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Term 3 - Ductwork > Ducting PPT > Flashcards

Ducting PPT Flashcards

1
Q

Air obeys which two gas laws?

A

Charles and Boyles

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2
Q

Moving air prevents ____________

A

Stratification

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3
Q

Air settling at different heights according to temperature is described as?

A

Stratification

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4
Q

What components have an effect on stratification?

A

Thermostats and ducting outlets

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5
Q

Factors for calculating air changes (6)

A
  1. # occupants
  2. use of space
  3. dry-bulb temps
  4. RH
  5. fresh air admitted by infiltration
  6. efficiency of unit
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6
Q

Name four types of duct systems:

A

Radial
Extended Plenum
Reducing Trunk
Perimeter loop

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7
Q

Name a few non-metal duct types

A

Fiberglass
Urethane
Plastic
Sheetrock
Textile

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8
Q

Ducts made of fibreglass or asbestos should be ____________

A

plastic-coated

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9
Q

Which types of ducts must be replaced when installing a new furnace?

A

Asbestos

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10
Q

Asbestos is classified as a _________

A

carcinogen

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11
Q

Removal of asbestos shall be done only by who?

A

abatement companies

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12
Q

Duct size transitions should be tapered:
- Reductions: __” for every 4” in length.
- Enlargements: 1” for every 4 - __” in length

A

1”
4-7”

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13
Q

Aspect ratio of ducting shall be :

A

1:1

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14
Q

Diffusers spread air more uniformly than registers. True or False?

A

True

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15
Q

Grilles are non-adjustable fixtures that cover return duct inlets. True or False?

A

True

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16
Q

Registers do what?

A

Deliver air to a room

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17
Q

Dampers control air flow; name 3 types

A
  1. multiple-blade damper
  2. butterfly damper
  3. split-damper
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18
Q

Most dampers have automatic controls that open or closed based on the __________

A

thermostat

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19
Q

Power devices for dampers include 4 types; name them

A
  1. electric motors
  2. pneumatic motors
  3. hydraulic motors
  4. solenoids
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20
Q

In a pneumatic system, air lines are controlled by the?

A

thermostat

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21
Q

Pneumatic systems are most commonly used in what applications?

A

large commercial and industrial systems

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22
Q

What are the two types of fire dampers?

A

static and dynamic

23
Q

What are the three rating classifications for fire dampers?

A

Class A
Class B
Class C

24
Q

Before installing ducts, check local ____ damper regulations

A

fire

25
Q

Turbulence can be caused by abrupt changes in _______ of airflow

A

direction

26
Q

_____-______ elbows minimize turbulence

A

long-radius

27
Q

You can minimize turbulence in short-radius elbows by using elbows with built-in ________ _____

A

directional vanes

28
Q

Never install duct at the end of ?

A

The plenum

29
Q

Some things to consider when designing ducting (4)

A
  1. air handler central
  2. short runs
  3. minimize fittings
  4. avoid obstacles
30
Q

Before sizing ducts, the technician must know what?

A

Heating and cooling loads

31
Q

Which mode requires more CFM and why?

A

Cooling due to moist coil and dense air must be overcame

heat rises

32
Q

Airflow through a blower depends on what two factors?

A

External static pressure and blower speed

33
Q

What is ASP?

A

Available static pressure

  • amount of friction or resistance used to design longest duct run
34
Q

What is DPL?

A

Device pressure losses

  • pressure losses in system caused by devices other than ducts
35
Q

Friction losses are expressed in what units?

A

inches of water column

36
Q

Where do friction losses occur?

A

pressure drops inside the duct resulting from air contacting the surfaces

37
Q

To determine duct size, what are two tools you may use?

A
  1. airflow friction chart
  2. duct calculator
38
Q

Name some variables to consider when using an airflow friction chart?

A

duct diameters
airflow rates
pressure drops/friction losses
air velocities

39
Q

What is the total pressure drop allowed?

A

0.5” w.c between supply and return air duct

40
Q

Device that blocks infiltration of outside air through an opening?

A

Air curtain?

41
Q

Ducting sections are connected with what type of cleats/fasteners?

A

S fasteners and D cleats

42
Q

Flexible duct connections reduce?

A

vibration/noise

43
Q

Where are duct connections assembled?

A

in the field

44
Q

Round ducting sections are connected with?

A

self tapping sheet metal screws

45
Q

Round duct requires more or less clearance than square/rectangular duct?

A

More

46
Q

Insulation and acoustic lining can be applied to the inside or outside of the duct. True or False?

A

True

47
Q

How is interior insulation secured to the duct?

A

tabs and washers, glue, or both

48
Q

Interior duct insulation is usually coated with what?

A

fibreglass

49
Q

One thing to be aware of when using interior acoustic lining for a duct is what?

A

reduces cross sectional area of the duct

50
Q

Ductboard can be fabricated easily using special?

A

knives

51
Q

How are sections of ductboard secured?

A

taping and stapling

52
Q

Flexible ducting should be stretched to prevent duct collapsing. True or False

A

True

53
Q

Flexible ducting has low initial costs and does not transmit noise well. True or False

A

True

Term 3 - Ductwork (4 decks)

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