HVAC Building Automation Systems 5 — Questions and Answers
Question 1: What is the purpose of a BAS 'global controller' or 'central plant optimizer'?
- Store all controller programs as a backup
- Coordinate chiller, boiler, and cooling tower sequencing to minimize total plant energy (Correct answer)
- Provide a graphical interface for the building operator
- Manage fire alarm integration with HVAC
Correct answer: Coordinate chiller, boiler, and cooling tower sequencing to minimize total plant energy
A central plant optimizer coordinates multiple pieces of equipment to minimize total energy consumption while meeting load requirements.
Question 2: A BAS trend log shows supply air temperature consistently 3°F above setpoint. After confirming the setpoint is correct, what is the most likely issue?
- BACnet communication fault on the trunk
- Sensor offset or calibration error (Correct answer)
- Actuator priority array conflict
- Incorrect baud rate on the MS/TP network
Correct answer: Sensor offset or calibration error
A consistent offset between setpoint and measured value typically indicates a sensor calibration error or transmitter offset rather than a control logic problem.
Question 3: What does 'load shedding' mean in a BAS demand-limiting strategy?
- Removing electrical panels from the main switchboard
- Temporarily reducing HVAC loads to prevent exceeding a peak demand threshold (Correct answer)
- Shedding excess heat from the condenser to the cooling tower
- Balancing airflow between multiple air handling units
Correct answer: Temporarily reducing HVAC loads to prevent exceeding a peak demand threshold
Load shedding strategically reduces non-critical HVAC loads when electrical demand approaches a utility-defined threshold to avoid demand charges.
Question 4: In BAS terminology, what is a 'soft point' or 'virtual point'?
- A physical sensor with dampened response time
- A calculated or logical data point that exists only in software, not tied to a physical input or output (Correct answer)
- A BACnet device with no physical enclosure
- An alarm that is suppressed but still logged
Correct answer: A calculated or logical data point that exists only in software, not tied to a physical input or output
Virtual or soft points are software-calculated values derived from physical points, such as average zone temperature or total airflow.
Question 5: Which standard governs cybersecurity requirements for building automation and control network systems?
- ASHRAE 90.1
- NIST SP 800-82 and ASHRAE Guideline 13 (Correct answer)
- UL 864
- NFPA 72
Correct answer: NIST SP 800-82 and ASHRAE Guideline 13
NIST SP 800-82 and ASHRAE Guideline 13 address cybersecurity best practices for industrial and building control network systems.
Question 6: What is the function of an 'interlock' in a BAS sequence of operations?
- A hardware lock that prevents controller cabinet access
- A logical condition that prevents equipment from operating unless a prerequisite condition is satisfied (Correct answer)
- A BACnet object that links two controllers on the same network
- A safety device that locks damper blades in the open position
Correct answer: A logical condition that prevents equipment from operating unless a prerequisite condition is satisfied
Interlocks are software or hardware conditions that prevent unsafe or inefficient operation, such as requiring the supply fan to run before opening the outdoor air damper.
Question 7: In a BAS, what is 'trend logging' primarily used for?
- Sending real-time alerts to technicians via SMS
- Recording time-stamped historical data from points for analysis and diagnostics (Correct answer)
- Synchronizing controller clocks across the network
- Automatically adjusting setpoints based on seasonal changes
Correct answer: Recording time-stamped historical data from points for analysis and diagnostics
Trend logging records time-stamped values from sensors and control outputs, enabling historical analysis, fault diagnostics, and energy auditing.
HVAC Building Automation Systems 5
What is the purpose of a BAS 'global controller' or 'central plant optimizer'?