This article presents the first monitoring results of an existing system combining solar collectors and heat pumps at large scale. This system provides heating and domestic hot water to a new housing complex (∼10'000 heated m2) in Geneva, Switzerland. A detailed monitoring of one of the buildings was implemented in November 2011, and enabled to describe the behavior of the system (control strategy, temperature levels…) and to calculate the System Coefficient of Performance for winter 2011-2012. The results show a very low heating demand for Switzerland (∼20 kWh/m2/yr), but unusually high domestic hot water consumption (∼35 kWh/m2/yr). The System Coefficient of Performance varied between 1.7 and 5.6 depending on the month considered. Summer 2012 results will enable to calculate the annual System COP. The results are part of an ongoing research project aiming to assess the relevance of the concept of coupling solar and heat pumps in various types of building (especially existing buildings with imperfect thermal envelope).