HVAC systems have a significant contribution to the building energy demand and greenhouse gases emissions. The use of effective evaluation indicators and accurate analysis method are very important for improving the energy performance of HVAC systems. The second law of thermodynamics analysis is an appropriate approach to evaluate HVAC system performance.  This thesis presents the second law of thermodynamics analysis of a Water Loop Heat Pump (WLHP) system, applied to a commercial building located in Montreal. This system allows for the heat recovered in the core zone to be used partially in the winter for heating the perimeter zones. The analysis covers both peak design and annual operating conditions. The following equipment is included in the analysis: the water-to-air heat pumps, the boiler, the water circulating pumps, the fan and the heat ejector (e.g., cooling tower). Primary and secondary energy sources are considered, for instance in the case of the generation of electricity. Mathematical models developed in this study are implemented in the Engineering Equations Solver (EES) environment. The performance of the WLHP system is evaluated using indicators such as: the energy and exergy efficiency, the energy and exergy demand, the exergy lost, and the equivalent CO 2 emissions due to the system operation.  The results show that the exergy efficiency of the WLHP system has an annual average value of 2.8%. The annual average value of the Coefficient of Performance (COP) of the WLHP system is evaluated at 1.68. The major exergy destruction components of the WLHP system are the boiler, the heat pumps in core zone and the cooling tower