Cooling Tower Fan Control for Energy Efficiency

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Title: Cooling Tower Fan Control for Energy Efficiency
Author: Stout, Malcolm Russell Jr.
Advisors: Dr. James W. Leach, Committee Chair
Abstract: This thesis evaluates the economics of alternative cooling tower capacity control methods. Annual fan electrical energy requirements are calculated for towers with single-speed, two-speed, and variable-speed fans. Fan energy requirements are determined for counter-flow and cross-flow towers designed for low initial cost and for energy efficiency. Effectiveness-NTU equations are solved to predict cooling tower performance at various fan speeds. Natural convection, which determines the cooling capacity when the fan is off, is accounted for using a mean enthalpy difference. Ambient conditions are simulated using typical meteorological year data for five locations. The results show that potential savings are not strongly dependent on the approach temperature, but do increase with increasing range in colder climates. The potential for saving is greatest for cooling towers designed for low initial cost, and is generally higher in locations where the wet-bulb temperature remains relatively constant throughout the year. Two-speed fans that can operate at half speed are generally more suitable for low-cost cooling towers. Two-speed fans that can operate at two-third speed are better for towers designed for energy efficiency and are generally better when the range exceeds 10 F.
Date: 2003-05-08
Degree: MS
Discipline: Mechanical Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/2694


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