hvac duct construction wasilewski

HVAC Duct Construction

Bob WasilewskiProject Manager, Technical Resources

SMACNA

HVAC Duct Construction Standards

WHAT?

WHY?

HOW?

Today's Program

1st – 2nd Edition HVAC-DCSReview Joints and LimitationsTransverse Joints & ReinforcementsUse of the Pressure Class TablesTie Rod Addendum

Documents Preceding 2nd Edition HVAC-DCS

Low Velocity Systems Duct Manual– First Edition 1959– Second Edition 1963– Third Edition 1967

Low Velocity Duct Construction Standard– 1969


Low Pressure Duct Construction Standard– Fifth Edition 1976

High Velocity Duct Systems Manual– First Edition 1965

High Velocity Duct Construction Standards– Second Edition 1969


High Pressure Duct Construction Standards– Third Edition 1975

Duct Liner Application Standard– First Edition 1971– Second Edition 1975


Flexible Duct Installation Standards– First Edition 1979– Second Edition 1980

HVAC Duct Construction Standards --Metal and Flexible– First Edition 1985

Major Changes from First Edition

GENERALText edited to be more reader-friendly

Reading aids added

Static pressure only as the basis for duct construction classification -- velocity levels deleted (Table 1-1)


Chapter 7 revised to facilitate use for equivalent and comparable tests and ratings

Model project specification added

Reminders to designers to show all required fire, smoke, radiation and volume control dampers on contract drawings are accented


Boiler breeching omittedVolume damper construction is more specificLead radiation shielding addedMetrics are includedAir terminal runouts and supports are revised


RECTANGULAR DUCT REVISIONSNegative pressure construction given for 4", 6", and 10" w.g.

Six feet reinforcement schedules added

Reinforcement schedules extended to 120" width


Tie rod alternatives expanded for both positive and negative pressures

TDC and TDF joint systems included and rated as T-25a and T-25b joints

T-24a joint added as a modification of T-24


Use of 26 gage added for 4", 6" and 10" pressuresTrapeze hanger tables expanded to cover the 120" width rangeDuct liner pin schedule adjustedInfrequently used joints (T-4, 8, 17, 18, 19, 20 and 23) omitted


Round, Flexible and Oval Duct RevisionsDuct pressure classes revised to be positive and negative at 2", 4" and 10" w.g.Crimped joint connection length changed from 1" to 2"Rectangular branch taps into round added for straight or 45 degree lead-in-entry


Type 1 reinforcement of oval duct now has an internal tie rod (based on ASHRAE test program)Maximum support spacing for round flexible duct and connector changed from 10 feet to 5 feetAdditional riser support details are provided

DUCT SYSTEMS

SIZINGSFITTINGS, ETC.

FIRE/SMOKEPROTECTION

CODECOMPLIANCE

DUCTCONSTRUCTION

CODECOMPLIANCE

SMACNAHVAC-DCS

2ND ED. 1995

INSPECTION CODECOMPLIANCE

DUCT SYSTEMS

ENGINEERDesign Considerations:

CFM

Static Pressure

Duct Size

Fitting Type

Construction Pressure Class

CONTRACTORConstruction Considerations:

Panel Thickness (Gage)

Pressure Class (as specified)

Panel Width/Height

Joint Type/Spacing

Intermediate Reinforcement Type/Spacing

DEPENDENT VARIABLES

REGULAR DUCTS

+10%+7.5%

Tolerance:Tolerance:

1" on 85"-120"

Class Rating + 25%3/4" on 25"-84"

Field:5/8"on 19"-24"49"-120"

1/2" on 13"-18"W/200 on

Class Rating + 50%3/8" on 12" Dn.1/4" on 48" w.

Lab:Sheet:Joint and Reinf.

Maximum Test Pressure

Maximum Deflection

Duct Systems

Used for the movement of air in HVAC/Exhaust systemsDucts are classified based on maximum operating pressure– 0.5" w.g. positive or negative

– 1.0" w.g. positive or negative


Duct Systems (Continued)

Ducts are classified based on maximum operating pressure– 3.0" w.g. positive or negative




TABLE 1-2

STANDARD DUCT SEALING REQUIREMENTS

EXAMPLE 1

Duct Size 24" x 24"Pressure Class 2" w.g.Sheet StockJoints/Reinforcements 8 ft / 4 ftStanding S

EXAMPLE 2

Duct Size 42" x 24"Pressure Class 3" w.g.5 ft Coil LineJoints/Reinforcements 5 ft / 2 ½ ftTDC or TDF

MIDPANEL TIE ROD (MPT)

½" w.g. - 6" w.g.

37" - 96"

Duct Dimension

Rectangular Duct

Mid Panel Tie Rod Addendum

Joints – All

Tie Rods – Threaded Rod or Tubing/Conduit with Threaded Insert

Additional Application Tables, Qualifications and Reader Aids Included

FIGURE 1-3 TIE ROD ATTACHMENTS

FIGURE 1-4 TRANSVERSE (GIRTH) JOINTS

FIGURE 1-4A SPECIAL JOINT PROFILES

FIGURE 1-5 LONGITUDINAL SEAMS –RECTANGULAR DUCT

TABLE 1-24 UNREINFORCED DUCT (WALL THICKNESS)

TABLE 1-25T-1 FLAT DRIVE ACCEPTED AS REINFORCEMENT

FIGURE 1-7 UNREINFORCED DUCT

FIGURE 1-8 CROSSBROKEN DUCT & BEADED DUCT

FIGURE 1-9 DUCT REINFORCED ON TWO SIDES

FIGURE 1-10 DUCT REINFORCED ON ALL SIDES

FIGURE 1-12 DUCT OVER 120" (3048 MM) WIDE

FIGURE 1-15 CORNER CLOSURES - FLANGES

FIGURE 2-22 DUCT LINER INTERRUPTION

TABLE 3-2A ROUND DUCT GAGE UNREINFORCED POSITIVE PRESSURE

TABLE 3-2B ROUND DUCT GAGE NEGATIVE PRESSURE

FIGURE 3-1 SEAMS – ROUND DUCT AND FITTINGS

FIG. 3-2 TRANSVERSE JOINTS – ROUND DUCT

FIGURE 3-6 FLAT OVAL DUCTS

FIGURE 3-9 FLEXIBLE DUCT SUPPORTS

FIGURE 3-10 FLEXIBLE DUCT SUPPORTS

TABLE 4-1 RECTANGULAR DUCT HANGERS MIN. SIZE

TABLE 4-2 MINIMUM HANGER SIZES FOR ROUND DUCT

FIGURE 4-4 LOWER HANGER ATTACHMENTS

Questions&

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