The development of control strategies is a challenge for optimal use of low-temperature heat in complex energy systems. In the energy system of the considered building, several different combinations of active system components lend themselves to supply a given energy demand. Within preceding research, we transformed the considered building into a multi-functional test bench for control techniques that offers optimal conditions for the demonstration and evaluation of control strategies. This paper describes a control strategy for the complex heat pump system based on operation modes. It enables us to integrate a geothermal field into the system with respect to exergetic principles. The paper presents results of the control strategy's first year of operation. It correlates between active operation modes and the respective electrical consumption of the building. We derive the potential of the implemented operation modes for demand response applications. A mode-based control strategy enables the robust and efficient operation of complex building energy systems. We show that the integration of renewable energy sources becomes easy and flexible. (C) 2017 Elsevier B.V. All rights reserved.