Steve Richmond from Rehau Building Solutions looks at the key considerations when commissioning a district heating network – an key option to consider in the race to reduce carbon in residential developments.
Though the UK’s green transition will likely be ushered in by a multitude of technologies, district heating has emerged as one of the forerunners of a low-carbon nation. Recent schemes such as the £288m Green Heat Network Fund (GHNF) as part of the wider £338m Heat Network Transformation Programme (HNTP) have demonstrated government faith in the technology as a key method of achieving net zero.
For this reason, many housing developers are beginning to explore the possibility of using district heating for their low-carbon housing projects. Here, it is important to examine the key considerations for integrating a district heating system into a low-carbon housing development in order to derive the maximum benefit.
SUCCESSORS TO THE GAS BOILER
There is much debate around which technology will succeed the traditional gas boiler come the introduction of the Future Homes Standard in 2025. Of these, heat pumps, district heating networks and hydrogen appear to be the most touted. However, it should be noted that with the latter currently early in its R&D phase, it won’t be available come the scheme’s introduction, meaning it remains a long-term potential solution.
For this reason, heat pumps and district heating networks remain the most sensible options. That said, many heat networks can make use of a large, centralised heat pump as a heat source, with the latest statistics from the Heat Networks Planning Database (HNPD) indicating that this is the case for over 70% of planned installations.
Naturally, this means that the question is not of heat pumps versus heat networks, but individual heat pumps versus heat networks. This subject should therefore be broached on a project-by-project basis, with both technologies able to offer a wide variety of benefits.
Initiatives such as the Boiler Upgrade Scheme (BUS) offer ample support for the uptake of domestic heat pumps, but do not extend to new build properties, unlike the GHNF. Regardless of which technology is opted for, it is critical that these alternatives are adopted sooner rather than later, ahead of the UK Government’s ambition to phase out all new purchases of gas boilers by 2035.
THE GENERATION GAME
The first thing to be aware of before undertaking a district heating installation is the fundamental differences between each generation of this technology, as the applications and benefits can vary wildly depending on the system specified.
At present, most district heating networks installed in the UK are third generation, circulating water at 70-95°C with a gas combined heat and power (CHP) system usually as the source. While these systems still make use of fossil fuels, distributing heat from a singular energy centre proves more efficient than heating homes individually, resulting in carbon savings.
That said, the true potential for district heating networks lies in fourth generation systems. This technology operates at a lower flow temperature than its predecessor, usually around 40-60°C, reducing heat losses and increasing energy efficiency. It should also be noted that due to this lower temperature, fourth generation heat networks are ideally suited to polymer pre-insulated pipework.
Moreover, this also presents an opportunity for the build to be heated by a number of more environmentally-friendly sources – a key consideration for any low-carbon housing development. This includes heat pumps, solar thermal systems and even waste heat recovery systems from nearby data centres. Fifth generation systems, using ambient loops and heat pumps in each building to boost the temperature are also in development, though the main focus remains on transitioning from third generation networks to fourth generation.
MATERIAL SPECIFICATION
One of the final considerations before commissioning a heat network for a housing project should be material specification – namely, polymer or steel pre-insulated pipework. The choice here can have a knock-on effect on network design and installation, so it is important to weigh up the applications of each.
Steel has traditionally been used for district heating networks, is available in larger sizes and can also withstand higher temperatures (above 100°C) and pressures. However, with newer low-temperature systems, these high temperatures are not typically needed anymore.
By its very nature, the installation of steel pipework is more complex, requiring wider trenches and specialist welding contractors. Moreover, due to the large forces involved, steel pipework requires expansion loops to be fitted, adding to the overall complexity of the build as more joints and pre-fabricated sections are needed.
Together, these factors result in a slower installation, which presents the risk of running over and impacting the wider build. Polymer pipework, on the other hand, facilitates a much quicker installation in order to minimise the impact on the rest of the project.
Large diameter polymer pipes made of PP-R can be used for the main spine of the network, creating a fully polymer system from the energy centre to each individual house. A whole polymer network will typically have lower heat losses than an equivalent size steel network as the lambda value of the polyurethane foam used in PE-Xa pipe is lower.
Lastly, and perhaps most critically, polymer pipework also provides the best level of corrosion resistance compared to rival solutions. This provides the housebuilder with the highest confidence level in the system’s long-term performance.
CLOSING THOUGHTS
Entering the world of district heating can be a daunting prospect for any housebuilder, with multiple factors to take into consideration. The points outlined here offer only a glimpse into the vast potential of this technology, though should offer a good starting point for any developer looking to make use of a heat network for their housing project.
Primarily, housebuilders should consider fourth generation networks due to their synergy with low-carbon heat sources such as heat pumps, which will help the site achieve a lower carbon footprint once in operation. Here, specifying polymer pipework over steel might also be a sensible choice, as it is better suited to fourth generation networks and quicker and easier to install.
Steve Richmond is head of marketing and technical at Rehau Building Solutions