This is why the same industrial air cooler can produce different cooling results under different operating conditions.
1. Ambient Air Temperature
Outdoor air temperature is one of the basic factors affecting cooling performance.
An evaporative air cooler draws warm outdoor air through a wet cooling pad. As water evaporates, heat is absorbed from the air and the supply-air temperature decreases.
When the outdoor temperature is high, there is generally more sensible heat available for evaporation.
However, temperature should never be considered separately from humidity. A high outdoor temperature combined with high relative humidity can provide a very different cooling result from the same temperature in dry weather.
2. Relative Humidity
Relative humidity has a direct effect on evaporative cooling capacity.
Dry air can absorb more water vapor, allowing greater evaporation through the cooling pad. As humidity increases, the air becomes closer to saturation and the available evaporative cooling potential decreases.
For this reason:
Lower humidity → greater evaporative cooling potential
Higher humidity → lower evaporative cooling potential
This is one of the most important differences between evaporative air cooling and mechanical refrigeration.
3. Wet-Bulb Temperature
Wet-bulb temperature provides a more useful indication of the potential of evaporative cooling than dry-bulb temperature alone.
The theoretical lower limit of an evaporative cooler's leaving-air temperature is closely related to the entering-air wet-bulb temperature.
A simplified way to understand the available cooling potential is:
Wet-Bulb Depression = Dry-Bulb Temperature − Wet-Bulb Temperature
For example, if outdoor air is:
Dry-bulb temperature: 35°C
Wet-bulb temperature: 24°C
The wet-bulb depression is:
35 − 24 = 11°C
The larger this difference, the greater the theoretical potential for evaporative cooling.
The actual outlet-air temperature will not normally reach the wet-bulb temperature because real cooling pads and air coolers have finite efficiency.
4. Evaporative Cooling Efficiency
Cooling efficiency describes how closely the air cooler can approach the entering-air wet-bulb temperature.
A commonly used simplified expression is:
Cooling Efficiency = (Entering Dry-Bulb Temperature − Leaving Air Temperature) ÷ (Entering Dry-Bulb Temperature − Entering Wet-Bulb Temperature) × 100%
For example:
Entering dry-bulb temperature: 35°C
Entering wet-bulb temperature: 24°C
Leaving air temperature: 26°C
Then:
(35 − 26) ÷ (35 − 24) × 100% ≈ 81.8%
The actual efficiency depends on the cooler design, cooling pad, airflow velocity, water distribution, and operating conditions.
5. Airflow Rate
Airflow also affects the cooling performance of an industrial air cooler.
If air passes through the cooling pad too quickly, there may be less time for effective heat and moisture transfer.
If airflow is too low, the system may not move enough cooled air through the workshop.
Therefore, the relationship between airflow rate and cooling pad performance needs to be considered when evaluating cooling capacity.
The rated airflow of the fan should not be interpreted as the same thing as cooling capacity.
A unit may have a high airflow rating but provide a different temperature reduction depending on the entering air conditions and cooling-pad efficiency.
6. Cooling Pad Performance
The cooling pad is the main heat-and-mass-transfer surface in an evaporative air cooler.
Its performance is affected by:
Pad material
Pad thickness
Surface area
Air velocity
Water distribution
Pad wetting
Cleanliness
Service condition
A dirty or unevenly wetted cooling pad can reduce evaporation and therefore reduce the cooling effect.
The cooling pad must receive sufficient water while maintaining an appropriate airflow path through the wetted surface.
7. Water Distribution
Water needs to be distributed evenly across the cooling pad.
If some areas remain dry, only part of the pad contributes effectively to evaporation.
Poor water distribution can result from:
Blocked water channels
Pump problems
Incorrect water flow
Mineral deposits
Damaged distribution components
Regular inspection of the water circulation system helps maintain consistent cooling performance.
8. Workshop Heat Load
The air cooler's rated cooling performance does not automatically determine the temperature that will be achieved inside a factory.
The workshop itself continuously gains heat from:
Production machinery
Furnaces
Ovens
Motors
Compressors
Lighting
Workers
Solar radiation
Hot products
If a production line generates a large amount of heat, the cooling system needs enough airflow and appropriate air distribution to remove or dilute that heat.
This is why outlet-air temperature and actual workshop temperature are two different measurements.
9. Ventilation and Air Exchange
An evaporative industrial air cooler introduces cooled air into the workshop while adding moisture to the air stream.
The warm indoor air needs to leave.
If exhaust openings are insufficient, the additional moisture can accumulate and indoor humidity can rise.
This can reduce the effective temperature drop and make the cooling system less effective.
Therefore, cooling capacity should always be considered together with the factory's ventilation arrangement.
10. Airflow Distribution
Even when an industrial air cooler is operating at its rated capacity, poor airflow distribution can create hot spots.
For a large workshop, cooling performance depends on whether the cooled air actually reaches the occupied areas.
Machinery, storage racks, walls, columns, and partitions can obstruct airflow.
The system should therefore be designed around:
Air Cooler → Air Distribution → Working Area → Heat Removal
rather than focusing only on the total airflow supplied by the equipment.
11. Water Quality and Scale
Water quality can affect long-term cooling performance.
Hard water contains minerals that can accumulate on the cooling pad and water distribution components.
Scale buildup can:
Reduce water absorption
Restrict airflow
Create uneven wetting
Reduce evaporation
Increase maintenance requirements
For this reason, water management is an important part of maintaining the cooling capacity of an evaporative air cooler.
12. Cooling Capacity vs. Temperature Drop
These two terms should not be confused.
Temperature drop refers to how much the air temperature decreases as it passes through the cooler.
Cooling capacity refers to the amount of heat that the cooling process can remove or transfer under specified conditions.
A simplified sensible cooling relationship can be expressed as:
Cooling Capacity ≈ Air Mass Flow × Specific Heat × Temperature Difference
For air-conditioning calculations, humidity and latent heat may also need to be considered.
For an evaporative air cooler, however, the moisture added to the air and the associated evaporative heat transfer are central to the cooling process.
Therefore, a single temperature-drop number does not fully describe the performance of the equipment.
13. Why Cooling Capacity Changes With Weather
Consider two days with the same outdoor temperature:
Day A
Temperature: 35°C
Relative humidity: 30%
Day B
Temperature: 35°C
Relative humidity: 75%
The dry-bulb temperature is identical, but the moisture content of the air is very different.
The evaporative cooling potential on Day A is generally much greater because the air has more capacity to absorb additional water vapor.
This is why industrial air cooler performance should be evaluated using actual local climate conditions rather than a single outdoor temperature.
14. What Determines the Actual Cooling Result?
In practical factory applications, cooling performance is the combined result of several factors:
Ambient Temperature + Humidity + Wet-Bulb Temperature + Cooling Efficiency + Airflow + Heat Load + Ventilation
Changing one factor can affect the overall result.
For example, increasing airflow may improve air movement but cannot fully overcome unsuitable humidity conditions. Similarly, a highly efficient cooling pad cannot provide its expected performance if the water distribution system is blocked.
Industrial Air Cooler Cooling Capacity Checklist
When evaluating an industrial air cooler, check:
Entering air temperature
Relative humidity
Wet-bulb temperature
Cooling efficiency
Airflow rate
Cooling pad design
Water distribution
Water quality
Workshop heat load
Ventilation
Airflow distribution
These factors provide a much more useful picture of cooling performance than looking at the rated airflow alone.
Final Considerations
The cooling capacity of an industrial air cooler is determined by the interaction between the ambient air condition, evaporative efficiency, airflow, cooling pad, water system, workshop heat load, and ventilation.
For evaporative cooling, relative humidity and wet-bulb temperature are particularly important because they determine how much additional moisture the incoming air can absorb.
When evaluating an industrial air cooler for a factory, do not rely on a single temperature-drop or airflow figure. The equipment should be assessed under the expected operating temperature, humidity, airflow conditions, and workshop heat load.
This approach provides a more realistic understanding of the cooling performance that an industrial air cooler can deliver in an actual factory.
