Unit 37: Air Distribution and Balance
infiltration air.
Air that enters a structure from leaks around windows and doors is best described as
equipment cycling is noticeable by the occupants of the structure.
All of the following are desirable characteristics of a forced-air system except
speed of air flowing through a duct.
An anemometer is used to directly measure the
hot water baseboard heating.
An example of a natural-draft system is
34 feet
At standard conditions, atmospheric pressure can support a column of water that is approximately how high?
friction within the duct system.
Duct systems must be properly sized and designed to reduce and overcome the effects of
is ideally used for very short, direct duct runs.
Flexible duct
Zinc
Galvanized sheet metal is treated/coated with which substance to slow the corrosion process?
583 cfm
How much air is flowing through a 10 in. x 12 in. duct if the air is traveling at a speed of 700 feet per minute?
Improperly balanced air distribution system
If a gas-fired furnace is constantly tripping on a high limit safety control, which of the following is likely NOT a cause for this condition?
3
If an air-conditioning system has three independent zones, how many space thermostats will the system have?
The system air filter is dirty.
If there seems to be reduced airflow at all supply register locations, which of the following is the most likely problem with the system?
slips and drives.
Rectangular metal duct sections are commonly joined together with
16 in.
Referring to Figure 37.90, a rectangular duct with cross-sectional measurements of 20 in. x 11 in. will be the equivalent of a round duct with a diameter of
the supply air is directed onto the walls of the room.
Supply registers should be positioned and configured so that
manometer.
The instrument that is used to measure duct system pressures is the
static pressure.
The pressure that represents the force pushing outward against the walls of the duct system is referred to as the
Inches of water column (IWC)
The pressures in a duct system are measured in which units?
belt-drive blower assembly.
The type of blower assembly that utilizes both motor shaft and blower shaft bearings is the
direct-drive blower assembly.
The type of blower assembly that utilizes only motor shaft bearings is the
Perimeter loop system
Which of the following air distribution systems is commonly installed in a poured slab floor?
Reduced airflow, increased noise, evaporator coil freeze-ups
Which of the following are challenges that need to be addressed when a single speed blower motor is used on a zoned air-conditioning system?
Belt-drive blower assembly
Which of the following blower assemblies is used in conjunction with changeable or adjustable pulleys that can vary the blower speed?
The velocity of the air is maintained throughout the system
Which of the following is a benefit of the reducing plenum air distribution system?
Velocity Pressure = Total Pressure - Static Pressure
Which of the following is an accurate expression that relates the three duct system pressures?
Increased noise levels
Which of the following is false regarding a duct system that is oversized?
Motor amperage will go up if the door on the blower compartment is removed.
Which of the following is true regarding the amperage draw of a blower motor being used to move air through a duct system?
Anemometer and velometer
Which of the following sets of instruments are most similar to each other?
Zone dampers are automatically operated based on space temperature.
Which of the following statements is accurate with regards to simple system zoning?
prevent duct sweating and decrease the heat transfer rate between the air in and around the duct
Ducts are insulated to
make the duct section more rigid.
Sheet metal duct sections are often fabricated with cross-breaks to
are able to overcome the pressures that are present in the duct system.
Squirrel-cage-type blowers are used in conjunction with duct system because they
takeoff fitting
The branch duct is connected to the main trunk line with a
900 fpm with a friction loss of 0.15 IWC/100 feet
Using the chart in Figure 37.88, what is the velocity and friction loss of a 400 cfm airstream that is flowing through a 9-in. round duct?
a throat that is larger than the runout duct it is connected to.
A streamlined takeoff fitting is designed with
440 fpm
A technician is traversing a duct and obtains the following 8 velocity readings: 500 fpm, 400 fpm, 375 fpm, 625 fpm, 275 fpm, 360 fpm, 420 fpm, and 575 fpm. What is the velocity value that will be used for system calculations?
as close as possible to the main supply trunk.
Balancing dampers are ideally located
