Improving Cooling Tower Water and Energy Efficiencies based on a New Analytical Method

Sammanfattning: Cooling towers are largely used in many industrial processes for cooling purposes. The basic concept of a cooling tower includes cooling down water by means of evaporation, thus giving it the terminology “evaporative cooling”. Air mixes with water in a cooling tower and is ejected carrying the heat that is transferred from the water. Evaporative condensers also follow the same evaporative cooling process, however, could differ in design and application. A lot of water is consumed by cooling towers to perform the cooling process and maintain the quality of the water. The common method that is used to calculate the amount of water consumed due to evaporation is by following the rule of thumb, which states that approximately 1% of the water flow rate is evaporated for a cooling range of 6.5 ℃. There are also empirical formulas that have been developed to calculate the amount of water consumed due to evaporation. However, the rule of thumb, which is followed the most, is not a very accurate method of evaluating the amount of water consumed since it does not depend on ambient conditions. This report dives into the details of the empirical formulas and the rule of thumb. In addition, a more accurate method of calculating the evaporation of water is developed to create an established benchmark that cooling tower operators can use to evaluate their water efficiencies. A study was conducted on a hypothetical cooling tower with the following design conditions: 3 500 kW cooling capacity, 3 ℃ approach, and 5 ℃ range. The motive of this study began with ClimaCheck’s desire to explore a way to define a water efficiency KPI to enhance analyses of cooling towers. ClimaCheck measures the heating load of a chiller, the inlet and outlet water temperatures of the water in a cooling tower. They also measure the ambient temperature and humidity conditions at any time required, which was vital in conducting the study. The results showed that the ambient conditions (dry bulb and wet bulb temperatures) highly impact the amount of water evaporated. The data was compared with the rule of thumb/empirical formula, which resulted in the same amount in all locations since it does not depend on the ambient conditions. In addition, to further validate the study, the analysis was performed on a site monitored by the minute by ClimaCheck that has a cooling tower. Comparing the actual water consumption with what the rule of thumb indicates showed that the latter is not accurate. The study is concluded by illustrating the importance of operating at appropriate air flow rate and water conditions, how cooling tower operators can analyze the water efficiency of the cooling tower using the developed technique, while providing some guidelines on how to maintain high cooling tower performance.