Hotel resource efficiency: choose the right denominator

The fix is to keep two views rather than choose between them, and to be precise about what each is for.

Absolute consumption — kilowatt hours, cubic metres, tonnes — is what the property actually used and paid for. It is the figure a budget is built from and the figure that responds to a tariff change. It does not, on its own, tell you whether the property is being run well, because it depends on how much service was delivered.

Reporting only absolute consumption makes a property look better simply because it was quieter. Reporting only intensity allows absolute consumption to rise on the strength of a favourable denominator while the underlying cost grows. The pair, read together, is what supports a decision.

A metric can only support a claim about the boundary of its data. If a single incoming meter feeds the whole property, a reading from it supports a statement about the property total. It does not support a statement about guest rooms, restaurants or pools individually, because the reading cannot distinguish between them.

The common error is to take a whole-site utility bill, divide by occupied rooms, and present the result as an accommodation figure. The number is arithmetically correct and analytically meaningless for the question it is being used to answer.

Sub-metering is therefore not a reporting nicety but the enabling condition for the metrics above. Where sub-metering exists, each service can be given a denominator that matches its own meter. Where it does not, only a whole-site figure is available, and any attempt to attribute consumption to a service is an allocation rather than a measurement. Where a property pursues a wider environmental programme, published criteria such as those behind the EU Ecolabel [A] — including the accommodation criteria in Commission Decision (EU) 2017/175 [B] — can inform what is worth measuring, but they do not supply the measurement itself.

An allocation can still be a reasonable basis for internal cost recovery. It should simply be described as an allocation, so that a later decision does not treat an apportioned share as though it were measured.

Separating baseload from occupancy-driven consumption is what makes a per-occupied-room figure interpretable. Baseload is the consumption that continues regardless of how many rooms are let; the occupancy-driven element scales with use.

The split can be estimated from a property's own records by comparing consumption across periods of materially different occupancy, which turns a utility bill into an operational insight. It also explains many apparently anomalous results: a ratio that worsens in a quiet month is often showing baseload being divided by a smaller denominator, not a system running poorly.

The illustration below makes the arithmetic of that effect explicit. The figures are hypothetical and chosen to make the mechanism visible; they are not benchmarks, and no tariff or consumption rate is asserted.

Consider a hypothetical property whose utilities have an assumed monthly baseload of 60,000 kWh that does not vary with occupancy, plus an assumed 12 kWh of additional consumption for each occupied room-night. In a month with 3,000 occupied room-nights, total consumption is 60,000 + (3,000 × 12) = 96,000 kWh, and the per-occupied-room figure is 96,000 ÷ 3,000 = 32.0 kWh.

In a quieter month with 2,000 occupied room-nights and the same assumed baseload, total consumption is 60,000 + (2,000 × 12) = 84,000 kWh, and the per-occupied-room figure is 84,000 ÷ 2,000 = 42.0 kWh.

Absolute consumption fell by 12,000 kWh — a genuine reduction in spend — while the per-occupied-room ratio rose by 10 kWh, or about 31%. The efficiency of the property, as constructed here, did not change at all: the same baseload and the same per-room consumption applied in both months. Only the denominator moved.

The lesson is not that the ratio is useless. It is that the ratio must be read alongside the absolute figure and the occupancy level, and that a baseload-inclusive ratio will penalise a quiet period for reasons outside management control. A property that manages on the ratio alone risks cutting the very baseload services that guests notice, in pursuit of a number that never measured efficiency.