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Commercial and Industrial HVAC > Industrial Exhaust > Flashcards

Industrial Exhaust Flashcards

1
Q

What is the gauge relationship between straight duct and elbow fittings or hoods?

A

Elbows and hoods should be two gauges heavier than the straight pipe.

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2
Q

What is the correct ruling for tapered lengths?

A

For every unit change in diameter for duct enlargement or contraction there should be a five unit change in length. Example: If you had a 4” to 6” transition the difference is 2, so you would go 2 x 5 = 10, making the taper 10” long in length.

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3
Q

A main 10” diameter entry branch tapers to a 14” diameter main exit and has a small 8” diameter entry at 30 degrees. What is the minimum length that the taper must be to meet requirements?

A

20”

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4
Q

What is the best angle for an incoming branch intersecting a conical taper in a blow pipe system?

A

30 degrees

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5
Q

What is the best throat centre line radius to use for a 90 degree seven piece elbow?

A

2-1/2 Centre Line Radius

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6
Q

When would it be appropriate to use stainless steel for an exhaust system?

A

When materials are either very corrosive or abrasive

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7
Q

How many classifications are there in industrial exhaust systems?

A

Five

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8
Q

What duct class deals with contaminants of a corrosive nature?

A

Class Five

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9
Q

What does dilution ventilation do?

A

It dilutes contaminated air in the whole building or room by bringing in clean outside air and exhausting some dirty air.

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10
Q

What are local exhaust ventilation hoods used for?

A

They are used to remove highly toxic chemicals and large amounts of process dusts or fumes.

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11
Q

Where are local exhaust ventilation hoods located?

A

They are located as close as possible to the source of contamination to capture contaminants before they are released into the work area.

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12
Q

Hangers and supports should be placed in sufficient quantity and capacity to carry the weight of the duct system if it is filled with how much material?

A

Half filled

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13
Q

To determine the diameter of each branch connected to the equipment you are exhausting, what do you need to measure?

A

You need to measure the factory collar (or port opening) for each component.

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14
Q

What is the minimum velocity (fpm) as recommended by the manufacturer for production machines required to do?

A

Maintain the required velocity of the air stream traveling through the pipe, keep smaller particles from clogging the pipes, and keep dust particles from settling in elbows and vertical sections.

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15
Q

When you are sizing the main truck line for a velocity of 4000 fpm and the required pipe diameter falls between 6” and 7”. Why is it recommended that you round down to 6” instead of 7”?

A

To ensure there is adequate airflow. (Always pick the smaller number)

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16
Q

What should always be considered in industrial exhaust systems?

A

Makeup or replacement air should always be considered

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17
Q

What are the 6 different types of hoods?

A

Slot, flanged, plain opening, booth, and canopy type

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18
Q

What is a sash (sash stop)?

A

Sash is the term used to describe the movable glass panel that covers the face area of a fume hood

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19
Q

What should you never do to a sash stop?

A

Sash stops should never be removed, overridden or modified.

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20
Q

What is face velocity?

A

Face velocity is a measurement of the average velocity at which air is drawn through the face of the exhaust.

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21
Q

What is the acceptable range of face velocity?

A

Between 60 fpm to 100 fpm, with the ideal average range at 100 fpm for most operations.

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22
Q

Hoods should be how many gauges heavier than the straight sections of the connecting branch lines?

A

They should be a minimum of two gauges heavier than the straight sections.

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23
Q

How is dilution ventilation accomplished?

A

By mounting large exhaust fans on the walls or roof of a building or room.

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24
Q

When is local exhaust ventilation required?

A

When employees are exposed to high toxicity chemicals and when large amounts of processed dusts or welding fumes are generated.

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25
Q

What must be provided to replace the air that is exhausted in order for an exhaust system to operate properly?

A

Makeup air

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26
Q

What is a hood designed for?

A

To confine or capture the contaminant at its source.

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27
Q

Air velocity in local exhaust systems is measured in what?

A

feet per minute (fpm)

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28
Q

The volume of air though a local exhaust system is measured in what?

A

cubic feet per minute (cfm)

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29
Q

The pressure in a local exhaust system is measured in what?

A

Is measured in units called inches of water

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30
Q

What are the two common classes of hoods?

A

Enclosing and capturing

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31
Q

Why are enclosing hoods not very feasible?

A

Because they often interfere with the work being done by the employee

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32
Q

Where can capturing hoods only be located?

A

Near the sourced of contaminant

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33
Q

What is the recommended face velocity for fume hoods under normal conditions?

A

100 fpm

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34
Q

What happens when face velocities are greater than 125 fpm?

A

They can create turbulence

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35
Q

Which hoods are not recommended for use in local exhaust ventilation?

A

Canopy hoods because they push contaminants into the work area and they often draw air through the breathing zone.

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36
Q

What type of duct is recommended for local exhaust systems?

A

Smooth round ducts

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37
Q

Ducting should be straight for at least ___ duct diameters before it enters the fan in order to maintain smooth airflow into the fan?

A

two duct diameters

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38
Q

What are the most common type of air cleaners found in industry?

A

Dust filters

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39
Q

What are the workhorses of exhaust ventilation systems?

A

Fans

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40
Q

What two types of exhaust fans are used for exhaust ventilation systems?

A

Axial fans and centrifugal fans

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41
Q

Which fan wheel in an exhaust ventilation system has the highest efficiency?

A

The air-handling wheel

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42
Q

How much straight duct is required on fan discharge for velocities of 2500 fpm?

A

2.5D of straight is required and add the equilvalent of one diameter for every extra 1000 fpm over that.

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43
Q

Exhaust stacks should be located no closer than ____ to a building’s fresh air intake?

A

50 feet

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44
Q

Stacks work best when they are at least ____ above the roof line.

A

10 feet

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45
Q

Air velocity out of the stack should be at least ____ per minute to overcome the downdrafts from wind blowing into the building?

A

3000 feet per minute (fpm)

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46
Q

What should you avoid using placing on stacks?

A

Rain caps because they tend to force contaminants back inside the building.

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47
Q

What is the spacing for cleanout doors?

A

It should not exceed 12 ft for ducts measuring 12” in diameter or less.

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48
Q

Explosive doors, explosive curtains, and pressure relief vents must be installed in accordance with the _____ standards and all other applicable codes?

A

National Fire Protection Association (NFPA)

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49
Q

What is the purpose of explosive doors, explosive curtains, and pressure relief vents?

A

To provide for instantaneous pressure discharge from inside the duct.

50
Q

What are blast gates used for?

A

They are used when a positive seal is desired. They are used to close off/isolate parts of the system to save air, heat and power when equipment is not being used.

51
Q

What are the three common types of longitudinal seams?

A

The butt weld, the pipe lock grooved seam, and the spiral lock seam.

52
Q

What is the strongest longitudinal seam and can also be used for all 5 classes?

A

The butt-welded seam

53
Q

What is the minimum length for a commercial small end lap going into a pipe?

A

2” minimum

54
Q

What type of duct can only be fabricated for Class 5?

A

Stainless steel only

55
Q

What must ducts be when aluminum is used?

A

Class 1 only and must be two gauges heavier than the chart values.

56
Q

Longitudinal joints or seams should be lapped and riveted or spot welded on a maximum of ____ on centre?

A

3” on centre

57
Q

All girth joints, except welded or flanged joints, should be made with an inner lap in the direction of flow of at least ____ minimum?

A

1.5” minimum and riveted or spot welded on 4.5” on centre.

58
Q

Elbows and any changes in cross sectional areas should be a minimum of ____ gauges heavier than the straight lengths of equal diameter?

A

Two gauges heavier

59
Q

Elbows should be ____ diameters centerline radius?

A

2.5 diameters centerline radius

60
Q

What is the best number of pieces to use for an elbow?

A

7 pieces is the best, the more the better.

61
Q

When sizing the duct, you should always size by?

A

Speed (velocity) fpm

62
Q

All branches should enter the main at the large end of the transition at an angle not to exceed at?

A

45 degrees or at the preferred angle of 30 degrees

63
Q

Where should branch connections always be installed?

A

Always on the top or side and should never enter from the bottom.

64
Q

Industrial exhaust system standards are based on?

A

Occupational exposure limits (OELs)

65
Q

What is always required when workers enter confined spaces where there is a potential for exposure to toxic and flammable vapours, or to dust or oxygen deficiency?

A

Forced air (mechanical) ventilation

66
Q

What do VAV systems do in an exhaust ventilation system?

A

They allow the airflow in the exhaust system to match the supply airflow requirements of the building.

67
Q

What agencies and standards have a role in determining exhaust system standards?

A

ANSI, NFPA, SMACNA, and ASHRAE

68
Q

What does Class 1 round industrial duct consist of?

A

Non abrasive, non corrosive applications

69
Q

What does Class 2 round industrial duct consist of?

A

Light to moderately abrasive particulate in light concentration

70
Q

What does Class 3 round industrial duct consist of?

A

Highly abrasive particulate in low concentrations

71
Q

What does Class 4 round industrial duct consist of?

A

Highly abrasive particulate in high concentration

72
Q

What does Class 5 round industrial duct consist of?

A

Applications with corrosives such as acid vapours

73
Q

What type of radius should elbows have in a dust collection system to minimize clogging?

A

Long radius

74
Q

What is the most important factor in an efficient dust collection system?

A

Proper hood design

75
Q

What are the major components in dust collection systems?

A

The hood, the ductwork, the fan, the cyclone cleaners, and the stacks.

76
Q

What is the fan used or in a dust collection system?

A

It is used to generate negative pressure at the inlet side of the duct system, as well as positive pressure at the outlet side of the system.

77
Q

What is a cyclone cleaner?

A

It is a device used to separate contaminants from the flowing air.

78
Q

What is necessary when using flexible duct in a dust collection system?

A

Always use a non-collapsible duct type and only at the required measurement.

79
Q

What is a baghouse dust collection system configured for?

A

To clean and return air back into the plant

80
Q

What is required if a stack extends more then 10 ft. (3m) above a roof?

A

A guy wire set is required (3 guy wire assemblies per set minimum)

81
Q

What are the two stages to designing a dust collection system?

A

Sizing your ductwork for adequate volume and velocity, and computing the static pressure of the system to determine the size and power of the dust collection system.

82
Q

What are the five components to designing a exhaust system?

A

Identification of contaminants, determining how much airflow is needed to maintain velocity, determining the ductwork sizing, calculation of resistance, and finalizing the capacity of the blower.

83
Q

What is done to a machine that is seldom or is a pick-up hood that is added to the system between primary machines?

A

The size of the run is not increased.

84
Q

What is used to measure pressure within a local exhaust ventilation system?

A

inches of water column (wc)

85
Q

What is static pressure?

A

The resistance of airflow

86
Q

Static pressure losses in local exhaust systems are determined by?

A

Size of the duct, roughness of the duct material, number and type of elbows and changes in size, type of air cleaner, type of hood, volume of air flowing through the system, and stack design.

87
Q

What happens if proper makeup air is not provided?

A

Carbon monoxide poisoning can happen

88
Q

Static electricity build-up in a duct system increases the risk of?

A

A flash explosion or fire

89
Q

Where should you always run your ground wire to prevent static build-up?

A

Through both the inside and around the outside of all the piping.

90
Q

What type of wire should be used to safely ground the system?

A

Aluminum or copper wire

91
Q

What is the maximum face velocity when exhausting toxic fumes?

A

125 fpm

92
Q

What units are used to measure air velocity in a local exhaust ventilation system?

A

fpm

93
Q

What units are used to measure air volume in a local exhaust ventilation system?

A

cfm

94
Q

What is the formula used to figure out the volume of air flowing through a local ventilation exhaust system?

A

cfm=fpm x area

95
Q

What are 2 common classes of hoods used in a local ventilation exhaust system?

A

Enclosing and capturing

96
Q

What does a heavy material wheel look like?

A

A propeller made from extra steel plate with no backing and is used for handling air with material in it such as wood.

97
Q

What does a material handling wheel look like?

A

A propeller made from extra steel plate and has back plate as well to help prevent clogging

98
Q

Describe air-handling wheel?

A

It has the highest efficiency out of the three wheels and looks like a wheel.

99
Q

What does it mean to “place no charge on the connecting equipment” when talking about an industrial exhaust system?

A

You cannot hang from equipment, the duct must be independently hung.

100
Q

What is the maximum distance from a joint or a connection that a hanger can be placed?

A

2 diameters

101
Q

What is the minimum length of a draw band used in an industrial exhaust system?

A

4” inches

102
Q

What two things are compensated for by using an expansion joint?

A

Duct expansion and contraction

103
Q

What are two common wear areas?

A

Elbow heels and intersections of y-branches

104
Q

What is another name for a blast gate?

A

Slide damper

105
Q

What are common materials used in an industrial exhaust system?

A

Hot rolled carbon steel, cold rolled carbon steel, galvanized steel, aluminum and stainless sheets, and plastic materials (PVC)

106
Q

What is the minimum pitch to fasten the transverse seam on a round pipe in an industrial exhaust system?

A

6” on centre

107
Q

What classes can we use spiral round duct in an industrial exhaust system?

A

Class 1 and 2

108
Q

What class can we use aluminum duct in an industrial exhaust system?

A

Class 1 only

109
Q

Who is responsible to make sure workers have a safe working environment free from air born contaminants?

A

The employers

110
Q

What can be done to reduce energy consumption in a lab that employs a lot of exhaust systems?

A

A heat recovery system

111
Q

What type of system can optimize energy consumption in an industrial exhaust system?

A

VAV technology

112
Q

What is the minimum exit velocity in an industrial exhaust system?

A

3000 fpm

113
Q

What is the most important characteristic of the air travelling through the industrial exhaust duct system?

A

Conveying velocities

114
Q

Would a tube axial propeller be found in a centrifugal fan assembly?

A

No

115
Q

Where would you install a blast gate?

A

Close to the equipment that needs to be isolated

116
Q

What is the preferred centre line radius of an elbow?

A

2 1/2”

117
Q

What is the only choice for high toxic environments?

A

Local exhaust systems

118
Q

What type of pressure do axial fans have a hard time overcoming?

A

Static pressure

119
Q

What is the purpose of local exhaust hoods?

A

To capture contaminants and emissions

120
Q

What is the main advantage of using an auxiliary air fume hood?

A

To save heating energy costs

121
Q

What happens to the velocity when you lower the sash stop?

A

The face velocity increases

Commercial and Industrial HVAC (2 decks)

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