good better best duct design

7/31/2019 Good Better Best Duct Design

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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



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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



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Total Pressure = Static Pressure + Velocity Pressure

TP = SP + VP

WHERE:

TP in wg

SP in wg

VP in wg

Fundamentals



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Duct static pressure on various duct shapes

Fundamentals


Round Duct

Flat Oval Duct

Rectangular Duct


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Fan and duct pressure changes in duct

Fundamentals


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)



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Good, Better, & Best Duct DesignDesign Considerations


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Duct Types

Design Considerations


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




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Fitting Types

Elbows

Pleated 45 and 90, 3- to 16-inch diameter



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Fitting Types

Elbows

Gored std


Gored long radius


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Fitting Types

Elbows

Mitered vanes


Mitered no vanes


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click to play video


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.wmv


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Fitting Types

Divided Flow

Straight Tee


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Fitting Types

Divided Flow

Conical Tee



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Fitting Types

Divided Flow

LoLoss Tee



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Fitting Types

Divided Flow

Y-Branch


Reducing Y-Branch


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Fitting Types

Divided Flow

Bullhead Tee vanes


Bullhead Tee no vanes


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Fitting Types

Divided Flow

Laterals



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Fitting Types

Converging Flow



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Supply Design Methods



2. Static regain

1. Equal friction

3. Velocity reduction

4. T method


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Exhaust/Return Design Methods


1. Exhausta. Constant velocityb. Equal friction

2. Returna. Equal frictionb. Velocity reduction



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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


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:



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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



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Duct System Acoustics

Sound Control



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Calculate Resultant Sound Levels

Sound Control



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Sound Control Devices

Sound Control


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



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Duct static pressure on various duct shapes

Fundamentals


Round Duct

Flat Oval Duct

Rectangular Duct


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Fan and duct pressure changes in duct

Fundamentals


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



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Leakage Classes

SMACNA



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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


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


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:



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Impact of Leakage




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Suggested Leakage Levels




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Leakage Specification (minimum requirements)


1. Test pressure (in wg)

2. Allowable leakage (cfm/100 sq ft)3. Test procedure

4. Report of findings

5. Certified test equipment



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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



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Exposed Ductwork


Institutional


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Exposed Ductwork


Commercial


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Exposed Ductwork


Industrial


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Controlled Air Distribution

Exposed Ductwork



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High Bay and Boot Taps

Exposed Ductwork



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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



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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



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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



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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?


An Overview

Exposed Features


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Exposed Features

Diffusers, what type?


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


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

good better best duct design

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