Regulations will require minimum technical standards, under a Heat Network Technical Assurance Scheme (HNTAS), for all new-build heat networks from 2025, including the 50,000 residential connections already happening each year. This could rise to 100,000 heat interface units being installed annually in the foreseeable future, partially driven by the regulations themselves.

All 14,000 existing (legacy) heat networks will also be covered, including the 500,000 residential customers currently supplied by heat networks. However, the number of networks is probably a significant underestimate, and improved data could easily indicate there are more like 18,000 legacy networks.

Both communal and district heat networks will be included in the regulations, with the majority of legacy networks being relatively small, communal (single block) networks. The regulations will recognise that many of these communal systems are old and not in the best state of repair, often resulting in poor performance and customer outcomes.

HNTAS is addressing how we can bring these up to a reasonable performance standard over a reasonable period of time. The technical standards will be outcomes-based, so networks will need to meet key performance indicators (KPIs) to gain Heat Network Certification.

For the past 18 months, the Department for Energy Security and Net Zero (DESNZ) has been developing HNTAS, building on CP1 (2020). The work has been led by technical author FairHeat, in partnership with Gemserv, which is focusing on procedural aspects of the assurance scheme.

HNTAS is proposing that a single ‘responsible person’ be accountable for each heat network

Normative documents have now been developed, setting out the necessary governance, structures, procedures and technical standards required to ensure a minimum level of performance and reliability for heat networks.

HNTAS core principles are that the scheme will be outcomes-orientated, preventative, proportionate, deliverable, adaptable, and enforceable. See ‘Assuring quality of heat networks’, CIBSE Journal, May 2023.

The technical normative documents set out clear and measurable KPIs (technical minimum requirements) to be met for each element of a network, plus the evidence required and depth of assessment, along with ‘key failures’ that need to be avoided.

Draft normative documents have been developed in collaboration with sector stakeholders through an extensive series of technical sub-working groups. This involved 25 technical sub-workshops, bringing together 69 stakeholders from 44 diverse organisations, including manufacturers, housing associations, local authorities, consultancies, developers, contractors, energy service companies, trade associations, and professional bodies. This industry engagement will continue with a HNTAS consultation in the summer.

HNTAS’s proposed approach is to certify individual heat networks. Our work-in-progress model is shown in Figure 1. It combines a series of assessment gateways (orange) that, ultimately, lead to certification (blue). Most of the detailed technical assessment work, carried out by registered and trained assessors, will take place across the orange stages, with the clipboards showing assessment points, and the dotted lines as gateways to proceed to the next stage.

The normative documents set out the detailed minimum requirements at each assessment through design, construction and commissioning. These design/construct/commissioning gateways aim to ensure the network is likely to meet future operational performance targets and gain full certification. There is a clear requirement to have binary yes/no decisions, with certification (authorisation to supply heat to customers) awarded to networks that meet minimum technical requirements. By requiring responsible persons to demonstrate that their heat network performance meets KPI thresholds, before allowing a network to pass through each assessment gateway, the scheme is ‘preventative’ and ‘outcomes-based’ (two of the core principles of HNTAS).

This approach aims to ensure that the great majority of heat networks pass at the point of certification, and that key failures in the market are avoided. There are 28 KPIs, categorised into six categories, that set a framework for measuring and monitoring heat network performance. The six categories are: energy centre; district distribution network; thermal substation; communal distribution network; consumer connection; and consumer heat system.

Existing legacy networks will, inevitably, find it harder to meet the HNTAS minimum standards than new networks. So, HNTAS is taking a pragmatic transitionary approach to bring legacy networks as close to full standard as possible, as soon as possible. HNTAS will set out a transition period, during which improvement plans will need to be submitted and minimum levels of metering will need to be installed. Once metering is in place, networks will be in a position to evidence-measure performance accurately and move to full certification.

Fixing legacy networks

For legacy networks, HNTAS aims to ensure the market is able to comply and that the very worst-performing networks are addressed early. To achieve a steady improvement in performance over time, the goal is for every network to be fully certified to a minimum level of performance by a set future date. The proposal for legacy networks is a two-stage transitional approach, which will require minimum levels of metering and monitoring to be installed, followed by the need to report performance, with a minimum threshold that all heat networks must meet within a set period.

Operators will be required to submit a Heat Network Improvement Plan, setting out how they will achieve certification within a set period following the installation of metering, and will need to prove in-use performance after two years of operation, based on real data. It is proposed that networks installed before 2015 will be allowed more relaxed targets than those installed post-2015, when the Heat Networks (Metering and Billing) Regulations came into force.

HNTAS is proposing that a single ‘responsible person’ – such as the owner or developer – be accountable for each heat network. Duty holders of the designated designer, contractor and heat network operator are accountable to the overall responsible person for the day-to-day running of each project stage. This designation of duty-holder responsibilities is similar to the requirements in the Building Safety Act.

The project team is keen to ensure that this is a deliverable scheme, which is proportionate and does not place too much burden or cost on heat network operators or consumers.

During the operational stage, if the network achieves HNTAS minimum performance standards it moves into a stage where the heat network operator regularly submits data to the HNTAS portal (currently being developed), to show that it is still meeting the HNTAS KPIs.

More detailed assessments are only triggered where it falls outside the KPIs. Essentially, this allows a level of ongoing self-assessment for networks that meet minimum performance levels.

Evidence and data requirements will form a ‘golden thread’ throughout all stages of a network’s life, requiring submission of data into the HNTAS and Ofgem digital platforms. It is hoped much of this data submission will be automated, to minimise time and cost.

It is clear that significant change is coming in 2025 as the sector transitions to a regulated heat network market, and setting minimum technical standards is a key part of this. Assessing and certifying heat networks that meet the minimum standards will raise sector performance.

HNTAS is moving into a pilot phase across 2024, to test that it works in practice on real networks, before final implementation in 2025. Engagement with stakeholders throughout this process will continue, as this is key to achieving sector buy-in for the assurance scheme.

There are significant benefits and opportunities that will come from HNTAS: a commercial market for trained and registered assessor services; a general improvement in heat network performance, with consumers seeing improved reliability and service levels; social landlords and local authorities being able to provide more affordable heat; and investors viewing networks as more investable.

There is still a great deal to do to develop heat network regulations, through consultations and secondary legislation. DESNZ aims to publish the HNTAS normative documents in some form this year. HNTAS piloting will take place throughout the year, and DESNZ is seeking heat network operators and assessors that would like to take part. Plans to update CIBSE CP1 are also being put in place, to ensure alignment before regulations are implemented in 2025. A methodology to calculate the carbon content of heat should also be in place by that date.

Heat networks are complex and introducing regulation is not straightforward, so it is important to give this sector early sight of direction of travel. As such, this is a work in progress and does not represent government policy. A DESNZ HNTAS consultation this summer will continue sector engagement, and this work will put in place the missing piece of the heat network jigsaw, namely heat assurance. 

• Based on a paper presented at the 2024 CIBSE Technical Symposium www.cibse.org/symposium

About the authors: 
Professor Phil Jones is an independent consultant working on the DESNZ HNTAS team; Gareth Jones is managing director of FairHeat, the HNTAS technical author

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The HNZ consultation is part of wider changes and proposals, including the December proposals for heat networks in the Future Homes and Buildings Standards (FHS/FBS) and the upcoming regulation of heat by Ofgem. As part of this, the Department for Energy Security and Net Zero (DESNZ) is creating a Heat Network Technical Assurance Scheme, and networks will have to meet its criteria to be allowed to operate.

The current proposals allow for the continuing development of high-carbon networks for years to come, but without doing enough to support their decarbonisation, said CIBSE, which called for the decarbonisation of existing and planned networks to be addressed. It noted that, based on the current data available through the heat metering regulations, 91% of the UK’s 11,847 networks currently use natural gas or oil as their primary fuel. CIBSE also noted that, based on DESNZ data about the pipeline of heat networks, more than 45% of heat network expansions in the pipeline are proposing gas – for boilers or combined heat and power (CHP) – as their primary fuel. However, neither consultation sets out a clear expectation and reasonable timeframe for decarbonisation of heat networks, said CIBSE.

Zoning
The HNZ consultation is significant: in zones identified by a new ‘central authority’ and local zone coordinator, new buildings, existing communally heated buildings, and some existing non-domestic, non-communally heated buildings would have to connect to the heat network. A national zoning methodology would determine which areas are suited to a heat network in terms of value for money and deliverability. It is not clear at this stage how the methodology would assess networks against alternatives, in terms of carbon impacts and costs to consumers. CIBSE does not agree that the main counterfactual to heat network zoning is ‘do nothing’ (as is the case in the heat zoning consultation’s impact assessment), and said there needs to be a focus on other options for heat decarbonisation: ‘This is the real test of whether heat networks offer a cost-effective decarbonisation option,’ it said.

CIBSE is concerned that carbon performance and costs to heat-network consumers did not appear central to the current zoning proposals: for buildings that have to connect to a network, exemptions on grounds of carbon performance and consumer protection are unclear, while they were more prominent in the 2021 consultation, said CIBSE. ‘It is a serious risk to carbon emissions reductions, and to consumers. This must be revisited,’ it said.

CIBSE agrees that building owners should be able to apply for exemptions to connection on grounds of capital cost and timing, but said there must also be exceptions for low carbon buildings. High operational costs for consumers of a heat network must also be a reason for exemption.

Carbon limits
While CIBSE welcomes the fact that networks within a heat zone would have to meet minimum carbon content of heat criteria, it has concerns about the carbon emissions methodology used to demonstrate these criteria, which risks ‘significantly underestimating and misrepresenting the operational carbon impacts of heat networks’.

First, it said the methodology proposes to use a carbon factor for CHP-generated electricity of 304g/kWhe– this is much higher than the current grid average, and is only exceeded by the grid for a small number of hours in the year (eg, around 30-40 hours in 2030, according to data from Carbon Intensity). This means the methodology would attribute benefits to CHP-generated electricity that are unlikely to be realised in practice, and even less so in the future as the Grid continues to decarbonise, said the response.

Second, the methodology does not include secondary losses in the distribution system, which could mean the underestimation of emissions, added CIBSE. While secondary systems are often under different ownership and responsibility, the secondary losses must be accounted for in one way or another, as losses are often significant, contributing to energy waste and overheating in communal parts, said CIBSE. The record of heat networks under the heat metering regulations showed 29% losses  on average, even in communal rather than district networks.

DESNZ should provide a trajectory of carbon limits applying to heat networks, so that networks are encouraged to take early measures before being required to do so, said CIBSE’s response, which also called on government not to wait until the mid-2030s, as proposed, to develop low carbon standards for networks. It proposes standards are created as soon as possible given the significant time lags between planning and operation of heat networks, and would welcome dialogue with DESNZ, as it believes CP1 Heat networks: Code of Practice for the UK could play a role in this.

Public register
CIBSE’s recommendation for the HNZ and the FHS/FBS is to create and maintain a public register of networks, which would be operated by organisations independent from heat networks’ interest. According to CIBSE, this should be publicly available and independently audited, and be the single source of information for any policy relying on operational performance of networks, including Building Regulations, zoning, funding, and so on.

The register should have information currently included in the heat metering register, and have additional data on individual networks – including energy use per fuel – allowing analysis of primary and secondary losses, and carbon content of heat, said CIBSE. It added that this is not the case currently, with the heat metering register providing information on the heat generated and supplied, and on the type of fuel used, but not its amount, preventing an estimate of energy efficiency and carbon content of heat. 

The upcoming regulation of heat by Ofgem creates the perfect opportunity to address this, added the Institution, and it would be happy to discuss this with DESNZ.

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