[L7]_Ductwork Sizing & Design

Question 1

IND405

What is the goal of an air distribution system?

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Answer 1

Provide thermal comfort and ventilation for people in a space.

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Question 2

IND405

What are the three (3) categories of Space Air Diffusion?

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Answer 2

1. Fully (thermally) Stratified Systems
2. Partially Mixed Systems
3. Fully Mixed Systems

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Question 3

IND405

Is this example room Fully Stratified or Mixed?

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Answer 3

Fully Stratified Room

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Question 4

IND405

What are the three (3) example fans used for thermal destratification?

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Answer 4

1. HTHV (High-Temperature Heating & Ventilation) Fan
2. Large Circulation Fan
3. Compact Jet Stream Fan

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Question 5

IND405

What type of air-flow jet stream is shown in the image below?

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Answer 5

Isothermal Jet Stream, the temperature of the jet stream is the same as the proposed space.

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Question 6

IND405

True or False: Non-isothermal jet streams have the same starting temperature different from the ambient air.

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Answer 6

False. The starting temperature for a non-isothermal jet stream is different.

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Question 7

IND405

How many Diffuser Outlet Group Classifications are there?

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Answer 7

There are five (5) outlet diffuser group classifications.

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Question 8

IND405

What diffuser outlet group is in the sample photo?

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Answer 8

Group A: Diffusers mounted in or near the ceiling that discharge air horizontally.

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Question 9

IND405

What diffuser outlet group is in the sample photo?

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Answer 9

Group C: Diffusers mounted in or near the floor that discharge air vertically in a spreading jet.

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Question 10

IND405

What diffuser outlet group is in the sample photo?

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Answer 10

Group E: Diffusers mounted in or near the ceiling that project air vertically down.

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Question 11

IND405

Name four (4) main components of air distribution systems.

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Answer 11

1. Ductwork
2. Diffusers
3. Dampers
4. Insulation Wrapping & Lining

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Question 12

IND405

What is the typical galvanized steel ductwork thickness used for low pressure systems?

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Answer 12

22-gauge galvanized steel

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Question 13

IND405

Mastic Sealant is used for what type of ductwork systems?

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Answer 13

Medium & High Pressure Ductwork Systems

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Question 14

IND405

Gasket Clamp systems are used for what type of ductwork systems?

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Answer 14

Combustion Flue or Chimeny Ductwork Systems.

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Question 15

IND405

List the six (6) required ductwork layout distribution design considerations.

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Answer 15

1. Space Availability
2. Installation Cost
3. Air Friction Loss
4. Noise Level
5. Duct Heat Transfer & Leakage
6. SMACNA Ductwork Construction Standards

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Question 16

IND405

What does SMACNA stand for?

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Answer 16

Sheet Metal and Air-Conditioning Contractors’ National Association

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Question 17

IND405

What type of ductwork layout is shown in this example?

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Answer 17

Core & Shell, Trunk & Branch Layout

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Question 18

IND405

What are the three (3) types of duct sizing methods?

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Answer 18

1. Static Pressure Recovery Method (Static Regain Method)
2. Velocity Method
3. Constant Pressure Method aka (Equal Friction Method)

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Question 19

IND405

Which duct sizing method is the most complicated that is almost always only performed by computer?

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Answer 19

Static Pressure Recovery Method (Static Regain Method)

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Question 20

IND405

Define the Velocity duct sizing method.

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Answer 20

Velocity Method is based on the fan discharge speed to provide progressively lower duct velocities as the air proceeds from the main duct to the branches and outlets.

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Question 21

IND405

What are the two (2) design requirements when using velocity ductwork sizing method?

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Answer 21

1. Application for Use Space Occupancy
2. Noise Criteria for designated Use Space Occupancy

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Question 22

IND405

Name five (5) different types of dampers for a ductwork system?

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Answer 22

1. Gravity Damper
2. Volume Damper
3. Motorized Damper
4. Smoke Damper
5. Fire Damper

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Question 23

IND405

What is the recommended maximum air velocity (FPM) for space “Above Suspended Acoustical Ceiling” @ 25 NC level?

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Answer 23

1,200 FPM

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Question 24

IND405

What are the two (2) types of pressure required to calculate to ductwork total pressure?

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Answer 24

Static Pressure & Velocity Pressure

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Question 25

# IND405 What is the formula for ductwork **Dynamic Pressure**? ## Footnote [L7]

Answer 25

**Pv** = [Density * (Velocity^2)]/2 or **Pv** = (V/4005)^2 ## Footnote [L7]

Question 26

# IND405 List the **static pressure ranges** for the following duct systems. * **Low-Pressure** Ductwork System * **Medium-Pressure** Ductwork System * **High-Pressure** Ductwork System ## Footnote [L7]

Answer 26

* Low-Pressure Ductwork System: <=2-in. w.c. * Medium-Pressure Ductwork System: > 2-in. w.c. and <= 3-in. w.c. * High-Pressure Ductwork System: > 3-in. w.c. ## Footnote [L7]

Question 27

# IND405 What is the **base ductwork shape started** with then converted depending on the shape of the ductwork you want for your design? ## Footnote [L7]

Answer 27

You will always start with a **ROUND** ductwork sqft area equivalent to then change to **RECTANGULAR** or **OVAL** systems. ## Footnote [L7]

Question 28

# IND405 What is the **ratio** that must be maintained for **rectangular ductwork**? ## Footnote [L7]

Answer 28

Rectangular Duct Aspect Ratio is **4:1** ## Footnote [L7]

Question 29

# IND405 **True or False**: The Equal Friction method creates an **automatic** velocity reduction through the system. ## Footnote [L7]

Answer 29

True. ## Footnote [L7]

Question 30

# IND405 What is the **typical equal friction loss pressure drop** assumed for **low-pressure** ductwork systems? ## Footnote [L7]

Answer 30

0.1-in.w.g./100-FT ## Footnote [L7]

Question 31

# IND405 When calculating ductwork using the **Equal Friction Method** what are the **three (3) component pressure loss categories** you must calculate? ## Footnote [L7]

Answer 31

1. Straight Duct Losses 2. Duct Fitting Losses 3. Accessories Losses ## Footnote [L7]

Question 32

# IND405 What **manual** do you reference to find all **ductwork fitting pressure losses** when sizing a system? ## Footnote [L7]

Answer 32

SMACNA HVAC Duct System Design Manual ## Footnote [L7]

Question 33

# IND405 What type of **diffuser** is shown in the image? ## Footnote [L7]

Answer 33

2'x2' Square Ceiling Drop ACT Diffuser ## Footnote [L7]

Question 34

# IND405 What type of **diffuser** is shown in the image? ## Footnote [L7]

Answer 34

Four (4) Slot Architectural Linear Diffuser ## Footnote [L7]

Question 35

# IND405 What is the **typical insturment** used to **measure actual air-flow** from a **supply diffuser**? ## Footnote [L7]

Answer 35

Anemometer ## Footnote [L7]

Question 36

# IND405 What type of **diffuser** is shown in the image? ## Footnote [L7]

Answer 36

Single-deflection side wall supply grille ## Footnote [L7]

Question 37

# IND405 What is the **HVAC ductwork component** shown in the image? ## Footnote [L7]

Answer 37

Motorized Opposed Blade Damper ## Footnote [L7]

Question 38

# IND405 Which company manufactures the **most prevalent motorized damper actuator** utilized in the HVAC industry? ## Footnote [L7]

Answer 38

Belimo ## Footnote [L7]

Question 39

# IND405 Given an elbow fitting with a loss coefficient K of 0.75 and an airflow velocity of 900 feet per minute (FPM), calculate the pressure loss (ΔP) in the fitting. Use the following formula: **ΔP = 0.5 × ρ × V^2 ×K** ## Footnote [L7]

Answer 39

**ΔP** = 0.5 × 0.075lb/ft^3 × (900/60)^2-ft/s^2 × 0.75 **ΔP** = 0.5 × 0.075 × 225 × 0.75 **ΔP ≈ 8.44-inches wc.** ## Footnote [L7]

Question 40

# IND405 A straight duct has a fitting with a coefficient **C** of **0.35**. If the airflow velocity in the duct is **800-FPM**, calculate the total pressure loss (TP) using the formulas: **Vp = 0.5 × ρ × V^2** & **TP = C x Vp** ## Footnote [L7]

Answer 40

First, calculate **Vp**: Vp = 0.5 × 0.075-lb/ft^3 × (800/60)^2-ft/s^2 Vp = 0.5 × 0.075 x 177.78 **Vp ≈ 6.67-inches wc.** Then calculate the **TP**: TP = 0.35 × 6.67 **TP ≈ 2.33-inches wc.** ## Footnote [L7]