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By Josh Thompson
Building Automation Article Use Policy
Whenever a building management system (BMS) is considered, the topic of wireless options is bound to enter the discussion. "Going wireless" seems the simplest of decisions: no wires to run, no conduit to buy, and no holes to drill. When considering the construction costs of a hard-wired solution, the argument in favor of wireless integration is both compelling and often valid. That said, all things come at a cost; before making any decision it is always best to be well informed.
All BMS communicate by using a language that is understood by every device connected to the system. Unfortunately, these languages, or "protocols" vary from system to system, and not all languages conform to a uniform standard of communications. Some systems have specifications that are accepted by standards organizations, such as the ISO/ESA; others do not. It is also important to note that not every BMS protocol will communicate over every wireless technology. Thankfully, there have been significant advances in translation, and for a relatively small investment, most BMS languages can be converted into a standard that can be communicated wirelessly, one way or another.
With that in mind, there is a wide variety of ways to transmit data between devices without wires. The simplest and most common is infrared, such as in motion and occupancy detectors that use body temperature to trigger an event. IR is an important wireless control tool as it is secure — it can't penetrate walls, and it can be passive (a motion detector) or active (a remote control). But its communications are typically "simplex," either sending or receiving information in one direction. Since in a BMS system it is as important to know the status of a device as it is to control the device, "duplex," or bi-directional wireless communication systems have come into favor.
One of the latest solutions is EnOcean. Focusing on energy harvesting, EnOcean devices use the energy in the environment to operate. A light sensor uses light energy; flow and movement sensors use kinetic energy; etc. They transmit at a data rate of 120Kbps in a mesh/grid network with a relatively low frequency range, which allows for transmissions of up to 300 meters and separates them from other nearby devices.
Another wireless control protocol is Zigbee. It has vast market acceptance in the commercial building control systems community, which keeps development costs lower and, thus, offers a lower cost of deployment. Zigbee is a standards-based protocol (IEEE 802.15.4), with data rates of 250Kbps across a self-forming meshed network. Manufacturer and user support resources for Zigbee systems are readily available. When professionally integrated, most BMS, administrative reporting and even audiovisual controls can be managed with little or no translation.
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