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.
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.
A key concern many enterprise professionals raise about wireless-transmission technology relates to security. Because wireless signals travel over the air, access to information cannot be secured physically, as with traditional cable. This gives many people the false impression that wireless technologies are highly vulnerable to attack. In reality, with proper authentication and encryption technology, wireless transmission is just as secure as, if not more secure than, wired networking. Without a physical cable to splice into, signals are difficult to intercept. Therefore, it is important to choose a wireless product that employs standard encryption and authentication protocols to ensure the highest level of security. Most state-of-the-art wireless solutions incorporate these standards.
Interoperability is the ability of devices that follow a certain technology and standard to work and communicate seamlessly together to fulfill a specific application, regardless of manufacturer. The tools used to configure and commission a system should be interoperable, allowing integrators to replace system devices with products from other manufacturers. The interoperability of wireless components from different manufacturers is questionable with regard to certain wireless technologies and standards.
Building owners have voiced the need for interoperable devices. (For example, it would be convenient if a thermostat from one company could communicate with a wireless-compliant intelligent controller from another company.) If a technology or standard does not allow the replacement of a device from one manufacturer with a device from another manufacturer, the solution becomes locked in, and the end user is forced to buy products from a single source.
Because power requirements of various wireless devices differ, sensors powered by batteries must be monitored constantly for battery condition. Preventive battery-replacement cycles assuming worst-case battery life help avoid this problem, but also cause more frequent battery changes, leading to increased costs and toxic waste. Also, it takes considerable logistical effort to stock and properly dispose of batteries and log service cycles. Battery-driven maintenance is amplified with added features, such as mesh networking, which add complexity, require significant power, and lower battery life. Integrators often are forced to predict needs and find balance between radio performance and battery/maintenance considerations.
WHAT IS IN IT FOR A BUILDING OWNER?
The initial demand for wireless solutions often is problem-driven. If a project or installation does not allow for easily accessible wire runs to control points, a wireless solution may be needed. For example, facilities with multiple buildings might require tunneling under existing driveways and parking lots to install wire runs. In retrofit situations, it is difficult, if not impossible, to run wire to all parts of a building. These types of situations present opportunities for wireless solutions.
Integrating the disparate systems of a building into a coherent communication and control infrastructure long has been a goal of facility engineers. However, completely connected facilities remain a challenge because wireless-system integration is not always straightforward. As previously mentioned, some wireless technologies use a significant amount of power, requiring frequent battery changes and causing maintenance issues. Also, wireless networks can be a concern when frequency bands become overcrowded. However, with sensor-placement flexibility, relocation feasibility, and reliable operation, facilities executives can consider wireless technology an option to solve problems in existing plants or for deployment in new facilities.
From a general topology and infrastructure point of view, there is no significant difference between HVAC control systems in industrial and commercial buildings. However, because the buildings' construction characteristics and controlled-zone sizes are different, point-to-point distance control and sensor information has to travel. Network architecture generally should be kept flat, meaning the number of network communication levels should be kept to a minimum.
On the field level of a BAS, the requirements for wireless communications are relatively simple. Sensors, intelligent control units, and actuators operate in proximity and communicate relatively infrequently with little data. Therefore, they do not require high communication bandwidth. Self-powered low-energy radio sensors are most appropriate for these types of applications. Because ambient conditions in a building change slowly, related sensor readings and transmissions can occur in minutes. This allows a solar-powered sensor device, for example, to operate with minimal power and to store excess light energy in a supercapacitor for later use.
AVOIDING WIRELESS-INSTALLATION PITFALLS
It is a good idea to compare retrofit projects with similar sites using the same radio-frequency test-equipment recommendations. A radio-frequency site survey can be conducted to identify possible interferences caused by machinery or other radio devices.
The deployment of all radio components should be planned properly, following the installation and range-planning guidelines provided by the technology supplier. Before physical installation work begins, blueprints of the building, including locations of production equipment and furniture, should be analyzed. This kind of survey can help identify the parts of a building that prevent the propagation of radio waves, such as elevator shafts, fire-protection walls, and staircases. This engineered approach can predict the ideal placement of remote radio-sensor devices with regard to building-system access points.
Wireless equipment should be installed after construction is finalized — once power cabling, conduits, and ducts have been established — to avoid possible radio-path obstructions. This is particularly important for wireless infrastructure equipment, such as routers, repeaters, and gateways to the central building system. It is important that mechanical engineers, control contractors, and other stakeholders communicate before construction begins. In a retrofit situation, there is not much that can be done about mechanical installations. A wireless integrator has to work around given obstructions by placing radio components in the best possible locations and, if necessary, using additional radio-range extension components, such as repeaters, to create a communication bypass.
President and founder of Koenig Consulting, an independent industry representation and consultancy company specializing in sustainable and energy-efficient building-automation solutions, Volker Koenig has 25 years of experience in systems engineering and is an expert in control networks. An applications engineering manager for EnOcean Alliance, Eugene You has experience in radio frequencies, switching-mode power supplies, and industrial automation.