Tian Building Engineering uses the in-house software BIM HVACTool to calculate and analyze energetic and comfortable concerns of rooms, buildings and neighborhoods. Fields of activity include the calculation of the summer heat protection according to DIN 4108-2 or the cooling load calculation according to VDI 2078. The comfort can be determined by the methods Fanger, Pierce, KSU and according to DIN EN 15251. Optionally available for the calculation is the building simulation solver EnergyPlus developed by Department of Energy or building simulation solver NANDRAD developed at the TU Dresden. Further work points are the energy optimization and the inclusion of regenerative energy sources. Especially in this field, the consideration of the heat storage mass of buildings is very interesting. The most relevant calculation results are heat fluxes, envelope surface temperatures and mean air temperatures and CO2 concentration.