HVAC Building Automation Systems 2 — Questions and Answers
Question 1: Which communication protocol is most commonly used for BAS integration with lighting control systems?
- DALI
- BACnet (Correct answer)
- Modbus RTU
- KNX
Correct answer: BACnet
BACnet is the dominant open protocol for BAS integration across HVAC, lighting, and other building systems.
Question 2: In a BAS, what does a PID controller stand for?
- Pressure-Integrated-Damper
- Proportional-Integral-Derivative (Correct answer)
- Program-Interface-Device
- Peripheral-Input-Driver
Correct answer: Proportional-Integral-Derivative
PID stands for Proportional-Integral-Derivative, a feedback control algorithm that minimizes error between setpoint and measured value.
Question 3: What is the primary function of a supervisory controller in a BAS hierarchy?
- Directly actuate dampers and valves
- Coordinate multiple field controllers and enforce global strategies (Correct answer)
- Log sensor data to a local memory card
- Convert analog signals to digital
Correct answer: Coordinate multiple field controllers and enforce global strategies
Supervisory controllers coordinate field-level DDC controllers and implement global optimization strategies like demand limiting.
Question 4: An HVAC technician notices a BAS trend log shows supply air temperature oscillating rapidly around setpoint. What is the most likely cause?
- Sensor failure
- PID loop with too-high proportional gain (Correct answer)
- Communication bus fault
- Low refrigerant charge
Correct answer: PID loop with too-high proportional gain
Excessive proportional gain causes hunting or oscillation around setpoint in a PID control loop.
Question 5: What BACnet object type is used to represent a physical analog input such as a temperature sensor?
- Binary Value
- Analog Input (Correct answer)
- Multi-State Output
- Schedule
Correct answer: Analog Input
The BACnet Analog Input object type represents a physical analog measurement such as temperature or pressure.
Question 6: Which topology is most commonly used for BACnet MS/TP field-level networks?
- Star
- Mesh
- Daisy-chain (bus) (Correct answer)
- Ring
Correct answer: Daisy-chain (bus)
BACnet MS/TP uses a daisy-chain bus topology where all devices share a single twisted-pair cable segment.
Question 7: In BAS programming, what is a 'setback' schedule typically used for?
- Increasing equipment runtime during peak hours
- Relaxing temperature setpoints during unoccupied periods to save energy (Correct answer)
- Reducing sensor polling frequency overnight
- Backing up controller programs automatically
Correct answer: Relaxing temperature setpoints during unoccupied periods to save energy
Setback schedules relax HVAC setpoints during unoccupied periods, reducing energy consumption while maintaining acceptable conditions.
HVAC Building Automation Systems 2
Which communication protocol is most commonly used for BAS integration with lighting control systems?