Wet bulb temperature is the lowest temperature air can reach through evaporative cooling, measured with a thermometer whose bulb is wrapped in a wet cloth exposed to airflow. This temperature always equals or falls below dry bulb temperature and reflects the air’s actual heat content and humidity level. Wet bulb temperature determines cooling tower effectiveness and evaporative cooling system performance.
HVAC Significance
The difference between dry bulb and wet bulb temperatures indicates relative humidity levels. At 50 percent relative humidity and 90°F dry bulb, wet bulb temperature is approximately 70°F. This 20-degree difference guides evaporative cooler sizing and cooling tower design. Wet bulb temperature directly limits cooling tower performance, as cooling below wet bulb is thermodynamically impossible.
System Design Applications
Cooling tower selection depends on wet bulb temperatures, with manufacturers publishing performance data at 75°F and 85°F wet bulb conditions. Design dry bulb temperatures for sizing HVAC equipment are typically 95°F, but wet bulb values prove more critical for cooling tower efficiency. Engineers in humid climates face higher wet bulb temperatures, requiring larger cooling towers or complementary mechanical cooling systems to meet setpoint temperatures.