HOW TO REDUCE COOLING TOWER OPERATION COSTS
HOW TO REDUCE COOLING TOWER OPERATION COSTS?
Cooling towers are designed to draw heat from the water used to cool chillers in HVAC systems or other process equipment. The heat absorbed from the cooling water is rejected through evaporation. Ambient air enters the sides of the cooling towers to remove heat from the cooling water. Make-up water is added to cooling towers for continuous operation and to compensate for other water losses.
Four Ways How Water is Lost in Cooling Towers
- Evaporation. This is the process wherein cooling towers release heat from the cooling water to the environment.
- Drift. It is a small amount of water exiting the cooling tower as mist or small droplets. The air moving up the tower carries some of the cooling water sprayed at the top of the tower. Inhalation and deposition of drift on nearby surfaces can cause significant issues. The quantity of drift loss is less than the water losses due to evaporation and blowdown.
- Blowdown. Blowdown refers to dumping some water from the cooling water to keep mineral concentration at acceptable levels. As the water evaporates, the mineral concentration in the cooling tower water increases, which causes scaling.
- Overflows. If the water level in the basin becomes exceedingly high, the water will flow out to the drain.
Cooling Tower Operation Best Practices
Install Flow Meters
The use of flow meters to monitor both make-up and blowdown water will help identify and resolve problems on excess water use. The ratio of blowdown water to make-up water should be as close as possible to the target cycles of concentration. If the ratios do not match, there can be leakage or unauthorized draw-off that needs immediate attention.
Measure and Monitor Mineral Concentration in the Cooling Tower Water
The mineral concentration in the cooling tower can be measured by a conductivity meter. Monitoring the mineral concentration in the cooling tower allows for the accurate determination of the cycle of concentration, a parameter used to evaluate a cooling tower operation. The cycle of concentration is the ratio of the concentration of dissolved solids in the blowdown water and the make-up water. Typically, cooling towers operate at two to four cycles of concentration. Maximizing the cycles of concentration minimizes quantities of blowdown and make-up water. However, increased dissolved solids in the circulating water may cause scaling and corrosion problems. Knowing the cycles of concentration and the water quality will allow for strategic scheduling of blowdown. Increasing cycles of concentration from three to six may decrease make-up water demand by 20% and blowdown quantity by 50%.
Selection and installation of appropriate drift eliminators will minimize the amount of mist emitted from the cooling tower.
Acids such as sulfuric, hydrochloric, and ascorbic acid can reduce scaling when added to circulating water, thus, allowing cooling tower operations at higher cycles of concentration. As acids decrease the pH of the water, bicarbonates and carbonates that contribute to scaling formation are converted into more soluble forms. To avoid overdosing acid on circulating water and damaging the cooling system, install a continuous pH monitoring system.
Use Alternative Sources of Make-Up Water
Reusing and recycling water from other facilities is one way to carry out efficient cooling tower operations. Air handler condensate, treated effluent from other processes, and treated municipal wastewater effluent are some alternative sources of make-up water. Ensure that the chemicals used to treat other sources of make-up water are compatible with the cooling tower system to avoid encountering issues.
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