Enter the inlet dry-bulb temperature, the outlet temperature, and the maximum possible temperature drop (dry-bulb minus wet-bulb) into the calculator to determine the evaporative cooling effectiveness (often called “efficiency”).
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Evaporative Cooling Efficiency Formula
The following formula is commonly used to calculate the saturation effectiveness (often called “efficiency”) of a direct evaporative cooler—how close the outlet air temperature gets to the inlet wet-bulb temperature.
eff = (DB - OT) / (DB - WB)
- Where eff is the evaporative cooler effectiveness (as a fraction; multiply by 100 to get percent)
- DB is the inlet (ambient) dry-bulb temperature
- OT is the outlet (supply air) dry-bulb temperature
- WB is the inlet (ambient) wet-bulb temperature
To calculate evaporative cooling effectiveness, subtract the outlet temperature from the inlet dry-bulb temperature, then divide by the maximum possible temperature drop (inlet dry-bulb minus inlet wet-bulb).
What is evaporative cooling?
Definition:
Evaporative cooling is a process by which heat is transferred from an object or air through the evaporation of water. When water evaporates, it requires heat in order to do so, as a result, it takes heat away from whatever it was in contact with, which then causes cooling on that object.
How to calculate evaporative cooling efficiency?
Example Problem:
The following example outlines how to calculate the evaporative cooling effectiveness (“efficiency”) of a machine.
First, determine the inlet dry-bulb temperature. In this example, the dry-bulb temperature is measured to be 50 °F.
Next, determine the inlet wet-bulb temperature. In this example, the wet-bulb temperature is measured to be 35 °F.
Next, determine the outlet temperature. For this machine, the outlet temperature is measured to be 40 °F.
Finally, calculate the evaporative cooling effectiveness using the formula above:
eff = (DB - OT) / (DB - WB)
eff = (50 - 40) / (50 - 35)
eff = 10 / 15 = 0.667 = 66.7%
