Wet Bulb Temperature Calculator

Calculate wet bulb temperature and related air properties using psychrometric formulas.

Determine wet bulb temperature, humidity ratio, and saturation pressure from dry bulb temperature, relative humidity, and atmospheric pressure measurements.

Examples

Click on any example to load it into the calculator.

Comfortable Indoor Conditions

Comfortable Indoor Conditions

Typical comfortable indoor air conditions for human comfort and productivity.

Dry Bulb: 22 °C

RH: 50 %

Pressure: 1013.25 hPa

Hot Summer Day

Hot Summer Day

Hot and humid summer conditions that require air conditioning.

Dry Bulb: 35 °C

RH: 70 %

Pressure: 1013.25 hPa

Cold Winter Day

Cold Winter Day

Cold winter conditions with low humidity typical of heated indoor spaces.

Dry Bulb: 5 °C

RH: 30 %

Pressure: 1013.25 hPa

Tropical Conditions

Tropical Conditions

High temperature and humidity conditions found in tropical climates.

Dry Bulb: 30 °C

RH: 85 %

Pressure: 1013.25 hPa

Other Titles
Understanding the Wet Bulb Temperature Calculator: A Comprehensive Guide
Explore the science of psychrometrics and learn how to calculate air properties essential for HVAC design, meteorology, and industrial processes. This guide covers everything from basic concepts to advanced applications.

What is Wet Bulb Temperature?

  • Core Concepts
  • Psychrometric Properties
  • Measurement Methods
Wet bulb temperature is a fundamental concept in psychrometrics—the study of air and water vapor mixtures. It represents the lowest temperature that can be achieved by evaporating water into the air at constant pressure. This temperature is crucial for understanding air conditioning processes, evaporative cooling, and human comfort.
The Science Behind Wet Bulb Temperature
When water evaporates, it absorbs heat from its surroundings, causing the temperature to drop. The wet bulb temperature is measured using a thermometer with a wet wick around its bulb. As air passes over the wet wick, water evaporates and cools the thermometer until it reaches equilibrium with the surrounding air. This equilibrium temperature is the wet bulb temperature.
Why Wet Bulb Temperature Matters
Wet bulb temperature is essential for several reasons. It determines the minimum temperature achievable through evaporative cooling, which is crucial for air conditioning and refrigeration systems. It also affects human comfort and health, as it represents the body's ability to cool itself through sweating. In industrial processes, wet bulb temperature influences drying rates and material properties.
Relationship to Other Air Properties
Wet bulb temperature is closely related to other psychrometric properties. It's always less than or equal to the dry bulb temperature, with the difference indicating the air's capacity for moisture. The wet bulb temperature, combined with dry bulb temperature, can be used to determine relative humidity, humidity ratio, and other air properties using psychrometric charts or equations.

Key Psychrometric Properties:

  • Dry Bulb Temperature: The ambient air temperature measured with a standard thermometer
  • Wet Bulb Temperature: The temperature achieved through evaporative cooling
  • Dew Point Temperature: The temperature at which air becomes saturated with water vapor
  • Relative Humidity: The ratio of actual water vapor to maximum possible water vapor
  • Humidity Ratio: The mass of water vapor per unit mass of dry air

Step-by-Step Guide to Using the Calculator

  • Gathering Measurements
  • Inputting Data
  • Interpreting Results
Using the wet bulb temperature calculator requires accurate measurements and understanding of the input parameters. Follow these steps to ensure reliable results.
1. Measuring Dry Bulb Temperature
Use a calibrated thermometer to measure the ambient air temperature. Ensure the thermometer is not exposed to direct sunlight or heat sources. For outdoor measurements, place the thermometer in a shaded, well-ventilated area. For indoor measurements, avoid placing it near heating or cooling vents.
2. Determining Relative Humidity
Relative humidity can be measured using a hygrometer or calculated from other psychrometric properties. Digital hygrometers provide the most accurate readings. Alternatively, you can use a sling psychrometer to measure both dry bulb and wet bulb temperatures, then calculate relative humidity.
3. Accounting for Atmospheric Pressure
Atmospheric pressure varies with altitude and weather conditions. At sea level, standard atmospheric pressure is 1013.25 hPa. For locations at higher altitudes, use a barometer to measure local pressure or estimate it based on altitude. Pressure affects the calculation of air properties and should be as accurate as possible.
4. Understanding the Results
The calculator provides three key results: wet bulb temperature, humidity ratio, and saturation pressure. The wet bulb temperature indicates the cooling potential of the air. The humidity ratio shows the actual moisture content. The saturation pressure represents the maximum water vapor pressure possible at the given temperature.

Measurement Best Practices:

  • Use calibrated instruments for accurate measurements
  • Take measurements in representative locations away from heat sources
  • Allow instruments to stabilize before taking readings
  • Record measurements at consistent times for trend analysis
  • Consider the effects of altitude on atmospheric pressure

Real-World Applications and Industrial Uses

  • HVAC Systems
  • Industrial Processes
  • Meteorology and Weather
Wet bulb temperature calculations have numerous practical applications across various industries and fields.
HVAC and Air Conditioning Design
In HVAC systems, wet bulb temperature is crucial for designing cooling towers, evaporative coolers, and air conditioning equipment. It determines the efficiency of heat exchangers and the capacity of cooling systems. Engineers use wet bulb temperature to size equipment and optimize energy consumption.
Industrial Drying and Processing
Many industrial processes rely on controlled drying conditions. Wet bulb temperature affects drying rates and product quality in industries such as food processing, paper manufacturing, and chemical production. Understanding wet bulb temperature helps optimize drying processes and reduce energy costs.
Meteorology and Weather Forecasting
Meteorologists use wet bulb temperature to assess heat stress, predict weather patterns, and issue heat warnings. It's particularly important for understanding heat index and human comfort in different weather conditions. Wet bulb temperature data helps in climate studies and weather modeling.

Industrial Applications:

  • Cooling tower design and efficiency optimization
  • Evaporative cooling system sizing
  • Industrial drying process control
  • Heat stress assessment in workplaces
  • Weather forecasting and climate modeling

Common Misconceptions and Technical Considerations

  • Wet Bulb vs. Dew Point
  • Measurement Accuracy
  • Environmental Factors
Understanding wet bulb temperature requires clarity on several common misconceptions and technical considerations.
Wet Bulb vs. Dew Point Temperature
Wet bulb and dew point temperatures are often confused but serve different purposes. Wet bulb temperature represents the cooling potential through evaporation, while dew point temperature indicates when condensation will occur. Wet bulb temperature is always higher than or equal to dew point temperature.
Measurement Accuracy and Calibration
Accurate wet bulb temperature measurement requires proper instrument calibration and technique. The wet wick must be clean and properly saturated with distilled water. Air velocity around the wet bulb affects the measurement, so consistent conditions are essential for reliable results.
Environmental and Operational Factors
Several factors can affect wet bulb temperature calculations. Altitude changes atmospheric pressure, affecting air properties. Air velocity influences evaporation rates and wet bulb temperature. Contaminants in the air can affect water evaporation and measurement accuracy.

Technical Considerations:

  • Instrument calibration and maintenance requirements
  • Effects of air velocity on wet bulb measurements
  • Impact of altitude on atmospheric pressure
  • Influence of air contaminants on evaporation
  • Temperature and humidity sensor placement guidelines

Mathematical Derivation and Advanced Calculations

  • Psychrometric Equations
  • Iterative Methods
  • Software Implementation
The calculation of wet bulb temperature involves complex psychrometric equations and iterative methods.
Psychrometric Equations and Relationships
Wet bulb temperature calculation uses the relationship between dry bulb temperature, relative humidity, and atmospheric pressure. The process involves solving for the temperature at which the enthalpy of the air-water vapor mixture equals the enthalpy at the wet bulb condition. This requires iterative calculations due to the non-linear nature of the equations.
Iterative Solution Methods
Since wet bulb temperature cannot be solved directly, iterative methods such as Newton-Raphson or bisection are used. The calculation starts with an initial estimate and refines it until convergence. The accuracy of the result depends on the convergence criteria and the quality of the initial estimate.
Software and Computational Considerations
Modern calculators and software use optimized algorithms for wet bulb temperature calculation. These algorithms balance accuracy with computational efficiency. The mathematical models are based on empirical relationships and thermodynamic principles, ensuring reliable results across a wide range of conditions.

Mathematical Relationships:

  • Enthalpy balance equations for wet bulb conditions
  • Water vapor pressure relationships with temperature
  • Humidity ratio calculations from psychrometric properties
  • Iterative convergence criteria for accurate results
  • Thermodynamic property correlations and empirical data