HVAC Unit 77 Flashcards

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.