We have reached the point where any new (or replacement) BAS is expected to support one or more open protocols. It also is an expectation that when we specify large pieces of equipment or even complete subsystems, that they will also be able to support open protocols. In theory for the designer, systems integration is readily accomplished, but in reality, there is still a fair amount of work needed to design and specify systems and equipment for ready integration. Here is what we look for in developing an integrated systems design.
Protocol Support. This may be somewhat obvious, but both the BAS and the system to be connected need to be able to support the same protocols. We generally start by checking with potential suppliers to see what options for connectivity they offer. Most of our designs are based around BACnet, but some equipment and systems may only have options for Modbus or other protocols. Once we settle on a systems integration protocol, the next step is to specify a physical link. This is generally an IP connection, if possible, but can also be a BACnet MSTP (RS-485) connection as well. If using MSTP, be sure to specify the communications rate, and ideally place each system to be integrated on a dedicated link to simplify testing and checkout.
Most integrated systems use a fairly basic set of services such as reading and writing data. In most cases, this is adequate, and more advanced system functions such as alarming, scheduling, and trending can be done up at the BAS. The use of advanced protocols such as BACnet, though, allow these functions to be shared between the equipment and the BAS. In some cases, it may make more sense to use these advanced services to improve overall system performance and reliability, but doing this requires fairly significant coordination by the designer, systems integrator, and equipment supplier.
Points or Objects to be Integrated. As you develop your controls sequences and points lists, you need to keep in mind how this will work with integration. For example, if you are integrating to a rooftop unit and you want to do static pressure reset based on VAV box position, then the setpoint for discharge static pressure needs to be a writable BACnet object. In many cases, the available points for equipment to be integrated may be limited. It is essential to get this information in advance of developing your sequences and points list.
Checkout and Test. Much of the challenge in making an integrated systems work falls to the controls contractor/systems integrator. When you are commissioning an integrated system, be sure that the systems are communicating properly, that the desired data is being shared, and that control values and sequences are working across the two systems. ES
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