05-01: 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 nominal condenser water flow of 3 GPM/ton and a 10°F range. In recent years there has been considerable debate on the merits of designing around lower nominal 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 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 nominal 500 ton water cooled, centrifugal chiller system. This paper reports on the findings from that study.