Integrating power monitoring systems

03/12/2014


Figure 3: The photo shows branch circuit level power monitoring integrated into the writing gutter of a typical electrical panelboard.Q: How large does a power load profile of a commercial building need to be to justify a power monitoring system? To justify integrating the power monitoring system into a BAS or with other engineered systems?

Shapiro: A power monitoring system should be recommended for all commercial buildings regardless of the size. The nature of the system depends on the size and tenants of the building. Power usage at the service as well as throughout the major portions of the distribution facility allow for proper operation of the facility as well as a functional method of understanding the possible maintenance requirements and load growth possibilities without subjecting operating personnel to the risk of arc flash by actually opening electrical equipment to measure loads.

Strang: I don’t think a particular load profile would be the determining factor for justifying a power monitoring system, or for integrating it with an overall BMS. I suppose if you were looking at only ROI of the power monitoring system based on energy savings, you could prognosticate typical payback numbers. I think the criticality of the load would be the biggest factor in implementing the power monitoring system. A strip plaza could have a larger load than a small data center, but the small data center may serve critical 24x7 customers (i.e., a bank) where the data from a power monitoring system would provide much more value.

Yoon: It goes beyond the size of the load profile. To say that a building falls into a specific utility rate class doesn't justify it by itself. Concepts of load profile variability and value of business continuity also factor into it.

Q: How have power monitoring systems helped ensure a building’s power quality is stable?

Shapiro: Power monitoring systems have given operating personnel a tool to diagnose internal as well as external power quality issues. Having power quality monitoring at the facility on a continuous basis allows for immediate identification of power quality issues before they can cause operational problems. As equipment is added to the distribution system or changes are made to the distribution system, the power quality is monitored and anomalies can be identified. The monitoring provides evidence of power quality before and after changes to help identify the causes of power quality issues, help remedy them, and ensure power quality stability.

Strang: Power electronics have come a long way. A 256 sample/cycle analog-to-digital converter is nothing today. Many of the power monitors today can easily achieve this resolution and much higher. This monitoring resolution allows capturing of sub-cycle events and THD that, years ago, required more expensive portable equipment. So, in addition to seeing general trends to ensure power stability, now we can easily see sub-cycle aberrations that can be indicative of equipment that hasn’t quite failed yet but may fail very soon. A power monitoring system can also be very valuable in analyzing what events are produced internally vs. from the utility. For example, a motor starting the same time every day could be easily identified and turned off to see the effect.

Yoon: We have seen situations where utility side power quality issues such as brownouts and single phasing have caused or contributed to equipment failures. However, we've typically seen power monitoring systems used simply to record such disturbances and not necessarily to automatically take equipment offline.

Q: When working with a building’s operations and maintenance (O&M) staff to set up training, systems manuals, etc., what guidelines do you provide for system testing and/or maintenance of the power monitoring system?

Shapiro: EPMS system testing and maintenance goes hand-in-hand with the electrical system testing and maintenance program. As the electrical systems are operated and tested, the EPMS is used to document the positions of circuit breakers, facility load changes, power quality impact of load shifts, etc. As long as the proper signals are received by the EPMS through the electrical equipment and LAN systems, the actual maintenance of the EPMS system and interfaces is limited to the meters and LAN infrastructure, which is minimal.

Strang: When implementing a power monitoring system, testing, commissioning, and training are definitely requirements. We have seen projects where a power monitoring system was installed as part of the original contract, with all of the capabilities intended to be brought back to a PC for remote monitoring and trending. However, the communication cables were never terminated. All the capability was there and the owner was completely unaware. Typically, we specify that the system be completely tested and commissioned by the installer in cooperation with the vendor, and after complete functionality is achieved, a vendor’s representative (of the equipment manufacturer) provides at least 8 hr of training to the O&M staff. Obviously, the actual duration should be adjusted based on the number of staff and complexity of the project, but the goal is for the staff to be comfortable with basic operations before this new system is dropped in their laps. The system will have no value if no one knows how to use it. Lastly, be careful to specify a system that will not hold the customer hostage for minor assistance and changes.

Yoon: One of the biggest gaps that we've experienced in the design process is how to define the look and feel of the HMI and the commissioning of the overall system. Every integrator does things just a bit differently.

Young: For system testing, the specifications are written requiring a 1% calibration between the power monitoring system and calibrated test equipment. A maintenance contract is usually required from respective vendors, as well as 8 hr on-site staff training on all systems.



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