Wet-Bulb Temperature Calculator

Air Temperature (\( T \)):

Relative Humidity (\( RH \), %): %

Globe Thermometer Temperature (\( T_g \)):

Wet-Bulb Temperature (\( T_w \)):

Wet-Bulb Depression:

Wet-Bulb Globe Temperature (Outdoor):

Wet-Bulb Globe Temperature (Indoor):

1. What is the Wet-Bulb Temperature Calculator?

Definition: This calculator computes the wet-bulb temperature (\( T_w \)), wet-bulb depression, Wet-Bulb Globe Temperature (WBGT) Outdoor, and Wet-Bulb Globe Temperature (WBGT) Indoor based on air temperature, relative humidity, and globe thermometer temperature. The wet-bulb temperature is the lowest temperature to which air can be cooled by evaporating water into it at constant pressure.

Purpose: It is used in meteorology, occupational health, and sports science to assess heat stress, evaluate the risk of heat-related illnesses, and ensure safety in warm environments.

2. How Does the Calculator Work?

The calculator uses the following formulas:

Wet-Bulb Temperature (\( T_w \)) using the Stull Formula:

Wet-Bulb Depression: \[ \text{Wet-Bulb Depression} = T - T_w \] Wet-Bulb Globe Temperature (WBGT) Outdoor: \[ \text{WBGT}_{\text{outdoor}} = 0.7 T_w + 0.2 T_g + 0.1 T \] Wet-Bulb Globe Temperature (WBGT) Indoor: \[ \text{WBGT}_{\text{indoor}} = 0.7 T_w + 0.3 T \] where:

\( T_w \): Wet-bulb temperature (°C, °F, K)
\( T \): Air temperature (°C, °F, K)
\( RH \): Relative humidity (%)
\( T_g \): Globe thermometer temperature (°C, °F, K)

Unit Conversions:

Temperature (Air Temperature, Globe Temperature):
- 1 °C = 1 °C
- 1 °F = (T - 32) × 5/9 °C
- 1 K = T - 273.15 °C
- For output: 1 °C = (T × 9/5) + 32 °F, 1 °C = T + 273.15 K

Steps:

Enter the air temperature in °C, °F, or K (default is 25°C, step size 0.00001).
Enter the relative humidity in % (default is 50%, step size 0.00001).
Enter the globe thermometer temperature in °C, °F, or K (default is 0°C, step size 0.00001).
Convert air temperature and globe temperature to Celsius (°C).
Calculate the wet-bulb temperature (\( T_w \)) using the Stull formula.
Calculate the wet-bulb depression as the difference between air temperature and wet-bulb temperature.
Calculate the WBGT Outdoor using wet-bulb temperature, globe temperature, and air temperature.
Calculate the WBGT Indoor using wet-bulb temperature and air temperature.
Convert all results to the selected temperature unit and display them, using scientific notation if the absolute value is less than 0.001, otherwise rounded to 4 decimal places.

3. Importance of Wet-Bulb Temperature Calculation

Calculating wet-bulb temperature and related metrics is crucial for:

Heat Stress Assessment: Wet-bulb temperature and WBGT are used to evaluate the risk of heat-related illnesses in occupational and sports settings, ensuring safety during hot conditions.
Meteorology: Wet-bulb temperature indicates the potential for evaporative cooling, which affects weather phenomena like thunderstorm development and fog formation.
Climate Studies: High wet-bulb temperatures can indicate dangerous conditions for human survival, as they limit the body's ability to cool through sweating, a key concern in climate change research.

4. Using the Calculator

Examples:

Example 1: Calculate the wet-bulb temperature, wet-bulb depression, WBGT Outdoor, and WBGT Indoor with an air temperature of 25°C, relative humidity of 50%, and globe temperature of 0°C, in °C:
- Enter Air Temperature = 25 °C.
- Enter Relative Humidity = 50%.
- Enter Globe Temperature = 0 °C.
- Wet-Bulb Depression:
  \( 25 - 16.5572 = 8.4428 \, \text{°C} \).
- WBGT Outdoor:
  \( 0.7 \times 16.5572 + 0.2 \times 0 + 0.1 \times 25 = 11.5900 + 0 + 2.5 = 14.0900 \, \text{°C} \).
- WBGT Indoor:
  \( 0.7 \times 16.5572 + 0.3 \times 25 = 11.5900 + 7.5 = 19.0900 \, \text{°C} \).
- Result:
  \( T_w = 16.5572 \, \text{°C}, \text{Wet-Bulb Depression} = 8.4428 \, \text{°C}, \text{WBGT Outdoor} = 14.0900 \, \text{°C}, \text{WBGT Indoor} = 19.0900 \, \text{°C} \).
Example 2: Calculate the wet-bulb temperature, wet-bulb depression, WBGT Outdoor, and WBGT Indoor with an air temperature of 86°F, relative humidity of 70%, and globe temperature of 77°F, in °F:
- Enter Air Temperature = 86 °F, convert to °C: \( (86 - 32) \times 5/9 = 30 \, \text{°C} \).
- Enter Relative Humidity = 70%.
- Enter Globe Temperature = 77 °F, convert to °C: \( (77 - 32) \times 5/9 = 25 \, \text{°C} \).
- Convert to °F: \( 24.1904 \times 9/5 + 32 = 75.5427 \).
- Wet-Bulb Depression:
  \( 30 - 24.1904 = 5.8096 \, \text{°C} \), convert to °F: \( 5.8096 \times 9/5 = 10.4573 \).
- WBGT Outdoor:
  \( 0.7 \times 24.1904 + 0.2 \times 25 + 0.1 \times 30 = 16.9333 + 5 + 3 = 24.9333 \, \text{°C} \), convert to °F: \( 24.9333 \times 9/5 + 32 = 76.8799 \).
- WBGT Indoor:
  \( 0.7 \times 24.1904 + 0.3 \times 30 = 16.9333 + 9 = 25.9333 \, \text{°C} \), convert to °F: \( 25.9333 \times 9/5 + 32 = 78.6799 \).
- Result:
  \( T_w = 75.5427 \, \text{°F}, \text{Wet-Bulb Depression} = 10.4573 \, \text{°F}, \text{WBGT Outdoor} = 76.8799 \, \text{°F}, \text{WBGT Indoor} = 78.6799 \, \text{°F} \).

5. Frequently Asked Questions (FAQ)

Q: What is wet-bulb temperature?
A: Wet-bulb temperature (\( T_w \)) is the lowest temperature to which air can be cooled by evaporating water into it at constant pressure. It reflects the combined effect of temperature and humidity on evaporative cooling.

Q: Why is WBGT important?
A: Wet-Bulb Globe Temperature (WBGT) combines wet-bulb temperature, air temperature, and (for outdoor) globe temperature to assess heat stress. It is used to determine safe working conditions in hot environments, preventing heat-related illnesses.

Q: What is the difference between WBGT Outdoor and Indoor?
A: WBGT Outdoor includes the effect of solar radiation via the globe thermometer temperature (\( T_g \)), while WBGT Indoor, measured without direct sunlight, only considers wet-bulb and air temperatures, making it more relevant for shaded or indoor environments.