Managing Alerts and Events with BACnet’s A&E Services
Imagine a smart building with a central command center that receives alerts from everywhere: “The temperature in the server room is too high!”, “A window on the 3rd floor is open!”, “The fire alarm has been triggered!” Without a system to organize these alerts, the command center would be chaos. That’s where BACnet’s Alarm and Event (A&E) services come in—they’re the building’s “emergency dispatch system” that manages who gets what alert, when, and how.
In this article, we’ll explore BACnet’s sophisticated A&E management system. We’ll differentiate between Change of Value (COV), intrinsic reporting, and algorithmic change notifications. We’ll also explain how Event Enrollment and Notification Class objects work together to route alerts to the right operators.
What Are BACnet A&E Services?
BACnet’s Alarm and Event services provide a standardized way for devices to report changes, exceptions, and emergencies. They’re like the building’s nervous system—sensing changes and sending signals to the right places.
Key Functions:
- Support different notification priorities
Why A&E Services Matter
- Data for Analysis: Event logs help identify patterns and improve building performance
Three Types of Event Notification
BACnet supports three main types of event notification, each designed for different scenarios:
1. Change of Value (COV): “Tell Me When Something Changes”
COV is the simplest form of event notification—it sends an alert when a value changes beyond a specified threshold.
How It Works:
- The threshold can be fixed (e.g., ±1°F for temperature) or dynamic
Building Example: A temperature sensor in a server room is set to send a COV notification when the temperature changes by more than 2°F. When the temperature rises from 72°F to 75°F, it sends an alert.
When to Use COV:
- When you want to minimize network traffic (only sends alerts on change)
2. Intrinsic Reporting: “Tell Me When Something Goes Wrong”
Intrinsic reporting is for devices that have built-in alarm capabilities. The device itself determines when to send an alert.
How It Works:
- Common for devices like smoke detectors, leak sensors, and motion detectors
Building Example: A smoke detector has built-in logic to detect smoke. When it detects smoke, it immediately sends a “fire alarm” notification without waiting for a poll.
When to Use Intrinsic Reporting:
- For simple on/off alarm conditions (smoke/no smoke, leak/no leak)
3. Algorithmic Change Notification: “Tell Me When the Pattern Changes”
Algorithmic change notification uses complex algorithms to detect patterns or anomalies.
How It Works:
- Examples include trend analysis, rate-of-change detection, and statistical anomalies
Building Example: An energy meter analyzes power usage over time. When it detects an unusual spike in energy consumption at 2 AM, it sends an alert, suggesting a possible equipment malfunction or unauthorized use.
When to Use Algorithmic Change Notification:
- For optimizing energy usage
The Event Enrollment Object: “Setting Up the Alert”
The Event Enrollment object is like a “subscription form” for alerts. It defines what event to monitor, how to detect it, and where to send notifications.
Key Properties of Event Enrollment
| Property | Description | Example |
|————–|—————–|————-|
| Monitored Object | What device/object to monitor | Temperature Sensor 203 |
| Monitored Property | What property to watch | Present Value (temperature) |
| Notification Class | Where to send alerts | Security Office Notification Class |
| Event Type | What kind of event to detect | COV, Intrinsic, or Algorithmic |
| COV Increment | How much change triggers an alert | ±2°F for temperature |
| Event State | Current state of the alert | Normal, Alarm, Offnormal |
| Acknowledgment Required | Whether the alert needs acknowledgment | True for critical alerts |
How Event Enrollment Works
1. Configuration: A building manager creates an Event Enrollment object for a temperature sensor
2. Monitoring: The sensor monitors its temperature value
3. Detection: When the temperature changes by more than 2°F, the Event Enrollment detects it
4. Notification: It sends an alert to the specified Notification Class
The Notification Class Object: “Routing the Alert”
The Notification Class object is like a “mailroom” that routes alerts to the right recipients. It defines who gets what alerts and how they get them.
Key Properties of Notification Class
| Property | Description | Example |
|————–|—————–|————-|
| Recipients | Who gets the alert | Building Manager, Security Office |
| Notification Types | How alerts are sent | Email, SMS, Building Dashboard |
| Priority | How important the alert is | High (fire alarm), Medium (temperature), Low (light status) |
| Notification Interval | How often to resend unacknowledged alerts | Every 5 minutes for critical alerts |
| Acknowledgment Required | Whether acknowledgment is needed | True for critical events |
| Event Message Texts | Custom messages for different events | “Temperature in Server Room Too High” |
How Notification Class Works
1. Receive Alert: Gets the alert from an Event Enrollment object
2. Check Priority: Determines how urgent the alert is
3. Select Recipients: Chooses who gets the alert based on priority
4. Send Notification: Delivers the alert via the specified methods (email, SMS, etc.)
5. Track Acknowledgment: Monitors if the alert was acknowledged
6. Resend if Needed: Sends reminders for unacknowledged alerts
How Event Enrollment and Notification Class Work Together
Let’s see these objects in action with a real building scenario:
Scenario: A server room temperature sensor exceeds its setpoint
1. Event Enrollment Monitors: The Event Enrollment object watches the temperature sensor’s Present Value
2. COV Detected: When the temperature rises from 72°F to 75°F (exceeding the 2°F COV increment), the Event Enrollment detects it
3. Event State Changes: The Event Enrollment changes its state from “Normal” to “Offnormal”
4. Notification Sent: It sends a notification to its assigned Notification Class
5. Notification Class Routes: The Notification Class checks the alert priority (Medium)
6. Recipients Notified: It sends emails to the building manager and IT staff
7. Alert Delivered: The building manager receives an email: “Temperature in Server Room 203 is 75°F, exceeding setpoint of 72°F”
8. Acknowledgment: The manager acknowledges the alert, which updates the Event Enrollment state
Advanced A&E Features
BACnet’s A&E system includes several advanced features for complex building scenarios:
1. Event Logging: “Black Box for Building Events”
- Useful for compliance reporting and troubleshooting
2. Event Trend Logging: “Pattern Analysis”
- Supports predictive maintenance
3. Group Alarming: “Alert Groups”
- Example: “3 windows open on the 2nd floor”
4. Alarm Shelving: “Temporarily Ignore Alerts”
- Example: Shelving temperature alerts while changing HVAC filters
5. Cross-System Integration: “Alert Cascading”
- Example: A fire alarm can trigger HVAC shutdown, door unlocking, and elevator recall
Best Practices for BACnet A&E Implementation
1. Prioritize Alerts: Assign appropriate priorities to prevent alert fatigue
2. Use the Right Notification Type: COV for continuous values, intrinsic for safety devices, algorithmic for patterns
3. Configure Acknowledgment Requirements: Only require acknowledgment for critical alerts
4. Test Alerts Regularly: Ensure all alerts are working correctly
5. Document Alert Procedures: Define who gets what alerts and how they should respond
6. Use Alert Groups: Combine related alerts to reduce operator workload
7. Implement Event Logging: Keep records for compliance and analysis
8. Train Staff: Ensure operators know how to respond to different alerts
Real-World Example: Hospital Alarm System
A hospital uses BACnet’s A&E services to manage hundreds of alerts:
- Informational Alerts (Priority Low): Door access events, lighting schedule changes
When a fire alarm is triggered:
1. The smoke detector’s intrinsic reporting sends an alert
2. The Event Enrollment object detects the critical event
3. The Notification Class routes it to security, building management, and local fire department
4. It triggers cross-system actions: HVAC shutdown, door unlocking, elevator recall
5. The alert is logged for compliance reporting
Conclusion: The Building’s Emergency Dispatch System
BACnet’s Alarm and Event services are the building’s “emergency dispatch system”—they monitor devices, detect events, and route alerts to the right people at the right time. By understanding COV, intrinsic reporting, and algorithmic notifications, and how Event Enrollment and Notification Class objects work together, you can create a robust alarm system that keeps your building safe, efficient, and compliant.
Whether you’re managing a small office or a large hospital, BACnet’s A&E services provide the flexibility and sophistication needed to handle everything from simple temperature alerts to critical safety events. With proper configuration and best practices, you can create an alert system that keeps your building running smoothly while minimizing operator fatigue.
So, the next time you receive an alert from your building system, remember the complex BACnet A&E services working behind the scenes—detecting, prioritizing, and delivering that alert to keep your building safe and efficient.
