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HVAC Systems_SP25 > [L9]_Ductwork Sizing & Design > Flashcards

[L9]_Ductwork Sizing & Design Flashcards

1
Q

IND405

What is the goal of an air distribution system?

[L9]

A

Provide thermal comfort and ventilation for people in a space.

[L9]

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2
Q

IND405

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

[L9]

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

[L9]

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3
Q

IND405

Is this example room Fully Stratified or Mixed?

[L9]

A

Fully Stratified Room

[L9]

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4
Q

IND405

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

[L9]

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

[L9]

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5
Q

IND405

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

[L9]

A

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

[L9]

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6
Q

IND405

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

[L9]

A

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

[L9]

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7
Q

IND405

How many Diffuser Outlet Group Classifications are there?

[L9]

A

There are five (5) outlet diffuser group classifications.

[L9]

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8
Q

IND405

What diffuser outlet group is in the sample photo?

[L9]

A

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

[L9]

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9
Q

IND405

What diffuser outlet group is in the sample photo?

[L9]

A

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

[L9]

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10
Q

IND405

What diffuser outlet group is in the sample photo?

[L9]

A

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

[L9]

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11
Q

IND405

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

[L9]

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

[L9]

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12
Q

IND405

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

[L9]

A

22-gauge galvanized steel

[L9]

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13
Q

IND405

Mastic Sealant is used for what type of ductwork systems?

[L9]

A

Medium & High Pressure Ductwork Systems

[L9]

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14
Q

IND405

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

[L9]

A

Combustion Flue or Chimeny Ductwork Systems.

[L9]

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15
Q

IND405

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

[L9]

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

[L9]

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16
Q

IND405

What does SMACNA stand for?

[L9]

A

Sheet Metal and Air-Conditioning Contractors’ National Association

[L9]

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17
Q

IND405

What type of ductwork layout is shown in this example?

[L9]

A

Core & Shell, Trunk & Branch Layout

[L9]

18
Q

IND405

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

[L9]

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

[L9]

19
Q

IND405

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

[L9]

A

Static Pressure Recovery Method (Static Regain Method)

[L9]

20
Q

IND405

Define the Velocity duct sizing method.

[L9]

A

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.

[L9]

21
Q

IND405

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

[L9]

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

[L9]

22
Q

IND405

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

[L9]

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

[L9]

23
Q

IND405

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

[L9]

A

1,200 FPM

[L9]

24
Q

IND405

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

[L9]

A

Static Pressure & Velocity Pressure

[L9]

25
Q

IND405

What is the formula for ductwork Dynamic Pressure?

[L9]

A

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

[L9]

26
Q

IND405

List the static pressure ranges for the following duct systems.
* Low-Pressure Ductwork System
* Medium-Pressure Ductwork System
* High-Pressure Ductwork System

[L9]

A
  • 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.

[L9]

27
Q

IND405

What is the base ductwork shape started with then converted depending on the shape of the ductwork you want for your design?

[L9]

A

You will always start with a ROUND ductwork sqft area equivalent to then change to RECTANGULAR or OVAL systems.

[L9]

28
Q

IND405

What is the ratio that must be maintained for rectangular ductwork?

[L9]

A

Rectangular Duct Aspect Ratio is 4:1

[L9]

29
Q

IND405

True or False: The Equal Friction method creates an automatic velocity reduction through the system.

[L9]

A

True.

[L9]

30
Q

IND405

What is the typical equal friction loss pressure drop assumed for low-pressure ductwork systems?

[L9]

A

0.1-in.w.g./100-FT

[L9]

31
Q

IND405

When calculating ductwork using the Equal Friction Method what are the three (3) component pressure loss categories you must calculate?

[L9]

A
  1. Straight Duct Losses
  2. Duct Fitting Losses
  3. Accessories Losses

[L9]

32
Q

IND405

What manual do you reference to find all ductwork fitting pressure losses when sizing a system?

[L9]

A

SMACNA HVAC Duct System Design Manual

[L9]

33
Q

IND405

What type of diffuser is shown in the image?

[L9]

A

2’x2’ Square Ceiling Drop ACT Diffuser

[L9]

34
Q

IND405

What type of diffuser is shown in the image?

[L9]

A

Four (4) Slot Architectural Linear Diffuser

[L9]

35
Q

IND405

What is the typical insturment used to measure actual air-flow from a supply diffuser?

[L9]

A

Anemometer

[L9]

36
Q

IND405

What type of diffuser is shown in the image?

[L9]

A

Single-deflection side wall supply grille

[L9]

37
Q

IND405

What is the HVAC ductwork component shown in the image?

[L9]

A

Motorized Opposed Blade Damper

[L9]

38
Q

IND405

Which company manufactures the most prevalent motorized damper actuator utilized in the HVAC industry?

[L9]

A

Belimo

[L9]

39
Q

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

[L9]

A

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.

[L9]

40
Q

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

[L9]

A

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.

[L9]

HVAC Systems_SP25 (12 decks)

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