Utilization rate

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Degree of utilization is the quotient of the actually achievable and the maximum possible value of a reference value , e.g. B. Area or machine utilization. See also use (technology) .

It is most often used as a technical term for energy yield . The degree of utilization of an energy system or device relates the energy made usable in a certain time to the energy supplied. The periods under consideration can include break, idle, start-up and shutdown times. An exergetic degree of utilization can also be formed as the quotient of the exergy made usable and supplied .

In the building sector, the reciprocal of the degree of utilization is sometimes referred to as the expenditure figure .

Heating technology

The degree of utilization of a boiler is the heat that can be used during a year, based on the heating energy supplied with the fuel. The degree of utilization is determined in accordance with DIN 4702 T8 and specified in the manufacturer's device documentation as the standard degree of utilization, which is quantified with up to 111% for gas condensing boilers, as reference is made to the lower calorific value , condensing boilers but also the latent value contained in the exhaust gas Heat , in this case the heat of the water vapor, can be used. (The reason for this reference to the lower calorific value by the device manufacturer is probably that it is used by the gas supplier. The gas price is calculated by the supplier for the kilowatt hour the lower calorific value, although this does not take into account all of the energy contained in the gas.)

Standard utilization rate

The standard degree of utilization is determined in accordance with DIN 4702 Part 8 and includes, among other things, tests at 5 typical power levels in order to reflect a realistic degree of efficiency of the heat generator (boiler, thermal bath). It is determined on the manufacturer's test stands.

Annual efficiency

The heating energy supplied to the system can be estimated using the amount of fuel actually consumed (gas meter, oil meter), reduced by waste gas , boiler loss , standstill losses, losses from hot water storage tanks and distribution losses (estimate). This important variable can only be measured with heat meters that are connected directly downstream of the heating system.

Measured over a year and divided by the amount of energy contained in the fuel, this gives the annual degree of utilization of the system. In relation to the upper calorific value, this can amount to 90% in good systems, ie 10% of the energy contained in the fuel cannot be used.

A "standard degree of utilization" of 85% can be compared to an actual annual degree of utilization of only 30%. In summer in particular, the provision losses of a common heating system are relatively high. This means that 30–50% of the fuel requirement can easily be used to operate the system (see boiler # Waste of energy ).

CHP plants

In the case of power generation plants with combined heat and power , the degree of utilization or overall degree of utilization denotes the ratio of the total energy output used (sum of electricity and heat output) to the energy input, as a distinction to the (electrical) efficiency , which only takes the electricity output into account. Since the degree of utilization is also determined by the heat demand and can therefore fluctuate strongly with the seasons, the annual degree of utilization is usually used to evaluate systems . Typical values ​​for systems in which the heat can be sensibly used all year round are around 85–90%, but values ​​of only 50–60% are possible for older or incorrectly set systems.


In the case of springs , the degree of utilization describes the ratio of real to ideal work absorption capacity.

A distinction is made between:

  • Type utilization rate η A
  • Volume efficiency η V
  • Weight efficiency η Q .

See also

Web links


  1. Viktor Wesselak; Thomas Schabbach; Thomas Link: Joachim Fischer: Handbook Regenerative Energy Technology . 3. Edition. Springer-Verlag GmbH, 2017, ISBN 978-3-662-53072-6 , 2.1 Approaches to reducing energy consumption, formula 2.3 .
  2. Albert Albers: Fundamentals of the calculation and design of machines . In: Waldemar Steinhilper (ed.): Construction elements of mechanical engineering . 8th edition. tape 1 . Springer-Verlag, Berlin / Heidelberg 2012, ISBN 978-3-642-24300-4 , Degree of utilization, p. 206 .
  3. ^ Dubbel: Pocket book for mechanical engineering . In: W. Beitz, Karl-Heinz Grote (Hrsg.): Construction elements of mechanical engineering . 20th edition. Springer-Verlag, Berlin / Heidelberg 2001.
  4. G. Niemann, H. Winter, B.-R. Höhn: machine elements . 3. Edition. tape 1 . Springer-Verlag, Berlin / Heidelberg 2001.