Hybrid Cooling Systems for Low-Temperature Geothermal Power Production

Abstract

Geothermal power plants that use air-cooled heat rejection systems experience a decrease in net power production during hot periods of the day. This decrease in power output typically coincides with the time when utilities need power to meet high air-conditioning loads. A hybrid cooling system uses both air and water to mitigate reduction in power. In this paper, these systems are assessed as to how effectively they can reduce the net power decrease from the plant. In the analysis, a 20-MWe power plant located in northern Nevada was analyzed. The hybrid cooling systems were able to mitigate the decrease in power during hot periods of the day by as much as 2 MWe using only 3% of the water that would normally be used in a fully wet-cooled system. Payback periods for various methods to implement hybrid cooling systems were also determined. Although a water-assist option is generally a retrofit for existing power plants, we suggest that such an option become part of the initial design process (whether it gets implemented at a later date or not). With foresight, such designs are likely to be more tolerant of local wind conditions, making implementation more effective. Further, with the introduction of brazed aluminum air-cooled condensers in the HVAC industry, the performance and cost of using those heat exchangers in geothermal power systems deserves a thorough evaluation, with or without wet assist.