In May 2017, this column addressed additions to existing BAS. It recommended that most building owners should sole-source these projects using the base-building’s BAS manufacturer. However, large and multi-building owners may not have this liberty, and/or they may even benefit from regularly trying other manufacturers or contractors. These owners also may have the expertise to deal with the challenges that come from mixing various manufacturers within a BAS. This column explores these challenges a bit further.


Do Some Interoperability Testing

Large BAS owners considering the use of multiple DDC controller manufacturers typically will also choose a single operator interface (OI) to simplify day-to-day operations. If so, the existing and/or selected OI will need to use BACnet communications; if not, then the top level DDC controllers (e.g., B-BC listed) will all need to be by the same manufacturer as that of the OI, which might be a bit too constraining. If the selected OI is BTL-listed, then a good first step would be to bring in some other manufacturers’ B-BC controllers to perform some interoperability testing. The intent is to see how much functionality and object visibility the OI will have with the various manufacturers’ controllers. This will provide realistic expectations (and specification requirements) about life with a multi-manufacturer system.


Plan for Changes to the Existing BAS and/or OI

If a BAS from manufacturer “A” (which will also be used as the OI) is expanded using DDC controls from another manufacturer, then changes will be needed to manufacturer A’s OI (e.g., added graphic screens) and perhaps even their DDC controls (e.g., if the expansion affects the control in building areas with existing manufacturer A controllers). Typically, these changes can’t be made by the new BAS contractor. One approach might be for the owner to develop an open-ended contract with manufacturer A to make these changes. However, this could easily lead to competitive jostling (e.g., fingerpointing) between the two competing controls contractors. The better approach is for the owner to develop the expertise needed to make the necessary changes themselves.


Create Islands of Single-Manufacturer Systems

When integrating a BAS to another brand of controllers, changes needed to the existing BAS can be minimized by designing the addition so that it requires little or no interaction with the existing BAS (except with the OI). This might mean that an AHU and all other associated controllers (e.g., terminal unit) should always be controlled by a single manufacturer’s BAS. And owners with multiple buildings should restrict each building’s BAS to that of a single manufacturer. These “islands” will also minimize the issue of “who you gonna call” when there’s a problem.


Tenant Finish Additions

A simpler approach to learning what a multi-manufacturer BAS might be like would involve trying a different manufacturer’s terminal controllers on a small tenant remodel project (or just change out one terminal’s controls). Even though this type of integration can be the simplest, a lot can be learned about how to deal with the “big three” BAS functions: day/night scheduling, alarming, and trending. Most terminal controllers are B-ASC listed and therefore generally will not have a time clock needed for a day/night schedule, nor will they issue alarms or store trend data. Instead, the associated higher-level controller (typically that for the AHU) will handle these functions through simple read/write services. However, there is a trend towards B-AAC listed terminal controllers with built-in scheduling, alarming, and/or trending capabilities. The upper-level controller performs less supervisory control over these types of controllers. Trying both types of controllers will provide insights in to how integration efforts vary based on how the “big three” functions are handled.


A Final Word

BACnet was created to provide more flexibility to an owner when making changes/additions to their BAS. There are many ways to take advantage of this flexibility, as long as you approach it with some upfront planning bolstered by real-life testing.