Bachelor's thesis Julia Granacher


Optimal design of energy systems for buildings with consideration of the part load behavior

Within the European Union, the climatisation in industry and private housing accounts for 50% of the overall primary energy consumption, which makes the reduction of the energy usage in this sector an important requirement for the successful achievement of the Unions's climate and energy goals. Apart from the legal environment, an optimum
system layout is a crucial requirement for the development of ecologically and economically pro table energy systems for buildings. When approaching the layout of energy systems by implementing optimization methods, Mixed-Integer Programming (MIP) is commonly disposed, often comprising signi cant simpli cations.

In this work, a MIP for the design of energy systems for residential buildings is developed, taking the part load behavior of heating devices into account by the usage of piecewise linearization over implemented performance maps. Using Multi-Criteria Optimization, a decision guidance for the trade-o between energy costs and CO2 emissions is generated for di erent residential buildings. The developed model is applied to multiple
scenarios considering di erent composition of devices. For each scenario, trends of costs and emissions in the optimal solutions are analyzed regarding in uences of key factors such as device-con guration, capacities allowed and power shares. A special focus is laid on the di erences between scenarios considering combined heat and power (CHP) units and scenarios where no CHP unit is allowed, enabling the analysis of impacts of CHP usage on costs and emissions. Since the German e orts of promoting the installation of CHP units do not concede the desired results, the economical investment costs under which CHP units are competitive are derived. As a last point, the e ects of the part load behavior regarding runtime and results of the multi-criteria optimization are analyzed.
The results show that with increasing relevance of the minimization of emissions, more heat is generated by heat pumps and boilers while combined heat and power units lose importance. Furthermore it is conducted that the competitive investment costs under which CHP units are pro table are located 35-120% below the actual investment costs. Generally, CHP units are more pro table for larger buildings. For the comparison of both modeling approaches, it is derived that the runtimes increase by 190%, whereas deviations in the objective functions costs and emissions of up to 9% are observed.