Attaining better monitoring of energy use is one of the oldest energy management concerns. A monitoring program is necessary to determine how much energy a facility uses and to evaluate the progress of energy management measures. In order to control energy use, energy has to be measured.
Today, advances in metering technology provide managers with new tools to measure energy and to determine trends and patterns of use. New metering devices and networks provide the information needed to reduce demand, contain cost, locate opportunities to improve equipment performance, identify energy conservation measures (ECMs), and curtail use when suppliers request.
With electric deregulation expected to continue in some form, facilities that have demand-pattern and time-of-use data will be in the best position to obtain the most favorable rates. In addition, metering data must be available to forecast daily energy use for energy managers who purchase energy on day-ahead markets.
The search for the proper metering equipment can be daunting. Before starting to look for meters, managers should pause and reflect on their needs. Several questions need to be answered in this preliminary stage. For example, in a campus or multi-building enterprise, is there a need to sub-meter by departments, organizations, or tenants, or will building-level meters suffice?
Submeters can reveal how building occupants actually use energy and often help locate energy waste. Savings resulting from eliminating this waste can help pay for the meters.
In an industrial facility, is detailed usage broken down by product line required? Do meters need to be aggregated to accumulate all the energy by product or organization? Will the energy data be used to allocate utility cost to each organization, department, or profit center? Are there existing meters in the facility that need to be included in the expanded network? Is power quality data needed in addition to power usage statistics? Answers to these questions will help guide the selection process.
Older methods of dividing cost among multiple users can be unfair and unreliable. Some facilities still allocate cost on the basis of square footage. Departments with heavy loads, such as large computer users or laboratories, will be billed significantly below their measured actual use. Metering is fairer and more reliable than estimates or square-foot formulae for all parties.
Many who have installed metering systems recently have found power quality (PQ) measurement capability to be very important. Voltage sags, harmonics, or transients thus revealed may be the cause of equipment malfunctions, data distortion, or circuit breaker nuisance tripping. Savings from locating and solving these problems can quickly pay for the additional metering capability.
The characteristics and features of metering equipment need to be reviewed before the purchase. Only rugged meters should be considered for long-term (10-15 years) survival in less than spotless equipment rooms. Meters should be equipped with data ports that can be easily networked and programmed. They should provide data at a minimum of every five minutes so that the information can be used with time-of-use rates. A pager alarm feature can help avert power outages and production downtime. Many electronic power meters can be connected to an Ethernet network. Some systems provide metered data to be published to the Internet or to Intranet sites at selected intervals. The data can be viewed in summary form and in graphical views of load profiles.
Obvious locations for power meters include:
- service entrance switchboards
- panelboards
- medium-voltage circuit breakers
- medium-voltage motor starters
Additional meters should be considered for measuring:
- building lighting
- mechanical loads
- outputs of automatic transfer switches
- tenant spaces
The large quantity of data from the metering system can be analyzed and stored on a PC. Some of the features available include:
- Ethernet and Internet network capability
- task- or condition-based information collection and distribution
- historical data storage and retrieval
- rate comparison
- utility bill verification
- utility cost allocation
- bill creation for sub-metered entities
- custom report generation
- custom alarms and alerts
Case Histories
Duke University, Texas A&M University, and the University of New Mexico have installed large campus-wide metering systems. The reports of their experiences can be found in the article "Energy Metering: Costly Overhead or Cost-Effective Conservation" by John McBride (EUN, June 2002). This article can be found on the EUN web site at: www.energyusernews.com.
Metering is required of all federal ESPC (energy savings performance contracting) projects, using the measurement and verification protocol (IPMVP). The IPMVP outlines methods of verifying saving and emphasizes that savings cannot be measured-equipment performance is what needs to be measured. Option A provides the measurement of equipment performance of building energy systems before and after a retrofit and then calculates energy savings by multiplying this difference by a determined value for hours of use.
The importance of measuring energy use instead of estimating it is best understood when ESPC projects end up in litigation. Steve Sain of Sain Engineering Associates teaches measurement and verification seminars and often serves as an expert witness in ESPC lawsuits. He advises his seminar attendees, "I have never seen a case where energy savings were heavily disputed when there was significant metering data available." Sain further advises, "To avoid litigation, use reasonable and technically appropriate metering."
A number of electric utilities now provide metering services, including sub-metering and precise mapping of peak demand. In addition, some provide energy tracking for any energy resource-electricity, natural gas, or water. They can assist in the design and installation of a metering system, and many provide engineering, commissioning, training, and technical support, including maintenance.
An exciting development should reduce the cost of metering in the near future. An inexpensive (about $5 in 1000 lot quantities) energy-metering integrated-circuit device was announced in the fall of 2002. This single chip features an analog front-end with on-chip phase compensation and connects directly to current transformers (CTs). The device allows high-end, three-phase, multifunction electricity meters to measure active energy, apparent energy, and rms voltage and current. The device also performs waveform sampling. An interface allows meter manufacturers to compensate for errors introduced by external components and to digitally calibrate the device. The chip has excellent accuracy with less than 0.1% linearity error over a dynamic range of 1000 to 1.
Metering systems should be considered fundamental to any energy management program. The information gained on usage and patterns of use can be used to develop new energy savings strategies. Revenue from metered tenants, organizations, or product lines can help maintain the system. Favorable electric rates can be negotiated once the facility demand patterns and time of use data are available. Using part of the annual energy management budget, the system can be expanded each year until all buildings, systems, and tenants are metered.
Test your understanding
1. Monitoring is an important energy management strategy to:
A. determine how much energy a facility uses.
B. evaluate the progress of energy management measures.
2. In order to measure energy use, it has to be controlled.
True or False
3. Advances in metering technology provide managers with new tools to:
A. determine trends and patterns of use.
B. browse the Internet.
C. provide the energy management program with new revenue.
4. Revenue received from metered tenants can
A. drive accountants crazy.
B. help maintain the metering system.
C. be difficult to collect.
5. Before starting a search for metering equipment, managers should determine their needs.
True or False
