The Hardware in the Loop (HiL) approach applied to heat pump (HP) systems has proven to be effective in understanding the real behavior of the unit under realistic operating conditions. In this study, a novel HiL methodology is proposed for the experimental evaluation of the seasonal energy performance of Dual-Source Heat Pumps providing space heating and domestic hot water production. The methodology is described in four main steps: i. numerical simulation of a reference building-HVAC system; ii. selection of a limited number of representative days (RDs) of the year; iii. reproduction of the RDs in a controlled test rig following the HiL approach; iv. extrapolation of the seasonal performance. In order to prove the feasibility of the methodology, in this preliminary work only the first three steps were followed, and an exemplary test was conducted to validate the method and evaluate the daily energy efficiency of the tested HP. The results focus on the benefits obtainable by using the HiL approach under typical operating conditions and demonstrate that the experimental setup can perfectly follow the boundary conditions requested by the procedure with negligible deviations. Moreover, the methodology applied to the HP unit promises also to be effective in: i) identifying dynamic phenomena that cannot be predicted through standard steady-state testing; ii) optimizing control logics; iii) providing deeper knowledge of the HP transients that can be taken into account in numerical models.