Fmds0145 Air Conditioning and Ventilating Systems

January 2012 of 23

AIR CONDITIONING AND VENTILATING SYSTEMS

Table of ContentsPage

1.0 SCOPE ................................................................................................................................................... 31.1 Changes ............................................................................................................................................ 3

2.0 LOSS PREVENTION RECOMMENDATIONS ....................................................................................... 32.1 Construction and Location ............................................................................................................... 3

2.1.1 Ducts ..................................................................................................................................... 32.1.2 Automatic Fire Doors and Fire Dampers .............................................................................. 52.1.3 Air Filters ............................................................................................................................... 72.1.4 Fans, Air Intakes, and Outlets ............................................................................................... 72.1.5 Design ..................................................................................................................................... 7

2.2 Protection ......................................................................................................................................... 82.3 Equipment and Processes .............................................................................................................. 92.4 Operation and Maintenance ........................................................................................................... 10

2.4.1 General ................................................................................................................................. 102.4.2 Moisture and Humidity Control .............................................................................................. 12

2.5 Utilities ........................................................................................................................................... 122.6 Ignition Source Control .................................................................................................................. 132.7 Smoke Control ................................................................................................................................ 13

3.0 SUPPORT FOR RECOMMENDATIONS ............................................................................................. 153.1 Air Conditioning and Ventilating System Applications ................................................................... 153.2 Fire and Smoke Hazards ............................................................................................................... 15

3.2.1 Temperature Effect of Fire ................................................................................................... 163.2.2 Stack or Chimney Effect ...................................................................................................... 163.2.3 Mechanical-Air-Handling Systems ....................................................................................... 16

3.3 Panel Filters ................................................................................................................................... 213.3.1 Disposable Filters ................................................................................................................ 213.3.2 Permanent Filters ................................................................................................................ 21

3.4 Dry-Type Extended Surface Filters (Bag Type) ............................................................................ 213.5 Automatic Moving-Curtain Viscous or Dry Impingement Filters ................................................... 223.6 Automatic Self-Cleaning Viscous Air Filters .................................................................................. 223.7 Electronic Air Filters ....................................................................................................................... 22

3.7.1 Electronic Type Filter ........................................................................................................... 223.7.2 Electronic Air Filters with Extended Surface Filter Storage Section ................................... 223.7.3 Electronic Air Filters with Automatic Roll Filter Storage Section ........................................ 23

4.0 REFERENCES ..................................................................................................................................... 234.1 FM Global ...................................................................................................................................... 234.2 Other .............................................................................................................................................. 23

APPENDIX A GLOSSARY OF TERMS ..................................................................................................... 23APPENDIX B DOCUMENT REVISION HISTORY ..................................................................................... 23

List of FiguresFig. 1. Automatic hinged damper at junction of branch duct with main vertical duct. .................................. 4Fig. 2. Fire damper requirements at duct shafts and other fire separations ................................................. 4Fig. 3. Typical smoke control arrangement by using pressurization-exhaust method. ................................ 5Fig. 4. Automatic fire door in duct at major fire separation. Duct to be independent of fire separation. ...... 6Fig. 5. Automatic hinged damper at interior fire cutoff .................................................................................. 6Fig. 6. Louvered automatic damper ............................................................................................................... 7

FM GlobalProperty Loss Prevention Data Sheets 1-45

©2007-2012 Factory Mutual Insurance Company. All rights reserved. No part of this document may be reproduced,stored in a retrieval system, or transmitted, in whole or in part, in any form or by any means, electronic, mechanical,photocopying, recording, or otherwise, without written permission of Factory Mutual Insurance Company.

Fig. 7. Combination fire and smoke dampers. (Courtesy of Sheet Metal and Air ConditioningContractors National Association, Inc.) ............................................................................................... 8

Fig. 8. Typical smoke-control arrangement for filter fires (plan view) ........................................................... 9Fig. 9. Mode of operation of the air conditioning system in case of fire in the filters ................................. 10Fig. 10. Psychrometric chart showing cooling and reheating ...................................................................... 13Fig. 11. Typical smoke control arrangement by pressurizing the protected area (plan view) ..................... 14Fig. 12. Panel filters, permanent (Courtesy of American Air Filter Co.) ...................................................... 17Fig. 13. Dry-type extended surface filters (bag type) (Courtesy of American Air Filter Co.) ...................... 18Fig. 14. Moving-curtain viscous or dry impingement automatic roll filters

(Courtesy of American Air Filter Co.) .............................................................................................. 18Fig. 15. Automatic self-cleaning viscous air filters (Courtesy of American Air Filter Co.) ........................... 19Fig. 16. Electronic air filters (Courtesy of American Air Filter Co.) .............................................................. 20Fig. 17. Electronic air filters with extended surface filter storage section

(Courtesy of American Air Filter Co.) .............................................................................................. 20Fig. 18. Electronic air filters with automatic roll filter storage section (Courtesy of American Air Filter Co.) . 21

List of TablesTable 1. Inspection and Maintenance Schedules ........................................................................................ 12

1-45 Air Conditioning and Ventilating Systems FM Global Property Loss Prevention Data Sheets

©2007-2012 Factory Mutual Insurance Company. All rights reserved.

1.0 SCOPE

This data sheet provides guidelines to prevent or restrict the spread of fire, smoke, and heat through airconditioning and ventilating systems. It also provides some general guidance on smoke control systems.

These guidelines are particularly applicable to occupancies that are highly susceptible to smoke damage.These include large commercial and public buildings, stores and shopping centers, healthcare facilities, dataprocessing areas, clean areas, printing operations, textile processing, photographic material processing, foodprocessing, pharmaceutical, and electronic and semi-conductor industries.

Guidelines also are provided to prevent damage or business interruption resulting from excess humidity ormoisture from contaminating hospital operating and surgical supply rooms caused by air conditioning chillers.For information regarding the contamination of clean rooms refer to Data Sheet 7-7/17-12, SemiconductorFabrication Facilities, and Data Sheet 1-56, Cleanrooms.

1.1 Changes

January 2012. Clarified the use of Class1/Class 2 air filters per revised UL listing process. Added detail onMERV ratings for filters.

2.0 LOSS PREVENTION RECOMMENDATIONS

2.1 Construction and Location

2.1.1 Ducts

2.1.1.1 Use ducts constructed of steel, aluminum, concrete, masonry, or FM Approved materials. Do notuse foam plastics, which will generate additional smoke in a fire.

2.1.1.2 Construct duct linings and coverings (including thermal insulations) of noncombustible orFM Approved material. Do not install internal duct linings constructed of foam plastic. Interrupt the lining atfire dampers so as not to interfere with their operation. Also, interrupt the lining and coverings at the heatsource area in a duct system containing electric resistance or fuel burning heaters. An alternative is to providea clear space of the liner near fire dampers or heat source areas.

2.1.1.3 Do not extend duct coverings through walls or floors that need a fire-resistive rating.

2.1.1.4 An attic, basement, or concealed space may be an integral part of a duct system, but protect it fromfire hazards that may expose the duct system.

2.1.1.5 Do not use hallways as plenums.

2.1.1.6 Provide a minimum 6 in. (150 mm) clearance between metal ducts and stored combustible material.Provide a minimum 2 in. (50 mm) clearance between metal ducts and combustible construction.

2.1.1.7 Where ducts pass through walls and floors serving as fire subdivision, limit the opening in theconstruction around the duct to no larger than 1⁄2 in. (13 mm) average clearance on all sides. Seal the openingwith FM Approved penetration fire stop material to obtain a rating equal to that of the wall or floor.

2.1.1.8 Protect ducts that pass through concealed spaces of combustible construction or that are locatedinside combustible partitions or walls with 1⁄4 in. (6 mm) noncombustible insulating material, or maintain aminimum clearance of 2 in. (50 mm) between ducts and all combustible construction. Fill the spaces betweenthe ducts and the combustible construction solidly with brick, mineral wool, or other noncombustible material.Maintain the integrity of firestopping at penetrations.

2.1.1.9 Enclose ducts that pass through more than one floor needing protection of vertical openings withwalls having a fire rating equal to that of the floors. A fire-resistive shaft used as a duct need not be additionallyenclosed (Figs. 1, 2 & 3).

a) The enclosure of ducts is not required for branches that are cut off from the main portion of the ductby fire dampers (Fig. 2).

b) When ducts extend through only one floor, and fire dampers are installed at each point where the flooris penetrated, the fire dampers may be used in lieu of the enclosure.

Air Conditioning and Ventilating Systems 1-45FM Global Property Loss Prevention Data Sheets


c) Do not locate two or more ducts serving separate floors within the same fire-resistive enclosure unlessfire dampers are installed where each branch extends from the enclosure.

2.1.1.10 Do not install ducts adjacent to unprotected structural members. To be effective, fireproof structuralmembers before adjacent ductwork is installed.

2.1.1.11 Design and install ducts in accordance with national trade association specifications.

Note: The Sheet Metal and Air Conditioning Contractors National Association Inc. (SMACNA) publishesdesign and installation specifications for metal and fibrous glass ducts.

2.1.1.12. Identify air conditioning and ventilating systems that support critical processes or storage that, ifunable to function properly, would cause significant exposures from interrruption to operations or product

Fig. 1. Automatic hinged damper at junction of branch duct with main vertical duct.

Fig. 2. Fire damper requirements at duct shafts and other fire separations



spoilage (example: electronic data processing, telecommunications). Inspect and test these systems asoutlined in Section 2.4 with records maintained on file.

2.1.2 Automatic Fire Doors and Fire Dampers

2.1.2.1 Design duct systems so ducts do not pass through walls or floors serving as fire subdivisions.However, if penetration is necessary, install automatic fire doors or dampers in accordance with Data Sheet1-22, Maximum Foreseeable Loss, and Data Sheet 1-23, Protection of Openings in Fire Subdivisions.SMACNA is also a useful reference for the arrangement of fire dampers and fire damper frames passingthrough walls or floors.

2.1.2.2 Wherever ducts pass through interior horizontal fire subdivisions of three-hour-fire resistance ratings,protect openings 18 in. (455 mm) or more in diameter or on longest dimension by a door arrangement havingan overall fire rating equal to that of the subdivision (Fig. 4). At openings not exceeding 18 in. (455 mm)in diameter or longest dimension, use 1⁄8 in. (3.2 mm) steel plates (Fig. 5).

2.1.2.3 Arrange dampers as follows:

Fig. 3. Typical smoke control arrangement by using pressurization-exhaust method. Fire is in Floor No. 3. Dampers SD1,SD2, SD4, SD5, and ED3 remain open. Dampers SD3, ED1, ED2, ED4, and ED5 will close. (section view)



a) FM Approvals does not presently Approve fire or smoke dampers. Equip walls that have less thanthree hours fire resistance with automatic fire dampers of either the solid or louvered type (Figs. 1,5 & 6).

b) Install automatic fire dampers either at the outlet and inlet openings in the main vertical duct, orat the duct penetration in walls or floors serving as fire subdivisions (Fig. 2).

c) For solid type dampers, use No. 16 U.S. ga (1.6 mm) steel on ducts up to 18 in. (455 mm) in diameteror longest dimension, No. 12 U.S. ga (2 mm) for ducts up to 36 in. (910 mm) in diameter or longestdimension, and No. 7 U.S. ga (4 mm) for ducts above 36 in. (910 mm) in diameter or longest dimension.

d) Construct louvered-type automatic dampers of No. 18 U.S. ga (1.3 mm) steel, provided theindividual louvers are not over 6 in. (150 mm) wide.

2.1.2.4 When duct smoke detectors are used for interlocking with fans, provide and arrange detectors asoutlined in Data Sheet 5-48, Automatic Fire Detection.

2.1.2.5 Arrange fire doors and fire dampers to close automatically, in the direction of the air movementwhenever possible, and to remain tightly closed upon operation of a fusible link, other FM Approvedheat-actuated devices, or FM Approved smoke detectors. Use fusible links with a temperature approximately50°F (28°C) above the maximum temperature that would normally be encountered within the system, butnot less than 165°F (74°C).

Fig. 4. Automatic fire door in duct at major fire separation. Duct to be independent of fire separation.

Fig. 5. Automatic hinged damper at interior fire cutoff



2.1.2.6 Equip hinged fire doors and dampers with spring catches to hold them closed, with the pins of hingesmade of corrosion-resistant material.

2.1.2.7 When the damper is intended for both fire-stopping and smoke-stopping, use combination smokedetectors (sensitive to both heat and smoke) for activation.

2.1.2.8 When fire dampers and doors are designed to serve the dual function of fire-stopping and smoke-stopping, provide special features such as gaskets to ensure adequate sealing against any smoke leakage.

2.1.2.9 Design fire doors and dampers at duct openings in fire walls or at floor levels so the destruction ofthe duct will not affect the operation of fire walls or dampers. This can be accomplished by mounting the unitsin the fire wall or floor opening by a collar held in place with perimeter angles on each side of the opening.Then the ductwork is brought into the collar but not through the opening (Figs. 1, 4, 5, 6 and 7).

2.1.3 Air Filters

2.1.3.1 Use noncombustible filters in all air conditioning systems, when possible. If combustible filters areused, ensure they are listed in accordance with UL 900, Standard for Safety Air Filter Units or equivalent localstandards.

2.1.4 Fans, Air Intakes, and Outlets

2.1.4.1 Locate fan motors outside of ducts.

2.1.4.2 Locate inside air intakes and outlets at least 3 in. (75 mm) above the floor. When located less than7 ft (2.1 m) above the floor, provide them with a substantial grill or screen of 1⁄2 in. (13 mm) steel mesh forprotection.

2.1.4.3 Locate the outdoor air intakes where there is the least possibility of drawing smoke back into theair conditioning and ventilating systems. Since smoke normally rises, the lower the intake, the less possibilityof drawing in smoke. As a less desirable alternative, provide charcoal filters or other special air filtrationdevices at the air intakes.

2.1.5 Design

2.1.5.1 Provide emergency power for critical air conditioning and ventilating systems.

Fig. 6. Louvered automatic damper



2.2 Protection

2.2.1 In cases where there is the possibility of accumulating combustible contaminants in the noncombustiblefiltering system, do the following:

a) Provide sprinkler protection in filter systems with capacities of 10,000 ft3/min (283 m3/min) and above.Arrange the sprinklers to wet the entire surface of the filters upon operation. Install sprinklers on a delugesystem using ordinary-hazard pipe schedule. Activate the system by combination smoke detectors(sensitive to heat and smoke) arranged in accordance with Data Sheet 5-48, Automatic Fire Detection.

b) To prevent smoke spread from the filters to the conditioned areas, do the following:

i) Provide a one-hour-rated fire door or damper downstream from the filters (Fig. 8). Arrange the dooror damper for closing by the activation of combination smoke detectors. Arrange the smoke detectorsin accordance with Data Sheet 5-48. Do not cross-zone the system. (The same detection system canbe used to activate the deluge system.)

ii) Install an exhaust fan to exhaust smoke to the outside in case of a fire in the filters. Activate theexhaust fan by combination smoke detectors (Fig. 8).

iii) Arrange the supply and return fans of the air conditioning system to shut down on activation ofcombination smoke detectors.

iv) Provide duct detectors in supply and/or return ducts as outlined in Data Sheet 5-48.

Note: These same combination smoke detectors can be used to activate the deluge sprinkler system.

c) Protect filters with capacity less than 10,000 ft3/min (283 m3/min) in accordance with RecommendationNo. 2.2.1 b above.

2.2.2 Protect combustible filters in an air conditioning system as follows:

a) Provide sprinkler protection in filtering systems with capacity over 5000 ft3/min (142 m3/min) inaccordance with Recommendation No. 2.2.1 a, with the exception that ordinary closed heads areacceptable.

Fig. 7. Combination fire and smoke dampers. Operation: (A) Fire damper mode: high temperaturemelts fusible link closing fire damper. (B) Smoke damper mode: smoke detector upon sensingheat/smoke actuates damper motor to close damper. (Courtesy of Sheet Metal and AirConditioning Contractors National Association, Inc.)



b) To prevent smoke spread from the filters to the conditioned areas, provide protection in accordancewith Recommendation No. 2.2.1 b.

c) Protect filters with capacity less than 5000 ft3/min (142 m3/min) in accordance with RecommendationNo. 2.2.1 b.

2.2.3 As an alternative to Recommendation No. 2.2.1 b, design the return-exhaust fan and other equipmentof the air conditioning system (dampers, etc.) to exhaust the smoke from a filter fire as shown by Figure9.

2.2.4 Provide adequate sprinkler water drainage in the filter assembly when sprinklers are installed. (Referto Data Sheet 7-78, Industrial Exhaust Systems.) Provide a u-bend water seal in the drainage line as needed.

2.2.5 Do not introduce combustible environments and electrical wiring or combustible pneumatic tubing inair conditioning ducts. However, when the presence of combustible materials in the air conditioning systemis absolutely necessary, or when the ducts themselves are combustible, provide sprinkler protection asrecommended in Data Sheet 7-78, Industrial Exhaust Systems.

2.2.6 Combustible exterior duct linings, e.g., thermal insulations of materials such as foamed plastic, requireprotection. Building sprinkler protection is generally sufficient, although materials like elastomeric insulationsmay need special treatment. In unsprinklered areas, one can provide a thermal barrier or submit the materialfor risk service testing to assess it’s flammability.

2.3 Equipment and Processes

2.3.1 Enclosed fan-cooled motors are preferable, but open squirrel-cage induction motors can be used.

2.3.2 Protect motors located inside air ducts or plenum chambers against overheating with a deviceresponsive to motor temperature and integral to the motor.

Fig. 8. Typical smoke-control arrangement for filter fires (plan view)



2.4 Operation and Maintenance

2.4.1 General

2.4.1.1 When FM Approved fibrous glass ducts are used, the following restrictions apply.

a) Use ducts only in horizontal installations.

b) Ensure the temperature of the air handled by the ducts does not exceed 250°F (121°C).

c) Ensure the maximum static pressure in the duct does not exceed ±2 in. of water gauge (±500 Pa).

d) Ensure the maximum air flow velocity in the duct does not exceed 2000 ft/min (610 m/min).

e) Do not use ducts for the purpose of smoke control.

f) When mounting equipment, dampers, control motors, etc., adequately reinforce and support the fibrousglass duct system to accommodate the additional weight of material and equipment without damage tothe duct material.

g) Do not use fibrous glass ducts outdoors.

h) Use fibrous glass ducts only in areas of noncombustible construction and occupancy. In areas ofcombustible construction or combustible loading, use fibrous glass ducts only if sprinkler protection isprovided in these areas, and the ducts are not used for smoke control.

2.4.1.2 Make ducts reasonably tight throughout with no openings other than those required for properoperation and maintenance of the system. Wired glass is acceptable for inspection windows in ducts.

2.4.1.3 Construct plenums and ducts, other than vertical ducts, so the interior is accessible for cleaningaccumulations of dust and combustible material. Provide cleanout openings at approximately 20 ft (6 m)intervals and at changes of direction. Removable grills are acceptable as cleanout openings. When plenumspose fire and smoke hazards, provide protection as described in Recommendations 2.7 and 2.2.5.

Fig. 9. Mode of operation of the air conditioning system in case of fire in the filters



2.4.1.4 Provide suitable hand-hole openings with tightly fitted covers near the fire doors or dampers to makethem accessible for inspection and maintenance.

2.4.1.5 Install fans to be readily accessible for inspection and maintenance. Secure these to substantialsupports.

2.4.1.6 Examine the fresh-air intake when ducts are inspected. Items to be noted are accumulations ofcombustible material near the intake, presence of buildings or structures that may present, an exposure tothe intake allowing smoke and fire to be drawn in, and the operating condition of any automatic damperdesigned to protect the opening against an exposure fire.

2.4.1.7 If accumulations of combustible material are noted, remove them immediately, and makearrangements to avoid further accumulations. This could include things such as exposed plastic foam orroofing tar within the HVAC condensate pans. Thereafter, make inspections more frequently. If newly erectedexposures are present, provide adequate protection at the intake.

2.4.1.8 Make quarterly inspections to determine the amount of dust and waste material in the ducts (bothdischarge and return). If, after several inspections, such frequent inspection is found to be unnecessary, adjustthe interval between inspections to suit the conditions.

2.4.1.9 Clean ducts whenever inspection indicates the need. Cleaning may be by vacuum or hand brushing.

2.4.1.10 Clean cooling and heating coils, if necessary, at the time the ducts are cleaned.

2.4.1.11 Inspect plenum chambers quarterly. If, after several inspections, such frequent inspection is foundto be unnecessary, adjust the interval between inspections to suit the conditions.

2.4.1.12 Clean plenum chambers whenever inspection indicates the need. Do not use plenum chambersfor storage.

2.4.1.13 Keep all air filters free of excess dust and combustible material. Renew or clean unit filters whenthe resistance to air flow has increased to two times the original resistance, or when the resistance hasreached a value of recommended replacement by the manufacturer. Use draft gauges of a type that willoperate a warning light or produce an audible signal when excessive dust loads have accumulated. If thefilters are of the automatic liquid-adhesive type, regularly remove sludge from the liquid-adhesive reservoir.

2.4.1.14 Never clean or re-use filters designed to be thrown away after use.

2.4.1.15 Check the system activating devices, such as fusible links, heat and smoke detectors, and electricthermostats to see that they are not loaded with residue or otherwise impaired.

2.4.1.16 Have adequately trained personnel inspect and test heat and smoke detector systems. Followmanufacturer’s or installer’s recommendations in maintaining, inspecting, and testing the equipment.

2.4.1.17 Arrange the overall system so that it can be adequately tested every six months by simulatingemergency-mode conditions.

2.4.1.18 Ensure all equipment requiring servicing and testing is readily accessible. Provide practical meansfor adequate cleaning.

2.4.1.19 Inspect electrical equipment of automatic filters quarterly, observing the operation cycle to see thatthe motor, relays, and other controls function as intended. Inspect drive motors and gear reductions at leastsemiannually, and lubricate these when necessary.

2.4.1.20 Inspect fans and fan motors at least quarterly, and clean and lubricate when necessary. Do not allowoil to run onto the fan blades. Check fans for alignment, and to see that they are running freely.

2.4.1.21 Examine automatic fan controls at least once a year to ensure they are in operable condition.

2.4.1.22 Examine each fire door and fire damper once a year to ensure it is in good operating condition,giving special attention to hinges and other moving parts.

2.4.1.23 Never perform hot work operations on ductwork containing combustible deposits except as a lastresort, and then only after a thorough cleaning. Use the FM Global Hot Work Permit System for cutting andwelding (refer to Data Sheet 10-3, Hot Work Management).

2.4.1.24 Use an inspection form to obtain a thorough inspection. Ensure the form applies to the system orsystems involved, listing the items needing attention.



See Table 1 for a detail of many of the required inspections and tests for equipment associated with airconditioning and ventilating systems.

Table 1. Inspection and Maintenance Schedules

Device FrequencyInspection of ducts Quarterly

Inspection of plenum chambers QuarterlyInspection of filter electrical equipment Quarterly

Inspection of fan and fan motors QuarterlyTest overall air conditioning/ventilating system Biannually

Inspect drive motors and gear reductions BiannuallyInspect automatic fan controls Annually

Inspect each fire door and fire damper Annually

2.4.2 Moisture and Humidity Control

To control moisture build-up in the air conditioning and ventilating systems of sensitive occupancies, adhereto the following recommendations:

2.4.2.1 Interlock the air handler supply fans serving hospital surgical areas or similar occupancies with airhandler cooling coil temperature, or with chilled water flow and temperature at the chiller. However, a slighttime delay may be needed for contamination control and completioin of ongoing hospital surgical procedures.If the coil temperature is high (about 10% over setpoint), or if either chilled water flow is low or chilled watertemperature is high, arrange the fan to shut down and not start again until chilled water conditions are withinan acceptable range. Note that paddle- or sail-type flow switches are commonly used and are not as reliableas other types of flow sensors such as differential pressure transmitters; a broken paddle can shut down thechiller.

An alternative method is to interlock the chiller unit to shut down the fan. Ensure the supply fan does notstart (by operating procedure or startup permissive) until the chilled water temperature has reached itssetpoint. If two chillers are used, have the shutdown (safety control shutdown) of either one cause a fan trip(since one chiller might not carry the load) unless there is also a chilled water temperature shutdown interlockin series with the chiller interlocks, which can then be in parallel. Ensure the shutdown of both chillers,manual or automatic, causes a fan trip.

If there is a backup system that can be put on line quickly and automatically such as a direct expansion(refrigerant) coil , the chilled water interlocks need not shut down the fan. They will be needed to initiate startupof the backup cooling system, however, and also can be used as a startup permissive for the air handlersupply fan(s).

The chilled water interlocks can be bypassed during winter months if there is no danger of hot, humid outsideair (depending upon geographic location). If an outside dewpoint transmitter is installed, this device can beused in parallel with the chilled water interlocks; if the outside dewpoint remains below the lowest anticipatedindoor room temperature, the fan can operate.

2.4.2.2 Provide reheat to control humidity, using either local coils or a central reheat coil. Keep reheat inservice. Never mix humid outside air with conditioned air. See Figure 10. Develop a contingency plan forrepair/replacement of reheat coils. Have a qualified engineer review and approve the HVAC psychrometrics,system and controls design and customize the overall design to the local conditions.

2.4.2.3 Protect the chilled water system with a relief valve to prevent overpressurization caused by a faultymakeup water valve. Overpressurizing the pipes has caused underground pipe cracking and unexpectedshutdown of the chillers.

2.5 Utilities

2.5.1 Install electrical wiring and equipment in accordance with the National Electrical Code (NFPA 70).

2.5.2 Install electric lights located within the equipment enclosure of the system in jacketed globes.

2.5.3 Ensure motors are readily accessible for inspection, lubrication, and maintenance.



2.6 Ignition Source Control

2.6.1 Protect air-intake openings with automatic fire doors or dampers if the fire exposure is severe. ProvideFM Approved heat-activated devices at air-intake openings to shut down fans in case of exposure fires.

2.6.2 Do not recirculate air from any space in which noticeable quantities of flammable vapors or combustibledust are given off. This does not consider industrial exhaust systems covered by other FM Global data sheets.

2.6.3 Screen and locate the outside air intake to avoid drawing in combustible or other foreign materialsand to lessen the hazard from exposure fires. Also remove any accumulated rubbish or other waste fromthe vicinity of all air intakes.

2.6.4 Protect open motors having commutators or sliding contacts so that sparks from the motors cannotreach adjacent combustible material.

2.7 Smoke Control

2.7.1 The air conditioning system can be designed to control smoke and thus lessen smoke damage by usingany one of the following methods.

Outside air at point 1 (80°F, 80% RH) is cooled to point 2 (70°F, 100% RH). The air is further cooled to the cooling coiltemperature at point 3 (50°F, 100% RH). The dewpoint of the outside air at point 1 is 70°F. If the air is not reheated (points 3 to4), the inside air may be saturated. Fogging may occur if the outside air is admitted to the saturated room when the insidetemperature is below 70°F.

Fig. 10. Psychrometric chart showing cooling and reheating



a) Pressurization-Exhaust Method. The air conditioning system in this method is designed to switch toa smoke control mode upon detection of smoke in the fire area (Fig. 3). This operation automatically putsthe fire area under exhaust, and areas adjacent to the fire into supply. To accomplish this, ensure thereturn-exhaust damper(s) in the fire area remain open, and the supply damper(s) close on smoke detection.In all other areas adjacent to the fire, ensure the supply dampers remain open and the exhaust-returndampers close on smoke detection. The intent is to prevent smoke spread to the adjacent areas of thefire and purge the smoke from the fire area via exhaust (Fig. 3).

b) Pressurization Method. The pressurization method can be used to protect a property against smokedamage from exposure fires. This can be accomplished by designing the air conditioning system of theexposed property to pressurize it by maintaining the supply damper(s) in the open position and closing theexhaust damper(s) on smoke detection (Fig. 11).

2.7.2 Design the smoke-control system to maintain the areas adjacent to the fire area with a pressure of atleast 0.20 in. water gauge (50 Pa) higher than the fire area.

Fig. 11. Typical smoke control arrangement by pressurizing the protected area (plan view)



2.7.3 Activate the smoke-control system by using FM Approved smoke detectors located within the zonecovered by the specific smoke-control system. Arrange the type, location, and spacing of detectors inaccordance with Data Sheet 5-48, Automatic Fire Detection.

2.7.4 Evaluate duct materials and other air conditioning equipment for their fire hazards, their ability to conveysmoke and gases, their ability to withstand additional pressure (both positive and negative) from the supplyand exhaust systems, and their ability to maintain structural integrity under fire exposure conditions. Seeguidelines for suitable materials in Data Sheet 7-78, Industrial Exhaust Systems.

2.7.5 Ensure dampers used for the smoke control arrangement have the dual function of stopping both fireand smoke, and are equivalent to the fire resistance rating of the assembly (Fig. 7).

2.7.6 Do not pass supply and exhaust ducts serving one smoke zone through another smoke zone, unlessthey are enclosed in a fire-smoke resistant enclosure (Fig. 3).

3.0 SUPPORT FOR RECOMMENDATIONS

3.1 Air Conditioning and Ventilating System Applications

This data sheet applies to air duct systems that move air mechanically and are used for heating, cooling,and ventilating. It does not apply to systems in dwellings, to systems for removal of flammable or corrosivevapors and residues, or to systems for conveying dust, stock, or refuse by means of air currents.

An air conditioning system consists of fans, ducts, controls, dampers, filters, intakes, and heating and/orcooling apparatus that remove used air from occupied spaces and recondition it. The air is then circulatedback to occupied spaces to provide comfort to occupants or to provide a specific set of environmentalconditions established within the conditioned space. The air conditioning system provides the simultaneouscontrol of temperature, humidity, air motion, noise level, air cleanliness, and quality of ventilation.

In recent years, the characteristics of air-handling systems have changed. While separate steel duct systemshave not been abandoned, many air-handling systems are using new methods to accomplish air distribution.Air is moved through cells integral with the structural load-bearing elements of the floor slabs, through ceilingvoids, through shafts that act simultaneously as air ducts and enclosures for air ducts, and through variousother means. Discharges are made through light fixtures, slits, and perforations. Air may be induced,recirculated, or exhausted. Steel ducts are frequently insulated externally or internally for thermal, vapor, orsound control. There are also new duct materials. Aluminum and glass fiber boards are commonly used forducts, and frequent proposals are made for the use of plastics or paper-based ducts or channels. Flexibleconnectors, used in great numbers, frequently employ various plastics. The use of plastic ducts should bediscouraged because they pose serious fire and smoke hazards.

One important function of many air conditioning systems is to control relative humidity. Primary and secondarycooling coils are often provided to cool the air as much as possible. The air is then reheated to a specifiedtemperature, which lowers the relative humidity. Without reheat, room air could become saturated (100%relative humidity). This increases the chance that room air fogging (condensation of water vapor into moisture)and condensation on surfaces will occur.

3.2 Fire and Smoke Hazards

The principal hazard associated with air-handling systems is the propagation of fire and/or smoke throughthe air movement channels. The use of new types of interior finishes and plastic furnishings has increased theproblem of smoke development in a fire. Some of these new materials can release great quantities of smokeand toxic gases when exposed to fire conditions.

Smoke in untenable concentrations can migrate to remote parts of a building in a matter of minutes viaair-handling systems. On numerous occasions fire has been confined to its area of origin with limited firedamage, but smoke has spread through the air conditioning system to other areas, causing extensive damageand hampering manual fire fighting efforts.

The major factors that cause smoke to spread to areas outside the fire area are 1) temperature, 2) stackor chimney effect, and 3) mechanical air handling systems.



3.2.1 Temperature Effect of Fire

An expansion process is created during the initial stages of fire due to a continuous increase in temperature.This process causes smoke to move from the vicinity of the fire to adjacent areas, and it continues until thetemperature rise stops.

3.2.2 Stack or Chimney Effect

Stack or chimney effect is air movement resulting from the difference in density between two interconnectedcolumns of air at different temperatures. Hot smoke and gases from a fire generally move upward in climateswhere the outside temperature is lower than the indoor temperature. If the smoke temperature is higher thanthe ambient temperature, smoke rises. If the smoke temperature is lower than the ambient temperature,smoke descends.

In summer, when the outdoor temperature is higher than inside, the flow pattern is the reverse of that inthe winter. However, air flows are considerably lower in the summer because the inside-to-outsidetemperature difference is much smaller.

The stack or chimney effect, therefore, accounts for most air movement in buildings under normal conditions.It also is responsible for the widespread distribution of smoke during the early stages of a fire. This is mostevident during a smoldering fire or in areas far from the fire where the smoke has cooled off.

3.2.3 Mechanical-Air-Handling Systems

An air-handling system can rapidly transfer smoke from a fire area to other parts of the building. Centralsystems, therefore, have a potential for spreading smoke far beyond the origin of the fire.

This exposes a large area of the property to smoke damage and hampers manual fire fighting. For this reason,the system is sometimes shut down during fires. The ducts interconnecting various floors or areas may stillprovide significant paths for smoke migration, however, even though the system is shut down.

The ducts and other components of the system provide a ready means of spreading fire, smoke, and toxicgases throughout a building.

3.2.3.1 Plenums

A plenum is an air compartment or chamber in which one or more ducts are connected, and which formspart of an air-distribution system.

Plenums generally are constructed of galvanized steel or aluminum. However, the space above suspendedceilings or below raised floors is frequently used as a supply, return, or exhaust plenum to reduce the amountof sheet metal work. The plenum chamber is connected with the conditioned area by openings through eitherthe floor or ceiling. These spaces may be insulated and they are generally used to run electrical wiring andother auxiliary services. When a fire occurs in this occupancy, fire and smoke may spread to the conditionedarea.

3.2.3.2 Plastic Ducts

Despite being a hazard, plastic ductwork is used in buildings. Fire can quickly penetrate plastic ductworkfrom either the exterior or the interior. Invariably, such ductwork will add fuel to the fire and will release largevolumes of smoke. Fiberglass-reinforced plastic ducts are solid, high-density materials generally 1⁄8 in. (3.2mm) to 1⁄4 in. (6.35 mm) thick with a hard, shiny surface. PVC and polypropylene are other plastics oftenused for ductwork, although their use is predominantly industrial.

3.2.3.3 Fibrous Glass Ducts

Some fibrous glass duct materials of low combustibility have been FM Approved. Some of the fire testsconducted on this material have shown that, under severe fire exposure, the duct will spread fire and collapse.Consequently, ductwork fabricated of this material should be used only in buildings of noncombustibleconstruction and occupancy, unless automatic sprinklers are provided.

Fibrous glass ducts consist of a low-density composition of noncombustible glass fibers and a small quantityof resin binder, preformed or prefabricated into units of circular and rectangular cross-section and havingan exterior jacket of aluminum foil or pigmented film.



The fibrous glass duct can be used in mechanical air-handling systems that operate from -2 to 2 in. (-500to 500 Pa) water gage static pressure with a conveying velocity of 2000 ft/min (610 m/min) or less. This typeof system is known as a low-pressure ductwork system.

Space limitations in modern buildings have restricted the size of air conditioning ducts. Therefore, highvelocities must be employed to convey the necessary volume of air. The increased velocities are accompaniedby higher duct friction losses. In order to maintain flow against the higher duct friction, it is necessary to havegreater pressures at the air source and through the ducts.

The terms ‘‘high velocity’’ and ‘‘high pressure’’ refer to design and construction requirements for a velocityabove 2000 ft/min (610 m/min) and static pressure above 2 in. (500 Pa) or below -2 in. (-500 Pa) water gage.Smoke removal systems usually operate within this high-velocity range; fibrous glass ducts are suitable onlyfor low-pressure duct work systems, and thus, not for smoke removal purposes.

3.2.3.4 Filters

Noncombustible filters can collect combustible dust and lint during normal air conditioning operation.Therefore, the combustibility and smoke generation of a filter after a period of service partly depends on thenature and quantity of contaminants collected. Consequently, each case must be evaluated individually.

The most common types of filters used in modern air conditioning systems are panel filters (Fig. 12), dry-typeextended surface filters (bag type) (Fig. 13), automatic moving-curtain viscous or dry impingement filters(Fig. 14), automatic self-cleaning viscous air filters (Fig. 15), and electronic air filters (Figs. 16, 17 & 18).

Minimum efficiency reporting value (MERV) ratings are used to quantify the ability of an air conditioning filterto remove dust from the air as it passes through the filter and as a means of evaluating filter efficiency. HigherMERV ratings mean fewer dust particles pass through the filter. MERV ratings range from 1 to 16. Filterstypically used for residences are often in the 1 to 4 MERV range and usually disposable filters. Filters forcommercial and industrial use are typically in the 9 to 12 MERV range. Hospitals and other very cleanenvironments will use filters in the 13 to 16 MERV range.

Fig. 12. Panel filters, permanent (Courtesy of American Air Filter Co.)



3.2.3.5 Fire Doors and Dampers

Fire subdivisions are vital in the control of fire spread. Consequently, openings in fire subdivisions must beprotected. Fire doors and dampers can protect openings in fire subdivisions through which ducts, registers,and grills penetrate.

Fire doors and fire dampers are primarily for the prevention of fire spread, while smoke dampers are forthe prevention of smoke spread. A fusible link responds to a rise in temperature, which is an indication offire, but a smoke detector should be used if it is important to sense cool smoke. Fire dampers or doors canbe arranged to have a dual function of stopping fire and/or smoke. To perform dual functions it is necessaryto provide a release mechanism that is both thermally responsive and sensitive to signals from smokedetectors (Fig. 7).

Fig. 13. Dry-type extended surface filters (bag type) (Courtesy of American Air Filter Co.)

Fig. 14. Moving-curtain viscous or dry impingement automatic roll filters (Courtesy of American Air Filter Co.)



Fig. 15. Automatic self-cleaning viscous air filters (Courtesy of American Air Filter Co.)



Fig. 16. Electronic air filters (Courtesy of American Air Filter Co.)

Fig. 17. Electronic air filters with extended surface filter storage section (Courtesy of American Air Filter Co.)



The air-conditioning system can spread smoke rapidly, and is normally shut down in the event of fire. However,special operating modes, other than shutdown, may be devised in particular situations to help restrict thespread of fire and smoke (Figs. 3 & 10). Such systems must be designed with a knowledge of the fire andsmoke situations that may occur, of the dominant mechanisms of smoke movement, delineation of smokecontrol objectives, and building air leakage characteristics. (See Recommendation No. 2.4.6.)

The sprinkler alarm may be interconnected with the smoke control system to activate this system in casethe smoke and heat detectors fail.

3.3 Panel Filters

3.3.1 Disposable Filters

Disposable panel filters are widely used as pre-filters to higher efficiency filters or to protect heating andcooling coils from becoming coated with dirt. These filters are made up of coarse fibers with high porosity.The filter media is coated with a viscous substance, such as oil, which acts as an adhesive on particles thatimpinge on the fibers.

3.3.2 Permanent Filters

Permanent metal filters are coated with a viscous adhesive to increase dust holding capacity. When the filtersare fully loaded they are cleaned, a fresh coating of adhesive is applied, and they are reinstalled (Fig. 12).

3.4 Dry-Type Extended Surface Filters (Bag Type)

The media used in this type of filter are random fiber mats or blankets of varying thickness, fiber, size, anddensities. Media of bonded glass fiber, cellulose fibers, wool felt, asbestos, synthetics, and other materialshave been used commercially. The medium in filters of this class is frequently supported by a wire frame in

Fig. 18. Electronic air filters with automatic roll filter storage section (Courtesy of American Air Filter Co.)



the form of pockets or V-shaped pleats. In other designs, the medium may be self-supporting because ofinherent rigidity or because air flow inflates it into extended form (Fig. 13). When the filters are filled with dirt,they are discarded and replaced with clean media.

3.5 Automatic Moving-Curtain Viscous or Dry Impingement Filters

Automatic moving-curtain viscous filters are available in two main types. In one type, random fiber mediumis furnished in roll form. Fresh medium is fed automatically across the face of the filter, while the dirty mediumis rewound onto a roll at the bottom. When the roll is exhausted, the tail of the medium is wound onto thetake-up roll, and the entire dirty roll thrown away. A new roll is then installed, and the cycle repeated (Fig.14). Random fiber (nonwoven) dry media of relatively high porosity also are used in moving-curtain (roll) filtersfor general ventilation service (Fig. 14). The arrangement is similar to the moving-curtain viscous impingementtype filters. The main difference is that the medium is dry.

3.6 Automatic Self-Cleaning Viscous Air Filters

This type of filter is made in vertical self-contained sections of one base width and in a wide range of standardheights of 6, 8, 9, 10 and 12 ft (1.8, 2.4, 2.7, 3 and 3.65 m).

Each section consists of a base or reservoir assembly and top assembly joined by vertical side panels. Thepanels are arranged to overlap and form filtering curtains across the air openings at front and rear of thefilter (Fig. 15). The traveling curtain intermittently passes through the viscous adhesive reservoir, where themedia give up dust load and at the same time take on a new coating of viscous adhesive. The media thusform a continuous curtain which moves up one face and down the other face. The media curtain, being formedof metal and continually cleaned and renewed with fresh adhesive, lasts the life of the filter mechanism.

Periodically, the precipitated dirt must be removed from the viscous adhesive reservoir. This is generally doneby scraping the dirt into a tray, which can be conveniently suspended from the reservoir lip.

3.7 Electronic Air Filters

Electronic air filters use electrostatic principles to collect particle matter. However, they operate on lowervoltages than the type commonly used in industrial systems. The more commonly used filters are theElectronic type (Fig. 16), the Electronic Air Filters with Extended Surface Filter Storage Section (Fig. 17), andthe Electronic Air Filters with Automatic Roll Filter Storage Section (Fig. 18).

3.7.1 Electronic Type Filter

The collector plate assembly in this type of filter consists of alternately grounded and charged aluminumplates (Fig. 16). A strong electrostatic field is set up between the plates by applying approximately 5800 voltsdirect current to the charged plates. Upon entering the field, the charged dust particles are repelled by theplates of the same polarity and attracted to the plates of opposite polarity. As these particles are precipitatedonto the plates, they are held there by a viscous adhesive coating applied to the plates.

The filters are equipped with a motorized vertical washing header and adhesive applicator header completewith spray nozzles. The completely automatic washing and adhesive cycle may be initiated manually orautomatically through a timing mechanism preset for job conditions. Frequency of maintenance varies withdirt load (approximately 2 to 6 weeks).

3.7.2 Electronic Air Filters with Extended Surface Filter Storage Section

The filter consists of a close-coupled agglomerator section and a storage section (Fig. 17). The agglomeratorsection contains the all-aluminum plates. The ionizer voltage is 12.0 KV and the plate voltage 5.8 KV. Allinsulators are shielded from the dirty air stream.

The storage section consists of 2 by 2 ft (0.6 by 0.6 m), high-efficiency, dry-type replaceable cartridges. Thecartridges are made of fiberglass fibers, supported on the air-leaving side by flexible scrim. This preventsthe metal boxes from closing the grid. The replaceable cartridges are collapsible and do not require storagespace of more than 2 by 2 by 4 ft (0.6 by 0.6 by 1.2 m) per cartridge.



Minute dust particles are electronically attracted and adhere to each other on the dry plates of theagglomerator section. As the trapped dust particles build up (agglomerate) on the collector plates, the massincreases until the accumulation is swept off the plates by the air stream. Dirt is then carried onto the mediain the storage section.

3.7.3 Electronic Air Filters with Automatic Roll Filter Storage Section

The unit consists of an agglomerator section and storage section combined into one integral filter (Fig. 18).

The electronic precipitation principle employed in the agglomerator section is a method of removing dustand smoke from the air by electrical attraction. This is accomplished by imposing an electrostatic charge ofdefinite polarity on the dust particle through ionization, and collecting the charged particles on metal platesof opposite polarity.

Minute dust particles are electrostatically attracted and adhere to each other on the dry plates of theagglomerator section. As the trapped dust particles build up on the collector plates, the mass increases untilthe accumulation is swept off the plates by the air stream. This accumulation is then carried onto the bondedglass fiber media of the storage section.

The glass fiber blanket is fed automatically in small increments down the face of the storage section froma roll at the top. The used media and accumulated dirt are wound tightly into a compact roll at the bottom.The used roll is discarded and replaced with a new one.

Though the filtering medium itself may be noncombustible, in some cases, combustible dust and lint mayaccumulate in the filters during normal operations. This may cause substantial increase of the fire hazard inthe air conditioning system.

4.0 REFERENCES

4.1 FM Global

Data Sheet 1-22, Maximum Foreseeable LossData Sheet 1-23, Protection of Openings in Fire SubdivisionsData Sheet 1-56, CleanroomsData Sheet 5-48, Automatic Fire DetectionData Sheet 7-7/17-12, Semiconductor Fabrication FacilitiesData Sheet 7-78, Industrial Exhaust SystemsData Sheet 10-3, Hot Work Management

4.2 Other

NFPA 70, National Electrical Code®

NFPA 90A, Installation of Air Conditioning and Ventilating Systems

UL 586, Standard for High Efficiency, Particulate, Air Filter Units

UL 900, Standard for Safety Air Filter Units

APPENDIX A GLOSSARY OF TERMS

FM Approved: References to ″FM Approved″ in this data sheet mean a product or service has satisfied thecriteria for FM Approval. Refer to the Approval Guide, an online resource of FM Approvals, for a completelisting of products and services that are FM Approved.

Noncombustible filter: An air filter that will not contribute flame or smoke when exposed to an ignition source.An example of this would be a microfiberglass pleated filter with a metallic frame.

APPENDIX B DOCUMENT REVISION HISTORY

January 2012. Clarified the use of Class1/Class 2 air filters per revised UL listing process. Added detail onMERV ratings for filters.

May 2007. Added additional detail on fabric air duct systems and pre-insulated duct systems.

January 2001. The document has been reorganized to provide a consistent format.



Fmds0145 Air Conditioning and Ventilating Systems

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