The practicality of polymer district heating systems

The rapid decarbonisation of the country’s building stock in line with net zero targets is continuing to affect how we supply heating and hot water. This change has brought technologies like district heating into the spotlight, which can offer carbon emission reductions while remaining easy to maintain. Such practicality and efficiency can make these systems an attractive option for building professionals, says Alexandra Leedham, Technical Leader – Renewable Energy at REHAU, who offers a deep dive into the technology.

District heating networks supply hot water to numerous properties via pre-insulated pipework while eliminating the need for individual heat sources. This technology has proved very popular with contractors, as the majority of maintenance can be carried out at a single central point. Similarly, it allows emissions reductions in line with sustainability-minded legislation – most prominently, the Government’s target to reduce carbon emissions to ‘net zero’ by 2050.

The targets’ passing into law in June 2019 made sourcing low-carbon heating and hot water systems a priority for building professionals. This, combined with the constant drive to lower energy bills and find new efficiencies, means that district heating systems have to fulfil three overarching criteria – lowering emissions, increasing heating efficiency, and lowering heat loss across the network.


Evolving heat networks

Currently, the majority of district heat networks across the UK and Europe are classed as third-generation, with water circulating at 70-95oC. Yet fourth-generation systems, which enjoy a comparatively lower 50-60oC flow temperature, are becoming more popular. This is because the lower temperature design results in less wastage and heat loss across the network, making it more efficient and cost-effective.

Alongside these new benefits, fourth-generation systems, due to their centralised design, reap the same benefits as their predecessors. This includes reduced carbon emissions and simpler, more cost-effective maintenance due to a lack of individual boilers.

Fourth-generation systems were also developed with low-carbon heating sources in mind. Their lower flow temperatures suit centralised heat pumps and waste pump sources, which can be introduced to the network after initial installation, further reducing time and money spent on maintenance.

Upcoming legislation such as the Green Heat Networks Scheme also favours these low-carbon schemes in both residential and commercial applications. Due for launch in 2022, the Green Heat Networks scheme, will replace the existing Heat Networks Investment Project, and will similarly award grants to domestic and commercial projects implementing sustainable, low-carbon district heating systems. This is clearly a key consideration for future developments that building professionals need to be aware of.

Shifting standards and regulations are also creating an environment more amenable to district heating systems. For instance, the latest version of the Standard Assessment Procedure for building regulations (SAP 10.1) sets standards for a new lower emissions factor for electricity, which advocates heat pumps as a ‘greener’ solution. Compared to the SAP 2012 metric of 0.519 kgCO2/kWH, SAP 10.1 proposes a value of 0.136 kgCO2/kWH – a 75% improvement in heat pump derived electricity carbon savings from previous figures.

As we continue to progress greener, carbon-neutral legislation, low-carbon, energy-efficient heat pumps are therefore set to grow in prominence next to traditional systems. With this in mind, it is key for building professionals to understand what innovations best complement low-carbon networks, and the impact of material choice.


An alternative to steel

Steel has traditionally been the most popular material to use for district heating systems. However, all-polymer networks are establishing a growing foothold in the market. With a main spine made of reinforced polypropylene (PP-R) pipe, these networks are able to provide higher loads to more buildings. Flexible PEXa pre-insulated secondary spines can then be easily connected to this main spine, ensuring more cost-effective installation as the network expands.

The growth of fourth-generation district heating technology has further increased the prominence of all-polymer networks. The lower flow temperature allows for less heat losses across the network – when considered alongside the material’s expected 50-plus year lifespan, polymer systems are increasingly being seen as a sustainable way of futureproofing a building’s heating and hot water supply.

By implementing a PP-R pipe into its main spine, building professionals can help developments realise reduced pressure losses of up to 19 per cent across the system when compared to a steel solution. Minimised corrosion risks also help drive down the possibility of system failure risk and ensuing, expensive repairs, with costs further reduced due to lower pumping costs.

Furthermore, PP-R being 37 per cent lighter than steel results in not only easier handling on site, but also lower emissions at the transportation stage. This sustainability is improved further by the fact that the material is 100 per cent recyclable.

While building professionals are increasing pressure to decarbonise their operations and select low-carbon solutions, considerations around reducing materials used and installation times continue to endure. Because PP-R pipes do not require the expansion bends present in steel networks, installation times can be shortened, with less materials and welding also required across the network. Additionally, the PP-R pipe’s lighter weight and the PE-Xa pipe’s flexibility allows contractors a quicker, more practical and adaptable installation.

In conclusion, new pressures to decarbonise heating and hot solutions, combined with traditional concerns around a quicker, more cost-effective installations without compromising quality, means building professionals are under more pressure than ever before. Polymer district heating systems, specifically of the fourth generation, provides a practical, low-cost way to deliver these amenities that are easy to implement and maintain.

For more information on district heating and PP-R pipework, visit

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