A central station air handling unit
Consists of a fan and coil and usually handles a single room or zone
Is used instead of a fan and fan motor
Combines the functions of the evaporator blower and the condenser blower
Is used for large systems and is assembled on site using separate components
A system that uses the space above a drop ceiling for return air is called
a drop ceiling return system
a spatial air distribution system
an extended plenum system
a static regain system
Larger fan coil units are most commonly used to condition
Factories
Offices and stores where common air distribution is feasible
Schools
Hotel and motel rooms
How is the airflow adjusted on most commercial air handlers?
By increasing or decreasing the voltage to the fan motor
By adjusting the pitch of the blades on the blower wheel
By moving the speed tap on the blower motor
By adjusting the sheave on an adjustable pulley
Why do air handling units require field adjustment during the commissioning phase?
Manufacturing errors that affect blower performance are common
To match the blower performance to the system requirements
Because the performance requirements of the blower cannot be determined in advance
Air handling units normally do not require field adjustment
The components of a commercial fan coil unit include
A compressor, condenser, metering device, and evaporator
A fan, compressor and condenser
A fan and electric strip heaters
A fan, a water coil, a filter, a fresh air supply, and a control system
Where are unit ventilator fan coil units installed in schools?
Outside each classroom on a concrete pad
On the roof above each classroom
In the school mechanical room
Below window level in each classroom
The major components of an air handling unit include
Air compressor, water separator, and air tank
Compressor, evaporator, and condenser
Heating and cooling coils and electric heat strips
Fan and motor, heating and cooling coils, air filter, dampers
Immediately after making adjustments to an air handler, it is important to check
The compressor shell temperature
The return air temperature
The blower motor amp draw under load
The outdoor ambient temperature
What advantage do hot water heating coils have over steam heating coils?
They operate at a higher temperature than stem heating coils
They produce more heat
Hot water coils can be smaller than steam heating coils
They are easier to control
Why does a chilled water cooling coil have more rows of coils than a hot water heating coil?
hot water heating coils can take advantage of radiant heat transfer and cooling coils cannot
most buildings require more cooling than heating
heat does not travel into cold water as readily as it does into hot water
more surface is necessary for dehumidification
Hot water heating coils should be piped
for parallel flow so that the warmest water meets the coldest air
for counter flow so that the warmest water meets the warmest air
with iron pipe for durability and strength
with PVC pipe to take advantage of PVC's natural insulating ability
What happens if the steam trap at the outlet of a heating coil is stuck in the closed position?
steam flow through the coil will be excessive and air temperatures will be too high
steam flow through the coil will stop and the air temperature will be too low
the steam coil will flood with condensate water
the boiler will stop producing steam
The advantage of the backward curved centrifugal fan over the forward curved centrifugal fan is that
backward curved fans operate at lower RPMs
backward curved fans are normally quieter in operation
backward curved centrifugal fans are well suited for small airflow quantities
backward curved fans are non-overloading
The two main types of fan drives are
Planetary gear drive and worm gear drive
Direct drive and belt drive
Magnetic drive and hydrodrive
Serpentine belt and chain drive
The most common fan used for moving air through ductwork in residential air conditioning is
Propeller
Forward curved centrifugal
Vane axial
Backward curved centrifugal
The most common fan used for moving air across outdoor condenser coils in residential air conditioning is
What is an "air-over" motor?
A motor that is designed for units with the fan located at the top of the unit
A motor that is cooled by airflow over the motor
A motor that is designed to be installed on the bottom of a fan unit
A motor whose function is to blow air over the fan motor to cool it
After making a belt or pulley adjustment to a belt drive fan, it is crucial to check
the fan motor operating current reading
the resistance of the motor winding insulation with a megohm meter
the resistance of the motor windings
the level of the blower housing
The best way to remove a belt from a belt drive is to
Roll the belt over the edge of the larger pulley
Roll the belt over the edge of the smaller pulley
Remove the drive pulley from the motor
Loosen the mount on the drive pulley to create slack in the belt
What are the advantages of backward curved air foil centrifugal fan blades?
Fans with backward curved blades generally operate at lower RPMs
The air foil shaped blades result in less turbulence and noise
The air foil shaped blades are less expensive
The two basic types of fans used in most air handling units are
reciprocating and orbital
centrifugal and axial
positive pressure and negative pressure
clockwise rotating and counter clockwise rotating
Three types of fan blades used with centrifugal fans include
Concentric, isentropic, and exothermal
Straight, forward curved , and right angle
Forward curved, backward curved, and backward curved airfoil
Straight, right angle, and airfoil
The three common types of axial fans are
Box fan, window fan, and oscillating
Propeller, vane axial and tube axial
Clockwise, counterclockwise, and oscillating
Forward curved, backward curved, and propeller
A type of fan that is designed for producing high static pressure in a duct distribution system is:
Condenser
Impeller
Axial
Centrifugal
This type of fan is commonly used on condenser motors because it moves high volumes of air in low static conditions:
Forward-curved centrifugal
Backward-curved centrifugal
Tube axial
The amp draw of a propeller fan will ________ if the airflow leaving the blower is blocked or restricted.
Amp draw cannot be determined on a propeller fan
Decrease
Not change
Increase
The two broad types of fan designs are
Forced draft and induced draft
Forward curved and backward curved
Centrifugal and axial
Propeller and squirrel cage
If the air inlet to a centrifugal fan is restricted
The fan operation will be unaffected
The fan RPM will decrease
The fan motor current draw will increase
The fan motor current draw will decrease
When is a forward curved centrifugal blower motor most likely to draw high amps?
when the motor RPM is set lower than the manufacturer's specifications
when there is no restriction to the airflow in or out of the blower
when the airflow leaving the blower is restricted
when the airflow to the blower is restricted
Airflow through an axial fan is
From the inside of the fan blade outwards in a radial pattern
At a 45° angle to the fan shaft
Parallel to the fan shaft
Perpendicular to the fan shaft
Axial fans are commonly used on applications where
large volumes of air are required at a relatively high static pressure
Reverse loading of the blower bearings is desired
large volumes of air are required at a relatively low static pressure
small volumes of air are required at a relatively high static pressure
Compared to a centrifugal fan, an axial fan is generally
About the same noise level
Noisier at low volumes and quieter at high volumes
Quieter
Noisier
Technicians should know that fan speed is directly related to the amount of air a fan can move; therefore, doubling the fan speed will ________ the amount of air flow.
Increase by 10%
Double
Triple
Increase by 25%
What is the RPM of a fan that uses a 4 inch motor pulley, 8 inch fan pulley, and a motor RPM of 1750?
750
500
1250
875
In order to double fan RPM, the motor horsepower
Must increase by a factor of 4 (2 × 2)
Will not be affected by the fan RPM
Must also double
Must increase by a factor of 8 (2 × 2 × 2)
What speed will a fan turn if the drive motor is turning at 1250 RPM, the motor pulley is 4 inches in diameter, and the fan pulley is 8 inches in diameter?
2500 RPM
1250 RPM
625 RPM
The fan RPM cannot be determined using this information
AMCA fan performance classifications are based on
the minimum and maximum motor horsepower
Minimum and maximum fan RPM for the design airflow
The upper and lower ranges of static pressure and outlet velocity
The physical design of the fan wheel
What fan performance characteristics are shown on a typical fan curve?
pressure drop, efficiency, and horsepower
RPM, tip speed, and horsepower
sound levels, bearing temperatures, and reluctance
horsepower, RPM, and reluctance
To use a fan curve, you need to know
the horsepower and efficiency
the CFM and the RPM
the RPM and tip speed
the required CFM and the static pressure the fan must operate against
Why should ultraviolet germicidal lamps not be handled with bare hands?
The oil from your fingerprints can lead to premature failure of the lamp
The coating on the outside of the lamps is toxic
The exterior UV coating will wipe off, reducing the UV output
The residual UV in the lamp coatings can cause severe burns
What is a HEPA filter?
a filter for heated pans
a filter for a steam heating coil
a very high efficiency air filter
a high efficiency water filter
Which of the following filters would be appropriate for a large industrial air handler?
an electronic air cleaner
a washable hogs hair filter
a 16" × 20" × 1" panel filter
a large fiberglass roll filter
What is the difference between a viscous impingement filter and a standard filter?
viscous filters are tested for viscosity
viscous filters are specifically for filtering oil
viscous filters are treated with a sticky substance to trap and hold dirt
viscous filters use an electrical charging system
To minimize the buildup of dangerous levels of static electricity in industrial processes, industrial air conditioning systems often have provisions for
Humidification
Grounding the air conditioning cabinet
Arc arrestors
High level electromagnetic radiation pulse control to reduce static
Poorly maintained humidifiers can become indoor air quality concerns because of
increased static discharge around all electrical connections
mold and mildew growth
increased outgassing of volatile organic compounds
unintended chemical reactions with HFC refrigerants
The steam grid humidifier works by
Introducing live steam into the air stream through a grid of orifices
Spraying water through nozzles and atomizing it to steam
Passing air over a wetted element
Boiling water in a pan to steam
Types of humidifiers used with commercial air handling equipment include
steam grid, steam pan, and direct water spray
direct expansion, steam, and hot water
bypass, atomizing, and wetted media
direct expansion, chilled water, and steam
The economizer on a commercial packaged air conditioning system
Reduces the indoor blower speed during peak loads to produce cooler air and save energy
Reduces the voltage to the compressor during peak loads to save power
Limits the operating cycles of the system to no more than 15 minutes
Uses outdoor air to provide cooling at low ambient temperatures
What is the function of an energy recovery unit?
To use waste heat for on-site power generation
To recover energy used to cool electric motors
To exchange heat between outdoor air being introduced for ventilation and exhaust air
To recover waste heat from a combustion process
