Voice/Data wiring schemes and media are ideally suited to many of the building-oriented control systems described by the Intelligent Buildings Institute.
New applications for structured cabling systems are beginning to emerge and are worth noting. These new applications represent new business opportunities for not only cabling installers but for consultants, engineers, and building owners and users as well.
Why stop with voice/data?
If you stop to consider the range of wired systems that typically go into the construction, use, and maintenance of buildings, clearly there's more to the picture that just voice/data. Shouldn't we attempt to apply the same concept of structured cabling, along with all its benefits, to the other systems that are just as important and just as costly to support when it comes time to add, change, or upgrade systems?
The answer is that we are doing just that. But so far, the trend to do so would seem to be moving at a snail's pace. But before we examine this slow moving trend, let's take a look at the range of possibilities in terms of how structured cabling might be applied to non-voice/data applications.
Perhaps the best way to explore these new opportunities for the use of structured cabling systems is to approach the subject from the perspective of "the intelligent building." This broad view of modern buildings and their constituent elements is best described by the Intelligent Buildings Institute (IBI) in Washington, D.C. The IBI defines the intelligent building as comprised of 4 groups of building elements.
* Building structure (the physical structure itself and its elements).
* Building management (the people and process side of facilities management).
* Building services (occupant-oriented support services including voice/data).
* Building systems (building-oriented control systems including HVAC, etc.)
In Fig. 1, the definition of building services (top left) includes most of what we would describe as voice/data systems and, therefore, is the major province of structured cabling systems.
The make-up of building systems (lower left), however, has gone virtually untouched by vendors of structured cabling systems, with few exceptions. That make-up, then, would seem to hold some real promise for the use of structured cabling in the following major systems.
* Heating, ventilation and air conditioning (HVAC) systems.
* Lighting control systems.
* Electric power control.
* Elevator control.
* Domestic hot water and plumbing systems.
* Access control.
* Security systems.
* Life safety systems.
While theoretically any of the above systems types could be supported with structured cabling systems, the opportunity to benefit from pre-wiring is limited to only a few for practical reasons.
This raises a question of criteria: how do you identify an application for pre-wiring with structured cabling, versus situations in which the better decision might be to go ahead and conform to the equipment vendor's proprietary cabling scheme?
When does structured cabling make sense?
Much can be learned from the vast amount of industry experience in the voice/data worlds in our attempt to apply the same cabling concepts to the building automation arena. If we look at what makes structured cabling successful in the context of voice/data, we can draw the following conclusions.
High density of devices. In the voice/data world, there's a high density of devices in the sense that the potential exists for the use of a telephone and a data terminal at virtually every workstation in a building. In many cases, typical offices are also prewired with more than one faceplate given the uncertainty as to exactly where occupants might choose to position their furniture. This results in a relatively high density of faceplates and outlets per square foot and, given the size of office buildings, invariably results in quantities of faceplates that number in the hundreds or thousands. Each set of cables installed to a faceplate is referred to as a "drop."
The point relative to density is that each drop requires a separate effort on the part of the installer, thereby leading to higher incremental costs to complete the job. This has produced a fairly good rule of thumb that's often used to estimate the cost of installing a complete cabling system: approximately $300 to $600 per drop in a new construction scenario and two to three times that in an existing or an old building. Of this cost per drop to install cabling, the majority stems from the cost of labor, while the rest is relegated to the cost of materials.
The major point here is that in cases where device density and location counts are high, there are significant dollars to be saved by prewiring during the course of initial construction, and the ability to effectively do so is enhanced by standards relative to the type of cabling used and the topology in which it is installed.
Media and topology standards. There was a time when all cabling schemes for voice/data systems were different from one another. These differences were twofold. First, the type of media itself differed. Some vendors used twisted pair; others used shielded cable; some used coax, twinax, dual coax, etc.; and all of them were proprietary.
The second difference pertained to topology. This refers to the physical layout or pattern in which cabling was installed to support devices in an office. The four basic topologies of interest in this context, three of which are shown in Fig. 2, are as follows:
* Bus topology with "T" Taps. This topology was based on a logical bus network, with physical connections to the bus achieved through use of "T" shaped taps that would literally pierce the network cable plant (usually co-axial cable).
* Daisy chained topology. Sometimes referred to as a "multi-drop" scheme, daisy chained networks usually relied on a polling protocol scheme that would poll all devices on the chain to either pick up or deliver data.
* Ring topology. This network scheme entailed the connection of network devices to one another via a logical ring and was characterized by the use of an electronic token that would be shared to gain access to the network's services.
* Star topology. This topology provided network access and connectivity to other devices on the network via the hub of the star. This communications scheme was typical of most host computers that would support data communications between peripheral devices via a central point (i.e., the host computer).
Each of these topologies produced distinctly different installations that, when coupled with the proprietary nature of the cabling itself, invariably became obsolete after a period of time. With every change or upgrade in systems, therefore, it was necessary for building occupants to rewire their space, thereby increasing the cost of communications wiring over time.
This trend produced a major incentive in the industry to evolve a standard for communications wiring that would not only resolve the media-type disparities between vendors of different systems, but would also result in a standard topology. That standard topology turned out to be the star.
The star topology not only explicitly supports star-wired systems, but can also support the other three topology types through creative cross-connection schemes at the hub of the star. In the voice/data world, this is commonly done inside wiring closets and theoretically could be done for building automation systems as well.
As far as the standard media type itself is concerned, the preferred cable for voice/data has clearly become unshielded twisted pair (UTP), 24 AWG.
What's happening in the industry?
If we attempt to apply the observations noted above to the building automation arena, you can conclude the following.
* Density. Any building automation system that can be characterized as having a high density of devices per square foot (or in absolute number) is a candidate for the use of structured cabling concepts, along with the associated cost savings.
* Topology. Building automation systems that do not impose a proprietary cabling topology and that, ideally, can be supported over a star-wired scheme are excellent candidates for a structured cabling system.
* Media. Building automation systems that meet the criteria noted for density and topology above must also support the use of a standard media type before a structured cabling system can be seriously considered.
Arriving at conclusions
So, if we attempt to apply the three criteria outlined above (density, topology, and media) to the list of building automation systems identified earlier in this discussion, we might draw the following conclusions.
* Density. Of the eight system types identified by the Intelligent Buildings Institute, it would appear that all but two (elevator control and electric power control) do meet this first criterion. Each of the following system types, therefore, should be regarded as perspective candidates for the use of structured cabling systems: HVAC systems, lighting control systems, domestic hot water and plumbing systems, access control, security systems, and life safety systems.
* Topology. Most of the native cabling topologies used to support the six systems are highly varied and inconsistent with one another. This is typical of the pre-standards stage for structured cabling systems, but is by no means insurmountable.
* Media. The cable types used by vendors in each of the six systems are also highly proprietary but are not as far apart from one another as, say, data cabling was in the form of twisted pair versus coax. As it turns out, several manufacturers are already in the process of transitioning their cabling schemes to an industry standard, which, not surprisingly, turns out to be the standard of choice in the voice/data world: UTP. The make-up of these new cabling schemes, along with several underlying industry initiatives, warrant some special attention.
As a provider of independent cabling systems, AT&T's activities on most fronts are always of interest. For example, AT&T's groundbreaking work in the structured cabling systems arena for voice/data applications attracted widespread attention and led the way in the evolution of these compelling solutions for premises wiring in the industry. Not surprisingly, AT&T has also entered the market with a new solution geared to the needs of building automation known as the Systimax Intelligent Building System.
The AT&T Intelligent Building System (IBS) is really little more than a repacked implementation of their highly successful Systimax system for voice/data applications. The IBS system, however, is geared toward support of the HVAC; fire, life and safety; security, CCTV and access control; and energy management and lighting control.
To understand how the AT&T scheme, and others like it, can support systems of the types listed above, a quick review of how it works in conjunction with a major manufacturer of building automation systems should be of use. For discussion's sake, we'll refer to the manufacturer of the building automation system of interest as "Brand X."
As in the case of voice/data systems in years past, Brand X has historically relied on proprietary wiring schemes for its products that were largely based, and still are, on 2-to 8-wire signaling schemes. Many of these schemes, it turns out, actually rely on some well known communications protocols in the voice/data world. These protocols go by names such as RS-232 (probably the most common protocol used in the connection of "dumb" terminals to host computers), and RS-484, which is a communications protocol characterized by daisy-chaining devices across a shared circuit back to a controller of some kind.
The devices of interest in this case are not computer terminals but temperature sensors (thermostats), variable air volume units (VAVs), controllers, and other systems germane to the subject of building automation. These systems have historically relied on fairly simple, low voltage cabling schemes for signaling purposes and are, therefore, relatively easy to support over UTP. While there are some gauge differences between native building automation systems and today's standards for voice/data (24 AWG), most of these differences are minor and can easily be resolved by the equipment manufacturers, including Brand X. The use of 24 AWG UTP for these systems is, therefore, becoming increasingly more common. Even the use of connector types that originated in the voice/data world, such as 8-wire RJ-45 type jacks, is beginning to show up in building automation product lines.
The prospect of supporting Brand X systems with voice/data-related wiring concepts did not come without challenge. As noted earlier in the context of voice/data, there were a number of native wiring schemes in the building automation arena that had to be dealt with. These native schemes included the following.
* Star-wired branched connections. This topology, as shown in Fig. 3 on page 62, supports the distribution, or sharing, of a circuit by multiple devices through branches that connect to the shared circuit via a junction, referred to as a "bridge."
* Daisy chained connections. This topology, as shown in Fig. 4, on page 62, acts very much like the same topology in the voice/data world and is essentially a form of the bus type of topology; however, each device connects directly to the branch circuit, as opposed to doing so via a "T" type connection.
* T-tapped connections. This topology, as shown in Fig. 5, see page 62, is also very similar to its voice/data counterpart; it involves the sharing of a single circuit via "T" type tapped connections.
* Fault-tolerant circuits. This topology; as shown in Fig. 6, supports fault tolerance for fire and/or life safety systems. It usually takes the form of a point-to-point connection (device or chain of devices connected to their respective controller) but features a second, redundant connection between the same two points. The failure of one such connection is therefore backed up by the presence of another. This, of course, would only hold true in the event that the two redundant circuits take physically diverse paths between the two points that they support.
Suffice it to say that AT&T has developed a way of supporting all of the native cabling schemes noted above using a decidedly non-native approach. The technique in doing so is not at all unlike the approach used to support disparate systems with different cabling requirements in the voice/data fields. Basically, the solution involves identification of a standard cable type that all equipment vendors can live with (UTP in this case), followed by the development of a creative topology that can support all of the required protocols. The preferred topology is a physical star consisting of individual UTP drops installed to end-device locations from a common point (i.e., a wiring closet). While variations may exist in terms of how many pairs or conductors of UTP are supplied to each location, ideally, the star-topology should be adhered to as rigidly as possible.
Once the star topology has been installed, any of the native wiring schemes shown above for building automation systems can be supported by cross-connecting individual connectors to one another in prescribed ways at the center of the star. Changes in these requirements can then also be made over time by simply reconfiguring cross-connections to suit the needs of new or expanded systems, but the building need not be re-wired.
While AT&T has appeared to have taken the lead in the application of structured cabling systems to building automation, it should be noted that virtually any structured cabling system, even ad hoc designs, can be applied in the same way.
Standards to the rescue
While the AT&T solution for Brand X systems is clearly innovative and absolutely on the right track, it is nevertheless, like most early innovations, proprietary. And while it's true that most of the Brand X devices can be supported over the star-wired scheme described, certain variations on this theme are required at times, which by any other definition spells "proprietary." But not to worry, we're getting there. It turns out that while all of this early innovation and the like has been underway, the industry association known as ASHRAE (American Society of Heating, Refrigeration and Air-Conditioning Engineers) has been working on the development of a standard to be known as "BACnet."
The "BAC" in BACnet stands for "Building Automation Control"; the "net", of course, stands for "Network." BACnet will probably be the single most important factor in the industry that will lead to the establishment and adoption of communications standards for signaling in the building automation arena. As a communications protocol at what the communications field refers to as the "application layer," BACnet will define how building automation devices communicate with one another at the highest level, and will potentially serve to eliminate the differences in how these devices send and receive signals at the physical, or wiring, level. In fact, as BACnet is currently defined in its advanced draft form, the underlying cabling schemes will not only be standardized as well, but will be expressed in the form of five choices that all users and manufacturers can choose from. The five choices will include pre-existing industry standard communications schemes (e.g., Ethernet and RS-485), as well as a low-cost ASHRAE-proposed standard called master slave token passing (MSTP). MSTP is a networking scheme that originated in the data networking field several years ago and is still widely in use today in many other industry settings. As a result, its appearance in the building automation field over UTP is not at all surprising.
Thus, the last piece of news in this discussion would seem to be what no one should be surprised to hear; namely, that structured cabling concepts and technologies have made the transition from voice/data to building automation, and that the building automation industry itself is in the process of establishing related standards. This can only be regarded as good news by the building owners/occupants community and the construction trades alike. It will certainly broaden the scope of opportunities for the low-voltage communications wiring industry in the years ahead.
For more information on the progress of the BACnet standard, contact the Standards Department at ASHRAE in Atlanta at (404) 636-8400.
Mark W. McElroy is the Partner-In-Charge of KPMG Peat Marwick's Enterprise Networks Practice and is based in Radnor, PA.