Scientists from the Polytechnic University of Madrid have explored the environmental and social sustainability of district heating and cooling systems powered by renewable energy sources. For that purpose, they tested the systems at three pilot sites in different European climates: Romania, Sweden and Spain. The results were mixed: despite impressive reductions in emissions, major social problems were identified.
Nearly half of all energy consumed in Europe is spent on heating and cooling buildings. About two-thirds of thermal energy continues to be generated by gas, coal and other fossil fuels. This not only produces high CO₂ emissions but also makes national economies dependent on imported raw materials. The European Union has set a goal of reducing emissions by 55% by 2030 and achieving climate neutrality by the 2050s. This strategy views district heating and cooling systems as a key tool: they make it possible to integrate major renewable energy sources and distribute the resulting energy across entire districts.
The researchers tested several systems as part of the European WEDISTRICT project at various sites in Romania’s Bucharest, Sweden’s Luleå and Spain’s Córdoba.
In Bucharest, the study focused on a building located on the campus of the Politehnica University of Bucharest. The building used to be heated by a 110 kW gas boiler, with electric heaters providing hot water and air conditioners providing cooling. The researchers switched the heating system to geothermal heat pumps and solar panels. This reduced carbon dioxide emissions by 67%, and the replacement of coal- and gas-fired generation in the national grid resulted in a negative carbon footprint. However, the new technologies required greater quantities of metals and rare minerals, increasing the pressure on land resources, which meant that additional space was required for the equipment.
In Luleå, a pilot project was implemented at the science park where the RISE research center is located. The park used to receive thermal energy from a district heating network powered by gases from a steel mill. As part of WEDISTRICT, a data center was connected to the system: its servers were converted to liquid cooling, and excess heat was sent to solid oxide fuel cells powered by biogas. The units generated electricity for the data center, producing heat for the district heating network. This reduced emissions nearly by half, with a negative carbon footprint when accounting for the energy displaced. At the same time, water consumption increased along with the use of chemicals in biogas production.
In Córdoba, a demo project was implemented on Rabanales Campus. Before the introduction of new technologies, some of its buildings had been heated by heat pumps and a gas oil boiler. As part of WEDISTRICT, three types of solar concentrators, a biomass boiler with an emissions control system, absorption refrigerators and an air-cooled module were installed. Additionally, heat storage tanks were assembled to ensure the system could operate during cloudy hours. As a result, CO₂ emissions went down by 63%, with reductions in water and fossil fuel consumption. At the same time, demand for metals increased sharply, and so did the area required for solar installations and associated infrastructure.
The environmental benefits of integrating renewable energy into centralized heating and cooling systems are generally evident: all three projects have managed to significantly reduce their carbon footprint. However, other challenges arose, such as increased demand for rare metals, water and land. In other words, the pressure did not disappear, but rather shifted from one part of the ecosystem to another.
The social effects proved contradictory as well. On the one hand, employment increased across all projects. In addition, workplace accidents were eliminated. On the other hand, wages were below the national average, and at some sites, employment for people with disabilities became impossible.
In this regard, the researchers emphasize that an effective energy transition can only be achieved when technical innovations are accompanied by measures to create jobs with decent wages, maintain social benefits and engage vulnerable groups.
