ASHRAE Journal - April 2011 - 21

for tripped breakers, which expose them to arc flashes and other dangers. Meters also eliminate guesswork and save time by quickly pinpointing problems.

New vs. Existing Buildings
In a new building, design engineers have an opportunity to assess and specify the latest technologies. The staff is unencumbered by existing systems, but will need training on the new metering system. New metering systems offer interoperability with other systems (such as energy management systems and building management systems) because engineers can design them to operate on platforms based on open standards. In addition, a new installation requires all new energy meters and possibly a separate network to process the data from these meters. As a result, the initial investment is greater than it would be to just add points to an existing system. In an existing building, installing additional energy monitoring points may reduce overall costs because the equipment and network are already in place. However, equipment interoperability may become an issue when adding new points. If an existing power monitoring system operates smoothly, it offers proven, known value. System expansion, however, may be complicated by the need to install system-compatible metering points. The use of noncompatible metering devices could lead to limited functionality (e.g., one brand of meter data management software may not be able to read the advanced registers in a different brand of meters).

ally billing them for their energy use—can be an effective way to promote energy conservation and help control costs. Intelligent metering systems enable building owners to take advantage of demand management opportunities (e.g., utility company incentives to prechill a building or reduce energy consumption during peak periods) and to calculate needs based on historical records. They also validate energy conservation measures, enabling design engineers or building engineers to build a business case for purchasing new equipment or modifying an existing system.

Justifying the Cost of a Metering System
Not every facility warrants a metering system, and a simple way to cost-justify a utility meter was developed by the U.S. Department of Energy:
   Installed Cost  + Annual Cost      Minimum Annual  Desired Simple Payback   =  Electric Bi ll % Annual Savings

Goals of Energy Metering
The rationale for installing energy meters is twofold: to control energy consumption/costs and to improve equipment energy use/reliability.

where Installed Cost is the total cost to purchase, install and commission the meter. Desired Simple Payback represents the number of years it will take the metering system to produce the cost savings equal to the installed cost. In the federal sector, the simple payback period should be 10 years or less. Annual Cost is the total annual cost of the fees and expenses to cover communications, data collection and storage, data analysis, as well as meter operations and maintenance. Percent Annual Savings is the estimated cost savings benefits to be realized from the productive use of the metered data (typically a minimum of 2%).

Controlling Energy Consumption and Costs
The savings realized by a metering program depend largely on the actions taken with the meter data. Estimates of energy savings have ranged from 1% to 20%, depending on the application of the metering systems (Table 1). The low-end savings of 0% to 2% is generally attributed to the “Hawthorne Effect,” a phenomenon whereby individual behaviors may be altered as a result of the individuals knowing that they are being studied. These savings quickly erode if the occupants realize that the meter data is not being used. To maximize energy savings, the meter data must be used to drive action. Managing equipment based on real-time needs helps maximize the efficiency of building equipment and systems. For instance, turning off certain equipment after-hours will conserve energy and eliminate unnecessary costs associated with operations and maintenance. Time of use or load shifting impacts energy use by staggering when systems start and when they perform certain operations (e.g., precooling a building during off-peak periods). Allocating costs based on consumption—whether the information simply raises awareness among users rather than actuApril 2011

Improving Equipment Use and Reliability
Modern mechanical systems (e.g., chillers, compressors, VFDs, lighting ballasts) generally rely on advanced electronics for their control and operation. Because electronics are sensitive to power quality, mechanical systems may be adversely affected by over- and under-voltage, surges, spikes, transients and harmonics. Advanced submetering systems detect these damaging, power quality events and alert system operators so they can take remedial action before damage occurs. Building and design engineers can improve equipment use by accurately measuring how much equipment and electrical capacity are required for optimum building operation. “Right sizing” mechanical and electrical systems enables engineers to not only improve system efficiencies, but also to better manage utility costs and possibly delay capital expenditures for replacement or expansion systems until absolutely necessary.

Specifying the Right Meter
Energy travels from a utility company’s power supply into a facility’s electrical distribution (ED) system, with the energy handoff occurring at a “service entrance.” In a large commercial building, the service entrance typically sends the high-voltage
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ASHRAE Journal - April 2011

Table of Contents for the Digital Edition of ASHRAE Journal - April 2011