Air Flow 110301d

Question 1

What is the typical nominal airflow for a typical air conditioner

Answer 1

400 cubic feet per minute per tonne

Question 2

When selecting the heating unit, you must never select one that has an output less than (……) of the calculated heat loss of the house

Answer 2

100%

Question 3

The standard specifies that the heating system shall be no more than (….) larger than the heat required for the house at that design temperature?

Answer 3

40%

Question 4

The standard specifies that the heating system shall be no more than (….) larger than the heat required for the house at that design temperature?

Answer 4

40%

Question 5

Why is there a 40% allowance as a standard for sizing the heating system?

Answer 5

To allow margin for error in calculations and also permits some over sizing to bring a house back up to temperature.

Question 6

When a system is designed properly to handle cooling the ductwork will be (….) than the ductwork for heating only system.

Answer 6

Larger.

Question 7

If the homeowner is complaining of cold areas in the house, the easiest way to approach the problem is to?

Answer 7

Ask where are the areas that seems warmer than they should be ?

Question 8

What are the advantages of continuous blower operation?

Answer 8

Improved air filtration that will lower the indoor dust levels.

Increased building comfort

Reduced temperature variation

Question 9

Disadvantages of continuous blower operation.

Answer 9

Higher electrical costs.

If blower isn’t rated for continuous duty it may need to be replaced sooner.

Question 10

Running the blower continuously will result in what ?

Answer 10

Continuous conditioning of the air

Question 11

Name the different type of air measuring instruments

Answer 11

Dwyer Air Metre
Pitot Tube
Manometers
U-tube manometre
Inclined Manometre
Well-type manometre
Electronic (digital) manometre
Magnehelic Gauge
Velometer
Velometer Junior
Anemometer
Thermal Anemometer
Rotating vane anemometer
Balometers (Flow hoods)

Question 12

What is the atmospheric pressure at sea level

Answer 12

14.7 PSIA

Question 13

Is the air pressure in HVAC system high or low ?

Answer 13

Low

Question 14

Duct pressure is classified by three separate terms.

Answer 14

Static
Velocity
Total pressure

Question 15

What does the word static mean

Answer 15

Still or at rest

Question 16

A gauge connected to a tank of compressed air will indicate what ?

Answer 16

Static pressure

Question 17

How would you connect the tube to the manometre to measure velocity pressure ?

Answer 17

A manometre can be made to indicate the velocity pressure directly by connecting the total and static pressure tubes to the opposite ends of the manometre.

Question 18

What is total pressure

Answer 18

Total pressure is the sum of the static and velocity pressures.

Question 19

Why is it important to balance the hvac system.

Answer 19

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

Question 20

What is static pressure

Answer 20

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

Question 21

Choosing the best aspect ratio can ?

Answer 21

Reduce friction loss

Question 22

What does friction loss refers to ?

Answer 22

The portion of pressure lost by fluids while moving through duct or other limited space.

Question 23

What are some things f the cause of friction loss

Answer 23

The movement of air against each other

The movement of air against the inside surface of the duct, particularly if the inside surface is rough, textured or otherwise not smooth.

Question 24

What are dynamic pressure losses the result of ?

Answer 24

Changes in the direction and velocity of air flow.

These losses occur whenever an airstream makes turns, diverges, converges (narrows, widens), enters, exits or passes dampers, gates, coils, filters or sound attenuators.

Question 25

What is the disturbance of the airflow referred to?

Answer 25

Turbulence !

Question 26

While straightening of the airflow ends some distance after the air passes the fitting; this distance is usually assumed to be no shorter than(…)?

Answer 26

Six times the duct diameter or width of the straight duct.

Question 27

Air turbulence in an elbow ?

Answer 27

The air travelling on the outer edge tend to follow the curve and the air travelling on the inner edge tend to continue straight and impede with the flow creating turbulence within the elbow

Question 28

Why is it important that you always state the width of the cheek of the elbow first ?

Answer 28

Eliminate confusion when ordering.

Question 29

When using aspect ratio to choose duct sizes.

Answer 29

A round duct has the least friction loss
After round duct, a square duct is best.
After a square duct, flat oval duct is the best.

Question 30

As the aspect ratio increases ?

Answer 30

The friction loss increases

Question 31

Why should you avoid an aspect ration bigger than 4:1.

Answer 31

Increasing friction loss and increased cost to fabricate

Question 32

The aspect ratio for elbows and straight duct are defined the same ?

Answer 32

False,
Straight duct is always equal to long side of the duct divide by its short side.

Elbows, aspect ratio is always equal to the depth of the elbow dived by the width

Question 33

What is the centreline radius (CL)

Answer 33

The distance from the throat radius point to the center of the cheek.

Question 34

What are splitters

Answer 34

Splitters are pieces of material that are formed to the concentric radius of the elbow.

Question 35

Why are splitters installed ?

Answer 35

They are installed to improve the radius ratio.

Question 36

What cause dynamic pressure losses

Answer 36

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