October 2010

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Are There Too Many Choices For Wireless Building Systems?

Wireless technologies such as ZigBee, EnOcean, Z-Wave, Wi-Fi, RFID, Insteon, Bluetooth, etc. are a snapshot

Jim Sinopoli PE, RCDD, LEED AP
Managing Principal,
Smart Buildings LLC

Contributing Editor 

“I do not think that the wireless waves I have discovered will have any practical application”
Heinrich Rudolf Hertz, German physicist. First to broadcast and receive radio waves. The hertz (Hz), a unit of frequency in cycles per second, is named for him.

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Overview
Sometimes we’re given too many choices which can lead to confusion and paralysis. That may be the case with wireless network platforms for building systems. The use of wireless networks control systems in buildings has many advantages. By eliminating the need for cable and related conduit and containment the initial costs for deploying system sensors, meters and control devices are reduced and installation time is shortened. Wireless is the ideal approach for retrofitting existing buildings where a lack of cable pathways is an issue or impediment.

The major difference between the performance of wired networks and wireless networks is network communication capacity or bandwidth. However buildings systems field devices generally do not need much bandwidth and conduct their business at relatively low data rates. Another potential issue with wireless is that some wireless transceivers may use batteries which require regular replacement. The low data rates and possibility of periodic battery replacements are minor strikes against wireless compared to its flexibility, cost advantages and installation time. What follows are some of the choices for wireless networks for building control systems as well as some of the building devices that can be deployed wirelessly.

Wireless Network Types
There are wireless networks using licensed radio frequencies and unlicensed radio frequencies. There are wireless technologies such as ZigBee, EnOcean, Z-Wave, Wi-Fi, RFID, Insteon, Bluetooth, etc. This is a snapshot of some of the major technologies:

• ZigBee
ZigBee is a wireless technology standard (IEEE 802.15.4) which provides for low data rate networks. It uses unlicensed frequencies (900 MHz in the US, 868 MHz in Europe, and 2.4 GHz worldwide) which are also available for cordless phones Wi-Fi, and other devices. The standard is aimed to address residential, building and industrial control devices. It is specifically useful for sensors and control devices of building automation systems within a smart building where very small amounts of information or data are being transmitted. ZigBee also has uses in home automation, industrial automation, home entertainment systems and smart meters.

The maximum speed of ZigBee devices varies up to 192-250 Kbps (a measure of bandwidth, kilobits per second). The maximum distance varies between 20 and 50 meters. ZigBee has several advances: (a) low power usage as the devices only requires two AAA batteries, (b) wide support from more than 100 companies supporting the standard (names such as Motorola, Honeywell, Samsung, Mitsubishi, and others), (c) mesh technology which allows ZigBee, like Wi-Fi, to be configured in several topologies including a mesh topology allowing multiple transmission paths between the device and the recipient, and (d) system scalability where thousands of ZigBee devices can deployed within a building.

• EnOcean
EnOcean Alliance is a consortium of companies in North America and Europe that are developing and promoting wireless devices that are self-powered. The initial consortium formed in 2008, includes Texas Instruments, Omnio, Sylvania, Masco, and MK Electric. They claim the largest installed base of wireless building automation networks.

The main objective of this technology is to allow sensors and radio switches to operate without batteries thus almost being maintenance free. To do this the technology uses “energy harvesting” which exploits slight changes in motion, pressure, light, temperature or vibration to transform small energy fluctuations into usable electrical energy. The devices transmit at 120 Kbits per second, up to 300 meters with a data packet of 14 bytes. The transmission frequency used for these devices is 868.3 MHz, an unlicensed radio frequency.

EnOcean GmbH, a spin-off company of Siemens, supplies the transmitters, receivers, transceivers and energy converters to companies such as Distech Controls, Zumtobel, Omnio, Osram, Wieland Electric, Peha, Thermokon, Wago, Herga and MK Electric, who then develop and manufacture products. While the products tend to focus on building automation they are also targeted for industrial automation and automotive markets.

EnOcean is not an international standard at this time but may apply for ratification as an international standard at some point. They have created EnOcean Equipment Profiles (EEP) for EnOcean devices that ensure interoperability of different end-products based on EnOcean technology; thus equipment from one manufacturer can communicate with equipment of another manufacturer.

• Z-Wave
Z-Wave is about wireless solutions for residential and light commercial applications. The Z-Wave Alliance is an open consortium of over 160 manufacturers. Members include Cooper Wiring Devices, Danfoss, Fakro, Ingersoll-Rand, Intermatic, Leviton, Universal Electronics, Wayne-Dalton, Z-Wave and Zensys.

At the core is the Z-Wave protocol, developed by Zensys, a division of Sigma Designs. Sigma Designs provides embedded networking software and Z-Wave chip solutions for manufacturers and OEMs. The Z-Wave protocol stack is embedded in the chips and flash memory is available application software. The standard is not open and available to only Zensys/Sigma Design customers.

Z-Wave operates as a mesh network in the 900 MHz radio frequency range and is optimized for low-overhead commands such as on-off (as in a light switch or an appliance), with the ability to include device metadata in the communications.

Each device on the Z-wave network has an individual code or address. A single Z-wave network supports up to 232 devices. Multiple Z-wave networks can be combined via gateways. The controllers can be handheld remotes, wall panels or an internet interface via a browser. Like some of the other wireless networks, Z-Wave is a mesh networking technology where each node or device on the network is capable of sending and receiving control commands. Z-Wave can also use power line communication technologies.

PlantPROCORE Z-Wave has a speed of 40 Kbit/s with a range of about 100 feet or 30 meters. The radio frequencies used include 900 MHz ISM band: 908.42MHz (United States), 868.42MHz (Europe), 919.82MHz (Hong Kong) and 921.42MHz (Australia/New Zealand).

• RFID
Radio-frequency identification (RFID) is different than the other building wireless systems, it can’t control anything, it only identifies things. Its use is in primary in asset management and security. RFID tags are incorporated into products or equipment or carried by people to identify and track their location using radio frequencies. RFID is deployed in retail, hospitals, airports, education and other building uses.

Systems generally consist of RFID readers and tags. RFID tags are simply radio transponders. They are a small integrated circuit or computer chip which has a tiny radio antenna built in. In passive RFID systems the tag does not have its own power source, the tag absorbs energy from the system reader antenna, a process called “coupling”. The tag is programmed with a unique identification. When the tag is “excited” by and absorbs the radio waves of the reader antenna it sends out its unique ID which is picked up by the reader antenna.

In active RFID systems tags have their own power source and don’t need to use the reader’s antenna radio waves to power up and transmit their identity. Active tags have a greater range, can stored larger amounts of data and are larger than passive tags.

RFID tags come in a variety of sizes and shapes to address a variety of uses. The tag can be paper thin to fit inside a book. They also can be directly mounted onto equipment, embedded in wrist straps, attached to clothing or worn on a belt.

Wireless tracking systems are only as good as their networks. RFID readers have an antenna attached to them. Essentially the reader interfaces or sits in between the wireless portion of the system (the antenna) and the head end or host system. The antenna attached to the reader sends radio signals out to activate tags. It listens for tags to communicate and once a tag responds, reads the data transmitted by the tag and sends it to the reader. Readers can have multiple antennas attached. The reader can decipher the signal and send the data to the host server.

RFID operates in several radio frequencies: 125 kHz or 134 kHz low-frequency systems, 13.56 MHz for high-frequency system, and 2 or 3 frequencies for ultra high frequency systems.

• Wi-Fi
Wi-Fi basically replaces a cabled Ethernet connection with a wireless device. Current “Wi-Fi” systems operate in two unlicensed radio frequencies, 2.4 GHz and 5 GHz. The Institute for Electrical and Electronics Engineers (IEEE) has set four standards for Ethernet communications via these frequencies which are commonly referred to as 802.11a, 802.11b, 802.11g, and the latest, 802.11n. 802.11n has a throughput of 110 Mbps.

The user’s distance from the Wi-Fi antenna, the uses of the same unlicensed frequencies by other devices, and the obstacles within and the structure of buildings which could interfere with the radio signals all affect the communications bandwidth received from the Wi-Fi antenna. Typical coverage areas indoors for omni-directional Wi-Fi antenna are 100 to 300 feet.

In the past, the typical use of Wi-Fi in buildings has coexisted with other wireless systems using the 2.4 GHz radio frequency such as ZigBee and Bluetooth. However, Wi-Fi has started to very gradually move in to the building control systems. Examples include Wi-Fi temperature sensors (temperature@lert product), Wi-Fi CO2 sensors (AirTest Technologies), Ethernet field panels with capability to use Wi-Fi transceivers to establish wireless connectivity (Siemens), and Real Time Location Systems (RTLS) (Cisco).

With more sensors, meters and control devices generally needed in buildings, expect the adoption of wireless buildings systems to accelerate. The trick may be sorting through the wireless marketplace and selecting the right technology.

For more information, write us at info@smart-buildings.com

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