What is district heating? District heating (DH) relies on a central heating plant and a heat distribution network to supply heat at a district level to homes, businesses, public buildings, industrial facilities, etc. District can mean anything from a neighbourhood to a rural town to a large city. Modern heat distribution networks are made of highly-insulated pipes buried in the ground, in which hot water is circulated at temperatures ranging from 110°C down to 60°C for the so-called 4th generation district heating (more on that later).
Individual buildings’ central heating systems are connected to the district heating via “heat user interface” (HUI) units, either directly (no heat exchanger) or indirectly (with heat exchanger). HUIs typically interact with the space heating system controls on the user side, and they generally include heat meters as well as safety devices (pressure regulation, leak detection, etc). Domestic hot water (DHW) is either produced instantaneously through a heat exchanger located in the HUI or accumulated in individual DHW tanks.
A district heating company acts as a utility to operate and maintain the district heating assets, as well as manage the heat metering and billing to individual customers. In large district heating systems, heat production/ distribution/supply operations can be undertaken by separate entities. The legal status and ownership of district heating companies can also vary significantly, from private for-profit utilities, to user-owned, not-for-profit cooperatives, and public utilities owned by the State or local authorities. There are also many variations in between.
Solving heat decarbonisation There are more than 6,000 DH schemes in Europe. In Northern Europe, 50% of heat users are serviced by district heating. In Scandinavia in particular, the deployment of district heating was accelerated in response to the oil crises, and it continues to be seen as the solution of choice – not only to increase resilience and decrease import dependency, but very importantly as a foundation stone for their energy systems’ decarbonisation.
In Ireland, we have very limited experience of district heating. The now defunct Ballymun District Heating system has left some reputational damage to the technology, but recent projects such as Tralee and Cloughjordan are pioneering the re-birth of district heating here. The Dublin Docklands district heating project is also getting some traction with the construction of the waste-to-energy plant in Poolbeg from which the equivalent of 50,000 houses’ heating requirement could be recovered.
Other initiatives ongoing in Irish towns such as Killarney, Killorglin, Kilkenny, Claremorris, etc are laying the foundations for new district heating projects.
There are several key reasons why district heating is important for Ireland’s energy transition. First, district heating can be a transformative solution to help implement at scale the transition of our urban centres’ heat supply to low-carbon and renewable energy sources. We are in serious trouble meeting our renewable heat targets for 2020 (we are not even half way there!) and we’ll need radical solutions to bridge the gap. District heating is a practical solution to recover waste heat from electricity generation plants and from industrial processes, or to take advantage of significant economies of scale to deliver renewable heat cost-effectively from biomass, solar thermal, geothermal and other local energy sources.
Recent studies have shown that Ireland has a waste heat potential of 102 Petajoule (PJ), compared to a national heat demand of 117 PJ. This is virtually free heat our energy system is currently dumping. Secondly, by tapping into our local, indigenous heat resources, district heating will help make our energy system more secure and less dependent on fuel imports. We currently depend on over 90% of imported fossil fuels to heat our buildings. Shifting our energy expenditure from imported fuels to capital investment in our energy system and the production of local renewable fuels will create thousands of jobs in construction, engineering, operation and maintenance, farming energy crops, etc.
Thirdly, we have learned from Denmark that large-scale heat storage is an excellent companion for district heating systems as it offers greater flexibility for combined heat and power plants (CHP) and enables high levels of solar thermal energy input into the heat supply. More importantly, large heat stores can be used to harness excess electricity from intermittent renewable sources such as solar and wind power which can then be stored as thermal energy via direct electrical heaters or heat pumps. Storing electricity in this way is 100 times cheaper than in batteries.
Together, district heating and large-scale heat storage is a very effective tool to achieve the shift to renewable energy in our electrical system and heat supply. This is increasingly becoming mainstream in Denmark in what is referred to as 4th Generation District Heating systems.
Deployment of district heating in Ireland XD Sustainable Energy Consulting Ltd, Kerry County Council and the Tipperary Energy Agency – together with their European colleagues in the EU SmartReFlex project – have assessed current barriers to DH deployment and have started addressing the issues with key stakeholders at local and national level. Critically, our energy policy-makers need to be educated as to the role district heating can play in our energy transition and to integrate it into long-term energy planning at national and local level. In this regard, the current policy of continually expanding the natural gas network is locking the heating sector into fossil fuels for the long-term. Let’s keep this precious fuel for cleaner (than coal or peat) electricity generation from which we can harness cheap heat as a by-product, as well as for transport.
Secondly, the large capital investment required for district heating needs to be de-risked and the cost of project financing reduced with government-guaranteed longterm loans. In addition, in a context of cheap fossil fuels, financial incentives such as the Renewable Heat Incentive will help district heating systems fuelled by renewable fuels compete with oil and LPG heating in areas outside of the natural gas network.
Thirdly, local authorities should be mandated and equipped with the capability to support DH project development, notably by engaging in local heat planning and integrating district heating in plans for future infrastructure works such as road, drainage, etc. Moreover, confidence and know-how along the whole supply chain, including among the engineering profession, needs to be reinforced through education, training and support for innovation. Pilot projects have a key role to play in building experience and focussed government support is required in this regard.
EU SmartReFlex The EU SmartReFlex project continues to provide a framework for addressing some of the issues identified here. We will have an opportunity to discuss the practical impact of the project in future articles. Readers of Building Services News will also have a unique opportunity to develop their knowledge by participating to a 2-day training course on design and planning of Renewable District Heating & Cooling, on 24-25 January 2017 in Dublin. For further details, please visit: http:// tippenergy.ie/event/technical-design-planningres-district-heating-cooling-dhc-trainingcourse-2/
To find out more about SmartReFlex, visit www.smartreflex.eu.
Contact: Xavier Debuisson. email: firstname.lastname@example.org