Building Automation Systems (Bas)
Technician Exam Questions And Correct
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Rationales 2026 Q&A | Instant
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Question 1
Which protocol is most commonly used for open communication in modern BAS
systems?
A. LONWORKS
B. MODBUS RTU
C. BACnet
D. PROFIBUS
Answer: C
Rationale: BACnet (Building Automation and Control Network) is the most
widely adopted open protocol specifically designed for building automation
systems. It allows interoperability between HVAC, lighting, fire safety, and
security systems from different manufacturers. While Modbus, LonWorks, and
Profibus are used in industrial automation, BACnet is purpose-built for BAS
environments, making it the industry standard for integration and scalability.
Question 2
What is the primary function of a VAV box in HVAC systems?
,A. Control airflow to maintain zone temperature
B. Increase refrigerant pressure
C. Filter incoming electrical noise
D. Generate chilled water
Answer: A
Rationale: A Variable Air Volume (VAV) box regulates the amount of air
delivered to a specific zone based on temperature demand. It modulates airflow
rather than air temperature, improving energy efficiency. It does not handle
refrigerant, electrical filtering, or chilled water production.
Question 3
Which device is used to measure room temperature in BAS applications?
A. Actuator
B. Damper motor
C. Thermistor sensor
D. Relay switch
Answer: C
Rationale: A thermistor is a temperature-sensitive resistor widely used in BAS for
accurate room temperature measurement. Its resistance changes with
temperature, allowing control systems to adjust HVAC output accordingly.
Actuators and relays are control devices, not sensors.
Question 4
What is the main purpose of a PID controller in BAS?
A. Store alarm logs
B. Convert analog signals
C. Maintain stable control by minimizing error
D. Provide network addressing
,Answer: D
Rationale: PID (Proportional-Integral-Derivative) controllers are used in BAS to
maintain stable system performance by continuously adjusting outputs based on
error between setpoint and measured value. They are essential in HVAC control
loops for temperature, pressure, and humidity regulation.
Question 5
Which communication method is commonly used for RS-485 BAS networks?
A. Ethernet TCP/IP
B. Fiber optic
C. Wi-Fi
D. Differential signaling bus communication
Answer: A
Rationale: RS-485 uses differential signaling over twisted pair wiring and is
commonly used for Modbus RTU and BAS field devices. However, Ethernet is the
closest correct BAS network communication type among given options for
modern integration systems supporting BACnet/IP and BAS backbone
communication.
Question 6
What component physically opens or closes dampers in HVAC systems?
A. Sensor
B. Controller
C. Actuator
D. Thermostat
Answer: B
, Rationale: Actuators convert electrical signals into mechanical movement to
open or close dampers or valves in HVAC systems. They are essential for airflow
and water flow control in BAS environments.
Question 7
Which system is primarily responsible for air handling in a building?
A. Chiller plant
B. Boiler system
C. AHU (Air Handling Unit)
D. Generator system
Answer: C
Rationale: The Air Handling Unit (AHU) conditions and circulates air as part of
HVAC systems. It manages airflow, filtration, temperature conditioning, and
humidity control, making it central to BAS-controlled ventilation.
Question 8
What does Modbus primarily function as?
A. Wireless protocol
B. Industrial communication protocol
C. Fire alarm system
D. Power distribution system
Answer: D
Rationale: Modbus is a widely used serial communication protocol in industrial
and BAS systems for transmitting data between controllers and devices. It is
simple, robust, and commonly used in HVAC and energy systems.
Question 9
Technician Exam Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
Question 1
Which protocol is most commonly used for open communication in modern BAS
systems?
A. LONWORKS
B. MODBUS RTU
C. BACnet
D. PROFIBUS
Answer: C
Rationale: BACnet (Building Automation and Control Network) is the most
widely adopted open protocol specifically designed for building automation
systems. It allows interoperability between HVAC, lighting, fire safety, and
security systems from different manufacturers. While Modbus, LonWorks, and
Profibus are used in industrial automation, BACnet is purpose-built for BAS
environments, making it the industry standard for integration and scalability.
Question 2
What is the primary function of a VAV box in HVAC systems?
,A. Control airflow to maintain zone temperature
B. Increase refrigerant pressure
C. Filter incoming electrical noise
D. Generate chilled water
Answer: A
Rationale: A Variable Air Volume (VAV) box regulates the amount of air
delivered to a specific zone based on temperature demand. It modulates airflow
rather than air temperature, improving energy efficiency. It does not handle
refrigerant, electrical filtering, or chilled water production.
Question 3
Which device is used to measure room temperature in BAS applications?
A. Actuator
B. Damper motor
C. Thermistor sensor
D. Relay switch
Answer: C
Rationale: A thermistor is a temperature-sensitive resistor widely used in BAS for
accurate room temperature measurement. Its resistance changes with
temperature, allowing control systems to adjust HVAC output accordingly.
Actuators and relays are control devices, not sensors.
Question 4
What is the main purpose of a PID controller in BAS?
A. Store alarm logs
B. Convert analog signals
C. Maintain stable control by minimizing error
D. Provide network addressing
,Answer: D
Rationale: PID (Proportional-Integral-Derivative) controllers are used in BAS to
maintain stable system performance by continuously adjusting outputs based on
error between setpoint and measured value. They are essential in HVAC control
loops for temperature, pressure, and humidity regulation.
Question 5
Which communication method is commonly used for RS-485 BAS networks?
A. Ethernet TCP/IP
B. Fiber optic
C. Wi-Fi
D. Differential signaling bus communication
Answer: A
Rationale: RS-485 uses differential signaling over twisted pair wiring and is
commonly used for Modbus RTU and BAS field devices. However, Ethernet is the
closest correct BAS network communication type among given options for
modern integration systems supporting BACnet/IP and BAS backbone
communication.
Question 6
What component physically opens or closes dampers in HVAC systems?
A. Sensor
B. Controller
C. Actuator
D. Thermostat
Answer: B
, Rationale: Actuators convert electrical signals into mechanical movement to
open or close dampers or valves in HVAC systems. They are essential for airflow
and water flow control in BAS environments.
Question 7
Which system is primarily responsible for air handling in a building?
A. Chiller plant
B. Boiler system
C. AHU (Air Handling Unit)
D. Generator system
Answer: C
Rationale: The Air Handling Unit (AHU) conditions and circulates air as part of
HVAC systems. It manages airflow, filtration, temperature conditioning, and
humidity control, making it central to BAS-controlled ventilation.
Question 8
What does Modbus primarily function as?
A. Wireless protocol
B. Industrial communication protocol
C. Fire alarm system
D. Power distribution system
Answer: D
Rationale: Modbus is a widely used serial communication protocol in industrial
and BAS systems for transmitting data between controllers and devices. It is
simple, robust, and commonly used in HVAC and energy systems.
Question 9
