Identification of Individual District Heating Network Conditions using Equivalent Full Load Cycles

Repeated loading in district heating networks is occurring inconstantly. There are small and great load amplitudes in the system. As small load amplitudes are usually observed more frequently than great load amplitudes, their accumulation with respect to great load amplitudes is of common interest. A growing share of renewable energy can be noted in energy markets. Because of this, flexible operation of combined heat and power plants is necessary. For the connected district heating network this means additional temperature amplitudes in the system, causing higher stresses for the network. Repeated loading in the system has to be considered in the fatigue analysis. For a suggested lifetime of a district heating network of 30 years, an estimated number of cycles for the temperature load were accumulated for standardization. Nevertheless a longer lifetime than 30 years for district heating pipes is expected in the district heating sector, which also means higher cyclic loading. Due to individual operation parameters and individual network conditions, the equivalent action cycles are expected to be different at every element in the network. The paper is based on a review on damage accumulation theories that may be used for district heating systems regarding future developments. Some examples are shown for equivalent full load cycles for different locations in district heating networks.