District Heating pipework

Pipe layout patterns and the benefits

Solving the future challenges of heating and hot water systems is key to reducing carbon emissions. At REHAU our pre-insulated pipe systems have been developed with over 20 years experience combined with operational experience.

One key element in successful district heating projects is pipe layout and how different selections lead to a variety of benefits.

Connection options

The concept of the layout and how consumers will be connected to the source of heat generation would be the first step for a network designer to settle on. There are a variety of options here that depend on the size of the project and number of heat sources, so it is important to identify which is best suited to the project.

Currently, the most widely used connection option is a radial system, with underground pre-insulated pipes branching away from a larger main pipe called the spine. For improved efficiency and lower investment cost, plant rooms for these layouts are best located either as close as possible to the centre of the network, or satellite to the network. Networks of this type are easy to plan, and can offer lower construction costs and minimal thermal losses thanks to shorter pipe runs and smaller diameters.

However, due to this type of system having a specified limited network capacity, the scope for expansion is limited. An alternative choice here could be a ring network, which lends itself to larger, typically urban, supply areas with multiple heat sources. Here, the heat network is designed in a circular shape with heat sources on opposite sides.

This results in higher security of supply, as customers can receive heat and hot water through two sources – likewise facilitating easier expansion. Advanced layouts also allow ring networks to be nested inside one another for maximum security and extension opportunities, though this is best suited to larger, city-wide projects and would typically require a higher capital investment.

Material specification

Once the concept of the layout is agreed, the choice of route available to the installer largely depends on what kind of district heating pipework is used for the project. Namely, this concerns steel or polymer pre-insulated pipework.

Though steel has long proved a popular choice of material for underground heating pipes, it is not without its limitations. Steel networks are complex by design, requiring wider trenches and the integration of expansion loops to alleviate forces that would otherwise break pipes apart. This also requires the use of more pre-fabricated elbows, which means more of the project budget needs to be spent on custom fittings.

Polymer solutions, on the other hand, such as RAUTHERMEX pre-insulated flexible pipe, are far more malleable. This is helpful if the build is slightly out of tolerance, as it allows the pipe to be simply curved around obstacles. The current generation of shrouds also allows pipes to be bent at opposite acute angles at a joint, facilitating easy installation and simpler design than a steel network.

Moreover, the innate properties of polymer pipe and its outer casing makes it more resistant to thermal expansion through self-compensation, eliminating the need for expansion loops.

Radial network

Ring network

Meshed network

Secondary spines

A final consideration should be whether or not to incorporate a secondary spine, an option which appears to be a growing trend, particularly in polymer district heating systems. Here, branches leading to individual properties are first connected to a secondary spine before the main line.

The primary benefit here is cost savings, with less of the more expensive large tees required for the build. As smaller pipework is required for the build, it also presents a greater opportunity to use DUO pipework instead of UNO for further savings.

Moreover, this configuration creates clusters, which enables isolation without disturbing the main line. Using clusters also makes it easier to future-proof entire phases as branches can be left off of the main spine during installation.