Electric Power

Application
and
Installation
Guide

Ventilation

W H E R E

T H E

W O R L D

T U R N S

F O R

P O W E R

Table of Contents
Ventilation Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Ventilation Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Ventilation Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Ventilation Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Air Quantity Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Ventilating Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Fan Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Fan Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Fan Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Required Air Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Combustion Air Ducts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Crankcase Ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Heat Rejection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Engine Room Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Radiators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Moveable Louvers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Enclosures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Special Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

Ventilation

Ventilation Terms

Ventilation Purpose
Six to ten percent of fuel consumed by
an engine is lost as heat radiated to the
surrounding air. In addition, heat from
generator inefficiencies and exhaust piping
can easily equal engine radiated heat.
Any resulting elevated temperatures in
the engine room may adversely affect
maintenance personnel, switchgear, and
generator set performance.

Ventilation Flow
Ideally, clean, cool, dry air circulates around
switchgear, flows through the rear of the
generator, across the engine and discharges
through the radiator (see Figure 1). Cool air
should always be available for the engine
air cleaner.

Ventilation Air:
The flow of air required to carry away the
radiated heat of the engine(s) and other
engine room machinery.
Combustion Air:
The flow of air required to burn the fuel
in the engine.
Crankcase Fumes Disposal:
Elimination of oil laden combustion fumes
that collect in the engine crankcase (see
Crankcase Ventilation).
Radiator Cooling Air:
Air flow passing through the radiator
normally to cool the engine. Certain
installations utilize radiator cooling air flow
for ventilation purposes.

Ventilation Considerations
Routing
Comfortable air temperatures in the engine
room are impossible without proper routing
of the ventilation air.
Intake
louvers

Exhaust
fan

Figure 1. Ideal ventilation.

Locate room air intakes to provide maximum

cooling air to the generator set, yet avoid hot,
stagnant air in other areas. Multiple generator
sets necessitate additional openings and fans.

Fresh air should enter the engine room as

far from the sources of heat as practical and
as low as possible. Since heat causes air to rise,
it should be discharged from the highest
point in the engine room, preferably directly
over the engine. Avoid incoming ventilation
air ducts which blow cool air toward hot
engine components. This mixes the hottest
air in the engine room with incoming cool air,
raising the temperature of all the air in the
engine room, and leaves areas of the room
with no appreciable ventilation.

Units not using radiators require a forced air

draft. Openings for intake air should be low,
near the rear of the generator set. Outlets
should be positioned high on the opposite wall.
Another way of ventilating the engine room is
the use of air curtains, although this is not so
commonly utilized. The advantage of an air
curtain system is that the engine room is
exposed to lower air velocity than a system
with radiators.

Relative Efficiency Routing

The sketches below (see Figure 2) illustrate
the relative efficiency of various ventilation
routing. Frouting is a factor which relates
the relative efficiency of various ventilation
air routing.

across heat sources such as the engine,

exposed exhaust, generator, etc. (see Figure 3).

Example:
If the routing in Figure A (upper left) is used
as a base to which the others are compared:
1.4 times more air is required (duct
cross-sectional area and fan capacity) to
adequately ventilate the machinery space
illustrated in Figure B (upper right).
It takes twice as much air (duct crosssectional area and fan capacity) to
adequately ventilate the machinery space
illustrated in Figure C (lower left).
3.3 times more air is required (duct
cross-sectional area and fan capacity) to
adequately ventilate the machinery space
illustrated in Figure D (lower right).
Horizontal Air Flow
Cool, dry, clean air should enter the engine
room as close to the floor as possible using
fans/ducts. Allow this air to flow horizontally
across the engine room from the entry point

Figure 1.1

Figure 3. Horizontal air flow.

For best results, air should flow first

across the generator then to both sides
of the engine.
If engine mounted radiators are not used,
air discharge fans should be mounted or
ducted at the highest point directly over
the heat sources.
Inlet air must circulate between the engines
in a multiple engine installation.
Inlets located at the end of a room with
multiple engines will provide adequate
ventilation only to the engine nearest
the inlet.

Figure A (Superior)
Frouting = 1.0

Figure B (Better)
Frouting = 1.4

Figure C (Good)
Frouting = 2.0

Figure D (Poor)
Frouting = 3.33

Figure 2. Efficiency of various routings.

Providing horizontal air flow will dissipate

engine heat but a certain amount of heat will
still radiate and heat the engine room.
Air Curtains
Air curtains, totally enveloping the generator
set, provide ventilation without exposing
the equipment room to high air velocities
(see Figure 4). Radiated heat is removed with
approximately half the air flow of a horizontal
flow system.
It is important to stretch the air curtain inlet
the full length of generator set.

Because this system interferes with the

natural rising of hot air, ducting should be
used to prevent air from taking the shortest
path out of the engine room and bypassing
the engine.
Radiator Air
Installations utilizing local free standing or
engine-mounted radiators may provide
sufficient air flow for cooling. Total ventilation
air flow requirements must be compared to
radiator fan capabilities.
Intake and exhaust ventilators may have
movable or fixed louvers for weather protection.
If movable louvers are used, they should be
actuated by pneumatic, electric, or hydraulic
motors. Do not depend on air pressure
developed by the radiator fan to open the
vanes. In cold climates, movable louvers can
be arranged to provide circulation inside the
room until jacket water temperatures reach
88C (190F) (see Figure 6).

Figure 4. Air curtains.

Air curtains present ducting challenges when

local fan radiators are used.
Vertical Air Flow
The least desirable ventilation system
discharges outside air directly down on
the engines with inlet fans (see Figure 5).
Exhaust fans should be mounted in the
corners of the room.

Figure 6. Moveable louvers for recirculation.

Figure 5. Vertical air flow.

Once jacket water temperatures reach 88C

(190F), the radiator must be furnished with
sufficient cooling air. Use a number of small
ventilating fans rather than a single large unit.
Selective fan operation compensates for
varying ambient temperatures while
maintaining engine room temperatures.

Increase air flow 10 percent for every 763 m

(2500 ft) above sea level to maintain original
cooling capability. Final ventilation calculations
must use precise heat radiation of selected
engine, generator, and power output.
Engine Driven Fans
For most local radiator generator sets, a
blower fan (air discharges from engine through
radiator) is recommended. The blower fan
will move the incoming ventilation air from
the generator, past the engine block and
manifolds and use that air to cool the radiator.
If a suction fan is used, special considerations
must be considered to avoid recirculation of
the generator cooling air. It is also much more
efficient to use the engine driven blower fan
as a room evacuation device than to try to
force heated air from a room by pressurizing
the room with preheated air from the radiator.

Air Quantity Required

In general, changing the air in the engine
room every one or two minutes will be
adequate, if flow routing is proper.
Combustion air would be required solely for
burning the fuel in the combustion process.
Hence the total air intake into the engine room
would be the sum of both the combustion air
and the cooling air. The quantity of air required
for combustion is explained below.
Provisions should be made by the installer
to provide incoming ventilation air of
0.1 0.2 m3/min (4-8 cfm) per installed
horsepower. This does not include combustion
air for the engines.
Engine room exhaust ventilation air should be
110 to 120% of the incoming ventilation air.
The excess exhaust ventilation air accomplishes
two things:
It compensates for the thermal expansion
of incoming air.
It creates an in draft to confine heat and
odor to the engine room.

Operation in extreme cold weather may

require reduced ventilation air flow to avoid
uncomfortably cold working conditions in the
engine room. This is easily done by providing
ventilation fans with two speed motors (100%
and 50% or 67% speeds).

Ventilating Fans
In modern installations, natural draft ventilation
is too bulky for practical consideration.
Adequate quantities of fresh air are best
supplied by powered (fan-assisted) systems.

Fan Location
Fans are most effective when they withdraw
ventilation air from the engine room and
discharge the hot air to the atmosphere.

Fan Type
Ventilating air fans may be of the axial flow
type (propeller fans) or the centrifugal type
(squirrel cage blowers). When mounting
fans in ventilating air discharge ducts (most
effective location), the fan motors should be
outside the direct flow of hot ventilating air for
longest motor life. The design of centrifugal
fans (squirrel cage blowers) is ideal.

Fan Sizing
The name plate ratings of fans do not
necessarily reflect their as-installed conditions.
Just because a fans name plate says it will
move 1000 cfm of air does not mean it will
move 1000 cfm through an engine room
which has severely restricted inlet and/or
outlet openings. Fans are often rated under
conditions which do not reflect as-installed
flow restrictions. In general, the as-installed
conditions will be more severe than the fans
name plate rating conditions.

Combustion
Required Air Flow
Engine room ventilation can be estimated by
the following formula. assuming 38C (100F)
ambient air temperature:
H
+ engine combustion air
V = D 3 Cp 3 T
Where:

Air Cleaners
Engines must be protected from ingesting
foreign material. The engine-mounted air
filter elements must never be remotemounted, without factory approval.
If large amounts of sea spray, dust, or insects
are expected, external, remote-mounted,
precleaners may be installed at the inlet
to a duct system to extend the life of the
engine-mounted filter elements.

V = Ventilating Air (m3/min), (cfm)

H = Heat Radiation i.e. engine, generator,
aux (kW), (Btu/min)
D = Density of Air at 38C (100F)
(1.099 kg/m3), (0.071 lb/ft3)
Cp = Specific Heat of Air
(0.017 kW 2 min/kg 2 K), (0.24 Btu/F)
T = permissible temperature rise in engine
room (C), (K)
Note: If duct work is used to bring in air for
the engines combustion air, the last term in
the equation can be dropped.
Example:
A 3412 DITA genset has the following data:
Heat rejection: 659 kW (37 478 Btu/min)
Temperature rise: 11C (20F)
Solution:
The estimated engine room ventilation
required for this arrangement:
V=

659
= 3206.61 m3/min
1.099 2 0.017 2 11

V=

37478
= 109970.7 cfm
0.071 2 0.24 2 20

Combustion Air Ducts

Design combustion air ducts to have a
minimum flow restriction. Note that very
large amounts of air flow through the
combustion air ducts.

Location
The combustion air ducts should be located
close to the engine. Usually, flexible connections
are used to reduce noise from the ducting
system. In addition, all duct work must be
supported on the engine to avoid unnecessary
loading on the turbochargers.
Duct Restriction
Total duct air flow restriction, including air
cleaners, should not exceed 2.49 kPa (10 in.
H2O) measured while the engine is producing
full rated power. It is good design practice to
design combustion air ducts to give the lowest
practical restriction to air flow, since this will
result in longer times between filter element
service or replacement.
Air Velocity in Combustion Air Ducts
Combustion air duct velocity should not
exceed 610 m/min (2000 ft/min). Higher
velocities will cause unacceptable noise levels
and excessive flow restriction.
Water Traps
Traps should be included to eliminate any
rain or spray from the combustion air. Rain
and spray can cause very rapid plugging of
the paper air filter elements on some engines.
This will reduce the flow of air through the
engine, raising the exhaust temperature with
potentially damaging effects.

Crankcase Ventilation
Normal combustion pressures of an internal
combustion engine cause a certain amount of
blowby past the piston rings into the crankcase.
To prevent pressure buildup within the
crankcase, vent tubes are provided to allow the
gas to escape. Each engines fumes disposal
should have separate discharge pipes.

Crankcase fumes must not be discharged into

air ventilating ducts or exhaust pipes. They will
become coated with oil deposits. Crankcase
fumes must be either ingested by the engine
or piped out of the engine room.
The crankcase vent pipe may be directed into
the exhaust gas flow at the termination of the
exhaust pipe.
Preferably, the crankcase vent pipe will vent
directly to the atmosphere. The vent pipe
termination should be directed to prevent
rain/spray entering the engine.

Solution:
P = 975 ekW
Eff =

92%
= 0.92
100%

HRG 5 975 2

1
1
0.92

HRG = 84.78 kW
HRG 5 975 2

1
1 2 56.9
0.92

HRG = 4824 Btu/min

Design Considerations
Heat Rejection
Engine Radiant
The heat input into the engine is the sum
of the work output and the heat generated.
Besides the work output, heat is rejected
to the atmosphere, into the oil cooler,
aftercooler, through the exhaust stack and
also through the jacket water. Hence, while
designing the ventilation system in a room,
the engine generated heat should be taken
into consideration. This information can be
found in TMI.
Generator Radiant
The heat radiated by the generator can be
calculated by the following formulas:
HRG (kW) 5 P 2

HRG (Btu/min) 5 P 2

[ EFF1 ]
1

[ EFF1 ]
1

2 56.9

Where:
HRG = Heat Radiated by the Generator
(kW), (Btu/min)
P = Generator Output at Maximum Engine
Rating (ekW)
Eff = Generator Efficiency %/100%
(Example: Eff = 94%/100% = 0.94)
Example:
A 3512B, 975 ekW standby generator set has
a generator efficiency of 92%. What is the
generator radiant heat for this genset?
10

Engine Room Auxiliaries

The consultant should take all auxiliary
equipment besides the generator set into
consideration while designing the ventilation
system. Auxiliary equipment such as
switchgear, compressors, pumps, lighting,
piping etc. are sources of heat. Thus the
design should cover all main and auxiliary
equipment so that the room temperature is
maintained.

Engine Room Temperature

A 8.5C (15F) temperature rise above the
ambient temperature is a reasonable target
for engine rooms. (Ambient air temperature
refers to the air temperature surrounding the
engine room.) However, in cold climates this
may cause discomfort from the flow of cold
air. Restrict flow only if engine combustion
air is available and engine jacket water is
adequately cooled. In general, engine room
temperature should not exceed 49C (120F).
Air Velocity for Personnel Comfort
Maintain air velocity of at least 1.5 m/s
(5 ft/s) in working areas adjacent to sources
of heat, or where air temperatures exceed
100F (35C). This does not mean that all the
air in the engine room should be agitated so
violently. High air velocity around engines
and other heat sources is not good ventilation
practice. High velocity air aimed at engines
will hasten transfer of heat to the air, raising
average engine room air temperature.

Table 1 lists typical air motions:

Air Velocity
m/min

(fpm)

Conditions

15.2

50

30.5

100

Factory, standing worker

45.7

150

Capture velocity, light dust

61

200

Maximum continuous
worker exposure

1300

Capture velocity, rain

1000-2000

Maximum intermittent
exposure

396
306
610

Offices, seated worker

Table 1. Air velocity.

Radiators
Installations with engine-mounted radiators
using engine room air for cooling (Figure 7),
generally provide more air flow than is needed
for adequate ventilation. The high air flow
combined with low ambient temperatures,
below 21C (70F), may cause water to
condense inside exposed engine components,
like valve covers. This can result in oil and
maintenance problems. Therefore, special
installation considerations must be made in
cold climates.
There are two methods that can be used to
overcome this problem.
Remote mounted and specially ducted
engine-mounted radiators do not require
engine room air for cooling (see Figure 8).
One advantage of such a system is that

the air used to cool the radiator is not

pre-heated by the engine, thus increasing
the ambient capability (or reducing the
size) of the unit. The disadvantage is that
motor-driven fans must be installed to
provide ventilation for the engine, generator
and other equipment which increases the
overall cost of the system. This system is
suitable for continuous duty applications.
Thermostatically controlled louvers can be
installed to recirculate some of the radiator
exhaust in order to maintain a warm air
flow across the engine (see Figure 9).
This also maintains a comfortable working
environment for maintenance personnel.
Caution must be exercised so that the
recirculated air is reintroduced upstream
of the engine and is well mixed by the time
it reaches the radiator.
For any arrangement where a radiator fan is
used to ventilate an engine room, the vacuum
created in the engine room must not exceed
0.12 kPa (0.5 in. H2O). Any restriction above
this limit could reduce air flow through the
radiator and overheat the engine.
Radiator Sizing
Radiator core frontal area should be as large
as possible to minimize restriction to airflow.
Low radiator core restriction usually results
in being able to provide a larger slower
turning fan.

Figure 7. Engine driven fan arrangement.

11

Figure 8. Engine driven fan arrangement.

Figure 9. Radiator with thermostatically controlled louvers.

Radiators which are nearly square can provide

the most effective fan performance. They can
be installed with a minimum of unswept core
area. As a general rule, keep core thickness
to a minimum with a maximum of 11 fins per
2.54 cm (1.0 in.). Increasing the number of
fins per cm (in.) does increase the radiator
heat rejection for a given air velocity through
the core but also increases the resistance to
air flow.
While the most economical initial cost will be
maximum core thickness and fins per cm (in.),
12

this involves higher fan horsepower with

consequent operating cost and noise penalties
throughout the life of the installation. In addition,
a radiator with more fins per cm (in.) is much
more susceptible to plugging from insects
and debris.
Fan Sizing
As a general rule, the most desirable fan is
one having the largest diameter and turning
at the lowest speed to deliver the required
airflow. This also results in lower fan noise and
lowest fan horsepower draw from the engine.

Blade tip speed, while being only one of the

elements of cooling fan design, is an item
easily changed by choosing an appropriate
fan drive ratio. An optimum fan tip velocity of
6096 cm/s (12,000 fpm) is a good compromise
for meeting noise legislation requirements and
cooling system performance requirements.
Maximum acceptable tip speed is 7620 cm/s
(15,000 fpm) for Caterpillar fans.

Moveable Louvers
If moveable louvers are used, specify those
which open in a positive manner. Pneumatic
and electric-actuated louvers are satisfactory
(see Figure 10).

Enclosures
Enclosures trap radiated heat and direct it
through the radiator decreasing cooling
capabilities 8 to 10C (14 to 18F). Even
with doors open, radiators can derate 5 to
7C (9 to 13F) when enclosed.

Special Considerations
Refrigeration Equipment
Prevent refrigerant leakage into the engines
air intake system. Freon or ammonia will
cause severe engine damage if drawn into the
engines combustion chambers. The chemicals
in refrigerants become highly corrosive acids
in the engines combustion chambers.
If refrigeration equipment is installed within
the same compartment as a diesel engine,
the diesel engine must take its combustion air
from a specially supplied ductwork system
which carries air to the engine from an area
free of refrigerant fumes.

Figure 10. Moveable louvers.

Louver Operation

Louvers which open from the discharge

pressure of the radiator fan are discouraged.
Rain, ice, and snow can render them
inoperative within a short time and result
in engine overheating and shutdown.

Exhaust Pipe Insulation Recommended

Long runs of hot, uninsulated exhaust piping
will dissipate more heat into the engine room
than all the machinery surfaces combined.
Completely insulate all exhaust piping within
the engine room area. All hot surfaces within
the engine room should be insulated if high
air temperatures are to be avoided. Do not
insulate engine turbochargers.

Do not wait to activate the louvers until the

engine warms up. In an emergency, the
engine will be loaded immediately and
require full air flow. Open the louvers as
soon as the engine starts and install them
to open fully in case of an emergency.

Test With Doors and Windows Closed

Ventilating systems must be designed to
provide safe working temperatures and
adequate air flow when windows, doors, and
other normally closed ports are secured for
bad weather conditions. Test the ventilation
system fully secured for bad weather. This
condition will reflect the most severe test of
the ventilation system. Remember that a small
room suction can exert a large pressure on an
entrance door or window.

Heat sensors needlessly complicate the

system and their malfunction can reduce
air flow to the engine which can cause
shutdown.

Ducting Considerations
Design all ducting to withstand extremes
of vacuum or pressure and still maintain
tight joints.
Provide inspection ports (or areas that are
easily disassembled) to allow removal of
foreign objects especially for standby
applications.
13

Notes

14

Notes

15

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Materials and specifications are subject to change without notice.