05 Dec

Product Migration: BACnet to the Future

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 Origin: NB Series à Destination: CB Series

With the introduction of the CB line of BACnet products, AAM now provides more choices when engineering a BACnet site. While the NB controllers will continue to be available, the CB controllers will be where the development efforts are focused for AAM going forward. The intent of this article is to provide a high level overview of the differences between these 2 two BACnet product lines offered by American Auto-Matrix.

Different Accents

First of all, let’s talk about how BACnet devices can be different from each other. You might be asking yourself, “a BACnet controller is a BACnet controller, right?” Yes and no. The intent of the BACnet protocol is to unite the building automation industry so that multiple vendor products on a site can communicate with each other and provide a single interface to the end user. As far as the end user is concerned, everything talks together and they have a unified system. In the real world, the experience can be quite different than the BACnet utopia described above. When selecting BACnet controllers, it is a good rule of thumb to select controllers that are BTL listed. Every vendor’s products talk BACnet a little differently but still conform to the ASHRAE standard, kind of like people speaking the same language will have a slightly different accent depending on what part of the world they are from. Think of someone from the Deep South with a strong Cajun accent having a conversation with someone who has a Russian English accent. They will likely get the point across but they will miss a bit in the translation, similar to two products from different vendors trying to communicate over BACnet. Think of a BTL listing as a speech coach to help vendors communicate properly with the greater BACnet community. This is why AAM products are BTL listed, and are occasionally re-tested to current BTL standard when a change has been made to BACnet services. It’s important that when you install an AAM product on a site, it plays nicely with other BACnet products out there. Currently, AAM is in the process of relisting the CB controller line for the BACnet Advanced Application Controller (B-AAC) BTL listing. To accomplish this, we are adding some of the BACnet goodness to the CB line that has been the heart & soul in the NB product line in order to provide a more cohesive user experience.

The Means to Get There

Another significant difference in BACnet devices is in how their applications are programmed. This brings us to the first major difference between the NB and CB series of products. The NB products were engineered to be fully accessible and configurable through a standard BACnet tool, like NB-Pro. AAM has essentially created the application, and the configuration parameters are all available over BACnet. This does provide some advantages in that a proprietary tool is not required to program the units as everything is available to anyone talking BACnet. It also means that the programming can be easily changed on the fly without having to recompile code for the controller. However, because all of the programming is stored in BACnet properties, it’s also difficult to troubleshoot an installed application if outside documentation does not exist. The CB products were designed with a focus on flexibility. The controller application, or strategy, is programmed using block based logic with the Engineering Center software, similar to the logic used in Aspect programming. Built-in debugging features in Engineering Center make it easy to troubleshoot code in real time by stepping through an application. While products like the CBT12iVAV and the CBT14 ship with strategies for standard applications, you are free to wipe the controller strategy and create a new one. This was never possible with the NB series of products, so if you ran across unique applications that the factory application did not support, you were left to install a more expensive option like an NB-GPC 2 to control a special application that a more flexible NB-VAV could have covered.

What options are available?

So, now that you are ready to start using the CB series of products, which do you choose? In general, there is a counterpart CB series product for each NB series product. Plant Controller On the plant controller level, the CBM product takes the place of the NB-GPC controllers. The CBM comes in several different I/O configurations and the addition of UniPut technology, hardware points are not fixed as Analog/Digital or even Inputs/Outputs, which allows for greater flexibility from the available hardware points. The GPC controllers hold an advantage by supporting I/O expansion modules which allow a single BACnet controller to double its I/O count. I/O expansion modules are in development for the CB product line with the intent to allow for a single controller to expand its I/O count even further. While the programming of the CBM controllers allows for more flexibility, they are also blank slates from the factory. With the NB-GPC controllers, the application had to be configured but it was available out of the box. To help with the learning curve of designing your own logic we’ve introduced additional Macros, pre-configured of segments for common logic applications, in the latest release of the Engineering Center commissioning tool. One final hardware difference to note between NB and CB platforms is the lack of onboard HOA switches on the CB products. Currently the NB-GPC1 and NB-GPC4 have HOA switches on the Digital Outputs for manual control from a hardware level. The CBM does not yet offer hardware HOA switches, however, they will be available on the upcoming I/OX modules. Terminal Controllers In the application specific controller level, the CBT products replace the ASC family of devices. For applications such as heatpumps and packaged rooftops, the CBT14 controller provides the answer for the NB-ASCe controller. The CBT14 uses a different smart stat, the CBT-STAT, for control applications however the prepackaged strategy also has the option to control based on a standard type 3 thermistor or even a return temperature sensor. As mentioned previously, if the prepackaged strategy does not meet your needs, you are free to create your own from a blank canvas. The NB-ASCe controller does have one additional Analog Output instead of the three UniPuts found on the CBT14, however, the CBT14 wins on Inputs by having six dedicated and three available as UniPuts. VAV Controllers Finally for VAV applications, it only takes one CBT12iVAV model to meet the applications that formally multiple NB-VAV variations would address. As with the other CBT14 controller, the CBT12iVAV can control a zone based off a CBT-STAT smart stat, a standard wall thermostat, or return temperature. It can also be completely re-engineered using the Engineering Center software to meet any application. The CBT12iVAV does require the additional step of using the Encoder file to create generate the configuration codes, but once configured the setpoints and other configuration parameters can be adjusted over BACnet using NB-Pro.

End of the Line

The key aspect to remember with the CB line of products is the strength in application flexibility, but the Engineering Center configuration software is required to create and compile the logic routines. The CB product gives a technician the ability to engineer projects in the past that were not easily accomplished with the NB controllers’ locked applications. In particular, unique applications for the VAV or Heatpump projects could not be accomplished with the NB products. While the NB products do have a more fixed application, everything is accessible and programmable using any standard BACnet system. The NB products will continue to be available as a solid BACnet product, although the CB series builds on the BACnet legacy and adds significant flexibility to the American Auto-Matrix product line. 
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