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Sheet Metal 3rd Yr > HVAC System Design > Flashcards

HVAC System Design Flashcards

1
Q

What is the maxium angle of an eccentric diverging fitting?

A

30*

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2
Q

How much heavier is Mercury than water?

A

13.6 times

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3
Q

What is the maximum angle of a concentric diverging fitting?

A

60*

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4
Q

What are 2 disadvantages of running the furnace fan continuous?

A
  1. Higher electrical costs
  2. The blower fan will take excessive wear, especially if it is not rated for continuous duty.
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5
Q

Define : Pressure

A

The amount of force over an area

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6
Q

Define : Velocity

A

The distance over Time that air travels through a duct.

fpm (feet per minute)

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7
Q

What is the purpose of a splitter in an elbow?

A

Splitters are installed in elbows to reduce the dynamic pressure losses.

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8
Q

A typical air conditioner has a normal airflow of what and uses how many Btuh?

A

400-425 cfm

12,000 Btuh

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9
Q

What is Aspect Ratio?

A

Aspect Ratio is the ratio between the width and hieght of a duct.

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10
Q

What is a Dwyer Air Meter?

A
  • It measures Air Velocity (fpm) and Static Pressure (w.c.)
  • Air enters a hose that is connected to scale chamber and pushes a white plastic ball.
  • Offers 2 diferrent ranges - low/high
  • Low Range

260fpm - 1200fpm

  1. 0005” w.c. - 0.09”w.c.
    * High Range

1000fpm - 4000fpm

0.05”w.c. - 1.0”w.c.

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11
Q

What is an Anemometer?

A

An instument thet measures Air Velocity directly at the duct treminals.

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12
Q

A duct system that is designed for a heating only system will be of sufficient size if you wanted to add cooling to it.

TRUE or FALSE

A

FALSE

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13
Q

That is a Pitot Tube?

A
  • Devices that tests Total Pressure and Static Pressure.
  • It consists of a tube inside a tube
  • Inner tube tests Total Pressure
  • Outer tube tests Static Pressure

.

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14
Q

What are the 3 classifications of duct pressure?

A
  1. Static
  2. Velocity
  3. Total Pressure (static + velocity)
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15
Q

A velometer cannot be used to measure static pressures over what wc (water colume)?

A

10” wc (water colume)

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16
Q

What is the maxium recommended aspect ratio for rectangular duct?

A

Avoid using duct with an aspect ratio greater than 4 :1 , if possible. In addition to increasing friction loss , it costs more to fabricate.

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17
Q

When selecting a heating unit, what must be the output be?

A

Between 100%-140% of the building design temperature required heat on its coldest day.

18
Q

What is 1 psi equal to in w.c. (water colume)

A

27.72 inches w.c.

19
Q

Why is it important to balance a residential HVAC system?

A

If a system is not balanced properly, the end result will be cold areas in the building.

20
Q

List the 3 advantages of having the blower set for continuous operation.

A
  1. Improved air filtration
  2. Increased building comfort
  3. Reducing cold areas in the building
21
Q

Manometers are filled with alcohol.

TRUE or FALSE

A

FALSE

22
Q

How is the radius ratio of an elbow calculated?

A

The radius ratio is calculated by using the centerline radius (one-half the width of the elbow + the throat radius) of the elbow and dividng it by the width of the elbow.

23
Q

What is Static Pressure?

A

The pressure air will exerts on the walls of the vessel in which it is confined.

24
Q

What is another term for a pressure of zero?

A

Vacuum

25
Q

What is a Well-Type Manometre?

A

A U-Tube Manometre with one-half of the tube is enlarged and takes the form of a well.

  • Readings are only taken from the tube side.
26
Q

What is a Velometer?

A

Is a device that reads air flow in fpm (feet per minute) and is used for taking direct readings of air velocities.

  • Not for gass mixtures other than air
27
Q

What is a U-Tube Manometre?

A
  • A glass or transparent plastic that is formed in the shape of a U.
  • Tube is graduated in inches and filled with liquid.
  • One end is open to atmosphere, The other end is connected to a Pitot Tube and placed in duct.
  • Amounts shown on both sides of tube are added together to get Total Pressure.
28
Q

Define : Equivalent Length

A

Equivalent Lenght is the comparision of the calculated pressure drop through a fitting to the pressure drop through a straight length of duct of the same size

29
Q

Will running the furnace fan continuosly CAUSE statification?

TRUE or FALSE

A

FALSE

30
Q

Where would a 2-piece streamliner be used?

A

Two-piece streamliners are used in areas where the ductwork cannot be made to offset around an obstruction that would exceed 20% of the cross-sectional area of the duct.

31
Q
A
32
Q

Define : Volume

A

Amount of air moving in a duct over a distance.

cfm (cubic feet per minute)

33
Q

What is the atmospheric pressure at sea level?

A

14.7 psia

34
Q

What is a Inclined Manometre (Slant Gauge)

A

Is a Manometre what was the top slanted at a 10 to 1 slope.

Used to read w.c. of 1” or less

35
Q

What is a Magnehelic Gauge?

A

A sensitive differential pressure or vacuum gauge that uses a precision diaphragm to measure pressure differences.

36
Q

What height of a colume of water will support 1 psi?

A
  1. 31 feet
  2. 72 inches
37
Q

What is a Monometre?

A
  • A device that is used to measure small pressures.
  • Uses air pressure to move a column of liquid in a tube.
38
Q

Which of these 2 instruments is the most accurate?

Inclined Manometer

U-tube Manometer

A

Inclined Manometer

39
Q

What are the 2 basic types of Anemometers?

A
  1. Thermal
  2. Rotating Vane
40
Q

Dwyer air meter can measure CFM directly.

TRUE or FALSE

A

FALSE

41
Q

What causes Dynamic pressure Losses?

A

Dynamic losses are the result of changes in the direction and velocity of air flow.

This occures whenever an airstream makes turns, diverges, concerges, narrows, widens, enters, exits or passes dampers, gates coils, filters or sound attenuators.

42
Q

What is Total Pressure?

A

The total pressure is the sum of the static and velocity pressures.

Sheet Metal 3rd Yr (7 decks)

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