Polymer vs. Steel: Making the Right Call to Hit Housing Targets for District Heating

01.11.2024

Polymer vs. Steel: Making the Right Call to Hit Housing Targets for District Heating

With the Government raising annual housebuilding targets, there will be a growing number of new homes requiring heat and hot water from district heating services. To meet this need, the correct specification of pipework will be crucial for projects to run efficiently, which is where the material will become a vital selection. As fourth-generation networks grow in popularity, so has the market acceptance of modern polymer pipes. However, the UK construction market is typically slower to move away from traditional materials to modern flexible pre-insulated pipes, perhaps due to some common misconceptions.

With this in mind, Steve Richmond, Head of Marketing & Technical at REHAU Building Solutions, investigates some of the issues faced by energy service companies (ESCOs), consultants, and contractors when selecting pipework materials, and looks at how best to understand the applications of each and where they can be deployed.

The market for district heating in the UK is a vital part of the transition to net zero, with the Government expecting £60 to £80 billion to be invested in the sector by 2050[i]. With the Future Homes Standard coming into effect in 2025, banning gas boilers in new build homes, developers are already looking for low carbon alternatives, meaning there are more opportunities than ever within this space. Moreover, with the new Labour government pushing for increased housebuilding through raising annual targets, developers and ESCOs are being encouraged to design and install efficient heat networks.

However, this is bringing up further debates as to what kind of pipework is best to use for certain projects. Steel is the traditional choice for many, but polymer is increasing in popularity as a viable alternative. The reality is that this decision is not a simple one, and hinges of a variety of factors that must be considered.

Pain Points for Decision Makers

There are many pain points when selecting the most suitable material for a project, many of which will cause headaches for decision makers. One of these issues is the risk of corrosion, with some pipe materials being more susceptible than others. Corrosion can be a concern for operators, as it can lead to the pipes failing and replacements being needed. Therefore, picking the right material to withstand the conditions they will be put under is paramount.

Steel pipes are known for their high temperature and pressure resistance and very large sizes. However, they also have a higher risk of failure due to their greater susceptibility to corrosion, should water ingress occur through the outer casing or at the joint.

Polymer pipes, on the other hand are much more resistant to corrosion, meaning they are less likely to become compromised once in the ground. REHAU’s latest solution, RAUVIPEX, features a new longitudinal water barrier for added protection and reliability, just one example of innovation in this field.

Skills Shortages

Another factor to consider is the ease and methods of installation. When looking at fittings, steel uses prefabricated fittings which are connected via straight shrouds. The use of these fittings, along with welding for joining steel pipes, is a well-established technique, ensuring strong connections for pipe systems when installed correctly. However, the requirement for prefabricated parts risk project delays if unexpected changes are needed during installation. This differs from polymer pipes, which use standard fittings within universal shroud systems, that are readily available as standard parts.

In order to install steel, there is the need for specialist coded welders on-site, this also requires the use of an open flame, which naturally presents further health and safety considerations. Therefore, with skill shortages causing difficulties throughout the industry, the demand for specialist personnel can potentially cause delays throughout a project.

In contrast, polymer pipes can be installed by a trained mechanical or utility contractor thanks to jointing systems such as EVERLOC. This is a trusted and reliable system, which has been used over 1 billion times globally. Additionally, methods such as the compression sleeve jointing technology used on REHAU’s RAUVIPEX PE-Xa pipe enable these pipes to be installed without any hot works. They also support extreme angle deviations thanks to technology such as CLIP-FLEX, which allows angles of up to 22.5° in the trench.

The delivery of each product also differs. Steel is delivered to site as straight lengths, requiring multiple welds to join lengths and navigate obstacles. Polymer pipes up to 140mm come in coils, allowing for a reduced number of joints and the ability to easily install around obstacles, with REHAU’s RAUVIPEX making this even easier with the reduced bending forces required. Polymer pipes also have no requirement for expansion joints, which means they can be installed without additional elbows in the ground. This makes them the ideal choice for use in compact or constrained environments. The absence of expansion joints also reduces the risk of failure by reducing the number of joints in a network. For larger diameter pipework(160-315mm), PP-R (fibre-reinforced polypropylene) is now making a 100% polymer heat network possible. It has the benefit of being lighter than steel but most importantly, has excellent corrosion resistance and does not require expansion loops.

Following the Best Path

Besides these factors, there are other considerations to ensure that best practice is being followed during specification. For example, the specifier must ensure that the material chosen can handle the temperature and pressure requirements of the network, which is intrinsically linked to the generation of technology being used.

Steel has typically been the best choice for use where there are high operating temperatures and pressures, thanks to its durability under these conditions. Typically, this pipework has been used in combination with a third-generation system that commonly uses a gas boiler or gas combined heat and power (CHP) system as the source.

But, thanks to advances within the space, the operating temperatures required for district heating systems are reducing. This is in part to help with energy efficiency and the introduction of low carbon heating sources such as centralised heat pumps.

This has seen the introduction of fourth-generation systems, which many view as the future of district heating. These systems typically operate at a lower flow temperature than their predecessor, usually around 40-65°C. Thanks to these lower temperatures, the high temperature requirement is removed, allowing polymer piping systems to be a viable option.

Making an Informed Choice

The choice between polymer and steel pipes for district heating systems depends on various factors including the specific requirements of the system, the budget of the project and the specific environment the system will be built in. However, making the correct choice for a project can have a multitude of benefits that extend beyond fiscal choices.

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