is installed.
A typical drying-time for epoxy paints is 7 days and for acrylate latex 2-4 days, for wall
temperatures of +20°C.
2.3.5 Insulation
2.3.5.1 Moisture insulation and gas tightness
The diffusion of moisture and gases through the walls should be avoided. Holes and cracks
in the structure have to be filled with an airtight material. Surfaces to be sealed by specially
selected paints such as Epoxy and acrylate latex paints.
Alloprene and vinyl paints are not recommended, since they emit chlorine and hydrochloric
acid during a fire.
19
Vapour barriers should be on the high moisture content side, usually the process side. The
electrical equipment room surfaces should be painted to bind any dust. The cavity in the
outer walls should be painted from inside.
2.3.5.2 Thermal insulation
The heat load from the surrounding spaces into electrical equipment rooms might be high
in excess of 100 W per-m2 floors. Normally the main portion of the surrounding loads
comes through the roof and/or the floor from the cable spaces. In the case of a wall
separating a hot process area, thermal insulating is not normally economical unless other
advantages are achieved such as improved reliability of temperature control in the case of
ventilation plant failure.
2.3.6 Fire protection
Requirements concerning fire protection are covered in National Building Regulations and
in the requirements of insurance companies.
During a structural or cable insulation fire toxic gases are emitted to a room (a typical
example is PVC -> HCl). Care has to be taken in the design of exits from these areas. The
water used for fire fighting these toxic gases forms an aggressive liquid that destroys
equipment and primary structures. Typical conditions during a fire are covered in IEC
60721-2-8.
2.4 Target level assessment
2.4.1 The effect of environmental parameters on electrical equipment
2.4.1.1 High temperature
Effects of temperature on electrical equipment must consider: • The air temperature
• The equipment temperature.
The equipment temperature depends on its electrical loading and its ability to liberate this
heat to the surroundings.
The convection to the surrounding air has a major influence on the rate of heat transfer.
When the equipment has a cover, the thermal conductivity of the equipment and the path to
the cover is an essential factor to consider. The actual temperatures at which a fault occurs,
varies with different equipment. For example semiconductor silicon components can
tolerate a range of 125 to 175°C while germanium components can only tolerate 70 to
100°C. The memory in a hard disk is damaged with a temperature in the 70 ºC range.
The failure frequency of plant depends on the surrounding conditions, the load and the age
of the equipment. A typical failure frequency curve for electronic equipment is shown in
figure 2.4.1. The service life of equipment can be divided into three stages.
20
•
•
•
The early operating period lasting for 0,5 to 2 years, when the failure frequency is
2-10-fold compared to the actual operating period.
The actual operating period that in the normal conditions lasts for 10...20 years after
which the equipment is usually replaced with more efficient equipment.
The ageing period when the frequency of failure increases rapidly.
Figure 2.4.1. A typical graph for the fail frequency of an electronic equipment (Z (t)=fail
frequency)
The temperature rise has a great influence on the failure frequency of electronic equipment.
It is said that when the temperature rises by 10°C the frequency of failure doubles. It is
assumed that the failure frequency of electronic components follows Arrhenius’ law:
z=z0*e-E/(k*T)
where
(3)
z= failure frequency
z0=failure frequency in the normal conditions
k=Bolzmann's constant
E=the activation energy of the fault mechanism
T=the component temperature K
The formula shows that temperature increase influences exponentially the failure frequency
of components. If the electrical stress rate is high, the temperature effect increases the
failure rate. Figure 2.4.2 indicates how temperature, affects the failure frequency of
components. The figure indicates the mean time between component failures as a function
of the temperature. The mean time between failures (MTBF) is the inverse value of the
failure frequency. Except for MTBF, the temperature will also influence also component
efficiency.
21
Figure 2.4.2. The predicted mean time between failures of equipment with different
component choices (A and B) as a function of the temperature (m (h)= the mean time
between failures)
Excessive high temperatures ages electrical equipment reducing considerably their working
period. It has been claimed that a temperature rise of 14°C reduces the lifetime of
electronic components by 50% Cable insulating materials age with temperature increase,
the lifetime of rubber insulating materials at different operating temperatures is given in
table 2.4.1:
Table 2.4.1 The rubber insulation service life at
different operating temperatures
Temperature
Insulation service life
years
°C
25
30
32
15
39
7,5
46
3,7
International research work has been carried out covering the environmental factors and
their effects on electrical equipment. This work is published in the IEC (International
Electronic Commission) standards, many of which have been adopted as European
Standards. In standard EN 60068-1 the principal effects of environmental factors and
typical faults caused by them are covered. The effects of high temperatures are shown in
table 2.4.2:
22
Table 2.4.2. The main effects of a high temperature and typical faults in electrical
equipment
Main effects
Typical faults
Thermal aging
Oxidation
Cracking
Chemical reactions
Growth of mechanical stress
Softening
Melting
Sublimation
Reduction of viscosity
Evaporating
Thermal expansion
Insulation faults
Structural faults
Impairment of greasing properties
Increase in the wearing of moving parts
High temperatures also damages equipment indirectly by accelerating chemical reactions,
resulting in corrosion by the air contaminants. For example when the temperature rises
from 20°C to 30°C the reaction rate doubles. Evaporating of solvents and insulating
materials resulting in an acceleration of gaseous contaminants, which further increase
contact surfaces fouling.
2.4.1.2 Low temperature
Low temperatures alone do not increase the failure frequency, provided the temperature
stays above 0°C. See figure 2 where, the meantime between failures stay almost as constant
between 0° and 20°C. Instability of equipment can cause a change in the parameter values,
such temperature reduction, humidity, and air movement. If the intake air temperature is
near to the room air dew point, moisture will condense on the surface of electrical
equipment, with serious results.
When the temperature falls below 0°C, the rate of failures increases rapidly. When the
temperature drops to -40°C the failures of different components are about 10-fold
compared to normal conditions. When the temperature is below 0°C, moisture condensing
on surfaces will freeze in narrow spaces causing joint failure.
The main effect of low temperatures and faults caused by them according to EN 60068-1
are shown in table 2.4.3:
Table 2.4.3 The main effects of low temperatures and typical faults in electrical equipment
Main effects
Typical faults
Increase in viscosity
Ice formation
Embrittlement
Shrinking
Impairment of mech. strength
Insulation faults
Impairment of greasing properties
Sealing faults
Cracking
Failure
Structural faults
Increase in wearing of moving parts
23
2.4.1.3 Rate of change in temperature
Due to different thermal expansion coefficients, component can develop serious stresses if
the component temperature varies from its design value. If the temperature changes
constantly, the component will experience fatigue" and in time will fail. For example
memory protection batteries will be damaged if the temperature increases too often above
the permitted value. A single temperature increase above the permitted value will affect the
storage capacity.
In the EN 60068-1 standard the main effects of the temperature changes are thermal shocks
and local temperature differences are covered. Typical faults caused by these are
mechanical and insulation faults resulting in cracking and electrical leakage.
Temperature changes influence the relative humidity of the surrounding air causing cause
moisture to condense locally on components.
2.4.1.4 High relative humidity
Changes in humidity influence the resistance of electrical insulating materials. These
changes result in static electricity, particle formation and corrosion between different
materials. It will also cause corrosion by:
1. Directly, by chemical reaction on metals and plastics.
2. 1. Corrosive compounds forming with other gases in the air, e.g. sulphuric acid,
H2SO4 with sulphur dioxide SO2 and nitric acid HNO2 with nitrogen oxides. NOx
3. Electrochemically as an electrolyte on two different metals causing corrosion. For
example: - a copper plate coated with gold, if moisture condenses on it electrolysis
may result causing hairline cracks.
The main problems and typical faults of high relative humidity is given in EN 60068-1 are
listed in table 2.4.4.
Some insulating materials adsorb moisture at high relative humidity. This results in the
electrical conductivity of insulating material increasing with electrical leakage causing
equipment damage. Dust particles in the air, below a 1 µm (micrometer), can adsorb
moisture and gaseous contaminants. This may accelerate equipment corrosion. Corrosion
due to gaseous contaminants grows exponentially with an increase in relative humidity
If the air relative humidity increases above 80%,the silver used in the circuit cards may
develop a "migration phenomenon” causing short circuits. The gold used to fasten chips to
their beds also suffers from humidity and the chips may loosen and fail.
24
Table 2.4.4. The main effects of a high relative humidity and typical faults in electrical
equipment
Main effects
Typical faults
Absorption of humidity and condensation on the surface of an article
Swelling
Impairment of mechanical
Strength
Chemical reactions such as: - corrosion and electrolysis
Increasing of the conductivity of the insulation
Mechanical faults
Breaking
Insulation faults
When the relative humidity increases to 80 %, a water film forms on the equipment
surfaces.
High humidity is not an actual a problem in an automation/electrical equipment room with
well-designed ventilation systems, as air movement at the correct temperature removes the
moisture from the space. However if the intake air temperature is low, local moisture will
condense. A failure in room over-pressurization and a poor moisture barrier will cause an
increase in the local relative humidity.
2.4.1.5 Low relative humidity
The main effects due to low relative humidity and the typical faults caused by them
according to EN 60068-1 are given in table 2.4.5:
Table 2.4.5. The main effects of low relative humidity and typical faults in electrical
equipment.
Main effects
Typical faults
Drying
Embrittlement
Shrinking
Impairment of mechanical strength
Increase in wearing of contact surfaces
Developing of static charge
Mechanical faults of non-metallic parts
Cracking
Electrical faults
The worst threat to electrical equipment from the above-causes is that low relative humidity
increases the incidence of static charges. A static charge is when similar charges build up in
a substance and do not immediately become neutralized with opposite charges. A typical
electrostatic phenomenon is to have high potential differences, but the appearance of small
quantities of electricity. Normally an electrical charge leaks slowly along the surface of a
material or through it, without causing any problems. If the potential of a charged area
becomes high, a powerful discharge occurs which may cause damages to equipment wiping
out memory, cause electrical shocks to employees and create fire hazards.
The aim of protection is to keep the leakage rate greater than its rate of generation. By
maintaining the relative humidity in the 60-70 % range will eliminate static electricity
problems. As the temperature inside electrical motors is greater than that of the surrounding
air, the relative humidity in the surrounding should be 65% or more. The problems of static
25
electricity are minimised when the relative humidity of the surrounding air is greater than
55%.
Relative humidity influences occupant’s safety. For example cotton clothing is safe due to
its good electric conductance. This is true when the relative humidity is high, but below
40% relative humidity, cotton is a good insulating material. The value of clothing electric
conductance is important to neutralize the electrical charges between man and electrical
equipment. Wrist and foot straps will prevent electrostatic discharge from the people to
equipment; this is often a much cheaper solution than humidifying the room.
If the relative humidity drops below 40% static charges will attract dust particles and cause
undesirable dust forming. The formed dust causes wear of contact surfaces, breaks and
corrosion depending on the dust properties. The increase in contact faults with a decrease in
relative humidity is covered in figure 2.4.3
Figure 2.4.3. The effects of relative humidity on the functioning of tele-exchanges.
2.4.1.6 Rate of change of the relative humidity
Rapid changes in relative humidity may cause local condensation resulting in corrosion.
The corrosion rate caused by gases increases considerably when the rate of change of the
relative humidity is greater than 6% in an hour.
2.4.1.7 Chemically active substances
The effect of chemically active corrosive gases on electrical equipment according to EN
60068-1 is given in table 2.4.6.
26
Table 2.4.6 The main effects of chemically active gases and typical faults in electrical
equipment.
Main effects
Typical faults
Chemical reactions
Corrosion
Electrolysis
Surface decay
Increase in conductance
Increase in contact resistance
Increased wearing
Mechanical faults
Electrical faults
2.4.1.8 Mechanically active substances
The effect of mechanically active substances, such as particulate matter, on electrical
equipment is given in table 2.4.7.
Table 2.4.7. The main effects of mechanically active gases and typical faults in electrical
equipment.
Main effects
Typical faults
Friction, wearing
Clogging
Getting stuck
Frictional electricity
Increase in thermal
insulation
Mechanical faults
Increased wearing
Electrical faults
Over heating
2.4.2 Basis for design of electrical equipment rooms
2.4.2.1 Introduction
The equipment supplier defines the environmental demands for each room, and the
equipment heat loads. Initial information is given by the electrical designer. Table 1.1.1 can
be used to initially define the room environmental information during the preliminary
design. Other heat loads are calculated individually for each case.
Condition information/ checklist:
Temperature
• Environment class + the requirements of air conditioning
• Target value
• Accuracy (range of variation)
• Steadiness (rate of change)
• Maximum and minimum values in the case of disturbance
Humidity
• As temperature
Chemical contaminants
• Environment class
• Permitted concentration for each gas
27
Particle contaminants
• Environment class
Over-pressure/outdoor airflow
• Electrical equipment rooms are designed in over-pressure against environment. In
normal case 20 Pa over-pressure is enough. It is reached in a tight room with makeup airflow of approx. 2,1 l.s –1 per m2 wall see figure 2.3.4.
The room design criteria will define the choice of the air conditioning system required. In
addition to system selection the following have to be considered: - available space (foot
print and height) reliability in use, and possible room future extension.
2.4.2.2 Pressurization
As the requirements for electrical equipment room conditions are usually stricter than those
in the surrounding areas, they require pressurising. Normally 20 Pa excess is adequate for
rooms that border on outdoor air, see 2.3 and figure 2.3.4 for details. When the conditions
are extreme such as exposed sites high buildings and spaces having high negative
pressures, the over-pressure and the air flow rates required, have to be calculated
separately.
2.4.2.3 Introduction to the environmental parameter concept
When the operating conditions of electronic equipment are defined, all the condition factors
have to be determined for several operating parameters. The parameters can be divided
into: Base value i.e. normal conditions
• Range of variation above and below the base value
• Minimum and maximum values required when the equipment is in operation
• Minimum and maximum values required when the equipment is not operating
• The real limit values necessary to avoid equipment damage.
The relationship between the parameters is shown in figure 2.4.4:
28
Figure 2.4.4. Operating parameters and reliability of electronic components.
The design value relates to the constant operating conditions (temperature, humidity,
particulate matter etc.) required in the area where the equipment is in use. It is necessary
these parameters be met to ensure operation reliably over its lifetime. When perfect
functioning of equipment is required the conditions defined by the base values must be
worked to.
The variation range design values define the choice of surroundings in which the
equipment reliability remains constant. The reliability over this range is obviously
influenced by the rate of change of conditions.
The design value and its variation range define the design conditions to be selected.
Equipment in normal operating situations provides the initial values for the air conditioning
designer.
Maximum and minimum conditions, when the equipment is operating, define the extreme
environmental values surrounding the equipment in a special case. These cover the event of
failure of the air conditioning plant. When conditions reach the extreme values, there is a
risk of equipment failure the maximum and the equipment manufacturer provides minimum
conditions for equipment, these are based on test performance under given conditions.
When designing electrical equipment room ventilation systems, it should be considered that
the air conditioning system must operate after a malfunction, before extreme environmental
conditions are reached and the manufacturing process fails.
Environmental tests for electrical equipment have been standardised. The key methods of
the testing are given in EN 60068-1. The environmental standards and the tests related to
29
them are used for defining the greatest short-term environmental stresses encountered for a
product. However, these classes do not provide information regarding long-term stresses
that influence the equipment for its lifetime. Even remaining within the tested
environmental class does not guarantee a perfect function of the product in these conditions
Long-term stresses can slowly influence the product quality and result finally in failure.
The classification considers that different environmental parameters (temperature, humidity
of air etc.) are symmetrically divided. The extreme values of classes have been chosen so
that average equipment can tolerate that the conditions do not exceed the extreme value
for no more than 1% of the operating time.
Maximum and minimum values for non-operating periods are used for defining the
equipment storing conditions. During installation and shutdown periods the air
conditioning must operate to ensure the operating conditions are achieved as soon as
possible. When conditions reach the equipment critical limit immediate failure may result.
2.4.2.4 Climatic conditions (temperature and humidity)
As the basis for designing air conditioning systems, a conditions curve of 75% is used. In
practice the humidity can be varied over a wider range of this curve because air humidity in
a space changes with the seasons, hence the risk of extreme humidity does not continue
over the whole of the time.
Some classes are more flexible regarding the requirements of air conditioning. Hence
certain precautions can be permitted so that the temperature approaches the outdoor
extreme design conditions. The extreme conditions of electrical equipment correspond to
the 99% values on the conditions curve.
Air-conditioning design has to ensure that the room conditions achieve average values in
the middle of the permitted area. Hence care has to be taken with selection of the air
terminal devices and their actual positioning.
Design requirements are compiled by considering the electrical equipment in the room.
Extra requirements for each room, such as workplaces, have also to be considered, see
2.4.3.
Rooms with high heat loads must be prepared for a sudden temperature change due to
malfunction or failure of the air conditioning. This is achieved by reducing the room
temperature level with backup equipment or by natural ventilation.
The conditions that correspond to individual rooms requirements should be maintained
during shutdowns, as moisture condensing on electrical equipment may cause damage on
plant start up.
When the temperature rate of change is calculated during the design, the initial assumption
is perfect mixing. The rate of change has to remain in the given range during a period of 5
30
minutes. The calculations have considered the structural damping effect on temperature
change. This is achieved by the use of two time-constants models.
During operation, the room conditions have to stay within given limits of the electrical
equipment. This means the volume around the equipment measured from the floor level up
to two meters, and at least to the 50 cm from the equipment surface. The measuring should
not be carried out near an air conditioning unit (the minimum distance is 1 m) or in its
airflow. Hence positioning of control sensing devices must be taken into account.
The design basis given is intended for forced ventilation design. Natural ventilation can be
applied by applying the design values of electrical equipment (extreme values). Table 2.4.8
and climatographs (see Appendix 1) the air conditioning design conditions for different
climatic conditions have to be considered.
2.4.2.5 Special climatic conditions
Most equipment permits air velocities greater than those mentioned above. This is dealt
with separately in special climatic conditions categories. The permitted air velocities in the
different classes are given in table 2.4.9.
Table 2.4.9. Special climatic conditions; the permitted air velocity in the different
condition classes
Condition class
3Z4
3Z5
3Z6
Permitted air velocity m.s-1
5 m.s -1
10 m.s -1
30 m.s –1
2.4.2.6 Chemically active substances (corrosive gases)
The permitted concentrations of chemically active gases in electrical equipment
environments are defined in the classes C of the EN 60721-3-3, standard as are chemically
active substances. In table 2.4.10 the maximum values of different gases for air
conditioning design are given. Since the concentrations in the strictest classifications are
extremely small, comparison at the size range level with classes (G1-G3, GX) of standard
ISA-71.04-85 are used. The copper-strip method in the above standard can be used to
estimate the rooms surrounding classification.
The following are the two most critical classes, since concentrations of the other classes are
so high, that these other classes are irrelevant for electrical equipment rooms.
31
3C1:
The average air concentration in areas with no emissions of harmful
gases. Near industrial plant emissions and in some city areas, chemical
filtering is necessary to achieve this class. This corresponds to class ISA
G1-G2, even though the concentrations are a little higher than in the ISA.
3C2:
Corresponds to class ISA G3-GX. Causes corrosion of unprotected
electrical equipment.
In laboratory tests for chemical filters it is shown that the filters in the tests could not
remove nitrogen oxides from the air. Therefore the customer has to specify in his
equipment inquiry a wider class of filter that will deal with NOx if the concentrations of
nitrogen acids rise over 0,1 mg. (nitrogen oxides alone can cause corrosion of metal
surfaces, but together with other gases corrosion is accelerated)
The ozone concentration range in the standard, is critical as the concentration of class 3C2
is exceeded e.g. in Finland on background levels. In practice the permitted ozone
concentration should be classified to class 3C3 with the present outdoor concentrations.
Ozone is not considered to be a corrosive substance, however it oxidizes plastics, rubber
and textiles, and accelerates the corrosion caused by other gases.
32
Table 2.4.8. Design conditions for air conditioning in different climatic condition classes
DESIGN CRITERIA FOR VENTILATION IN DIFFERENT CLASSES OF IEC 60721-3-3(CLIMATIC CONDITIONS)
ENVIRONMENT CLASS
3K1
3K2
3K3
3K4
3K5
3K6
3K7
3K8
EXTREME OPERATION
CONDITIONS
-MIN:
OF ELECTRIC
-MAX:
EQUIPMENT *
18°C
27°C
15°C
30°C
5°C
40°C
5°C
40°C
-5°C
45°C
-25°C
55°C
-40°C
70°C
-55°C
70°C
+19-26°C
0,5°C
+15-30°C
0,5°C
+10-30°C
0,5°C
-5-+35(45)°C
0,5°C
5-95%
min 0,7g/kg
max 28g/kg
5-95%
min 0,7g/kg
max 29g/kg
10-100%
min 0,4g/kg
max 29g/kg
10-100%
min 0,1g/kg
max 35g/kg
10-100%
min 0,1g/kg
max 35g/kg
DESIGN
TEMPERATURE
**
-RATE OF CHANGE
(5 MINUTES AVERAGE)
+22-23°C±2°C
0,1°C
RELATIVE HUMIDITY
ABSOLUTE HUMIDITY
40-50%±10% (in +22°C)
-
INLET AIR
-TEMPERATURE
-RELATIVE HUMIDITY
min 16°C
max 75%
min 16°C
max 75%
min 10°C
max 85%
min 5°C
max 95%
min -5°C
max 95%
-
-
-
0,5m/s
1,0m/s
1,0m/s
1,0m/s
1,0m/s
1,0m/s
5,0m/s
5,0m/s
AIR MOVEMENT
(SEE ALSO SPECIAL
CLIMATIC CONDITIONS)
NOTE
10-65%
min 1,5g/kg
max:min roomTemp./65%
(e.g. 19°C->9g/kg)
Change of conditions outside limits Design temperature-area is chosen
for normal operation causes an alarm.inside above mentoined area.
It is recommended, that room temperature is regulated in accuracy of
±2°C around chosen temperature.
EQUIPMENT REQUIREMENTS: -HEATING
(Things in parentheses must be-COOLING
considered case by case)
-DEHUMIDIFIER
-HUMIDIFIER
-HEATING
-COOLING
-DEHUMIDIFIER
(-HUMIDIFIER)
5-70%
min 0,7g/kg
max:min roomTemp./70%
(e.g. 19°C->9,5g/kg)
-25-+45°C(55°C)-40-+45°C(70°C)-55-+45°C(70°C)
0,5°C
1,0°C
1,0°C
Design temperature-area is chosen Design temperature-area is chosen It is recommended that temperature It is recommended that temperature
inside above mentoined area.
inside above mentoined area.
difference between in- and outcomingdifference between in- and outcoming air
During exceptionally warm season During exceptionally warm season air is 10°C in mechanical ventilation is 15°C in mechanical ventilation.
may temperature rise to +35°C, if the may temperature rise to +35°C, if the and 15°C in natural ventilation.
heat-load in room is under 100W/m². heat-load in room is under 100W/m².
In natural ventilation extreme operation conditions
can be used for bases for design.
-HEATING
-COOLING(outdoor air if possible)
( -DEHUMIDIFIER)
-HEATING
-COOLING(outdoor air if possible)
(-HEATING during shutdown)
-COOLING(primarily outdoor air )
-COOLING(primarily outdoor air )
* CONDITIONS DURING VENTILATION BREAKDOWN
** DURING NORMAL OPERATION
33
Table 2.4.10. The permitted maximum concentrations of chemically active substances in
different conditions classes, according to EN 60721-3-3.
Environmental factor
salts
Unit
3C1
3C2
3C3
3C4
mg/m3
no 1)
salt
mist
salt
mist
salt
mist
0,1
0,037
0,3
0,11
5,0
1,85
13
4,8
0,01
0,0071
0,1
0,071
3,0
2,1
14
9,9
0,1
0,034
0,1
0,034
0,3
0,1
0,6
0,2
0,1
0,066
0,1
0,066
1,0
0,66
1,0
0,66
0,003
0,0036
0,01
0,012
0,1
0,12
0,1
0,12
0,3
0,42
1,0
1,4
10
14
35
49
0,01
0,005
0,05
0,025
0,1
0,05
0,2
0,1
0,1
0,052
0,5
0,26
3,0
1,56
10
5,2
cm3/m3
sulphur dioxide
mg/m3
cm3/m3
hydrogen sulphide
mg/m3
cm3/m3
chlorine
mg/m3
cm3/m3
hydrogen chloride
mg/m3
cm3/m3
hydrogen fluoride
mg/m3
cm3/m3
ammonia
mg/m3
cm3/m3
ozone
mg/m3
cm3/m3
nitrogen-oxides3)
mg/m3
cm3/m3
1) Sea salt mist can occur in weather protected spaces on the shore and in the spaces that are in costal areas.
2) Values are both calculated in cm3/m3 And mg/m3 values at 20°C temperature. The values of the table are rounded.
3) Is given as equivalent of nitrogen dioxide
2.4.2.7 Mechanically active substances (sand, dust)
The permitted concentrations of particulate matter in the operation environment of
electrical equipment are presented in table 2.4.11. The classification does not consider the
position for measuring the dust or it’s the origin.
34
Table 2.4.11. Maximum concentrations of mechanically active substances for different
classes.
CONDITION CLASS
SAND
3S1
3S2
3S3
mg.m-3
no
30
300
DUST
(suspended
particulate)
mg.m-3
DUST
SEDIMENTATION
0,01
0,2
0,4
10
35
350
mg.m-3 per day
2.4.2.8 Biological conditions
The classification concerns the protection of electrical equipment against mildew, fungi,
organisms and small animals. Usually electrical equipment rooms are class 3B1 and these
rooms have been protected against these factors. This is not normally considered in
standard air conditioning design
2.4.2.9 Mechanical conditions
This classification describes the influence of mechanical stress, including vibration and
impact directed to the electrical equipment. This factor is normally not considered in
basic air conditioning design.
2.4.2.10 Special requirements of different equipment
The storage capacity of batteries decreases with a temperature decrease
2.4.3 Human occupancy.
Work places should be located separately from the actual electrical equipment rooms. If
they are permanent (for more than occasional work) they must be taken into account
while designing the air conditioning. See 3.1.4 Ventilation.
35
Table 2.4.12. Requirements for work places
LIMIT VALUES
TEMPERATURE °C
-Sedentary work
-Light, moving work
RELATIVE
HUMIDITY %
AIR VELOCITY
(m.s-1 at 20 °C)
-Sedentary work
-Light, moving work
NOISE dB(A)
TARGET
VALUES
20-28
18-25
15-70
21-25 1)
19-23 1)
30-50 2)
0,15
0,25
55 3)
0,15
0,25
55 3)
1) There should not be any extreme thermal radiation, hot or cold, which may cause damage to the
equipment
2) To reach the target value, means that the air humidity has to be controlled
3) National regulations or standards may define a lower limit value.
The air purity has to achieve values necessary for office spaces. For electrical equipment
air purity of class 3C1 is usually adequate for plant and occupants
2.5 Source description
2.5.1 Introduction
Waste heat generated in electrical equipment is transferred almost entirely by air
convection to the room through the equipment cabinets. The surface temperature of the
cabinets is normally not much higher than the surrounding temperature, so radiant heat
transfer can be ignored.
2.5.2 Estimation of heat loads
The maximum heat loads in electrical equipment rooms have to be calculated with
accuracy. The final design should be based on the heat loads given by the electrical
equipment supplier. When changes are made to existing rooms, it is essential to
determine the heat loads both by measurement and calculation. Care has to be taken if
rule of thumb methods are used for this purpose
2.5.2.1 Rough estimation of heat loads in electrical equipment rooms
The power losses of low-voltage equipment and its associated cables in the cable space
equal to the loading losses of the supplying transformer. The transformer power loss is
obtained from the manufacturers technical specifications. A 1.6MVA transformer
dissipates 14,6 kW at full load.
36
The power losses at low-voltage (< 500 V) in equipment rooms are about 0,3.to 0,5 % of
the electrical power supplied. The dissipation power losses in low-voltage centres can be
estimated on floor area of the distribution centre. A useful estimation is 800 W. m –2 of
floor area of a distribution centre. The heat load generated by other equipment in the
room, such as AC-inverters, lights, fans etc has to be determined separately and added to
the total load.
2.5.2.2 Heat loads of different equipment
The following clause, gives power losses provided by electrical equipment
manufacturers. These can be used if no other information available. The values are
approximate further checks are required with the chosen equipment supplier.
Motor control equipment (source: ABB Strömberg, Finland, 1993)
Motor control equipment having the following dissipation powers:
The supply voltage of the device
Power losses (% of the nominal power)
380 V
2.0 %
500 V
1.5 %
When direct current is used, the power losses do not vary much. With alternating current
the power losses depends on the rate of utilization.
Automation equipment (source: Valmet Automation, Finland, 1993)
The power losses of automation cabinets is <500 W/cabinet (Length x Depth = 600x400),
the power is almost constant regardless of the utilization rate.
Control room equipment source: Valmet Automation, Finland, 1993)
The power losses of control room equipment are: -:
Power losses [W/equip.]
Monitor
70
Keyboard
70
Printer
75
UPS-equipment
Table 2.5.3 presents power losses of single and three phase UPS-equipment within the
range of 5-150 kVA.
37
Table 2.5.3. Power losses of single and three phase UPS-equipment,
range 5-150 kVA.
Size [kVA]
Number of phases
Maximum heat losses[kW]
5
1
1,2
10
1
2,2
12
1
2,5
15
1
3,1
20
1
3,6
25
1
4,4
30
1
5,2
40
1
6,7
50
1
8,1
60
1
9,7
75
1
11,3
10
3
2,7
15
3
3,8
20
3
4,5
30
3
5
50
3
7
75
3
10
100
3
12
150
3
18
ADP-equipment
The power losses of ADP-equipment depend on the equipment supplier. Hence the
precise information must be obtained from the suppliers.
TELE-equipment
The information regarding power losses of tele-exchange equipment has to be determined
from the equipment supplier. The percentage of power losses has reduced by half, with
the new generation of equipment on the market. The room loads however have not
reduced, as the equipment sizes become smaller in the same ratio. For coming third
generation telecommunication system, heat dissipation will increase dramatically.
2.5.2.3 Total heat loads of electrical equipment room in Pulp and Paper mills
Table 2.5.4 shows total heat load values (internal and external loads) measured in the
electrical equipment rooms of pulp and paper plants. The differences between different
rooms are considerable The loads in similar electrical equipment rooms for the same
38
kind of plant can differ from each other depending on the location of the electrical
equipment and the external load. When AC- is used the power losses depends on the
motor utilization rate. The power losses for DC-use and for automatic equipment are
normally constant regardless of the utilization rate.
Table 2.5.4. Total heat loads measured in electrical equipment rooms for pulp and paper
plants.
Heat load [W.m-2 ]
Average load [W.m-2 ]]
Control rooms
60-200
160
Automation rooms
100-350
260
Electrical equipment rooms
100-2000
250-300
10-130
50*
Cable spaces
* The designed heat load of cable spaces is usually 20-25% of the electrical equipment
load.
2.5.3 Battery rooms.
Batteries produce hydrogen during charging. To ensure that fire and explosion does not
occur, adequate ventilation by flameproof fans is required the ventilation requirements
must be based on electrical safety regulations.
2.5.4 Sources of the contaminant loads.
In addition to the filtered intake, particle and gaseous loads enter by leakage from the
surrounding spaces and from employees. If smoking is forbidden in the room and the
instructions given in this text are followed in the ventilation design, the human loads can
be ignored.
2.6 Load calculations
2.6.1 Heat loads
The electrical equipment supplier provides the heat loads generated by his equipment.
During the design the initial heat loads are provided by the electrical designer. Clause 2.4
gives methods by which an approximate estimate of the maximum heat load can be
obtained.
In addition to the maximum loads the average heat loads in the room have to be
determined. They can differ considerably from the maximum values due to the equipment
use.
In addition to the heat load from electrical equipment, attention has to be paid to other
heat loads: such as: - uncooled intake air, other heat generating devices such as fans,
occupants working in the space, surrounding spaces, outdoor conditions, lighting, solar
39
radiation etc. External loads can be high both on heating and cooling and they must be
allowed for, these loads vary according to the seasons. Clause 2.3.5.2 gives an example
regarding calculating the surrounding heat loads.
If the mean heat loads differ considerably from the maximum loads, these have to be
taken into account when designing the air-cooling control. See 3.3.2.2 for cooling control.
2.6.2 Contaminant loads
Clause 2.1 gives the means of estimating the surrounding contaminant loads.
2.6.3 Pressure conditions.
In clauses 2.3.1 and 2.3.2 consideration is given to wind effects, and temperature on the
pressure ratios in the electrical equipment room.
40
3 SYSTEM PERFORMANCE
3.1 Selection of system
3.1.1 Air conditioning systems for electrical equipment rooms
This clause describes air conditioning systems suitable for serving transformer, cable,
electrical equipment, automation, cross-connection and tele spaces and control rooms.
The air conditioning solutions shown cover all electrical equipment rooms. These are
considered from the industry point of view. There are five basic solutions, see figure
3.1.1:
1. Natural ventilation
2. Forced extract ventilation
3. Over-pressure ventilation
4. Cooling with circulated air
5. Separate cooling placed to the room.
The systems and their most important properties are covered in table 3.1.1.
Factors influencing system selection are: the position, layout and structure of the room,
environmental conditions, room heat load reliability of equipment use, space
requirements, fire areas and initial costs. If necessary, the possible requirement of future
extension has to be considered. A summary on the conditioning classification for
different systems is shown in table 3.1.2.
41
Table 3.1.2. Condition classes that are reached with different air conditioning systems
(number of system refers to clause 3.1.1)
CONDITION
AIR CONDITIONING SYSTEM
CLASS
1
2
3
4
5
3K1
-
-
-
+
+*)
3K2
-
-
-
+
+
3K3
+**)
+**)
+**)
+
+
3K4
+**)
+**)
+**)
+
+
3K5
+**)
+**)
+**)
+
+
3S1
-
-
+
+
+
+***)
+***)
+
+
+
3C1****)
-
-
+
+
+
3C2*****)
+
+
+
+
+
3S2-4
*
**
***
****
*****
Attention shall be paid to cooling control
Depending on the maximum temperature and heat loads
Depending on the location
Requires a chemical filtering in areas with highly polluted outdoor air
Not close to process emissions without a chemical filtering
42
TABLE 3.1.1 Air conditioning systems used in electrical equipment rooms.
VENTILATION SYSTEMS USED IN ELECTRICAL EQUIPMENT ROOMS
SYSTEM
SCEMA NUMBER
FUNCTION
PRINCIPLE
1. NATURAL VENTILATION
1.1
Heat load of the room cause cooling air-flow
through the room.
2.FORCED EXHAUST VENTILATION
1.2
Room temperature is hold at setpoint by starting
the exhaust fan according the demand.
3.OVER-PRESSURE VENTILATION
1.3
Room temperature is hold at setpoint by regulating make-up air temperature. Room is in overpressure against surroundings and warmed air
goes away from room through constructions.
4.COOLING WITH RECIRCULATED AIR
1.4
Room temperature is constantly controlled by
cooling.
Room is hold in overpressure against environment with make-up unit.
SYSTEM
Inlet- and outletlouver or -duct.
Inlet- and outletlouver end exhaust fan.
Make-up and Recirculation units.
Usable in rooms, where is located equipments
that tolerate environmental conditions, high and
low temperatures and the heat load is small.
Used in rooms with main transformers.
Usable in rooms, where is located equipments
that tolerate environmental conditions, high and
low temperatures and the heat load is small.
Used in rooms where natural ventilation is not
sufficient, such cable rooms. If cable room is
up- or downside of electrical equipment room
also make-up fan should be installed.
Not suitable for rooms, where clean air is
demanded. Rooms where unprotected electronic compounds is used should be kept in overpressure by ventilation.
Make-Up unit and, if air-flow rate is high,
overpressure damper to prevent too high
pressure level in ventilated room.
System is suitable for equipment rooms, where
temperature and air quality is controlled, but
temperature level is allowed to rise in some
extent during summer.
COMPONENTS
APPLICABILITY
LIMITATIONS
Cooling effect is sufficient only with low heat
loads.
DIMENSIONING
Temperature difference between supply and
exhaust air is 15°C in design temperature.
Temperature difference between supply and
exhaust air is usually 10-15°C in design temperature.
ADVANTAGES
Cheap and sure operation.
Simple in use.
DISADVANTAGES
Cooling effect is sufficient only with small heat
loads.
In time dust is collected, which may make
cooling of equipment difficult.
DIFFERENT
VARIATIONS
With high air-flow rate it is recommended that
also make-up fan is installed to ensure cooling
and to avoid too high underpressure. Make-Up
fan should be equipped with mechanical filter.
5.SEPARATE COOLING PLACED TO ROOM
1.5
Room temperature is constantly controlled by
cooling. Accuracy of regulation depends on
chosen cooling system.
Room is hold in overpressure against environment with make-up unit.
Make-up unit and separate cooling system inside
the equipment room.
Primary solution for rooms, where climatic
classes 3K1 or 3K2 is demanded.
Level of climatic conditions reached is depending on chosen cooling system. When choosing
the system one has to make sure with calculations that demanded level can be reached.
Temperature difference between supply and
exhaust air is usually 5-10°C in design temperature, depending on heat load and equipments.
In order to pressurize the room, the rate of change
of air should be at least 2,5 1/h. Overpressure
damper don´t open until overpressure in the
room is more than 20 Pascal.
Supply air is filtered and spreading of impurities
from environment is prevented.
Temperature difference between exhaust and
recirculation air. Make up air flow is 2,5 1/h in
order to pressurize room to at least 20 Pascal
overpressure.
Temperature difference between exhaust and
recirculation air. Make up air flow is 2,5 1/h in
order to pressurize room to at least 20 Pascal
overpressure.
Indoor climate is controlled.
Indoor climate is controlled, it is true that rough
temperature control cause temperature swing,
which may exceed allowed rate of change.
In summer room temperature is risen already in
normal operating conditions. During ventilation
breakdown gets temperature quickly too high,
if heat loads in room are big. Therefore in rooms
,where are located equipments that are vital to
whole process and can't be driven down,
mechanical cooling should be considered.
By installing return air part into make-up unit can
heat energy be saved, when recirculation and
outdoor air is mixed.
Ducts in recirculation system becomes big in
rooms with big heat loads, which may cause
space problems. Location of ventilation equipment room and space demands of equipment
and ducts should be taken in account already
in the beginning of design.
Maintenance of ventilation equipment is more
difficult than if they were located in separate
room. Maintenance cause also extra movement
in electric al equipment room, which is not
desirable.
Air flow of the make-up unit can be led to suction
side of the recirculation unit. This measure
improve efficiency of chemical filtering, if there is
chemical filter both in make-up and recirculation
unit. Problem is that the whole system must be in
also during shutdown in order to keep equipment
room in overpressure.
Recirculation unit have to be supplied with humidifier and drying cooling coil, if there is need to
control air humidity(3K1). Make-up unit should
supply with cooling coil for two reasons:
-Major part of humidity load is from outdoor air.
-Rise in room air humidity during shutdown can
be prevented and avoid disturbances during
process start.
As cooling system fancoils, room air conditioner
units, and in control rooms also cooling panel
systems is used.
When using cooling panels, must be taken care
of that air humidity don't condense on the surface
of the coil. To prevent water getting into equipment coil must not be located above them.
Recirculation unit have to be supplied with humidifier and drying cooling coil, if there is need to
control air humidity(3K1). Make-up unit should
supply with cooling coil for two reasons:
-Major part of humidity load is from outdoor air.
-Rise in room air humidity during shutdown can
be prevented and avoid disturbances during
process start.
Due to small temperature difference between
supply and room air needed cooling air flow
rate becomes high with big heat loads.
In areas, where chemical filtering is needed
make-up air flow is recommended not to be
bigger than 2,5 1/h, due to filtering cost.
Warm exhaust air from electric equipments can
be blown out of the room, which degreases in
room influencing heat load.
43
Figure 3.1.1. Basic ventilation and air-conditioning systems for electrical equipment
rooms.
1.1. Natural ventilation
1.2. Forced extract ventilation
1.3. Over-pressure ventilation
1.4. Cooling with circulated air
1.5. Separate cooling unit within the room.
44
3.1.2 Reliability
The basis for the design of different rooms and the reliability level should be discussed
thoroughly with the customer as early as possible. If the reliability of use is taken into
account during the design stage, the study can include the whole factory. Spare parts are
essentially to ensure operational reliability. Their amount can be reduced by careful
planning and at the same time improve the reliability of use.
The required reliability of use of air conditioning system depends on the importance of
the air-conditioned room when related to the whole process. Equipment rooms can be
considered to have three different stages of the reliability
1) The lowest requirements for the reliability of use are for rooms in which the
device can be stopped for a while without influencing the main process. The
function of the air conditioning system in this type of room does not require a
backup system. The system consists of reliable components, and rapid servicing is
necessary to ensure the minimum of shut down time.
2) Rooms in which a temporary temperature increase cannot be allowed, require
attention in order to determine the reliability of use. Equipment in this kind of
room cannot be stopped without disturbing the main process. However the
equipment may tolerate a small temperature rise with associated malfunctions
without causing major problems the air conditioning design must ensure the room
temperature will not exceed the maximum operating temperature of the electrical
equipment even during a malfunction.
This requirement can be met if the cooling capacity is divided into several units
independent of each other. In case of the failure of one or more units at the same
time will not cause the room temperature to rise above the maximum operating
temperature. Any electrical work on the air-conditioning equipment can then be
carried out without isolating all the equipment. In addition rapid service is
necessary. If damaged equipment cannot be replaced quickly enough by the
equipment supplier, the user has to ensure that adequate spare parts are available
for his own maintenance staff to get the plant on line again without delay.
The requirement for spare parts also depends on the extent of the heat loads. For
example if the heat load is under 100 W.m-2, the room temperature will not rise
above +40°C when the outdoor temperature is +25°C.
3. Rooms in which equipment failure causes a shutdown should always be
equipped with a double cooling system. Typical rooms are computer- and
automation rooms. In these malfunctions increase even with a small temperature
rise. Hence a rapid repair service is essential.
The reliability of use and the effect of damaging of different component can be
observed by analysis of the reliability of operation. An analysis of this type will
pin point the equipment weak spots.
45
3.1.3 Extension reserve
Electrical equipment rooms tend to fill up in time with extra electrical equipment, so it is
important in air conditioning design to be prepared for system extension this is achieved
in principle in two different ways.
1) Cooling equipment designed to deal with the "full" space. Then reliable and
economical use of the cooling system must be secured on partial loads.
2) The space is cooled by the use of modular units, provision being made for extra
space that will allow more units to be added when necessary
3.1.4 Air distribution
3.1.4.1 Objectives of air distribution
Supply air entering electrical equipment rooms should be mixed effectively with the
room air-cooling the whole space evenly. The room conditions should be determined in
the manner shown in 2.4.2.3 the air distribution has to be able to deal with the room
pressure ratios to stop uncontrollable air leaks. When floor or ceiling flow (laminar
ceiling) is used it is critical to pay attention to pressure ratios.
Air velocity is not a critical factor in electrical equipment room for temporary occupancy
the permitted air velocities in different classes are given in 2.4.2.5 (see table 2.4.9).
Usually the electrical equipment manufacturers permit higher air velocities in the
equipment specifications (climatic special conditions: classes 3Z4-6). A critical factor
concerning the air distribution is when the space is permanently occupied
3.1.4.2 Air distribution systems used in electrical equipment rooms
The most common methods of air distribution are mixing air distribution and floor
discharge. The mixing air distribution is achieved by using ceiling-diffusers, grilles or
direct discharge In rooms where people are working, laminar ceiling, active displacement
and radial whirl diffusers for air distribution are used.
Floor discharge
In floor discharge systems the intake air is discharged into the space through a raised
floor. This space acts a plenum. Intake air flows to the air-conditioned room through floor
grilles or through the equipment cabinets. The raised floor works also serves as a cable
space and an air conditioning duct. This principle of air distribution is shown in figure
3.1.2
46
Figure 3.1.2. Floor discharge
Floor discharge is the most common method of distributing air in medium-sized and large
computer centres. Other air distribution solutions are not recommended for computer
rooms except the floor discharge, together with the exhaust air removal from the ceiling.
Comfort criteria can be met with this method up to a cooling load of 150 W.m-2
There are some problems with floor discharge systems, these being fire safety due to the
floor void. It is recommended that the cable space and the electrical space are different
fire areas. In such cases the raised floor has to be fire proof and the intake air grilles have
to be equipped with fire dampers. Additionally the space under a raised floor is difficult
to keep clean. Therefore a cable space is often separated from other spaces, regulations
may stipulate that the minimum height is two meters and has it own air conditioning
system.
Mixing air distribution.
When air distribution is by ceiling diffusers, excellent air mixing with good dilution
occurs. The cooling capacity and the air flow, required in electrical equipment rooms are
normally high resulting in problems in achieving comfort conditions.
Laminar ceiling.
In a laminar ceiling, air is discharged from the ceiling through a perforated plate into the
room. Cool air flows with low velocity through the holes and is mixed with room air. The
air flowing downwards warms up to the design temperature before it reaches the critical
areas in the space.
A laminar ceiling is an ideal air distribution system for control- and automation rooms.
Air can be introduced into the room without draught up to a cooling capacity of 170-200
W.m-2 A perforated ceiling requires accurate design to avoid uncontrollable flow. The
perforated area of the whole ceiling area should not be more than 50%. A laminar ceiling
system can be used in electrical equipment rooms with the air being introduced above the
aisles and the exhaust extracted above the equipment cabinets see figure 3.1.3.
47
Figure 3.1.3. A laminar ceiling in an electrical equipment floor
Active displacement
Active displacement operates by means of nozzle ducts. Manufacturers state that a
cooling capacity of 240 W.m-2 and airflow of 40 l.s-1 can be achieve without draught The
nozzle ducts system operates by means of small air jets that induce a large volume of
secondary air ensuring good mixing Air distribution patterns can be adjusted by changing
the number of nozzles and the blowing sector. With nozzles evenly distributed around a
duct, the conditions are almost equal to a perforated ceiling. The use of a nozzle duct in
an electrical equipment room is shown in figure 3.1.4.
The nozzle duct it is a factory-made product, and provides good environmental conditions
Full use of the equipment manufacturer data should be used to achieve the desired result.
Figure 3.1.4. Active displacement
Closed air circulation
If people are working in an electrical equipment room, a closed air circulation is the only
way to provide comfortable working conditions for cooling capacity (> 400 W.m-2). The
principle of the closed air circulation is shown in figure 3.1.5.
48
Figure 3.1.5. Closed air circulation
Designing and operating a closed air circulation is more complicated than other systems.
It requires the electrical equipment supplier to designing airflows for each cabinet. In
addition the cabinets have assemblies for the air conditioning. A dual ductwork system
requires more space making the equipment cable- laying difficult. The closed air
circulation system is more sensitive to cooling equipment malfunctions, as the air
circulation capacity is less than the case of when the whole equipment room is ventilated.
Half-open systems
One solution is the combination of a closed air circulation and ceiling discharge. A
portion of the air is discharged directly into the equipment cabinets and the remainder in
to the room space. The exhaust is placed above the equipment cabinets as in open
systems. This provides the best characteristics of both systems. The equipment cabinets
receive controlled clean air, and the equipment space provides a buffer against the
surrounding. During a malfunction all of the room air capacity can be used. Another
problem in this case is how to introduce the correct air quantity into each cabinet. The
principle of this arrangement is shown in figure 3.1.6.
Figure 3.1.6. A half-open system; blow into the equipment cabinets.
In rooms with high heat loads (500 W.m-2) the temperature difference between intake and
exhaust air can be increased, and the air flow reduced. The warm exhaust air is induced
49
directly from the equipment cabinets. In this case information regarding thermal power
and airflows for each cabinet has to be obtained from the electrical equipment supplier.
The principle of the system is shown in figure 3.1.7.
Figure 3.1.7. A half-open system; suction from the equipment cabinets
3.1.4.3 Workplaces.
Workplaces are normally in separate control rooms near to electrical equipment rooms.
The conditions in these rooms correspond to office spaces. In addition to the above
methods of air distribution in control cabinets a chilled ceiling may be used, this reduces
the airflow rate. Care has to be taken to ensure that condensation in or on the ceiling does
not take place. This is achieved by ensuring the supply air is of the correct moisture
content (See 3.1.1, system 5).
In practice electrical equipment rooms, especially for automation spaces, have work
places, where people may stay for long time. The draught and noise prevention in rooms
with heat loads (>200 W.m-2) requires special attention. Workplaces should be separated
from the other parts of the room by a movable wall, or by air conditioning solutions.
Using partly or totally closed air circulation in the cabinets can reduce the heat load and
airflow required in the room. See 2.4.3 for conditions of workplaces.
3.1.5 Air conditioning costs
3.1.5.1 Building costs
Purchasing air conditioning equipment is carried out by tender; the actual price
depending on market forces. Material quality and component also influences the price.
Components used for industrial applications are usually more expensive than standard
comfort-units. The cost is related to the required environmental conditions, the largest
single cost is that of chemical filtering. The reliability of use of equipment has to be
considered carefully, due to its effect on the initial costs.
50
The air conditioning costs can be estimated approximately see. Table 3.1.3, which shows
the costs per square meter in the type room (200m2) that can be used in calculations, for
different system solutions with two different values of cooling capacity.
3.1.5.2 Operating costs.
The most important item in air conditioning operating costs is that of replacing the
chemical filter medium.
Due to the high cooling load, the use of electricity by air conditioning and cooling
devices is large. Thus the economical performance and the choice of operating conditions
is critical, consider absorption refrigeration
51
Table 3.1.3. Purchase costs of air conditioning plant in a type room €/m2 (price level of
1991-1992). Prices include the installation costs of the device, design costs excluded.
1
2
3
4
5
450
200
X
X
X
X
X
X
450-570
350-480
X
X
3K1/3S1/
NO CHEMICAL
FILTERING
450
200
X
X
X
X
X
X
370
280
X
X
3K2/3S1/
3C1
450
200
X
X
X
X
X
X
380-570
300-480
300-570
250-530
3K2/3S1/
NO CHEMICAL
FILTERING
450
200
X
X
X
X
X
X
300-370
220-280
220-280
170-230
3K3-4/3S1
/3C1
450
200
X
X
X
X
X
X
380-500
300-480
300-570
250-530
3K3-4/3S1
/NO CHEMICAL
FILTERING
450
200
X
X
X
X
430
220
300-370
220-280
220-280
170-230
3K5/3S1/
NO CHEMICAL
FILTERING
450
200
X
X
X
X
230
120
300-370
220-280
220-280
170-230
3K5/3S2/
NO CHEMICAL
FILTERING
450
200
X
X
100
50
230
120
220-300
130-220
800-220
80-170
3K5/NO
FILTERING
450
200
X
X
100
50
170
100
220
130
150
100
3K6/NO
FILTERING
450
200
X
20
80
30
150
80
220
130
150
100
150%EXTRA
COOLING COST
450
200
X
X
100
-
-
130
100
130
100
REQUIREMENTS
OF THE ROOM
3K1/3S1/3C1
HEAT
LOAD
W/m2
X=required conditions are not reached with the system
52
3.2 Selection of equipment
3.2.1 Introduction
EMC-compatibility:
The European EMC-directive gives requirements for equipment in industrial
environments. The EMC-directive allows determination of the permitted disturbance
radiation of electrical equipment to its environment, and disturbances along a flex.
Standard EN 50081-1 gives general disturbance emissions experienced in light industry.
Higher disturbance emissions are permitted in heavy industry according to standard EN
50081-2.
It always possible that old equipment can achieve the essential requirements of the EMCdirective, covered in the above standards. This is the case with equipment having tyristor
control or similar, which cause disturbances that is not allowed in the standard, unless
these disturbances have been covered in the design and documentation.
Equipment has to tolerate disturbances according to standard EN 50082-2 or EN 50082-1
depending on the place of use.
3.2.2 Selection of chemical filter.
3.2.2.1 Basic data for filter selection.
The following covers the basic data required in the selection of a chemical filter. The
customer should use this as the requirements and guarantee values in tendering. In
addition to the basic data, the names of filter manufacturers should be given.
The minimum following basic data should be provided:
• The filtered air flow [m3.s-1]
• The lifetime target of the filter medium [a]
• The average concentration of the filtered gases in the air [ppb]
• The maximum concentration of the filtered gases in design [ppm]
• The concentration of gases [ppb] after the filtering or the required filtering
efficiency
The lifetime of filter medium is normally assumed to be at least one year. Often the
average concentrations of filtered gases are not based on measuring information and have
to be estimated. The actual replacement intervals can be considerably different from the
target. The filter life for circulated air may be less than its estimated life due to pollution
leakage in to the filtered space and/or ductwork.
The capacity of a chemical filter has to be designed with the given maximum
concentration. The concentrations of filtered gases may not exceed the planned values
when the concentrations upstream the filter is below the maximum. Due to process
disturbances the maximum concentrations can be high. The efficiency of the outdoor
53
filter has to be over 99% of the maximum critical gas concentration. In filtering circulated
air the collection efficiency is not normally a critical factor.
3.2.2.2 Design of a chemical filter.
The time for air to pass through the filter varies usually between 0,5-2,0 seconds
depending on the outdoor air purity, selected lifetime of the filter and filter type. A delay
under 0,5 seconds should not be allowed for filtering outdoor air Usually the delay in
circulated air filters is about 0,1-0,2 seconds.
The air velocity through the filter medium is designed to be less than 0,5 m.s-1.
Increasing the velocity decreases the filtering efficiency and increases the pressure loss in
the filter. The pressure loss of a chemical filter varies between 250-2500 Pa depending on
the filter type and airflow; this has to be considered in the fan selection. Pressure loss
does not usually change during use, as is the case with particle filters.
The filter frame and body have to be leak tight and by-pass leakages should not exceed
1% of the nominal airflow in the outdoor air filters. Attention should be paid to corrosion
problems of the material. Acid-proof material is normally used in the casing of the
outdoor air filters.
When the filter is selected, its space requirement and pressure loss should be designing
other parts of the system. The space required for filter changing must be considered.
3.2.2.3 Guarantee values.
At present no guarantee values are normally given for chemical filters. If guarantee
values are given, there are difficulties in measuring them The wearing out of chemical
filters is usually controlled by sending filter samples to the laboratory of the filter
supplier, who analyses the samples and determines the time frequency at which the filter
has to be changed. Different methods are given in 2.1.2.1. For chemical filters the
defined guarantee values obtained for laboratory and field teats should be given
The lifetime of a filter cannot be guaranteed or defined with accuracy. But the filter
supplier should provide an estimation of the filter lifetime when the system is
constructed.
There are two methods of filter testing:
-Testing the filter under laboratory-controlled conditions before accepting the filter for
use and before the supplier accepts it. An example of laboratory test is reported in
(Enbom 1994)
Testing the guarantee values in the field, with a possible follow-up of the decrease of
filter capacity. A problem is that there is not a suitable practical multi gas instrument on
the markets to measure the small concentrations required.
54
The gas concentration after the filter, and the filter capacity to bind contaminants can be
used as a guarantee value for a chemical filter. If the customer is unable to measure the
gas concentrations, the method that is based on the corrosion of a copper-strip can be
used as a guarantee.
Figure 3.2.1 shows the documentation to define the design basis of a chemical filter, and
figure 3.2.2 gives the guarantee values. The average outdoor air values used in the
example are from pulp and paper industry plants in the referred research projects.
55
EXAMPLE
BASIC VALUES FOR DIMENSIONING
TARGET LIFETIME OF MEDIA
YEARS
MAKE-UP AIR FILTER
AVERAGE (ANNUAL) GAS CONCENTRATIONS IN MILL AREA
GAS
CONCENTRATION
3
µm/m
ppb
LITERATURE
REFERENCE
NRP, E-G, T&T
b) Sulphur di(tri)oxide
SO2,3
10-20
c) Hydrogen sulphide
H 2S
10-200
d) Chlorine
e) Hydrochloric acid
f) Hydrogen fluoride
g) Ammonia
Cl2
ClHF
NH3,NH4+
10
h) Ozone
i) Nitrogen oxides
TRS ( incl. H2S)
O3
NOX
40
20
30
1
10-20
80
40
NRP, E-G
NRP
TO BE TAKEN INTO ACCOUNT BY THE SEE
APPLICABLE ONLY IN SOME BRANCHES
NRP
HAPRO
NRP, T&T
Other gases in the factory area.
CIRCULAR AIR FILTER
AVERAGE (ANNUAL) GAS CONCENTRATIONS IN CIRCULATING AIR
GAS
CONCENTRATION
3
µm/m
ppb
b) Sulphur di(tri)oxide
SO2,3
c) Hydrogen sulphide
H 2S
14
20
d) Chlorine
e) Hydrochloric acid
f) Hydrogen fluoride
g) Ammonia
Cl2
ClHF
NH3,NH4+
80
200
2
20-40
h) Ozone
i) Nitrogen oxides
O3
NOX
80
40
74
200
160
80
LITERATURE
REFERENCE
NRP, E-G, T&T
NRP, E-G
E-G, NRP: 20-30 µg/m3 ?
TO BE TAKEN INTO ACCOUNT BY THE SEE
APPLICABLE ONLY IN SOME BRANCHES
NRP
HAPRO
NRP, T&T
SPECIFICATION OF THE FILTER
FOLLOWING TECHNICAL FIGURES SHALL BE GIVEN OF THE OFFERED FILTER
- Filter media
- Delay in filter media
1. step
2. step
3. step
4. step
Seconds
- If delay/step is not a constant, shall delays of different steps also be given.
- Method to control workability of the filter media and the amount of unused media (%).
Figure 3.2.1. The basic design data and dimensioning of chemical filters
56
GUARANTEE VALUES OF THE FILTER
The concentration of the chemical gases after the chemical filter shall remain in every situation
below the limit values stated here, when the incoming concentration is same or lower than
maximum concentration. Concentrations after filter shall be fulfilled for each of defined gases alone
and together with other gases.
MAKE-UP AIR FILTER
GAS
MAX. CONCENTR.
ppb
µg/m3
CONCENTRATION
AFTER FILTER
ppb
µg/m3
REMARK
b) Sulphur di(tri)oxide
SO2,3
1000
2700
37
c) Hydrogen sulphide
H2S
1000
1500
7,1
10
d) Chlorine
e) Hydrochloric acid
f) Hydrogen fluoride
g) Ammonia
Cl2
ClHF
NH3, NH4+
1000
3000
3
100
100
3
300
Do electrical equipment supplier guarantee
300
34
66
3,6
420
h) Ozone
O3
150
50
100
Demand 3C3.
i) Nitrogen oxides
NOX
150
52
100
Medias normally used don't filter NOX.
420
100
operation. ISA GX: 10 ppb.
Usually it is not noticed.
Analogues guarantee values, when tested with indirect method are following:
Thickness of a corrosion film on a copper strip;
- Before filter
- After filter
10000
300
A
A
or less
or less
CIRCULATION AIR FILTER
GAS
MAX. CONCENTR.
b) Sulphur di(tri)oxide
SO2,3
c) Hydrogen sulphide
H2S
d) Chlorine
e) Hydrochloric acid
f) Hydrogen fluoride
g) Ammonia
Cl2
ClHF
NH3, NH4+
h) Ozone
O3
i) Nitrogen oxides
NOX
ppb
µg/m3
CONCENTRATION
AFTER FILTER
ppb
µg/m3
REMARK
74
200
19
14,2
20
3,5
50
5
68
200
3
420
300
17
33
1,6
210
50
50
1,5
150
150
50
100
Demand 3C3.
150
52
100
Medias normally used don't filter NOX.
Analogues guarantee values, when tested with indirect method are following:
Thickness of a corrosion film on a copper strip;
- Before filter
- After filter
2000
300
A
A
or less
or less
METHODS TO CONTROL FULFILLMENT OF TARGET VALUES
Shall be controlled by measurements. There are two methods possible:
- DIRECT METHOD
- Using gas-analyzer
- INDIRECT METHOD
- Corrosion coupon test
- Gas concentrations before filter can be found out with gas-analyzer also in this case.
REFERENCES
NRP
E-G
HAPRO
T&T
Nordic Research Project: Corrosion of electronics.
Enso-Gutzeit Ltd. measurements.
Finnish Environmental Ministry, Acidification in Finland, Final-raport (in Finnish).
Tekniikka & Talous-magazine,
Figure 3.2.2. Guaranteed values of chemical filters
57
3.2.3 Selection of mechanical filter
The recommendation for filtering classes used to provide the required conditions in an
electrical equipment room is given in table 3.2.1.
Table 3.2.1. Recommendation for the filtering classes used in electrical equipment
rooms. Filter classes according to EN 779:
CONDITION CLASS
FILTERING CLASS
3S1
F 7(F 8)
3S2
G 3(G 4)
3S3
-*
*Near an emission source G3 is recommended.
A filter for circulated air should be at least to class F6.
Upstream of a chemical filter it is recommended that a F7 (or F8) filter is installed, as
small particles in the air reduce the capacity of a chemical filter. Downstream of a
chemical filter another mechanical filter should be installed, with a similar capacity, to
filter any dust leaving the chemical filter.
Special attention has to be paid to the filter air tightness and its frames, to avoid dust
penetration into the supply air. The allowed by-pass leakage depends on the filtering class
according to table 3.2.2.
Table 3.2.2. The permitted by-pass leakage of a particle filter in different filtering classes
(EN 1886:1998).
G 1-4
F5
F6
F7
F8
F9
6%
6%
4%
2%
1%
0,5%
3.2.4 Cooling.
3.2.4.1 Selection of cooling medium.
There are three reasons why water should be used in the first place as a cooling medium:
1) ENVIRONMENTAL ISSUES: The amount of refrigerants used should be
minimized for environmental reasons. Cooling water can be produced from a
centralised plant with a water chiller, and in some cases without the use of
refrigerants.
2) CONTROLLING THE COOLING: The step less control approach is simple
similar to a water radiator. When cooling media is used a continuous control,
leads to more difficult solutions and periodic control causes changes in the
conditions.
58
3) FREE COOLING: With the free cooling water, outdoor air is readily cooled
during the winter.
Refrigerant systems have to be used when cooling equipment is placed in electrical
equipment rooms, as water may presents electrical problems in the case of leakage.
Cooling a single space with a compressor set is usually more economical, if cold water is
not available.
3.2.4.2 Control of a cooling coil.
OUTDOOR APPLIANCE: The purpose of a cooling coil in an outdoor appliance is to
cool the supply air and to remove outdoor air moisture. The control of a cooling coil can
be achieved in two ways: Keeping either the dew point or the temperature of the intake
air constant. In a supply air unit, the cooling coil is placed before the fan and the chemical
filter. Placing the coil directly after the chemical filter makes coil control more difficult.
Also the temperature measuring of the supply air should be carried out before the
chemical filter, since the filter causes delay, influencing the control In addition the
temperature varies after the filter.
Dew point method: Supply air is cooled in the coil to the desired dew point temperature
(for example +8°C). The cooling coil sensor is located directly after the cooling coil. A
separate reheat coil controls the air supply temperature, its sensor is positioned after the
fan and before the chemical filter. The air supply temperature is kept constant 16°C. The
principle of this control method is shown in figure 3.2.3.
Figure 3.2.3. Dew point control method
Inlet air temperature method: The inlet air is kept at a constant temperature of 16 ºC,
during the winter by heating, and cooling the outdoor air in the summer. To avoid
concurrent heating and cooling with the associated energy loss, the heating is isolated
when the outdoor air temperature is 14°C. The cooling coil keeps the supply air
temperature constant, say at 16 ºC. The sensor is placed after the fan and before the
chemical filter. In the design of the cooling coil it is essential to consider the fan gains
For example if a 2 ºC gain takes place in the fan, the leaving design temperature for the
coil must be 14°C for a discharge temperature into the room of 16°C. As the relative
59
humidity of the supply air may be high, it has to be ensured that the supply air mixes
effectively with the room air; otherwise unsatisfactory moisture levels may enter the
electrical equipment.
The dew point method is more expensive and consumes more energy than the constant
inlet air temperature method. The last-method is unable to keep the humidity of the inlet
air constant and cannot be maintained as low as with the dew point method.
Figure 3.2.4. Control of intake air temperature
CIRCULATED AIR COOLING: The aim is to remove the heat generated by equipment.
The room temperature exhaust air is kept at its set point by controlling the supply air
temperature (see figure 3.2.5). In addition there is a minimum value for the supply air. A
continuous control method is essential as periodic control causes undesired temperature
variations in the room. If periodic control for is used, care must be taken that the capacity
step is small enough, as the temperature has a requirement for the rate of change and has
to be met. Problems are given in detail in clause 3.3.2.
Figure 3.2.5. Constant room/exhaust air temperature control method.
60
The air is dried in the supply air unit where condensation will not occur or the circulated
air coils during normal conditions of use. However, the cooling coils should be equipped
with drip pans with adequate drain lines and drop separators if necessary.
The controlling detector is located in the exhaust air duct, or if no ductwork exists for
circulated air, or when it is follow up the conditions in the room (for example work
places). The detectors in the room must be placed according to the instructions given in
2.4.1.2, and ensure that the average room conditions are met.
3.2.5 Selection of other equipment.
When equipment is selected, attention should be paid to the ductwork and equipment
tightness. The system must meet the tightness class B of prEN 1507. The ductwork
should meet class C, and the air-handling units class B (in low-pressured and small
systems ductwork they may meet class B and the units class A). The reason for this is,
that leakages increase the handling costs of the air, cooling costs and the depletion of the
chemical filtering medium. They also make air control more difficult, and depending on
pressure ratios may allow contaminants to enter the room.
Fire dampers should be as tight fitting as possible, and be of good quality to ensure they
operate in fire conditions It is wise to consider connecting fire dampers with the
automation system allowing the a damper to be tested automatically at set intervals.
The hygiene aspects of humidifiers must be considered, according to EN 13053, to reduce
the possibility of growth of microorganisms. It is recommended that steam humidifiers be
used. A humidifier requires to be fitted with a drop separator to ensure droplets do not
come into contact with electrical equipment.
In the selection and placing of the control device the special requirements placed by the
environment have to be taken into account (the environment tolerance of the equipment).
Cooling and heating coils and heat recovery units are heat exchangers. When these are
selected, the normal requirements (tightness, materials, de-icing, control, removing
condensate etc.) have to be considered.
Electrical equipment rooms are provided with electrical radiators to ensure they are
warmed up during down time. As a set point, the radiator thermostat is +15°C to control
concurrent heating and cooling.
Installing sewers and water pipes that pass through electrical equipment rooms should be
avoided. If this is not possible the pipes have to have a waterproof cover. The walls floors
and ceilings where these pipes pass through have to be carefully sealed
It is recommended that electrical equipment rooms be provided with a central vacuum
cleaning system, or provided with a vacuum cleaner with high-quality filters. The use of
61
an ordinary vacuum cleaner increases the particle concentration in the space being
cleaned
3.2.6 Selection of materials.
While selecting materials, attention has to be paid that on the dirty side the corrosion
conditions on some fields of industry (pulp & paper, chemical, petrochemical industry)
may present many problems. Issues to consider are: -acid-proof or aluminium outdoor
grilles, acid-proof or stainless steel for the first part of the ductwork, Al-HSt-structure for
the gate valves and stainless steel for the coils.
3.3 Implementation design
3.3.1 Location of ventilation equipment
3.3.1.1 Air conditioning units
The air conditioning units serving electrical equipment rooms will be positioned in a
separate space close to the room for maintenance reasons. This will minimise the
unnecessary occupancy in the electrical room for maintenance. If the air conditioning
equipment is located inside the electrical equipment room, the equipment must be
provided with safe access for the maintenance personnel. It must be ensured that
maintenance will not cause damage to the electrical equipment. Special attention has to
be paid to removing the condensate from the coils from the room.
If the air of the room is filtered chemically, the filter has to be positioned with the
following issues in mind
1. The chemical filter mounted upstream the fan: The intake air of the ventilation
equipment plant room should be chemically filtered, to reduce the risk the fan
inducing dirty air from the room in to the electrical equipment room.
2. Chemical filter downstream of the fan: A recommended position as all the air
entering the electrical equipment room will flow through the chemical filter.
The filter for circulated air is designed on the concentration level in the electrical
equipment room. Leakages from the ventilation plant room will reduce the filter
capacity considerably. The two solutions for this problem are:
• The supply air to the plant room is to be filtered
• Leakages will be considered in filter designing for the circulated air, which
increases the particulate contact time in the filter.
3. No chemical filter in the circulated air unit.
If the circulated air unit is in the ventilation equipment room a chemically filtered air
supply is required for the room, due to leakages (clause 1.)
62
If the cooling system is inside the electrical equipment room, and the chemical filter is
placed after the fan, the air in the ventilation plant room does require filtering
3.3.1.2 Outdoor air inlets
Air inlets should be located so that the entering outside air is as clean as possible and for
summer operation as cool as possible.
An air inlet should not be located close to process emissions. The introduction of
moisture through air inlets should be eliminated
In some branches of industry, e.g. pulp & paper, the humidity in the factory environment
is high resulting in condensation problems on air inlets, these will freeze in the winter.
Defrosting coils are required in this instance for deicing.
3.3.1.3 Ductwork
The supply air ductwork to electrical equipment rooms must be as short as possible. Care
being taken so that the ductwork does not pass through dirty process spaces.
When the ductwork is manufactured consideration must be made that the electrical
equipment room will form its own fire compartment. Insulation, fire dampers etc. should
be cleared in advance with regards to suitability with the local fire authorities and
insurers.
3.3.2 Control and monitoring.
3.3.2.1 Introduction.
This clause deals with control at a basic level, so that the design room conditions are
maintained. The principles of different air conditioning systems are given in clause 3.1.1.
The control of each method covered in clause 3.2.4.
At the commencement of a project it is essential to determine if the air conditioning is
controlled locally, or if the control is connected with the factory automation system, or
with a separate building automation system. Alarms warning of plant malfunction should
be connected to areas of regular occupancy.
3.3.2.2 Control
Control of temperature and relative humidity are important factors in electrical equipment
rooms. Humidity control is based on the requirement that the maximum relative humidity
is a fixed point If the room humidity constantly adjusted (class 3K1), it will be controlled
by the measurement of room or exhaust air. The maximum humidity of the intake air
must be limited.
63
The requirements for thermal conditions and control are given in clause 2.5. The room
temperature is maintained within the required range and rate of change by the controls.
The temperature control should be continuous as periodic control causes adverse
temperature variations.
When periodic control is used, the design should ensure that the cooling capacity is
divided to several capacity steps to achieve the rate of change requirements. The size of
the capacity steps can be evaluated during the designing process with the help of a twotime constants model.
Example:
A space has a volume of 1000m3 with a temperature change of 2,5°C in five minutes
(average 0,5°C/min). This change is caused by a power input of 18 kW (90 W.m-2)
If the total cooling capacity is 400 W.m-2 the cooling should be divided into steps of 20%
(400/90).
In clause 2.5.1.2 it is shown in which cases the room design conditions have to be
maintained. The method of air distribution selected will have a considerable influence on
the actual conditions.
The following deals with the methods of temperature control of the air conditioning with
different system.
NATURAL VENTILATION:
Gravity ventilation is designed with a temperature difference of 15°C. It will be
appreciated that this system provides no direct control of the cooling. If necessary, a
separate heating system can be used to ensure that the temperature is maintained above
the lower limit in the winter.
FORCED EXTRACT VENTILATION:
The space temperature is kept at the set point by starting and stopping the fan (On-Off
control). Control for example is achieved in the following manner (3K5): A thermostat
starts the fan when the room temperature reaches 35°C and stops the fan when it reaches
30°C. In the winter the requirements of warming the air in the classes 3K3-5 must be
considered
OVER PRESSURE VENTILATION:
The supply air unit works continuously keeping the room at a positive pressure to the
surroundings the room temperature is maintained at the set point (for example 20°C), by
adjusting the supply air temperature. Supply air can be warmed either by a heating coil or
with re circulated air. The room temperature may increase above the set point in the
summer depending on the room heat loads
Air conditioning is more effective with a summertime fan, if there is no need for
chemical filtering. This fan will start when the temperature of the room rises to the upper
64
set point (e.g. 30°C) and stops when the temperature drops below the lower set point
(e.g.25 °C).
COOLING WITH CIRCULATED AIR:
The supply air unit operates continuously ensuring over pressurisation of the room. The
temperature and humidity of the supply air is kept constant.
The exhaust air or room temperature is maintained at the set point by controlling the
cooling of the circulated air. The temperature and humidity of the intake air is maintained
at a maximum and minimum value. If periodic control is used the next capacity step will
depend on if the temperature rises or falls above the upper and lower set points.
SEPARATE COOLING PLACED IN THE ROOM:
The control is achieved in the same manner as in the circulated air-cooling.
3.3.2.3 Monitoring.
The alarms fitted to air conditioning equipment are divided into different categories on
the grounds of importance.
Urgent alarms are those that immediately influence the working capacity and require
service persons' immediate attention. Urgent alarms should always be directed to the
manned control room. These alarms are:
•
•
•
•
•
Increase of room/exhaust air temperature to a limit that results in an alarm
sounding.
If a fan or duct air flow stops.
If the temperature of the intake air falls below the permitted minimum.
Failure of thermostat resulting in the freezing of a heating coil.
(If the air humidity exceeds the control range).
Less urgent alarms are e.g.:
• Pressure difference alarms on mechanical filters
Issues that have to be monitored regularly:
• When chemical filters wear out
• Maintaining the room over pressure
In the use and service plan, the frequency of regular servicing and checks belonging to
normal maintenance of the equipment should be listed.
The aim is to ensure the reliability of use and should be directed to eliminating plant
failure the most important components are fans and cooling equipment.
Controlling detectors should not be placed after a chemical filter.
65
4 COMMISSIONING
4.1 The construction schedule
In figure 4.1.1 a construction schedule for an electrical equipment room is shown which indicates the dependences between different
measures. If an old electrical equipment room is to be renovated, the schedule will be different and will depend on the quality and
extent of the work.
Figure 4.1.1 Construction Schedule for an Electrical Equipment Room
DESIGN
CONSTRUCTION
GUARANTEE PERIOD
OPERATION TIME
ACCEPTANCE OF SYSTEM & EQUIPMENT SELECTION
CONSTRUCTION OF THE ELECTRICAL EQUIPMENT ROOM
SEALING AND SURFACE FINISHING OF THE CONSTRUCTION
HVAC & ELECTRICITY INSTALLATIONS
SEALING OF THE HVAC-PENETRATIONS
PERFORMANCE TESTS FOR MAKE-UP AIR UNIT
ADJUSTMENT OF THE CONTROL SYSTEM FOR MAKE-UP AIR UNIT
OPERATION TESTS FOR THE MAKE-UP AIR UNIT
OVERPRESSURIZING OF THE EL. ROOM
>
INSTALLATION OF ELECTRICAL EQUIPMENT
SEALING OF CABLE PENETRATIONS
PERFORMANCE TESTS FOR AIR CONDITIONING SYSTEM
ADJUSTMENT OF THE CONTROL SYSTEM OF AIR CONDITIONING
OPERATION TESTS AND CHECKINGS FOR AIR CONDITIONING SYSTEM
CHECKING OF THE ROOM TIGHTNESS AND MAKE-UP AIR FLOW
RECEPTION OF HVAC & AC SYSTEM
ADDITIONAL SEALING, IF NEEDED
CHECKING THE ROOM TIGHTNESS AGAIN, IF NECESSARY
INTRODUCTION OF THE ELECTRICAL EQUIPMENT
CHECKINGS OF THE HVAC-CONTROL SYSTEM DURING OPERATION
- FOLLOW-UP OF TEMPERATURE CONDITIONS (SUMMER/WINTER)
CHECKINGS OF CONTAMINANT CONCENTRATIONS OF THE EL. ROOM
CHECKING THE ROOM TIGHTNESS
GUARANTEE CHECKINGS
REGULAR MAINTENANCE AND CHECKINGS
- CHECKING OF THE CONTAMINANT CONTROL
- OVERPRESSURE OF THE ROOM
- TEMPERATURE CONDITIONS
- CONDITION OF THE HVAC-EQUIPMENT
66
4.2 Checks
For the acceptance of the electrical equipment room air conditioning, a group of checks
over and above those normally carried out on an ordinary HVAC-project are necessary.
The following are recommended extra checks during different stages in the project:
Structural, device and installation checks:
• Tightness test for the air conditioning units (in the factory)
• By-pass leakage of the filter package (a factory-made package)
• Filling of the chemical filter.
• Air Tightness test of the ductwork.
• Guarantee values of the chemical filter medium (tests in advance?)
Performance tests:
• Timing the test of over pressure equipment.
Test run:
• Test run for the whole air conditioning system.
• Measuring the over pressure in the electrical equipment room during the test run.
• Comprehensive check measurements of the air and water flow rates.
Guarantee period:
• Operating the air conditioning control during different situations in the summer
and winter (Thermal conditions/ balanced operation of equipment).
• The contaminant concentration of the room; at the start and end of the guarantee
period.
• Operating of the chemical filtering, if necessary.
• Checking the over pressure in the end of the guarantee period.
Operation:
• Thermal conditions.
• The contaminant concentration in the room.
• Operating of the chemical filtering, if necessary.
• The over pressure measurement in the room.
4.3 Spare parts
To secure reliability of use, spare parts must be stored for the most important
components. They should be purchased at the same time as the main equipment. To
minimize the amount of spare parts and for reliability in use, spare parts should be
evaluated as soon as possible in the project. The best results for the whole factory will be
achieved if the reliability of use and spare parts planning are part of the main design
67
4.4 Documentation
During different stages of design, the basic data and the system solutions with their
reasons should be well documented, and all participants in the project should be informed
consider the documentation examples in figures 4.1.2-4.1.4.
Changes made during the construction, in connection with the acceptance tests and during
the guarantee period should be updated in the design and maintenance documents.
Updated documentation is an essential part of plant reliability.
68
Figure 4.1.2 Check List for the Project (Ventilation of Electrical Equipment Rooms)
PHASE/TASK
REPORT
REFERENCE
SCHEDULE
2.1
EGO XXX
13.11.1993
1.2, 1.1
3.1.2
EXPLANATIONS:
REPORT: Refers to applicable clause in text
REFERENCE: E.g. Standard or guideline that is to be followed in task
PROGRAM PHASE (Preliminary plan)
GIVEN DATA
- Location of building
- Outdoor air dimensioning criteria (preliminary)
- Summer/Winter
- Dimensioning criteria for electrical equipment's
- Level of reliability (generally)
SYSTEMS, ALTERNATIVE SYSTEMS
- Going through all solutions
3.1.1
Fig 4.1.3
- Factory level
- Cooling solutions water/refrigerant/?
- Production of cooling water centralized/dissipated
- Connections of HVAC-systems to other networks
- Premise level (types)
- Cooling water/refrigerant/?
- Need of chemical filtration
- Air conditioning system options
- Equipment loads in different types of premises
PLACEMENT OF HVAC SYSTEMS AND REQUIRED SPACE (prelim.)
- Placement
- Required space
READY
#######
APPR.
e-b/nnn
APPENDIX
CL.NO 11972-001
3.2.4.1
3.2.4.2
3.2.4.2
2.1.2.1
3.1.1
2.5.2
2.3.1
69
Figure 4.1.2 Check List for the Project (Ventilation of Electrical Equipment Rooms)
PHASE/TASK
REPORT
REFERENCE
SCHEDULE
READY
APPR.
APPENDIX
DESIGN PHASE 1 (scetch plan)
GIVEN DATA
- Documentation and approval
- Outdoor-air conditions for dimensioning
- Conditions of surrounding premises
- Structures
- Dimensioning conditions of single premises
- Loads of premises (preliminary)
- If loads for premises will be approximated in the first phase
of scetch, then it has to be reserved enough time in last phase
that plans can be updated to the real level of loads.
- Requirement for reliability, premise by premise
SELECTION OF SYSTEM (FACTORY/PREMISES)
- Documentation and approval
- Selection criteria
PREDESIGN PLAN (based on the selected system)
- System schemes and equipment lists
- Selection of equipments, requirements for components
- Drawings
- Placement of HVAC-equipment in the building
- Duct routes and placement of main ducts
- Control and automation
- Air conditioning process
- Connection to the automation system
COMMENT OF OPERATIONAL AND MAINTENANCE PERSONNEL
70
Figure 4.1.2 Check List for the Project (Ventilation of Electrical Equipment Rooms)
PHASE/TASK
DESIGN PHASE 2 (Detailed design)
GIVEN DATA (in detail, look scetch plan)
- Evaluation, documentation and approval
- Electrical equipment supplier: Heat loads of single cabins
(air-flows), if not available on the scetch phase.
DESIGN
- Precision of dimensioning calculations and documentation (approval?)
- Precise placement of HVAC-systems in the building
- Connection of HVAC-equipments to other systems
- Control and automation
- detailed
- Holes in structures
- Explanation (pictures of holes)
- Tightening
- Spare parts/Reliability
REPORT
REFERENCE
SCHEDULE
READY
APPR.
APPENDIX
2.1
2.5.2
3.3.1
3.3.2
2.3.2
3.1.2
COMMENTS of OPERATIONAL AND MAINTENANCE PERSONNEL
71
Figure 4.1.2 Check List for the Project (Ventilation of Electrical Equipment Rooms)
PHASE/TASK
REPORT
TASKS DURING CONSTRUCTION PHASE
ADDITIONAL AND MODIFICATION TASKS
- Design
- Same principles and procedures as during design phase
is followed
4.1
REFERENCE
SCHEDULE
READY
APPR.
APPENDIX
SUPERVISION
- Supervisors tasks
- Agreement of supervision
CHECKINGS
- Construction, equipment and installation checks
- Performance tests
- Functional tests
- Check measurement
- ACCEPTANCE TESTS
4.2
POSTACCEPTANCE TESTS
4.2
AS BUILT DRAWINGS
- Documentation if changes made during construction
- Documentation of accomplished system
4.4
MAINTENANCE
- Operation and maintenance plan
- Training of operation and maintenance personnel
- Spare part plan
4.4
72
Figure 4.1.2 Check List for the Project (Ventilation of Electrical Equipment Rooms)
PHASE/TASK
REPORT
INTRODUCTION (Guarantee period)
MAINTENANCE
- Obtaining of spare parts (if not included in the initial delivery)
4.4
CHECKINGS DURING GUARANTEE PERIOD
4.2
REFERENCE
SCHEDULE
READY
APPR.
APPENDIX
GUARANTEE TESTS
POSTACCEPTANCE TESTS
DOCUMENT UPDATE
- Documentation of changes made during guarantee period
OPERATION
CHECKINGS
- According to operation and maintenance plan
4.2
MAINTENANCE
- According to operation and maintenance plan
MODIFICATIONS AND EXTENSIONS
- Documentation of changes
73
Figure 4.1.3. System selection, example
SYSTEM SELECTION
ROOMTYPE
ELECTRICAL ROOM
CONDITION CLASS:
3K3/3Z2/3Z4/EB1/3C1/3S1
(EN 60721-3-3)
ALTERNATIVE AIR CONDITIONING SYSTEMS
1.
2.
3.
OVER-PRESSURE VENTILATION
COOLING WITH CIRCULATED AIR
SEPARATE COOLING PLACED TO THE ROOM
PROPERTIES OF ALTERNATIVE AIR CONDITIONING SYSTEMS
(Clause 3.1.1)
ENCLOSURES:
1-3
SELECTED SYSTEMS
2. COOLING WITH CIRCULATED AIR
GROUNDS FOR SELECTION
1. Centralized cold supply and cold water pipeline
in the building.
2. It is prohibited to bring waterpipes into el. room.
3. The temperature conditions can be hold uniform,
which improve the reliability of operation.
3. SEPARATE COOLING PLACED TO
THE ROOM
1. Cheaper solution to single rooms far away of the
main building, where extending of the cold air
pipeline is to expensive.
2. The ventilation equipment room size can be
minimized in a separate building.
REJECTED SYSTEMS
1. OVER-PRESSURE VENTILATION
REASON FOR REJECTION
1. System is not suitable for rooms that have heavy
heatloads and need for chemical filtering.
74
Figure 4.1.4 Table of Start Values for Design, Example
ELECTRICAL EQUIPMENT ROOMS; START VALUES AND DESIGN CRITERIA FOR VENTILATION DESIGN
SUBJECT: Pulp & Paper Mill, Moodyriver, Woodland
PROGRAM PHASE
PRE DESIGN PHASE
DESIGN PHASE
OUTDOOR AIR
- Temperature winter/summer
- Air Humidity summer/winter
- Corrosive gases*
DESIGN CRITERIA
1. ELECTRICAL ROOMS
- Condition classification
- Dimensioning temperature**
- Relative Humidity**
- Heat loads from el. equipment
- Reliability demand
2. AUTOMATION ROOMS
- Condition classification
- Dimensioning temperature**
- Relative Humidity**
- Heat loads from el. equipment
- Reliability demand
3. CONTROL ROOMS
- Condition classification
- Dimensioning temperature**
- Relative Humidity**
- Heat loads from el. equipment
- Reliability demand
30°C/-15°C***
15g/kg / 1,5g/kg
Filtering needed
32°C/-10°C****
17g/kg / 1g/kg
Filter for circulation system
only in boiler house
REMARKS
No changes
Table 1.1.1, Class B
300 W/m
2
Max 25°C****
Max 50%****
Loads in different rooms,
see Appendix N
Appendix N, Rev. B****
150 %
Table 1.1.1, Class A
250 W/m
2
Max 25°C****
Max 50%****
Loads in different rooms,
see Appendix N
Appendix N, Rev. B****
200 %
Table 1.1.1, Class A
150 W/m
2
Workers; see Table 2.4.12
Max 28°C****
Loads in different rooms,
see Appendix N
Appendix N, Rev. B****
100 %
* Dimensioning of gas filter, see separate Appendix.
** Shall be announced only if is wanted more strict conditions than is stated for condition class.
*** Source: Ashrae-weather data (HVAC-Designer).
**** Binding Criteria (by Client)
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APPENDIX 1 - BASIS FOR DESIGN FOR VENTILATION IN ELECTRICAL
EQUIPMENT ROOMS, CLIMATIC CONDITIONS
CLIMATOGRAMMES FOR CLASSES 3K1-3K4 (EN 60721-3-3)
GUIDE FOR THE READER
AREA 1:
Design conditions for ventilation. During normal operation of ventilation
system shall conditions stay inside the borders. Conditions shall be on an
average in the center of the area.
AREA 2:
Area, that is expanded from area 1 with dash line, classes 3K3 and 3K4.
Conditions may slide to this area during extremely heavy outdoor
conditions during summer, if the heat load of the room is under 100 W/wallm2.
AREA 3:
Border of the environment class of the electrical equipment. Conditions
shall not exceed the border in any conditions, when electrical equipment is
in operation, including the breakdown in ventilation equipment.
* Relative humidity and minimum temperature define together the allowed absolute
humidity
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APPENDIX 2 - THE MEASURING PRECONDITIONS OF GASES
Environmental measurements
• Instruments suitable for emission and environment measurements can be
purchased at reasonable prices. With most gases an accuracy of tenths of ppm can
be achieved. To obtain reliable results a long-term follow-up (6 months) is
necessary.
•
Measuring methods available:
1. Direct measurements.
• Gas analysers
2. Indirect measurement based on the aggressiveness of the contaminants in
the environment
• Copper-strips (ISA-S71.04-1985)
• Metal spirals (ISO 9223)
Electrical equipment rooms
The required concentrations are very low, and acceptable measurements can be only be
determined with accurate instruments. With the indirect measurement the aggressive
nature of contaminants in the air can be observed.
•
•
Measuring methods available:
1. Direct measurement.
• an expensive and unsuitable option for continuous follow-up.
2. Indirect measurement.
• Copper-strips, different options (30 days follow-up and analysis;
comparing with the reference-strips). With copper-strips the
seriousness of the corrosion can be determined however different
gas concentrations cannot be determined.
"Purafil"-instrument (on-line, Cu-Ag-corrosion measurement, temperature,
humidity and the rate of change; this can be connected with the building control
system. The price is in the 6.000 € or USD.range.
Efficiency measurements of the filter medium in a laboratory
• direct measurement, high quality instruments requirements for high-class results.
• a SO2-converter is required to measure hydrogen sulphide H2S.
• chlorine measurement by means of a sampling collector method.
• The filtering ability in a steady-state (storage capacity) is easily tested in a
laboratory.
Determining filter efficiency and the time when filter medium replacement is
necessary in the field
•
The following methods are in common use:
1. Taking a sample of the filter medium.
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2. A change in colour of indicator paper.
•
Other possible methods:
3. Concentration measurement from inside the filter medium.
4. The copper-strip in the duct after the filter
- filter medium is changed too late.
When acceptance tests are made, it is possible to measure the filtering capacity of the
gases with indicating instruments (a Research Institute services would be required), the
cost of this service is high, about 2.000 € or USD/room, gas. The test would have to be
repeated in order to obtain a meaningful answer.
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APPENDIX 3 - REFERENCES
Enbom, S., Hagström,K. and Railio, J., Laboratory tests of chemical filters. In: Anders
Jansson and Lars Olander (Eds): Proceedings of Ventilation 94, Vol.2, p. 441-446. Arbete och
Hälsa 1994:18, Part 2. Arbetsmiljöinstitutet, Sweden
Olander,L., Beräkningsamband för luft och luftföroreningar. En litteratursammanställning.
Arbetarskyddstyrelsen. Undersökningsrapport 1982:14, Sweden.
International standards
ISO 9223
Corrosion of metals and alloys -- Corrosivity of atmospheres – Classification
IEC 60721-2-8 Classification of environmental conditions - Part2: Environmental conditions
appearing in nature. Section 8: Fire exposure.
European standards
EN 779
Particulate air filters for general ventilation - requirements, testing, marking
EN 1886
Ventilation for buildings - Air handling units - mechanical performance
EN 13053
Ventilation for buildings - Air handling units - ratings and performance of units,
components and sections
EN 61000-6-1 Electromagnetic compatibility (EMC) - Part 6-1: Generic standards. Immunity
for residential, commercial and light-industrial environments
EN 61000-6-2 Electromagnetic compatibility (EMC) - Part 6-2: Generic standards. Immunity
for industrial environments
EN 61000-6-3 Electromagnetic compatibility (EMC) - Part 6-3: Generic standards. Emission
standard for residential, commercial and light-industrial environments
EN 61000-6-4 Electromagnetic compatibility (EMC) - Part 6-4: Generic standards. Emission
standard for industrial environments
EN 60068-1
Basic environmental testing procedures. Part 1: General and guidance
EN 60721-3-0 Classification of groups of environmental parameters and their severities.
Introduction
EN 60721-3-3 Classification of environmental conditions. Part 3: Classification of groups of
environmental parameters and their severities. Section 3: Stationary use at
weatherprotected locations
prEN 1507
Ventilation of buildings - Ductwork - Rectangular sheet metal air ducts,
requirements for testing strength and leakage
Other standards
ISA 571.04-85 Environmental conditions for process measurements and control systems:
Airborne contaminants.
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