An advanced simulation model of a packaged air cooled water chiller was developed. The nominal cooling capacity of the chiller is about 70 kW at 35°C dry bulb outdoor air temperature, and it consists of a single refrigerating circuit with two identical scroll compressors. The compressor was characterized by its experimental performance curve according to EN 12900 for both R410A and R32. Off-the-shelf copper tubes and louvered aluminum fins were considered for the condenser and typical brazed plates configuration for the evaporator. The finned coil condenser and the brazed plate heat exchanger evaporator were modeled by an elementary finite volumes technique, previously validated in other papers; for each volume the heat transfer coefficient and the pressure drop were calculated using semi-empirical correlations chosen among the most accurate available in the literature. The aim of the paper is to compare the performance of R410A with that of R32 which is considered a possible HFC substitute with lower GWP (675 instead of 2088). The condenser heat exchanger was optimized for R410A and R32 independently with regard to the number of internal circuits according to the Total Temperature Penalization Performance Evaluation Criteria (Cavallini et al., 2010), without changing the overall heat exchanger dimensions. Furthermore a seasonal efficiency analysis is carried out for different finned coil circuit configuration in terms of European Seasonal Energy Efficiency Ratio (SEER) calculated according to the European Standard EN 14825 for water chillers. Basing on the proposed modeling work, it is possible to conclude that R32 system efficiency performance is acceptable as alternative to R410A for water chillers and further simulation analyses will include evaluating the HFO blends.