Nate Air Distribution Flashcards
1
Q
What does the register do?
A
Controls velocity, flow rate, and direction of airsrteam.
2
Q
What does the register do?
A
Controls velocity, flow rate, and direction of airsrteam.
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.
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.
5
Q
How to find Curve ratio
A
inner side (throat radius) Ra/Rb outer side.
6
Q
How to find Radius Ratio
A
legnth of center R of elbow /W
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
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.
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”
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”
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”
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”
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).
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.
15
Q
Duct approaches to outlets must be______ for good air distribution.
A
perpendicular.
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
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.
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.
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.
20
Q
How do fire dampers operate?
A
a fuse link reaches it rated melting temperature and releases damper.
21
Q
How many types of fire dampers are there and what are they called?
A
- single blade
- Connected multiple blade
- interlock multiple blade.
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.
23
Q
A velocity change of ___per minute equal 1 degree of temperature. The more velocity tge cooler.
A
15 ft/min
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.
25
On the exterior walls, what natural convections are made in cooling and heating mode.
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
26
How can natural convection be eliminated in heating mode and cooling mode.
In cooling mode oulet need placed near the ceilings
in heating outlets installed near the floor.
27
Free Area of supply register
the amount of unobstructed air space through the register
28
Jet in register
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.
29
Throw in registers
The distance that the jet/air stream travels between the register and where the velocity terminates to certain level (50-35 ft/minute)
30
Drop in a register
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.
31
Spread in a register
the maximum divergence or width of an airstream at is terminal velocity.
32
Throw, drop and spread is limited by what...
volume of air flow causing higher face velocities on the register and the free area of the register and obstructions to air flow.
33
How can. a throw and drop be shortened
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.
34
What are the 4 groups of Registers.
Group A horizontal high
Group B vertical non spreading
Group C vertical spreading
Group D horizontal low.
35
How many air changes per hour are recommended to prevent stagnation regions?
8 to 10 and hour.
36
What is the definition of stagnant air?
regions of air motions less than 15 ft/min
37
excessively long or sagging duct will ______ air flow
restrict
38
always wear _______&______ when working with sheet metal
glasses and gloves
39
equipment efficency is only as good as the_______ allows it to be.
duct system.
40
the 5
| main types of duct systems & configurations are:
1. reducing trunk duct system
2. extended plenum system
3. box duct system.
4. perimeter loop
5. perimeter radial
41
a well designed supply plenum will not have _______ of air in layers and will have _____ resistance.
stratification, low
42
stack heads are usually made of _______ or aluminum with _____ guage sheet metal.
galvanized, 30
43
standard depth of stacks inside of walls are ___" and widths of __" __"&___"
3 1/4, 8,10,12
44
stud are 16 inches separate on center but have____" in between studs
14 3/8"
45
the studded space can be used as long as it is not on an
exposed wall.
46
return duct can be _______,______ or______
galvanized steel, aluminum or any fire resistant material.
47
for basements or crawl spaces the joist space used for a return duct (panning) the space must be sealed with _____.
sheet metal, sime local codes may require the space to be lined with metal.
48
there is a ______ resistence to air flow at the dischare side of the blower.
substantial
49
round ducts have an __________ advantage of rectangular ducts
economical
50
metal branch ducts are made of ____ or ____ guage metal
30 or 28
51
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
exhausting.
object is to provide ultra clean air
air changes an hour can be 150 an hour.
52
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)
1 foot
53
Make sure to select registers that dont _____ or under throw.
overthrow causes cieling drafts and turbulences.
- underthrowing air velocity before reaching the near end of the room causes stagnant zones and uneven tempratures.
54
Return are ideally located in _____ zones.
stagnant
55
For cooling you want _____ outlet with considerable spread. For heating you want fewer outlets with as little _____ as possible.
many, spread.
56
Returns should be installed ______ of the location of the supplies. But primarily in the _____ zones.
opposite, stagnant.
57
for grills not to exceed acceptable sound levels, velocity should not exceed ____ ft per minute.
500
58
commercial return grill free areas are mostly between and 55%
45%
59
if register is near the ceiling, the largest stagnant zone is in the floor in______ season.
heating
60
Perferablly return should be located in the______ for cooling and on the floor for ______
cieling, heating
61
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.
500 ft/minute.
62
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 ______ _____
cieling outlet
63
For metal ducting joints can be sealed with mastic or approved _____.
tape
64
Square or Rectangular duct may be held together by ________, or various types of _______,________. Or Pittsburgh lock
button type snap locks, slips and drive clips
65
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
sheet metal screws, draw band, 1"1/2, cleats, slip
66
For metal ductwork, _______ straps are to be secured to the ductwork and to the duct connections.
metal
67
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.
1", Galvanized steel, 10feet
68
Duct systems must be at least___ above earth surface.
4"
69
Encase a duct system in at least __" of concrete when installed under a concrete slab.
2"
70
UL_____ duct tape is approved for use with duct materials.
181
71
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.
3", 1"
72
A fire___ may be required when ducts run vertically through floors. Fire and fumes could travel up duct.
stop
73
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.
extended plenum, 24, 2
74
If the AHU is located at one end of the building the ______ system shall be used to maintain air velocity.
reducing extended plenum
75
Plenums and duct work may be insulated to reduce the likely hood of _______ or _______ problems.
condensation, noise
76
Heavier ductwork. can be hung with _____ ____ or angle iron.
threaded rod.
77
Single phase electric heaters cannot exceed __ amps and the breaker must be a double-pole single - throw with a maximum ___ amps
48, 60
78
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____"
1"/2",1", 1-1/2"
79
flex duct core need at least __ wraps of approved tape and a ________ when connecting to boot or collar.
2, drawband.
80
flex duct runs should avoid _____ bends and kept ____ and straight as possible to minimize pressure loss.
sharp, short
81
the diameter of the flex duct should never be less than its ______ diameter.
original
82
Horizontal duct should be supported every ___' and sag no less than a __" per foot in between supports of ___ wide.
4ft, 1/2", 1 1/2"
83
Make sure supports dont restrict duct ______.
diameter.
84
sheet metal collars for flexible duct must be at least ___ long.
4"
85
sheet metal sleeves used to join 2 sections of ductwork must be at least ___ long
4"
86
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.
tape, 2,2
87
metalic flex duct needs masic when system is over ___ wg.
4"
88
For installs leas than 4" wg seal with ________ over screw heads.
2 wraps of duct tape
89
Slide metalic flex duct at least ___" over collar bead or 4" sleeve when joining metalic flex ducts
1"
90
Secure metalic flex duct with #__ spaced equally around the circumference. 3 are used below 12" and 5 above 12" diameter of duct.
#8 sheet metal screws
91
Tape insulation with 2 wraps around joint or use a _____ or a combination of both.
drawband
92
The outside of a duct board is foil and it reflects ______ and _______.
heat, moisture.
93
The outside surface of ductboard cannot excees ____degrees and the inside 250 degrees
150
94
What is the Mixed air temprature formula for an air distribution system which includes outside air and return air for total return air flow?
Mixed air temprature = ( ( Return Air %) (Return Ait Temprature) + ( Outside Air %)(Outside Air Temprature)
95
what are some properties of air
pressure, drybulb, wetbulb, absolute humidity( grains of moisture), relative humidity, volume, enthalpy.
96
how many properties need to be known to plot a condition of the air?
3
97
a pychrometrics chart represents what measurement of air?
1 pound of moist air.
98
Do we use the same or different pychrometric chart for higher elevations
different
99
as the volume of air changes the density or barometric pressure changes?
density
100
a pychrometrics chart is nothing more than _____ of scales on top of eachother
many
101
what are the 3 benefits of the pychrometrics chart
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
On the Pychrometrics Chart the straight veetical lines represent what property of air
Dry bulb temprature.
103
On a Pychrometrics Chart what do the diagnol lines represent and are read on the left side on a pychrometrics chart?
wet bulb temprature
104
what property of air do the curved lines represent and are read on the scale lines on a pychrometrics chart?
relative humidity
105
What do the horizontal lines represent and are read on the left side of the pychrometrics chart?
dew point temprature
106
what do the horizontal lines represent and are read on the right side of the pychrometrics chart?
absolute humidity (grains of moisture)
107
one pound of water holds ______grains of water but is rounded to______ normally in the industry.
7007, 7000
108
The property of air that has diagnol lines running through the. Pychrometrics chart but the value is read in within the lines is what?
specific volume
109
the btu/lb is has lines running diagnol but are reaf on what side(s)
left, right, and bottom
110
If a process plotted on pychrometrics chart runs diagnolly down towards the left, what process does this represent?
sensible and latent heat removal (cooling)
111
If a process is plotted on a pychrometrics chart runs vertically straight towards the right, what does this represent?
no latent heat change but sensible geat added (heating)
112
If a line of a process is running upward towards the left on a pychrometrics chart what does it represent?
sensible heat removal' latent heat added ( evaporative cooling)
113
How does air move from point to point?
By pressure difference between 2 point no matter how small.
114
What are typical fan speed percentages in a residential direct drive mutispeed blower equipment?
high 100%
medium 90%
low 80 %
115
What is the airflow rating for cooling
400 cfm per ton
116
what is the air flow rating for heat pumps
425-450 cfm per ton
117
what is the airflow rating for electric heat?
min or max velocity or max temp output.
118
what is the air flow ratong for gas heat
the correct temprature rise
119
what is the airflow rating for ventilation
airchange rate per hour
120
it is impossible to get the exact air flow on a system but get as _____ as possible
close
121
What does an air capture hood measure. to calculate cfm?
static pressure or temperature.
122
What does a vane anemometer measure and what mechanism does it use? Has a _____ or ______ display.
it measures rpm of the mechanical vane and uses it to calculate air velocity.
It has a mechanical or digital display
123
What does a Hot wire anemometer measure and how?
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
What does a manometer measure?
measures duct pressure with two hoses in inches of water column. they measure negative, positive and differential pressure.
125
What does a digital manometer measure
Draft pressure, pressure switch, system return, supply and total static pressure.
126
Manehelic Guages measure what?
Low pressure by dwyer
pressure differential
various ranges
Capsuhelic for water pressure.
127
Inclined manometers are used when
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
U- Tube manometers are used when?
A colored liquid raises and lowers in response to pressure.
| -made of glass or soft rolled up plastic.
129
Digital Contact Thermometer
measures only dry bulb air temprature.
130
Digital non-contact thermometer
Hard to reach dry bulb temps, structure dry bulb temps, unit component drybulb temp.
131
sling pychrometer
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
digital pychrometer
db, wb, dp, & rh tempratures.
133
Airflow Measurement Methods
- 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
For small ducts measure velocity in the _____ of the duct
center
135
for large duct _____ to find the average velocity
traverse
136
Velocity measurements need a correction factor for high altitudes. Why?
altitude affects density. and volume of air. This will render incorrect readings without a correction factor.
137
electric heat formula
CFM = Watts/ (TDx .316)
| Blower must be clean
138
Fuel temprature rise formula
CFM= BTU Output/(TD x 1.08)
139
Fans (axial)
- Propellar type(condenser fans)- high flow, low static
| - High noise tube axial and vane axial.
140
Blowers ( centrifugal fans )
```
Squirrel cage (indoor blowers)
High flow
low noise
high static
forward curve
Backward curved( commercial)
radial ( commercial )
```
141
What is the Stepwise air balancing method
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
What is rhe process for the proportional balancing method
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
when adjusting damper to lower air flow for one branch duct what happens to the others
the air flow increases in the other run outs
144
What are the advantages and disadvantages to the Step wise Method of air balancing
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
what are the advantages and disadvantages of the. proportional balancing method
advantage: tight balance
disadvantage: time consuming
146
The only changes to a system the Air Balancer makes to a system is what
increasing/decreasing fan speed/rpm
| adjusting dampers and air control devices.
147
What is required on a Report
room name
grille number
grille size
cfm design
148
What can stop an air balancing from being complete.
- system is incomplete
| - not having nameplate data
149
What blower amperage indicates damaged blower
65% of fla
150
what rpm indicates damaged blower
20%
151
a system that is not within +/- 10% must be balanced by what method & how would the design air flow be adjusted in the report.
proportional method
divide the total measured airflow by the design airflow. Multiply each register design airflow by the calculated ratio.
152
Air balancing hoods are pre-programmed for what type of air
70 degree air at see level.
153
if a registar is lower than _____% of design airflow duct work needs inspected.
70
154
noise is proportional to ____
airflow
155
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
first, shorter, longer
156
For flat sheetmetal duct connections the _____ is used for flat. The ______ for round duct.
Groove seem, Acme Lock
157
For corners of sheet metal duct the corners are joined by either the ______ or the ______ connection
snap lock, Pittsburgh lock
158
Ductboard is made of ____, ____, and ______.
Fiberglass, rockwool, and slag wool.
159
thickness of ductboard is ___, ____, or ___ in depth. Requires external support or ________ reinforcment.
1", 1-1/2",or 2", reinforcement.
160
Joining ductboard must be either ______ or _______.
stapling flaps, cross tabs.
161
Ductboard can be condigured in either of the what following shapes
polygon, rectangular, round or square.
162
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.
500, 150, 3, bonding
163
When fastening ductboard with screws, use screws that are __" longer than board thickness.
1/2"
164
when securing ductboard to metal surface, use #__ screws with ____ inch washers
10, 2 1/2
165
strategies for sealing ductboard are
- pressure sensitive aluminum foil tape
- heat activated aluminum foil tape
- glass fabric tape with mastic
166
For shiplap joints, staple the flap of the seam every __" on center. Tape must overlap flap joint a minimum of __" on both sides.
2, 1
167
for joints without flaps and seams ( buttjoints ) _________ must be used. they must be __" long and place perpendicularly every __" across tapped joint.
cross tabs, 8, 12
168
foil tape under 50 degrees needs ______ before use.
preheated
169
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.
Tie rods, 12, 16, 4, 3.
170
the shape of the tie rods washer can either be ____ or _____
round, square
171
To prevent water damage to furnace and ducts always use horizontal wall registers in _____, _____, or _____.
bathrooms, kitchens, and utility rooms.
172
Branch ducts should never be connected to the _____ of the plenum. It will act as an extended plenum and throw off the air balance.
end
173
Fan powered and atomizinv humidifier is mounted on the ____ side of unit.
supply.
174
___________ filters provide odor removal.
charcoal
175
particals pass through EAC and become positively charged by _____ _______ and than collected by the ______ collector plates. Plates must be claened.
ionizing wires, negatively charge
176
use bead fittings when using _________ clamps
non metalic
177
Cant use non metalic clamps past ___ wg. positive.
6 in
178
MERV is an acronym for
| and HEPA is for
Minimum Efficiency Reporting Value
| High Efficiency Particulate Absorbing
179
Maximum velocity recommended for return grill is ____ and for filter return grill ____
500, 300
180
Recommended velocities for a disposable filter are____ for a hepa filter ____ and a eac_____
700-750, 250, 500
181
recommended velocities across coils are ____ for evaporators____ for condensing coils and ___ for hot water coils.
500 ft/min, 1000ft/min,, 700ft/min
182
Static pressure is proportional to the ___ percentage of velocity.
square
183
for the supply flexable duct maximum velocities are ___ for branch and trunk ducts but recommended at ____.
700, 600
184
for flexable return duct maximum velocities of ____ are for branch and trunk but ____ for branch and ____for trunk are recommended
700, 400, 600
185
face velocity for register maximum _____ and recommended ____
700, size for throw
186
for supply rigid duct work velocities of ____ is maximum for branch and trunk but ___ is recommended for trunk and ____ for branch.
900, 700, 600
187
for ruturn rigid duct work velocities of _____ is maximum for trunk and branch but ____ is recommended for trunk and ____ for branch
700, 600, 400
188
Pressure loss due to resistance in a reducer at 60degrees is ___% and for an increaser ___%.
5.4%, 10%
189
An angle of ____ to ____ degrees is used for increasers
10-20
190
For abrupt change from small duct to large duct, what would the be ideal to decrease pressure loss/ decreasing the angle of transition.
degrees/ number of spiltter = new angle ( 10 to 20degrees perferred.)
