Unit 37 Air Distribution and Balance
4 x 12 with six readings 1= 525 fpm 2=550 fpm 3= 500 fpm 4=600 fpm 5= 575 fpm 6 =495 fpm How many cfm are entering the room using whole numbers and rounding properly.
180
4 x 16 with six readings 1= 625 fpm 2=550 fpm 3= 550 fpm 4=600 fpm 5= 575 fpm 6 =595 fpm How many cfm are entering the room using whole numbers and rounding properly?
259
4 x 12 with six readings 1= 525 fpm 2=550 fpm 3= 500 fpm 4=600 fpm 5= 575 fpm 6 =495 fpm What is your average fpm in whole numbers rounding the tenths column?
541
4 x 16 with six readings 1= 625 fpm 2=550 fpm 3= 550 fpm 4=600 fpm 5= 575 fpm 6 =595 fpm What is your average fpm?
583
Where is the best place to balance air flow?
As close to the trunk line as possible.
What is the difference between balancing dampers and zone dampers?
Balancing dampers are designed to be set into position and then never moved. Zone dampers are controlled by a motor and open and close depending on temperature.
What are the two reasons for using a reducing plenum?
Conserving materials Maintaing constant air pressure
An amperage reading is useful tool in setting up belt driven motors. What are the two examples listed that would show increased amperage?
Driven pulley is too small Drive pulley is too large
Direct drive motors are mostly used on systems up to how many tons?
Five
What are the four materials used to build a duct system?
Galvanized-Steel Fiberboard Flex Spiral Metal
When using a single speed motor in a zoned system, what two ways can be used to make sure that there is no air flow restriction when only the smallest zone is calling?
Oversizing the supply ducts for each zone Using a bypass
Which type of fan is typically used a s an exhaust fan or condenser fan?
Propeller Fan
What two parts does a belt-driven motor have that direct drive does not?
Pulleys two extra bearings
radial duct system
System A
Reducing Plenum Duct System
System B
Extended Plenum Duct System
System C
Perimeter Loop Duct System
System D
On a centrifugal blower the current draw of the motor is proportional to what?
The pounds or amount of air that the motor is moving.
Why does the current draw of a PSC motor in an air handler increase when the service panel on the blower side is removed?
The return side restrictions have been removed and the blower is now moving more air. This increase in air movement is what creates the increase in current.
What is the object of the forced air system?
To deliver the correct quantity of conditioned air to the occupied space.
Why does a zoned system need a discharge air sensor installed in the main supply plenum?
To shut down the compressor if the supply air gets too cold and shut do the heat if the supply air gets too hot.
What component provides the pressure difference needed to through the duct system?
blower
What are the components of a forced air system in which the air enters and leaves the space through?
grills and registers
Pressure in a duct is measured in what units?
inches of water column
High pressure duct systems have pressures of ___ inwc or higher.
one
Of the two fan types which one creates more pressure from the inlet to the outlet and moves more air against pressure?
squirrel cage blower
What is the pressure that pushes against the walls of the duct?
static pressure
What is used to connect the main trunk line and the branch duct?
takeoff fitting
What is used in a square-throated elbow to allow air to move smoothly through the turn?
turning vanes
What is the pressure in the duct created by the moving air?
velocity pressure
What is the name of the housing that a propeller fan is set into?
venturi
What is it when the needs of one zone always come before the other zones?
zone priority
