A Novel Free-Cooling Scheme for Combustion Turbine Inlet Air Cooling

Abstract

Free cooling is a well-known concept in the HVAC industry in which the cold water produced by a cooling tower is used directly to satisfy the requirement of the cooling load without assistance by the chiller; this concept, however, is not reported in the turbine inlet air-cooling applications. Free cooling works well as long as the ambient wet bulb temperature (WBT) is sufficiently low to produce cold water at the required temperature, but once WBT reaches its threshold value (hence, free-cooling mode is ceased) and the chiller kicks off working under its normal mode of operation, i.e., free cooling is either enabled or disabled. The proposed system in this paper provides, in addition to the above modes of operation, a novel mode that utilizes the cooling tower as a primary source of cooling simultaneously with the chiller that serves as a secondary source at elevated WBT. This new feature significantly reduces the yearly operating hours of the chiller and possibly its size, depending on the desired inlet air temperature, actual weather conditions, and design WBT. Chiller size can vary between 0% and 100% as compared to a similar classical chiller system with significant reduction in the operating hours. The proposed system consists basically of chiller, cooling tower, cooling coils, interconnecting piping, and controls. The arrangement of the system equipment changes with the operation modes in two configurations: dual water circulation loops and single water circulation loop. In the dual-loop configuration, the system has two separate loops such that the evaporator and the cooling coils are tied in one loop, while the cooling tower and condenser in the other loop; whereas in the single-loop configuration, all equipment is connected in series in one water circulation loop. This paper presents the major equipment and characteristics of the novel chiller scheme. In addition, the study outlines the potential reduction in the chiller load, size, and operating hours under a generalized weather envelope. The paper portrays the feasibility of using the proposed cooling scheme for turbine inlet air cooling.