Chapter 37

Canvas collars are generally made of canvas rather than other materials such as rubber.

False

Airflow pressure in ductwork is measured in inches of _____.

water column

When is insulation required on air ducts?

when there's a 15º F difference between the outside air and the air inside the duct

The atmosphere exerts a pressure of _____ at standard atmospheric conditions.

14.696 psi

A(n) _____ºF temperature difference from the inside to the outside of the duct is considered the maximum difference allowable before insulation is necessary.

15

The simple way to check for airflow is to see if you can feel the airflow at a distance of about _____ from each register.

2 to 3 ft

Flexible round duct comes in sizes up to about _____ in. in diameter.

24

Adjusting the tension on the belt will alter the rate at which air is moving through the system but does not affect the amperage draw of the motor.

False

Friction due to air rubbing the walls of the ductwork can be eliminated.

False

A device used to put trunk duct or extended plenum sections together is called a drive clip.

True

Duct systems can be plenum, extended plenum, reducing plenum, or perimeter loop.

True

Oversized duct systems cost more to fabricate and install and will also result in the slowing of the air as it flows through the duct.

True

The ducts total pressure equals the velocity pressure plus static pressure.

True

The forced-air system is different from a natural-draft system, where the air passes naturally over the conditioning equipment.

True

The main drawback of the extended plenum system is that the velocity of the air is lower as the air reaches the last takeoffs on the extended plenum.

True

The _____ provides the pressure difference needed to force the air into the duct system, through the heat-transfer surfaces in the conditioning equipment, through the grilles and registers, and into the room.

blower

How is the cetrifugal blower turned?

by a motor

Branch ducts should always use what component to balance the air to the individual areas?

dampers

The supply duct system distributes air to the terminal units, registers, grills or _____ in the conditioned space.

diffusers

Baseboard hot water heat is an example of _____ heat.

natural draft

If the equivalent length of a transition piece of ductwork is 10 feet and the main duct in series with it is 20 feet, what is the length used to estimate the total frictional loss?

30 feet

Each foot of duct offers a known resistance to airflow which is called _____.

friction loss

Galvanized sheet metal comes in several different thicknesses, called the _____ of the metal.

gauge

The pressure in a duct system is measured in ____.

in. WC

Why is the airflow from a register not the same across the entire surface?

it depends on how the register is attached to the ductwork

The reason for using a reducing plenum system is to ____.

maintain a constant pressure throughout the length of the trunk duct

A(n) _____ can be connected to measure the velocity pressure of the air moving in a duct.

manometer

The _____ is constructed as two concentric tubes and is bent into a 90-degree angle.

pitot tube

One reason for using an extended plenum system is to _____.

prolong the main plenum closer to the farthest supply register

The plenum system is easy to install, is generally inexpensive and is well suited for a job in which the _____.

room outlets are all close to the unit

The components that make up the forced-air system are the _____, the air supply system, the return air system, and the grilles and registers where circulated air enter the room and returns to the conditioning equipment.

the blower

A duct system is pressurized by static, velocity and _____ pressures.

total

An instrument that is commonly used on air distribution systems is the anemometer, or _____.

velometer