Airflow Flashcards
List 3 advantages of having the blower set for continuous operation
Improved air filtration
Increased building comfort
Reducing cold areas in the building
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
False
Why is it important to balance a residential hvac system
There will be cold areas in the building
Dwyer air meters can measure CFM directly
T OR F
False
Manometers are filled with alcohol
T OR F
FALSE
Which of these two instruments is most accurate
Inclined manometer
Or
U-tube manometer
Inclined manometer
A velometer cannot be used to measure static pressure over how many inches of WC
10”
What are the 2 basic types of anemometers
Thermal
Rotating vane
What is the atmospheric pressure at sea level
14.7 psia
What is static pressure
Air exert pressure on the walls of the vessel in which it is confined
What is total pressure
Sum of static and velocity pressure
What causes dynamic pressure losses
Result of change in direction and velocity of air flow
What is aspect ratio
Ratio between the width and height of the duct
Define equivalent length
Comparison of calculated pressure drop through a fitting to the pressure drop through a straight piece of duct
What is the maximum recommended aspect ratio for rectangular duct
4:1
How is the radius of an elbow calculated
1.5 the width of the elbow plus the throat radius divided by the width of the elbow
What is the purpose of a splitter in the elbow
To reduce dynamic pressure losses
What is the maximum angle of an eccentric diverging fitting
30 degrees
What is the maximum angle of a concentric diverging fitting
45 degrees
Where would a two piece streamliner be used
Where the ductwork cannot be made to offset around an obstruction that would exceed 20% of the cross sectional area of the duct
Running a blower continuously at low speed will result in________
Continuous conditioning of the air in the building
Operating a fan continuously prevents______?
Hot and cold blasts/ stratification (layering)
What are the 2 disadvantages of continuous blower operation?
Higher electrical costs
If blower is not rated for continuous duty operation it may need replacement sooner
Return air should be sized to remove the same amount of air that’s supplied into any given area
T or F
True
What is the easiest way to approach cold areas in a home?
Asking if any areas are warmer than they should be and throttling back dampers in those areas
Ductwork should be larger than a heating only system when also providing cooling
T or F
True
A typical air conditioner has a nominal airflow of __________?
400 cfm/tom to 425 cfm/ton
When selecting a heating unit you must never select one that has an output less than__________?
100% of the calculated heat loss of the house
The standard specifies that the heating system shall be no more then _______ larger than the heat required for the house at that design temperature
40%
Which manometer cannot be used to measure the small pressures in a typical hvac system
Bourboun tube type
What is used to take direct readings of air velocity
Velometer
What type of anemometer uses a heated wire
Thermal anemometer
What can static pressure be measured with
Manometer
Can velocity be measured?
Velocity can never truly be measured
What causes friction loss?
Movement of air against each other
Movement of air against the inside surface of the duct, especially if it’s not smooth
What ducts in order are the best for friction loss
Round
Square
Oval
What’s the best possible aspect ratio for an elbow ?
1:1
What’s the purpose of splitters?
Improves the radius ratio of an elbow
Define static regain
Process of converting velocity pressure to static pressure
Define static regain
Process of converting velocity pressure to static pressure
What should be stated first when ordering an elbow
Width of cheek
How do you calculate the radius ratio
RR= CL/WIDTH
What’s the purpose of turning vanes
Reduces turbulence and provides a more uniform velocity distribution downstream from the bend
What Flow measurement device is used to measure fluid flow velocity
Pitot tube
U tube manometers are only accurate when pressures of approximately______WC or greater are being measured
1”
What gauge is used to take readings of pressure 1” WC or lower
Inclined manometer or slant gauge
What is a balometer used for
Direct cfm readings out of grilles and diffusers
