Criterion to evaluate the convenience of implementing evaporative precooling in air-cooled chillers

Abstract

This study presents a criterion to determine if local conditions of meteorology and the cost of energy and water favor the use of evaporative precooling in air-cooled chillers. It has been found that when the energy saved per unit of water consumed is higher than the ratio between the cost of water and electricity, it is economically attractive to operate the chiller with evaporative precooling. Furthermore, we found that the energy savings are proportional to the annual average wet-bulb depression (AWBD) temperature. As a case study, we tested this criterion by comparing it with results of monitoring every ten minutes and for more than five months, the operation of a frequently used chiller (82 RT) working in northern Mexico. Considering the past six years of hourly meteorological conditions of this region, we found that, on average, 4.4% of the annual energy consumption can be saved by evaporative precooling. That saving could be up to 23% at some hours of the year. These results represent a potential saving of 35.7 MWh/year. However, it requires the use of 1,759 m3/year of water to moisten the air. Considering the current water and energy prices in the study region, the evaporative precooling represents a saving of USD 2,704/year. This monetary saving is relevant considering that many companies and buildings use tens of these chillers in their production line or air conditioning systems.