Hybrid energy system optimization for buildings

The European Commission has announced that buildings as end-users of energy in the European Union (EU) are responsible for 40% of energy use and 36% of greenhouse gas emissions. Improving energy efficiency can be the main key to reducing energy use, leading to reduced greenhouse gas emissions, and decreasing energy costs. The nearly zero-energy building (nZEB) requirements for EU countries set cost-optimal minimum energy performance requirements for new buildings, existing buildings undergoing major renovation, and for replacing or retrofitting building elements like heating and cooling systems, roofs, and walls. One approach to improving energy efficiency and meeting nZEB requirements lies in optimal planning and operation of building hybrid energy systems. Depending on local conditions, such systems include locally produced renewable energy, such as solar power, solar heat, wind power, ground source heat, and biofuels. This thesis aims to develop methods for optimal planning and operation of renewable-based hybrid energy systems for different kinds of buildings: office, residential, and mixed-use. The energy systems include electric power from the grid, district heating, district cooling, heat pumps, photovoltaics, and storages for heat, cooling, and power. In such hybrid energy systems, different energy forms and technologies interact in a complex manner. These interactions are resolved by optimization modelling. Linear and mixed integer linear programming is applied in this thesis.This thesis includes three studies. The first study developed a combined configuration, sizing (dimensioning), and operational model to minimize the energy costs for hybrid energy systems of buildings. The model was applied to a mixed-use building in Finland. Besides reducing energy costs, energy efficiency was improved, and nZEB requirements were satisfied with a clear margin. The second study extended the model for multiple power storages and operation under the future 15-minute power balance settlement. The model was applied to plan the refurbishment of an office building in Finland and a residential building in Estonia. The optimized configurations caused significant annual savings in energy costs for both buildings. Power storages were not cost-efficient in either building, even if it caused savings in operational costs. These savings were not significant enough to cover the investment. Photovoltaic power was cost-efficient only in the Helsinki building. The third study developed models and methodology to optimize buildings' hybrid energy systems while participating in the Finnish Frequency Containment Reserve (FCR-N) market. The model was applied to an office building in Finland. Results show that FCR-N trade is profitable, and power storages can be cost-efficient together with FCR-N trade.