A plant consumes 200 t of coal at 4500 kcal/kg and 1200 MWh of electricity in a month. In kilocalories the coal represents
Answer: C
Two hundred tonnes is two hundred thousand kilograms, and at 4500 kilocalories each that is nine hundred million. Putting the electricity on the same basis, at 860 kilocalories a kilowatt hour, gives about \( 1.03 \times 10^{9} \) and lets the two be compared.
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For that same plant, the electricity at 860 kcal/kWh represents about
Answer: D
1.2 million kilowatt hours times 860 is 1.03 billion kilocalories, slightly more than the coal. The comparison shows electricity to be the larger stream in energy as well as almost certainly in cost, which directs the audit accordingly.
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A plant's load factor is the ratio of its average demand to its
Answer: A
A low load factor means the plant's peak is far above its average, which is expensive because the supply and the tariff are sized for the peak. Flattening the profile reduces the demand charge without reducing the energy consumed.
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A site with a maximum demand of 800 kVA and an average demand of 320 kVA has a load factor of
Answer: B
Correct answer: 0.40
\[ \frac{320}{800} = 0.40. \] A load factor of 0.4 means the site is drawing on average less than half its maximum demand, so it is paying for capacity it rarely uses. Improving it by shifting or staggering loads reduces the demand charge without reducing consumption at all.
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Cumulative sum analysis tracks performance by accumulating
Answer: C
The expected figure comes from the regression against production, and accumulating the residuals turns a scatter of noisy monthly points into a line whose slope changes visibly when performance changes. A step in the slope dates the change precisely.
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A cumulative sum plot that turns downward after a measure is implemented indicates
Answer: D
Consumption is running below what the baseline relation predicts, and the accumulated shortfall grows month by month, which is what a real saving looks like. A plot that flattens again says the saving has stopped accruing.
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A cumulative sum plot that flattens some months after a measure suggests
Answer: A
A flat plot means actual and expected have come back into agreement, so the plant is once more performing as it did before. Set points quietly restored and repairs undone are the usual causes, and the plot dates when it happened.
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The advantage of cumulative sum analysis over comparing monthly figures is that it
Answer: B
Correct answer: accumulates small changes that monthly noise would hide
A cumulative sum adds up the differences between actual and expected consumption month by month, so a persistent small deviation builds into a visible trend while random scatter cancels. A change of a few per cent that no single month would reveal shows as a clear change of slope, and the month it began can be read off directly.
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Consider the following statements about energy balances.
1. The input equals the useful output plus the losses 2. A balance that fails to close indicates a missing stream or a measurement error 3. The boundary may be left implicit
Answer: C
Correct answer: 1 and 2 only are correct
Statements 1 and 2 state the first law and its practical use as a check. Statement 3 is the error that invalidates most poorly drawn balances - without a stated boundary there is no saying what counts as entering and leaving, and the balance can be made to close by moving the boundary rather than by finding the missing stream.
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Consider the following statements about specific energy consumption.
1. It normalises for output 2. It may rise while total consumption falls 3. It equals the marginal energy per unit produced
Answer: D
Correct answer: 1 and 2 only are correct
Statements 1 and 2 are correct, and the second is the point of the preceding calculation: specific consumption can rise while the total falls, if output falls further. Statement 3 confuses two different quantities - specific consumption is an average and includes a share of the fixed load, while the marginal figure is the slope and excludes it.
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