Energy units carry different physical meanings

An energy balance can fail before its arithmetic begins if the quantities being combined have different meanings. Power describes a rate of energy transfer. Energy describes a quantity accumulated over an interval. An equipment rating is therefore not an annual consumption record, and an annual consumption record does not establish peak demand. A proposal that lowers annual electricity use can still increase the capacity needed at a critical moment. A proposal that reduces a peak can leave annual consumption largely unchanged. The unit dictionary should preserve these distinctions because different engineering and commercial decisions depend on them.

Units also have boundaries. Electricity at the facility meter, fuel energy entering a furnace and useful heat reaching a material can all be expressed as energy while referring to different stages of conversion. Adding them without identifying the stage can double count an input or confuse useful service with purchased energy. A furnace consumes fuel to deliver thermal service through a process with losses. An electrical process consumes electricity to deliver service through its own conversion and control arrangement. Comparing the purchased energy totals alone does not establish whether the same service is provided.

The analyst should write the physical quantity before choosing the unit. A field labelled consumption is ambiguous if it could mean fuel volume, electrical input, delivered heat or a bill amount. A field labelled capacity is ambiguous if it could mean rated power, process throughput, grid connection or energy storage. Naming the quantity disciplines both data collection and later interpretation. The unit then provides a consistency check. A cost per unit of purchased electricity cannot be multiplied by useful heat without a conversion relation that describes the actual equipment and operating state.

Conversion efficiency is a relationship between specified inputs and outputs. Its meaning depends on the boundary and the operating conditions. An equipment efficiency stated at a design point may not represent the annual duty. An efficiency improvement can reduce losses while leaving an important operating constraint unchanged. A service improvement can require a different quality of output that changes the appropriate comparison. The dictionary should record what enters the denominator, what enters the numerator and which operating envelope makes the ratio relevant. The word efficient is insufficient without that record.

Useful heat introduces a quality question as well as an energy quantity. A process can need a temperature, distribution pattern or response that a proposed technology cannot deliver reliably. Recoverable heat may be available at a condition unsuitable for the required service. Treating all thermal energy as fully interchangeable can create an apparent saving that the production process cannot use. This study does not supply a thermal engineering model. It uses the heat example to show why energy units alone do not establish service equivalence, and why a broader electrification appraisal needs an operating specification.

A practical dictionary should distinguish physical units from reporting conventions. Electricity demand is an energy quantity over the declared period. A supplied emission factor links a specified energy basis to an attributed emissions quantity. A price links an energy quantity to a particular commercial charge. An efficiency percentage expresses a proportional change in the particular demand to which it applies. An annual cost and an upfront capital cost have different time bases. Keeping these fields separate prevents a technically valid multiplication from answering the wrong accounting or financial question.

The renewable supply field requires particular care. In the annual electricity engine it represents an additional annual quantity available within the illustrative balance. The quantity actually used cannot exceed the remaining annual demand. Any supplied quantity beyond that cap is labelled curtailed in the simplified annual model. This convention does not represent a storage asset, an export agreement or hourly coincidence. It prevents the screen from assigning negative grid demand or unlimited savings to excess supply. It also tells the user which more detailed questions the annual cap cannot resolve.

The cost per tonne field combines another set of bases. The numerator is an annualised net cost within the supplied horizon and discount convention. The denominator is annual modelled abatement within the supplied emissions boundary. The result is meaningful only when the abatement denominator is positive and the numerator and denominator describe the same package and period. A raw capital amount divided by annual abatement would have a different interpretation. A discounted lifetime financial amount divided by an annual emissions quantity would also require explicit treatment. The dictionary should prevent those bases from drifting between tables.

Currency units need an economic convention as well as a label. A flat supplied energy price says nothing by itself about escalation, tax, foreign-exchange exposure or the distinction between real and nominal analysis. The illustrative engine uses constant supplied prices and constant annual savings. A user who intends a real project appraisal should choose a coherent price and discount basis in a fuller model. Relabelling a currency amount cannot make incompatible bases consistent. The limitation is especially important when a long-lived physical intervention is compared with commercial terms that can change during its life.

A unit check should be paired with a conservation check. The first asks whether each operation combines compatible quantities. The second asks whether the resulting physical state has accounted for its inputs and outputs within the boundary. A calculation can pass a unit check while losing an energy source, because omitted energy still has compatible units. It can pass a simple total while counting the same supplied energy under overlapping measures. The reviewer should therefore ask both whether the arithmetic is dimensionally meaningful and whether the state it describes can be reconciled to the measure scopes.

The dictionary should remain stable across scenarios. If a favourable case interprets efficiency as a reduction in total facility demand while an adverse case applies it only to a targeted subsystem, the comparison changes more than the parameter. If a supply quantity means generated energy in one case and delivered usable energy in another, losses and curtailment have moved outside the record. Sensitivity is interpretable when the meaning of each field remains fixed while an explicitly stated assumption changes. Where the meaning must change, define a different model or study rather than silently reusing the same label.

A conservation failure can have a useful diagnostic consequence. Negative grid demand indicates that supply has exceeded a permitted demand cap without an explicit export or storage treatment. A missing carrier indicates that the calculation is incomplete for the intended intervention. A discrepancy between equipment and facility totals can reveal loads, losses or metering boundaries requiring investigation. The reviewer should use the discrepancy to identify the missing mechanism. Forcing the totals to agree with an unexplained adjustment would remove the diagnostic value while leaving the actual operating question unresolved.

Finally, numerical precision should reflect the distinction between computation and evidence. The engine can carry detailed arithmetic from supplied values, and the ledger retains exact results for replication. The manuscript displays quantities at an appropriate readable precision. Neither practice establishes that a demand, price or factor is known with the same confidence. The unit dictionary and evidence record should travel with the result so the reader can distinguish an exact conditional calculation from an uncertain input. A polished number becomes useful when its meaning and evidential basis remain visible.