For the purposes of this study, a hybrid cooling system is a combination of an open cycle heat sink such as a river and a closed cycle heat sink such as a cooling tower. Predicting the performance of power plants with hybrid cooling systems is an elaborate process. A typical hybrid power plant operates in four modes. 1) Once Through Mode 2) Hybrid Mode 3) Helper Mode and 4) Closed Cycle Mode. The variables affecting the operating mode of the plant are the ambient wet bulb, river water temperature, river water flow, and the permit allowed river water temperature rise. There are infinite possible combinations of these variables, and use of weekly or monthly average conditions may not capture sufficient detail for a rigorous economic analysis. The usual method to predict plant output, under varying conditions, would be to run heat balances for each case required. Such a process becomes extremely tedious when predicting hourly performance data, which can be desirable for economic studies of such systems. This paper will present a simplified method to predict the performance of a power plant with a hybrid cooling system for any given river water temperature, river water flow, ambient wet bulb temperature, and river water temperature rise. Such a method can be used in spreadsheets, which are convenient to use in financial calculations. This method was used to predict the performance of an actual power plant with hybrid cooling and yielded satisfactory results.

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