Wireless (with strings attached)

Our roundtable discusses the definition of what's wireless in a wireless system; the options for providing power to a wireless system; the financial benefits of a wireless system; and the unique solutions wireless systems provide.

12/16/2009


 

 

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CSE: In a wireless system, what's wireless and what's not?

Graham Martin: Ideally the sensors and switches providing the monitoring and control data will be wireless (and ideally also battery-less). The rest of the system will be line powered—the signal receivers which feed the information into line-powered backbones such as BACnet , LON , TCP/IP, or direct-to line-powered actuators.

 

David Fisher: Usually controllers, sensors, and actuators are hardwired together, typically with communications network wiring between peer controllers. In a wireless system, the peer network wiring, and in some cases the sensor/actuator wiring, can be replaced by a wireless scheme.

 

Patrick Harder: In any commercial BAS, there exists a hierarchy of wired communications networks. The top level, which is usually Ethernet-based, is where IT and computers reside. The second network level is where variable air volume (VAV), unit vent, and equipment controllers communicate and send information back to devices on the top level. The lowest network level is where sensors communicate with devices on the field bus.

 

The wireless sensor tier is constantly expanding and includes devices, among the many, for temperature and humidity sensors, switches, power outlets, window contact sensors, and occupancy sensors. Wireless communication is now readily available for all of these network tiers of a commercial BAS.

 

CSE: What are the wireless controls protocols today and in what applications are they best suited?

 

Fisher: It's hard to answer this question without being misleading. There are lots of wireless communications methods, but not so many that have been applied to building automation in a widespread way. One thing to keep in mind is that there are many vendors still in love with proprietary ideas that “lock-in” customers to their technology. To this end, there is no wireless solution today that is really open and interoperable. This is largely because of the lack of an adopted standard among product vendors. This lack of a standard leaves only proprietary solutions available. This highly fluid situation has left a void in the market at present.

 

• Wi-Fi, although widely thought of as standard, does not address how individual devices talk to each other. If I want to make a controller that can read the temperature from a sensor using Wi-Fi, there is no standard way to do it. There are many proprietary ways that make use of Wi-Fi, but that doesn't mean that vendor A can talk to vendor B, only that they won't mess up the Wi-Fi on your laptop while they do it.

 

• Similarly, Bluetooth doesn't provide the kind of device-to-device functionality that building automation requires, although some have adapted it this way using proprietary schemes.

 

EnOcean has made a big effort to try to provide a common platform for energy harvesting devices. So if energy harvesting is your goal, that's a good place to start. But in terms of making it easy to interface these devices with traditional building automation, there is no standard method.

 

ZigBee is a technology that addresses a lot of the transport issues, but not the interoperability issues for building automation. There are nascent efforts to define standardized gateways between ZigBee and the international standard BACnet for building automation. It should be pointed out, though, that these devices are not BACnet devices and rely on gateways for any real interoperability.

 

6LoWPAN is a transport technology that is focused on standard transport of wireless messages. Without the marketing muscle of the ZigBee Alliance, the technical issues and benefits of this technology have been underappreciated. But like the other technologies mentioned above, there is no device-to-device interoperability as yet defined.

 

Martin: All wireless protocols have their application sweet spot, e.g., local area networks (LAN) (computers), Bluetooth (mobile phones/headsets), and ZigBee (wide-scale mesh networking).

 

Harder : The main differences between the wireless technologies are cost, data throughput, and power consumption. Wi-Fi is the most expensive, has the highest throughput, and consumes the most power. ZigBee is low cost, has low to medium data throughput, and is low power. EnOcean is low cost, has low data throughput, and is extremely low power.

 

CSE: What are the options for providing power to wireless devices?

 

Matt Lininger: I have traditionally seen batteries used to power wireless sensor devices. It is important to understand what type of batteries the device is using and how often it is anticipated to be replaced. Replacing batteries every six months is not a sustainable automation system practice. Disposal also is an issue, especially when hundreds of batteries are installed in a facility.

 

Fisher: There are four basic options for wireless power:

 

• Wired power supply: A traditional wired power supply can be installed local to the wireless device to provide unlimited power. This is the most reliable and in a sense the most costly approach.

 

• Battery power: Batteries can be used to power wireless devices that are designed with ultra-low power technologies. Typically these kinds of devices resort to intermittent communication.

 

• Broadcast carrier: Some technologies rely on the actual radio signal used to transmit between devices as a source of power. The ultra-low power device captures radio frequency (RF) energy from the carrier that is sufficient to power the device for brief transmissions. A special challenge is the collocation of carrier emitters to assure that there is enough power available to devices for normal operation.

 

• Energy harvesting: Energy harvesting is a concept where devices capture and store small bursts of energy. When energy harvesting is combined with wireless devices, a “free energy” system can be made.

 

Harder: Power options vary depending upon how devices are used in the wireless system. Wireless controllers and repeaters are constantly sending and receiving data and therefore require constant power from a wired 24 Vac source. Wireless devices on the BAS sensor tier transmit their data at timed intervals or only when required from a user. These devices use far less energy, and can use batteries or energy harvesting techniques. Battery-powered wireless sensors typically feature a 3- to 7-year battery life using inexpensive alkaline or more costly lithium batteries.

 

CSE: What are the financial benefits associated with wireless controls? What are the drawbacks?

 

Harder: The financial benefits of wireless can be broken into two categories; first cost and future cost. The first cost differential between wired and wireless can vary significantly from installation to installation. In regions that require conduit with high-labor costs, this number can be significant. In regions with lower labor costs and less stringent wiring codes, the first costs differential may be a wash or even favor a wired solution. Keep in mind that there are other factors that weigh in on the first cost savings, most importantly, schedule compression.

 

In most cases, wireless installations are completed faster than wired equivalents. Schedule compression benefits can far outweigh the higher initial cost of wireless hardware. Future cost refers to financial benefits associated with wireless after an installation has been completed.

 

Martin: Installing wireless controls can save significant amounts of cable installation—and therefore time and costs in new buildings or retrofits. We are seeing typically 15% cost savings in new installations and up to 80% savings in retrofit scenarios in buildings where the technology has been installed. Wireless monitoring and controlling as part of a BAS can also help to save 20% to 40% energy consumption. The drawback is the fact that many building professionals are still not aware of how simple, reliable, and maintenance-free wireless monitoring and controls have become.

 

Lininger : Reduced material costs are starting to become more attractive as the price of building materials continues to escalate. In the future, the abundance of different devices that would be able to be integrated on a common protocol wirelessly will present the potential to truly integrate all energy systems into a BAS.

 

CSE: What challenges exist for local practitioners—engineers, contractors, operators—over the lifecycle of a wireless installation?

 

Lininger: At this point in time, the lack of knowledge, understanding, and opportunity are the biggest challenges facing the entire industry. There are a lot of myths and stories about systems, and the reality is that each application or potential project is unique and could present an opportunity for wireless systems integration. The industry needs to mature a bit more and everyone needs to get more comfortable with the technology, and it has the potential to grow into an industry standard.

 

Harder: Wireless technology is new and is still evolving in commercial BAS networks. Existing wireless installations may be impacted by new technologies that were not considered when current wireless devices were designed. Wireless systems can also be subject to multipath RF interference. This condition exists when wireless signals reflect off an object and cause interference with the original signal. As equipment in a facility is moved around, the multipath profile may change, disrupting communication. This issue can be resolved with directional antennas and close adherence to wireless installation guidelines during the planning and installation phases of wireless BAS networks.

 

Fisher: For battery-operated devices, maintenance and replacement is an issue. For energy harvesting devices that use mechanical translation for power, their mechanical parts are subject to wear and tear. In general for all wireless, changes in physical infrastructure such as walls and large ferrous masses such as chillers, boilers, pump motors, and elevators can affect transmission characteristics.

 

CSE: Describe how wireless control systems save money during retrofit projects.

 

Fisher: Wireless systems can sometimes provide a savings when retrofit wiring is unsuitable for a new wired system, requiring rewiring if a wired system would be used. This can even eliminate a whole class of labor in some cases where building automation technicians are all that may be required to install and test the new wireless system. This can also be a time and scheduling benefit.

 

Martin: Imagine you can retrofit your building (e.g., to become more energy efficient) without having to close part or all of the building and without any building noise or mess. In hotels, hospitals, retail, office, industry, and multiple other cases this alone saves vast amounts of money just by being able to continue normal operation during retrofit. In addition, the cost of opening and closing walls and laying new cables can be saved through wireless systems, and the cost for future retrofits will be drastically reduced. We have seen examples helping to save between 15% and 80% of the electrical costs during retrofit.

 

Harder: A major labor expenses for retrofit installations is electrical wiring costs. These costs are even higher in buildings with distinctive wall surfaces such as marble or in buildings with hazardous materials that require minimal disruption. In most retrofit opportunities, the 24 Vac power wiring infrastructure for the building controls and wireless hardware is already present; however, these buildings do not have the wiring infrastructure for tethered BAS communication networks.

 

CSE: What kinds of design challenges can be uniquely solved by using wireless devices?

 

Martin: The possibility to place sensors and switches around the building only when the user or tenant moves into the building is a unique advantage. During the planning and construction of many buildings, it is not known how exactly the building will be fitted out nor what the user's individual requirements will be. This increases the flexibility enormously and decreases the amount of expensive and time-consuming rework that is often required. Wireless and battery-less switches and sensors can also be placed on virtually any surface such as glass, stone, wood, furniture, or cubical walls and in virtually any location.

 

Lininger: The most common application might be the control of remotely located equipment to the main control wiring of a traditional BAS system. This is an application that has been used in wastewater utilities for a while with more industrial-type controls to monitor remote critical pump stations and other equipment.

 

Fisher: There are many circumstances that can benefit from a wireless solution. For example, sensing and control devices in high-atrium ceilings are much easier to install with wireless devices, since only the end point device must be managed, rather than the entire wired path across a high space.

WEB-EXTRA: CSE : What are the wireless integration issues within a single building? Among several buildings?
Fisher : Wireless systems are principally limited by the radius of geographic area that they reside in. Some wireless technologies are more limited in distance than others and some technologies are more susceptible to noise and interference. Typically integration within a building must deal with structural issues like metal skeleton, masonry, and other sources of transmission interference or electrical noise. Also, a balance must be achieved in the placement of repeater devices that are needed by most wireless technologies to boost radio signals beyond a maximum radius. Multiple buildings are better served by dedicated bridging using fiber optics for lightning protection unless they are unusually close together. Using wireless between buildings is possible, but doing this raises other issues like security and interbuilding distances.
Harder : Most wireless technologies used within buildings use low-power RF transmissions. This greatly extends battery life on battery-powered devices while causing minimal disruption to other wireless devices within the building. While low-power wireless communication has its advantages, it presents practical limitations in shorter communication distances between devices. Within a building, this distance is typically 30 to 100 ft and can be affected by obstructions such as duct work, elevator shafts, and thick concrete walls. Wireless communication between buildings is usually achieved using IT-based wireless technologies such as Wi-Fi. While intrabuilding and interbuilding wireless solutions face similar challenges, Wi-Fi products can use higher transmission power and established standards to help overcome these obstacles.
Martin : The wireless system within a building should be kept as simple as possible. Installers require easy-to-install plug-and-play systems without any complicated mesh networking features or high-level programming necessary. The installers need to be aware of the basics of wireless transmissions, which can be learned quickly. Between several buildings there are existing robust ways using cables or cell phone networks depending upon distance. Hopping low-power wireless systems across neighborhoods is not recommended (interference, security, complicated installation, etc.). The 2.4 GHz frequency band should be avoided due to its extremely short range and massive interference from wireless LAN.
Lininger : Redundancy seems to be the biggest issue with wireless communication systems integrating into a building, but this issue is not limited to only wireless integration of controls; it affects wired controls as well. It is often difficult to justify the expense of two different network communication backbones in a building in order to keep information systems networks separated from BAS. As the devices for the building automation industry become more secure and reliable, this separation issue will be less of an issue in the future. Within multiple structures, range of communication devices is always a concern, and again the redundancy issue is a factor. Sometimes it is easier to ask the questions, "does each building stand on its own with limited communication between them, or is the entire campus meant to be in constant communication?"

WEB-EXTRA: CSE: What are the security issues associated with wireless controls? Hacking, jamming, system interruption, theft, etc?
Lininger : Security is always a concern with wireless networks of any type, and BAS are no different. These systems, while still in their infancy, are looking to design devices from the ground up that incorporate end-to-end protection using encryption similar to those in Wi-Fi networks.
Fisher : One of the principal issues for security is physical access. With wired devices, gaining access to a network or interfering with it requires actually connecting physically to wires. With wireless, the whole point is to make this ubiquitous, so security must be reduced to techniques like encryption and detection. A wireless system can be jammed by introducing high-amplitude radio signals across multiple frequencies to defeat even frequency-hopping schemes. To deter hacking and theft of information, any wireless system must include security layers that provide encryption of data and authentication.
Martin : All wireless systems, including EnOcean, have some level of security or encryption possibilities and usually products have a unique ID. Any wireless system can be jammed or hacked by anyone with enough criminal energy and an extremely high-level of wireless and computer expertise. Highest security installations may, however, want to avoid relying entirely on wireless controls in certain cases.

WEB-EXTRA: CSE: Do wireless controls for building systems conflict with other wireless networks such as LAN and Wi-Fi?
Martin : EnOcean systems do not conflict as they operate in licensee-free bands with virtually no traffic-315 MHz in North America. Low-power wireless systems that operate at 2.4 GHz have significant conflict with WLAN/Wi-Fi. Dealing with this interference is power-hungry, time-consuming, and can lead to dangerous or frustrating system failure.
Lininger : In the past this might have been an issue, but using the protocols that the industry is beginning to adopt in the commercial market, these interference issues should become less prevalent. Of course other building systems such as power and lighting systems might still have an effect where large amounts of power are present.
Fisher : No. The reason is that most technologies for wireless automation use different RF bands that do not interfere with LAN and Wi-Fi technologies.
Harder : Wireless controls using ZigBee wireless technology are designed to work alongside wireless LANs using Wi-Fi. This compatibility is based upon two main factors: RF power and wireless channel separation. Most wireless building system networks operate at only 1/10 the power of the building wireless LAN system, which helps to ensure against Denial of Service interference caused by adjacent wireless networks overpowering each other. While both ZigBee wireless building systems and Wi-Fi operate in the 2.4 GHz Instrumentation, Science, and Medical band, the channels used for ZigBee networks are narrower than the channels used in Wi-Fi networks. Because of this, ZigBee networks can be configured to operate between Wi-Fi channels. Most ZigBee networks automatically configure themselves to run on the quiet channels between Wi-Fi channels.

 

 

Participants

David Fisher President, PolarSoft Inc. Pittsburgh

 

Patrick Harder Product Manager, Johnson Controls Milwaukee

 

Matt Lininger , PE, LEED AP Mechanical Engineer, GRAEF Milwaukee

 

Graham Martin , CEO and Chairman, EnOcean Alliance San Ramon, Calif.



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