products Double-Wall, Insulated Duct - McGill …

1 3 double -Wall, Insulated duct and FittingsDOUBLE-WALL, Insulated , ROUND and FLAT OVAL DUCTand FITTINGSa McGill airflow product 2001 McGill airflow CorporationUnited McGill productsMcGill airflow enterprise of United McGill Corporation Founded in 1951 SPIRAL LOCKSEAM DESIGNDOUBLE-WALL duct & LOLOSS TEEDOUBLE-WALL, FLAT OVAL DUCTDOUBLE-WALL, ROUND DUCTSPIRAL LOCKSEAM/STANDING RIB DESIGNOUTER SHELLINSULATIONINNER LINERD ouble-Wall, Insulated Ductand FittingsMcGill airflow Corporation s double -wall, Insulated duct and fittings pro-vide exceptional noise and thermalcontrol in air handling systems. Theyare constructed of a solid sheet met-al outer pressure shell and a sheetmetal inner liner with a layer of insu-lation sandwiched between. We offerdouble-wall, round duct in three outershell constructions: spiral lockseam,spiral lockseam with a standing rib,and longitudinal seam.

2 Double-Wall, flat oval duct is available in spirallockseam and longitudinal seam con-structions. Our standard double -wallduct and fittings have galvanizedsheet metal outer walls and a layerof fiberglass insulation surroundingthe inner liner. The insulation isavailable as standard fiberglass orACOUSTI-LINE insulation with anacrylic coating that resists air erosionof fibers and the growth of fungusand bacteria. Standard duct has aperforated metal inner liner, whilestandard fittings have a solid metalinner liner. Options include otherthicknesses and types of insulation,stainless steel and aluminum outerwalls, and specification of solid-wallor perforated-wall inner liners asnonstandard options and the numeroussheet metal gauges that are availableenable McGill airflow to provide dou-ble-wall duct and fittings for a widerange of environments, includinghospitals, laboratories, food andpharmaceutical plants, and corrosiveindustrial areas.

3 We also supply sys-tems to convey hot air and gases,even when temperatures exceed1,000 BenefitsPerformance RatingsThrough extensive testing in acousti-cal laboratories, we have generateda large database of insertion lossesand airflow -generated sound powerlevels for our double -wall duct and fit-tings. Such information is essentialfor optimizing noise control in air han-dling systems. Our UNI- duct com-puter-aided duct system designprogram, which is equipped with thisdata, makes it easy to analyze theacoustical design of an air handlingsystem while simultaneously analyz-ing and balancing the airflow perfor-mance of the Noise ReductionFan noise can travel to every air out-let and inlet in an air handling systemand create unacceptable noise levelsin the rooms or areas served by thesystem. Our double -wall duct and fit-tings provide exceptional control offan noise, often eliminating the needfor additional duct airflow -GeneratedNoiseThe insulation in our double -wall ductand fittings is located outside theduct system s air passage, where itcan absorb sound without interferingwith the airflow .

4 duct silencers, onthe other hand, interfere with the air-flow. Turbulent airflow at the inlet andoutlet of a silencer generates noisethat can create acoustical problemsupstream and downstream of thesilencer. With our double -wall duct ,there is very little airflow -generatednoise. In fact, the insulation continu-ously reduces what noise there is,effectively creating an air handlingsystem that is quieter than a single-wall Sound-TransmissionLossNoise traveling along a duct path canradiate through the walls of the ductand fittings. Sheet metal duct wallshave higher sound-transmission lossthan lightweight duct materials suchas fiberglass duct board and flexibleduct. Acoustical laboratory tests showthat in similar sizes and shapes ourdouble-wall duct and fittings canreduce radiated noise by 25 dB ormore, compared with fiberglass ductboard, and by 30 dB or more, com-pared with Insulated flexible double -wall duct and fittingsalso control radiated noise better thansimilar sizes and shapes of externallyinsulated sheet metal duct .

5 The inter-nal insulation continuously reducesthe noise flowing along the duct path,while external insulation has little orno effect on this noise. With externalinsulation, excessive noise travelsundiminished throughout the ductsystem and can radiate into rooms orareas served by the and Cross-Talk Noise ControlWhen a duct system passes throughnoisy environments such as mechan-ical equipment rooms and productionareas, its walls can pick up flanking-path noise and convey it to otherareas served by the duct in duct systems (for exam-ple, diffusers, registers, and grilles)allow even low-level backgroundnoise into the duct system where itcan be conveyed to other openingsand radiate outward as cross-talknoise. The internal insulation of ourdouble-wall duct begins absorbingexternal noise as soon as it entersthe duct system, effectively prevent-ing the duct system from becoming aspeaking BenefitsControl of Heat Loss andHeat GainThe insulation in double -wall ductand fittings acts as a thermal barrier,increasing a duct system s effective-ness by helping to maintain the temperature of heated or cooled airbeing ducted through the airflow s standard 1-inch layer of insulation has a maximumthermal conductance of F.

6 Where lower thermalconductance values are desired, we also offer double -wall duct and fittings with insulation thicknesses of 2 inches ( Btu/hr/ft2/ F) and 3 inches ( Btu/hr/ft2/ F).2 United McGill and UNI- duct are registered trade-marks, and McGill airflow , ACOUSTI-LINE , andSilverGuard are trademarks of United McGill Vapor BarrierThe sheet metal outer shell of ourdouble-wall duct and fittings servesas an integral and permanent vaporbarrier to prevent moisture from con-densing in the insulation. The vaporbarriers of externally Insulated ductsystems usually are thin plastic ormetal foil membranes that are difficultto seal properly, especially wherethere are penetrations for hangerrods, straps, and external reinforce-ment. With double -wall duct , all hang-ers and reinforcements are attachedoutside the vapor barrier, so there areno penetrations.

7 The integrity of ourvapor barrier is checked during installa-tion when the duct system is pressuretested for leaks. If air cannot leak out,condensation cannot get in. Vaporbarriers for external insulation arerarely Condensation ControlCondensation can form on the out-side of duct systems that convey coldair, especially at times during thesummer when the ambient relativehumidity is high and a large tempera-ture differential exists between theinside and outside of the duct standard 1-inch-thick insulationprevents external condensation in allbut the most extreme combinationsof relative humidity and temperaturedifferential. For extreme conditions,we can supply 2- and 3-inch-thickinsulation to prevent condensationand the water damage it can cause(for more information, see McGill airflow s Engineering Bulletin Vol.)

8 2 No. 11, Lined duct for ThermalInsulation ). External insulation doesnot always prevent condensationproblems because duct hangers andexternal reinforcements penetrate theinsulation, often resulting in localizedexternal BenefitsDamage ProtectionOur sheet metal outer shell protectsthe insulation from damage duringconstruction and maintenance. Inoutdoor applications, it protects theinsulation from damage caused bysun, wind, rain, snow, oxidation, andother environmental Erosion ProtectionHigh airflow velocities and turbulentair streams can erode internalinsulation. The sheet metal inner liner in our double -wall duct and fittings protects the where fiber erosion is of special concern, we can supplyACOUSTI-LINE insulation with anerosion-resistant acrylic standard double -wall duct hasbeen tested at an independent labora-tory according to UL-181 standardduct testing procedures for impactand erosion resistance at an internalairflow velocity of 10,000 feet perminute.

9 These tests showed no evidence of insulation erosion and,according to UL-181, our double -wallduct is rated for airflow velocities upto 4,000 feet per CoatingsMcGill airflow offers two types ofantimicrobial protection with our double -wall duct and insulation is avail-able with an acrylic coating formu-lated with an antimicrobial agentthat is EPA registered. The coatingresists the growth of fungus andbacteria, as determined by tests inaccordance with ASTM C 1071 andASTM G21 and G22. For added pro-tection againstmicrobial growth, the coated surface can be cleanedaccording to the proceduresdetailed in the North American Insulation Manufacturers Associa-tion (NAIMA) duct Cleaning double -wall product line isalso available as SilverGuard ductand fittings. SilverGuard ductwork ispre-coated with the AgION antimi-crobial compound.

10 It is a second lineof defense in the control of bacteria,molds, mildew, and fungus found inHVAC duct systems. The inner wallof the outer shell and both walls ofthe inner shell can be Friction and DynamicPressure LossThe inner liner in a double -wall sys-tem presents a uniform cross sectionfor airflow , resulting in nominal pres-sure losses essentially equal to thoseof single-wall duct and fittings. Sincesheet metal screws used in theassembly of double -wall duct are hid-den in the insulation, they do not pro-ject into the airstream where theycan increase pressure install insulation in our double -wall duct and fittings at the factory,reducing your field-installation timeby eliminating the job of applyingexternal insulation. The componentsof a double -wall duct system arejoined by specially designed double -wall slip couplings and fitting have an extended inner collarso that the inner liners can be matedbefore the outer shells are two-step assembly procedureeliminates alignment problems duringinstallation.