Upgrading Old BAS: Is A Gateway In Your Future
In the last two columns, I explored BAS integration to factory-mounted controls and controls additions to existing BAS. This month, I will cover the last major reason for considering integration: upgrading old BAS.
Why? Old BAS don’t fail in totality; instead, partial system failures typically become more frequent and/or more challenging to resolve. Also, many components such as sensors, wiring/conduit, and even some controllers may still be usable. So, while a total and all-at-once system replacement may sound like a good idea, financial considerations may dictate otherwise. Therefore, it makes sense to consider a phased approach to the upgrade and/or an upgrade that retains some of the existing controllers. So upgrading an old BAS often involves integration to a new BAS.
If the BAS uses BACnet communications, then the upgrade should be simpler, although most older systems probably use proprietary communications. If so, using the same manufacturer ideally should lead to a reasonably straightforward approach, assuming that their newest-generation BAS is designed to be backward compatible. However, the client may want the upgrade bid on by multiple manufacturers, which complicates the meaning of “backward compatibility.”
Therefore, there’s a good chance that a gateway will be needed. “Gateways” (often called “drivers”) provide communications protocol conversion. They are needed to integrate to an older proprietary BAS, but they also are used to connect a LonTalk system to one that uses BACnet.
Gateways get a bad rap, mostly due to the fact that protocol conversion can never be perfect. The reason is that a communications protocol is designed to support the data that is deemed to be important to BAS operations. This involves many subjective choices, with results that will vary depending on the designer. As a result, the big difference between protocols can be about which data is or is not supported.
Why is this a Challenge?
The first step is to determine whether the old system has an available integration path. Unfortunately, a gateway (typically to BACnet) may not be available for older proprietary systems. In this case, it would be best to entirely replace the old BAS all at once. A second choice would be to replace it in phases with the understanding that there will be two separate BAS (with two separate operator interfaces) in use during the transition.
A gateway to an old, proprietary system is often only available via the same manufacturer (i.e., using the backward compatibility of their latest-generation BAS). If so, then the project delivery choices are expanded to include sole-sourcing it to the same manufacturer. The next question is whether the gateway fully supports all important BAS functions or not. The best way to determine this is to view an actual operating system that uses the same old and newer BAS. If the gateway clearly doesn’t do very much (i.e., the old system’s operator interface needs to be retained and used on a regular basis), then the fully replaced route is probably the best choice.
If the BAS uses BACnet communications, beware that most early BACnet systems unintentionally implemented the protocol in various non-standard ways. This could lead to unexpected integration issues with any current BACnet-based system. Again, seeing an example of this integration combination should help to define the risks and/or shortcomings.
Lastly, the same challenges with specifying the integration as discussed in the two previous columns apply here. The objects to be shared and the services to be used need to be specified. This is necessary to assure that the old and new BAS are made to work together as a unified system. If the new BAS will be bid on by multiple manufacturers, it is not reasonable to expect a designer to research the objects and services variations between each new BAS choice. In that scenario, a “basis of design” approach may be beneficial.
What’s the Solution?
Clearly, the best approach to upgrading an old BAS is via a complete, all-at-once replacement, but financial considerations may dictate a partial or phased approach. Unfortunately, there is no simple integration solution to these latter approaches and, in fact, each situation needs to be uniquely researched. Either way, there’s probably a gateway in your future!