District Energy

District Energy, which is also known as District Heating and Cooling (DHC), are energy systems formed by a network of pipes that provide either or both heating and cooling from one or more central points of generation to multiple buildings within a district, neighbourhood or city. These systems have been widely deployed as a way to provide low carbon energy to end users, leading to significant financial and environmental advantages. From an economic perspective, DHC systems benefit from economies of scale, as utilising energy produced from a larger source to feed a number of buildings can often be more efficient than utilising individual cold or heat sources. ¹ These systems also enable the exploitation of locally available energy sources, which can be renewable (such as geothermal, biomass and solar thermal) or based on the recovery of energy that would otherwise be wasted, therefore achieving higher efficiencies and reducing the carbon footprint associated with heating and cooling. Another advantage of district energy systems is their flexibility; by enabling the integration of a diverse number of energy sources, end users are not dependent upon one single source, thereby providing greater energy security. This gives the system operator choice to ensure that the best energy source can always be selected to deliver the lowest cost and carbon energy possible. ²

Much of the energy consumed globally is for thermal comfort purposes. According to the International Energy Agency ³ heat is the largest single energy end-use, representing around 50% of the world’s energy consumption. Cooling currently accounts for only 6% of consumption in buildings, but the amount of energy used for this purpose is expected to grow rapidly as temperatures increase due to global heating and growing urbanisation of our cities. For these reasons, changing the way energy is provided for heating and cooling is crucial to tackle the climate breakdown and guarantee access to sustainable and clean energy for all.

The flexibility of district energy systems provides a key mechanism for the transition from fossil fuel based to low-carbon energy sources, as they can incorporate more efficient and clean energy sources as the network grows and new opportunities for renewable energy generation or waste heat recovery become available. The potential of waste heat recovery and reuse for domestic heating is particularly associated with DHC systems, as they enable the efficient transport of waste heat from its generation point to where end users are located. Waste heat can be recovered from a variety of urban sources, e.g. data centres, electrical systems, railway tunnels and sewage systems. ² As many of these sources typically provide heat at low temperatures, heat pumps are commonly deployed to upgrade the heat to an appropriate level for domestic use. Heat pumps, along with thermal storage technologies, represent important features of district energy systems, particularly as they can be utilised to provide heating and cooling simultaneously as well as to balance the intermittent generation of renewable power. This is achieved by converting renewable electricity to thermal energy (heat or cold) when costs are low and power generation is abundant. The stored energy can then be used to meet seasonal or daily peak demands. The coupling of renewable power and district energy enables the optimised use of energy resources by matching local production and demand, an essential aspect of future energy systems.

Case Studies

Recent innovation in district energy systems include the development of the 5th generation of district heating and cooling (5GDHC) which operates at ambient temperatures (typically between 15 to 25°C) [4]. These lower operating temperatures reduce heat losses, and thus both heating and cooling can be supplied with higher efficiency. One exciting case study of a 5GDHC is the GreenSCIES project, led by London South Bank University in the London Borough of Islington. The project involves the design of an ambient temperature loop connected to locally available urban waste heat sources such as data centres and underground railway tunnels. End users can either consume heat or reject it onto the system using reversible heat pumps and thermal stores which are distributed across decentralised energy centres. The energy centres also act as a hub for renewable electricity generation using photovoltaic (PV) panels and charging/storage points for electric vehicles. The integrated approach of this 5GDHC system, shown in Figure 1, is expected to deliver low carbon heat, mobility and power to more than 10,000 urban residents, reducing carbon emissions by 80% (over existing systems), improving local air quality, and addressing fuel poverty by providing a 25% reduction on consumer bills. ⁴

Figure 1 – A schematic of the conceptual design of the GreenSCIES project. [reference number =5]

Taking Action

In light of the climate crisis, there has been a growing interest in the benefits of district energy systems, particularly as we must not only change the way we generate energy, but also how efficiently we use it. We must realise the impact of the heating and cooling sector in terms of carbon emissions and demand more action from decision makers when it comes to sustainable methods to provide thermal comfort.

 A great way to get involved is staying tuned to the projects and initiatives that support the development of district energy technologies and raise awareness to their benefits. For instance, the UK’s LoT-NET project ⁶ is championing innovation in low temperature networks, researching new technologies that can accelerate the decarbonisation of heat and the uptake of district energy systems. Other international associations that are actively advocating for the development of the district energy sector include e.g. Euroheat & Power ⁷ and the UN District Energy in Cities Initiative, ⁸ which frequently organise workshops and conferences for district energy professionals and enthusiasts. Attending these events is a great way to learn more and meet professionals who are at the forefront of the energy transition and see district energy as a turning point in the fight against climate breakdown.