DUCT CONSTRUCTION Flashcards
What is the range of the ductwork static pressure classification?
½” wc to 10” wc
What do the letters STD indicate in duct construction?
Standard (non-variable volume) air duct construction requirements.
What do the letters STV indicate in duct construction?
The standard construction classification for variable volume ducts.
What is the minimum length for beaded sleeves that join transverse round ducts?
At least the same gauge as duct and 4” long minimum.
By how many inches should round duct transverse joints that are beaded and crimped slip into one another?
1”
What is most commonly used for round duct reinforcement?
Angle rings
What is the part of a fitting collar that slips into the large end of a spiral pipe called?
Slip Joint/ Lap joint
What Seal Class must all duct constructed for the 1” (250 Pa) and ½” (125 Pa) pressure class meet?
Seal Class C
Who provides all the required elements that are necessary to produce project plans and specifications
Designer
Where are design specifications found
Various publications by SMACNA
Duct construction and installation standards in SMACNA’s HVAC Duct Construction Standards Metal and Flexible Engineering and Design include
illustrations, optional alternatives and general requirements.
The most important function of a properly assembled duct system is to_______?
convey air between two points
where no pressure classes are specified by the designer the 1” wc pressure class is the basis of compliance with these standards
T or F
TRUE
-all variable volume duct upstream of VAV boxes have a 2” wc basis of compliance when designer does not give a pressure class
T or F
TRUE
What is the range of a medium pressure duct system
3-6” of WC
What is the range of a high pressure duct system?
10” WC
What is the range of a low pressure duct system
1/2” to 2” if WC
What are Duct dimensions shown on contract drawings for
Airflow area
What typically should happen when ducts need to be acoustically lined
Upsize dimensions
essentials that make up the complete duct assembly are___________?
the material sheets, reinforcements, seams and joints
How much thicker should aluminum duct be compared to galvanized iron
44% thicker
In light commercial/ single story duct systems pressures and velocity’s tend to go up, why?
in effort to move a larger volume of air
Fibrous ducts can be used in systems that operate up to_______?
2” WC and 2400 fpm
Acoording to SMACNA, duct construction standards define relationships between what ?
static pressure, wall thickness, width and durability
Joint seams, reinforcement, duct support can be selected by fabricators and installers to conform to the SMACNA manuals
T Or F
True
The impact of duct air leakage depends on what 4 factors?
duct location, length, design and pressure.
Where is elastomer butyl used
Flanged joints
The use of a saddle or a direct connection of a branch into a larger duct is acceptable
T or F
True
How many screws do you use on a slip joint connection ?
A minimum of three screws should be placed along a diameter of 14” or less and these must be used at uniform intervals of at least 15” along the circumference.
A butt weld is not suitable for all pressure classes
T or F
False
A Flanged joint is used for ducts over how many inches
60”
What is another name for a segmented standing seam elbow
BETA ELBOW
