The Energy Wiz: Metering and Monitoring
A Little HistoryFor decades, larger power customers (those with a peak demand of 1 MW or more) have routinely been monitored by utility meters that measure usage in short time intervals (typically 15 or 30 min) that find the time and magnitude of peak demands under time-of-use electric rates. Such interval metering (generally called automated meter reading, or AMR) used phone lines to report data from each meter back to a central utility monitoring system.
The expense of such systems and relatively low demand charges (in most of the United States), limited AMR to only a very small portion of the customer base (less than 1%). California's original deregulation plan called for interval meters for all customers with peak demands of only 20 kW (later changed to 50 kW) to allow power pricing based on the hourly spot market. The door was also opened (in both California and a few other deregulating states) to competition for metering services at the sales/installation and meter reading levels.
Fast forward to today: Limited telephone lines, higher-than-expected costs, and the self-immolation of California's deregulation scheme moved AMR to the back burner. While many new interval meters have been installed in the last few years, they still represent only a tiny fraction of the metering business. Impact has been muted due to a lack of standards, a wide cost range (depending on many technical factors), lack of time-of-use tariffs, and minimal interest from competitive power suppliers.
But Nothing Stays the Same for LongIncreasing costs for power and the volatility of power prices have now lead many customers to look for more sophisticated ways to understand and control their demand in real time. Doing so requires interval metering. Fortunately, some past problems are gradually being overcome: Meter costs are dropping, some state energy agencies are providing incentives for installing advanced metering, new customer load management programs require interval meters, and ANSI-level standards now exist for AMR. When combined with software that digests such a data stream, interval metering may reveal ways for customers to control demand much more precisely than ever before.
Getting Started With This TechnologyAs with many complex tasks, the first step is a needs assessment: What does the organization need (and want) in the way of energy data, and how will it be processed and used to make the effort worthwhile? Once that question is answered, a rough schematic design is developed, showing the locations and types of meters to be installed. The method(s) for communicating with the meters are then evaluated (e.g., wireless, PLC, fiber optic), and a data collection system is considered (e.g., BMS). This effort is then formalized through a master metering specification to allow bidding out.
Individual vendors can help you get a grip on the choices, but a good and unbiased source of information is Automated Meter Reading Association (AMRA, http://www.amra_intl.org), the industry trade association. It has a good directory of AMR products and services, and provides guidance on the new ANSI metering standards. While slightly dated, a good start on a metering spec is available from Association of Higher Education Facilities Officers (http://www.appa.org/downloads/energy/cimms.zip).
An Important Tip While data from an AMR system can prove invaluable in finding and proving energy savings, an ongoing human review of such data is needed before entry into accounting software, or using for real-time control. Meter errors (especially for steam and chilled water) can lead to incorrect billing and control actions. A good data acquisition system will employ "smart" programming to warn operators when readings are too suspicious to be immediately accepted. ES