ASHRAE 135 defines BACnet, an open protocol standard for building automation and control networks. This standard enables interoperability between HVAC systems, thermostats, sensors, and other building equipment from different manufacturers. BACnet allows seamless data exchange, remote monitoring, and centralized control of complex building systems through a common communication language.
Protocol Architecture and Communication
ASHRAE 135 supports multiple data link layers including Ethernet, MS/TP (Master-Slave Token Passing), and ARCNET. Data transmission rates range from 9,600 bits per second on slower networks to 100 megabits per second on Ethernet connections. The standard defines application objects, services, and device profiles ensuring that controllers from different vendors can communicate and exchange real-time information about temperature, humidity, pressure, and equipment status.
HVAC System Applications
BACnet enables advanced building automation through integrated HVAC control, allowing simultaneous management of multiple zones, chiller plants, and air handling units. Facility managers access system performance data, set temperature schedules, and implement demand-response strategies remotely. The open standard reduces vendor lock-in, lowers long-term system costs, and supports building energy management systems (BEMS) for continuous monitoring and optimization of HVAC operations.