A system combining uncovered solar collectors (116 m2) and heat pump for space heating and domestic hot water production to a new multifamily building (927 heated m²) in Geneva, Switzerland was monitored for 2 years. This paper presents a simulation model that was developed to carry out a sensitivity analysis regarding different sizing and control strategies, as well as the adaptability of the concept on existing buildings (retrofitted or not).The validation of the model with the monitored data was accomplished with good accuracy for monthly and annual values. In particular, the SPFSystem simulated of 3.1 is similar to the monitored value of 3.0. The sensitivity analysis shows that the replacement of a non-inverter by an inverter heat pump would decrease the electricity demand by a factor of 0.8 and increase the SPFSystem to 3.8. As for the implementation of this concept in an existing retrofitted building (demand 1.5 times higher than the monitored building), without resizing the system, an increase of the annual electricity consumption by a factor of 1.6 is observed. If all system components are resized, the annual electricity consumption would increase by a factor of 1.5. When implementing this concept in existing non retrofitted buildings (demand 2.1 times higher than the monitored building) with all system components resized, an annual electricity consumption 2.2 times higher is observed. The system resizing may not be viable due to lack of space in the roof for the needed solar collector's area and the financial investment may not be affordable.