Wireless technology continues to expand into the world of building controls as part of increasingly sophisticated, highly integrated building-automation systems (BASs). A key driver of this trend is the advent of wireless control networks enabled by mesh technology. With each implementation, the technology is proving it can deliver secure, reliable solutions that provide optimum control and unprecedented flexibility.

NO HARD-WIRED TRUNK

Wireless-mesh-technology devices include application-specific controllers (ASCs), point modules, variable-frequency drives, and meters. These devices sit on a field-level network (FLN) distributed throughout a facility and connected to a supervisory controller that performs central-monitoring and control functions. With wireless mesh technology, there is no need for a hard-wired trunk for these devices to communicate.

Because they are relatively power-hungry, FLN devices must be line-powered. That means their related radio-frequency (RF) electronics are able to scavenge power from the same source. Because they always are on, FLN devices are able to both receive messages and route messages to neighboring devices.

BATTERY-POWERED DEVICES

Recently, there has been a push to add battery-powered devices (e.g., room-temperature and other ambient sensors), which are easier for system designers to “hang,” to BAS control networks. Because they are battery-powered, these devices must conserve energy. They do that by “sleeping” most of the time, awakening periodically to see if an event (e.g., a change in temperature) has occurred and, if one has, transmitting a message to a line-powered node. The device then returns to sleep mode, resting until the next cycle.

Because battery-powered devices are asleep most of the time, they do not transmit messages to neighboring devices. However, because they can communicate with multiple line-powered nodes, there are multiple communication paths, ensuring reliability.

Mesh topologies swiftly are changing perceptions of wireless' reliability. As a result, more and more BAS engineers and designers are installing systems that would not have been economically or physically possible just a few years ago.

FLEXIBILITY

Efficient heating and cooling schemes require accurate inputs, which often are dependent on the final configuration of a space. Wireless sensors can be positioned after a space is finished. Rather than on a wall that is bathed in sunlight all morning or in shadow all afternoon, wireless sensors can be placed where they will provide the most accurate inputs for the ambient conditions of a space.

IMPLEMENTATION

A wireless-mesh-controller network can be implemented two ways:

• The controller communicates wirelessly through an external radio mounted in close proximity.

• RF electronics are embedded in the controller.

Typically, the location of a controller is dictated by the location of the equipment to which it is mounted. The biggest advantage of deploying an external radio is that, if necessary, the radio — and its antenna — can be located away from the controller to optimize the number of communication links to other radios or circumvent obstructions. Embedding RF electronics in a controller eliminates the need to mount and power an additional device; however, it restricts location of the antenna, which can be mounted no farther than approximately 1 ft from the controller to minimize attenuation losses.

CASE STUDIES

Following are three case studies involving use of external IEEE 802.15.4-2006, Wireless MAC and PHY Specifications for Low Rate Wireless Personal Area Networks (WPANs)-compliant physical radios and wireless communications based on the ZigBee standard. Radios are mounted at each ASC, with one radio for each network of ASCs at the higher-level building controller. Each radio has two switches: one for selecting from 16 2.4-GHz frequency channels and another for selecting a unique network identification. Installation and startup consisted of ensuring the two switch settings were correct; mounting the radios; connecting ANSI/TIA/EIA-485-A-98, Electrical Characteristics of Generators and Receivers for Use in Balanced Digital Multipoint Systems-compliant communication ports to the controllers; and connecting the power.