A key element of today's sustainable building management system (BMS), compact submeters acquire and transmit a variety of energy data parameters for analysis and reporting through the BMS for common area cost allocation, fair and accurate tenant billing, power factor penalty identification, utility meter shadowing and other energy saving capabilities of tangible value to the facility's operational bottom line.
Scraping the sky at 975 feet above ground, the tallest building on the Philadelphia skyline is also the loftiest “green building” in the United States. Completed in June 2008, the 58-story skyscraper’s 1.25 million-square-foot, state-of-the-art structure received a Gold rating under the U.S. Green Building Council’s LEED-CS (Core & Shell) category in April 2009.
The sustainable design philosophy guiding the construction of the building resulted in 40 percent less water use than typical office buildings and a 70 percent lower heat-island effect from the pavement. Equally important to the developer's sustainable design goal was the implementation of an energy-efficient building management system (BMS) to optimize comfort and facilitate productivity for the building's more than 3,000 occupants.
In operation, the BMS provides a state-of-the-art control system that coordinates all of the climate, lighting, energy consumption and scheduling systems through a single integrated, Internet-based source. The building's intelligent infrastructure compiles large amounts of data and sends it via the Internet to a central monitoring and control location for daily operations management. The BMS calculates the exact cost of producing BTUs for heating, cooling and steam, including the electrical cost for pumps and steam for driving the air-conditioning system. Chilled water, gas and other measurements are also factored into the mix.
Submetering system extends performance of skyscraper's BMS
Operating in parallel to the BMS, a facility-wide network of E-Mon D-Mon electric submeters accepts energy data from the BAS and imports it into E-Mon Energy software. This PC-based energy intelligence software analyzes and converts the raw meter data into monthly utility billing statements for the building's tenants. Shown in Figure 1, elements of the system include some 205 Class 3000 E-Mon D-Mons, 91 BTU meters, seven steam meters, 17 water meters, eight gas meters and 58 airflow meters. This does not include utility meters, of which two steam, and one each gas and water meter are also part of the system. The airflow meter data is also imported into E-Mon Energy software from the BMS.
Figure 1. Block diagram showing the parallel operation of the facility's BMS and the submetering system used for utility metering and tenant billing via a single hardware/software platform.
The submetering system not only accurately meters the electrical, but meets the user’s complex billing requirements of incorporating gas, water, steam and BTU metering into a single hardware/software platform. Coincidental demand billing-the peak demand (kW) of the entire building not just the individual tenant-is also factored into the mix, along with the ability to identify tenants that cause a power factor penalty to the building. Because this facility buys high-voltage electricity in bulk rates and transforms it down, the power is less expensive than electricity purchased at 480 or 208V levels. Consequently, that cost savings is passed through directly to the tenants.
The billing software factors not only electrical into the mix but also allocates costs to those tenants using water, steam, gas and other utilities. The facility’s sophisticated “coincidental demand” structure views tenant energy consumption patterns from a number of different angles, including:
- Comparison of present to previous month;
- Comparison of year to date with previous year;
- Watts per square foot;
- Ratchet charge billing;
- Power factor corrected billing;
- Percentage of highest load.
Figure 2. Submeters acquire the energy data using 0-2V output split-core current sensors that are installed non-invasively around the electrical feeds being metered. This eliminates having to power down the load and makes for a safer, faster install for the electrical contractor.
How Submeters Facilitate BMS Performance
The level of profiling needed by high-volume energy consumers is simply unobtainable using the standard utility meter found at the main electrical service entrance. That's why growing numbers of facilities like the aforementioned Philadelphia skyscraper are using submeters to help identify opportunities to save literally thousands of dollars in reduced energy costs through:
- Usage analysis and peak demand identification;
- Time-of-use metering of electricity, gas, water, steam, BTUs and other energy sources;
- Cost allocation for tenant billing;
- Measurement, verification and benchmarking for energy initiatives, including LEED Energy & Atmosphere (EA) and Water Efficiency (WE) credits;
- Load comparisons;
- Threshold alarming and notification;
- Multi-site load aggregation and real-time historical monitoring of energy consumption patterns for negotiating lower energy rates, and more.
Table 1. Whether designed in or retrofitted, submeters are installed on the "building side" of the main utility meter to measure energy usage from the enterprise level all the way 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 and energy intelligence software to provide a total facility energy snapshot. Non-socket type electronic submeters are less expensive initially, quicker and easier to install and offer superior performance and options compared to other types.
Of the three main submeter types shown in Table 1, the first two-feed-through and current trans-former (CT)-based (Figure 2)-are socket-type meters. CT-style socket meters are used with loads of 400A and above. In commercial applications, they may be specified but will take up a lot of space in the electrical room due to the need for CT cabinets and the meter bases. The extra space requirement cuts into the available rental space, which is undesirable in the commercial marketplace. Another major disadvantage in many jurisdictions-socket meters are not UL listed. The third type is the electronic submeter, a non-socket device that provides clear advantages over the previous two.
Since their introduction in the 1980s, submeters have grown dramatically in functionality and usefulness, providing great value to facility owners and operators as “front-line” energy data gathering tools in an era of rising utility costs and tightening budgets. Today submeters are coming out of the electrical room onto the factory floor and into building lobbies to give users, tenants, employees and others visibility on actual energy usage and its impact in terms of CO2 emissions, kWh dollars and other parameters easily understood by laymen. Submeters not only improve the facility bottom line, but facilitate implementation of building retro-commissioning projects and other energy initiatives while also encouraging every level of the enterprise to become a stakeholder in the energy management and conservation process. A new generation of advanced submeters (Figure 3) offers a number of important functions and capabilities for new construction or retrofit applications, including:
- Scrolling LCD display of kilowatt-hour (kWh) usage;
- kWh in dollars;
- Current demand load (kW);
- Cost per hour, based on current load;
- Estimated CO2 emissions in pounds, based on DOE standards;
- Estimated hourly CO2 emissions based on current load;
- Net metering, including utility-delivered vs. user-received power and net usage;
- Compatibility with pulse-output utility meters, including water, gas, BTU, steam, etc.
Figure 3. In response to EPACT 2005, EISA 2007 and other federal energy guidelines dotting the facility landscape, E-Mon and other manufacturers have developed advanced hardware and software tools that specifically address the needs of the sustainability market. Certified to ANSI C12.1 & C12.16 national accuracy standards, new-generation advanced meters like E-Mon's Green Class meter (shown here) offer a number of important functions and capabilities for new construction or retrofit applications.
Figure 5. Meter dashboards are a great way to visualize what your electrons are doing on a 24/7 basis to impact your facility's operational profile. Shown here, are comparative demand graphs for the metered lighting and HVAC panels over a three-day period, monitored in time intervals of 15, 30 or 60 minutes.
Meter dashboards for BMS energy data presentment
Where high-volume energy consumers pay for both consumption and peak demand, potentially greater savings may be realized, especially where high demand is created for short periods of time-as, for example, as the result of inefficient air conditioning or some energy-intensive device or process occurring during peak periods. If tariff rates for consumption vary based on time-of-day or season, and peak demand charges are high, on-going potential benefits may become significant. If power is being purchased under a real-time pricing tariff or contract, even greater benefits may result.
By importing data from electric submeters and other metering devices into Web-based communications (Figure 4), interval data may be cost-effectively collected, analyzed and displayed in near real-time to allow facility managers to shed load and perform other peak-shaving actions to lower their demand charges. Meter dashboards often include:
- Automobile-style gauges showing how power, fuel, energy budgets are being consumed on a real-time basis;
- 24-hour load profiles for power, chilled water, steam or other building systems;
- Historical comparisons of current usage versus previous time periods under similar conditions (time, day of week, temperature) (Figure 5);
- Automated carbon foot-print calculations;
- Tenant- or consumer-level information about energy use and efficiency efforts.
Bottom line considerations
There is no question that green building construction will continue to be a major trend across the facility landscape. An enabling technology, submeters can help facilities improve their bottom lines by benchmarking, measuring and verifying compliance with major energy initiative guidelines, while also encouraging every level of the enterprise to become a stakeholder in the energy management and conservation process. The Philadelphia skyscraper highlighted at the beginning of this paper is a textbook example of how submeter networks are helping state-of-the-art facilities support sustainability and improve energy efficiency, while optimizing tenant satisfaction and providing a very high degree of granularity in terms of visibility of the facility's total energy profile.
In addition to the direct benefits of improving operational efficiency through implementation of green practices, some states are beginning to offer tax credits for both new and renovation projects that incorporate sustainable building practices based on LEED certification levels (by scannevin). As today's facility operators face ever-tightening operational challenges, new technologies and strategies will be needed to keep pace with rising costs while, at the same time, maintaining or improving service quality levels.
One such energy strategy, performance-based contracting, can result in major cost savings with little or no up-front investment. Utilizing project-related savings to underwrite energy improvements on a pay-as-you-go basis, submetering technology can be used to identify inefficiently operating equipment, allowing repair or replacement. The cost savings realized from reducing operational inefficiencies can then be applied to other areas, including deferred maintenance or installing other energy-saving equipment or services.
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