Visions for future energy efficient district energy systems

This report gives the vision of the future district energy systems and describes the state-ofthe art of district heating related energy systems in Finland. The challenges and future needs of the energy business and services are described. The approach for scenario analyses is presented using the district heating system of Keski-Uusimaa as a case study. The scenarios of the energy system selection and energy consumption for the next 20 years (2015-2035) were presented for the case study. The scenarios were based on the assumptions of development scenario of the building stock and energy efficiency of the buildings. Two different types of scenario simulations were done. The first one, system optimization, search for optimal system concept taking into account the investment costs for the energy production system including centralized and decentralized systems. The second one, energy simulation, studied the influence of the decentralized energy production on the energy efficiency, emissions and energy costs. Both the simulation cases had the time frame of 20 years. The optimization model can be used to study the influence of production unit costs and external conditions on the optimal system typology. The energy system optimization study was based on three main scenarios: the existing bio CHP plant and gas boiler would be useable during 2015-2035, the CHP plant will be stopped in 2025 or there are no existing units in the region. The optimization takes into account costs of the equipment and energy, external conditions (solar, wind) as well as heating and power needs. The study of alternatives showed that it is cost optimal to use the already existing CHP plant. The heat pumps, gas boilers and wind and gas turbines will support the energy system when the CHP is not used anymore. In the energy simulation study, a set of scenarios for the development of the case area's district heating system have been made. The purpose of the scenarios was not to make a prediction of what the future heating energy systems will be like, but rather to examine what different possible development pathways there are and compare them in terms of technical, environmental and economic criteria. The conservative, extensive and extreme scenarios assumed different amounts of solar energy and ground source heat pumps to be implemented as decentralized systems (1%, 10% or 50% of floor area implemented decentralized RES). The industrial heat was used or the consumer acted as an active prosumer selling the excess solar heat back to network. In the case of simulations, the extreme scenario with ground source heat pumps and a solar thermal system decreased the annual centralized heat production by 34% and, in the case of industrial waste heat by 32% at the end of the scenario timeframe compared to starting year. The non-renewable heat consumption decreased 46% in case of industrial waste. In the case where 20% of the district heating was originating from the industrial waste heat source, the CO2 emissions decreased by 50%. The energy costs depend strongly on the scenario assumptions. The yearly energy costs of reference case decreased 22% compared to the starting year, and the biggest reduction (34 %) was gained in the extreme scenario. In the conservative, extensive and extreme scenarios using heat pumps, the CO2 emissions increased compared to the reference case, due to the increase in electricity use by heat pumps. The case studies showed that environmental performance depends strongly on the source of emission factors for the primary energy, e.g., if the real factor based on local conditions or average national values will be used. The energy-saving benefits of the prosumer scenario were quite small