In this study, a new methodology to evaluate the impact of heat pump's operating faults on its performance and the building energy consumption is proposed. In a first approach, a single operating fault-the evaporator fouling, is studied. In order to analyze all possible evolutions of the evaporator fouling at each time step, we use the Petri net approach. It describes any changes of the evaporator filter from the state without fault to a state with a specific fault level. Since it changes, the heat pump performance is reassessed by an adapted vapor compression model. A building simulation model developed by CSTB is then used to simulate the annual energy consumption, which includes the evolution of evaporator fouling. It is illustrated by a case study-a residential house. At 20% of fault level, the compressor power increases by 5.5% and 7.3% respectively in heating and cooling mode. This leads, at the end of the first year of the building simulation, the increase of heating and cooling power by 1.1% and 0.66% respectively. The results highlight the possibility of this methodology for analyzing the impact of the operating fault on the heat pump performance and the building energy consumption.