Energy Balance and Benchmarking Questions and Answers

Answer: A

Correct answer: 2, 1, 4, 3

The data must exist before anything can be regressed, and the regression is what separates the fixed from the variable component. Only then is there an expected consumption against which residuals can be computed, and tracking those cumulatively is the last step - and the one that reveals when performance changed.

Answer: B

Correct answer: the consumption of a plant making a different product

A benchmark must compare like with like, and a different product means a different process with a different energy requirement, so the comparison establishes nothing. The other three are all valid bases: the plant’s own history, the best in the sector, and the theoretical minimum.

Answer: C

Correct answer: an increase in output at constant efficiency

Raising output spreads the fixed load over more units, so specific consumption falls even though the total rises. The other three all raise it: fouling reduces heat transfer, a leak wastes compressed air, and a fall in output leaves the fixed load spread over fewer units.

Answer: D

An apparent improvement can be nothing more than a rise in output spreading the fixed load, which no measure caused and which will reverse when output falls again. Normalising properly is what distinguishes a real gain from an arithmetical one.

Answer: A

A plant that halves its output halves much of its consumption without having improved at all, which is precisely why the total tells one so little. Dividing by output, and allowing for the fixed component, is what isolates the performance.

Answer: B

The average divides the whole consumption, fixed component included, by the whole output; the marginal figure is the slope of the relation and excludes the fixed part. They coincide only if the fixed load is zero, which no real plant achieves.

Answer: C

A tight boundary makes each stream measurable and the loss attributable, which is exactly what a targeted audit wants. It says nothing about the heat that leaves in the product and is then wasted elsewhere, which only the wider boundary reveals.

Answer: D

Correct answer: the heat carried away in the cooling water

An energy balance accounts for energy, so every stream carrying it belongs - including the losses, of which cooling water is usually one of the largest. Capital cost, staffing and product price are all real quantities and none of them is energy, so none of them appears in the balance.