Nettowirkungsgrade

Nettowirkungsgrade, literally net efficiency, is a term used in German-speaking technical literature to describe the efficiency of a device or system when the energy boundary definitions include or exclude certain internal consumption and losses. In general, it is defined as the ratio of useful energy output to the energy input, within a defined system boundary.

The exact calculation depends on the field and the standard used. A simple form is η_net = E_useful / E_input, where E_useful is the energy delivered to the intended load (for example heat supplied to a building or electrical power delivered to a consumer) and E_input is the energy content of the energy source consumed by the device. Some definitions subtract the energy consumed by auxiliary components (pumps, fans, control electronics) from the numerator or include it in the denominator; others treat them as separate parasitic losses. Because of these variations, different standards may yield different net efficiencies for the same device.

Examples: In a heating plant with a boiler and a circulating pump, the nettowirkungsgrad would reflect the share of fuel energy that becomes useful heat in the building, after accounting for pump and flue losses. In a combined heat and power (CHP) plant, it can refer to the efficiency of converting fuel into useful electrical energy and usable heat, sometimes reporting separate net electrical efficiency and net overall efficiency.

Nettowirkungsgrad is a boundary-dependent concept; when comparing systems, it is important to specify the exact definition and the included losses. It complements the broader Wirkungsgrad concept by highlighting performance after internal consumption and losses are considered.