An office building of 2'200 m² in Geneva (Switzerland) was renovated in 2007 according to the low-energy-consumption standards of the Minergie label. Along with the renovation, a new floor (1'450 m²) was added. The oil boiler was replaced by two 120 kWth heat pumps coupled with 2'700 m of geothermal boreholes. This article presents the results of a 2-year energy monitoring (Oct. 2010-Oct. 2012) of the overall system. Detailed instrumentation has been implemented in order to evaluate its performance. The results show that the heating demand has been divided by 4, decreasing from 108 to 27 kWh/m²/yr: the envelope of the building is now very efficient. The electricity consumption of the heating system is less than 10 kWh/m²/yr for 2011-2012, which is very low. The annual system SPF is 3. This value is modest taking into account that: (1) the heat source is of good quality (geothermal boreholes) (2) no domestic hot water (i.e. high temperature heat) has to be produced (tertiary building). This low performance can partly be explained by the fact that the heat pump works at around 10K higher than required by the distribution, due to the hydraulic configuration of the system.