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67 Cards in this Set
- Front
- Back
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What is the density of air? |
How much air weighs per cubic foot |
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What is the specific volume of air? |
How much volume one pound of air occupies. |
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What is the relative humidity of air? |
The percent of moisture the air is holding vs the amount it could hold if saturated. |
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Air __________ as it's heated. |
Expands |
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Air pressure in a sealed balloon is an example of ___________ _____________. |
Static pressure. |
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A blower, when connected to a length of duct, creates: |
Static pressure, which is then converted to velocity pressure. |
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Velocity pressure is determined by: |
Subtracting static pressure from total pressure. Tp = Sp + Vp |
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Velocity pressure can be mathematically converted to: |
FPM FPM = 4005(sqrt Vp) |
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An inclined manometer is basically: |
A u-tube manometer tilted at a steep angle. |
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What is the formula used for determining CFM using velocity and duct cross sectional area? |
CFM = A x V Where: A = cross sectional area in sq ft V = velocity in FPM |
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A duct measures 18" x 24". The air velocity is 600 FPM. How many CFM are being delivered through the duct? |
1800 CFM 18" = 1.5ft 24" = 2ft A = W x H = 1.5 x 2 = 3sqft CFM = A x V = 3 x 600 = 1800CFM |
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The static pressure of a duct is 1.76" and the total pressure is 2". What is the velocity pressure? |
.24" Tp = Sp + Vp Tp - Sp = Vp 2 - 1.76 = .24 |
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A pitot tube can directly measure: |
Total pressure Static pressure |
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A series of carefully spaced Vp readings that can be converted to FPM using an equation. |
Duct traverse. |
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How many holes must be made in a round duct in order to take a series of traverse readings? |
Two. |
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A thermo-anemometer measures: |
FPM directly. |
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The temperature at which water vapor in the air will condense into a liquid. The temperature at which air gives up its moisture. The saturation temperature of water in a body of air. These are all definitions of: |
Dew point. |
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Dehumidification occurs when an air conditioning coil operates... |
... at or below he dew point of the air moving across it. |
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Who usually decides if a duct leakage test is to be performed, as well as the test pressure as which it will be performed? |
The design engineer. |
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The six things that happen as dry bulb temperature increases are: |
-The wet bulb temperature increases -The dew point remains the same -The relative humidity decreases -The specific humidity remains the same -Specific volume increases -Density decreases |
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There are __________ grains of water vapor per pound of water. |
7,000 |
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There are _________ lbs/cuft of air. |
0.075 |
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Cooling the air raises its __________________. |
Relative humidity |
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When wet and dry bulb temperatures are the same: |
-Relative humidity is 100% -Dew point is equal to the wet and dry bulb readings. |
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A sensible heat ratio of 1.0 means that the evaporator coil will: |
Only cool the air with no change in specific humidity. |
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Decreasing the CFM over an evaporator will _________ the amount of moisture removed from the air. |
Increase |
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A rotating velometer measures: |
Feet. (Must monitor gauge for 60sec to determine FPM) |
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Return air grilles are not to be installed in: |
Kitchens or bathrooms. |
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Proper CFM for each room is determined by: |
A detailed room-by-room heat load calculation. |
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On residential duct installations, the accepted method of attaching duct sections to each other is the __________________ method. |
Slip and Drive |
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5ft off the floor on an inside wall. Near a return air register. In the most central location of the home. These are all examples of what? |
Acceptable thermostat mounting locations. |
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5ft off the floor on an outside wall is an example of what? |
Unacceptable thermostat mounting locations. |
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What is the definition of Accuracy when applied to instruments? |
A measure of how close the measurement is to being correct. |
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What is the definition of Precision when applied to instruments? |
How small a value the instrument can detect. |
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What is the definition of Range when applied to instruments? |
The difference between the lowest and highest readings an instrument can measure. |
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A duct with an inside area of 4sqft has a velocity of 1000fpm. What is the CFM being supplied through the duct? |
4,000 CFM = A x V = 4 x 1,000 = 4,000 |
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A 32" x 32" square duct is to be changed to a height of 28" as to fit around an obstruction in a boiler room. How wide must the duct be to maintain the same area? Round to the nearest whole number. |
37" H x W = H1 x W1 32 x 32 = 28 x W1 1024 = 28 x W1 1024 / 28 = W1 W1 = 36.57 |
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Register boot End boot Starting collar These are all examples of what? |
Sheet metal duct fittings. |
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The greater velocity, the greater _______________ there is to a change in direction. |
Resistance |
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If duct area decreases, velocity ________________. |
Increases. |
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Which of the following is not a duct system type? -Radial duct system -Extended plenum duct system -Perimeter duct system -Equal friction duct system |
Equal friction duct system. |
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A 24" x 8" rectangular duct has an aspect ratio of: |
3:1 W / H |
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The most efficient method of air balancing a duct system is the: |
Proportional method. |
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Which style of turning vanes produce the least dynamic system loss? |
Single wall. |
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Formula for determining actual operating capacity of a system. (In BTUH) |
BTUH = 1.08 x CFM x TD |
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A sheet metal square to round transition is used.... |
... when it is necessary to convert a section of flex duct trunk to rectangular metal duct. |
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Thickness of duct insulation is governed by __________ codes. |
Municipal |
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A traverse joint is used to... |
... connect ductwork end to end. |
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Metal ductwork used in heating only applications covered in fibrous insulation must be _______________________ and ______________________. |
-Insulated to local code -A vapor barrier added to eliminate condensation. |
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Location of condensate drains is typically governed by __________ codes. |
Local |
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The UMC states that condensate drains must have a pitch of ________________, as well as the size and location of the pipe used for secondary drains. |
1/4" per foot |
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What is the minimum diameter of schedule 40 PVC pipe used for secondary drains? |
3/4" |
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Secondary drains should terminate in a _______________ location. |
Conspicuous |
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Attic mounted furnaces must have a permanently mounted light fixture. The switch must be located at the required ___________________________. |
Passageway opening. |
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Cloth tape and mastic must be used when sealing interior joints of ____________ and _____________. |
-Chases -Return ducts |
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An extended plenum duct system extends in one or two directions and has ____________________. |
Multiple branch ducts. |
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Fiberglass and sheet metal ducts are joined using: |
Sheet metal screws and washers. |
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All ductwork must be mechanically connected and _____________. |
Sealed. |
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A basic duct board trunk utilized 3 v-grooves and one __________________ on one corner. |
Shiplap joint |
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The shiplap joint must have a _________________ and be stapled with __________ outward clinching staples. |
-3" staple flap -1/2" minimum |
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Flex ducts should be supported every __________ with a metal strap or saddle of 1.5" minimum. |
5 feet maximum |
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What is the maximum sag allowed for flex ducting? |
1/2 inch per foot |
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Flex duct, when ran vertically, must be supported every 6ft and may not be used as a riser over ____________. |
2 stories. |
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Flex duct may rest on joists as long as: |
The 5' rule applies. |
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Pressure sensitive aluminum foil tape can be used on: |
Flex or metal ducts |
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Heat activated aluminum foil tape is used for: |
Duct board joints |
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Mastic and glass fabric tape system is used on and mechanical joint, metal duct board, or _____________. |
A combination of both. |
