Intake Operation for Deep Cooling Reservoirs

Abstract

Most cooling reservoirs in the U.S. employ a surface intake, but many could obtain improved performance (decreased intake temperature during summer) by using a submerged intake. Potential improvements were studied using mathematical hydrothermal modeling applied to five hypothetical reservoirs located in Augusta, Ga. For the base case reservoir—characterized by an average depth of 30 ft (9.1 m), surface area of 2,000 acres (809 ha), and areal loading of 0.99 MWt/acre—and a range of vertical mixing parameters, intake temperatures from Apr.–Oct. decreased by an average of 0.7–1.2 °F (0.4–0.7 °C) using a submerged intake as compared with a surface intake. For a range of assumed turbine performance curves and cost parameters, these temperatures yield estimated energy savings of 1,200,000–20,400,000 kWh annually and total, present valued, cost savings of $700,000–$11,600,000. Savings increase as the reservoir area and depth increase and vertical mixing decreases. In most cases, performance also improves with combined use of a surface and a submerged intake, with the former used during initial periods of the annual stratification cycle.