The efficiency of a heat pump system is strongly dependent on the temperature level of the ambient heat source. Compared to ambient air heat pumps, the seasonal performance factor of a heat pump system can be increased through shallow geothermal heat sources. For sites with local regulatory restrictions or area constraints for ground-based heat sources, a new heat pump system with three building integrated heat sources is presented. In addition to an ambient air heat exchanger (AAHX) a façade-integrated massive solar-thermal collector (MSTC) can be applied to regenerate a horizontal ground collector thermal energy storage (GCTES) underneath the building, which serves as heat source for the heat pump. The area of the ground collector is limited to the size of the building’s footprint. Due to its limited thermal capacity the GCTES does not meet the heat demand of even a highly insulated building as a sea-sonal heat storage. Therefore, the storage is regenerated repeatedly during the heating season to be used as a medium-term thermal energy storage. A control strategy for this system, regarding overall performance, has been developed and applied to a pilot plant. Operating results of the system with three heat sources gained during two heating periods are analyzed regarding the interseasonal regeneration of the GCTES The heat extraction from the GCTES was increased by 48% to 56% compared to a pure seasonal heat storage. The system is compared to the performance of an air-sourced heat pump system, showing a 50% increase of the seasonal coefficient of performance.