Energy Auditing involves using various measuring equipment depending on the investigation being carried out. In order to fully understand energy auditing it is imperative to have some idea of the equipment that is used and the various parameters being measured.
We have divided this into four categories: –
- Electrical Measurement
- Temperature Measurement
- Exhaust Gas Measurement
- Speed of Rotating Equipment
Electrical Measurement
For measuring the electrical parameters the following instrumentation are included:
1. Ammeter: measures the current absorbed by motors/machines.
2. Voltmeter: measures the voltage or voltage drop in the grid or electrical circuits.
3. Watt-meter: measures instant power demand of motors/ machines or the power performance of generators.
4. Cosö-meter: measures the power factor or monitors the rectification devices
5. Multi-meter: measures all the above quantities and some other quantities (e.g. frequency, reactivity, phase angle, etc)
All of the above instruments are usually portable. They are connected to the wiring with the use of nippers and they could feature a data-logger. Measurements of electrical power and energy consumption should be made on all energy-intensive areas and installations.
During the measurement of all the above quantities, the total power (metered in kVA) and the active power (usually metered in kW) should be distinguished. Common measuring instrumentation is based on a sinusoidal waveform, which gives incorrect readings for VSDs (Variable speed drives). In such cases, the use of meters measuring real RMS (Root Mean Square) values is necessary.
Measurement of electrical parameters requires use of a complex instrument called a power analyzer. After the instrument’s proper connection to the electrical panel of machinery or the substation under examination, measurement readings are presented on its display, which include instantaneous and programmable duration measurements for each phase and for the total voltage, current, apparent reactive and active power, cosö and energy consumption. The instantaneous measurements are repeated every 20 seconds (CRES, 2000).
Temperature measurement
The most common temperature measuring technologies include:
a) Resistance Thermometer Detectors (RTD): One of the most technologically-advanced instruments with internal signals for calibration and resetting and a high level of accuracy.
b) Thermocouples: Widely used and not expensive, covering a wide range of temperatures, from a few degrees up to 1000 °C and are usually portable. They need frequent calibration with specialized instruments. Their main disadvantage is that they have a weak signal, easily affected by industrial noise.
c) Thermistors: Used as permanent meters and are of low cost and have an automatic resetting capability.
d) Infrared thermometers: Measure temperatures from a distance by sensing the thermal radiation. They sense “hot-spots” and insulation problem areas. Portable and easy to use, but with limited accuracy
Before auditing the heating systems (e.g. boilers), the equipment should operate at its normal temperatures, so that data coming from the measurements can be the representative of actual performance. In order to determine the heat losses from the building’s as well as the locations where insulation is degrading, the indoor temperature should be higher than the outdoor temperature. Thus, a cold and cloudy day should be chosen in order to avoid the heating effect on walls by incident radiation (CRES, 2000).
Flow measurements
To estimate heat flow through a fluid, it is necessary to measure its flux (mass or volume). Such measurements typically include air and liquid fuel, steam and hot or cold water, or airflow measurements. Combining a measurement of temperature difference with flow measurement allows for the measurement of the thermal and energy flows.
The meter should be carefully selected, taking into account the fluid type, any diluted and corrosive substances, the speed range and the relevant costs. Flow-metering sensors can be classified as follows:
• Differential pressure meters (of perforated diaphragm, Venturi or Pitot tube type)
• Interference meters (of variable cross section, positive shift, eddy or vortex metering type)
• Non-interference meters (of ultrasonic or magnetic meter type)
• Mass meters (Coriolis or angular momentum type)
Exhaust gas measurements
Exhaust gas measurements include CO2, CO, SOx, NOx, smoke content, and temperature measurement. Traditionally, these measurements are taken with low cost portable instruments called gas analyzers.
• Gas analyzers
Gas analyzers can rapidly measure all the above quantities and, at the same time, perform calculations for the combustion efficiency.
The traditional measurement instruments measure under dry gas conditions, while the electronic analyzers measure the gases composition continuously and under real time conditions. The appropriate sampling point is located where maximum temperature occurs, right in the middle of the gas flow
Once proper sampling is achieved, gases are analyzed by the gas analyzer and the percentage of the exhaust gases in CO, CO2, O2, SO2, NOx, CxHx is determined through built-in algorithms.
Speed of rotating equipment
Speed measurements of for example motors are critical as they may change with frequency, belt slip and loading. There are two main types of speed measurement instruments:
• Tachometer
• Stroboscope
In a contact-type tachometer, the wheel of the tachometer gets in contact with the rotating body. Due to friction between the two, after few seconds the speed of the wheel of the tachometer is the same as the speed of the rotating body.
The digital stroboscope is an instrument used to make a cyclically moving object appear to be slow moving, or stationary. When measuring the rotational speed of an object, set the flash rate is initially put on a higher setting than the estimated speed of the object. Then, slowly reduce the flash rate until the first single image appears. At this point, the strobe flash rate is equal to the rotational speed of the object.