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Energy audit instruments and energy balance

Short answer

Common instruments: power/energy analyser (kW, power factor), lux meter (illumination), flue gas analyser (O2, CO2, stack temperature), infrared thermometer (surface temperature), clamp-on ammeter, flow meter, and tachometer. An energy balance equates input to useful output plus losses. A Sankey diagram displays energy flows as bands whose widths are proportional to energy quantities, highlighting major losses like flue gas in a boiler.

List the instruments used in an energy audit with the quantity each measures. Explain the preparation of an energy balance and a Sankey diagram with an example.

Instruments

InstrumentMeasuresUse
Power/energy analyserV, I, kW, kVA, power factor, harmonicsMotors, transformers, panels
Clamp-on ammeter, multimeterCurrent, voltageQuick checks
Lux meterIllumination (lux)Lighting audit
Flue gas analyserO₂, CO₂, CO, stack temperatureBoiler and furnace efficiency
Infrared thermometer / thermographSurface temperatureHot spots, insulation, loose joints
Ultrasonic or clamp-on flow meterFlow of liquidsPumps, cooling water
Anemometer, pitot tubeAir velocityFans, ducts
Tachometer, stroboscopeRotational speedMotors, fans
Thermocouple and data loggerTemperature over timeProcess monitoring

Energy balance

It is an account of energy input equal to useful output plus losses, from the first law:

Energy input=useful output+losses\text{Energy input} = \text{useful output} + \text{losses}

Steps: draw a system boundary; list all inputs (electricity, fuel, steam) and outputs; measure each stream; check that the balance closes within about 5 %; find the largest losses.

Sankey diagram (example: boiler, 100 units of fuel)

 Fuel 100 ===+=========> Steam 82 (useful)
             |==> Flue gas 12
             |==> Radiation/convection 3
             |==> Blowdown, others 3

The width of each band is proportional to the energy it carries, so the largest losses (flue gas here) are seen directly. Boiler efficiency = 82/100 = 82 %, and the audit would address flue gas heat recovery and excess air.

✓ Answer checked by Claude Opus 5.5 (high effort)

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