Question 1

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

Accepted Answer

According to standard HVAC guidelines, one should be able to feel the airflow at a distance of about 2 to 3 feet from each register. Any further distance might signify poor airflow or clogged air ducts.

Question 2

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.

Accepted Answer

Adjusting the tension on the belt can affect the load on the motor, which in turn can change the amperage draw. A tighter belt increases friction and load, potentially increasing amperage draw, while a looser belt might decrease it.

Question 3

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

Accepted Answer

C

Question 4

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.

Accepted Answer

Oversized duct systems have a larger volume, which requires more material to fabricate and more effort to install. Additionally, the greater volume can lead to a reduction in air velocity, which can impact the effectiveness of the HVAC system.

Question 5

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

Accepted Answer

The standard atmospheric pressure at sea level is 14.696 psi or 1 atm.

Question 6

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

Accepted Answer

The forced-air system uses a fan or blower to push the air through the conditioning equipment, while a natural-draft system relies on the natural movement of air over the equipment.

Question 7

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

Accepted Answer

This statement is true. Duct systems can indeed be plenum, extended plenum, reducing plenum, or perimeter loop.

Question 8

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.

Accepted Answer

The extended plenum system can suffer from decreased velocity of air as it reaches the last takeoffs due to increased air resistance and pressure drop.

Question 9

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

Accepted Answer

Friction is a natural occurrence whenever there is movement between two surfaces, and in the case of ductwork, air is rubbing against the walls of the ducts. While measures can be taken to reduce friction, it cannot be completely eliminated.

Question 10

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

Accepted Answer

A reducing plenum system is designed to maintain a constant pressure throughout the length of the trunk duct by gradually reducing the size of the duct as it branches out to supply air to smaller rooms or areas. This helps to ensure that all areas receive adequate airflow and can improve overall system efficiency.

Question 11

The duct pressure equals the velocity pressure plus static pressure.

Accepted Answer

This statement is true. The total pressure in a duct is made up of the sum of the velocity pressure (which is a function of the velocity of the air flow) and the static pressure (which is a function of the pressure of the air at rest in the duct). The total pressure is also known as the dynamic pressure.

Question 12

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.

Accepted Answer

The blower is responsible for providing the pressure difference required to move the air through the entire HVAC system, from the duct system to the room.

Question 13

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

Accepted Answer

A manometer is specifically designed to measure pressure, including velocity pressure in air ducts. An ammeter measures electrical current, a pyrometer measures high temperatures, and a speedometer measures the speed of a vehicle.

Question 14

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

Accepted Answer

The answer of Canvas collars are generally made of canvas...

Question 15

Airflow pressure in ductwork is measured in inches of ____.

Accepted Answer

Airflow pressure in ductwork is commonly measured in inches of water column (WC) because it is a practical unit of measure that allows for precise readings of low-pressure airflows. Mercury pressure and mercury column are not used in HVAC systems, and while air pressure can be used to measure airflow, it is not typically used in ductwork.

Question 16

The pressure in a duct system is measured in ____.

Accepted Answer

The pressure in a duct system is commonly measured in inches of water column (in. WC). This is because the pressure is relatively low in duct systems and is often measured with a manometer, which measures the difference in pressure between two points in inches of water column. The other options, psig (pounds per square inch gauge), psia (pounds per square inch absolute), and in. Hg (inches of mercury) are not typically used to measure pressure in duct systems.

Question 17

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

Accepted Answer

An anemometer is a device used to measure the speed of air flow, and a velometer is a type of anemometer that specifically measures air velocity. B) and C) are not specific to air flow measurement, and D) measures electrical current, not air flow.

Question 18

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?

Accepted Answer

The equivalent length of the transition piece is added to the length of the main duct to estimate the total frictional loss, so the total length used for estimation is 10 + 20 = 30 feet. Therefore, the correct answer is choice C.

Question 19

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

Accepted Answer

A 15ºF temperature difference from the inside to the outside of the duct is considered the maximum difference allowable before insulation is necessary to prevent condensation and ensure energy efficiency.

Question 20

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

Accepted Answer

A drive clip is a commonly used device for connecting sections of trunk duct or extended plenum. It is designed to be hammered or driven into the metal to hold the two pieces together without the need for screws or other fasteners.

Quiz 37: Air Distribution and Balance