---
title: "Energy audit instruments and energy balance"
subject: "Energy Resources"
chapter: 9
key: "semester_6/energy_resources:energy-audit-instruments-measurements"
source: https://www.bctengineer.com/q/semester_6/energy_resources/energy-audit-instruments-measurements
site: BCT Engineering
---

# Energy audit instruments and energy balance

Energy Resources · Chapter 9: Energy audit

- Asked in: year not given, 5 marks
- Video: [Maximizing System Efficiency and Energy Audit Instruments- EECA by Dr. Digambar Singh](https://www.youtube.com/watch?v=cCwSWJ-27cA) — Arya College of Engineering and IT
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/energy_resources/energy-audit-instruments-measurements
- Whole chapter: https://www.bctengineer.com/md/semester_6/energy_resources/chapter-9

## Question

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.

## 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.

## Answer

#### Instruments

| Instrument | Measures | Use |
|---|---|---|
| Power/energy analyser | V, I, kW, kVA, power factor, harmonics | Motors, transformers, panels |
| Clamp-on ammeter, multimeter | Current, voltage | Quick checks |
| Lux meter | Illumination (lux) | Lighting audit |
| Flue gas analyser | O₂, CO₂, CO, stack temperature | Boiler and furnace efficiency |
| Infrared thermometer / thermograph | Surface temperature | Hot spots, insulation, loose joints |
| Ultrasonic or clamp-on flow meter | Flow of liquids | Pumps, cooling water |
| Anemometer, pitot tube | Air velocity | Fans, ducts |
| Tachometer, stroboscope | Rotational speed | Motors, fans |
| Thermocouple and data logger | Temperature over time | Process monitoring |

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

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

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)
```text
 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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What does a flue gas analyser measure?
   A. Illumination
   B. O2, CO2, CO and stack temperature for boiler efficiency
   C. Air velocity
   D. Rotational speed
   Answer: B. It is used to assess boiler and furnace combustion efficiency. (Key point: Flue gas analyser)

2. Which instrument-quantity pair is correct?
   A. Lux meter: current
   B. Anemometer: illumination
   C. Tachometer: rotational speed
   D. Power analyser: temperature
   Answer: C. Tachometers and stroboscopes measure speed of motors and fans. (Key point: Instrument matching)

3. What does an energy balance state?
   A. Input equals useful output plus losses, closing within about 5 %
   B. Output exceeds input
   C. Losses are zero
   D. Input equals losses only
   Answer: A. It follows the first law of thermodynamics. (Key point: Energy balance)

4. What does band width represent in a Sankey diagram?
   A. Time
   B. The amount of energy it carries, making largest losses visible
   C. Cost per unit
   D. Temperature
   Answer: B. Width is proportional to energy; in the boiler example flue gas is the biggest loss. (Key point: Sankey diagram)

## Related in Energy Resources

- [Energy audit types and audit procedure](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Aenergy-audit-types-procedure) — Energy Resources, chapter 9
- [Preparing and presenting an energy audit report](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Aenergy-audit-report-preparation-presentation) — Energy Resources, chapter 9
- [Solar radiation measuring instruments](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Apyranometer-pyrheliometer-sunshine-recorder) — Energy Resources, chapter 2
- [Energy saving calculation: lighting and motor](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Alighting-motor-energy-saving-case) — Energy Resources, chapter 9

## Related in other subjects

- [Need of energy audit and technique](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aenergy-audit-need-technique) — Industrial Power Distribution and Illumination, chapter 10, asked 3×
- [Energy audit definition and process](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Adefine-energy-audit-process) — Industrial Power Distribution and Illumination, chapter 10
- [Execution phase of energy audit](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aenergy-audit-execution-phase) — Industrial Power Distribution and Illumination, chapter 10
- [Energy audit technique and saving opportunities](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aenergy-audit-technique-opportunities) — Industrial Power Distribution and Illumination, chapter 10