An Analysis of the most Frequent Operational Temperature of four District Heating Networks of Germany

Abstract

Pre-insulated pipes according to EN 253:2019 that are used in District Heating (DH) networks comprise of minimum three layers. These layers are steel medium pipe, rigid polyurethane (PUR) foam as the insulation layer, and a polyethylene (PE) casing as the protection layer. Various studies show that the thermo-oxidation of the PUR foam is one of the most critical mechanism that determines the service-life of the pre-insulated bonded pipe systems. The deterministic approaches for service-life estimation considers the design temperature of the network e.g. 120°C, however the DH operational flow temperature is not constant. In recent decade, due to the decarbonisation trends and new artificial intelligent (AI) based techniques, the DH networks are optimized better than before and therefore, the DH operating flow temperature reduced to some extent. This temperature reduction affects the thermo-oxidation reaction speed, and the thermo-oxidation level of the PUR foam is very crucial to understand the adhesion of the PUR foam at the interface of the steel pipe and accordingly the service-life prediction of the pipe. Moreover, it affects the axial shear strength, which is necessary to impede the steel pipe movement that is caused by thermal expansion and to reduce the mechanical cyclic load. In this paper, the temperature changes of four different DH networks in Germany are analysed and the aim is to reveal the flow temperature of the in-operation DH pipes, Equivalent to Constant Continues Temperature (ECCT). The ECCT would be useful for different purposes such as thermo-oxidation analysis or to be utilize as a parameter in life-time prediction of the DH pipe.