One of the best ways I have encountered to envision an intelligent building automation system (IBAS) is by comparing it to how the human body functions. As with your body, an intelligent building has to have the capacity to control its own functions (internal and external), as well as how they affect occupants of that building. The primary functions needing to be addressed are energy conservation, and occupant comfort, productivity and safety.
As in the human body, an intelligent building must sense conditions in order to determine how to manage IBAS functions. These might include and be similar to the five human senses of sight, hearing, taste, smell and touch. The structure could achieve similar results via building monitoring systems (BMS) such as video analytics, two-way audio, dangerous gas detection, temperature sensing and more. Additionally, intelligent control of resources such as energy, temperature, security and life safety makes BAS a good business decision with demonstrable return on investment (ROI).
This month, we are going to look at some of the BAS technologies, products and applications, with an extra emphasis on wireless integration strategies.
Ins and Outs of Wireless BAS
One of the big challenges of retrofitting a BAS into an existing system is the cost of cabling and installation of controllers and sensors. Considerable cost can be saved in a BAS application by reliably utilizing existing networks and wireless technology. A better understanding of the technological limits of different wireless technologies will allow for more reliable wireless BAS performance.
Today’s building construction with metal reinforced concrete and metal studs provide additional challenges for establishing the backbone of your wireless BAS network. Having a good fundamental understanding of the basics of radio transmission and reception will go a long way in applying the right wireless device to the BAS application.
Different radio frequencies (RF) have unique characteristics and must be applied accordingly. Typically, the lower a frequency the better it is at penetrating building structures. This is why frequencies in the megahertz (MHz) range will often cover a greater distance within a building than those in the gigahertz (GHz) range. Actually, everything else being equal, the former will perform two to four times the distance of the latter. One should also consider how crowded certain radio spectrums such as 2.4GHz are with popular technologies like Wi-FI and Bluetooth.
One important area of RF devices is the performance of, and the relationship between, the transceiver and antenna. RF modules come in different radio power levels that often depend on what is legal by a governing agency (e.g. FCC) and equipment pricing. Applying an antenna to an RF module is more than just placing a wire on the device’s output. To maximize performance, be sure your antenna is specified for that particular module.
One should be cognizant of the voltage standing wave ratio (VSWR) between the RF module and antenna. Not properly matching the antenna and transmission cabling can create an impedance mismatch. This can cause radio energy to reflect back from the antenna and into the transceiver rather than into the air. This reduces the range and can, in some cases, damage the RF module. A VSWR of 2:1 (a reflection loss of 0.5dB) or less is often considered acceptable. You can measure this with a VSWR meter for confirmation.
The location and positioning of an antenna can be critical. Be aware of what may affect transmission. Also, in today’s buildings be aware of noise sources such as network Wi-Fi devices. RF energy can also be lost when packaging small antennas tightly in a plastic box made of common materials such as polycarbonate or ABS. These dielectric materials can affect the near-fields of the antennas and cause significant signal loss. Depending on the type of antenna, be sure to strategically locate it for maximum performance.
Remember that the gain of an amplifier is different than that of an antenna. The amplifier gain is created from electrical power while the antenna gain is generated by changing the focus of the RF energy. All antennas have some directional nature and, depending on the physical configuration of the antenna, the area covered can be wider or narrower. Check your antenna specifications and radiation pattern diagrams. Think of the focusing of RF energy similar to that of focusing a flashlight; as the light gets stronger the beam gets narrower. A good rule of thumb is that for every 6dB increase the distance is doubled, and for a 6dB decrease it is cut in half. Note that you may see the gain of an antenna expressed as dBi or dBd, the relationship is dBi = dBd + 2.15.
Attack of the Killer ‘Bees’
BAS integrators today are often faced with the challenge of integrating systems provided from different manufacturers. This can be simplified with the aid of equipment from companies such as the well-known Digi Int’l (see diagram).
Many of today’s wireless BAS solutions utilize some form of ‘Bee’ communications. It is important to learn the capability and limitations of this popular technology standard. Here are some basics:
ZigBee (zigbee.org) — The most popular and well-known Bee of all with more than 600 ZigBee Certified products. ZigBee devices are low-power and utilize the MHz and GHz spectrum. While individual devices have short transmission ranges of around 50 meters, each module is a low data rate (20-900kbps) transceiver that when linked with others can provide a multipath mesh network system. There are two specification categories: the popular ZigBee spec also has ZigBee PRO, which maximizes all the basic capabilities.
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