Common questions about heat networks
What is a heat network?
Heat networks provide heat and hot water from a single source (known as an energy centre) to multiple customers via insulated pipework. These networks can vary in size and scale up to whole cities. CIBSE CP1 defines them into two key categories:
- communal heating – supplying to a single building (typically multiple occupancy such as flats); and
- district heating – servicing more than one building (larger district heating networks may include more than one energy centre).
What is the difference between primary, secondary and tertiary heat network systems?
In order to get heat from the energy centre to the end user, heat networks feature extensive pipework and associated services. These are commonly placed into three categories:
- primary heat network systems – these are the large diameter distribution pipes which run from the energy centre to the building;
- secondary heat network systems – the pipework within the communal spaces of a building.
- tertiary systems – the pipework within a dwelling connecting to radiators (not featured in non-domestic buildings)
How can heat networks reduce carbon emissions?
At a basic level, heat networks can benefit from an economy of scale when compared with the traditional approach of fitting individual boilers within each property. This is particularly true when supplying heat to densely populated areas such as cities where more customers can be reached with smaller pipework networks. In practice, installing alternative low-carbon technologies, such as heat pumps, within these types of property can also be impractical making heat networks a better option.
Perhaps more significantly, heat networks are “fuel agnostic” giving designers the freedom to take advantage of low carbon options in the local area. This can include large heat pumps, combined heat and power (CHP) plants powered by waste and even utilising the heat from the London Underground.
How many heat networks are there in the UK?
There are currently estimated to be over 17,000 heat networks of different sizes within the UK. This meets around 2% of the total heating supply so there is still a long way to go to reach the CCC recommendations.
Common questions about CIBSE CP1 (2020)
What is CIBSE CP1 Code of Practice: Heat Networks?
The first edition of CP1 was published back in 2015 to support best practice when implementing what is a fairly new technology here in the UK. The document set out clear minimum standards and a code of practice with an aim of ensuring heat networks would meet their energy performance targets and provide long lasting benefits to customers.
CIBSE CP1 (2020) - published January 2021 - draws on industry feedback and research carried out since then to provide greater detail and clarity. It covers a wide range of issues which can occur over the course of a project such as determining system sizing and costs, appointing suitably qualified individuals, and developing communications with customers to ensure satisfaction.
Who is CIBSE CP1 designed for?
The process outlined within CIBSE CP1 is designed to support all parties involved in the planning, specification, installation, commissioning and maintenance of a heat network.
Does CIBSE CP1 apply to schemes for existing buildings?
Yes, the standard is applicable for networks serving both new and existing buildings.
Is compliance with CIBSE CP1 mandatory?
CIBSE CP1 (2020) is a voluntary document, however, the Department for Business, Energy and Industrial Strategy (BEIS) has indicated an intention to legislate around it in the current parliament. In addition, local planning codes – such as the London Plan, require an assessment of connecting to an existing heat network, or developing a site wide network.
What is new in CIBSE CP1 (2020)?
At more than twice the length of the original document, CP1 (2020) offers a much more in-depth approach to supporting industry practice. Key changes include:
- Expanded minimum requirements – the revised document provides a total of 540 minimum requirements covering many aspects of the system’s design, installation and operation
- Checklists, evidence packs and performance measuring – to support compliance, the new version includes checklists for all parties and several performance metrics such as absolute energy use per dwelling. This information is fed into evidence packs which are completed by the entire project team and provide an audited trail of the project. This means if anything goes wrong, it should be simple to identify the cause
- Addressing oversizing and lower operating temperatures – understandably, project teams often opt to oversize systems at the design stage to avoid heating issues for customers. Whilst this helps to keep properties warm, it can also create significant waste. CP1 (2020) provides clear information about the expected demand from each dwelling and how to size pipework accordingly to avoid wastage. It also provides guidance on lower temperature DHW supply to facilitate the move to introduce heat pump energy centres
For further information, CIBSE has provided a helpful overview of the key changes.
CIBSE CP1 and secondary heat networks
As part of efforts to simplify the guidance given to project teams, and address performance issues identified since the publication of CP1 (2015), CP1 (2020) provides a number of significant updates when specifying and installing pipework within buildings.
When should pipework insulation specification be considered in heat network development?
Under the process within CP1 (2020), pipework insulation needs to be considered from the very early stages of a project. Calculations for heat losses from pipework need to be carried out at the Feasibility Stage of the project (Stage 2) and detailed insulation specification is required as part of the Design Stage (Stage 3). In both cases, these calculations must be recorded and kept as part of the evidence packs.
Can heat loss from secondary pipework cause overheating?
Yes. As the pipework is in continuous operation, there is a clear risk of overheating from poorly insulated secondary pipework, particularly during the summer months. This is especially true in modern buildings as the improved fabric performance of these buildings mean space heating demand is much lower.
Objective 3.9 within CP1 (2020) has been developed to specifically address overheating risk as a result of heat losses from secondary systems in multi-unit residential buildings.
Research from AECOM has shown that use of enhanced specifications of pipe insulation can help to maintain internal temperatures within a more comfortable range for longer when compared with a specification completed to BS5422: 2023
Learn more about the pipework and overheating research
What performance targets does CP1 set for secondary systems?
CP1 states that, when designing systems for multi-residential buildings, the annual heat loss from secondary systems should not exceed 876 kW.h/dwelling/year, equivalent to 100 W/dwelling on average. It stresses this value should not be treated as a target and that well designed systems should aim to achieve heat losses of less than 50 W/dwelling.
Should I use the minimum pipework thicknesses recommended in CP1?
Unlike other insulation specifications (such as BS5422: 2023 and the Energy Technology List (ETL)) which specify maximum permissible heat losses per pipe size, objective 3.9.7 of CP1 (2020) instead provides a table with minimum insulation thicknesses for different diameters of steel pipe. The thicknesses are provided for both mineral fibre and phenolic insulation and in most cases are set at 50 mm. This may lead to the assumption that pipework insulated with either material will perform similarly. In reality, phenolic insulation such as that used in Kingspan Kooltherm Pipe Insulation has a much lower thermal conductivity than mineral fibre insulation and should therefore allow less heat loss at a given thickness. A modelled comparison of these materials on 60 °C pipework showed heat losses increased by between 30 and 39% when the minimum mineral fibre specification was used. In fact, the study showed that the mineral fibre specification would need to be over twice the thickness of the phenolic alternative to match its performance.
Again, rather than targeting these values, designers should think carefully about how they can optimise performance of the overall system. In practice, several ESCo’s (Energy Services Companies) who own and operate these schemes already require thicknesses greater than those within the revised CP1 and that practice is likely to continue as the focus on the energy performance of buildings, and risk of overheating, continues to grow.
What else does CP1 recommend regarding secondary pipe insulation?
In addition to ensuring pipework is well insulated, CP1 also states that all valves, flanges and fittings should be insulated and that insulation across the system should be continuous with vapour seals at all joints. It also highlights the need to ensure pipe supports are effectively insulated, recommending the use of “rigid low-conductivity inserts to maintain insulation quality at the support”.
Learn more about the considerations when insulating pipe supports
Ensuring continuity of insulation across the secondary system pipework is crucial to the performance of the system. Calculations show that a single 4” valve could allow 2240 kWh of additional heat loss per year on a system operating at 75 °C for 8760 hours. By comparison, the same valve insulated to an ETL specification allows just 153 kWh heat loss.
