Energy Balance and Benchmarking Questions and Answers

Answer: C

Correct answer: the energy required for each additional unit produced

The regression of consumption against output has a slope and an intercept, and the slope is the marginal or variable component - the extra energy each further unit of production costs. The intercept is the fixed load, drawn whether anything is produced or not, and separating the two is the whole purpose of the regression.

Answer: D

A large intercept says that much of the energy is spent regardless of production, which is by definition waste that no process improvement will touch. Idling equipment, permanent lighting and leaks are where it will be found.

Answer: A

Correct answer: its own performance in earlier periods

Internal benchmarking compares the plant with itself, which is the most defensible comparison available: the process, the products and the site are the same, so a change in specific consumption reflects a real change in performance rather than a difference in what is being made.

Answer: B

Two plants making nominally the same product may differ in grade, in age and in capacity, and attributing the whole gap to inefficiency is unfair and unhelpful. Adjusting for the differences, or comparing subsystems rather than whole plants, is the usual remedy.

Answer: C

Knowing that the thermodynamic minimum is a third of current consumption says the opportunity is large; knowing it is nine tenths says the process is near its limit and effort belongs elsewhere. No real plant reaches it.

Answer: D

Correct answer: 1-Q, 2-R, 3-P

The three benchmarks answer three different questions. Internal asks whether the plant is doing better than it was; external asks how it compares with the best in the industry; and theoretical asks how far it stands from the thermodynamic minimum the process itself imposes. The last sets the ceiling on what any improvement could ever achieve.

Answer: A

Correct answer: unit of floor area per year

The index is kilowatt hours per square metre per year, which normalises for the size of the building so that a large and a small office can be compared. It does not normalise for what the building is used for, which is why comparisons across building types are unsound.

Answer: B

Correct answer: the two building types have quite different service requirements

A hospital runs continuously, ventilates to a far higher standard, sterilises, and operates equipment an office does not. Its index is therefore several times an office’s for reasons that have nothing to do with how well it is run - so the comparison must be within a building type, against a benchmark for that type.

Answer: C

Coal in tonnes, gas in cubic metres, oil in litres and electricity in kilowatt hours cannot be added until they are converted, and the trading scheme's targets are denominated in this common unit. Each conversion needs the fuel's calorific value.

Answer: D

Gross assumes the water formed by combustion is condensed and its latent heat recovered, which an ordinary flue does not do. Quoting an efficiency against one value and a fuel price against the other is a common and material error.