1 HVAC DUCT CONSTRCTION EXAMPLESASHRAE January 26, 2009 Mark Terzigni Project Manager SMACNA

2 HVAC DUCT CONSTRUCTION STANDARDS METAL AND FLEXIBLE

3 Information Required for Duct ConstructionA comprehensive duct layout indicating sizes, design airflows, pressure class, and routing of the duct system. The types of fittings to be used based on the designer's calculations of fitting losses (i.e., square versus 45° entry taps, conical versus straight taps, etc.).

4 Information Required for Duct ConstructionUse of turning vanes or splitter vanes. Location of access doors. Location and type of control and balancing dampers. Location and types of diffusers. Requirements for duct insulation.

5 Information Required for Duct ConstructionLocation and types of any fire protection device including fire dampers, smoke dampers, combination fire/smoke dampers, and ceiling dampers. Building codes require this information to be shown on the design documents submitted for building permit.

6 Information Required for Duct ConstructionDetails of offsets required to route ductwork around obstructions (columns, beams, etc.).

7 Information Required for Duct ConstructionENGINEER Design Considerations: CFM Static Pressure Duct Size Fitting Type Construction Pressure Class CONTRACTOR Construction Considerations: Panel Thickness (Gage) Pressure Class (as specified) Panel Width/Height Joint Type/Spacing Intermediate Reinforcement Type/Spacing

8 DEPENDENT VARIABLES

9 Transverse Joints Rectangular Round

10 Longitudinal Seams Rectangular Round

11 Intermediate ReinforcementRectangular Round

12 Duct Construction ScheduleVerify pressure class Check corresponding table Check joint reinforcement tables Check intermediate reinforcement tables

13 Guide Summary (P 2.5) Circles are column numbersNumber in box is the minimum gage First letter is minimum reinforcement Second letter is downsized reinforcement when used with tie rod Xt – t means tie rod(s) is required

14 Rectangular Duct Reinforcement

15 Joint Reinforcement

16 Intermediate Reinforcement

17 Example 1 Pressure Class is 2 in. w.g. Dimensions are 60 in. x 26 in.5 foot joint spacing TDC or TDF joint No internal reinforcement

18 The Right Table (Pressure Class)Page 2.18

19 Joint Reinforcement Page 2.76

20 Intermediate ReinforcementPage 2.70

21 The Right Table (Pressure Class)Page 2.18

22 Joint Reinforcement Page 2.76

23 Example 1 Solution Duct gage is 20 Joint spacing is 5 feet (56 ¼ in.)TDC/TDF for transverse joint Intermediate reinforcement (2 ½ feet) G class Angle 1 ½ x 1 ½ x 1/8 Not required on the 26 in. side

24 Intermediate External ReinforcementReinforcement Intervals do not need to coincide At 4 in. positive pressure reinforcements must be tied Must be fastened to the duct within 2 in. from the corner (unless tied) Maximum fastener spacing is 12 in.

25 Reinforced on Two Sides

26 Reinforced on Four Sides

27 Reinforcement Attachment

28 Tie Rods Steel Rod Conduit Steel Pipe Steel Strap Angles (rare)Threaded (all thread) or partial Plain Conduit RC EMT (most common type) Steel Pipe Steel Strap 1 in. x 1/8 in. Angles (rare)

29 Tie Rod Attachment

30 Mid-Panel Tie Rods Do not use in underground/slab appsDo not use if air velocity > 2500 fpm Do not use where grease or condensation can collect Unless no penetration is made Or penetration is sealed water tight If tie rods occur in 2 directions in the same vicinity they must: (applies to JTR and MPT) Be prevented from touching Or be permanently attached

31 Mid Panel Tie Rods Negative pressure uses special tablesConcern is buckling Table 2-38 in HVAC DCS for EMT P 2.91

32 Example 2 Pressure class is positive 4 in. w.g.Dimensions are 36 in. x 24 in. 5 ft. joint spacing Transverse joint TDC/TDF Use tie rod(s) where possible

33 The Right Table (Pressure Class)Page 2.22

34 Joint Reinforcement Page 2.76

35 Mid Panel Tie Rod SchedulePage 2.100

36 Tie Rod Load Page 2.106

37 Mid Panel Tie Rod Size EMT conduit positive pressure ½ in. 900 lbsHVAC DCS p2.80 S1.19.4

38 The Right Table (Pressure Class)Page 2.22

39 Joint Reinforcement Page 2.76

40 Example 2 Solution Duct gage is 22 Joint spacing is 5 feet (56 ¼ in.)TDC/TDF for transverse joint Intermediate reinforcement (2 ½ feet) 1 MPT ½ in. EMT Conduit Not required on the 24 in. side

41 Tie Rod Layout

42 An Easier Way? Newest addition are the TDC/TDF tables Tables based onPressure class Joint length

43 Example 2 (revisited) 4 in. w.g. TDC/TDF 5 ft. joint spacing36 in. x 24 in.

44 Example 2 (revisited) Table 2-19 HVAC DCS Page 2.50

45 Example 2 (revisited) SolutionOption 1 20 gage JTR on 36 in. side No additional reinforcement on 24 in. side Option 2 22 gage MPT for 36 in. side

46 Duct over 120 inches Figure 2-13 in HVAC DCSUse standard tables for sizes < 120 in. P 2.117

47 Example 3 Round Duct Positive 10 in. w.g. 24 in. diameterLong seam or spiral Table 3-5 in HVAC DCS Applies to positive pressure up through 10 in. w.g.

48 Unreinforced Round Duct to Positive 10 in. w.g.Table 3-5 Page 3.8 Unreinforced Round Duct to Positive 10 in. w.g. Example 3 Round Duct

49 Example 4 Round Duct Negative 10 in. w.g. 24 in. diameterLong seam Spiral Table 3-9 in HVAC DCS for long seam Table 3-13 in HVAC DCS for spiral

50 Example 4 long seam Longitudinal Seam Page 3.16

51 Example 4 Spiral Spiral Seam P 3.24

52 Round Reinforcement Tables in the HVAC DCS 3-2 Reinforcement3-3 Attachment Schedule 3-4 Rings Used as Companion Flanges P 3.6

53 Oval Duct Approved for positive pressure onlyCan be used for negative pressure with special designs Reinforce like rectangular Based on the flat span Flat span = major - minor

54 Questions? Technical Inquiries: www.smacna.orgClick on technical services (left side) Click on technical inquiries (center) Fire fox users scroll down…