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Nate Air Distribution Flashcards

1
Q

What does the register do?

A

Controls velocity, flow rate, and direction of airsrteam.

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2
Q

What does the register do?

A

Controls velocity, flow rate, and direction of airsrteam.

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3
Q

On supply plenums, What is the purpose of the air cusion and how big should it be between the duct and end of plenum?

A

Air cushion ensures predictable flow to main ducts. Air cushion is eaqual to depth of the duct.

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4
Q

A standard elbow has:

A

curve ratio of 0.5 and a radius ratio of 1.5

- elbow shall be used where space permits.

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5
Q

How to find Curve ratio

A

inner side (throat radius) Ra/Rb outer side.

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6
Q

How to find Radius Ratio

A

legnth of center R of elbow /W

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7
Q

aspect ratio

A

relation between the width and depth of and elbow or rectangular ductwork.
- aspect ratio between .75-3.0 will not have an increase in friction loss. 6 is considered maximum

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8
Q

When shorter elbow must be used, what must be used to prevent friction loss

A

the turning vanes or splitters will bring it close to that of a standard elbow.

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9
Q

When having to choose between an elbow or square turn. When is it better to use a square turn.

A

when the throat radius is less than 4”

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10
Q

Take offs should not be placed closer than ___ duct diameters from tge downstream end of the elbow due to uneven turbulant air.

A

7’ 1/2”

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11
Q

What would reduce tubulant zone in half in a duct

A

a center splitter added to the trunk duct elbow would reduce the turbulant zone in half from 7’1/2” to 3’3/4”

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12
Q

If duct design requires a static take off to be very close to the trunk duct elbow what must be used in trunk duct elbow?

A

Elbow is to be changed to a square turn elbow

  • either formed blade turning vanes (2” 1/2) space.Turbulent zone is 1ft 6”3/4”
  • solid blade (3/4” spacing).Tubulent zone 5”5/8”
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13
Q

If velocity take-off is used within 7 1/2 duct diameters to a register, what precautions must be taken?

A
  • redesign of elbow with splitters or square elbow with turning vanes.
  • or static take-off needs to be used. (Typical take off perfered even with higher EL).
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14
Q

For a return duct, what take-off fitting shall be used?

A

-velocity, static take-offs causes higher friction loss due to air from take-off branch hitting the main air stream at right angle.

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15
Q

Duct approaches to outlets must be______ for good air distribution.

A

perpendicular.

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16
Q

What should be used when supplying air to a side wall outlet when duct is running perpendicular.

A

multiple curve deflectors at 90 degree angle to make air flow perpendicular to the outlet

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17
Q

For vertical stacks duct appraoch to outlets, what is not acceptable and the best fiiting to use?

A

round elbow with no splitters is unacceptable.

the best fiiting is a rectangular elbow with turning vanes.

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18
Q

What should the duct approach be to the ceiling outlet

A

Air has to make 90 degree before exiting the outlet.The closer the duct is to outlet the greater the need for correction. Vertical guide strips are to be installed in horizontal duct.

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19
Q

When should ductwork be insulated?

A

When temperature difference greater than 15 degrees between the inside and outside of the duct.

insulation needs to be lapped and stapled to prevent moisture entry.

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20
Q

How do fire dampers operate?

A

a fuse link reaches it rated melting temperature and releases damper.

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21
Q

How many types of fire dampers are there and what are they called?

A
  1. single blade
  2. Connected multiple blade
  3. interlock multiple blade.
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22
Q

When a fusable link in fire damper break, what is to be done to repair damper

A

replaced with the same rated fuse.

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23
Q

A velocity change of ___per minute equal 1 degree of temperature. The more velocity tge cooler.

A

15 ft/min

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24
Q

what should the local air velocities be in a residence

A

40 to 80 feet per min in cooling

below 40 in heating.

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25
Q

On the exterior walls, what natural convections are made in cooling and heating mode.

A

In heating mode the wall start as being cooler and current falls as room heats.

in cooling mode the walls are warmer and as room cools the air draft up

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26
Q

How can natural convection be eliminated in heating mode and cooling mode.

A

In cooling mode oulet need placed near the ceilings

in heating outlets installed near the floor.

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27
Q

Free Area of supply register

A

the amount of unobstructed air space through the register

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28
Q

Jet in register

A

the airstream that leaves the register. The supply air mixes with the room air and expands due to induction into the room.
- tends to to rise in heat mode and fall in cooling mode.

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29
Q

Throw in registers

A

The distance that the jet/air stream travels between the register and where the velocity terminates to certain level (50-35 ft/minute)

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30
Q

Drop in a register

A

The vertical distance that a horizontally projected airstream falls between the discharge and the end of its throw

Depends primarily on the amount if air and partially on the size of the outlet or velocity of air stream.

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31
Q

Spread in a register

A

the maximum divergence or width of an airstream at is terminal velocity.

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32
Q

Throw, drop and spread is limited by what…

A

volume of air flow causing higher face velocities on the register and the free area of the register and obstructions to air flow.

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33
Q

How can. a throw and drop be shortened

A

by lower airflow through duct and spreading the air. Also the airstream tends to hug the surface and contributes to comfort. use surfaces intentenally to minimize velocity in occupied space.

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34
Q

What are the 4 groups of Registers.

A

Group A horizontal high
Group B vertical non spreading
Group C vertical spreading
Group D horizontal low.

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35
Q

How many air changes per hour are recommended to prevent stagnation regions?

A

8 to 10 and hour.

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36
Q

What is the definition of stagnant air?

A

regions of air motions less than 15 ft/min

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37
Q

excessively long or sagging duct will ______ air flow

A

restrict

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38
Q

always wear _______&______ when working with sheet metal

A

glasses and gloves

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39
Q

equipment efficency is only as good as the_______ allows it to be.

A

duct system.

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40
Q

the 5

main types of duct systems & configurations are:

A
  1. reducing trunk duct system
  2. extended plenum system
  3. box duct system.
  4. perimeter loop
  5. perimeter radial
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41
Q

a well designed supply plenum will not have _______ of air in layers and will have _____ resistance.

A

stratification, low

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42
Q

stack heads are usually made of _______ or aluminum with _____ guage sheet metal.

A

galvanized, 30

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43
Q

standard depth of stacks inside of walls are ___” and widths of __” __“&___”

A

3 1/4, 8,10,12

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44
Q

stud are 16 inches separate on center but have____” in between studs

A

14 3/8”

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45
Q

the studded space can be used as long as it is not on an

A

exposed wall.

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46
Q

return duct can be _______,______ or______

A

galvanized steel, aluminum or any fire resistant material.

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47
Q

for basements or crawl spaces the joist space used for a return duct (panning) the space must be sealed with _____.

A

sheet metal, sime local codes may require the space to be lined with metal.

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48
Q

there is a ______ resistence to air flow at the dischare side of the blower.

A

substantial

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49
Q

round ducts have an __________ advantage of rectangular ducts

A

economical

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50
Q

metal branch ducts are made of ____ or ____ guage metal

A

30 or 28

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51
Q

For clean special rooms an average air motion of 100ft/min can be accomplished by supply air on one side of the room and _____ it at the other

A

exhausting.
object is to provide ultra clean air
air changes an hour can be 150 an hour.

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52
Q

high velocity from a register should have its jet at least ___ above the occupied zone in a room.
This will also provide the proper mixture of air in the room (air entrainment)

A

1 foot

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53
Q

Make sure to select registers that dont _____ or under throw.

A

overthrow causes cieling drafts and turbulences.

  • underthrowing air velocity before reaching the near end of the room causes stagnant zones and uneven tempratures.
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54
Q

Return are ideally located in _____ zones.

A

stagnant

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55
Q

For cooling you want _____ outlet with considerable spread. For heating you want fewer outlets with as little _____ as possible.

A

many, spread.

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56
Q

Returns should be installed ______ of the location of the supplies. But primarily in the _____ zones.

A

opposite, stagnant.

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57
Q

for grills not to exceed acceptable sound levels, velocity should not exceed ____ ft per minute.

A

500

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58
Q

commercial return grill free areas are mostly between and 55%

A

45%

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59
Q

if register is near the ceiling, the largest stagnant zone is in the floor in______ season.

A

heating

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60
Q

Perferablly return should be located in the______ for cooling and on the floor for ______

A

cieling, heating

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61
Q

For cooling a baseboard floor supply diffuser needs to have velocity of 750 ft/minute for a 20 degree split and _____ for a 15 degree split. Heating velocities in this application are not critical.

A

500 ft/minute.

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62
Q

vertical guide strips are to be applied in trunk duct in the static take off if the branch run out is to connect to a ______ _____

A

cieling outlet

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63
Q

For metal ducting joints can be sealed with mastic or approved _____.

A

tape

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64
Q

Square or Rectangular duct may be held together by ________, or various types of _______,________. Or Pittsburgh lock

A

button type snap locks, slips and drive clips

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65
Q

metal round duct is joined by either a crimpped end slipped into plain end by ______ or a ________. Pipes are to overlap at least ____and 3 screws evenly spread. If pipe is bigger than 12” 5 screws are to be applied.

Rectangular duct work use ____ or ____ fittings

A

sheet metal screws, draw band, 1”1/2, cleats, slip

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66
Q

For metal ductwork, _______ straps are to be secured to the ductwork and to the duct connections.

A

metal

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67
Q

Metal horizontal rectangular ducts up to 60” wide need supported with ___ wide ____ _______ hangers spaced no more than ____ apart. For heavier duct use threaded rod with angle iron.

A

1”, Galvanized steel, 10feet

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68
Q

Duct systems must be at least___ above earth surface.

A

4”

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69
Q

Encase a duct system in at least __” of concrete when installed under a concrete slab.

A

2”

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70
Q

UL_____ duct tape is approved for use with duct materials.

A

181

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71
Q

Roof top ductwork must have a insulation __” thick and an approved vapor barrier. For an attic, garage and crawl space insulation _” thick shall be used.

A

3”, 1”

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72
Q

A fire___ may be required when ducts run vertically through floors. Fire and fumes could travel up duct.

A

stop

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73
Q

If the AHU is centrally located. A _______ duct system should be used. The trunk ducts cannot exceed ___ feet in length without reduction. Branch ducts are to come out of the ____ sides of plenum.

A

extended plenum, 24, 2

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74
Q

If the AHU is located at one end of the building the ______ system shall be used to maintain air velocity.

A

reducing extended plenum

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75
Q

Plenums and duct work may be insulated to reduce the likely hood of _______ or _______ problems.

A

condensation, noise

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76
Q

Heavier ductwork. can be hung with _____ ____ or angle iron.

A

threaded rod.

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77
Q

Single phase electric heaters cannot exceed __ amps and the breaker must be a double-pole single - throw with a maximum ___ amps

A

48, 60

78
Q

Flex duct slides over collar bead at least __” but ___ with the mastic method.
For metalic flex duct slide __” minimum and tape over screw heads.
For metal duct slide____”

A

1”/2”,1”, 1-1/2”

79
Q

flex duct core need at least __ wraps of approved tape and a ________ when connecting to boot or collar.

A

2, drawband.

80
Q

flex duct runs should avoid _____ bends and kept ____ and straight as possible to minimize pressure loss.

A

sharp, short

81
Q

the diameter of the flex duct should never be less than its ______ diameter.

A

original

82
Q

Horizontal duct should be supported every ___’ and sag no less than a __” per foot in between supports of ___ wide.

A

4ft, 1/2”, 1 1/2”

83
Q

Make sure supports dont restrict duct ______.

A

diameter.

84
Q

sheet metal collars for flexible duct must be at least ___ long.

A

4”

85
Q

sheet metal sleeves used to join 2 sections of ductwork must be at least ___ long

A

4”

86
Q

A general guideline to join to flex duct together are to butt the cores together over the sleeve and ____ them together and secure with __ clamps. insulation jacket is to be pulled over and wraped with at least _ wraps of duct tape.

A

tape, 2,2

87
Q

metalic flex duct needs masic when system is over ___ wg.

A

4”

88
Q

For installs leas than 4” wg seal with ________ over screw heads.

A

2 wraps of duct tape

89
Q

Slide metalic flex duct at least ___” over collar bead or 4” sleeve when joining metalic flex ducts

A

1”

90
Q

Secure metalic flex duct with #__ spaced equally around the circumference. 3 are used below 12” and 5 above 12” diameter of duct.

A

8 sheet metal screws

91
Q

Tape insulation with 2 wraps around joint or use a _____ or a combination of both.

A

drawband

92
Q

The outside of a duct board is foil and it reflects ______ and _______.

A

heat, moisture.

93
Q

The outside surface of ductboard cannot excees ____degrees and the inside 250 degrees

A

150

94
Q

What is the Mixed air temprature formula for an air distribution system which includes outside air and return air for total return air flow?

A

Mixed air temprature = ( ( Return Air %) (Return Ait Temprature) + ( Outside Air %)(Outside Air Temprature)

95
Q

what are some properties of air

A

pressure, drybulb, wetbulb, absolute humidity( grains of moisture), relative humidity, volume, enthalpy.

96
Q

how many properties need to be known to plot a condition of the air?

A

3

97
Q

a pychrometrics chart represents what measurement of air?

A

1 pound of moist air.

98
Q

Do we use the same or different pychrometric chart for higher elevations

A

different

99
Q

as the volume of air changes the density or barometric pressure changes?

A

density

100
Q

a pychrometrics chart is nothing more than _____ of scales on top of eachother

A

many

101
Q

what are the 3 benefits of the pychrometrics chart

A
  1. Relationships between the properties of air
  2. The value of theses properties for a pound of moist air
  3. Used to measure changes of air through a process
102
Q

On the Pychrometrics Chart the straight veetical lines represent what property of air

A

Dry bulb temprature.

103
Q

On a Pychrometrics Chart what do the diagnol lines represent and are read on the left side on a pychrometrics chart?

A

wet bulb temprature

104
Q

what property of air do the curved lines represent and are read on the scale lines on a pychrometrics chart?

A

relative humidity

105
Q

What do the horizontal lines represent and are read on the left side of the pychrometrics chart?

A

dew point temprature

106
Q

what do the horizontal lines represent and are read on the right side of the pychrometrics chart?

A

absolute humidity (grains of moisture)

107
Q

one pound of water holds ______grains of water but is rounded to______ normally in the industry.

A

7007, 7000

108
Q

The property of air that has diagnol lines running through the. Pychrometrics chart but the value is read in within the lines is what?

A

specific volume

109
Q

the btu/lb is has lines running diagnol but are reaf on what side(s)

A

left, right, and bottom

110
Q

If a process plotted on pychrometrics chart runs diagnolly down towards the left, what process does this represent?

A

sensible and latent heat removal (cooling)

111
Q

If a process is plotted on a pychrometrics chart runs vertically straight towards the right, what does this represent?

A

no latent heat change but sensible geat added (heating)

112
Q

If a line of a process is running upward towards the left on a pychrometrics chart what does it represent?

A

sensible heat removal’ latent heat added ( evaporative cooling)

113
Q

How does air move from point to point?

A

By pressure difference between 2 point no matter how small.

114
Q

What are typical fan speed percentages in a residential direct drive mutispeed blower equipment?

A

high 100%
medium 90%
low 80 %

115
Q

What is the airflow rating for cooling

A

400 cfm per ton

116
Q

what is the air flow rating for heat pumps

A

425-450 cfm per ton

117
Q

what is the airflow rating for electric heat?

A

min or max velocity or max temp output.

118
Q

what is the air flow ratong for gas heat

A

the correct temprature rise

119
Q

what is the airflow rating for ventilation

A

airchange rate per hour

120
Q

it is impossible to get the exact air flow on a system but get as _____ as possible

A

close

121
Q

What does an air capture hood measure. to calculate cfm?

A

static pressure or temperature.

122
Q

What does a vane anemometer measure and what mechanism does it use? Has a _____ or ______ display.

A

it measures rpm of the mechanical vane and uses it to calculate air velocity.
It has a mechanical or digital display

123
Q

What does a Hot wire anemometer measure and how?

A

it measure temprature by an electric heater next to a thermister. The faster the air flow, the less heat reaches the thermister. The instrument measures air velocity.

124
Q

What does a manometer measure?

A

measures duct pressure with two hoses in inches of water column. they measure negative, positive and differential pressure.

125
Q

What does a digital manometer measure

A

Draft pressure, pressure switch, system return, supply and total static pressure.

126
Q

Manehelic Guages measure what?

A

Low pressure by dwyer
pressure differential
various ranges
Capsuhelic for water pressure.

127
Q

Inclined manometers are used when

A

often permanently mounted to equipment

and is either inclined or slanted and uses a colored liquid that raises and lowers in response to pressure.

128
Q

U- Tube manometers are used when?

A

A colored liquid raises and lowers in response to pressure.

-made of glass or soft rolled up plastic.

129
Q

Digital Contact Thermometer

A

measures only dry bulb air temprature.

130
Q

Digital non-contact thermometer

A

Hard to reach dry bulb temps, structure dry bulb temps, unit component drybulb temp.

131
Q

sling pychrometer

A

consists of 2 identical mercury bulb thermometers (very accurate) one has a moist cotton sock over it: they measure drybulb and wetbulb temprature to calculate relative humidity.

rotate 120 to 180 rpms with the cotton sock

132
Q

digital pychrometer

A

db, wb, dp, & rh tempratures.

133
Q

Airflow Measurement Methods

A
  • Directly (balometer)
  • velocity times duct area
  • square root of velocity pressure times 4005 times duct area
  • electric heat rise formula
  • fuel heat rise formula
  • manufacter performance data (TESP)
  • manufacters performance data (Watts)
134
Q

For small ducts measure velocity in the _____ of the duct

A

center

135
Q

for large duct _____ to find the average velocity

A

traverse

136
Q

Velocity measurements need a correction factor for high altitudes. Why?

A

altitude affects density. and volume of air. This will render incorrect readings without a correction factor.

137
Q

electric heat formula

A

CFM = Watts/ (TDx .316)

Blower must be clean

138
Q

Fuel temprature rise formula

A

CFM= BTU Output/(TD x 1.08)

139
Q

Fans (axial)

A
  • Propellar type(condenser fans)- high flow, low static

- High noise tube axial and vane axial.

140
Q

Blowers ( centrifugal fans )

A 
Squirrel cage (indoor blowers)
High flow
low noise
high static
forward curve
Backward curved( commercial)
radial ( commercial )
141
Q

What is the Stepwise air balancing method

A

1.Pass 1
2. Calculate measured airflow vs design air flow for percentage of design.
3. Reduce damper of the over design percentage register close to minimum percentage.
4. Pass 2
5. Repeat step 3
6 Pas 3

142
Q

What is rhe process for the proportional balancing method

A
  1. Pass 1
  2. List all Register from. measured lowest design at the top to the largest on the bottom
  3. Adjust the second lowest percentage till both the lowest and the second lowest match design percentage.
  4. repeat step 3 for the third lowest to the second lowest design percentage.
  5. Keep repeating step 3.
143
Q

when adjusting damper to lower air flow for one branch duct what happens to the others

A

the air flow increases in the other run outs

144
Q

What are the advantages and disadvantages to the Step wise Method of air balancing

A

Advantages: Quick
Disadvantage: Balance of a near by diffuser can be off by 20% a the most Even though the measurements are within rating. Not as tight of a balance.

145
Q

what are the advantages and disadvantages of the. proportional balancing method

A

advantage: tight balance
disadvantage: time consuming

146
Q

The only changes to a system the Air Balancer makes to a system is what

A

increasing/decreasing fan speed/rpm

adjusting dampers and air control devices.

147
Q

What is required on a Report

A

room name
grille number
grille size
cfm design

148
Q

What can stop an air balancing from being complete.

A
  • system is incomplete

- not having nameplate data

149
Q

What blower amperage indicates damaged blower

A

65% of fla

150
Q

what rpm indicates damaged blower

A

20%

151
Q

a system that is not within +/- 10% must be balanced by what method & how would the design air flow be adjusted in the report.

A

proportional method

divide the total measured airflow by the design airflow. Multiply each register design airflow by the calculated ratio.

152
Q

Air balancing hoods are pre-programmed for what type of air

A

70 degree air at see level.

153
Q

if a registar is lower than _____% of design airflow duct work needs inspected.

A

70

154
Q

noise is proportional to ____

A

airflow

155
Q

JOINING 2 Rectangular sheet metal ducts the slip fittings ( s- clip) is installed ____ on the longer sides of duct. Cut ______ than side of duct. The Drive cleat ( c- clip ) is installed second and is used on tbe shorter sides of duct. Cut _____ than the side of duct

A

first, shorter, longer

156
Q

For flat sheetmetal duct connections the _____ is used for flat. The ______ for round duct.

A

Groove seem, Acme Lock

157
Q

For corners of sheet metal duct the corners are joined by either the ______ or the ______ connection

A

snap lock, Pittsburgh lock

158
Q

Ductboard is made of ____, ____, and ______.

A

Fiberglass, rockwool, and slag wool.

159
Q

thickness of ductboard is ___, ____, or ___ in depth. Requires external support or ________ reinforcment.

A

1”, 1-1/2”,or 2”, reinforcement.

160
Q

Joining ductboard must be either ______ or _______.

A

stapling flaps, cross tabs.

161
Q

Ductboard can be condigured in either of the what following shapes

A

polygon, rectangular, round or square.

162
Q

Heat sensitive tape is to be heated to ______ degrees and than stress pressure is applied at ____ degrees and is __” wide. Green dots darken when ____ temprature is reached.

A

500, 150, 3, bonding

163
Q

When fastening ductboard with screws, use screws that are __” longer than board thickness.

A

1/2”

164
Q

when securing ductboard to metal surface, use #__ screws with ____ inch washers

A

10, 2 1/2

165
Q

strategies for sealing ductboard are

A
  • pressure sensitive aluminum foil tape
  • heat activated aluminum foil tape
  • glass fabric tape with mastic
166
Q

For shiplap joints, staple the flap of the seam every __” on center. Tape must overlap flap joint a minimum of __” on both sides.

A

2, 1

167
Q

for joints without flaps and seams ( buttjoints ) _________ must be used. they must be __” long and place perpendicularly every __” across tapped joint.

A

cross tabs, 8, 12

168
Q

foil tape under 50 degrees needs ______ before use.

A

preheated

169
Q

For larger ductboard systems, the use of ______ is applied. They must be ___ guage galvanized wire. Must be spaced __” apart vertically inside duct. Placed __” from female end and __” from butt joint.

A

Tie rods, 12, 16, 4, 3.

170
Q

the shape of the tie rods washer can either be ____ or _____

A

round, square

171
Q

To prevent water damage to furnace and ducts always use horizontal wall registers in _____, _____, or _____.

A

bathrooms, kitchens, and utility rooms.

172
Q

Branch ducts should never be connected to the _____ of the plenum. It will act as an extended plenum and throw off the air balance.

A

end

173
Q

Fan powered and atomizinv humidifier is mounted on the ____ side of unit.

A

supply.

174
Q

___________ filters provide odor removal.

A

charcoal

175
Q

particals pass through EAC and become positively charged by _____ _______ and than collected by the ______ collector plates. Plates must be claened.

A

ionizing wires, negatively charge

176
Q

use bead fittings when using _________ clamps

A

non metalic

177
Q

Cant use non metalic clamps past ___ wg. positive.

A

6 in

178
Q

MERV is an acronym for

and HEPA is for

A

Minimum Efficiency Reporting Value

High Efficiency Particulate Absorbing

179
Q

Maximum velocity recommended for return grill is ____ and for filter return grill ____

A

500, 300

180
Q

Recommended velocities for a disposable filter are____ for a hepa filter ____ and a eac_____

A

700-750, 250, 500

181
Q

recommended velocities across coils are ____ for evaporators____ for condensing coils and ___ for hot water coils.

A

500 ft/min, 1000ft/min,, 700ft/min

182
Q

Static pressure is proportional to the ___ percentage of velocity.

A

square

183
Q

for the supply flexable duct maximum velocities are ___ for branch and trunk ducts but recommended at ____.

A

700, 600

184
Q

for flexable return duct maximum velocities of ____ are for branch and trunk but ____ for branch and ____for trunk are recommended

A

700, 400, 600

185
Q

face velocity for register maximum _____ and recommended ____

A

700, size for throw

186
Q

for supply rigid duct work velocities of ____ is maximum for branch and trunk but ___ is recommended for trunk and ____ for branch.

A

900, 700, 600

187
Q

for ruturn rigid duct work velocities of _____ is maximum for trunk and branch but ____ is recommended for trunk and ____ for branch

A

700, 600, 400

188
Q

Pressure loss due to resistance in a reducer at 60degrees is ___% and for an increaser ___%.

A

5.4%, 10%

189
Q

An angle of ____ to ____ degrees is used for increasers

A

10-20

190
Q

For abrupt change from small duct to large duct, what would the be ideal to decrease pressure loss/ decreasing the angle of transition.

A

degrees/ number of spiltter = new angle ( 10 to 20degrees perferred.)

Nate (5 decks)

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