Submetering for Energy Savings and Cost Reduction
Installed at the point of load or any convenient location, submeters are useful for monitoring the energy usage of equipment items or circuits.
By Don Millstein
Installed at the point of load or any convenient location, submeters are useful for monitoring the energy usage of equipment items or circuits. Submeters can reveal operational inefficiencies, demand spikes and other bottom-line impacting events, while increasing facility operational effectiveness.
The level of sophisticated energy profiling needed by high-volume consumers is unobtainable using the standard utility meter found at the facility's main electrical service entrance. In response to the need for greater granularity in terms of the energy intelligence needed to optimize today's facility operations, electric submeters continue to provide a cost-effective way to help identify thousands of dollars in energy savings opportunities. First introduced in the early 1980s, submeters are metering devices with monitoring capability that are installed on the facility side (see Figure 1) of the master meter to provide any or all of the following:
|Figure 1. Submeters are installed on the main utility meter's "building side" to measure energy consumption from the enterprise level down to a single device or circuit panel. Sold through distribution, electric submeters are easily integrated with water, gas and other pulse-output utility meters, energy intelligence software and BMS to provide a total facility energy snapshot.|
• Usage analysis and peak demand identification;
• Time-of-use metering of electricity, gas, water, steam, British Thermal Units (BTUs) and other energy sources;
• Cost allocation for tenant or department billing;
• Measurement, verification and benchmarking for energy initiatives, including Leadership in Energy and Environmental Design (LEED) energy and atmosphere (EA) and water efficiency (WE) credits;
• Load comparisons;
• Threshold alarming and notification; and
• Multi-site load aggregation and real-time historical monitoring of energy consumption patterns for negotiating lower energy rates and more.
Of the three main submeter types shown in Table 1, the first two-feed-through and current transformer- (CT-) based-are socket-type meters. CT-style socket meters are used with loads of 400A and above. In commercial applications, they can be specified but occupy excessive space in the electrical room because of the need for CT cabinets and the meter bases. The extra space requirement also diminishes the available rental space, which is undesirable in the commercial marketplace. In addition, socket-type meters are not Underwriters Laboratories (UL) listed, a disadvantage in many jurisdictions. The third type is the solid-state electronic submeter, a non-socket device that provides clear advantages over the previous two.
Since their introduction, submeters have evolved in terms of functionality and usefulness, and have proven themselves valuable to facility operators as front-line energy data gathering tools in an era of rising utility costs and tightening budgets. Submeters help improve the facility's bottom line and facilitate implementation of building retro-commissioning projects and other energy initiatives while also encouraging facility occupants to become stakeholders in the energy management and conservation process.
In addition to installation as standalone devices in any convenient location, submeters can be mounted in multiple meter unit (MMU) housings for high-meter-density applications. As front-end energy data acquisition devices, submeters can contribute directly to certification of all facility types under major energy initiative guidelines, such as LEED, Green Globes and other high-performance building assessment systems that require measurement and verification of the facility's energy envelope, a tracking function provided by the facility's building management system.
|Table 1. Non-socket-type electronic submeters are initially less expensive, quicker and easier to install, and offer superior performance and options compared to other types-making them a cost-effective way to measure and verify facility energy retrofit program goals.|
Circle 33 on reader service card
Submetering for LEED Points in Existing Building Operations and Maintenance Applications
A large Midwestern utility serving some 1.2 million customers in 57 counties responded to a recent corporate mandate to save more energy, lower operating costs and improve the environment. A major renovation saw the utility's 708,000-square-foot headquarters facility upgraded with many energy-efficiency measures, including installation of more than 85 electric submeters to handle the consumption (kWh) and demand (kW) measurement and verification functions required by the LEED- Existing Buildings Operations and Maintenance (EBOM) certification process the utility had decided to pursue.
The utility's in-house engineering staff supervised the submeter installation process after it was determined that standard utility meters were neither cost-effective for the application nor could they provide the energy monitoring granularity that the LEED-EBOM certification process required. The meters included Class 2000 and 3000 E-Mon D-Mons (100-1600A) and interval data recorders (IDRs) for taking energy readings every 15 minutes on a 24/7 basis. The user interface was provided by E-Mon Energy software, which analyzed and displayed the energy data through the facility's Ethernet local area network (LAN) and through hard-wired connections. As shown in Table 2, submeters are useful for obtaining points under many EBOM subcategories.
|Table 2. Specific LEED Version 3 EBOM sections and potential points facilitated by the use of electric submeters|
Submetering for LEED Points in New Construction Applications
Southern California Edison's prototype high-performance service center in Wildomar, Calif., features two multi-level main buildings and a single-story structure in the service yard. The 97,553-square-foot facility is powered by solar panels and also features energy-efficient lighting that automatically adjusts based on natural light levels during daylight hours. As the first of a new type of service center, the facility's design was recently certified at the Gold level by the U.S. Green Building Council under its LEED-New Construction (NC) high-performance building assessment system.
The energy data acquisition front end of the facility's Building Management System (BMS) is provided by 277/480V, 3-phase/4-wire E-Mon D-Mon submeters that are used to monitor electrical consumption (kWh) and demand (kW) on two 200A and one each 1600A and 3200A circuits in the three main buildings and the main switch board. The meter installation took some 24 man-hours to install, during which one minor technical difficulty was self-diagnosed by the submeter in the form a current sensor error.
Communicating the raw energy data every 15 minutes to the energy manager's personal computer (PC) through the facility's Ethernet local area network, the meters were installed to see how much power was being consumed in each building and to compare this usage to similar non-green buildings. In LEED certification processes, submetering equipment is useful for a variety of functions. Commissioning agents can use energy intelligence software, for example, to identify functionality and performance of electric, water and gas systems. In new construction, submeters are useful for baselining facility energy performance and renovation scenarios where at least 12 months of energy data can be collected to provide a highly accurate profile of the using facility's energy patterns over time. Table 3 shows the many areas where electric submeters can be used to help facilities obtain LEED-NC certification points.
|Table 3. Specific LEED Version 3 NC sections and potential points facilitated by electric submeter use|
Encouraging Energy Efficiency by Example
Recent industry studies show that green building construction will continue to be a major trend across the facility landscape. Submeters, an enabling technology, can help facilities improve their bottom lines by benchmarking, measuring and verifying compliance with major energy initiative guidelines-while also encouraging every enterprise level to become a stakeholder in the energy management and conservation process. Installed at the point of load to monitor individual equipment items or circuits of interest, submeters can reveal operational inefficiencies, demand spikes and other profitability-impacting events that allow facility personnel to implement cost-effective mitigation strategies of tangible value to the facility's bottom line.
About the author: Don Millstein is president and CEO of E-Mon of Langhorne, Pa. As a veteran energy industry speaker and author, Millstein is a former participant in utility deregulation in California, New Jersey, New York and Pennsylvania. He is a member of the Department of Energy's Federal Energy Management Program task force, Alliance to Save Energy, the U.S. Green Building Council and other energy conservation-related organizations. He can be contacted at firstname.lastname@example.org.