Wet-bulb temperature plays a critical role in the performance and efficiency of cooling towers (cooling water towers). It is not just a measure of the cooling tower’s limit, but also a key factor influencing the cooling capacity, efficiency, and approach temperature of the system.

This article explains what wet-bulb temperature is, its impact on cooling towers, the lowest achievable cooling temperature, and the different types of cooling towers based on function and material.

1. What Is Wet-Bulb Temperature?

Definition

  • The wet-bulb temperature (WBT) represents the lowest temperature that water can reach through evaporative cooling at a specific location and time.
  • It determines the minimum possible temperature that the cooling tower outlet water can achieve.

Key Characteristics

  • Wet-bulb temperature has a major impact on the cooling tower’s outlet water temperature.
  • Weather reports usually show the dry-bulb temperature (DBT), while the wet-bulb temperature is always lower than the dry-bulb temperature.
  • It is measured using a thermometer covered with a wet cloth, as water evaporates from the cloth, cooling the thermometer.
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2. What Is the Lowest Temperature a Cooling Tower Can Achieve?

  • Theoretically, a cooling tower cannot cool water below the wet-bulb temperature.
  • In practical applications, the outlet water temperature is usually at least 4°C higher than the wet-bulb temperature. This difference is called the approach temperature (≥ 4°C).
  • The smaller the approach temperature, the harder it is to achieve.
  • To reach the exact wet-bulb temperature, the cooling tower would have to be infinitely large, which is not feasible.

Example Calculation

  • If the wet-bulb temperature in a city is 25°C, a typical cooling tower might achieve an outlet temperature of 29°C or higher.
  • A system aiming for 28°C or lower would require a larger tower, more airflow, or enhanced evaporation mechanisms.

3. Types of Cooling Towers Based on Function and Material

Cooling towers can be classified based on their usage, circulation type, and construction material.

3.1 Classification by Function (Application)

  1. Industrial Cooling Towers → Used in power plants, refineries, steel mills, and chemical plants.
  2. Commercial HVAC Cooling Towers → Used in office buildings, shopping malls, hospitals, and hotels.
  3. Process Cooling Towers → Used for cooling in manufacturing processes (e.g., food, pharmaceuticals, textiles).

3.2 Classification by Circulation Type

  1. Open-Circuit (Open-Loop) Cooling Towers
  • Directly exposes water to air for evaporative cooling.
  • Higher evaporation = better cooling efficiency.
  • More water loss due to evaporation.
  1. Closed-Circuit (Closed-Loop) Cooling Towers
  • Uses a heat exchanger to keep cooling water separate from the air.
  • Reduces water loss and contamination risks.
  • Common in HVAC and sensitive industrial applications.

3.3 Classification by Material

  1. Fiberglass Reinforced Plastic (FRP) Cooling Towers
  • Lightweight, corrosion-resistant, and durable.
  • Used in HVAC and industrial applications.
  1. Steel Cooling Towers
  • Stronger but susceptible to corrosion if not coated properly.
  • Often used in heavy industrial environments.
  1. Reinforced Concrete Cooling Towers
  • Used in large-scale power plants and chemical industries.
  • Extremely durable, but costly to construct.

4. Common Applications of Cooling Towers

Cooling towers are essential in two major fields:

  1. HVAC Cooling Towers
  • Supports air conditioning systems in buildings.
  • Removes excess heat from chillers and heat exchangers.
  1. Industrial Process Cooling
  • Used in power plants, steel production, pharmaceuticals, petrochemicals, textiles, and food processing.
  • Helps regulate temperatures in boilers, furnaces, and chemical reactions.

5. Conclusion

  • Wet-bulb temperature is a crucial parameter in cooling tower operation.
  • The cooling tower’s minimum achievable outlet temperature is always higher than the wet-bulb temperature by at least 4°C (approach temperature).
  • Cooling towers vary by function, circulation type, and material, with each type suited for different applications.

Understanding wet-bulb temperature and cooling tower classifications helps in selecting the most efficient cooling system for HVAC or industrial processes. 🚀

The Role of Wet-Bulb Temperature in Cooling Towers