Pre-insulated district heating (DH) pipes have been in use for more than 40 years. The thermal performance of these pipes decreases over time as a result of thermal and mechanical aging, which leads to higher heat energy losses. A non-destructive method based on a cooling method is under development for assessing the thermal performance of a DH network. The method utilizes the copper wire, which is already embedded in the polyurethane insulation for detection of water leakage, as a sensor for measuring the temperature at the position of the copper wire. The method involves a shutdown of a selected part of a network for less than 2 h and evaluating the cooling process by measuring the supply pipe temperature and the temperature of the copper wire. The method was applied in a DH network during heating season. The thermal conductivity calculated by the method [0.027 W/(m K)] was in good agreement with the reference value [0.026 W/(m K)]. The cooling of the network can be measured at a valve or at other more easily accessible steel parts. It was also shown that the method is applicable for DH networks without a copper wire. However, a temperature measurement is needed on the casing pipe.

中文翻译：

---

开发用于评估区域供热管道热状态的无损检测方法

预保温区域供热 (DH) 管道已经使用了 40 多年。由于热老化和机械老化，这些管道的热性能会随着时间的推移而降低，从而导致更高的热能损失。一种基于冷却方法的非破坏性方法正在开发中，用于评估 DH 网络的热性能。该方法利用已经嵌入聚氨酯绝缘材料中的用于检测漏水的铜线作为传感器来测量铜线位置处的温度。该方法涉及将网络的选定部分关闭少于 2 小时，并通过测量供应管温度和铜线温度来评估冷却过程。该方法在采暖季节的DH网络中得到应用。通过[0.027 W/(m K)]方法计算的热导率与参考值[0.026 W/(m K)]非常吻合。网络的冷却可以在阀门或其他更容易接近的钢部件上测量。还表明该方法适用于没有铜线的 DH 网络。但是，需要对套管进行温度测量。