386 Energy Project Financing: Resources and Strategies for Success
It is recommended that power measurement equipment meeting
the IEEE Standard 519-1992 sampling rate of 3 kHz be selected where
harmonic issues are present. Most metering equipment has adequate
sampling strategies to address this issue. Users should, however, request
documentation from meter manufacturers to ascertain that the equipment
is accurately measuring electricity use under waveform distortion.
Power can be measured directly using watt transducers. Watt-hour
energy transducers that integrate power over time eliminate the error
inherent in assuming or ignoring variations in load over time. Watt-
hour transducer pulses are typically recorded by a pulse-counting data
logger for storage and subsequent retrieval and analysis. An alternate
technology involves combining metering and data logging functions
into a single piece of hardware.
Hand-held wattmeters, rather than ammeters, should be used for
spot measurements of watts, volts, amps, power factor or waveforms.
Regardless of the type of solid-state electrical metering device
used, it is recommended that the device meet the minimum perfor-
mance requirements for accuracy of the American National Standards
Institute standard for solid state electricity meters, ANSI C12.16-1991,
published by the Institute of Electrical and Electronics Engineers. This
standard applies to solid-state electricity meters that are primarily used
as watt-hour meters, typically requiring accuracies of one to two percent
based on variations of load, power factor and voltage.
RUNTIME
Determination of energy savings may involve measuring the time
that a piece of equipment is on, then multiplying it by a short-term power
measurement. Constant load motors and lights are examples of equipment
that may not be continuously metered with recording watt-hour meters to
establish energy consumption. Self-contained battery-powered monitor-
ing devices are available to record equipment runtime and, in some cases,
time-of-use information. This equipment provides a reasonably priced,
simple to install approach for energy savings calculations.
TEMPERATURE
The most commonly used computerized temperature measure-
ments devices are resistance temperature detectors (RTDs), thermo-
couples, thermistors, and integrated circuit (IC) temperature sensors.