• What exactly are heat networks, and how do they work?

The first thing to know about heat networks is that they are not a heat source, but a system of transporting heat. Multiple homes or buildings are typically connected to a single heat source via a network of underground pre-insulated pipes, as opposed to having individual heating systems in every building. On a large scale, this is referred to as ‘district heating’, though the two terms are largely used interchangeably.

Perhaps one of the biggest benefits of heat networks is that they are heat source agnostic. The energy centre can be anything from a large heat pump, to waste heat, to a biomass boiler or deep geothermal, though more traditional fuel sources can be used. Regardless of the heat source, the role of pre-insulated pipework is always key here – minimising heat losses between the energy centre and the heat users

The success of heat networks is underpinned by efficiency, for both the end user and the operator alike. In the past, there have been cases of older, inefficient networks, though the introduction of frameworks such as OFGEM regulation and the Heat Network Technical Assurance Scheme (HNTAS) have established a mandatory framework of performance standards designed to improve network quality and operational outcomes. Combined with initiatives such as REHAU’s Advanced Design Support Package, which promotes detailed reporting, robust design practices, and system optimisation, these measures should help address many of the challenges experienced in the past. Looking ahead, the future of heat networks appears promising.

Rehau equipment for heat networks

  • How do heat networks compare to heating homes individually?

Heat networks and individual heating both have their benefits – for instance, the former offers the advantage of centralised maintenance, with only one heat source needing to be serviced and maintained rather than hundreds or even thousands. These large centralised systems also offer increased efficiency compared to individual boilers. Individual heating systems, on the other hand, give end users the freedom to switch suppliers if desired.

This said, taking a practical approach to net zero is always key, and every technology will have a role to play in the energy transition. Heat networks truly shine in new build housing developments, where they are usually the lowest cost low-carbon heating option when deployed at scale, or when there is a large waste heat source close by, such as a data centre. Naturally, it follows that district heating is likely to be the right choice for city centres, high rises, university campuses, social housing, or new housing developments, whereas a remote property will probably draw much more benefit from an individual heat pump.

  • What is the difference between fourth and fifth-generation heat networks?

One of the hottest topics in district heating is that of fourth- and fifth-generation networks, with the common assumption being that fifth-generation networks are a direct progression of the fourth. However, this isn’t quite the case, and should again come down to which is the right choice for the intended application.

The primary difference here lies in operating temperatures. Fourth-generation networks typically have flow temperatures of around 40-70°C, distributing ‘ready-to-use’ heat via underground pre-insulated pipework, such as RAUVIPEX. These networks are the most common type being installed in the UK and are ideal for new build housing developments.

Fifth-generation networks, by contrast, operate at much lower ‘ambient’ temperatures – usually around 10-30°C. This allows fifth-generation networks to cool as well as heat, but with the trade-off of added complexity and greater electricity dependence, with a heat pump required in each building. As such, fifth-generation networks typically use uninsulated pipework such as PP-R, and may be a better fit when both heating and cooling is the goal.

Trench for heat networks

  • How widespread are heat networks in the UK, and what needs to be done to improve uptake?

Despite the many benefits of heat networks, uptake in the UK is significantly lagging behind that of the continent, with just ~3% of heat demand currently met by the technology. Much of this is down to a long-term reliance on cheap gas. The UK ‘spark gap’ – the price ratio between a unit of electricity and a unit of gas – currently sits around 4.71 : 1, making electricity nearly five times more expensive. The lack of a coherent regulatory framework until now has also significantly limited scalability.

However, it’s clear that large-scale district heating is possible. In Germany, district heating currently supplies around of 15% of household heat, rising to over a third in Berlin, Hamburg, and Munich. Other European countries boast even higher levels.

Fortunately, the first key step to improving uptake is already underway – regulatory overhaul. Effective from the start of this year, Ofgem now serves as the regulator for all heat networks in the UK, while the introduction of HNTAS has helped set tighter operational efficiency standards, ensuring that the poorly optimised networks of the past are not repeated. Meanwhile, the introduction of heat network zoning is already helping to identify areas where district heating schemes are most feasible, while advanced planning support is helping to see these networks through from design to delivery – ironing out creases in plans and calculating hydraulics, pipe sizing and material lists.

Beyond this, skills and training will be key to enabling a swift rollout. Steel-based heat networks have traditionally been more complex due to the need for specialist coded welders, though transitioning to polymer systems allows contractors to circumvent this requirement. Using simple, yet reliable compression sleeve jointing systems such as REHAU’s EVERLOC, with manufacturer support, contractors can learn the skills required and have access to ongoing support.

  • What materials are typically used for heat network pipework, and how do they compare?

Another key discussion topic surrounding heat networks is pipework – specifically, which material is best?

The traditional choice for the sector is steel. It’s available in a variety of sizes, and can comfortably handle operating temperatures as high as 120°C. That said, steel pipework also comes with its limitations – it’s naturally heavy and inflexible, meaning it must be installed in angular patterns with expansion loops to mitigate pressure, requires specialist coded welders to install, and is at risk of corrosion once in the ground.

The alternative here is polymer pipework, which offers minimal heat losses while being lighter and more flexible, allowing it to be easily transported in coils and routed around obstacles within the trench. Unlike steel systems, polymer pipework offers three primary jointing methods: butt-fusion-welding, electrofusion, and compression sleeve systems.

Whilst polymer systems can handle temperatures up to 95°C, most district heating networks are now operating in the 40-70°C range, leading many specifiers to polymer pipework for the benefits listed above. However, many designers may still incorporate both steel and polymer pipework into their plans, which is where the role of design software again comes into play to help make the appropriate calculations.

  • What does the next ten years look like for heat networks?

The future is bright for heat networks. With the Future Homes Standard set to outlaw gas boilers in new homes from 2027 onwards, district heating systems will have an increasingly important role to play in meeting heat demand, with a surge in uptake hopefully on the horizon.

Thanks to the introduction of HNTAS, networks are only improving in quality too, which will helping to restore confidence where there have been reputational challenges. Meanwhile, manufacturers such as REHAU are continuing to innovate and deliver new technologies which will make heat networks more affordable, reliable, efficient, and accessible. Together, these advances will help district heating to reach its full potential and play a part in the UK’s decarbonisation journey.

Steve Richmond, Sales & Marketing Director at REHAU Water Technologies

Author  Steve Richmond, Sales & Marketing Director at REHAU Water Technologies

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