Necessary Measures to Include more Distributed Renewable Energy Sources into District Heating System

Low temperature district heating (LTDH) can substantially reduce total greenhouse gas emissions, increase reliability of the energy systems, enable transition to the renewable energy society, and secure energy supply for future development of society. LTDH can increase the integration of renewable and waste energy sources. However, renewable and waste energy sources have still lots of reliability and acceptance issues. Therefore, this article aims to identify some of the necessary measures to enable easier connection of the distributed heat sources such as solar and waste heat into the LTDH. An energy balance model for an area was developed on annual level. The heat supply model included a central plant and distributed solar collectors, heat pumps, and waste heat. Since the objectives were to minimize the specific heat cost and to minimize investments for distributed energy sources, a multiobjective, genetic optimization was used. The results showed that the investment cost for solar collectors, electricity price, heat pump performance and investment cost, and cost of the waste heat influenced mostly higher share of the distributed energy sources into the central district heating (DH) system. In addition, bigger building area showed to be more suitable to export heat to the central DH system. The paper presents the international co-operative work in the framework of the International Energy Agency (IEA), the District Heating and Cooling including Combined Heat and Power (DHC|CHP) Annex TS1.