What is the purpose of a trend log in a DDC system?

• A. To record historical data for analysis, troubleshooting, and performance verification.
• B. To alert operators to faults in real-time only.
• C. To adjust setpoints automatically.
• D. To store firmware updates.

Answer: (A)

Trend logs in a DDC system capture historical data from sensors and actuators over time. By recording periodic data points for variables like temperatures, airflow, valve positions, and energy use, they create a record you can review to analyze how the system behaved, diagnose issues, and verify that performance targets are being met. This historical view helps you spot patterns, drifts, or anomalies that aren’t evident from a single moment in time. Real-time fault alerts are handled by alarms, not trend logs, so trend logs aren’t meant for instant warnings. They also don’t store firmware updates, which belong to maintenance tasks. So the core purpose is to record historical data for analysis, troubleshooting, and performance verification.