When it comes to new district heating projects, choice of materials can have widespread ramifications on the wider build, impacting installation speed, performance and overall network design. With this in mind, Steve Richmond, Head of Marketing & Technical at REHAU Building Solutions, discusses the importance of pipework and shroud specification for contractors.
As the UK makes strides to achieve net zero, district heating is rapidly emerging as a key technology in enabling this transition. Its advantages are increasingly being recognised, and it is an affordable, low-carbon distribution method for heating and hot water for both urban and rural settings. This is best demonstrated by stats from the Association for Decentralised Energy, indicating that there are 17,000 heat networks in the UK, supplying half a million customers. This marks a substantial increase over earlier figures from 2013, when there were only 2,000 heat networks in the UK, with 211,000 users.
However, despite these successes, heat networks only contribute around 2-3% of the UK’s total heat demand at present, which is much lower than that of many European contemporaries. This is not to say that efforts are not being put in place to bring the UK’s heat network numbers in line with that of the continent, with the Government pushing this technology via a variety of initiatives and incentives.
Namely, the £288 million Green Heat Network Fund (GHNF) was introduced in March 2022 to support the development of new heat networks, alongside the retrofitting and expansion of older systems, with a view to accelerating the growth of the district heating market in the UK. In turn, this forms part of a wider commitment for heat networks to supply a fifth of the country’s total heat demand by 2050.
With all of this in mind, it goes without saying that close collaboration between suppliers will be paramount to achieving these ambitious goals. Simply bringing these technologies online is one thing, but ensuring they are efficient and effective is another challenge unto itself, and will require good design principles paired with high-performing materials.
Before specifying materials for a district heating project, understanding the key differences between the various generations of this technology is paramount, as the two are intrinsically linked. The latest district heating networks are fourth and fifth generation, with each offering their own advantages. First and foremost, fourth generation systems make use of flow temperatures between 40°C and 70°C, making them ideal for use with low-carbon sources such as air, ground or water source heat pumps, or waste heat, among other sources.
On the other hand, fifth generation networks use dramatically lower temperatures – between 5°C and 20°C. This means that individual heat pumps are required at the building level to boost the temperature. While both have their benefits, the choice on which to specify often comes down to individual project requirements.
With a singular heat source, fourth generation systems can be cheaper to install and maintain than their fifth generation counterparts, while also affording the operator easier maintenance and control for the same reason. However, fifth generation networks make good financial sense where there is free low-temperature waste heat available, and can also be useful in areas where simultaneous heating and cooling loads are present.
A Material World
Once designers and contractors know which generation of district heating they’re dealing with, they can make the correct choices in regards to material specification. In the realm of pre-insulated pipework, this is a choice between steel and polymer. The former has traditionally been the industry-standard, and is available in a large variety of sizes. Steel pipework is also able to withstand operating constant operating temperatures of over 90°C, though with the lower flow temperatures of fourth and fifth networks, this factor is largely redundant.
However, steel pipework is heavier, meaning that the carbon emissions from freight are much higher, while installation requires the use of welding, which requires both skilled workers and favourable weather or tents to be completed. As opposed to polymer, steel networks also need more joints due to the 12m pipe lengths and the requirements for expansion loops in the ground. Additionally, water ingress at the pipe join can lead to corrosion and even pipe failures.
Here, polymer pipework appears to better suit the needs of modern heat networks – particularly fourth generation systems. First and foremost, polymer pipework is lightweight and flexible, making it easier to transport, while also having less impact on the environment. A 2022 study from REHAU displays the true extent of this, indicating that polymer pipes can cut carbon emissions by up to 67% against steel, taking into account an average journey from Manchester to London.
Polymer’s flexible nature allows it to be coiled up to 570m or storage or transport, while also meaning that less joints will be required for the network when it comes to installation. Moreover, this allows the pipework to be curved in the trench to avoid obstacles or other utilities already in the ground during installation. To further simplify the installation process, polymer pipework can be installed without need for welding. REHAU’s RAUVITHERM and RAUTHERMEX pre-insulated pipework, for instance, instead make use of the bespoke Everloc compression sleeve jointing system, facilitating a quick and easy installation for mechanical and civil contractors.
It should be noted that material specification for district heating networks goes beyond that of pipework, and that shrouds also have a large role to play in maximising both installation speeds and performance. REHAU’s new Clip-Flex shroud, for instance, is universal with all REHAU pipe sizes between 90-250mm, while also able to support angle deviations of up to 22.5° in every direction. Combined with the flexible nature of polymer pipework, this means that contractors can benefit from unrivalled adaptability in order to work around the unique demands of the site, as opposed to a steel system which requires a much more angular network and has no flexibility on the shroud insertion angle.
A heat network is nothing more than the sum of its parts, and it is an unfortunate truth that not all parts are made equal. For this reason, material specification should be front-of-mind for any designer or contractor looking to undertake a new district heating project. First and foremost, parts should be selected in accordance with the generation of heat network that is being created, while specifying high-performance materials can help facilitate a faster and greener installation, alongside a more efficient system once in operation.
To read REHAU’s whitepaper, Trends in District Heating Pipework, CLICK HERE.