HVAC Unit 77 Flashcards
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Questions and Answers

What is a central station air-handling unit?

It is used for large systems and is assembled on site using separate components.

Larger fan coil units are commonly used to condition what?

Schools.

How is the airflow adjusted on most commercial air handlers?

By adjusting the sheave on an adjustable pulley.

Why do air-handling units require field adjustment during the commissioning phase?

<p>To match the blower performance to the system requirements.</p> Signup and view all the answers

What are the components of a commercial fan coil unit?

<p>A fan, a water coil, a filter, a fresh air supply, and a control system.</p> Signup and view all the answers

Where are unit ventilator fan coil units installed in schools?

<p>Below window level in each classroom.</p> Signup and view all the answers

What are the major components of an air-handling unit?

<p>Fan and motor, heating and cooling coils, air filter, dampers.</p> Signup and view all the answers

Immediately after making adjustments to an air handler, what is important to check?

<p>The blower motor amp draw under load.</p> Signup and view all the answers

Why does a chilled water cooling coil have more rows of coils than a hot water heating coil?

<p>More surface is necessary for dehumidification.</p> Signup and view all the answers

How should hot water heating coils be piped?

<p>For counter flow so that the warmest water meets the warmest air.</p> Signup and view all the answers

What happens if the steam trap at the outlet of a heating coil is stuck in the closed position?

<p>Steam flow through the coil will stop and the air temperature will be too low.</p> Signup and view all the answers

What is the advantage of the backward-curved centrifugal fan over the forward-curved centrifugal fan?

<p>Backward-curved fans are non-overloading.</p> Signup and view all the answers

What are the two main types of fan drives?

<p>Direct drive and belt drive.</p> Signup and view all the answers

What is the most common fan used for moving air through ductwork in residential air conditioning?

<p>Forward-curved centrifugal.</p> Signup and view all the answers

What is the most common fan used for moving air across outdoor condenser coils in residential air conditioning?

<p>Propeller.</p> Signup and view all the answers

What is an 'air-over' motor?

<p>A motor that is cooled by airflow over the motor.</p> Signup and view all the answers

After making a belt or pulley adjustment to a belt drive fan, what is crucial to check?

<p>The fan motor operating current reading.</p> Signup and view all the answers

What are the two basic types of fans used in most air-handling units?

<p>Centrifugal and axial.</p> Signup and view all the answers

What are three types of fan blades used with centrifugal fans?

<p>Forward-curved, backward-curved, and backward-curved airfoil.</p> Signup and view all the answers

What are the three common types of axial fans?

<p>Propeller, vane axial, and tube axial.</p> Signup and view all the answers

What type of fan is designed for producing high static pressure in a duct distribution system?

<p>Centrifugal.</p> Signup and view all the answers

What type of fan is commonly used on condenser motors because it moves high volumes of air in low static conditions?

<p>Propeller.</p> Signup and view all the answers

The amp draw of a propeller fan will __________ if the airflow leaving the blower is blocked or restricted.

<p>increase.</p> Signup and view all the answers

What are the two broad types of fan designs?

<p>Centrifugal and axial.</p> Signup and view all the answers

If the air inlet to a centrifugal fan is restricted, what will happen to the fan motor current draw?

<p>The fan motor current draw will decrease.</p> Signup and view all the answers

When is a forward-curved centrifugal blower motor most likely to draw high amps?

<p>When there is no restriction to the airflow in or out of the blower.</p> Signup and view all the answers

How is airflow through an axial fan characterized?

<p>It is parallel to the fan shaft.</p> Signup and view all the answers

Axial fans are commonly used on applications where?

<p>Large volumes of air are required at a relatively low static pressure.</p> Signup and view all the answers

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 airflow.

<p>double.</p> Signup and view all the answers

What is the RPM of a fan that uses a 4 in motor pulley, 8 in fan pulley, and a motor RPM of 1,750?

<ol start="875"> <li></li> </ol> Signup and view all the answers

In order to double fan RPM, the motor horsepower must what?

<p>Increase by a factor of 8 (2 x 2 x 2).</p> Signup and view all the answers

What speed will a fan turn if the drive motor is turning at 1,250 RPM, the motor pulley is 4 in in diameter, and the fan pulley is 8 in in diameter?

<p>625 RPM.</p> Signup and view all the answers

AMCA fan performance classifications are based on what?

<p>The upper and lower ranges of static pressure and outlet velocity.</p> Signup and view all the answers

What fan performance characteristics are shown on a typical fan curve?

<p>Pressure drop, efficiency, and horsepower.</p> Signup and view all the answers

To use a fan curve, you need to know what?

<p>The required CFM and the static pressure the fan must also operate against.</p> Signup and view all the answers

Why should ultraviolet germicidal lamps NOT be handled with bare hands?

<p>The oil from your fingerprints can lead to premature failure of the lamp.</p> Signup and view all the answers

What is a HEPA filter?

<p>A very high efficiency filter.</p> Signup and view all the answers

What filter would be appropriate for a large industrial air handler?

<p>A large fiberglass roll filter.</p> Signup and view all the answers

What is the difference between a viscous impingement filter and a standard filter?

<p>Viscous filters are treated with a sticky substance to trap and hold dirt.</p> Signup and view all the answers

Poorly maintained humidifiers can become indoor air quality concerns because of what?

<p>Mold and mildew growth.</p> Signup and view all the answers

How does the steam grid humidifier work?

<p>By introducing live steam into the air stream through a grid of orifices.</p> Signup and view all the answers

What types of humidifiers are used with commercial air-handling equipment?

<p>Steam grid, steam pan, and direct water spray.</p> Signup and view all the answers

Study Notes

Air-Handling Units

  • Central station air-handling units are utilized for large systems and assembled on-site from separate components.
  • Commercial fan coil units are primarily used in schools for conditioning air.
  • Airflow in commercial air handlers is typically adjusted by modifying the sheave on an adjustable pulley.
  • Field adjustments in air-handling units are necessary during commissioning to align blower performance with system demands.

Components of Fan Coil Units

  • Key components of commercial fan coil units include a fan, water coil, filter, fresh air supply, and a control system.
  • Unit ventilator fan coil units are installed below window level in classrooms to optimize air circulation.
  • Major components of an air-handling unit consist of the fan and motor, heating and cooling coils, air filter, and dampers.

Adjustments and Performance

  • After adjustments to an air handler, it's essential to verify the blower motor amp draw under load.
  • Chilled water cooling coils have more rows than hot water heating coils, as more surface area is necessary for effective dehumidification.
  • Hot water heating coils should be piped for counter flow, ensuring the warmest water meets the warmest air.

Fan Types and Operations

  • Backward-curved centrifugal fans are non-overloading, making them advantageous over forward-curved fans.
  • Fan drives come in two types: direct drive and belt drive.
  • The most commonly used fan in residential air conditioning for ductwork is the forward-curved centrifugal fan, while propeller fans are typical for outdoor condenser coils.
  • Air-over motors are cooled by airflow across the motor.

Fan Performance and Effects

  • After adjusting a belt or pulley on a belt drive fan, checking the fan motor operating current is crucial.
  • Centrifugal and axial fans are the primary types used in air-handling units.
  • Three blade types used with centrifugal fans include forward-curved, backward-curved, and backward-curved airfoil.
  • Common types of axial fans consist of propeller, vane axial, and tube axial.

Fan Pressure and Airflow

  • Centrifugal fans are designed to produce high static pressure in duct systems.
  • Propeller fans are suitable for condenser motors as they can move large volumes of air under low static conditions.
  • An increase in airflow blockage to a propeller fan leads to an increase in amp draw.
  • If a centrifugal fan's air inlet is restricted, the motor current draw will decrease.

Fan Speed and Efficiency

  • Airflow through axial fans is parallel to the fan shaft; they are used for high volume, low static pressure applications.
  • Doubling fan speed results in double the airflow capacity.
  • The RPM of a fan can be calculated based on pulley sizes, motor RPM, and pulley diameters.

Fan Classification and Characteristics

  • AMCA classifies fan performance by determining upper and lower static pressure and outlet velocity ranges.
  • A typical fan curve highlights characteristics like pressure drop, efficiency, and horsepower.
  • To utilize a fan curve effectively, knowledge of required CFM and opposing static pressure is necessary.

Air Quality and Filtration

  • Ultraviolet germicidal lamps should not be handled with bare hands to avoid oil that can cause premature lamp failure.
  • HEPA filters are extremely efficient filters commonly used for high-quality air filtration.
  • A large fiberglass roll filter is suitable for industrial air handlers.
  • Viscous impingement filters are treated with sticky substances to trap dirt, distinguishing them from standard filters.

Humidification Concerns

  • Poor maintenance of humidifiers can lead to indoor air quality issues due to mold and mildew.
  • Steam grid humidifiers work by inserting live steam into the air through a series of orifices.
  • Types of humidifiers utilized with commercial air-handling units include steam grid, steam pan, and direct water spray.

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Description

Test your knowledge of HVAC terminology with these Unit 77 flashcards. This quiz covers essential definitions and concepts related to air-handling units and their components. Perfect for students and professionals in the heating, ventilation, and air conditioning field.

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