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District heating and energy security

Paul Kando

When the 1970 oil crises hit, states heavily dependent on oil have found themselves in dire straits. Denmark, for instance, with more than 90% of its energy coming from imported oil whose price has quadrupled overnight. Danes shivered in their homes, factories shut down, alternate street lights were turned off, Sunday driving was banned. Denmark decided to get off imported oil, to improve its energy security, investing heavily in renewable energy, improved efficiency and district heating (DH) – a distribution system for centrally generated heat for space and water heating. The heat source may be a cogeneration, or combined heat and power (CHP) plant that may run on a fuel like biomass, or a heat pump, geothermal, or solar heat.

DH is more efficient and less polluting than separate, individual heating systems. According to research, district heating with CHP is the cheapest method of cutting the carbon emissions of fossil-fueled heating and also has the lowest carbon footprint among fossil fueled generating plants. CHP stations are more efficient than standard power plants because heat released during power generation is captured and used to heat homes and businesses, boosting a conventional power station’s 30-50% efficiency to 70-90%.

Today DH networks provide over two-thirds of Denmark’s heating needs. Instead of individual boilers, Danish homes have hot water piped in from one larger, more efficient, shared heat source. Also a network of pipes under towns and cities collects waste heat from factories, incinerators, and transportation systems, blending it with heat generated by solar thermal energy or conventional power stations, creating a low cost, highly efficient heat supply, saving everyone money. Beyond winter heating, DH is also used to store renewable energy whenever supply exceeds momentary grid demand. Wind-power comes to mind. The heat storage may be a borehole cluster or even a large, buried tank.

The use of solar heat for DH is increasing, combined with season to season thermal storage to ensure a consistent day to day heat output. In the Danish villages of Braedstrup and Marstal, for example, village-scale DH systems have been expanded to supply from 10% to 40% the villages' space heating needs with ground-mounted solar-thermal panels. In Canada, Alberta’s Drake Landing Solar Community has achieved a world record 97% annual solar fraction for heating, using solar-thermal panels on garage roofs and thermal storage in a borehole cluster.

The world’s first DH systems served ancient Roman thermal baths and greenhouses. They gained prominence in Europe during the Middle Ages and Renaissance, with one system in France in continuous operation since the 14th century. The US Naval Academy began steam district heating service in 1853. Other countries with significant DH market share include Iceland (95%), Estonia and Poland (52%), Sweden (50%), Czech Republic and Finland (49%), Slovakia (40%), Hungary (16%), Austria (12.5%), Germany (12%), Netherlands (3%).

In the UK, according to a 2013 report, there is enough heat wasted in London alone to meet 70% of the city’s heating needs. But, while Denmark has spent the past 40 years developing systems that capture and harness waste heat, North Sea oil-rich UK has focused on its gas grid. Now that North Sea reserves are dwindling and the Brits must increasingly rely on imported gas, the government aims to boost the number of households connected to DH networks to 20% by 2030 and 40% by 2050. It has made £7 million available to town councils for DH feasibility studies and over 50 municipalities signed up.

Greater London set a 2025 target of 25% of its energy supply coming from distributed sources. As a first step, a map of London’s energy resources was created, showing power plants, waste incinerators, CHP sites, proposed heating networks, etc.. Sheffield, Leicester, Bristol and Nottingham are also investing in DH. In return for the initial outlay on infrastructure, public buildings, hospitals, universities see their heating bills fall and residents pay less for renewably sourced energy.

DH is more energy efficient than individual heating systems. Carbon emissions are lower as well because larger combustion units have more advanced flue gas filtering than single boiler systems. Where surplus heat is available, e.g. from industries, DH doesn’t rely on additional fuel. Benefits to the community include avoided costs of energy and reduced investment in individual heating equipment. But DH requires long-term commitment. It fits poorly with a short-term investment mindset. It is also less attractive for areas with low population densities where the initial investment per household is higher. On the other hand, DH and CHP systems are scaleable and easily combined with any locally available energy source.

Is there a lesson here for Maine? Like the UK earlier, Maine is now splurging on gas pipelines even as fracked gas raises serious environmental concerns. Why not a systemic approach to energy, including DH, utilizing local energy sources? Insulated water pipes are cheaper to lay than underground gas lines. Safer too: no danger of accidental explosions when other underground utilities undergo emergency repair.