Realizing that he couldn't save what he didn't measure, Barham"s investigation led the convention center to select a submetering system that would allow facility engineers to monitor, record, and report energy usage as a tool for conserving energy and for lowering overall operating costs.

"We chose the system based on price, customer service, and flexibility in allowing future expansion," said Barham. "It was also mandatory that we have a hybrid system, and the vendor's OEM arrangement with a power quality meter company gave us the total solution we needed to not only record power consumption and demand, but to monitor power factor, total harmonic distortion, and other power quality parameters."

The facility's main electrical service entrances are located in two large sub-level electrical vaults, where multiple (480 volt) 1600 and 3200-amp loads are individually submetered. Low-voltage output current sensors, non-invasively installed around the electrical feeds in both vaults, supply the raw electrical data to five E-MON D-MON submeters in the west vault and four in the east. An I-MON computer interface module in each vault accumulates pulse outputs from the individual submeters, digitizes the data, and transmits it via an RS-485 communications link some 1600 feet to the laptop PC in Barham's office.

The Windows-based CE-MON software installed in the laptop can display electrical data gathered in 5, 15, 30, or 60-minute intervals. The load data are exported to a spreadsheet for analyzing energy consumption, accounting, and other useful functions. "Thanks to real-time metering capability, we're able to look at our energy consumption and make load adjustments in real time to avoid additional ratcheting charges, thus saving energy dollars," Barham said.

The program can profile the information in a number of useful ways, allowing management to view energy consumption, demand, and power quality functions in real time. Power quality or monitoring problems are time-stamped for Barham and his team to investigate, and, in this way, areas of inefficiency are quickly identified and corrected.

Currently, nine of the eleven meters in the Convention Center complex are submetered, with the remaining two meters slated for retrofit.

Up and running for more than two years now, the submetering system has already paid for itself in terms of the savings. "Thanks to this system, we estimate our savings to be about $13,000 annually," said Barham. Twice voted the number three facility of its type in the world, the San Diego Convention Center is a prime example of how submetering can accurately track energy usage, focus conservation efforts, and recoup operating costs.

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