Energief

Energief is a hypothetical energy-efficiency metric used in energy-systems analysis and education to compare how effectively different technologies deliver useful energy to end users. In its simplest form, energief is a dimensionless ratio defined as energief = useful energy delivered (Qout) divided by total primary energy input (Ein). In single-service systems, energief typically satisfies Qout ≤ Ein, so the value is at or below 1.0, with 1.0 representing a theoretical maximum where no losses occur. In multi-output or multi-service contexts, energief can exceed 1.0 if multiple useful outputs are counted against the same input, depending on the normalization used.

Origins and use in literature are informal rather than standardized. Energief has been discussed in theoretical and pedagogical contexts to illustrate the idea that simple input–output ratios may mislead when energy quality, service type, and system boundaries differ. It is not an officially recognized metric in major standardization bodies, and it is rarely used in formal policy analysis.

Measurement and interpretation pose challenges. Defining useful energy, service requirements, and system boundaries varies by application (for example heating, electricity, or mechanical work). Critics note that energief can obscure exergy quality and discards important differences between energy carriers. Proponents argue that, when clearly defined, it provides a straightforward, intuitive contrast to more complex metrics.

Related concepts include energy efficiency, exergy, COP (coefficient of performance), and EER (energy-efficiency ratio). Energief is primarily of academic interest and is used more as a teaching tool than as a substitute for established standards.