Post on 06-Apr-2015
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
Documents Preceding 2nd Edition HVAC-DCS
Low Pressure Duct Construction Standard– Fifth Edition 1976
High Velocity Duct Systems Manual– First Edition 1965
High Velocity Duct Construction Standards– Second Edition 1969
Documents Preceding 2nd Edition HVAC-DCS
High Pressure Duct Construction Standards– Third Edition 1975
Duct Liner Application Standard– First Edition 1971– Second Edition 1975
Documents Preceding 2nd Edition HVAC-DCS
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)
Major Changes from First Edition
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
Major Changes from First Edition
Boiler breeching omittedVolume damper construction is more specificLead radiation shielding addedMetrics are includedAir terminal runouts and supports are revised
Major Changes from First Edition
RECTANGULAR DUCT REVISIONSNegative pressure construction given for 4", 6", and 10" w.g.
Six feet reinforcement schedules added
Reinforcement schedules extended to 120" width
Major Changes from First Edition
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
Major Changes from First Edition
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
Major Changes from First Edition
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
Major Changes from First Edition
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
– 2.0" w.g. positive or negative
Duct Systems (Continued)
Ducts are classified based on maximum operating pressure– 3.0" w.g. positive or negative
– 4.0" w.g. positive or negative
– 6.0" w.g. positive or negative
– 10.0" 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 1-4 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&
Answers