Air Flow Flashcards
What are 3 advantages of having blowers set for continuous operation?
Improve air filtration
Increase building comfort
Reduce temperature variations
A duct system that is designed for a heating only system will be sufficient size if you want to add cooling to it ?
False, you would need to increase the size.
Why is it important to balance a residential hvac system?
If not done properly the end result will be cold areas in the building
Dwyer air meters can measure cfm directly?
False
Feet per minute velocity
Cfm is a volume
Manometers are filled with alcohol ?
False
Made with oils or water
Which of these two instruments are the most accurate?
Inclined manometers
U-tube manometers
Inclined
A velometer cannot be used to measure static pressures over ?
10” of water column
What are the two basic types of anemometers?
Thermal
Rotating vane
What is atmospheric pressure at sea level ?
14.7 Psia
What is static pressure ?
Air will exert pressure on the walls of the vessel in which it is confined
What is static pressure ?
Air will exert pressure on the walls of the vessel in which it is confined
What is total pressure ?
The sum of the static and velocity pressures
What causes dynamic pressure losses?
They are when there are changes in direction and velocity of air flow
When an airstream makes turns diverges converges narrows widens enters exits or passes dampers gates coils filters or sound attenuators
What is aspect ratio?
Ratio between width and height of the duct
Define equivalent length
Comparison of calculated pressure drop through a fitting to the pressure drop through a straight length of duct of the same size
What is the maximum recommended aspect ratio for rectangular duct ?
Avoid using duct with an aspect ratio greater than 4:1 if possible in addition to increasing friction loss it costs more to fabricate
How is the radius ratio of an elbow calculated?
By using centerline radius (one half the width of the elbow plus the throat radius ) of the elbow and dividing it by width of the elbow
What is the purpose of splitters in an elbow ?
Splitters are installed in elbows to reduce the dynamic pressure losses
What is the maximum angle of eccentric diverging fitting ?
30degrees
What is the maximum angle of a concentric diverging fitting ?
60 degrees
Where would a two piece streamliner be used ?
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 .
Turning vanes are designed for what ?
Reduce turbulence
What air pressures are measured using the inner tube of a pitot tube ?
Total
What instrument measures only atmospheric pressure
Barrometer
What is dynamic pressure loss
A loss caused by a change of direction
What happens when Increase in static pressure after diverging fitting
Static regain
How do u directly measure air volume
Barometer
Squat throat square heel turning vein included angle ?
If it’s a 90degree elbow then 90 degrees
A properly designed hvac system will have a good balance of what two things ?
Supply air return air
What is the result of running a blower on continuous low speed ?
Continuous conditiong of the air
Operating a blower continuously will prevent ?
Stratification
(Cold air sinks hot air rises )
What air pressures are measured using inter tube of a pilot tube ?
Total
What instrument measures only atmospheric pressure ?
Barrometer
What is dynamic pressure loss
A loss caused by change in direction
What is it called when Increase in static pressure after diverging fitting
Static regain
A properly designed hvac system will have a good balance of what two things ?
Supply and return air
Operates a blower continually will prevent ?
Stratification
