Optimization of Water - Cooled Chiller – Cooling Tower Combinations

Water-cooled chiller systems have typically been designed around entering condenser water temperatures of 85°F with a Optimization of Water Cooled Chiller – Cooling Tower Combinations The warm water leaving the chilled water coils is pumped to the evaporator of the chiller, where the unwanted heat from the building is transferred by the latent heat of vaporization of the refrigerant. The compressor of the chiller then compresses the refrigerant to a higher pressure, adding the heat of compression in the process. The high pressure refrigerant then moves to the condenser, where the unwanted heat is renominal condenser water flow of 3.0 USGPM/ton and a 10°F range. In recent years, there has been considerable debate on the merits of designing around lower condenser water flow rates with a higher range in order to improve system lifecycle costs. However, two other parameters must also be considered in any analysis approach and design wet bulb. The question to be answered is: What nominal condenser water flow rate and approach is best from a first cost standpoint as well as from a full load energy standpoint at any given wet bulb? A study was recently completed in an effort to answer this question using actual first cost and full load performance data from a variety of chiller, cooling tower, and pump manufacturers for a nominal 500-ton water-cooled, centrifugal chiller system. This paper reports the findings from that study. Introduction & Background Many facilities employ chilled water systems for comfort cooling. Three distinct parts comprise every chiller system: · The chilled water loop absorbs heat from the building and then rejects that heat to the chiller. · The evaporator in the chiller absorbs heat from the chilled water loop and rejects that heat, along with the heat of compression, to the condenser using a vapor compression cycle. · The condenser rejects that heat to the atmosphere. To start, chilled water coils located in air-handling units throughout the building absorb heat from the building air, transferring that heat to the chilled water loop. The air-handling units distribute the conditioned air to the building. Why use a two-step chilled water process to remove heat rather than removing it directly, such as in a room air conditioner? As buildings become larger, it becomes less practical to pipe refrigerant and/or duct cool air to the extremities of the building. Chilled water, on the other hand, can be easily distributed by insulated pipe, even when piping runs are very long. The larger the space a comfort cooling system serves, the more likely it is to use a chilled water system for cooling. jected by the latent heat of condensation of the refrigerant to the atmosphere. This system is illustrated in Figure 1 below: Figure 1 Chilled Water System Overview Note: AHU-1, 2, & 3 are air-handling units, which house chilled water coils for heat transfer. Cool air is ducted from each air-handling unit to the different conditioned spaces that each unit serves. Chillers can be classified as air-cooled or water-cooled depending on the method of heat rejection used. Air-cooled chillers reject heat to the atmosphere via a fan that draws air across the condenser coil, condensing the refrigerant within the tubes. Water-cooled chillers reject heat to the water that flows through the condenser tube bundle, typically condensing the refrigerant on the outside of the tubes. The lower process fluid temperatures (and corresponding refrigerant pressures) available through the use of water-cooled equipment lower system energy usage and