Energy audit provides a way to derive energy potential and to develop energy saving program in order to improve energy efficiency during early stage design decision process for new-developed systems that can reduce costs for project owner and for customer. This paper presents utilization of complex energy system (solar assisted heat pump) for heating and cooling purposes. Simulation has been carried out using TRNSYS 18 software for a complex energy system located in northern latitude. The results of such system configurations are presented in the paper. The results show that the solar collector, set at the angle of 30 degrees, facing southwest, with azimuth of 45°, offers up to 95% of optimal solar energy. For east or west orientation, it is possible to obtain up to 85% energy, with roof angles of 25° to 40°. By applying the solar thermal collector the customer can reduce borehole depletion that can provide great opportunities for construction sector