The wet bulb temperature (WBT) is a critical factor in the performance and efficiency of a cooling tower. Here’s how it affects cooling tower operation:
1. Determines Cooling Limit
- The lowest possible temperature to which water can be cooled in a cooling tower is the ambient wet bulb temperature.
- Cooling towers cannot cool water below WBT, no matter how efficient they are.
- The approach temperature (difference between cold water temp and WBT) indicates cooling tower performance (typically 5–10°F or 3–6°C for well-designed towers).
2. Impacts Cooling Efficiency
- Higher WBT reduces the cooling tower’s ability to reject heat because the temperature gradient (ΔT) between water and air decreases.
- Lower WBT allows for better heat transfer and more efficient cooling.
3. Affects Cooling Tower Size & Design
- In regions with high WBT, larger cooling towers or additional cooling capacity are needed to achieve the same cooling effect.
- Designers use WBT data to select the appropriate cooling tower type (e.g., natural draft, mechanical draft, or hybrid).
4. Influences Fan & Energy Consumption
- When WBT is high, cooling towers must work harder (higher fan speeds or more airflow), leading to increased energy consumption.
- Some towers use variable-speed fans to optimize energy use based on WBT fluctuations.
5. Impacts Industrial Processes
- Industries relying on precise cooling (e.g., power plants, refineries, HVAC systems) must account for WBT to maintain optimal process temperatures.
- High WBT can lead to reduced plant efficiency or even shutdowns in extreme cases (e.g., wet bulb globe temperature (WBGT) safety limits).
6. Seasonal & Climatic Variations
- Hot & humid climates (high WBT) reduce cooling tower performance compared to dry climates (where evaporative cooling is more effective).
- Cooling towers in arid regions can achieve near-WBT cooling, while those in humid areas may require supplemental cooling methods.