A case study of the reduction of district heating energy consumption in a residential building in Örebro (Sweden)

Abstract: One of the major challenges to be faced in the energy supply sector is related to the requirement of matching the demand side. This is especially the case for the countries characterized by a high share of renewable energy sources. Among the renewable energy sources the use of wind power and photovoltaics has a priority. For instance, in the European Union, these renewable energies shall account for about 20 % of the gross final energy consumption by 2020 and 60 % by 2050 [1]. These renewable sources are commonly known to be highly intermittent, i.e. they fluctuate depending on the weather conditions. As a consequence, relevant drawbacks, such as a low efficiency at the generation stage, are encountered. The current solution that make utilities be able compensate for this intermittency relies mainly on fossil fuels, meaning high operating costs and high environmental impact. It is thus evident that in order to increase the share of renewables the energy infrastructure should be characterized by a higher degree of flexibility. Flexibility is defined as a measure to keep the balance between generation and consumption of energy. In particular, heating supply and demand are considered flexible when generation and consumption can be controlled. This thesis work aims at exploring the potential of the thermal mass of residential buildings as flexible storage for heat energy. The indoor thermal comfort is considered as a key parameter when it comes to the optimization of the system.  Specifically, this report presents an analysis of different applications that can be implemented to reduce the existing district heating energy consumption of a residential building in Örebro (Sweden). Different perspectives were considered to find an optimal operation, both from a utility and a customer’s point of view. On one hand, the utility could offer substantial energy consumption reduction by optimizing the district heating supply temperature schedule. On the other hand, an improvement on the insulation of the building could be implemented by the customer’s side. In this thesis work, a performance simulation based on the thermal mass of the building and a 3D model visualization tool were developed. The space heating demand in a residential building supplied by district heating was considered. EnergyPlus was the selected tool to implement the model for the analysis of the energy performance of the building. Input information, such as different internal schedules for the building, internal gains and a concrete radiator system were collected by the company Power2U and later analyzed for this case-study. By means of a sensitivity analysis, it was found that by improving different technical indicators for the envelope of the building, such as the U-value for the windows, the thickness of the outer wall or its conductivity and insulation capability, a relevant amount of energy was saved. Still, the model shows that varying the temperature at which the utility supplies heat, offers larger savings from both a technical and an economical perspective. In this way, a preliminary assessment for the most optimal scenario to reduce the heating consumption by taking advantage from the heat stored in the thermal mass of the building was shown.