A dynamic model is proposed to use in investigating the exergy analysis of a solar ejector refrigeration system using R141, for office air conditioning application for a building in Tehran. Classical hourly outdoor temperature and solar radiation model in a hot summer day were used to provide basic data for analysis. To improve the efficiency of the system a hot water storage tank is used and analyzed dynamically. The results show that dynamic analysis is confidently more useful than analysis in a constant condition. This method is more completed because it can present efficiency of the system components at each time. The components have different efficiencies at different days and hours. Collector has the highest level of irreversibilities and ejector is in the next step. Irreversibilities at the first and the last hours of working-time are higher. In addition, using the hot water storage tank decreased auxiliary heating in the afternoon.