Technical analysis of using a multi-storage system for a university campus: A case study of a Norwegian district heating system

Abstract

The building sector accounts for 40% of the total energy use in the European Union. 80% of this use comes from space heating and domestic hot water systems. District heating (DH) systems make it possible to supply those demands by renewable energies, waste heat, and fossil fuel in a more efficient and environmentally friendly way. Peak load has a significant impact on the investment and operation cost of a DH system. Therefore, DH companies introduce DH price models that motivate heat users to reduce their peak load by charging for the heat rate extraction. The DH bill is divided into two parts: fixed and variable. The fixed part is counting for the extracted heat rate in kW, while the variable part is counting for the heat use in kWh. Depending on DH companies, some additional elements for volume or other expanses may be introduced. In this study, the focused was only on the two elements for the extracted heat rate and for the heat use, because they are taking the highest share of the DH bill. As a result of the above introduced approach for DH pricing models, introduction of thermal storage is a straightforward way for heat users to decrease their peak load. A DH system at a university campus in Norway is chosen as the case study. The entire system consisting of buildings, connection to a DH system, waste heat from the data center, and a multi-storage water tank (WT) was modeled in Modelica. In this study, instead of modeling the entire campus in one component, buildings are clustered, and one component modeled for each cluster of buildings. These clusters are based on heat demand profile of buildings. This could help to evaluate the performance of WT thermal storage system for different type of buildings. Result showed thermal storage system has better performance when it is implemented in a building with more fluctuation in heat demand. The system's peak is lower with a multistorage system compared to a single storage system. The main reason for this is reduced heat loss and improved adjustment in a multi-storage system.