State-of-the-art building energy systems exhibit a high technical complexity. In the commissioning phase, technical building elements (TBE) are put into operation trade-by-trade and as linked complete systems. Besides the correct wiring on component level, instantiating the building automation and detecting errors is a cumbersome process in practice. The paper addresses a novel interconnected toolchain to support commissioning energy systems through digital processes in combination with energy system related digital BIM twins - the "energyTWIN". This energyTWIN digitizes and automates the process chain in the commissioning of TBE and building automation with its highly complex interrelationships in constant exchange between reality and the BIM model (digital twin) as completely as possible. By increasing energy efficiency with the novel processes of energyTWIN, a contribution to the worldwide goal of reducing energy consumption can be achieved.