Debate continues over what comes next in home heating, but with sustainability, efficiency and cost effectiveness proving key, district heating networks are growing in popularity as a potential option.
With this in mind, Steve Richmond, Head of Marketing and Technical at REHAU Building Solutions division, explores considerations around installing schemes for new build developments, with a specific focus on low density housing.
The key figure in UK residential construction is 370,000. This is the number of homes the new government has committed to building annually. The feasibility of this number, revised upwards from 300,000, may be up for debate. However, the underlying sentiment – that the UK needs far more homes to meet the population’s housing demand – is not.
Running parallel to the national housing debate is the discussion around decarbonising home heating. The Government has long committed to a phase out of fossil fuel-burning gas boilers as part of its net zero 2050 goals. As this technology is still the most used when warming homes, the scale of this task is undeniable. As such, a multi-stage approach punctuated with specific deadlines is understandable and practical.
Though these deadlines have shifted, one key plank of the decarbonising homes strategy has not. Indeed, while the phase out of fossil fuels in off-gas domestic buildings and ban on gas boiler sales for housing – both scheduled for 2035 – no longer applies to all properties, the ban on these boilers for new build houses does apply from 2025 as part of the Future Homes Standard.
New heating options
This begs the question of where house builders go from here, with debates over replacement heating technology options continuing. In housing, this usually boils down to three options – heat networks, individual heat pumps or hydrogen. Though the merits of green hydrogen have been strongly debated, its viability for domestic heating has come under increasing scrutiny, with recent announcements showing a trend away from the technology at a governmental level.
For instance, the National Infrastructure Commission, the executive agency responsible for advising the Government on the UK’s infrastructure challenges, has advised that hydrogen should be ruled out for home heating applications, citing efficiency and cost concerns. Alongside this, Energy Minister Lord Callanan emphasised in a November interview that hydrogen would have only “a very small role, if at all” when it comes to domestic heating.
Though the government is not set to make a formal decision on hydrogen’s role in future domestic heating until 2026, events such as these show a clear trend. With hydrogen’s viability being questioned but the gas boiler ban remaining unchanged, house builders need to consider what sustainable and efficient options are available now.
Exploring the possibilities of low carbon district heating, and more specifically, fourth and fifth generation networks, will be a key part of this. Indeed, even before these developments around hydrogen, data from Energy Systems Catapult has stated that one in five homes are set to be heated via heat networks by 2050. With this in mind, this previously ambitious estimate might actually be conservative.
The Next Generation
Currently, third generation district heating systems remain the most commonly used type on live projects in the UK. Designed with flow temperatures of 80-90°C in mind, these networks often use a central fossil fuel-based source that will likely not support current heat decarbonisation goals. However, the rise of fourth generation heating models with flow temperatures of 60-70°C certainly do, as this lower heat means they are ideally combined with low carbon heat sources such as heat pumps, biomass, solar thermal, geothermal or waste heat.
Fifth generation systems are also using heat pumps, but differ from the single external plant model in favour of decentralised individual heat pumps for each building to boost flow temperatures. There are pros and cons of both 4th and 5th generation systems and the choice will need to be based on a project-by-project basis but 4th generation is a simpler design transition from a 3rd generation viewpoint.
District heating technologies have long been associated with high density urban areas, where it has undoubtedly thrived and will hold a key role in decarbonising the UK’s cities. Yet given the direction of travel on decarbonising heat, conversations must be had on the role of heat networks in the suburbs – especially on new, low density housing developments.
Low density, high practicality
The perceived barriers associated with district heating systems in these environments are usually around cost and practicality. Although the length of pipes required are longer in these lower heat density projects, the fact the pipes can be installed at the same time as other utilities in a trench makes the installation cost far lower than retrofit schemes. It is still possible to ensure heat losses are kept to a minimum over these distances using high quality PUR foam pipe systems.
The majority of district heating pipework for new build housing will be able to be installed in new open trenches which are already dug by the developers for water, wastewater, telecommunications and power. Often this will run under future front gardens or along pavements in the new streets being created. Flexible polymer pipes in long coils over 500m are perfect for these applications allowing a faster installation than traditional steel pipework, ordinarily available in 12 metre lengths.
For lower density development layouts, this combination of flexibility and ease-of-use may appeal to developers, especially combined with the possibility of narrower trenches because extra space is not required for welding or expansion loops as is necessary with steel. Taken alongside the decarbonised heat sources possible with modern heat networks, it is clear why polymer pipework-based pipework is being increasingly specified in new build housing developments.
Meeting growing demand
There are other practicalities behind decarbonising the nation’s heat which must be considered. The Government has previously set a goal of 600,000 heat pump installations per year by 2028, yet only 72,000 were installed in 2022. Given the ambition of this target and the pressure on the supply chain and associated workforce to meet it, avenues to streamline installation should be welcomed.
In this context, fourth generation district heating systems may stand out as a compelling option. The scheme’s potential use of a large single, external heat pump not only minimises maintenance requirements and issues around home access and remedial works, but it also ensures a singular installation can be used to heat multiple homes and the economies of scale associated with a larger heat pump.
As polymer pipework connections use permanent mechanical jointing methods, they can also be fitted swiftly by civil or mechanical contractors without specialist hot works. REHAU, for example, uses EVERLOC – a patented and proven compression sleeve technology developed in-house on the back of extensive research and customer feedback. It forms a leak-tight connection of PE-Xa pipework in a two-part system that can be fitted without specialist training which involves no O-rings and requires only a simple visual inspection.
Safeguarding homeowners
Finally, beyond the practicality and applicability of district heating systems in lower density housing developments, the energy regulatory landscape continues to favour fourth and fifth-generation schemes. The 11,800 registered heat networks in the UK, which deliver around 13.5TWh of heat annually to 470,000 domestic customers, will be coordinated by national energy regulator Ofgem from 2024.
With the technology regarded as key to the Future Homes Standard’s emission reduction aims, which mandates all new homes built from 2025 emit 75-80% less carbon dioxide, this move will likely have a major impact on the housebuilding industry. Specifically, the introduction of formal Ofgem regulation around performance, price, service and supply, moving away from the current self-regulating model that governs heat networks, making district heating more attractive to the sector.
When looking at the demand for new homes and the drive towards decarbonised heat, industry cannot look at these challenges separately. To remain on track in these areas, house builders and contractors must look for solutions that thread both needles. Given the advances in pipework materials and low carbon energy sources, district heating networks could be that solution – especially in the construction of low density housing.
To effectively meet demand, it is vital that industry engages with the supply chain to address key considerations around specification and installation. By doing so, project stakeholders can remain ahead of the curve from a technological and regulatory standpoint.
Image credit: REHAU
