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Views: 0 Author: Site Editor Publish Time: 2025-12-13 Origin: Site
Wet bulb temperature is one of the most important environmental parameters affecting the performance of a water cooling tower and any water cooling tower system. It defines the lowest theoretical temperature that circulating water can reach through evaporative cooling. Understanding wet bulb temperature is essential for designing, selecting, and operating water cooled towers, closed loop cooling towers, and chilled water cooling tower systems.
Manufacturers such as Mach Cooling (https://www.machcooling.com/) design cooling towers based on site-specific wet bulb temperature to ensure stable performance, efficient heat rejection, and reliable long-term operation.
Wet bulb temperature (WBT) is the lowest temperature that air can reach through the evaporation of water at a constant pressure. It is measured using a thermometer with its bulb wrapped in a wet wick and exposed to airflow.
Unlike dry bulb temperature (ambient air temperature), wet bulb temperature accounts for:
Air temperature
Humidity
Evaporative cooling potential
In a water cooling tower, cooling occurs primarily through evaporation. Therefore, wet bulb temperature determines the cooling limit of the system.
The cold water temperature leaving a cooling tower can never be lower than the wet bulb temperature of the entering air. This makes wet bulb temperature the most critical design parameter.
The difference between:
Hot water inlet temperature
Cold water outlet temperature
is known as the cooling tower range, while the difference between cold water temperature and wet bulb temperature is the approach.
A smaller approach indicates better cooling tower performance.
| Parameter | Wet Bulb Temperature | Dry Bulb Temperature |
|---|---|---|
| Includes Humidity | Yes | No |
| Indicates Cooling Potential | Yes | No |
| Affects Cooling Tower Design | Directly | Indirectly |
| Always Lower or Equal | Yes | No |
Cooling towers are always rated based on wet bulb temperature, not dry bulb temperature.
In open water cooling towers, wet bulb temperature directly limits heat rejection capacity. Higher wet bulb temperatures reduce cooling efficiency.
Although process fluid is isolated, closed loop cooling towers still rely on evaporative cooling, making wet bulb temperature equally critical.
In chilled water cooling towers, wet bulb temperature affects condenser performance and overall cooling tower chilled water system efficiency.
In blowdown water cooling towers, higher wet bulb temperatures increase evaporation rates, influencing blowdown volume and the concentration of cooling tower water treatment chemicals.
As wet bulb temperature increases:
Evaporation rate decreases
Cooling capacity reduces
Cold water temperature rises
Higher wet bulb temperatures require:
Increased fan operation
Higher pump loads
Greater energy use
Higher wet bulb conditions increase evaporation, affecting:
Make-up water demand
Blowdown rate
Concentration of cooling tower water treatment chemicals
| Climate Region | Typical Summer Wet Bulb |
|---|---|
| Cool / Dry | 18–22 °C |
| Temperate | 22–26 °C |
| Hot / Humid | 26–30 °C |
Cooling towers are selected based on the design maximum wet bulb temperature, not average values.
Wet bulb temperature is measured using:
Sling psychrometers
Electronic sensors
Weather station data
Measure near the cooling tower air inlet
Avoid direct sunlight
Ensure proper airflow across sensors
Accurate wet bulb measurement is essential for performance evaluation.
| Parameter | Description |
|---|---|
| Range | Hot water – Cold water |
| Approach | Cold water – Wet bulb |
| Efficiency | Range ÷ (Range + Approach) |
Lower wet bulb temperature allows:
Smaller approach
Higher cooling tower efficiency
Cooling towers are sized to meet required outlet water temperature at the design wet bulb temperature.
Proper fill design and high-efficiency fans help offset high wet bulb conditions.
Changes in wet bulb temperature affect evaporation and concentration cycles, requiring adjustment of cooling tower water treatment chemicals.
Mach Cooling (https://www.machcooling.com/) designs cooling towers based on accurate wet bulb temperature data, offering:
Optimized performance for local climate conditions
Reliable operation across water cooling towers, closed loop cooling towers, and chilled water cooling towers
Compatibility with advanced water treatment and blowdown control
Long-term efficiency for industrial and HVAC applications
Mach Cooling’s engineering approach ensures cooling towers meet required outlet temperatures even during peak wet bulb conditions.
This is incorrect. Cooling towers depend on wet bulb temperature, not ambient air temperature alone.
This is physically impossible due to thermodynamic limits.
Wet bulb temperature is the single most important environmental factor influencing cooling tower performance. It defines the lowest achievable cooling temperature and directly affects system efficiency, water consumption, and energy use.
Whether operating a water cooling tower, water cooled tower, closed loop cooling tower, or chilled water cooling tower system, understanding wet bulb temperature enables better design, selection, and operation. By integrating climate-based design and advanced engineering, Mach Cooling provides reliable cooling tower solutions that perform efficiently under real-world wet bulb conditions.
