Diagnostic Protocol for Thermal Performance of District Heating Pipes in Operation. Part 2: Estimation of Present Thermal Conductivity in Aged Pipe Insulation

Abstract

Buried and operating district heating (DH) pipes are exposed to thermal degradation of their polyurethane (PUR) insulation over time, and their status is hard to assess without excavation. By using DH pipe valves in manholes as measurement points during a shutdown with an ensuing cooling period, non-destructive assessments can be performed. This study compares new improved field measurements with numerical simulations of the temperature decline in drainage valves and shutdown valves. The drainage valve measurements were used to thermally assess part of a buried DH network. Results indicate that by using the drainage valves as measurement points in a cooling method, the thermal conductivity of the buried DH network could be predicted with an accuracy of >95%. In addition, a general diagnostic protocol has been established for assessing the thermal status of a DH network, ready for network owners to use.

Experimental Assessment of the Thermal Conductivity of Basalt Fibres at High Temperatures

“…During the experimental studies, the places of coolant leakage into the ground were identified together with the sections of heat pipelines with an unsatisfactory state of thermal insulation materials. A similar problem Energies 2022, 15, 2784 2 of 11 was addressed by researchers from the Chalmers University of Technology comparing the results of numerical modelling and measurements using non-destructive testing [5,6].…”

District Heating and Cooling towards Net Zero

“…The analysis was conducted whilst considering the perspectives of both the cogeneration plant and the end user. A very different subject was explored by Liden et al in a two-part article [5,6]. They addressed the problem related to the thermal degradation of DH pipe insulation over time, which is highly difficult to quantify without excavation.…”

“…As a next step, a diagnostic protocol was developed and established for application to DH pipes in operation [6]. In particular, the choice of the drainage valves as measurement points has proven to be the most appropriate for capturing the temperature decline in the DH pipe during the above-mentioned cooling period.…”