Pre-insulated district-heating pipelines: Design and operational advice

Steady-state temperature distributions have been measured within a cylindrical duct enclosing two different diameter pipes--one for district heating and the other for the supply of domestic hot-water; the gaps between the pipes being filled with well-packed fibrous thermal insulant. The procedure was repeated successively with each of three sets of different-diameter pipes. The recommended configuration was with the DH pipe coaxial with the centre of the pipeline and the DHW one located vertically below it: this corresponded to the minimum rate of heat loss from the district-heating pipe under the considered conditions. An overall improvement of ~8% in the thermal insulation of the DH pipe has been achieved compared with the current conventional practice of installing the DHW pipe above the DH pipe.