Following this year’s Future of Heat conference, we thought it would be timely to revisit the topic of 4^th and 5^th generation heat networks, and to examine the role that they can play in the effort towards decarbonising the UK.

As the industry continues to introduce newer, more efficient, and lower carbon solutions such as electronic heat pumps, NB-IoT HIUs, data driven optimisation systems, integrating networks into local resources and other potential sources such as hydrogen.

Adopting the next step forward in heat network tech, means transitioning away from 3^rd generation networks, which operate with higher, less efficient temperatures and are typically powered by Combined Heat and Power (CHP) energy centres, or gas boilers.

The heat decarbonisation challenge

Decarbonising heat is a big and complex challenge and the growth of low carbon heat networks is critical to delivering on this goal. The latest UK energy trends statistics show that domestic energy use contributes approximately 18% of CO2 emissions, which come mainly from natural gas used for heating, hot water, and cooking.

A key challenge for the sector is to improve heat network efficiency. This includes replacing gas on existing systems as soon as possible, while also building new schemes using clean alternatives to gas. This might involve connecting buildings to low carbon district heating or replacing gas boilers and CHP with alternative generation that uses waste heat; heat pumps (air, ground, or water source) or hydrogen further down the line. There's no single solution to the complexities this transition poses, but new generation district and community heating schemes have a vital role to play in the journey to net zero.

What are the 3 key types of heat network?

3rd Generation Heat Networks

Most of the UK's current heat networks are 3rd generation systems, usually fuelled by a gas boiler or CHP energy centre, only a small number are supplied by energy from waste and heat pumps. Heat is delivered through insulated pipes to the buildings served by the network and then distributed onwards to the individual units or homes within the buildings. Heat is typically supplied at around 90℃-70℃. These networks often contain centralised thermal storage, and any cooling requirement is met by a separate cooling network or different system.

4th Generation Heat Networks

4th generation heat networks are also supplied by a centralised energy centre but differ significantly from previous generations in having lower operating temperatures. Heat is supplied at below 70℃, improving efficiency across the heat network, especially in those energised by heat pumps or energy from waste, which perform better at low temperatures.

Highly insulated pipework is used (usually plastic rather than steel), with large, centralised thermal storage to smooth energy demand and improve plant efficiency.

3rd and 4th generation heat networks in the UK, mainly rely on a separate cooling system. However, there is future potential to follow the continental model, where a single heat network is used to deliver space heating and cooling on a seasonal basis, where hot water is provided separately using a centralised hot water network. As our climate warms and demand for cooling increases, the UK could use the same approach to deliver cooling more sustainably and cost effectively. After all, it is only in recent years that the UK has moved away from centralised hot water preparation in favour of twin plate heat interface units (HIUs).

Private wire electricity networks and on-site renewable generation, such as solar PV, can be integrated into both 4th and 5th generation networks. This can help reduce costs for customers, while achieving further carbon reduction.

5th Generation Heat Networks

5th Generation Heat Networks are radically different from all previous systems. Heat production is decentralised – using heat pumps – in each house or apartment. They operate at low temperatures and generally require supplementary immersion heating for hot water. In addition, cooling is integrated via a 2-pipe interchangeable system of heating and cooling between buildings.

There two types:

Those that use ambient temperature heat (i.e. the natural temperature of water as it comes out the ground), which is then distributed to heat pumps in each apartment.

Those that use <25℃ heat – where a central heat pump is used to maintain the distribution system at around 20℃ followed by a second lift in temperature by individual heat pumps in each apartment.

On residential schemes, this is a much more expensive way of delivering heat than a 4th generation system, especially on large developments. 5th generation schemes require supplementary domestic hot water cylinders with bulky immersion heaters, which presents space issues. It also involves purchasing power from the grid – often at premium domestic rates.

Our modelling shows that 4th generation schemes currently provide a much better option for large residential projects because they can deliver excellent carbon savings much more cost effectively and can use a diverse range of heat sources. They also provide much greater transparency via smart metered data.

We believe that 5^th generation systems are much better suited to industrial and commercial heat networks where there is more scope to balance heating and cooling demands and more chance of projects stacking up commercially. This does not mean that 4^th and 5^th generations cannot be deployed together on large mixed-use sites. This is an interesting opportunity to play to the strength of each system.

Managing the transition to lower carbon heat networks

4^th generation heat networks are fuel agnostic, and can use a range of heat generation solutions, the transition to electric heat pumps won't happen overnight. It will take time to wean the UK away from gas due to the favourable economics of gas heating. Heat pump costs will fall as the industry rapidly scales, but at the present time, the economic viability of using heat pumps in heat networks is extremely difficult to achieve without grant assistance. Financial support from the Heat Network Investment Project and Green Heat Network Fund, which started opening this year, are easing the transition.

Optimising heat networks for cost and carbon savings

In the transition phase, it is essential to optimise CHP and whole network efficiency, which can deliver dramatic cost and carbon savings, while also achieving lower temperature operation in readiness for conversion to heat pumps.

This also apples to future networks. In fact, efficiency and optimisation are critical to delivering expected performance standards as temperatures reduce and tolerances tighten. Switch2 is making impressive progress in retrofitting 3rd and 4th generation heat networks to raise them to expected high performance standards – at a price customers can afford.

Our artificial intelligence (AI) enabled Optimise technology uses big data and remote connectivity to gain complete visibility of performance. Optimise applies learning algorithms to the data it extracts from across the entire heat network to identify, diagnose and automatically remedy inefficiencies and faults. This informs a proactive ongoing management and maintenance regime – focused on reducing running costs and ensuring that heat schemes live up to the performance expectations in financial models. While Optimise was developed with new developments and the more modern technologies found in these heat networks, it is able to function in legacy networks also, where it is currently delivering savings of up to 35%.

Learn more about how Optimise can benefit the efficiency of your schemes, and lower your operational costs and the energy bills of your residents.

Mitigating higher costs

It’s possible to mitigate higher costs of transitioning to lower carbon heat sources by integrating on-site solar generation into projects. This can reduce the cost of powering heat pumps, while also providing an opportunity to stack revenues selling electricity to heat network customers. Thermal stores can also be added to use heat more cost-effectively.

Flexible pathway to net zero

Heat networks provide the ultimate flexible pathway to net zero as they can be adapted to switch to new lower carbon fuels and technologies, as they become commercially viable.

With a coordinated approach to design and delivery and continued government support, the next generation of heat networks can provide affordable and sustainable energy solutions for residents – helping the UK towards net zero.

You can view our webinar on 4th & 5th generation heat networks here