To discuss heating, ventilating and air conditioning (HVAC), I will return to the categories I used in my first column: power, control and communications. HVAC systems are a major part of the infrastructure of large buildings, and since they use a great deal of power, they have a large impact on a building’s energy usage. The way to optimize the energy efficiency of the HVAC system is to be able to smoothly control it, so it should have variable control and the ability to communicate with other building systems.

Variable control is achieved by operating the blowers with variable-frequency motor drives (VFDs). They can then be used in a variable-air volume (VAV) setup to optimize their speed. Controllable blowers are perfect for cooling racks of computers in data centers.

“With constant volume fans on the servers, you can only be right at one condition of server loading. The solution is to employ variable-speed server fans.” said Mark Hydeman, P.E., principal, Taylor Engineering LLC, Alameda, Calif. The cooling air supply can be controlled for constant pressure under the floor or desired temperatures at rack inlets.

But HVAC systems should be controlled intelligently. Although components had been controllable before BACnet, they often were run with proprietary software, so a user buying one brand of VFD was forced to buy all the other components of the system from the same manufacturer. Responding to the increasing desire for integration of building systems, a group of industry professionals from the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) started meeting in 1987 to address the issues. They designed BACnet, an open, nonproprietary, data communication protocol as the solution. It was adopted as ASHRAE/ANSI Standard 135 in 1995 and, in 2003, became an ISO international standard.

BACnet can be used in two ways-—the first being to control HVAC systems. Second, it can be integrated with other vital systems in a building, such as power distribution, lighting and life safety. Since BACnet-controlled devices can interface with a building’s communications network, a facilities manager can monitor and control these building systems from any PC connected to the network.

I received a verbal guided tour of BACnet from Bill Swan, Building Standards Initiatives Leader for Alerton and Honeywell and chairman of the BACnet committee for ASHRAE. He emphasized that this protocol is open for use by any manufacturer and is constantly monitored, updated and expanded.

Much of the update effort has been to extend BACnet to security and life safety systems, Swan said. In 1996, the committee started work on methods to integrate fire alarm systems. As a result, HVAC can respond to a fire alarm by going into smoke-control mode and adjusting air pressure to limit the dispersion of smoke throughout a building. It also can turn on all lights in the event of a fire. Access control and elevator monitoring also are being discussed.

Since BACnet is usable for lighting control, lighting can be scheduled according to time of day or turned off in unoccupied areas to save energy.

An extension was added in 2007 to enable utilities, with BACnet’s Web Services feature, to measure energy usage and cause a programmed load reduction to avoid a brownout. Large electricity users can sign up with a utility to allow them to interface in this way in exchange for being charged lower rates.

Case study

A November 2007 article in ASHRAE Journal by H. Michael Newman describes installing BACnet for campus-wide facilities management.

The fundamental problem that had to be addressed was addresses. Every building on campus and every system had to be identified by a unique address.

“The method we use for naming our BACnet objects is based on the concept of facility/system/point. The facility is typically a building and may be followed by a subfacility, such as the system’s physical location in the building. The system describes the type of equipment and may be followed by a subsystem. The point is the specific input, output or value that is being described.

“An example of this might be Duffield Hall/AHU-1.CW.STEMP, where the facility is Duffield Hall; the system is AHU-1 (air handler unit 1); the subsystem is CW (chilled water); and the point is STEMP (the supply temperature).”

Being able to control the climate within a building is a major tool for the all-important project of improving energy efficiency, which equals maximizing performance while minimizing the power consumed. BACnet is a medium to enable us to control and monitor the HVAC system while simultaneously making it possible to share information and control, to harmonize its operation in coordination with all other systems in a building.

BROWN is an electrical engineer, technical writer and editor. He serves as managing editor for SECURITY + LIFE SAFETY SYSTEMS magazine. For many years, he designed high-power electronics systems for industry, research laboratories and government. Reach him at