When operating cooling towers in subfreezing temperatures, avoid complications by following these 5 principles:
1. Always maintain a heat load. Without a heat load, water flowing through the tower will equalize at the air wet-bulb temperature and form ice. Excessive ice can impede airflow and damage the fill.
2. Maintain the tower’s water flow rate at the design minimum or greater. This ensures an even water distribution over the fill and, in turn, predictable performance.
3. Bypass the operating water flow directly to the cold water basin if the heat drops too low. This prevents water from freezing in low-flow areas.
4. While fan cycling or two-speed motors can be employed, a VFD is recommended to eliminate cell-to-cell temperature gradients. Sequential fan cycling can lead to significantly lower temperatures in cells where fans are off, which increases the risk of freezing. Equipping each cell with a VFD prevents freezing.
5. Monitor the tower at all times in subfreezing weather. No matter how automated the tower’s operation, inspectors must physically check the tower regularly.