The temperature of the turbine inlet-air has a significant effect on the power output and efficiency of gas turbine plants. In high ambient temperatures, there is a significant loss in air mass flow rate and consequently a considerable decrease in turbine output. In this paper, the effect of lowering the compressor intake-air temperature by means of a fogging system on the performance of a 79 MW gas turbine in Mashhad power plant is studied. Since Mashhad is located in a dry and relatively hot region, fogging method has been selected as the compressor inlet air cooling system. The result show that by employing this method during hot months of the year, there is 8.8% increase in the turbine output. In addition, the output power at best condition increases by 13 MW. Economic analysis shows that the pay back period is 1.66 years and rate of return is 60%. According to these calculations, evaporative cooling has economic advantage over other cooling methods in hot and dry climates. Results also reveal that ambient relative humidity plays an important role in the efficiency of fogging systems.

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