Utilization of short-term thermal energy storage for demand response and peak power reduction in district-heated buildings

Abstract

The European Commission has set ambitious targets to cut at least 55% of greenhouse gas emissions from 1990 levels by 2030 and to realize carbon neutrality by 2050. In 2020, space heating consumed 28% of the total energy consumption in Germany while only 18% was produced by renewable sources. In Finland, district heating is the most common source of space heating. In 2020, it covered 45% of the market share of space heating for residential, commercial, and public buildings. Therefore, decarbonization strategies should be developed for district heating systems and the connected buildings. When renewable energies are utilized more in production, there is the demand to enhance the smart readiness of buildings. Demand side management is an approach to adjusting consumer energy use and power demand according to the production pattern. By utilizing short-term thermal energy storage, such as building thermal mass and thermal energy storage tanks, energy flexible strategies could be applied to buildings and their energy systems for peak power cutting and load shifting.

This thesis investigated energy flexibility and the benefits of demand response based on dynamic district heat prices of space heating and a thermal storage tank for district-heated buildings. The meaning of building-level rule-based demand response control strategies on district heating production was also analyzed in the thesis. There were three different production scenarios. The first scenario utilized a biofuel CHP as the basic source and three gas boilers for backup. The second one had a biofuel CHP and a green-electricity heat pump as the basic source and two gas boilers as backup. The last one included a heat pump as the basic unit and an electric heater as backup used grid electricity. In addition, strategies were also developed for peak shaving and peak power limiting with a 5 m3 short-term thermal storage tank. Demand response of space heating cuts up to 9.6% of heating costs for building owners. The demand response control of the storage tank decreases the district heat energy cost by 3.4%. When employing the demand response control of space heating and the storage tank, it gains 12.8% of district heat energy cost savings. In addition, thermal energy storage provides the potential for peak shaving and peak power limiting. It reflects a higher peak shaving potential for colder days with a 31.5% maximum peak power decrease of a Finnish office building. The maximum heating power is limited by 43% and the power fee reduces by 41.2% without compromising room air and ventilation supply air temperatures. The large-scale demand response application decreases the total district heating demand from 3.6% to 3.9% with higher financial benefits and less CO2 emissions. Moreover, it increases the full load operation hours of renewable energy generation units, reducing emissions. Therefore, demand response effectively decreases fossil fuel usage and improves the energy resiliency of district heating systems.