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
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.
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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
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Power Meter Selection Guide for Large Buildings
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.
Table 1
Power Meter
Section Categories
Incomer
PM8000 Series
PM5500 Series
PM5300 Series
PM5100 Series
EM3500 Series
Enercept
Feeder
Panelboard
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Branch Circuit
Power Meter
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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:
•
•
•
•
•
Table 2
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.
Common Power
Meter Applications
Application
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
Incomer
Feeder
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Panelboard
■
■
■
■
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Legend
All requirements & variations of application
Most requirements for application
Minimum requirements for application
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Power Meter Selection Guide for Large Buildings
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
Class 0.5
Class 1
(0.2 % accurate)
(0.5 % accurate)
(1 % accurate)
Accuracy is an important consideration for the following applications:
•
•
•
•
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Electricity bill verification
Demand management for energy cost
Power Factor management for energy cost
Tenant billing – Sub billing
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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.
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Power Meter Selection Guide for Large Buildings
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:
•
•
•
•
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Demand management for energy cost
Power Factor management for energy cost
Electrical system efficiency
Electrical monitoring of equipment
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•
•
•
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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
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Power Meter Selection Guide for Large Buildings
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.
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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.
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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.
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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 overvoltages, 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.
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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
Table 3
Long-term power
quality disturbances
Page 14
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...)
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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
Table 4
Short-term power
quality disturbances
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
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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):
¾
¾
¾
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:
PM8000 Series
Power Meter
•
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)
PM5500 Series
Power Meter
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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).
PM5100 / PM5300
Series Power Meter
Feeder power meters are also
recommended for any circuit with important
loads or specialty equipment such as:
Main Electrical Switchboard in a large building
PM3200 Series
Power Meter
•
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:
Panelboard feeding
important equipment
•
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
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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.
Electrical distribution panelboards
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:
Page 18
•
Good accuracy (at least 1.0 class meter)
•
Basic real-time electrical values (including kWh
Energy) for energy monitoring
3 phase meter
Single phase meter
iEM3200 Series
Energy Meter
iEM2000 Series
Energy Meter
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Multi-circuit meters
Branch Circuit
Power Meter
(BCPM)
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Power Meter Selection Guide for Large Buildings
Schneider Electric
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.
All requirements &
variations of application
Most requirements
for application
Minimum requirements
for application
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Application
Electricity bill verification
Incomer
Feeder
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Panelboard
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.
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Schneider Electric
Power Meter Selection Guide for Large Buildings
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.
Application
Demand management for energy cost
Incomer
Feeder
Panelboard
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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).
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Schneider Electric
Power Factor management for energy cost is best accomplished by monitoring the realtime 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.
Application
Power Factor management for energy cost
Incomer
Feeder
Panelboard
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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.
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Page 21
Schneider Electric
Power Meter Selection Guide for Large Buildings
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.
Application
Electrical system efficiency
Incomer
Feeder
Panelboard
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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.
Distorted Voltage Waveform
Harmonic waveform distortion can cause sudden problems such as:
•
•
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Inexplicable electronic component failures
Circuit breakers tripping or fuses blowing for no apparent reason
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Schneider Electric
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 phaseto-neutral voltages (Vln) as the voltage reference. These Voltage Unbalance definitions
are shown below:
NEMA
% Voltage Unbalance = maximum voltage deviation from average line-to-line voltage x 100
average line-to-line voltage
IEEE
% Voltage Unbalance = maximum voltage deviation from average line-to-neutral voltage x 100
average line-to-neutral voltage
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Schneider Electric
Power Meter Selection Guide for Large Buildings
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).
Application
Electrical monitoring of equipment
Incomer
Feeder
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Panelboard
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:
•
•
•
Page 24
Nuisance breaker tripping
Transformer overheating causing accelerated wear, aging & reduced efficiency
Motor overheating causing accelerated wear, aging & reduced efficiency
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Power Meter Selection Guide for Large Buildings
•
•
•
•
Schneider Electric
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.
Application
Root cause analysis
Incomer
Feeder
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Panelboard
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.
Application
Electrical load balancing
Incomer
Feeder
Panelboard
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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
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Schneider Electric
Power Meter Selection Guide for Large Buildings
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
Application
Electrical capacity management
Incomer
Feeder
Panelboard
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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:
•
•
•
•
•
•
Page 26
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)
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•
•
•
Schneider Electric
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
Application
Energy monitoring
Incomer
Feeder
Panelboard
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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:
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Schneider Electric
Power Meter Selection Guide for Large Buildings
•
•
•
•
•
•
•
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.
Application
Energy cost allocation
Incomer
Feeder
Panelboard
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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
Application
Tenant billing – Sub billing
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Incomer
Feeder
Panelboard
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■
© 2015 Schneider Electric. All rights reserved.
P
Power
Meter Sele
ection Guide for Large Buildings
Schne
eider Electric
Green
G
buillding standard co
ompliance
e
Bu
uilding ownerss and propertty manageme
ent companiess are becomin
ng more and more
intterested in accquiring and maintaining
m
grreen building certifications or high energ
gy
effficiency desig
gnations to inccrease buildin
ng value, reta
ain tenants an
nd reduce ann
nual
en
nergy spend.
As
s a general tre
end, there is an
a increase in
n the amount of governme
ent legislation and
reg
gulation perta
aining to build
ding energy effficiency. The
ere are also many
m
program
ms that
pro
ovide funding
g support or grant money fo
or energy efficiency projeccts that lead to
o green
bu
uilding certifica
ation or ensure that the bu
uilding meets some govern
nment energy
effficiency stand
dard or regula
ation.
Globally there are
a many gree
en building orrganizations that
t
publish energy
e
efficien
ncy
uidelines or sttandards for green
g
building
g designationss. The most popular
p
organ
nizations
gu
tha
at promote an
nd support en
nergy efficienccy and green building conccepts are:
•
•
•
•
•
•
•
•
LEED
Energyy Star
BREEA
AM
ISO500
001
NABER
RS
Green Globes
ex
Green Building Inde
Green Building Councils
Altthough there are many diffferent green building
b
stand
dards and dessignations, most of
the
em do not go beyond requ
uiring basic en
nergy meterin
ng to account for energy ussage and
on
nly some have
e specific stan
ndards or guid
delines for “co
ontinuous energy monitoring”.
As
s a general ru
ule, most gove
ernment legisslation, regula
ations and standards that pertain
p
to
en
nergy or electrical monitorin
ng only requirre basic energ
gy usage mettering for variious
typ
pes of buildings, electrical services or lo
oads. They tyypically do nott go beyond basic
b
kWh
me
etering requirrements. In so
ome cases, re
egulations ma
ay require som
me way to collect and
report on the en
nergy usage data
d
on a reg
gular or audit basis.
b
This is usually accomplished
ne of two ways: meter read
ders collect en
nergy data fro
om meters (m
manual or sem
mi-manual
on
da
ata retrieval) or
o via communicating mete
ers that are co
onnected to software
s
for au
utomatic
me
eter reading and
a reporting. Power Mana
agement softw
ware (StruxurreWare Powe
er
Mo
onitoring Expert) is ISO500
001 complian
nt and exceed
ds any standa
ards or regulattions that
stipulate continuous energy monitoring orr energy usag
ge reporting.
Applicattion
Green
G
buildin
ng standard compliance
c
© 2015 Schneide
er Electric. All rig
ghts reserved.
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LLED DISTRIBUTION
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Feeder
Panelboard
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