The demand for installed wireless control networks in industrial buildings continues to grow because of the attributes inherent to wireless communication, such as flexibility, straightforward installation, and low material/labor costs. However, some industry leaders still hesitate to invest in wireless solutions because of concerns about the reliability and security of existing wireless standards and compatibility with established control-network infrastructures.

This article discusses eligibility and deployment aspects of wireless controls and how wireless controls can be applied in HVAC systems in a complex industrial-building environment to achieve greater energy-policy compliance.

Historically, process industries have adopted new technologies cautiously. However, because energy costs are increasing rapidly, facility executives feel an escalating need to reduce energy consumption by means of more sophisticated building controls and HVAC-optimization strategies. According to a study conducted by ARC Advisory Group, a research and advisory firm for manufacturing, energy, and supply-chain solutions, the worldwide market for wireless technology in industrial automation will have an annual growth rate of 32 percent, reaching $1.1 billion in 2012.

CONCERNS ABOUT WIRELESS NETWORKS IN INDUSTRIAL ENVIRONMENTS

Skepticism about wireless control systems still looms. Scalability and flexibility rarely are in question. However, security, interoperability, and reliability issues cause some engineers to question whether to abandon their wired designs for wireless. Additionally, battery-powered wireless devices are unacceptable to system integrators endeared to the concept of “install-and-forget” solutions.

Meanwhile, wireless technologies and communication protocols have matured, with improved security, interference immunity, and reliability. When retrofitting older buildings with modern controls, wireless solutions can simplify energy-saving installations. Combined with intelligent building-automation systems (BAS), wireless technology can offer potential operational savings and reliable performance.

Radio-frequency performance/choosing an operating frequency

Open building plans are common in industry, often providing good environments for wireless communications because radio waves carry well in line-of-sight conditions. Building materials, such as concrete and steel, can inhibit wireless transmission. Wireless ranges and material penetration correlate with transmission frequencies and corresponding wavelengths. When transmission power and antenna gain are held equal, low frequencies (with longer wavelengths) yield longer ranges and are better able to carry data through obstacles, such as walls, ceilings, and furniture.

The range yielded by 315-MHz and 2.4-GHz operating frequencies is roughly the same (Table 1). However, the range achieved using the 315-MHz frequency can be accomplished using a fraction of the transmission power. The 315-MHz frequency is less crowded than the unrestricted industrial, scientific, and medical radio bands commonly used for building automation. Systems using the 2.4-GHz frequency are susceptible to competing radio transmissions and suffer from propagation loss through walls and other obstacles. The ideal frequency range is between 300 MHz and 1 GHz, where signal attenuation is low and radio range is wider, meaning fewer devices are needed to cover a controlled space.

Radio interference

Wireless technologies commonly share a frequency band with wireless computer networks. The 2.4-GHz frequency band, for example, is crowded (with wireless local-area networks, Bluetooth devices, microwave ovens, cordless phones, Wi-Fi routers, etc.) and does not leave many time slots for low-powered building-sensor transmissions. Typical radio sensors emit less than 10 MW, yet must compete against other radios with a hundred times more power (Federal Communications Commission regulations allow 2.4 GHz radios to output up to 1 w). A legally installed high-power 2.4-GHz product could crash the performance of a 2.4-GHz sensor network next door.

Multipath wireless range

Tests conducted by the National Institute of Standards and Technology (NIST) have confirmed that heavy industrial plants can be highly reflective environments, erratically scattering radio waves and interfering with or blocking wireless transmissions. The manufacturing plants that NIST tested were crowded with stationary and mobile metal structures, such as fabrication and testing machinery, platforms, fences, beams, conveyors, forklifts, maintenance vehicles, and automobiles in various stages of production. There are a number of measures that can be taken to minimize radio interference on factory floors in newly constructed facilities. Most important, however, is the selection of a wireless-network technology with the proper frequency for an industrial project.

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