Solar water heaters are one of the most developed technologies of renewable energy used in the world. The satisfactory and reliable performance of solar water heaters require accurate sizing and designing of the components as well as precise prediction of useful energy intake. This is of greater significance in cold areas due to higher thermal loss and lower solar radiation. Hence, optimization of the system parameters to obtain sufficient efficiency is quite an important matter. This study evaluated the long-term and annual performance of solar water heaters in the cold city of Sanandaj, Iran using TRNSYS software. In the first phase, the general parameters and components of the system were optimized and in the second phase, the performance of the optimized system was assessed. The effects of changing parameters such as storage tank volume, collector area and collector slope on the monthly and yearly performance of the solar water system were analyzed. It was found that 0.35-0.45 m2 was the optimum annual volume of storage tank for the weather conditions of Sanandaj city. Moreover, the optimized values of collector area and its optimized slope were reported to be 8 m2 and 40-60º, respectively. The results showed a direct correlation between environmental conditions and useful energy intake. With regard to time and energy intake, August was found to be more uniform than other months. At the end, the monthly efficiency of the system was evaluated and the findings indicated a proportional efficiency for the system. The maximum monthly efficiency was found to be about 61% in July and minimum level was 42% in January.
