Complex HVAC Systems Flashcards
List 4 types of systems
Air, water, air and water, DX
What 3 components are part of the DCV control system?
BAS, motion, CO2
What happens to the bypass air from a VAV system?
Returns to the AHU though the return
What does the term Bucking refer to?
Operates inefficiently by heating and cooling the air at the same time
What is a regular VAV system?
Does not change the speed of the fan but throttles air through a damper
What is a true VAV system?
Changes the fan speed
I’m an induction reheat terminal what temperature causes condensation problems?
Coil temps cooler than 50F
What must be used if a DX coil is used in face bypass system?
Capacity control
How does the air flow in a centrifugal fan?
The air flow is perpendicular to the fan
How does the air flow in an axial fan?
It flows parallel
What 3 types of axial fans are there?
Propeller, tube, and vane
Describe propeller fans
They can move large volumes at low static pressure and have no ductwork. Elevator room exhaust fans.
Describe tube axial fans
Heavy duct propeller fans. Operate at a higher static pressure than propeller.
Describe a vane axial fan?
Much like tube axial fans except they have guide vanes to reduce turbulence. They are efficient and the vanes help promote laminar flow.
What type of centrifugal fan is most efficient and which one is the most least efficient?
Airfoil blades is most, and cross flow is the least
How are centrifugal fans constant displacement devices?
They move constant volume rather than constant mass. Despite the air density. Air velocity is fixed even though mass flow rate changes.
Backward inclined flat blades
Has 10-20 blades and are less expensive and less efficient than backward curved blades. Needs a large shaft.
Backward curved blade
Quieter, might produce humming sound. Moves high volumes at high static.
The air foil fan blade
Like a airplane wing, rotation is counter clockwise, most efficient, 8”-10” static pressure moved
Radial tip fan blades
Tips are perpendicular to the shaft. Moves large volumes of dirty air 2” to 7” static. Inducers, boilers, grain dryers.
Radial blade
Flat blade perpendicular to fan shaft. Workhorse of exhaust fan. 10” static pressure. Paddle type.
What percent of excess air is necessary for building systems?
5%
