Airflow

Question 1

List 3 advantages of having the blower set for continuous operation

Answer 1

Improved air filtration
Increased building comfort
Reducing cold areas in the building

Question 2

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

T OR F

Answer 2

False

Question 3

Why is it important to balance a residential hvac system

Answer 3

There will be cold areas in the building

Question 4

Dwyer air meters can measure CFM directly

T OR F

Answer 4

False

Question 5

Manometers are filled with alcohol

T OR F

Answer 5

FALSE

Question 6

Which of these two instruments is most accurate

Inclined manometer
Or
U-tube manometer

Answer 6

Inclined manometer

Question 7

A velometer cannot be used to measure static pressure over how many inches of WC

Answer 7

10”

Question 8

What are the 2 basic types of anemometers

Answer 8

Thermal
Rotating vane

Question 9

What is the atmospheric pressure at sea level

Answer 9

14.7 psia

Question 10

What is static pressure

Answer 10

Air exert pressure on the walls of the vessel in which it is confined

Question 11

What is total pressure

Answer 11

Sum of static and velocity pressure

Question 12

What causes dynamic pressure losses

Answer 12

change in direction and velocity of air flow

Question 13

What is aspect ratio

Answer 13

Ratio between the width and height of the duct

Question 14

Define equivalent length

Answer 14

Comparison of calculated pressure drop through a fitting to the pressure drop through a straight piece of duct

Question 15

What is the maximum recommended aspect ratio for rectangular duct

Answer 15

4:1

Question 16

How is the radius of an elbow calculated

Answer 16

1.5 the width of the elbow plus the throat radius divided by the width of the elbow

Question 17

What is the purpose of a splitter in the elbow

Answer 17

To reduce dynamic pressure losses

Question 18

What is the maximum angle of an eccentric diverging fitting

Answer 18

30 degrees

Question 19

What is the maximum angle of a concentric diverging fitting

Answer 19

45 degrees

Question 20

Where would a two piece streamliner be used

Answer 20

Where the ductwork cannot be made to offset around an obstruction that would exceed 20% of the cross sectional area of the duct

Question 21

Running a blower continuously at low speed will result in________

Answer 21

Continuous conditioning of the air in the building

Question 22

Operating a fan continuously prevents______?

Answer 22

Hot and cold blasts/ stratification (layering)

Question 23

What are the 2 disadvantages of continuous blower operation?

Answer 23

Higher electrical costs

If blower is not rated for continuous duty operation it may need replacement sooner

Question 24

Return air should be sized to remove the same amount of air that’s supplied into any given area

T or F

Answer 24

True

Question 25

What is the easiest way to approach cold areas in a home?

Answer 25

Asking if any areas are warmer than they should be and throttling back dampers in those areas

Question 26

Ductwork should be larger than a heating only system when also providing cooling T or F

Answer 26

True

Question 27

A typical air conditioner has a nominal airflow of __________?

Answer 27

400 cfm/tom to 425 cfm/ton

Question 28

When selecting a heating unit you must never select one that has an output less than__________?

Answer 28

100% of the calculated heat loss of the house

Question 29

The standard specifies that the heating system shall be no more then _______ larger than the heat required for the house at that design temperature

Answer 29

40%

Question 30

Which manometer cannot be used to measure the small pressures in a typical hvac system

Answer 30

Bourboun tube type

Question 31

What is used to take direct readings of air velocity

Answer 31

Velometer

Question 32

What type of anemometer uses a heated wire

Answer 32

Thermal anemometer

Question 33

What can static pressure be measured with

Answer 33

Manometer

Question 34

Can velocity be measured?

Answer 34

Velocity can never truly be measured

Question 35

What causes friction loss?

Answer 35

Movement of air against each other Movement of air against the inside surface of the duct, especially if it’s not smooth

Question 36

What ducts in order are the best for friction loss

Answer 36

Round Square Oval

Question 37

What’s the best possible aspect ratio for an elbow ?

Answer 37

1:1

Question 38

What’s the purpose of splitters?

Answer 38

Improves the radius ratio of an elbow

Question 39

Define static regain

Answer 39

Process of converting velocity pressure to static pressure

Question 40

Define static regain

Answer 40

Process of converting velocity pressure to static pressure

Question 41

What should be stated first when ordering an elbow

Answer 41

Width of cheek

Question 42

How do you calculate the radius ratio

Answer 42

RR= CL/WIDTH

Question 43

What’s the purpose of turning vanes

Answer 43

Reduces turbulence and provides a more uniform velocity distribution downstream from the bend

Question 44

What Flow measurement device is used to measure fluid flow velocity

Answer 44

Pitot tube

Question 45

U tube manometers are only accurate when pressures of approximately______WC or greater are being measured

Answer 45

1”

Question 46

What gauge is used to take readings of pressure 1” WC or lower

Answer 46

Inclined manometer or slant gauge

Question 47

What is a balometer used for

Answer 47

Direct cfm readings out of grilles and diffusers