2_-_Design_Analysis_Exhaust_Fans_Redacted(RS).pdf

FINAL DESIGN SUBMITTAL

DESIGN ANALYSIS

50th Civil Engineer Squadron

Schriever Air Force Base, Colorado

Repair by Replacing the Roof Mounted Exhaust Fans, B600

SAFB Project No. GLEN 16-2601

November 2017

TOC - 1

TABLE OF CONTENTS

SECTION 1 - CRITERIA ....................................................................................................................... 1-1

1.1 Codes and Standards ...................................................................................................... 1-1

1.2 Other Documents ............................................................................................................. 1-1

SECTION 2 - ANALYSIS SUMMARY .................................................................................................. 2-1

2.1 Scope of Work ................................................................................................................. 2-1

2.2 Justification for Criteria and/or Code Deviations ............................................................. 2-1

2.3 Project Phasing & Scheduling ......................................................................................... 2-1

2.4 Basis of Selection ............................................................................................................ 2-1

2.5 Maintainability of Selection .............................................................................................. 2-1

2.6 Recovered Materials ........................................................................................................ 2-1

SECTION 4 - EXISTING CONDITIONS ............................................................................................... 4-1

4.1 General ............................................................................................................................ 4-1

4.2 Structural .......................................................................................................................... 4-1

4.3 HVAC ............................................................................................................................... 4-1

4.4 Electrical .......................................................................................................................... 4-2

SECTION 5 - ANALYSIS ...................................................................................................................... 5-1

5.1 General ............................................................................................................................ 5-1

5.2 Structural .......................................................................................................................... 5-1

5.3 HVAC ............................................................................................................................... 5-1

5.4 Electrical .......................................................................................................................... 5-2

SECTION 7 - APPENDICES ................................................................................................................ 7-1

APPENDIX B – CALCULATIONS ................................................................................................ B

APPENDIX C – PRODUCT INFORMATION SHEETS................................................................ C

1-1

SECTION 1 - CRITERIA

1.1 Codes and Standards

A. Schriever Air Force Base (SAFB) Standards

1. SAFB Engineering Design Guide

B. Department of Defense and Unified Facilities Criteria (UFC)

1. UFC 1-200-01, General Building Requirements

2. UFC 3-401-01, Mechanical Engineering

3. UFC 3-410-01, Heating, Ventilating and Air Conditioning Systems

4. UFC 3-501-01, Electrical Engineering

5. UFC 3-520-01, Interior Electrical Systems

6. UFC 4-010-01, DoD Minimum Antiterrorism Standards for Buildings

C. National Fire Protection Association (NFPA) Compliance with all NFPA documents is required; the following list is not all inclusive.

1. NFPA 1, Chapter 16 – Safeguarding Construction, Alteration and Demolition Operations

2. NFPA 70, National Electrical Code

3. NFPA 72, National Fire Alarm and Signaling Code

4. NFPA 101, Life Safety Code

D. International Codes

1. International Existing Building Code

2. International Energy Conservation Code

3. International Mechanical Code

1.2 Other Documents

A. Statement of Work dated 14 April 2017

B. ASHRAE Handbooks

2-1

SECTION 2 - ANALYSIS SUMMARY

2.1 Scope of Work

A. The purpose of this project is to repair the central plant generator bay ventilation system airflow shortage by replacing the roof mounted exhaust fans with higher capacity fans.

2.2 Justification for Criteria and/or Code Deviations

A. During startup testing of new generators in 2011, a high bearing temperature alarm was activated by one of the generators. Subsequent analysis by Wagner Power Systems determined that the generator was experiencing localized recirculation of air around the generator due to inadequate generator bay ventilation airflow.

2.3 Project Phasing & Scheduling

A. The project construction schedule must be planned to only impact one generator’s operation at a time. The work associated with this project can be done during normal working hours and requires no special scheduling.

2.4 Basis of Selection

A. The manufacturers of the materials associated with this project are for the most part completely open. Much of the equipment will be manufactured in the United States.

B. The following major products and manufacturers were used as the basis of design for the project:

1. Roof mounted exhaust fans – Greenheck Fan Corporation.

2. Electrical distribution equipment – Motor Control Centers manufactured by Siemens.

2.5 Maintainability of Selection

A. The basis of design for proposed equipment associated with this project was selected based on the requirement for high reliability and low maintenance.

2.6 Recovered Materials

A. Most of the demolition effort consists of removing the existing rooftop exhaust fans that where originally installed on the central plant. The equipment is not reusable due to age (approximately 35 years old), but should be recycled.

The contractor will recycle metal and other material deemed applicable.

4-1

SECTION 4 - EXISTING CONDITIONS

4.1 General

A. The existing exhaust fans do not provide enough ventilation airflow during high outdoor air temperature conditions. As a result, the existing fans will need to be replaced with fans that can provide more airflow capacity.

4.2 Structural

A. The existing building is a single-story, steel w-beam roof purlin and girder system with steel columns and concrete spread footings for vertical support. The exterior walls are precast concrete panels and provide lateral stability for the building. The as-built plans list a design completion date of December 1983. The roof was originally designed for a series of exhaust fans with listed weights of 800 lbs.

4.3 HVAC

A. Ventilation of the generator bay is accomplished via eight roof mounted exhaust fans (EAF-CP-112 thru 117, EAF-CP-204 & 205) interlocked with intake louvers at floor level on the outside wall near each of the seven generators in the space.

B. Record drawings indicate that fans EAF-CP-112 thru 117 are each scheduled to provide 33,000 cfm at 0.375” static pressure with 7-1/2 HP, 460V, 3 phase motors. The record drawings have no information regarding EAF-CP-204 & 205.

C. In 2011 three of the seven generators were replaced with new Caterpillar C175-16 generators. During on-site startup services for generator unit #2, a high bearing temperature alarm was activated for the front bearing. Subsequent analysis by Wagner Power Systems determined that the generator was experiencing localized recirculation of air around the generator due to inadequate generator bay ventilation airflow.

D. Model information obtained during the site investigation on July 12, 2017 indicates the following:

1. EAF-CP-204 & 205:

a. Manufacturer: ACME Engineering and Manufacturing

b. Model: ECH72

c. Motor: 5 HP, 460/230V, 3 phase, 60 hz, 13.6/6.8 amps

d. Fan RPM: 368

2. EAF CP-112 thru 117:

a. Manufacturer: Loren Cook

b. Model: N/A labels were painted

c. Motor: 7 ½ HP, 460V, 3 phase 60 hz.

d. Fan RPM: N/A labels were painted

4-2

E. The ventilation system is controlled by three wall mounted thermostats that activate the exhaust fans when the room temperature reaches 85oF. The thermostats are not evenly distributed within the space.

F. The damper actuators (120 Volt) for the intake air louvers have been disconnected from the damper linkage. The existing dampers are only capable of being opened approximately 50%. The dampers near the new generators are approximately 45% blocked by the generator engine jacket and aftercooler piping which exits the building to the outdoor radiators.

G. The ventilation system does not appear to be tied into the existing building automation system.

4.4 Electrical

A. Power

1. The existing 7.5 HP Exhaust Fans EAF-CP-112 through EAF-CP-117 are fed from motor starters in Motor Control Centers MCC-1, MCC-2 and MCC-3. MCC- 1 feeds EAF-CP-112 and 113, MCC-2 feeds EAF-CP-114 and 115 and MCC-3 feeds EAF-CP-116 and 117.

2. Existing 5 HP Exhaust Fans EF-CP-204 and EF-CP-205 are both fed from motor starters in Motor Control Center MCCN-2.

3. There are Disconnect Switches on the roof adjacent to EAF-CP-112 through EAF-CP-117. There are no Disconnect Switches on the roof adjacent to EF-CP- 204 and EF-CP-205.

4. There are two duplex receptacles on the roof adjacent to EAF-CP-114 and EF- CP-204. The spacing of these receptacles do not meet code that requires a receptacle to be within 25 feet of a roof mounted mechanical unit. There is no duplex receptacle adjacent to EF-CP-205 which is located on a lower section of the roof than the other exhaust fans.

5. All exhaust fans have lightning protection system air terminals mounted on top of the unit enclosures, four per exhaust fan. These air terminals are 12” Aluminum, and are connected to the building lightning protection system perimeter roof conductors with #1/0 AWG AL conductors.

6. There are fourteen intake louvers on the east wall of the Generator room, each louver has a 120V actuator that have been physically disconnected so that they must be manually operated.

5-1

SECTION 5 - ANALYSIS

5.1 General

A. The increased physical fan size will necessitate changes to the fan power supplies and building structural modifications to support the additional fan weight.

5.2 Structural

A. The new proposed fans with curbs have an approximate weight of 2,075 lbs. A review the existing roof structure for the new fan weights indicate the roof structure is adequate as is with no supplemental structure needed. Roof member sizes appear to be designed to limit roof deflection to acceptable limits. The addition of the new heavier fans increases the total roof deflections but are still less than the code allowable limit of L/240 for combined loading. See the appendix for the supporting structural calculations. The additional dead weight of the fans would be negligible in relationship the building weight (<1%) and will not appreciably increase the seismic demand on the building. The wind profile of the building is unchanged.

5.3 HVAC

A. The engine room ventilation system sizing requirements for this project were based on caterpillar’s Engine Room Ventilation Application and Installation guide LEBW4971-06.

1. Calculations indicate that the existing ventilation airflow in the generator room needs to be increased.

2. Since the generator room intake air opening sizes cannot be increased, the static pressure drop through the louvers and dampers increases exponentially as the airflow rate through them increases.

B. The increased airflow and resulting higher static pressure requirement necessitates the use of high performance axial fans instead of hooded fans matching the appearance of the existing units. Direct drive fans will be utilized to reduce fan maintenance.

C. New intake dampers that can be fully opened will be provided to help reduce static pressure loss through the existing building openings. The dampers will be provided with end switches to verify opened/closed position and will be interlocked with the exhaust fans.

D. An additional room thermostat/sensor will be provided for improved space temperature monitoring and fan control.

E. The ventilation system will be tied into the existing building automation system.

5-2

5.4 Electrical

A. Power:

1. The eight (8) existing roof mounted Exhaust Fans shall be disconnected and all associated disconnect switches, conductors and conduit removed. Also, existing lightning protection air terminals and conductors shall be removed from existing Exhaust Fan housings, and the existing size 1 starter buckets should be removed from the MCC’s.

2 Existing Motor Control Centers MCC-1, MCC-2, MCC-3 and MCCN-2 which feed the Exhaust fans are all rated 600 Amps, 277/480V-3 Phase at 42KAIC.

2. Provide eight (8) new 460V, Size 2 reduced voltage soft start (RVSS) motor starters with integral motor-circuit protection (MCP) of 50 amps for the 25HP fans in the existing Siemens motor control centers. Provide new 1” conduit, with 3 #6 and 1 #8G. copper conductors from the new starters in the MCC’s to each roof-mounted exhaust fan for power.

3. The new 25 HP Exhaust Fans shall be connected to the same Motor Control Centers (MCC’s) currently serving existing fans. The new Size 2 starter buckets should be installed in the same cubicle as the original exhaust fan starters.

4. Existing roof mounted disconnect switches adjacent to exhaust fans EAF-CP112 through EAF-CP117 shall be removed and existing rigid conduit supports for these disconnect switches shall remain. A new 60A,3P NEMA 4X non-fused safety disconnect switch shall be provided adjacent to each new Exhaust Fan on the roof. At EAF-CP112 through EAF-CP117 mount new disconnect switch on existing rigid conduit support where existing disconnect switch is currently mounted. At EAF-CP204 and EAF-CP205, provide new rigid conduit support similar to existing rigid conduit supports since there are no disconnect switches mounted adjacent to these units.

5. Provide lightning protection system on each new fan housing consisting of four (4) 24” copper air terminals and new #1/0 copper conductors and connect to existing #1/0 copper perimeter lightning protection system conductors on the roof.

6. Disconnect existing 120V damper actuators at fourteen locations on east interior wall of Generator room and connect new actuators to existing 120V circuits.

7-1

SECTION 7 - APPENDICES

APPENDIX A – PROJECT DOCUMENTS

Wagner Power Systems 4000 Osuna Road NE Albuquerque, NM 87109 http://wagnerequipment.cat.com Phone (505) 345-8411

FAX: (505) 344-0397

December 21, 2011

Topic: C175 Caterpillar generator high bearing temperature alarm

Section I: Introduction

Wagner Power Systems was contracted in 2009 to provide 3ea. C175 generators for Schreiver AFB. The scope of work at that time was to provide the C175-16 Factory Packaged Diesel Generator Sets only, Switchgear, Paralleling Gear and Engineering Installation Services where declined. Wagner Power

Systems did provide submittals and Caterpillar Application and Installation Guidelines to Paul Basedow at that time. The units were installed by a General Contractor Del Rio Enterprises, contracted by

Schriever AFB. In June 2011 On-Site Startup Services began by Wagner’s Field Service Technicians.

During the start up procedure, each unit was run in a standalone mode for a 4 hour load bank test.

During the start up of Unit #2 in August 2011 a high bearing temperature alarm was activated for the

Front Generator Bearing. This is a concern because high bearing temperatures can lead to early bearing failure and could be indications of improper installation. Because of possible Warranty concerns

Wagner Power Systems contacted Schriever AFB representatives and sent a Technical White Paper dated 21 September 2011 and an additional letter on November 29, 2011. Schriever AFB representatives have requested additional information; the following information provides an analysis of the Startup information recorded and the perceived issues.

Section II: Test Conditions

As stated the Unit #1 was started up in the June time frame. The full load test took place on 21-Jun-11.

The outside temperature reached a high of 76.7 F. The engine room temperature was 77 F at the beginning of the test. It rose to 81 F by the end of the test. No alarms were recorded during this test of

Unit #1.

The full load test for the Unit #2 was conducted on 31-Aug-11. The outside temperature was 91.9 F.

The room temperature at the beginning of the test was 87 F. It rose to 93 F by the end of the test. A High

Bearing Temperature Alarm was activated during this test. Alarm set point is at 195 F, bearing temperature was recorded at 204 F for the Front Generator Bearing.

The full load test for Unit #3 was conducted on 22-Nov-11. The outside temperature was 55.9 F. The engine room temperature was 65 F. It dropped to 63 F by the end of the test. No alarms were recorded during this test of Unit #3.

The room temperature data was taken from a probe in the engine room that was installed by Schriever

AFB. Note; all recorded room temperatures during full test are within rise over ambient specifications per the Caterpillar Engine Room A&I guide (media #:LEBW4971-02, pg. 4).

Section III: Determining Possible Causes of High Temperature Alarm

In an effort to determine the cause of the alarm, WPS considered all the test data. In review of the test data, some possible causes of the alarm were determined: Insufficient air flow in engine room (which could be cause by a variety of issues), bad temperature sensor, or poor local air flow. Local air flow refers to the air flow around the engine and not the overall engine room. One way to determine if there is proper airflow is to look at the temperature rise in the engine room. It is expected to see some rise over room ambient due to the heat radiated from the engine and generator. The observed rise in room temperature was fairly consistent for the tests during each test day when the ambient was above the room temperature. Unit #1 showed a 4 F rise with an outside ambient of 78.1 F. Unit #2 was a 6 F rise with a 91.9 F ambient recorded. Unit #3 showed a 2 F decrease was recorded with an ambient of 55.9 F.

It is presumed that this is due to outside air being cooler than the inside air, causing the drop in temperature. The temperature rise in the engine room is well within Caterpillars specification of 15 F -

22.5 F. This shows that airflow in the room is adequate for one generator running.

The second possible concern was a bad temperature sensor. Caterpillar uses a 100 ohm resistance temperature measuring device (RTD). These sensors have a typical tolerance of +/- .5 F. They are very stable, reliable and repeatable. The system is not designed for any type of calibration. This was hard programmed into the RTD module at the factory. One way to determine if the RTDs were working properly was to look at the temperature difference between the front and rear bearings. If one of the sensors was bad, the temperature differential would vary significantly more than the others. The first unit had a differential of 36 F, the third unit was 39.6. On the Unit #2, the one in question, had a temperature differential of 34.2 F. Given that all of the differential temperatures are with 5 F, the sensors were reading correctly.

This leaves the local air flow as the most likely culprit. In a typical Start up, air flow measurements are not taken. In this case, no measurements were required by the specification and none were included in pricing. An observation by WPS Field Service Technicians helped to shed some light on air flow patterns around the generator. Schreiver AFB conducted a 40 hour load test on one of the units. When

WPS’ technician arrived after the test a large amount of oil mist was observed on the cooling air intake screen of the generator. The air intake screen is located at the back of the generator. This was caused by the crankcase fumes being exhausted in the room at the front of the engine. The presence of the oil mist shows that air is being pulled from the front of the engine into the back of the generator. According to the Cat A&I guide, air should be directed across the generator end first and then the engine. This prevents recirculation from occurring in a local area around the generator. Recirculation causes the air temperature to rise due to repeated heating in a localized area. This has the potential to overheat bearings and generator windings.

Another example of the recirculation effect was seen on the Rear Generator Bearing temperatures.

The room temperature was 81 F for Unit#1 and 63 F for Unit# 3. The bearing temperatures were 141.8 F and 140.0 F respectively. These temperatures were indicative of a normal bearing running temperature that was not dependant on the room temperature. However, in the case of Unit #2 the Rear Bearing temperature was much higher at 170.6. There was no indication during testing that there was an issue that might cause the bearings to run hot. The engine room temperature was 93 F that day. Recirculation causes the air around the generator to be much warmer than the ambient of the room.

Section IV: Engine Room Recommendations per A&I Guide

The Caterpillar Engine Room A&I guide gives requirements and suggestions for engine room considerations and design. Required air flow calculations start on page 3. These allow an engine room designer to calculate the basic air flow requirement based on the site conditions (altitude, maximum ambient temperature, engine room temperature rise etc.) for a single engine installation. For multiple engine installations, such as Schreiver AFB, other considerations are mentioned. The next step is air flow routing. Air routing considerations start on page 9.

In light of the current issues, WPS performed several calculations on the existing configuration. The basic air flow required equation on page 3 was used several ways. Refer to Appendix 1 for more details.

The first calculation was to determine the air flow required for one engine at maximum ambient temperature. This was calculated as 79,428 cfm. Since no air flow measurements were taken, it was determined that the engine room temperature rise could be used to get a relative estimate of the air flow in the room. The highest temperature rise was 6 F on unit 2. This yielded an approximate airflow of

297,857 cfm for the entire room. The approximation showed that adequate flow existed in the room with one unit running. Comparison of the maximum ambient temperature air flow and estimated room air flow showed that there was more than adequate flow to cool the generator if routed properly.

The next step was to consider the air flow routing. When comparing the air intake and exhaust fan locations at Schriever AFB, to the Caterpillar recommendations it was clear that the air flows paths were not optimal. Non-ideal air flow routing can lead to a number of issues. One such issue is high bearing temperatures. Pages 10 – 16 address the typical air flow paths Caterpillar recommends. For these paths routing factors are given. The factor multiplies the required airflow by a factor 1 or greater. For the most ideal conditions the factor is 1. For the least ideal conditions the factor was given as 2.5. Air flow routing outside of these assumptions are not covered by the guide. Therefore the factors and equations given in the guide can not be applied directly in this case. The air flow at Schriever AFB was not consistent with the recommended routings. The recommended air flow over the generator is in the opposite direction of the air flow in the engine room. The resulting improper air flow at Schreiver could potentially cause air to recirculate through the generator.

Section IV: Conclusions

The high bearing temperature alarm on Unit #2 was the cause of concern for the installation. Analysis performed by WPS, showed that the high bearing temperature alarm was related to the high outside ambient temperatures and localized recirculation around the generator when one unit was operated at stand alone at full load for 4 hours. When the outside temperature is lower, the units perform, standalone, as expected. No testing was done with multiple units running at the same time. This could potentially exacerbate the issues. This information will be noted on the start up reports submitted to

Caterpillar.

The concern being raised by Wagner Power Systems is the potential for denied warranty claims due to a known issue. Unknown at this point, are the potentially damaging effects of running all the units under load at the same time or standalone with high outside ambient temperatures. Wagner Power Systems recommends to Schriever AFB that they contact the General Contractor responsible for Engine Room installation to determine based upon delivered Caterpillar Application and Installation Guidelines what measures should be done to correct the air flow.

APPENDIX B – CALCULATIONS

MGA Structural Engineers, Inc.

115 South Weber Street, Suite 101 Telephone (719) 635-4473 Fax (719) 635-4795 Colorado Springs, Colorado 80903-1900

Calculations

APPENDIX B:

Structural Engineering

REPAIR by REPLACING the ROOF MOUNTED

EXHAUST FANS, B600

Schriever Air Force Base, Colorado

SAFB Proj. No. GLEN 16-2601

65% SUBMITTAL

August 14, 2017

Engineer of Record:

Jon A. Dietrich P.E.

Pg. 1

Pg. 2

Pg. 3

Pg. 4

Pg. 5

Pg. 6

Application & Installation Guide

Engine Room Ventilation

LEBW4971-06

Contents

Engine Room Ventilation

Sizing Considerations

Cooling Air

Combustion Air

Ventilation Airflow

Calculating Required Ventilation Airflow

Engine Room Enclosure Temperature

Atmospheric Heat Rejection Correction Factor

Ventilation Fans

Fan Types

Fan Location

Fan Sizing

Exhaust Fans

Two Speed Fan Motors

Routing Considerations

General Routing Principles

Single & Dual Engine Applications

Multiple Engine Applications

Special Application Routing

Marine Exhaust Ejector – Automatic

Ventilation System

Additional Considerations

Radiator Sizing

Radiator Fan Sizing

Moveable Louvers

Refrigeration Equipment

Exhaust Pipe Insulation

Foreword This section of the Application and Installation Guide generally describes Engine Room Ventilation for Cat® engines listed on the cover of this section. Additional engine systems, components and dynamics are addressed in other sections of this Application and Installation Guide.

Engine-specific information and data is available from a variety of sources.

Refer to the Introduction section of this guide for additional references.

Systems and components described in this guide may not be available or applicable for every engine.

Engine Room Ventilation Application and Installation Guide

©2015 Caterpillar All rights reserved. Page 1

Engine Room Ventilation This guide addresses engine room ventilation considerations that apply to the successful installation, operation and maintenance of Cat engines, generator sets, compressor units, and other packaged units.

The primary aspects of a properly designed engine room ventilation system are cooling air and combustion air. Cooling air refers to the flow of air that removes radiant heat from the engine, generator, other driven equipment and other engine room components. Combustion air describes the air the engine requires to burn fuel.

Cooling and combustion air directly impact engine and package unit performance and dependable service life; these must be considered in the design of an engine room ventilation system. It is also important to consider all engine room equipment in the design of a ventilation system and provide a comfortable environment for service personnel to perform maintenance.

Some driven equipment, such as a generator in a large engine installation, may require a dedicated ventilation source.

SECTION CONTENTS

Sizing Considerations

• Cooling Air

• Combustion Air

• Ventilation Airflow

Ventilation Fans

• Fan Types

• Fan Location

• Fan Sizing

Routing Considerations

• General Routing Principles

Additional Considerations .. 24

• Radiator Sizing

• Louvers

• Refrigeration Equipment

• Exhaust Pipe Insulation

• Ducting

Cold Weather Considerations

• Air Cleaner Icing

• Extreme Cold

• Boost Control

Application and Installation Guide Engine Room Ventilation

Page 2 All rights reserved.

Sizing Considerations

Cooling Air A portion of fuel consumed by an engine is lost to the environment in the form of 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 engine or generator set performance.

Engine room ventilation air (cooling air) has two basic purposes.

• To provide an environment that permits the machinery and equipment to function properly with dependable service life.

• To provide an environment in which personnel can work comfortably and effectively.

It is important to note that cooling air is needed for more than just the engine; the generator intake also requires cool clean air. The most effective way to do this is to provide a ventilation air source low to the ground at the rear of the package.

The use of insulation on exhaust pipes, silencers, and jacket water pipes will reduce the amount of heat radiated by auxiliary sources.

Radiated heat from the engines and other machinery in the engine room is absorbed by engine room surfaces. Some of the heat is transferred to atmosphere or, on marine installations, to the sea through the ship’s hull. The remaining radiated heat must be carried away by the ventilation system.

A system for exhausting ventilation air from the engine room must be included in the ventilation system design.

Combustion Air Combustion air is discussed in detail in the Air Intake Systems section of the Application and Installation Guide. Some aspects of the intake air system are discussed in this guide because they significantly impact the engine room ventilation system design.

In many installations, combustion air is drawn from outside the engine room via ductwork that is designed to move a large amount of air with very little restriction. These installations have very little impact on engine room ventilation design.

Other installations, however, require that combustion air be drawn directly from the engine room. In these installations, combustion air requirements become a significant ventilation system design parameter.

Approximate consumption of combustion air for a diesel engine is

0.1 m3 of air/min/brake kW (2.5 ft3 of air/min/bhp) produced. Engine-specific combustion air requirements can be found using the resources mentioned in the foreword of this guide.

Ventilation Airflow Required ventilation airflow depends on the desired engine room air temperature as well as the cooling air and combustion air requirements outlined above. While it is understood that total engine room ventilation airflow must take all equipment and machinery into

All rights reserved. Page 3 account, the following sections provide a means for estimating the airflow required for the successful operation of Cat engines and packages.

Calculating Required Ventilation Airflow Engine room ventilation air required for Cat engines and packages can be estimated by the following formula.

V = H

+ Combustion Air x F D x CP x #T!

Where:

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

H = Heat Radiation i.e. engine, generator, aux (kW), (Btu/min)

D = Density of Air at air temperature 38°C (100°F). The density is equal to

1.099 kg/m3 (0.071 lb/ft3)

CP = Specific Heat of Air (0.017 kW x min/kg x °C), (0.24 Btu/LBS/°F)

#T = Permissible temperature rise in engine room (°C), (°F)

(Note: Max engine room temperature is 120°F)

F = Routing factor based on the ventilation type discussed in the Routing Considerations section of this guide.

Note: If combustion air is supplied to the engine through dedicated duct work, “Combustion Air” should be omitted from the formula.

Example:

The engine room for a 3412 DITA genset has a Type 1 ventilation routing configuration and a dedicated duct for combustion air.

It has a heat rejection value of 659 kW (37,478 Btu/min) and a permissible rise in engine room temperature of 11°C (20°F).

Solution:

The estimated engine room ventilation required for this arrangement:

V =

+ 0 x 1

1.099 x 0.017 x 11

V = 3206.61 m3/min

V = 37478

+ 0 x 1

0.071 x 0.24 x 20

V = 109970.7 cfm

Proper ventilation is heavily dependent on the path of the ventilation air. Applications involving high load factors and continuous full power operation require a rigorous approach based on classical heat transfer calculations accounting for radiant heat and allowable room temperature rise and adjusting with a ventilation routing factor.

Page 4 All rights reserved.

Engine Room/Enclosure Temperature The primary reason for maintaining engine room temperature at an appropriate level is to protect various components from excessive temperatures. Items that require cool air are:

• Electrical and electronic components.

• Cool air to the air cleaner inlet.

• Cool air to the torsional vibration damper.

• Habitable temperatures for the engine operator or service personnel.

• Cooling air for the generator or other driven equipment.

A properly designed engine room ventilation system will maintain engine room air temperatures within 8.5 to 12.5°C (15 to 22.5°F) above the ambient air temperature.

For example, if the engine room temperature is 24°C (75°F) without the engine running, the ventilation system should maintain the room temperature between 32.5°C (90°F) and 36.5°C (97.5°F) while the engine is in operation.

Caterpillar recommends a ventilation design that ensures engine room temperature does not exceed 49°C (120°F). If the engine room temperature cannot be maintained below 49°C (120°F), cooler air should be ducted directly to the engine air cleaners.

Temperature limits of the driven equipment must also be considered.

For model-specific electronic components, reference the appropriate service manual or EDS sheet for that component’s allowed surface temperatures.

If the engine room temperature exceeds 40°C (104°F), the generator must be derated per the generator derate schedule and cool outside air must be ducted directly to the generator air intake. Alternatively, custom generators can be sized to handle specific ambient conditions.

In larger multiple engine sites, the normal 8.5 to 12.5°C (15 to 22.5°F) temperature rise guidelines for engine rooms may require unobtainable or uncomfortable air velocities. For these larger sites, a ventilation system needs to give priority to the five items listed above and provides a bottom to top airflow similar to that shown in Figure 8 and Figure 9. In all cases, engine room/enclosure design must ensure that air temperature around the engine will not exceed 50°C (122°F). Critical locations include the engine torsional damper and generator coupling. Air temperature reading should be taken no more than 6 inches away from these components. Note that in these extreme situations, it may be necessary to duct cool air directly to these critical components.

Atmospheric Heat Rejection Correction Factor Atmospheric heat rejection values published in TMI are based on ambient cell conditions between 25°C and 29°C. Engine rooms can be designed at much higher ambient conditions; therefore a correction factor can be utilized to define the atmospheric heat rejection at the higher ambient condition.

The correction factors defined below have been developed using fundamentals of heat transfer and can be applied to any object under the same conditions.

All rights reserved. Page 5

There are two distinct correction factors, one is used with wet exhaust and turbo manifolds, the other is used with dry exhaust and turbo manifolds. The skin temperature utilized in the dry manifold calculation is 200°C, approx value of the wrapped, or insulated manifold.

Wet exhaust and turbo manifold correction factor.

WCF = -.0156 * TER + 1.4505

Where:

WCF = Wet Correction Factor

TER = Ambient Engine Room Ambient (°C)

Dry exhaust and turbo manifold correction factor.

DCF = -.011* TER +1.3187

Where:

DCF = Dry Correction Factor

TER = Ambient Engine Room Temperature (°C)

To obtain the corrected atmospheric heat rejection value, multiply the TMI value by the WCF or DCF.

Radiant Heat

Radiant heat values for the engine and driven equipment is needed to calculate the required ventilation airflow.

Note: For the packaged generator sets, ensure that there is adequate airflow near the engine torsional damper. Excessive piping and cooling system structures may prohibit proper airflow near the torsional damper. Monitor damper temperatures per the recommendations found in the Operation and Maintenance

Service Manual.

This data is available in the TMI for Cat products. It is located in the Performance Data section.

Engine Engine generated radiant heat (heat rejection to atmosphere) is routinely provided with published engine technical data. Values are typically nominal with their tolerance noted.

Tolerance should always be added before using published data in calculations.

Page 6 All rights reserved.

Generator For generator set installations, the heat radiated by the generator can be estimated by the following formulas.

HRG (kW) = P x

[(1/Eff) – 1]

HRG (Btu/min) = P x [(1/Eff) –

1] x 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:

A 3512B, 975 ekW standby generator set has a generator efficiency of 92%. The generator radiant heat for this genset can be calculated as follows.

Solution:

P = 975 ekW

Efficiency = 92% / 100% = 0.92

HRG = 975 x (0.92 – 1)

HRG = 84.78 kW

HRG = 975 x (0.92 – 1) x 56.9

HRG = 4824 Btu/min

Note: This data is available in the TMI for Cat generators. It is located in the Performance Data section.

All rights reserved. Page 7

Ventilation Fans

Except for special applications, natural draft ventilation is too bulky for practical consideration. Adequate quantities of fresh air are best supplied by powered (fan-assisted) ventilation systems.

Fan Types The following types of ventilation fans are typically used.

• Vane-axial

• Tube-axial

• Propeller

• Centrifugal (squirrel cage blowers)

The selection of fan type is usually determined by ventilation air volume, pressure requirements and space limitations within the engine room. The fans have various qualities that make them better suited to certain applications.

Fan Location Fans are most effective when they withdraw ventilation air from the engine room and exhaust the hot air to the atmosphere. However, ideal engine room ventilation systems will utilize both supply and exhaust fans. This will allow the system designer the maximum amount of control over ventilation air distribution.

The fan motors should be mounted outside the direct flow of hot ventilating air for longest motor life.

The design of centrifugal fans (squirrel cage blowers) is ideal in this regard, but their size, relative to the vane-axial or tube-axial fans, sometimes puts them at a disadvantage.

Fan Sizing Fan sizing involves much more than just selecting a fan that will deliver the airflow volume needed to meet the cooling air and combustion air requirements. It requires a basic understanding of fan performance characteristics and ventilation system design parameters.

Similar to a centrifugal pump, a fan operates along a specific fan curve that relates a fan’s volume flow rate (m3/min or cfm) to pressure rise (mm H2O or in. H2O) at a constant fan speed. Therefore, fan selection not only requires that the volume flow rate be known, but also that the ventilation distribution system be known in order to estimate the system pressure rise. This information allows the optimum fan to be selected from a set of manufacturers’ fan curves or tables.

Exhaust Fans Ventilation air exhaust systems should be designed to maintain a slight positive or negative pressure in the engine room, depending on the specific application.

Positive pressure should normally not exceed .050 kPa or (0.2 in. H2O).

This positive pressure provides the following advantages.

Page 8 All rights reserved.

• It prevents the ingress of dust and dirt, which is especially beneficial for those applications involving engines that draw their combustion air from the engine room.

• It creates an out draft to expel heat and odor from the engine room.

Some applications, such as a marine application where the engine room is adjacent to living quarters, require that a slight negative pressure be maintained in the engine room. This negative pressure should not normally exceed 0.1275 kPa (0.5 in. H2O). The excess exhaust ventilation provides the following advantages.

• It compensates for the thermal expansion of incoming air.

• It creates an in draft to confine heat and odor to the engine room.

Two Speed Fan Motors Operation in extreme cold weather may require reducing ventilation airflow to avoid uncomfortably cold working conditions in the engine room. This can be easily done by providing ventilation fans with two speed (100% and 50% or 67% speeds) motors.

All rights reserved. Page 9

Routing Considerations

General Routing Principles Correct ventilation air routing is vital for proper operation of Cat engines and packaged units.

Maintaining recommended air temperatures in the engine room is impossible without proper routing of the ventilation air. The following principles should be considered when designing an engine room ventilation system.

• Fresh air inlets should be located as far from the sources of heat as practical and as low as possible.

• Ventilation air should be exhausted from the engine room at the highest point possible, preferably directly over the engine.

• Ventilation air inlets and outlets should be positioned to prevent exhaust air from being drawn into the ventilation inlets (recirculation).

• Ventilation air inlets and outlets should be positioned to prevent pockets of stagnant or recirculating air, especially in the vicinity of the generator air inlet.

• Where possible, individual exhaust suction points should be located directly above the primary heat sources. This will remove heat before it has a chance to mix with engine room air and raise the average temperature. It must be noted that this practice will also require that ventilation supply air be properly distributed around the primary heat sources.

• Avoid ventilation air supply ducts that blow cool air directly toward hot engine components.

This mixes the hottest air in the engine room with incoming cool air, raising the average engine room temperature. This also leaves areas of the engine room with no appreciable ventilation.

• For installations where engines draw combustion air from inside the engine room, the routing should provide the coolest possible combustion air to the turbocharger inlets.

• For marine and offshore applications, the potential exists for seawater to be drawn into the ventilation air supply; systems for these applications must be designed to prevent seawater from being drawn into the air intake filters and ingested by the turbocharger. Generator cooling air must also be filtered to minimize the ingestion of salt.

These general routing principles, while driven by the same basic principles of heat transfer, will vary with the specific application.

This section discusses the general considerations relating to single and dual engine applications, multiple engine (3+) applications, and several special applications.

Page 10 All rights reserved.

Single & Dual Engine Applications Single and dual engine applications are arguably the most common applications encountered, regardless of engine market.

These applications will generally require smaller engine rooms, which are especially challenging in regard to the use of good routing practices.

Recommended ventilation systems for these applications, presented in order of preference, are Type 1, Type 2, Type 3 and Type 4.

Ventilation Type 1 (Preferred Design) Note: In ventilation airflow calculations, Type 1 systems have a Routing Factor of 1.

Outside air is brought into the engine room through a system of ducts. These ducts should be routed between engines, at floor level, and discharge air near the bottom of the engine and generator as shown in Figure 1.

Ventilation air exhaust fans should be mounted or ducted at the highest point in the engine room. They should be directly over heat sources.

This system provides the best ventilation with the least amount of air required. In addition, the upward flow of air around the engine serves as a shield which minimizes the amount of heat released into the engine room. Air temperature in the exhaust air duct will be higher than engine room air temperature.

Ventilation Type 1

Ventilation Type 2 (Skid Design) Note: In ventilation airflow calculations, Type 2 systems have a Routing Factor of 1.

A skid design may be preferred in petroleum applications. Similar to the Type 1 system, Type 2 brings outside air into the engine room through a system of ducts and routes it between engines.

Type 2, however, directs airflow under the engine and generator so the air is discharged upward at the engines and generators as shown in Figure 2.

Figure 1

All rights reserved. Page 11

The most economical method to achieve this design is to use a service platform. The platform is built up around the engines and serves as the top of the duct. This requires the service platform to be constructed of solid, nonskid plate rather than perforated or expanded grating. The duct outlet will be the clearance between the decking and oilfield base. Regular care must be used to ensure grating remains clean and the airflow unrestricted.

Ventilation air exhaust fans should be mounted or ducted at the highest point in the engine room. They should be directly over heat sources.

This system provides the best ventilation with the least amount of air required. In addition, the upward flow of air around the engine serves as a shield which minimizes the amount of heat released into the engine room. Air temperature in the exhaust air duct will be higher than engine room air temperature.

Although the Type 1 system provides effective ventilation for the engine, it does not consider the special ventilation needs of the driven equipment. Large generators, configured with an air inlet positioned high on the generator, will require an additional source of ventilation air.

Ventilation Type 2

Ventilation Type 3 (Alternate Design) If Ventilation Type 1 or Type 2 is not feasible, an alternative is Type 3; however, this routing configuration will require approximately 50% more airflow than Type 1.

Note: In ventilation airflow calculations, Type 3 systems have a Routing Factor of 1.5.

As shown in Figure 3, outside air is brought into the engine room utilizing fans or large intake ducts.

The inlet is placed as far away as practical

Figure 2

Page 12 All rights reserved.

from heat sources and discharged into the engine room as low as possible. The air them flows across the engine room from the cool air entry point(s) toward the sources of engine and equipment heat; these include the engine, exposed exhaust components, generators, or other large sources of heat.

Ventilation air exhaust fans should be mounted or ducted at the highest point in the engine room.

Preferably, they should be directly over heat sources.

Engine heat will be dissipated with this system, but a certain amount of heat will still radiate and heat up all adjacent engine room surfaces.

If the air is not properly routed, it will rise to the ceiling before it gets to the engines.

This system will work only where the air inlets circulate the air between the engines, for dual engine applications. Air inlets located at the end of the engine room will provide adequate ventilation to only the engine closest to the inlet.

Ventilation Type 3

Figure 3

All rights reserved. Page 13

Ventilation Type 4 (Less Effective Design) If Ventilation Type 1, Type 2 and Type 3 are not feasible, the following method can be used;

however, it provides the least efficient ventilation and requires approximately two and a half times the airflow of Ventilation Type 1.

Note: In ventilation airflow calculations, Type 4 systems have a Routing Factor of 2.5.

As shown in Figure 4, outside air is brought into the engine room using supply fans, and discharged toward the turbocharger air inlets on the engines.

Ventilation exhaust fans should be mounted or ducted from the corners of the engine room.

This system mixes the hottest air in the engine room with the incoming cool air, raising the temperature of all air in the engine room. It also interferes with the natural convection flow of hot air rising to exhaust fans.

Engine rooms can be ventilated this way, but it requires extra large capacity ventilating fans.

Incorrect Airflow Figure 5 illustrates an incorrect method to vent engine room heat.

Although the inlet duct has louvers to direct airflow toward the engine, rising heat will warm the cool air before it can reach the engine.

Ventilation Type 4

Figure 4

Page 14 All rights reserved.

Incorrect Airflow

Multiple Engine Applications The ventilation systems recommended for single and dual engine applications also apply to multiple engine applications.

However, there are additional considerations that are specific to multiple engines.

As previously mentioned, using normal temperature rise guidelines will likely result in the requirement for extremely large volumes of air on multiple engine installations.

Although the guidelines for these sites may be more generous in regard to temperature rise allowance, the ventilation system must be designed to provide sufficiently cool air in the immediate vicinity of the engine and driven equipment to meet their ventilation requirements.

Large multiple engine sites will generally utilize multiple ventilation fans. These sites often use one or two fans for each engine and an additional fan to direct air to the inlet of the generator or other driven equipment.