Near-Optimal Control Strategies for Hybrid Cooling Plants

This paper develops and evaluates a set of operating strategies that when implemented together provide near-optimal performance for hybrid cooling plants in terms of operating costs. A hybrid chiller plant employs a combination of chillers that are “powered” by electricity and natural gas. Operating cost minimization for hybrid plants must account for effects of electrical and gas energy costs, electrical demand costs, and differences in maintenance costs associated with different chillers. Control strategy development was facilitated by separating hourly energy cost minimization from the problem of determining trade-offs between monthly energy and demand costs. A demand constraint is set for each month based upon a heuristic strategy and energy cost optimal strategies that attempt to satisfy the demand constraint are applied for cooling tower and chiller control at each decision interval. Simulated costs associated with the individual control strategies compare well with costs for optimal control.