Air Distribution Systems

Front 1

What 2 types of blowers are commonly used in air distribution systems?

Back 1

Belt-drive & Direct-drive

Front 2

Air that can be moved by creating a pressure above atmospheric pressure:

Back 2

Positive pressure

Front 3

Pressure below atmospheric pressure:

Back 3

Negative pressure

Front 4

CFM=

Back 4

Cubic feet per minute
cfm= area x velocity

Front 5

What are the 3 types of pressures in a duct system?

Back 5

Static pressure (s.p.), Velocity pressure, and total pressure

Front 6

Pressure exerted uniformly in all directions within a duct system:

Back 6

Static pressure

Front 7

Pressure in a duct system caused by the movement of the air:

Back 7

Velocity pressure

Front 8

Sum of the static and the velocity pressures in a duct system:

Back 8

Total pressure

Front 9

Senses total and static pressures:

Back 9

Pitot tube

Front 10

Measures velocity pressure (difference between total and static pressures) :

Back 10

Manometer

Front 11

The height, in inches, to which the pressure will lift a column of water (in. w.c.)

Back 11

Inches of water column

Front 12

Atmospheric pressure level:

Back 12

14.7 psia

Front 13

The atmospheric pressure will support:

Back 13

406.8 in. w.c. or 33.9' high

Front 14

1 psia =

Back 14

27.68 inches of water

Front 15

To convert psi to kPa (pascals):

Back 15

Multiply psi x 6.895

Front 16

These blowers are used with forced-air systems because they are designed to work against the resistance of the duct system:

Back 16

Centrifugal blowers

Front 17

Name 3 types of centrifugal blowers:

Back 17

Forward-curved, Backward-inclined, Radial

Front 18

These blowers are normally used in residential and light commercial heating and air conditioning systems:

Back 18

Forward-curved centrifugal blowers

Front 19

These blowers are used in commercial and industrial heating and cooling systems that require heavy-duty blower construction and stable air delivery:

Back 19

Backward-inclined centrifugal blowers

Front 20

These blowers are suitable for use in air systems that have large amounts of particles or grease in the air:

Back 20

Radial blowers

Front 21

Typically used in applications where high quantities of air are needed with little resistance to airflow:

Back 21

Fans

Front 22

Produce an airflow which is parallel or axial to the shaft on which the propeller is mounted:

Back 22

Propeller or axial fans

Front 23

The propeller is housed in a cylindrical duct or tube, which allows these fans to operate at higher static pressures than propeller fans. They are commonly used in spray booths and other ducted exhaust systems.

Back 23

Duct fans

Front 24

What are the 2 types of tachometers:

Back 24

Contact and non-contact

Front 25

The amount of air delivered by a fan varies directly with the speed of the fan.

Back 25

Fan Law 1

Front 26

The static pressure of a system varies directly with the square of the ratio of the fan speeds.

Back 26

Fan Law 2

Front 27

The horsepower varies directly with the cube of the ratio of the fan speeds.

Back 27

Fan Law 3

Front 28

These are used to find the relationships that exist for a set of system conditions involving: static pressures, blower/fan rpm, and cfm.

Back 28

Manufacturer's fan curve charts

Front 29

Consist of the supply duct system and the return duct system:

Back 29

Air distribution systems

Front 30

Sealed chamber at the inlet or outlet of an air handler:

Back 30

Plenum

Front 31

In cold climates, most buildings use:

Back 31

Perimeter duct systems

Front 32

Perimeter systems have 4 common layouts:

Back 32

Loop perimeter, Radial perimeter, Extended plenum, Reducing extended plenum