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An Overview for ASHRAE Bi State ChapterMarch 14, 2012
Good, Better, & Best Duct Design
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Why Duct Design?
How to Design?
Design Process (8 steps)
Fundamentals
Design Methods
Introduction
Good, Better, & Best Duct Design An Overview
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Ductwork Types
Sound Control
Leakage Control
Exposed Ductwork
Specifications
Introduction
Good, Better, & Best Duct Design An Overview
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Good, Better, & Best Duct DesignFUNDAMENTALS
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Flow Rate (Q)
Q = V x A
WHERE:
Q volume flow rate of airflow (cfm)
V velocity (ft/min)
A area (sq ft)
Fundamentals
Good, Better, & Best Duct Design An Overview
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Total Pressure = Static Pressure + Velocity Pressure
TP = SP + VP
WHERE:
TP in wg
SP in wg
VP in wg
Fundamentals
Good, Better, & Best Duct Design An Overview
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Duct static pressure on various duct shapes
Fundamentals
Good, Better, & Best Duct Design An Overview
Round Duct
Flat Oval Duct
Rectangular Duct
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Fan and duct pressure changes in duct
Fundamentals
Good, Better, & Best Duct Design An Overview
Entry Exit DiffuserAirflow
-12
-7
-2
3
8
0 2 4 6 8 10 12 14 16 18 20
ATMOSPHERIC PRESSURE
Velocity
Pressure TP SP
Total Pressure
Static
Pressure
Velocity
Pressure
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Fan Laws
Fundamentals
1
2
1
2
RPM
RPM
Q
Q
Q = volume flow rate of airflow (cfm)
RPM= fan speed (revolutions/minute)
BHP= brake horse power (hp)
FTP= fan total pressure (in wg)
Good, Better, & Best Duct Design An Overview
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Good, Better, & Best Duct DesignDesign Considerations
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Duct Types
Design Considerations
Good, Better, & Best Duct Design An Overview
Round spiral and longitudinal seam duct
Other semi/quarter round, triangular
Flat Oval spiral and longitudinal seam duct
Rectangular
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Fitting Types
Elbows
Pressed 45 and 90, 3- to 12-inch diameter
Design Considerations
Good, Better, & Best Duct Design An Overview
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Design Considerations
Fitting Types
Elbows
Pleated 45 and 90, 3- to 16-inch diameter
Good, Better, & Best Duct Design An Overview
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Design Considerations
Fitting Types
Elbows
Gored std
Good, Better, & Best Duct Design An Overview
Gored long radius
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Design Considerations
Fitting Types
Elbows
Mitered vanes
Good, Better, & Best Duct Design An Overview
Mitered no vanes
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click to play video
Design Considerations
Good, Better, & Best Duct Design An Overview
http://localhost/var/www/apps/conversion/current/tmp/scratch_6/Ping%20Pong%20Ball%20Fitting%20Loss%20Video.wmvhttp://localhost/var/www/apps/conversion/current/tmp/scratch_6/Ping%20Pong%20Ball%20Fitting%20Loss%20Video.wmv7/31/2019 Good Better Best Duct Design
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Design Considerations
Good, Better, & Best Duct Design An Overview
Fitting Types
Divided Flow
Straight Tee
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Design Considerations
Fitting Types
Divided Flow
Conical Tee
Good, Better, & Best Duct Design An Overview
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Design Considerations
Fitting Types
Divided Flow
LoLoss Tee
Good, Better, & Best Duct Design An Overview
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Design Considerations
Fitting Types
Divided Flow
Y-Branch
Good, Better, & Best Duct Design An Overview
Reducing Y-Branch
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Design Considerations
Fitting Types
Divided Flow
Bullhead Tee vanes
Good, Better, & Best Duct Design An Overview
Bullhead Tee no vanes
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Design Considerations
Fitting Types
Divided Flow
Laterals
Good, Better, & Best Duct Design An Overview
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Design Considerations
Fitting Types
Converging Flow
Good, Better, & Best Duct Design An Overview
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Supply Design Methods
Design Considerations
Good, Better, & Best Duct Design An Overview
2. Static regain
1. Equal friction
3. Velocity reduction
4. T method
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Exhaust/Return Design Methods
Design Considerations
1. Exhausta. Constant velocityb. Equal friction
2. Returna. Equal frictionb. Velocity reduction
Good, Better, & Best Duct Design An Overview
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Good, Better, & Best Duct DesignEnergy Consumption
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Energy Consumption
Factors
1. cfm, sp, efficiency, fuel cost, and hours2. Operation cost vs aspect ratio
Good, Better, & Best Duct Design An Overview
System Annual Operating Cost
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Good, Better, & Best Duct DesignPerformance Considerations
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Annual Operational Costs
Performance Considerations
kwh
$
Year
Hours
eff8,520
FTPQ
Year
Cost fan
Cost/Year = system first year operating cost ($)
Qfan= system volume flow rate (cfm)
FTP= system total operating pressure (in wg)
Hours/Year= number of hours the system operates in one year
$/kwh= cost of energy
eff= fan/motor drive combined efficiency
8,520 = conversion factor to kwh (kilowatt hours)
WHERE:
Good, Better, & Best Duct Design An Overview
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Good, Better, & Best Duct DesignSound Control
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Design Process
Sound Control
1. Determine acceptable noise criteria (NC) rating for the space
2. Determine the sound source spectrum
3. Calculate the resultant sound level criteria
4. Compare resultant sound levels
5. Select the appropriate noise control products to attainthe needed NC level
Good, Better, & Best Duct Design An Overview
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Duct System Acoustics
Sound Control
Good, Better, & Best Duct Design An Overview
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Calculate Resultant Sound Levels
Sound Control
Good, Better, & Best Duct Design An Overview
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Sound Control Devices
Sound Control
Good, Better, & Best Duct Design An Overview
Pressurized enclosure Round duct silencer
k-27 duct and fittings Rectangular duct silencers
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Good, Better, & Best Duct DesignWhy Leakage Control?
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Performance considerations
Leakage Control
1. Airflow quantities
2. Airflow quality
3. Airflow pressure
4. Energy consumption
5. Annual operational cost
6. Balanced airflow
Good, Better, & Best Duct Design An Overview
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Duct static pressure on various duct shapes
Fundamentals
Good, Better, & Best Duct Design An Overview
Round Duct
Flat Oval Duct
Rectangular Duct
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Fan and duct pressure changes in duct
Fundamentals
Good, Better, & Best Duct Design An Overview
Entry Exit DiffuserAirflow
-12
-7
-2
3
8
0 2 4 6 8 10 12 14 16 18 20
ATMOSPHERIC PRESSURE
Velocity
Pressure TP SP
Total Pressure
Static
Pressure
Velocity
Pressure
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Good, Better, & Best Duct DesignWhat does SMACNA say?
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Leakage cfm/100 sq ft vs Test Pressure
SMACNA
Good, Better, & Best Duct Design An Overview
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Leakage Classes
SMACNA
Good, Better, & Best Duct Design An Overview
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Good, Better, & Best Duct DesignDuct Geometry and Leakage
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Typical Duct Geometries1.Round2. Flat oval3. Rectangular
Duct Geometry and Leakage
Good, Better, & Best Duct Design An Overview
SMACNA Leakage Class at Seal Class A
1.Round: 3 cfm/100 sq ft2. Flat oval: 3 cfm/100 sq ft
3. Rectangular: 6 cfm/100 sq ft
WHAT IS WRONG WITH THIS PICTURE???
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Cost of Leakage
Duct Geometry and Leakage
kwh
$
Year
Hours
eff8,520
FTPQ
Year
Cost fan
Cost/Year = system first year operating cost ($)
Qfan= system volume flow rate (cfm)
FTP= system total operating pressure (in wg)
Hours/Year= number of hours the system operates in one year
$/kwh= cost of energy
eff= fan/motor drive combined efficiency
8,520 = conversion factor to kwh (kilowatt hours)
WHERE:
Good, Better, & Best Duct Design An Overview
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Impact of Leakage
Duct Geometry and Leakage
Good, Better, & Best Duct Design An Overview
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Suggested Leakage Levels
Duct Geometry and Leakage
Good, Better, & Best Duct Design An Overview
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Leakage Specification (minimum requirements)
Duct Geometry and Leakage
1. Test pressure (in wg)
2. Allowable leakage (cfm/100 sq ft)3. Test procedure
4. Report of findings
5. Certified test equipment
Good, Better, & Best Duct Design An Overview
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Good, Better, & Best Duct DesignExposed Ductwork
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A. Duct types1. Round2. Flat oval3. Rectangular4. Other: semi/quarter round, triangular
Exposed Ductwork
B. Elbow types1. Pressed2. Pleated3. Gored
C. Divided flow fittings1. Straight tee2. Conical tee3. LoLoss tee
Good, Better, & Best Duct Design An Overview
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Exposed Ductwork
Good, Better, & Best Duct Design An Overview
Institutional
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Exposed Ductwork
Good, Better, & Best Duct Design An Overview
Commercial
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Exposed Ductwork
Good, Better, & Best Duct Design An Overview
Industrial
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Controlled Air Distribution
Exposed Ductwork
Good, Better, & Best Duct Design An Overview
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High Bay and Boot Taps
Exposed Ductwork
Good, Better, & Best Duct Design An Overview
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Good, Better, & Best Duct DesignMaterial Considerations
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Metallic
Material Considerations
1. Galvanized steel, G60/G90/phosp.
2. Stainless steel, 304/316/finish #2d/#43. Aluminum, type 3003-H14
4. PVC-coated
5. SilverGuard antimicrobial
Good, Better, & Best Duct Design An Overview
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Non-metallic
Material Considerations
1. FRP (fiberglass reinforced plastic)
2. Fibrous duct board3. Flexible
4. Dry wall
5. Fabric, open or closed weave
Good, Better, & Best Duct Design An Overview
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Good, Better, & Best Duct DesignSealants and Adhesives
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Sealants and Adhesives
Common Properties
1. No surface preparation
2. +/- 40 in wg
3. High solids content
4. Curing time 24-48 hours
Types
1. Water based
2. Solvent based
Good, Better, & Best Duct Design An Overview
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Sealants and Adhesives
LEED Applications
1. Solvent/water based
2. Low VOCs
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Good, Better, & Best Duct DesignDiffusers, what type?
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Diffusers, what type?
Good, Better, & Best Duct Design
An Overview
Exposed Features
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Exposed Features
Diffusers, what type?
Good, Better, & Best Duct Design
An Overview
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Good, Better, & Best Duct DesignSpecification Considerations
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Specification Considerations
1. SMACNA duct construction standards 2005
2. Joint types
3. Hanging and support
4. Handling/shipping/cleaning5. Finish welding/pacification/grinding
Good, Better, & Best Duct Design
An Overview
6. Double-wall and lining
7. Painting
8. Material types
9. Leakage testing
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Conclusions
1. Fundamentals
2. Design methods
3. Energy consumption
4. Sound control5. Leakage control
6. Exposed ductwork
7. Materials
8. Specifications