Abstract
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.
Highlights
district heating (DH) networks have been used for decades and the usage increased substantially in the 1960s in the US and Europe
The energy companies can measure what they produce in heat energy and what they deliver to costumers, the heat losses for the whole network can be determined
In Sweden, around 10% of the energy supplied to the DH networks are lost through heat losses from the distribution pipes [2], where aging and degradation of the PUR increases the heat losses [3]
Summary
DH networks have been used for decades and the usage increased substantially in the 1960s in the US and Europe. The energy companies can measure what they produce in heat energy and what they deliver to costumers, the heat losses for the whole network can be determined. In Sweden, around 10% of the energy supplied to the DH networks are lost through heat losses from the distribution pipes [2], where aging and degradation of the PUR increases the heat losses [3]. A typical rigid DH pipe in the Swedish DH network consists of an inner service pipe of steel and an outer casing pipe of polyethylene (PE). Between the steel service pipe and outer casing there is a gas-filled closed cell PUR insulation and two thin (1.5 mm2) soft copper wires are embedded
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