Pushing BAS to Realize Its Full Potential
Building automation systems (BAS) are an effective tool for facility managers and operations personnel to resolve problems quickly, reduce energy consumption, improve system performance, increase occupant comfort and safety and manage maintenance costs. Developments in system architecture allow previously independent systems such as lighting, HVAC and fire and life safety to be seamlessly integ...
Building automation systems (BAS) are an effective tool for facility managers and operations personnel to resolve problems quickly, reduce energy consumption, improve system performance, increase occupant comfort and safety and manage maintenance costs.
Developments in system architecture allow previously independent systems such as lighting, HVAC and fire and life safety to be seamlessly integrated into a single comprehensive building system. But the only way to ensure that BAS operates correctly and to its full potential is proper commissioning.
It begins in the design phase, during which the focus of BAS commissioning is to determine the exact owner's performance requirements . But given the vast choice of BAS options available and the varying levels of technical experience of an owner's personnel, this can be a difficult task.
This is where the commissioning authority (CA) plays a vital role, by first assisting the owner in determining what the expectations of the completed system can and should be, then ensuring that these requirements are accurately documented. Once the owner's requirements are identified and documented, this information is not only used by the design team to provide a system design that meets all the requirements, but is also important for formulating documents for future operation and maintenance.
Today's highly sophisticated systems offer so many options and configurations that the designer's first task is to decide on a given level of performance and specify a system that will meet those goals. The design engineer uses many different load calculations, "rules of thumb" and assumptions on how the building will be occupied and operated. Because performance problems that arise when the system is up and running are difficult to analyze without information that was used for the basis of design, the CA must play an active part from the very beginning.
In the design phase, the CA facilitates the development of the basis of design document , which organizes all related load calculations, energy modeling reports, equipment performance ratings, occupancy expectations and any assumptions used by the design team to arrive at the final system design. The next step is construction document development, during which the CA fills other crucial functions.
Developing documents and procedures
During construction document development, the CA reviews the contract documents at the various stages of completion. Having the owner's project requirements and the basis of design documents available during reviews allows the CA to identify this information clearly in the contract documents.
When it comes to the specific issue of BAS commissioning, during this phase the CA reviews all BAS submittals and shop drawings provided by the controls contractor while cross-referencing the owner's project requirements and basis of design documents.
It is important that the sequence of operation described in a BAS submittal provides enough detail, and that the contractor clearly understands system performance requirements. System engineers and programmers must all know these requirements to ensure reliable and stable control operations.
In the construction phase, the CA will periodically visit the job site to witness BAS installation procedures. There are many variables involved in a typical installation, such as sensor location, wiring interface to equipment and routing of communication wiring. The CA can provide valuable oversight for these and other related issues throughout this project phase.
In preparation for the next phase—BAS operation—the CA develops detailed functional performance test procedures. The CA provides step-by-step instructions for operating the system through various load and alarm conditions. Once again, the groundwork for developing these procedures is all the way back at the beginning. It relies on the owner's project requirements and basis of design document.
Depending on the project's geographic location and the time of year, some load testing will have to be deferred to the proper season to accurately simulate outdoor loading conditions. This is particularly true in the northern climates. Any deferred testing requirements should be clearly stated in the project specifications and understood by the project team.
Throughout BAS performance testing, the operations and maintenance (O&M) manuals and system as-built drawings are referenced to guarantee the accuracy of these documents. All too often, as-built drawings are not updated, remaining the same as original submittal drawings, and O&M data are only copies of generic equipment information. Commissioning, however, requires the as-built drawings and O&M data be provided before any performance testing commences so the accuracy of the documents can be verified to ensure that reliable information is turned over to the owner.
Generally, BAS performance testing can be divided into three main categories: field controllers, systems integration and network communication.
Field controllers are the microprocessors that directly control the various pieces of equipment—HVAC, for instance. Proportional, integral and derivative (PID) control loops measure many different types of variables, such as temperature, humidity and pressure, and perform thousands of calculations to control analog and digital outputs to equipment and devices. Proper commissioning not only includes static testing of the logic and control of these PID loops, but also uses PID tuning software to verify the stable operation of the loop under varying load conditions.
Systems integration means many things to many people. For purposes of this discussion, it is the interconnection of the BAS with the other building systems. This interconnection can be as simple as a relay contact signal over a twisted pair of wire, or as complex as open protocol objects transmitted via Ethernet LAN.
Most project teams include many different subcontractors, each responsible for the installation of its own system. Each subcontractor usually does a fine job of checking the operation of its system but is probably not concerned with checking the operation of any system integration requirements.
The CA, however, has knowledge of the overall system performance requirements, including system integration testing procedures that figure in the performance testing process. Consequently, it is often only the CA who is in a position to ensure that operation of all system integration features is not only tested but also accurately documented on the as-built and O&M information that is turned over to the owner.
Finally, one usually thinks of commissioning as a process that ensures system accuracy and functionality. But there is another aspect to the CA's work: seeing that BAS is used to its full extent.
Network communication is growing by leaps and bounds, but too often, BAS is installed with only a small percentage of its system capabilities being utilized. Commissioning to make optimal use of the system consists of two broad categories: monitoring and alarming, and facilities management.
The monitoring and alarm functions are tested and verified while testing the field controllers and systems-integration operations noted above. The monitoring function deals mainly with the level of detail provided on workstation graphics: what information is displayed and what level of control (such as scheduling and set point adjustment) is available to operating personnel.
An example of an alarm function concern is whether the fan status will report OFF ALM to the correct workstations or printers, and whether the system will dial the appropriate cell phone or pager to notify maintenance personnel.
Facilities management functions, such as data trending, energy management and monitoring, or computerized maintenance management systems, are provided for all networked BAS. As for the installation of these applications, the CA ensures the correct software is loaded on the workstations and applicable documentation is provided.
The real benefit of utilizing these applications comes from the training of operations personnel to use the system. The CA will facilitate training sessions to make sure that all training that was specified is provided. In addition, the CA will provide follow-up feedback after the training has been completed to ensure the training sessions were worthwhile.
To recap, BAS systems today are quite complex. To achieve the desired level of performance, the commissioning process starts early in the design phase. Owner's requirements and the basis of design are defined and documented, and the information is then incorporated into the contract documents. Once all testing and training have been completed and accurate documentation has been turned over to the owner, the commissioning process extends beyond the completion of the construction project with follow-up reviews of system operations, trend logs and measurement and verification reports. In addition, a warranty review meeting is usually held 10 months after project completion to generate a "lessons learned" narrative for future projects.