CHIPKIN NEWSLETTER - MARCH 2023 EDITION

Commandable versus writable BACnet Objects

In BACnet, the Present Value property of an Analog Value (AV) object can behave differently depending on whether it is commandable or simply writable. A commandable Present Value requires the use of BACnet command priorities, meaning writes must include a priority and the object must implement a Priority Array and Relinquish Default, as defined in the BACnet specification.

Writable and commandable are not the same. A Present Value may be writable without supporting command prioritization, or it may only be writable when the object’s Out_Of_Service property is set to TRUE. The BACnet standard clarifies that if a Present Value is commandable, it must also be writable, and that Out_Of_Service forces writability even when normal operation restricts it.

Learning Center - Case Studies & Articles

Case Study - Using a Fieldserver to read data off an API (Using HTTP) and then serve it as BACnet/IP

Chipkin helped a school district integrate over 120 Pelican Wireless thermostats across six schools into a BACnet/IP-based Building Management System. Because the thermostats exposed data only through a cloud API, Chipkin used a FieldServer QuickServer to read the data over HTTP and serve it locally as BACnet/IP, enabling centralized monitoring and control.

To complete the integration, Chipkin developed a custom driver that translated string-based API values into numeric BACnet values and scaled the configuration to support a large number of points. This approach allowed seamless protocol conversion without modifying the existing thermostats or the BMS.