Improving Efficiency in the SIUC Campus Chilled Water System Using Exergy Analysis

Improving Efficiency in the SIUC Campus Chilled Water System Using Exergy Analysis

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This study evaluates the central chilled water system of the Southern Illinois University Carbondale campus, which consists of a primary-secondary-tertiary water distribution system cooled by two 12, 300 kW (3, 500 Rton) centrifugal chillers, each powered by a condensing steam turbine. Statistical and thermodynamic analyses of steady-state data characterize system performance with the goal of identifying opportunities to increase capacity utilization and reduce the unit cost of delivered chilled water. Chiller load is modeled as a function of wet-bulb temperature and hour of day. Secondary loop water flow rates are modeled and predicted from temperature measurements. A comprehensive exergy analysis is used to identify the sources and magnitudes of irreversibilities and to rationally cost these losses. Results show that the steam turbine is the largest source of exergy destruction in both chillers. Nevertheless, water distribution losses are the dominant exergy unit cost at low loads, while refrigeration cycle losses contribute most to costs at high loads. The results also demonstrate a significant cost advantage of a three-pass over a two-pass evaporator. Recommendations drawn from the study include conversion of the water distribution system to an all-variable-speed, direct-coupled configuration to eliminate mixing and unnecessary pumping, and controls upgrades such as automatic chilled water temperature reset based on building flow requirements and a more aggressive use of compressor speed for capacity control. Finally, the results suggest that the steam turbines should be replaced with variable-speed motors, however further study is required on the feasibility of utilizing the displaced steam load for cogeneration at the boiler plant.Additional help was obtained from experienced PSO maintenance and engineering staff and from the field technician and service manager from the Carrier Corporation, which produced the chillers. In addition, many hours were spent makinganbsp;...

Title:Improving Efficiency in the SIUC Campus Chilled Water System Using Exergy Analysis
Publisher:ProQuest - 2007


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