Power Meter Selection Guide

Power Meter Selection Guide For Large Buildings

Table of Contents

Table of Contents ............................................................................................................. 1

Introduction ....................................................................................................................... 2

Power Meter Selection Quick Reference ........................................................................ 3 Power Meter Selection Example ................................................................................. 3 Power Meter Selection Categories ............................................................................. 4 Common Power Management Applications ................................................................ 5 Important Power Meter Features ................................................................................ 6

Appendix ......................................................................................................................... 12 Energy monitoring - Why is it important? .................................................................. 12 What is energy monitoring compared to power monitoring? ..................................... 13 Power quality - What is it and why is it important? .................................................... 13 Power Meter Categories ........................................................................................... 15 Common Power Meter Applications ......................................................................... 19

Schneider Electric Power Meter Selection Guide for Large Buildings

Page 2 CONTROLLED DISTRIBUTION © 2015 Schneider Electric. All rights reserved.

Introduction Schneider Electric offers a full range of electrical power and energy metering devices from simple kWh pulse meters to programmable, high performance power quality metering devices.

The purpose of this document is to provide basic guidance with regards to selecting appropriate electrical power and energy metering devices for specific applications at the various locations in a low voltage, 3-phase / single phase electrical distribution system within a large building (e.g. office tower, shopping mall) or group of buildings (e.g. campus).

It is not intended to be a comprehensive guide that covers all aspects of electrical and power metering, but rather it is designed to make electrical meter selection as simple as possible for non-electrical experts.

Power Meter Selection Guide for Large Buildings Schneider Electric

© 2015 Schneider Electric. All rights reserved. CONTROLLED DISTRIBUTION Page 3

Power Meter Selection Quick Reference The following four sections (Power Meter Selection Example, Power Meter Categories, Common Power Meter Applications and Important Power Meter Features) are designed to make it quick and easy to select an appropriate power meter for common metering applications at typical metering points in a building’s electrical distribution system. For more information about the power meter categories, and common power meter applications, refer to the Appendix section of this document.

Power Meter Selection Example

The following illustration shows the recommended power meter categories for the various metering points throughout the electrical distribution system of a large retail building complex.

Illustration 1 Power Meter Selection Example



Power Meter Selection Categories For the purposes of this document, we have classified power meters into three basic categories based on where they were designed to be installed in the electrical distribution system of a large building or group of buildings (campus):

Incomer Incomer power meters are designed for monitoring connection points with external utility sources or local power sources such as solar, wind and distributed energy resources and are characterized by:

Feeder Feeder power meters are designed for monitoring the main distribution circuits from the main electrical switchboard in a large building or the main distribution feeders from a campus substation (multiple buildings). Feeder power meters are also recommended for any circuit with important loads or specialty equipment.

Panelboard Panelboard meters are designed for monitoring power distribution panels (distribution boards, panelboards, sub-panels, etc.) throughout the building that serve non-critical loads.

Use the following table to select an appropriate type of power meter for a given metering category. For more information about Power Meter Categories, refer to the Appendix section of this document.

Incomer

Feeder

Panelboard

Table 1 Power Meter Section Categories

PM5500 SeriesPM8000 Series

PM5300 Series PM5100 Series

EM3500 Series Branch Circuit Power Meter Enercept



Common Power Management Applications Most applications involving energy or power meters are not possible without software. Software plays a key role in common power management applications by providing the following:

• data acquisition from multiple sources for a system-wide data set • long-term storage of historical metering data in a database • business logic for virtual metering, aggregation and hierarchy definition • ability to share power management data with other systems • rich set of visualization and reporting tools

The following table lists common power management applications and indicates how well each power meter category supports the application.

Application Incomer Feeder Panelboard

Electricity bill verification ■■■ ■■ Demand management for energy cost ■■■ ■■ ■ Power Factor management for energy cost ■■■ ■■ ■ Electrical system efficiency ■■■ ■■ ■ Electrical monitoring of equipment ■■■ ■■ Root cause analysis ■■■ ■ Electrical load balancing ■■■ ■■ ■ Electrical capacity management ■■■ ■■ ■ Energy monitoring ■■■ ■■ ■ Tenant billing – Sub billing ■■■ ■■ ■ Energy cost allocation ■■■ ■■ ■ Green building standard compliance ■■■ ■■■ ■■■

All requirements & variations of application ■■■ Most requirements for application ■■ Minimum requirements for application ■

Table 2 Common Power Meter Applications

Legend



Important Power Meter Features Energy and power meters vary widely in their feature sets. The following section describes some important features and explains how they are beneficial and relate to common power meter applications.

Accuracy A fundamental property of any meter is the accuracy of the measurements it provides. However, the power meter is only one part in a series of components that sense, calculate, communicate and display electrical values including power demand (kW) and energy (kWh). In fact, every component between the electrical conductor and the electricity bill contributes to the overall accuracy of the resultant values. Important components and considerations relating to the accuracy of energy and demand values in a system include:

• Current transformer (CT) accuracy • Correct power meter wiring • Distance between CTs and power meter • Parasitic devices also connected to CT’s • Power meter measurement accuracy at low current levels • Format and scalability of communication protocol • kW and kWh are directly measured by power meter compared to calculated in

software from Volts and Amps readings • Resolution of values in software communication systems • Resolution of values in software graphical user interfaces • Correct energy aggregation for virtual metering points, net metering and in

defined hierarchies (e.g. energy by building; by area; by load type, etc.) There are international accuracy standards for power meters. The two most recognized standards for power meter accuracy are:

• IEC 62053-22/23 • ANSI C12.20

Both standards possess various “accuracy classes”. The common accuracy classes for power meters are:

• Class 0.2 (0.2 % accurate) • Class 0.5 (0.5 % accurate) • Class 1 (1 % accurate)

Accuracy is an important consideration for the following applications:

• Electricity bill verification • Demand management for energy cost • Power Factor management for energy cost • Tenant billing – Sub billing



Trend Data Logging Storing measurement values onboard a power metering device in non-volatile memory at regular intervals is an important feature for ensuring accuracy and reliability of long-term trend and billing data. Logging data onboard a power meter serves two main purposes:

• Generation of consistent and accurate trend data sets due to regular interval timestamping of the data directly by the power meter

• Buffers temporary communication loss between the device and the software reading the device

Even though many power meters offer a tremendous amount of onboard logging memory, it is rarely ever needed when power monitoring software is used to upload the onboard data. For example, StruxureWare Power Monitoring Expert and StruxureWare Power Manager software automatically scans for new data captured onboard natively supported devices (such as power meters, breaker trip units, automatic transfer switches and protection relays manufactured by Schneider Electric) and uploads the data to its database within seconds. As a general rule, data that is stored inside a power meter is not useful until it is uploaded to a software system for use and long term storage. Think of the onboard data logs inside power meters as temporary data storage buffers until the data can get transferred into the database of a software system.

Trend data logging is an important capability that is beneficial for all power management applications including:

• Electricity bill verification • Demand management for energy cost • Power Factor management for energy cost • Electrical system efficiency • Electrical monitoring of equipment • Root cause analysis • Electrical load balancing • Electrical capacity management • Energy monitoring • Tenant billing – Sub billing • Energy cost allocation • Green building standard compliance

Minimum – Maximum – Average Trending Capturing the minimum, maximum and average value for a set of measurements every logging interval is an important asset for many power meter applications because it provides a more insightful set of trend data compared to only capturing an instantaneous measurement. Having three measurements (min, max, avg) to represent what happened during a given period of time is far superior to only having a single sample measurement. A typical power meter can provide “real-time” electrical measurements (e.g. for voltage, current and power) every second or faster, so consider the difference between representing a 15 minute interval by the average of all 900 individual “real-time” measurements verses just taking a single measurement to represent the entire interval.

NOTE: 15 minutes is the most widely used evaluation interval for electric utility billing purposes and consequently it is also commonly used for power monitoring applications.



A sophisticated power meter will have an onboard clock, calendar and a large enough processor to compute minimum, maximum and average values on an ongoing basis while logging those values to non-volatile memory in the form of a detailed trend log. By contrast, basic power meters will only be able to place minimum, maximum and average values into “holding registers”. Some power meters will be able to timestamp the values and automatically reset them for a given evaluation period, but many power meters will only be able to provide these values as basic “read” registers.

Minimum, maximum and average trending provides an accurate and rich data set that is highly beneficial for the following applications:

• Demand management for energy cost • Power Factor management for energy cost • Electrical system efficiency • Electrical monitoring of equipment • Root cause analysis • Electrical load balancing • Electrical capacity management

Alarm configuration Capturing “timestamped” events in an alarm log in non-volatile memory onboard a power meter is an important capability for several power management applications. Advanced power meters have accurate clocks that may be synchronized to external signals such as Network Time Protocol (NTP), GPS or IRIG B for sequence of events recording. They also provide a wider variety of alarms (relative and absolute setpoints with dead bands and time delays) with programmable features such as the ability to associate a given alarm with a particular action (e.g. start high speed logging) or output (e.g. open a relay). Basic power meters usually only have a fixed number of pre-formatted alarms and they typically only respond to slow changes as most are not capable to detect events that occur very quickly.

The electrical parameters that are commonly monitored by onboard power meter alarms are:

• Per Phase Current (instantaneous) • Over Voltage • Under Voltage • Voltage Unbalance • Phase Loss • Over kW Demand • Total Power Factor • Over Frequency • Under Frequency • Over Voltage Total Harmonic Distortion (THD)

Configurable onboard alarms are useful for the following power management applications:

• Demand management for energy cost • Power Factor management for energy cost • Electrical system efficiency • Electrical monitoring of equipment



• Root cause analysis • Electrical load balancing • Electrical capacity management

Short-term disturbance detection Some electrical events only last for a very short amount of time and are not detected by most monitoring equipment. In order to detect and capture these “short-term” electrical disturbances, advanced power meters are required. A power meter with advanced Power Quality capabilities will have a high “sampling rate” (greater than 256 samples per cycle) in order to detect high-speed disturbances and capture the associated sinusoidal voltage and current waveforms. For more information about Short-term Disturbances, please refer the Power quality - What is it and why is it important? section in the Appendix of this document.

Short-term disturbance detection is an important feature for the following power management applications:

• Electrical system efficiency • Electrical monitoring of equipment • Root cause analysis

Additional Metering Inputs Power meters that have additional “metering inputs” on them can be used to bring in other measurements such as amount of water or natural gas consumed (usually via pulse inputs) or temperature or pressure (usually via 4-20mA or 0-1V analog inputs), for example. The meter inputs are hard wired to the “outputs” of other devices and the signals are transduced or converted to enumerated values inside the power meter. Meter inputs can be digital or analog and vary in their characteristics so it is important to ensure that the meter input used is compatible with the output it is connected to. A more advanced power meter will provide more physical inputs and provide more flexible input metering options such as unit conversion, alarming and onboard trend logging for automatic upload to power monitoring software. The benefit of additional metering inputs on a power meter is that separate I/O devices or PLC’s are not needed which simplifies the design and saves time, space and money.

Additional metering inputs are highly useful for the following power management applications:

• Electrical system efficiency • Electrical monitoring of equipment • Root cause analysis • Energy monitoring • Tenant billing – Sub billing • Energy cost allocation • Green building standard compliance



Advanced communication options Power meters that have advanced communication options can share its data in more ways and can help system architects design elegant and versatile solutions. Described below are a few of the important power meter communication options and the benefits that those features provide:

Multi-master Ethernet is the ability to allow multiple simultaneous connections from systems or devices (“masters”) over TCP/IP Ethernet. The primary benefit of this option is that meter data can be served to many systems or devices with a single Ethernet connection which saves time and money compared to wiring and configuring multiple serial communication ports. Compared to serial communications, TCP/IP Ethernet is also faster and supports multiple protocols such as:

• Data transport protocols (e.g. Modbus, BACnet) • HTTP for sharing onboard webpages via a browser • FTP for pushing data files from the device • SMTP for sending email alerts directly from the device • NTP for time synchronization of the clock inside the device • SNMP for interfacing with IT systems

In a large building, power meter data is usually served up to the Building Management System (BMS), Energy and Power Management System (EPMS) and/or the IT infrastructure monitoring system if one is present. In typical system architectures, it is very uncommon to have more than 5 masters requiring direct connections to power meters.

Ethernet daisychaining is the ability to “jumper” a series of Ethernet connected devices via Cat5 Ethernet patch cables without the need for a hub, switch or router between them. Basically, the power meter has a built-in Ethernet switch and provides an additional Ethernet port for a downstream device to use. This communication topology is simple and elegant and requires less equipment and saves time and money.



Transparent Ethernet gateway is the ability for a power meter to host Ethernet connections for downstream serially connected devices while allowing masters to poll those downstream devices directly. This communication option is highly valuable because it removes the need for installing an additional Ethernet – Serial gateway device which saves space, time and money.

Modbus Mastering in a power meter is typically used for monitoring parameters (including alarming) and creating timestamped historical trend logs for downstream Modbus devices. For some applications that require a reset, trigger or basic control, the power meter can also write to Modbus registers in downstream devices. Unlike a transparent Ethernet gateway, Modbus Mastering means that the power meter itself is polling the downstream devices and interacting directly with them via Modbus protocol. Modbus mastering is a very robust approach because it puts the application logic and data acquisition in the power meter which is faster and more reliable than using network communications back to software.



Appendix The following sections provide additional information to support the content presented in the Power Meter Selection Quick Reference at the beginning of this document. Use these sections to learn more about:

• Energy Monitoring

• Power Monitoring

• Power Quality

• Power Meter Categories

• Common Power Meter Applications

Energy monitoring - Why is it important? Given the ever-increasing prices for energy, the need to design and operate a sustainable, efficient building makes economic sense for building consultants, architects, managers and owners. Since you cannot control what you do not measure, electrical metering and sub-metering have become essential tools for addressing today’s energy efficiency and reliability requirements.

Understanding how to benchmark and monitor the efficiency of a facility's energy design is important. Adopting a holistic solution helps makes it possible to understand how a facility is performing, not only across its many infrastructure services (including mechanical, electrical, security and IT) but also down to the sub-building level.

Monitoring energy consumption is the foundation for conserving energy. Knowing how (and how much) energy is used by different areas of a facility, and by different systems, enables facility owners and operators to identify opportunities for Energy Conservation Measures (ECMs).

The approach of energy metering is to monitor energy flow into a facility, energy flow out of a facility, and where energy has been used inside the facility.



What is energy monitoring compared to power monitoring? In simple terms, energy monitoring is concerned with understanding and managing energy usage primarily for reducing energy consumption and increasing energy efficiency. Energy monitoring is diverse and can include the measurement of water, air, gas, electricity and steam (WAGES) usage. As a result, there are many different types of measurement devices and a wide variety of techniques to measure, calculate, collect, display and share energy data. Continuous energy monitoring is critical part of the energy management lifecycle for maintaining a high degree of energy efficiency and for making informed business decisions related to energy spend.

Power monitoring is a specialized discipline focused on managing electrical distribution systems primarily for maximizing the efficiency and reliability of the electrical infrastructure within a facility. Power monitoring utilizes electrical power metering devices for measuring the quality and quantity of power flowing through a given part of the electrical system.

Power monitoring systems are also designed to help identify which building systems or pieces of equipment are contributing most to electrical energy waste. They play an important role in maximizing efficient day-to-day operations by providing visibility of the real-time properties of the electrical supply throughout a building. When building management, operations and maintenance teams can see how different building systems and equipment affect the electrical system and how different systems and equipment affect each other electrically, they can detect and resolve problems more quickly, minimize electrical waste and operate the building more efficiently in general.

In most cases, power monitoring systems are well-equipped to do energy monitoring, whereas many systems (BMS, EMS, SCADA) that offer energy monitoring functions do not have power monitoring capabilities.

Power quality - What is it and why is it important? In an ideal three phase power system, the voltages are at their nominal magnitude, at their nominal frequency, perfectly balanced and with a perfect sinusoidal waveform. Any disturbance on one of these parameters (magnitude, frequency, waveform, symmetry) is classified as a power quality problem. Power quality problems are among the main causes for business downtime, equipment malfunction, and equipment damage.

There are a number of different power quality disturbances; all of them can have a negative impact on the electrical system and equipment. However, regarding their nature and their impact, power quality problems can be separated into two broad classes:

• Long-term disturbances, including harmonics, unbalance, under- and over-voltages, frequency variations, voltage variations (flicker), and power factor.

• Short-term disturbances, including transients and short-duration voltage variations, with duration inferior to 1 minute as defined by IEEE 1159-1995.



Long-term disturbances Long term power quality disturbances include steady state disturbances, such as voltage and current unbalance and harmonics, long-duration variations (under voltages and over voltages), and also intermittent voltage or frequency variations. The effect of this type of power quality disturbance is often quite negative: equipment failure, malfunction, overheating and damage.

Disturbance category Waveform Effects Possible causes

Under voltage Shutdown, malfunction,

equipment failure Load changes, overload, faults

Over voltage Equipment damage and

reduced life Load changes, faults, over compensation

Harmonics Equipment damage and reduced life, nuisance breaker tripping, power losses

Electronic loads (non-linear loads)

Unbalance

Malfunction, motor damage

Unequal distribution of single phase loads

Voltage fluctuations

Light flicker and equipment malfunction

Load exhibiting significant current variations

Power frequency variations

Malfunction or motor degradation

Standby generators or poor power infrastructure

Power Factor *

Increased electricity bill, overload, power losses

Inductive loads (ex. motors, transformers...)

Table 3 Long-term power quality disturbances



Short-term disturbances Short term power quality events regroup voltage dips, swells and interruptions, usually associated with system fault conditions, as well as voltage transients, due mainly to lightning strikes and switching operations (capacitors banks, tap changing transformers). Short term power quality events have usually a visible and immediate impact in the electrical installation. Voltage dips and interruptions result in unscheduled downtime. Voltage swells and transients cause malfunction, damage, and reduced efficiency of electric equipment.

Disturbance category Waveform Effects Possible causes

Transients Equipment malfunction and damage

Lightning or switching of inductive / capacitive loads

Interruption Downtime, equipment damage, loss of data possible

Utility faults, equipment failure, breaker tripping

Sag Downtime, system halts, data loss

Utility or facility faults, startup of large motors

Swell Equipment damage and reduced life Utility faults, load changes

Power Meter Categories Electrical power and energy meters vary considerably in terms of form factor and functionality. In their most basic form, they only display one value. They may also have a pulse output which can be physically wired to a different device for counting and converting the pulses into an enumerated value, but they do not have a true communications port for connectivity over a network. These simple devices are referred to as single function meters. For example, a single function volt meter only provides voltage readings and a single function kilowatt hour meter only provides kWh readings.

More sophisticated metering devices provide a variety of measurements such as volts, amps, kilowatts and kWh. These devices are referred to as multi-function meters. Inherently, electrical multi-function meters are power meters since they measure basic electrical parameters and provide more than just a kWh reading. Most multi-function power meters also provide kWh energy readings so they may be used for both power and energy monitoring applications.

When designing an electrical metering system for a large building, it is important to know the overall layout of the electrical distribution system and the nature of the various different loads that are intended to be connected to each circuit.

The most important part of a building’s electrical system is the main electrical switchboard. This piece of equipment is designed to safely distribute a main 3-phase electrical service into smaller 3-phase feeder or distribution circuits for further distribution to transformers, panelboards, control equipment and eventually to the individual 3-phase and single phase loads throughout the building. The main switchboard not only provides electrical switching and over current protection but it is also the most critical location to

Table 4 Short-term power quality disturbances



place power metering devices for monitoring the main distribution feeders that serve all of the loads in the building.

It is also important to have electrical metering points established at every electrical panelboard (also called sub-panels or distribution panels) to ensure visibility of the power flow and energy consumption throughout the building. Metering at this level of the electrical system is known as sub-metering and it is an essential part of any power and energy management system.

Other locations that are important to meter include all interfaces with major electrical sources that can supply electricity to the buildings electrical distribution system. The obvious example is the main utility incomer(s), but nowadays it is not uncommon to also have alternative local sources of electricity such as solar, wind and distributed energy resources including generators.

For the purposes of this document, we have classified power meters into three basic categories based on where they were designed to be installed in the electrical distribution system of a large building or group of buildings (campus):

Incomer Feeder Panelboard (including multi-circuit metering)

Incomer Incomer power meters are designed for monitoring connection points with external utility sources or local power sources such as solar, wind and distributed energy resources and are characterized by:

• High accuracy (0.2 class meter) to be equal or better than the utility meter • High sampling rate (256 or higher samples per cycle) for accuracy, individual

harmonics and to capture high resolution waveforms of high speed Power Quality events

• Short-term disturbances (transients, interuption, sag, swell) • Long-term disturbances (under voltage, over voltage, harmonics, unbalance,

voltage fluctuations, power frequency variations, power factor) • Onboard logging with device timestamp for reliable and accurate capture of

historical trend data and Power Quality waveforms in non-volatile memory in case of loss of communications to device

• Onboard alarming with device timestamp for reliable and accurate capture of events including short-term and long-term Power Quality disturbances for diagnostics and root cause analysis purposes

• Inputs to bring in additional energy measurements (WAGES) from other devices or to monitor status of breakers and other equipment

• Outputs to share energy pulses with external sources or alarm status • Communication Gateway function that supports a RS-485 serial daisy chain to

host communications to downstream devices (eliminates the need for an additional, separate communication gateway device)

PM8000 Series Power Meter




Feeder Feeder power meters are designed for monitoring the main distribution circuits from the main electrical switchboard in a large building or the main distribution feeders from a campus substation (multiple buildings).

Feeder power meters are also recommended for any circuit with important loads or specialty equipment such as:

• Chillers • IT load and its supporting equipment

(UPS, cooling, etc.) • Water pumps, sump pumps, etc. • Motor control centers • Laboratories • Emergency lighting • Fire Detection • Elevators • Refrigeration

Feeder power meters are characterized by:

• Good accuracy (0.5 class meter) • Long-term disturbances (under voltage, over voltage, harmonics, unbalance,

power factor) • Onboard logging with device timestamp for reliable and accurate capture of

historical trend data in non-volatile memory in case of loss of communications to device

• Onboard alarming with device timestamp for reliable and accurate capture of events including most long-term Power Quality disturbances for increasing power quality awareness and diagnostic purposes

• Inputs to bring in additional energy measurements (WAGES) from other devices or to monitor status of breakers and other equipment

• Outputs to share alarms status or energy pulses with external sources

Main Electrical Switchboard in a large building


Panelboard feeding important equipment

PM5100 / PM5300 Series Power Meter



Panelboard Panelboard meters are designed for monitoring power distribution panels (distribution boards, panelboards, sub-panels, etc.) throughout the building that serve non-critical loads such as:

• Non-emergency lighting • Room receptacles • Appliance loads for cafeteria

Panelboard meters come in a wide variety of form factors. Some panelboard meters are installed directly inside the panelboard and some are installed beside the panelboard in a separate enclosure.

Standard single-circuit panelboards meters only monitor a single circuit such as the 3 phase service coming into the panelboard or an individual circuit leaving the panelboard.

In additional to single-circuit panelboard meters, there are also multi-circuit meters that are specially designed to measure all of the individual circuits leaving the panelboard. Basic multi-circuit meters only measure the current of individual circuits but more advanced multi-circuit meters measure both the main service into the panel and all of the outgoing circuits regardless whether they are 3 phase, 2 phase or single phase circuits.

Panelboard meters are often installed for energy monitoring and sub-billing (e.g. tenant billing) purposes and are characterized by:

• Good accuracy (at least 1.0 class meter) • Basic real-time electrical values (including kWh

Energy) for energy monitoring

iEM3200 Series Energy Meter

Branch Circuit Power Meter

(BCPM)

Electrical distribution panelboards

Multi-circuit meters3 phase meter Single phase meter

iEM2000 Series Energy Meter



Common Power Meter Applications The following paragraphs are descriptions of the common power meter applications listed in Table 2:

Electricity bill verification Electricity bill verification is the process of inspecting the utility electricity bill for errors and incorrect charges. It is not uncommon for utility bills to contain significant mistakes and incorrect charges. Most mistakes go unnoticed and therefore unreconciled.

If a revenue accurate (0.2 Class accuracy) power meter is installed on the main service entrance of a large building alongside the utility billing meter (sometimes referred to as a “Shadow Billing” meter), it can be used to capture energy, demand and power factor readings that can be used to verify that the utility electricity bill is in fact correct. It is important that the Shadow Billing meter is at least as accurate as the utility meter and has the ability to timestamp the data while logging energy, demand and power factor especially when Time of Use (TOU) is applied in the utility tariff schedule. Detecting and reconciling significant mistakes in utility electricity bills often has a good return on investment, especially in the long run and typically pays for the cost to have a shadow billing meter installed many times over.

Power Management software (Power Manager for SmartStruxure solution or StruxureWare Power Monitoring Expert) is highly recommended for bill verification applications since it automatically captures all the necessary billing from the shadow billing meter into a SQL Server database, applies the rate schedule logic and presents the billing data is a way that is easy to compare to the actual utility electricity bill.


Electricity bill verification ■■■ ■■

Demand management for energy cost Often one of the largest components of an electricity bill is the “demand charge”. Electrical demand is the amount of power delivered in a given demand interval. Demand charges are typically based on “peak demand” which is the largest amount of power used in any given demand interval in the billing period. The most common demand interval is 15 minutes but it can vary depending on the region, the utility or the specific rate schedule. The most common demand measurement is kW demand (active power demand) but some rate schedules may specify kVA demand (apparent power demand) or even kVAr demand (reactive power demand).

Demand management is the process of operating a large building with the intent to keep the “peak demand” as low as possible each billing period. This is only accomplished with an understanding of the loads in the building and by continuously monitoring the power consumption throughout the electrical distribution system, especially at the main incomer(s) into the building where the total demand for the building is measured.

All requirements & variations of application ■■■ Most requirements for application ■■ Minimum requirements for application ■



Even though many power meters can capture and display a “peak demand” value, demand management is best accomplished by monitoring the real-time power flow throughout the building so that it is clear which circuits and which loads are contributing most to the building’s total power usage at any given moment. This way, facility management teams can operate the systems and equipment in a building such that the large loads are not drawing power at the same time and the building’s total demand is actively managed relative to its typical peak demand.

For demand management, is it recommended that the incomer and feeder meters capture power demand every interval and log the timestamped values into non-volatile onboard memory in case communications are temporarily lost to the meter. It is also desirable if the meters are as accurate as possible and they have the ability to timesynch their onboard clocks to an external clock source to ensure the interval timestamps are as close to the utility billing meter clock as possible.

In most cases, power meters are not enough; Power Management software (Power Manager for SmartStruxure solution or StruxureWare Power Monitoring Expert) is highly recommended for demand management applications since it not only acquires the demand interval data automatically, but it also provides the visualization tools necessary to actively manage a building’s total demand based on its constituent loads in real-time. Demand management is an active, real-time process. Once a new peak demand threshold is hit, it is too late. This will be reflected in the electrical utility bill.

Power Factor management for energy cost Many electrical utilities have tariff schedules that stipulate penalties if a facility or large building cannot maintain power consumption efficiency (i.e. Power Factor) above a given level. Similar to a “demand charge”, a “Power Factor penalty” may be a significant amount on the electricity bill, so it may be well worth installing power meters for greater visibility of the power consumption efficiency of the circuits and loads in a building in order to keep the building’s total Power Factor above the penalty limit.

Power Factor management for energy cost is the process of operating a large building with the intent to keep the total Power Factor better than a specified level for all intervals during the billing period to ensure that a “Power Factor penalty” is not applied to the electricity bill.

It is important that the reference meter(s) used for measuring a buildings total Power Factor is at least as accurate as the utility meter and has the ability to timestamp the data while logging energy, demand and power factor especially when Time of Use (TOU) is applied in the utility tariff schedule.

Even if the building’s electrical tariff schedule does not stipulate a Power Factor penalty, maintaining a high Power Factor level is beneficial because it means energy is being consumed in an efficient manner and it is not being wasted (see Electrical system efficiency for more information about Power Factor and how it relates to wasted energy).


Demand management for energy cost ■■■ ■■ ■



Power Factor management for energy cost is best accomplished by monitoring the real-time Power Factor throughout the building so that it is clear which circuits and which loads are contributing most to the building’s total Power Factor at any given moment. This way, facility management teams can operate the systems and equipment in a large building such that Power Factor correction equipment is installed where necessary and the building’s total Power Factor is actively managed to avoid Power Factor penalties on the electricity bill. For these reasons, Power Management software (Power Manager for SmartStruxure solution or StruxureWare Power Monitoring Expert) is highly recommended because it provides the system level views for real-time conditions and automatic interval data acquisition for historical analysis and comparisons to help ensure that Power Factor levels are maintained and Power Factor penalties are avoided.

Electrical system efficiency The physical design of an electrical distribution system (transformers, ties, switches, relays, switchboards, panelboards, conduit and conductors) and the systems and equipment connected to it (HVAC, lighting, variable speed drives, motors) contribute most to how efficient or inefficient an electrical system can be. However, electrical systems are not static; they are dynamic. As a result, electrical energy waste can be difficult to isolate as it fluctuates according to what is happening in a building at any given moment.

The efficiency of an electrical system can be measured in different ways, but the simplest and most common method is to monitor something called Power Factor. Power Factor is a simple ratio of useful power (to do work) to the amount of total power delivered. The technical term for useful power is “Active” power. Active power is most commonly measured in kiloWatts (kW). Total delivered power is referred to as “Apparent” power. Apparent power is most commonly measured in kiloVoltsAmps (kVA). This means that Power Factor is the ratio of kW to kVA.

A Power Factor of 1 indicates that the electrical supply is a perfect sinusoidal waveform with the voltage and current perfectly aligned. This state is known as “unity”. The closer to unity, the more efficient the electrical system is. However, unity is mostly a theoretical state since a real electrical system cannot operate at unity.


Power Factor management for energy cost ■■■ ■■ ■



Power Factor is expressed as a percentage or decimal. For a typical building in which the loads are mostly inductive, Power Factor will be a negative value between -0.80 (-80%) and -0.98 (-98%). A Power Factor of 0.98 (-98%) is extremely good. Power Factor above -0.80 (-80%) indicates considerable levels of electrical energy waste and should be investigated.

Most power meters provide Power Factor measurements. What is most important is to have Power Factor measurements available throughout the entire electrical distribution system so that inefficiencies and problems may be detected and located quickly.

Electrical monitoring of equipment It is important to monitor the properties of electricity that flows through electrical distribution equipment (e.g. transformers, breakers) and at the connection points to the loads that consume electrical power (HVAC equipment, lighting, motors, appliances, panel boards). This is because these pieces of equipment can cause damaging electrical effects or be themselves damaged by the quality of the power it is conveying or consuming. To determine which pieces of equipment are causing electrical problems and which ones may be damaged by poor power quality, it is recommended to install a continuous power monitoring system with power meters in all the right places in the electrical distribution system. Temporary or portable power metering can often detect some issues but it will not provide the continuous feedback over time as loads change and equipment ages.

Many types of equipment (especially non-linear loads such as electronic ballasts, computer power supplies, arc furnaces, variable frequency drives, DC drives, soft starters, UPS’s) draw electrical power in such a way that they cause something called “harmonics” which distort the fundamental sinusoidal waveform of the electricity.

Harmonic waveform distortion can cause sudden problems such as:

• Inexplicable electronic component failures • Circuit breakers tripping or fuses blowing for no apparent reason


Electrical system efficiency ■■■ ■■ ■

Distorted Voltage Waveform



Harmonic distortion can also cause chronic issues such as:

• Overheating electrical cables (conductors), transformers and motors • Degradation of insulating materials in conductors, transformers and motors • Shortened life span of electronic equipment

Harmonic distortion is measured by most power meters in the form of a parameter called Total Harmonic Distortion (THD). THD is a measurement that summarizes the total amount of electrical waveform distortion. THD is expressed as a percentage, with higher % THD values representing more waveform distortion and greater potential inefficiencies in the electrical system. THD is measured for either the voltage waveform (VTHD) or the current waveform (ITHD).

The most recognized standard that describes acceptable levels of harmonics for an electrical power system is published by the Institute of Electrical and Electronics Engineers (IEEE) and is called IEEE-519 1992. The principal goal of the standard is to limit Voltage THD (VTHD) levels to below 5% so that equipment is not damaged or malfunctions, but also so that the utility electrical supply is not polluted with harmonics affecting other nearby electricity consumers.

Another electrical parameter that is important to measure when monitoring equipment is something called Voltage Unbalance (V Unbal). In a stable, balanced 3-phase electrical system, the voltage of each phase should be the same. Voltage unbalance is when the phase voltages start to deviate from each other. This is most often caused by unbalanced single phase loads drawing different amounts of current on each phase of a 3-phase panelboard. This is why it is important to monitor and balance loads in an electrical system (see Electrical load balancing for more information), because it can easily lead to systemic voltage unbalance in the system. Voltage unbalance can also be caused by a Power Factor correction bank with a blown fuse or bad capacitor or unbalanced (impedance does not match) transformer banks.

Voltage Unbalance is worth monitoring since it contributes to premature equipment aging (especially 3-phase induction motors), causes power supply ripple and generates excess heat which can lead to significant insulation degradation (inside transformers, conductors, motors).

Voltage Unbalance is measured as a percentage of the largest difference between any individual phase/line voltage and the average phase/line voltage. NEMA (National Equipment Manufacturer’s Association) uses line-to-line voltages (Vll) to define voltage unbalance whereas IEEE (Institute of Electrical and Electronics Engineers) uses phase-to-neutral voltages (Vln) as the voltage reference. These Voltage Unbalance definitions are shown below:

% Voltage Unbalance = maximum voltage deviation from average line-to-line voltage x 100

average line-to-line voltage

% Voltage Unbalance = maximum voltage deviation from average line-to-neutral voltage x 100 average line-to-neutral voltage

NEMA

IEEE



In the majority of cases, Voltage unbalance can be corrected by redistributing and balancing single phase loads in panelboards. In some cases, unbalance correction may require voltage correction capacitors, power conditioners or capacitor voltage transformers (CVTs).

Monitoring the THD and Voltage Unbalance that flows through electrical distribution equipment (e.g. transformers, breakers) and at the connection points to the loads that consume electrical power (HVAC equipment, lighting, motors, appliances, panel boards) is a fundamental capability of any Power Monitoring System and is useful in determining which pieces of equipment may be causing electrical problems and which ones may be damaged by poor power quality. Many different issues may be detected and even corrected using this basic monitoring information, however; pinpointing the specific cause of an electrical problem and resolving it efficiently (fast and cost effectively) typically requires more advanced data collection and diagnostic analyses (see Root cause analysis of electrical and equipment problems for more information).

Root cause analysis of electrical and equipment problems Root cause analysis of electrical and equipment problems is the process of confirming the specific cause of an issue through high speed detection, specialized data collection and diagnostic troubleshooting techniques. Lots of electrical infrastructure and equipment problems are related to the quality of electrical flow into and throughout a building and the power quality supply in the circuits feeding equipment. Many of these problems go undiagnosed which leads to longer periods of downtime, slow recovery times and in some cases unnecessary equipment replacement.

Electrical infrastructure issues and equipment problems are typically caused by one of seven common electrical disturbances:

• Transients • Interruption • Sag • Swell • Waveform distortion - Harmonics • Voltage fluctuations • Power frequency variations

Root cause analysis of electrical infrastructure and equipment is a more advanced application that goes beyond basic electrical system efficiency and electrical monitoring applications. Power Factor, THD or Voltage Unbalance are all good indicators of electrical infrastructure issues or equipment problems, but these measurements alone do not provide enough information to determine the cause(s) and effect(s) of specific problems. Common problems include:

• Nuisance breaker tripping • Transformer overheating causing accelerated wear, aging & reduced efficiency • Motor overheating causing accelerated wear, aging & reduced efficiency


Electrical monitoring of equipment ■■■ ■■



• Electronic equipment malfunction or failure • Reduced occupant health and productivity due to subtle flickering of lights • Generators fail to synchronize and supply stable back up power • Power losses and safety concerns related to excess current and heat in the

neutral conductors

For root cause type applications, programmable Power Meters with high speed power quality detection, onboard logging capabilities are needed because many electrical issues occur very suddenly and temporarily and would otherwise go undetected by a typical electrical energy meter. Advanced Power Quality power meters (like the PM8000 Series and PM5500 Series meters) are specifically designed for root cause analysis and are most beneficial when installed at the main incomers to the facility, on the main distribution circuits (feeders) leaving the main switchboard in the building as well as on circuits that feed important, sensitive or expensive pieces of equipment.

Electrical load balancing In any large building, there are a mixture of 3-phase loads (HVAC equipment, lighting, motors), 2-phase loads (small compressors, dryers, large appliances) and single phase loads (receptacles, electronics). Load balancing is a simple concept but challenging to implement and maintain since different loads operate at different times. It also requires a detailed understanding of the impact that each load type has on the local circuit and the larger distribution circuits upstream. Unbalanced loads not only waste energy but also cause waveform distortion (harmonics), voltage unbalance and excess current in the neutral bus which is often the cause of many electrical infrastructure and equipment problems. Maintaining balanced loads in an electrical system is the single best way to ensure electrical system health and efficiency.

Load balancing in its most basic form requires real-time and historical power usage information from all phases of the circuits that feed a switchboard, distribution panel or panelboard. Since unbalanced loading of electrical panels causes harmonics, voltage unbalance and excessive current, it is recommended to use power meters that measure and capture these parameters as well.

Electrical capacity management Electrical capacity management is similar to electrical load balancing, but is more focused on ensuring that the total potential loading of any given circuit will not exceed its rated capacity or circuit breaker trip levels. This is done by monitoring current levels


Root cause analysis ■■■ ■


Electrical load balancing ■■■ ■■ ■



throughout the electrical system and managing loads relative to a circuit rating baseline. Electrical capacity management is a fundamental application that helps prevent:

• downtime due to breaker trips • energy waste • over specification of equipment (over building) • unbalanced loading in panels • overloading of circuits • underutilized circuits

Energy monitoring In simple terms, energy monitoring is concerned with understanding and managing energy usage primarily for reducing energy consumption and increasing energy efficiency. Energy monitoring is diverse and can include the measurement of water, air, gas, electricity and steam (WAGES) usage. As a result, there are many different types of measurement devices and a wide variety of techniques to measure, calculate, collect, display and share energy data. Continuous energy monitoring is critical part of the energy management lifecycle for maintaining a high degree of energy efficiency and for making informed business decisions related to energy spend.

Energy monitoring is a process that evolves. It starts with establishing energy consumption “baselines” (typical energy usage profiles) and then progresses to monitoring energy usage against those baselines and/or energy reduction targets. For electrical energy monitoring applications, kWh is usually the only parameter that needs to be metered. For this reason, advanced power meters are not required; any energy or power meter that provides kWh readings is adequate.

However, energy monitoring cannot be accomplished with metering alone. Software is required to:

• capture historical energy usage data from multiple sources • aggregate, normalize and compare energy usage data • provide visualization and reporting tools to actively monitor energy usage

Power Management software (Power Manager for SmartStruxure solution or StruxureWare Power Monitoring Expert) is highly recommended for energy monitoring applications because it is designed to acquire interval energy data from multiple sources and provides a rich set of tools for:

• energy period over period • energy comparison • energy breakdown • energy performance • total energy monitoring using common energy units (e.g. MMBTU, kWh, kJ) • energy normalization (building area, temperature, occupancy, time of day)


Electrical capacity management ■■■ ■■ ■



• energy by load type (HVAC, lighting, appliances [ovens, dryers, motor loads [escalators, elevators, pumps, compressors], IT loads and power receptacle loads [single phase loads])

• real-time “energy alarms” • regression analysis for correlating energy usage to other variables

Energy cost allocation More and more, businesses are becoming focused on the cost of energy and they want to manage their operations in terms of energy spend and not just energy usage. Energy cost allocation is the process of measuring energy usage and then calculating or estimating the cost of energy used for a given area, department, process, system, load type or piece of equipment. Energy cost allocation would be straight forward if the areas, departments, processes, systems, load types or pieces of equipment consumed a single energy source (water, air, gas, electricity, steam) and were individually and entirely metered. But in reality, this is never the case, so software is needed. It is inevitable that the areas, departments, processes, systems, load types or pieces of equipment in a large building are fed by or share various electrical circuits and consume more than one type of energy. As a result, cost allocation applications require software to provide the calculations and business logic for accurate estimation of the true cost of energy for a given entity within a facility. Software designed for cost allocation applications will support the following:

• support for any energy measurement type • energy unit conversion • energy aggregation within a defined hierarchy • net metering (difference between two meters) • apportionment (% of metered usage allocated)

Another significant consideration for energy cost allocation applications is the nature of the utility rates that will need to be applied to convert energy consumption into cost. Energy cost calculations/estimations are simplest when the charge for energy is a “flat rate” or a “blended rate” per unit of energy used. In this case, energy cost is a simple multiplier of energy usage. Most utilities still apply a simple flat rate when charging for water or natural gas usage, but electric utilities rarely use flat rate charges today. Electric utilities usually have a variety of rate structures depending on the voltage service level, size and type of facility. These “tariff schedules” can be very complex and almost always include charges for electrical consumption (kWh) and power demand (kW) (see Demand management for energy cost) and have different rates depending on the time of day (also known as ‘Time of Use’ [TOU]) or the peak demand or total usage. Many tariff schedules also include stipulations about maintaining Power Factor levels or the rate changes or a penalty is imposed (see Power Factor management for energy cost for more information). Due to the complex nature of electricity rate structures, cost allocation applications often require specialized software capable of applying electricity utility rate concepts such as:


Energy monitoring ■■■ ■■ ■



• total peak demand • ratchet demand • coincident demand • Power Factor • Time of Use • energy resets • energy roll over

Power Management software (Power Manager for SmartStruxure solution or StruxureWare Power Monitoring Expert) is highly recommended for energy cost allocation applications because it is designed acquire interval energy data from multiple sources (including power demand and power factor from electrical power meters) and can correctly allocate energy usage and then accurately calculate allocated energy cost since it supports most complex utility rate structures. Tenant billing – Sub billing Tenant billing or sub-billing is a specialized form of cost allocation (see Energy cost allocation for more information). It involves accurately calculating energy consumption for tenants or entities within a facility (departments, cost centers) and providing a statement, invoice or report of energy usage in terms of cost or money owed. Tenant and sub-billing applications vary widely in sophistication and scale. The most important considerations when selecting an electricity meter for tenant billing is the meter accuracy, onboard logging (data reliability and integrity) and power demand and power factor measurements (if required for the rate structure).

Software is almost always needed for tenant sub-billing applications because tenants are often fed by or share various electrical circuits and consume more than one type of energy. Tenant billing software provides the business logic for accurate estimation of the true cost of energy for a given tenant or entity within a building and is designed to support:

• any energy measurement type • energy unit conversion • energy aggregation within a defined hierarchy • net metering (difference between two meters) • apportionment (% of metered usage allocated) • tenant move in – move out


Energy cost allocation ■■■ ■■ ■


Tenant billing – Sub billing ■■■ ■■ ■

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