This book is part of a larger project called CiQuSo. The aim of CiQuSo is to maximize solar thermal utilisation in buildings and to optimize the shifting of loads within and between buildings within a city center. The work deals with the modeling of a multi-family house in Austria with the simulation software TRNSYS. The model consists of various necessary components such as Solar Collector (SC), Heat Exchanger (HX), Primary storage tank (PS), Auxiliary Heater (AUX), Domestic Hot Water (DHW), Space Heating (SH), Circulation pipes (Circ), District Heating (DH) and Pumps. After the model is built, various simulations with different settings were done. The simulation results will be later used for input in the training of a black box model needed to be created. This black box is called ¿District Algorithm¿. Through the District Algorithm, one can perform various simulations, for different building types, different loads etc. The DH has a very important role since it can be both supportive to the building¿s loads or be supported by the buildings surplus heat. The DH functions as an ¿infinite storage tank¿ for the surplus heat generated from solar thermal collectors.