Abstarct: Nowadays, due to concerns over polluting effects of fossil fuels, declining resources and increasing prices the necessity of greater attention to clean energies as the sun is clear and for this purpose there has been extensive research all over the world. In this study, focusing on optimizing the use of solar energy in the building, at first solar water heater and solar absorption chiller were selected as the two devices that use solar energy for hot water supply. Then these systems were simulated with software TRNSYS in Tehran, Bandar Abbas and Tabriz Climate, for both educational and residential consumption patterns and the impact of the flat plate collector area and storage tank volume Changes on the exergy efficiency of the various devices and economic factors was examined. Also, the impact of different patterns on economic functions and annual saving was assessed and feasibility of applying each of these devices in different climates was evaluated. In this process, fuel prices, were considered equivalent to the average price of Iran gas exporting. For water heater in each climatic zone annual saving was desirable and pay back was calculated between 8 to 10 years. Also for using water heater in residential buildings, economic optimum points of the collector area for storage tanks in different volumes were reported. The feasibility also was evaluated for solar chiller and annual saving and payback was calculated. The results showed that using solar energy for cooling in Tehran, even with the global price of fuel is not economical. But in Bandar Abbas results were positive for both educational and residential consumption patterns and economic function suggested the greatest area for collector surface and the greatest volume for storage tank. Defining exergy efficiency function for the solar part of the chiller, optimum efficiency was observed for the minimum collector area and minimum size of the storage tank. This means that improvement of the system in terms of exergy and economics were at odds with each other.