What is the primary purpose of fault diagnostics in DDC systems?

• A. To issue alarms when thresholds are exceeded.
• B. To log energy consumption for reporting.
• C. To identify root causes of sensor or actuator failures.
• D. To schedule maintenance windows automatically.

Answer: (C)

Fault diagnostics in DDC systems aim to determine exactly what failed and why it happened. The primary purpose is to identify the root causes of sensor or actuator faults so maintenance can address the real problem, restore proper control, and minimize downtime. Diagnostics continuously compare sensor and actuator behavior against expected relationships, using patterns in data to distinguish issues like a drifting temperature sensor, a stuck damper, a bad wiring connection, or a failing actuator. This lets technicians fix the correct component rather than chasing symptoms. Alarms are about alerting when values exceed limits, which is useful but doesn’t diagnose the problem. Logging energy use is for reporting and optimization, not fault identification. Automatically scheduling maintenance is helpful but not the core aim of fault diagnostics.