Chapter 37
Airflow pressure in ductwork is measured in inches of ______.
water column
The atmosphere exerts a pressure of ____ at standard atmospheric conditions.
14.696 psi
A(n) _____°F 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 feet
Flexible round duct comes in sizes up to about _____ in. in diameter.
24
If the equivalent transition piece of ductwork is 10 feet and the main series is 20 feet, what is the length used to estimate the total friction loss?
30 feet
How is the centrifugal blower turned?
A psc or an ECM motor
Describe a pitot tube
a probe device used to measure the air pressures in a duct
If the velocity of air through an 8"x20" duct is 700fpm, how many cfm of air is being carried by the duct?
air volume (cfm) = air velocity (ft/min) x cross sectional area (ft^2) 777 fpm
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
What are the components that make up the forced-air system?
blower, the air distribution system, the return air system, and grilles and registers where the circulated air returns to or enters the room
Explain the purpose of supply duct
distributes air to the terminal units, registers, grilles or diffusers, in the air conditioned space
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. (T/F)
false
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
The reason for using a reducing plenum system is to ______.
maintain a constant pressure throughout the length of the trunk duct
Baseboard hot water heat is an example of ______ heat.
natural draft
One reason for using an extended plenum system is to _____.
prolong the main plenum closer to the farthest supply register
A device used to put trunk duct or extended plenum sections together is called a drive clip. (T/F)
true
Duct systems can be plenum, extended plenum, reducing plenum, or perimeter loop. (T/F)
true
The duct pressure equals the velocity pressure plus static pressure. (T/F)
true
Canvas collars are generally made of canvas rather than other materials such as rubber. (T/F)
false
Friction due to air rubbing the walls of the ductwork can be eliminated. (T/F)
false
A(n) _____ can be connected to measure the velocity pressure of the air moving in a duct
manometer
A duct system is pressurized by what three pressures?
static, velocity, total
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. (T/F)
true
The forced air system is different from a natural-draft system, where the air passes naturally over the conditioning equipment. (T/F)
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. (T/F)
true
An instrument that is commonly used on an air distribution system is the anemometer, or ______
velometer
