DA-88-02-3 -- Investigation of Control Alternatives for a Steam Turbine Driven Chiller PDF

The subject of this paper is a large central plant with a steam turbine driven chiller whose refrigerant compressor is equipped with both variable speed and variable vane control. The cooling towers are multi-cell with both one- and two-speed fans. The primary goal of the project was to find ways to reduce the overall operating costs of the chiller plant.

To study the many different options and to assess their costs and benefits, a computer simulation of the chiller plant was developed for use with TRNSYS (Klein et al. 1983). Generic computer models were developed for each of the major equipment components, with the specific parameters determined through measurements on the system.

The control and equipment modifications investigated include alternative fan speed and tower cell sequencing, different fan motor speeds, different condenser water flow rates, free cooling, and the effect of tower air outlet recircul ation. Each control strategy was optimized on the basis of minimizing overall operating costs. Optimal control maps were generated to indicate the optimal setting of tower cells, fans, and chiller vane position. By simulating an entire cooling season, optimized control strategy guidelines were developed for various equipment configurations. Energy consumption under optimal strategies is compared to that under current operation.

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