Differences in air dry bulb temperature, wet bulb temperature, black bulb temperature, and dew point temperature

Dry bulb temperature, wet bulb temperature, black bulb temperature, and dew point temperature are four commonly used concepts in meteorology, HVAC, and industrial safety. They describe the state of the air and the human body's perception of the environment from different perspectives. Here are their core differences:

1. Dry bulb temperature (DBT)

• definitionIt is the true temperature of the air, which is what we call 'temperature' in our daily lives. It represents the mixed temperature of water vapor and dry air in the air, without considering the influence of humidity.
• measurementMeasured directly by ordinary thermometers (such as mercury in glass thermometers or electronic temperature sensors) exposed to air, the temperature sensing part of the thermometer needs to avoid direct sunlight and other radiation heat sources.
• meaningIt is the most basic physical quantity for measuring the degree of air temperature and is the basis for calculating other temperature parameters.

2. Wet bulb temperature (WBT)

• definitionIt refers to the temperature at which air and water come into full contact and reach saturation under adiabatic conditions (i.e. without heat exchange). It reflects the energy that can be achieved through water evaporation in the current air stateMINTemperature is a comprehensive reflection of air temperature and humidity.
• measurementMeasured by a thermometer wrapped in moist gauze. Immerse the lower end of the gauze in water to keep it moist. Due to the evaporation of water absorbing heat, the reading of a wet bulb thermometer is usually lower than the dry bulb temperature.
• meaningThe difference between dry and wet bulb temperatures can be used to calculate the relative humidity of the air. The larger the difference, the drier the air and the faster the evaporation of water; When the difference is zero, it indicates that the air has reached saturation (relative humidity is 100%).

3. Globe Temperature (GT)

• definitionAlso known as global temperature or composite temperature, it simulates the temperature at which a black sphere reaches thermal equilibrium in its environment. This temperature takes into account the temperature of the surrounding air, the radiation heat from the sun or other heat sources, and the influence of wind speed, and is closer to the actual "perceived" temperature of the human body or object in the environment.
• measurementUse a thin-walled copper ball of standard size (usually 15 centimeters in diameter) with a matte black coating on the outer surface (emissivity of approximately 0.95), and place the thermometer at the center of the ball for measurement.
• meaning: is an important parameter for evaluating the impact of thermal environment (especially the presence of strong radiation sources such as the sun, high-temperature furnaces, etc.) on human health. In outdoor or high-temperature workplaces, the temperature of black balls is usually much higher than that of dry balls.

4. Dew point temperature (DPT)

• definitionIt refers to the temperature at which water vapor in the air reaches saturation and condenses into liquid water (condensation) through cooling, under the condition that the water vapor content and air pressure in the air remain constant.
• measurementDew point temperature cannot be directly measured by a simple thermometer. It is usually calculated by measuring dry bulb temperature and wet bulb temperature (or relative humidity), looking up a table, or using a formula.
• meaningIt is an absolute indicator for measuring the water vapor content in the air. The higher the dew point temperature, the higher the water vapor content in the air. When the surface temperature of an object is lower than the dew point temperature of the surrounding air, water vapor will condense on its surface, forming dew or mist.

Summary and Comparison