Using BAS for M&V
In the past, the BAS was more about automating certain building control tasks. The main, if not only, diagnostic tool for older versions of BAS was relying on heating and cooling complaints or “cold calls.”
The next major advancement in BAS was lighting control and how lighting actions and tasks were automated based on occupancy, daylight, and task type.
One of the main goals of RCx projects is to detect any failed system parts. These faults include both hardware and software. Examples of hardware faults are failed valves, broken or stuck dampers, and noncalibrated or failed sensors.
However, when it comes to M&V and data collection, there are no standard methods, and it is an engineering art to envision the future M&V needs of a facility during the BAS design. Discussion of how BAS can provide the most effective system M&V during the RCx process is important, and should take place during BAS design when the BAS specifications are developed and documented.
In the recent years, BAS has achieved significant progress in hardware faults diagnostics. On the other hand, diagnostic and fault detection of the BAS control sequences is a more challenging task as the software should quality check software. Examples of software faults are self-evaluation of control sequences, design deficiencies or errors, and methodologies of reporting the actionable findings.
It is reasonable to assume that the major part of any fault detection and diagnostic (FDD) software should be based on measurement and verification process. Earlier versions of FDD tools were independent, stand-alone platforms that analyzed the collected trend data generated by the BAS. The FDD platforms usually analyzed these trends that were provided in batch file. One of the challenges with this method is that for the sites with high security protocols, an open bridge in the form of online access to their BAS would not be desirable. Recognizing the prerequisites of a facility’s IT securities is an important consideration when specifying BAS with FDD capabilities. Based on these types of constraints, statistical and numerical analysis, such as normalization and sensitivity analysis, can be done either on the BAS platform or on a cloud-based server. Integration of BAS and FDD tools is an ongoing development effort.
The best way to use a BAS for M&V purposes on a RCx project is to design the BAS with the M&V goals in mind. While data collection and data crunching are an integral part of RCx, as a designer and a specifying consultant, we would not like to be cumbersome or incur many unnecessary costs to the client. To design a robust BAS and to avoid value engineering later in a project, it is important to get input from the owner and O&M staff, while also educating parties involved on the benefits of a robust BAS capable of M&V. This process will help to ensure the inclusion of BAS requirements in the OPR document.
The first cost of installing a BAS with M&V capabilities can be very well justified by RCx benefits. A Lawrence Berkeley National Lab report states that RCx can have energy and maintenance cost savings of about 16%. In addition, a capable BAS can reduce the cost of RCx projects, which in turn enables the building owner and O&M staff to acquire RCx services more often.
Designing a BAS with M&V capabilities is not a task that should be done solely by the control contractor; the design should be a collaborative effort between all design disciplines including MEP, technology and security, process, and owner representatives. In this process, software design strategies and hardware are both required.
Whole-building benchmarking is an effective tool to evaluate the building energy and operation status. A lower building benchmark is an indicator of a building’s plant and system level energy and operational deficiencies. Whole-building level energy benchmarks are created using static data such as historical monthly utility bills, square footages, data representative of plug loads, etc. Whole-building benchmarking engines such as Energy Star use statistical data across the board for many building types, which are collected under different survey programs such as Commercial Building Energy Consumption Survey (CBECS).
One way that BAS can assist M&V is through the use of historical trend data for creating an isolated benchmark. Isolated benchmarking of a building is a comparison of a building with itself. When the BAS or the RCx agent performs a similar analysis, the actionable outcome could determine, for example, why the electrical demand is higher at night than during the day on weekends.
There are two conclusions to draw from this: First, with regard to new construction projects, to design a facility with robust capability for ongoing commissioning, the BAS should be designed with capabilities for conducting data driven M&V. Some of the M&V practices used in the RCx process could be used as guidelines when specifying and designing new building BAS. Some of the M&V tasks, which in most cases are done outside the BAS, can be specified during the control design process to be included as part of the BAS.
The second conclusion deals with existing buildings and showing the importance and advantages of BAS for conducting data driven M&V. To give owner and facility managers the ability to conduct such a data driven process, it is worthwhile to explore necessary upgrades. For potential BAS upgrades to satisfy the M&V, a complete investigation of existing control system hardware, software, and expectations (such as FDD capability) is required.
Moh Heidari is director of the energy solutions group at AlfaTech Consulting Engineers. He has more than 10 years of experience in energy engineering, Cx, RCx, and energy modeling. He has a master’s degree in mechanical engineering.