In modern building automation, efficient data exchange is essential. BACnet, the international communication standard for building management systems, has become a cornerstone of smart buildings and IoT integration. By providing a common language for devices such as HVAC controllers, lighting systems, and security equipment, BACnet makes it possible to coordinate and optimize building operations seamlessly (What is BACnet?).
However, not all data changes are equally important. Sensors continuously measure real-world values such as temperature, humidity, or pressure — and these values may fluctuate slightly every second. Continuously transmitting every micro-change would quickly overload the network, creating unnecessary traffic. This is where the Change of Value (COV) service comes in.
Real-world measurements, such as temperature or humidity, are in constant motion. A thermometer in a room may detect micro-variations every second, even if the perceived environment feels stable. If every one of these small variations had to be reported through the BACnet network, the result would be a flood of messages that would not only overload the system but also waste bandwidth and processing power.
This is why the COV service was introduced: it allows devices to report only the changes that actually matter. Instead of notifying the network every time the value shifts slightly, a threshold can be defined — for example:
“Notify me only when the room temperature changes by at least 0.5°C.”
By filtering out insignificant variations, the COV service ensures that the BACnet network transmits relevant, actionable updates, while avoiding redundant traffic.
The Change of Value (COV) service in BACnet allows devices to report updates only when certain conditions are met. Instead of a continuous stream of data, the network only receives information when it is meaningful.
Two main parameters are used to configure COV reporting:
⚠️ However, it is important to note that the BACnet standard does not define a minimum interval between notifications. If the threshold is set too low, devices may send too many updates, potentially flooding the system. Careful tuning is therefore essential.
| Parameter | Description |
|---|---|
| Change threshold | Minimum change in value required before a notification is sent |
| Maximum reporting interval | Guarantees updates at regular intervals even without changes |
The introduction of the COV service provides a major improvement in how BACnet networks handle data. Instead of being overwhelmed by redundant messages, systems receive only the information that matters. This leads to:
| Continuous polling | COV service |
|---|---|
| High network load | Optimized traffic |
| Repetitive & redundant data | Only meaningful updates |
| Waste of bandwidth & resources | Efficient use of system resources |
By focusing on useful updates rather than raw data streams, the COV service helps ensure both scalability and reliability in modern building automation systems.
While the COV service is a powerful tool, it must be used wisely to avoid unexpected issues. Here are some best practices to keep in mind:
⚠️ Remember: the BACnet standard does not define a minimum reporting interval. If thresholds are poorly configured, the system could easily be flooded with notifications, undermining the efficiency that COV was designed to deliver.
“The COV service is a cornerstone of BACnet efficiency: it ensures that networks carry only what really matters, balancing precision and scalability.“
This perspective highlights the key role of COV in making large-scale building automation both scalable and sustainable.
The Change of Value (COV) service is a fundamental feature of BACnet that ensures building automation systems remain both responsive and efficient. By reporting only meaningful changes and enforcing maximum reporting intervals, COV prevents network overload while still providing operators with the data they need to make informed decisions.
For a broader understanding of how BACnet enables interoperability across building systems, you can also read How does BACnet work?.
COV means Change of Value. It is a BACnet service that reports data only when a property changes significantly, instead of continuously sending all variations.
Because real-world measurements (temperature, humidity, etc.) change constantly. Without COV, reporting every micro-change would overload the network with unnecessary traffic.
COV filters out minor fluctuations and only transmits updates that exceed a defined threshold. This reduces redundant messages and makes the system more efficient.
Yes. You can set a change threshold (e.g., 0.5°C for temperature changes) and a maximum reporting interval to guarantee periodic updates.
No. BACnet does not define a minimum reporting interval. If you set the threshold too low, you may flood the system with notifications.
COV is particularly valuable in HVAC systems, energy monitoring, lighting control, and any scenario where real-time but efficient reporting is needed.
By reducing unnecessary data traffic, COV makes networks more scalable, saves energy, and ensures that only meaningful information reaches operators and controllers.
About Actility
Actility, one of the co-inventors of LoRaWAN® technology and a founding member of the LoRa Alliance, is the leader in industrial-grade low-power wide-area network (LPWAN) connectivity and IoT tracking solutions. Actility’s ThingPark™ platform, which supports multi-radio connectivity (LoRaWAN®, NB-IoT, LTE-M), powers the majority of public networks and numerous private and enterprise networks worldwide. Through its subsidiary Abeeway, Actility offers patented ultra-low power, multi-radio trackers and comprehensive indoor and outdoor geolocation services. Additionally, the ThingPark Market boast the largest catalog of LoRaWAN® devices, gateways, and solutions available.
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