HVAC and cooling
Estimate entering wet bulb, evaporative cooling potential, air enthalpy, moisture loading, and pressure-sensitive system behavior.
Calculator inputs
Select an input mode. Irrelevant fields are hidden automatically.
Condition presets
Load common environments, then adjust any input.
Batch weather calculations
Process up to 500 rows in Celsius, percent, kilopascals, and metres.
Session calculation history
Recent results are stored only in the current PHP session.
No calculations are stored yet.
Formulas and calculation methods
The default workflow derives vapor pressure, humidity ratio, enthalpy, and saturated wet-bulb state.
Pressure-corrected iterative method
The calculator first determines actual vapor pressure from the selected input pair. It then calculates humidity ratio at the specified atmospheric pressure.
W = 0.621945 × pᵥ ÷ (P − pᵥ)
The solver finds a saturated temperature whose moist-air enthalpy matches the initial state.
1.006Tdb + W(2501 + 1.86Tdb) = 1.006Twb + Ws(Twb)(2501 + 1.86Twb)
Ventilated psychrometer equation
This method relates measured dry-bulb and wet-bulb readings to vapor pressure. The coefficient changes with the selected instrument type.
pᵥ = pws(Twb) − A × P × (Tdb − Twb)
Stull approximation
This empirical equation provides a fast sea-level estimate from Celsius temperature and relative humidity.
Twb ≈ T atan(0.151977√(RH+8.313659)) + atan(T+RH) − atan(RH−1.676331) + 0.00391838RH³ᐟ² atan(0.023101RH) − 4.686035
Evaporative cooler outlet
Real coolers approach wet-bulb temperature according to their saturation efficiency.
Tout = Tdb − η(Tdb − Twb)
How to use this calculator
- Select the known-property input mode.
- Choose Celsius, Fahrenheit, Kelvin, or Rankine.
- Enter measured pressure or estimate pressure from elevation.
- Provide the required temperature and humidity values.
- Select the iterative, psychrometer, Stull, or comparison method.
- Set evaporative cooler efficiency when cooling analysis is needed.
- Open advanced options to adjust tolerance, iterations, and precision.
- Submit the form and review warnings before using results.
- Export the report or process many weather rows in batch mode.
Practical applications
Agriculture
Review greenhouse cooling potential, livestock housing conditions, fogging suitability, crop environment, and grain-drying context.
Weather analysis
Compare hot-dry, hot-humid, high-altitude, near-saturation, and cold-weather atmospheric states.
Education
Explore relationships among dry bulb, wet bulb, dew point, relative humidity, pressure, enthalpy, and humidity ratio.
Industrial processes
Screen evaporative drying, ventilation, air treatment, storage, process-air, and environmental control conditions.
Heat awareness
Use wet bulb as one environmental clue while following approved WBGT, workplace, athletic, and public-health protocols.
Frequently asked questions
What is wet-bulb temperature?
It is the equilibrium temperature approached by a wetted, ventilated sensor as water evaporates into the surrounding air.
Why is wet bulb below dry bulb?
Evaporation consumes energy and cools the wetted surface. The temperatures become equal when the air is saturated.
Is wet-bulb temperature the same as dew point?
No. Dew point describes saturation by cooling at nearly constant moisture content. Wet bulb includes evaporative cooling and energy exchange.
Is wet bulb the same as WBGT?
No. WBGT is a separate heat-stress index that may include natural wet bulb, globe temperature, and dry-bulb temperature.
Why does pressure matter?
Humidity ratio and evaporation relationships depend on total atmospheric pressure. Elevation can therefore change detailed psychrometric results.
Which method should I use?
Use the pressure-corrected iterative method for general analysis. Use Stull for a fast estimate within its published range.
Can this replace a calibrated psychrometer?
No. Input sensor quality, airflow, radiation shielding, wick condition, and water purity affect physical measurements.
What does cooler efficiency mean?
It describes how closely an evaporative cooler approaches the theoretical wet-bulb temperature under its operating conditions.
What CSV format does batch mode accept?
Use temperature in Celsius, relative humidity percent, optional pressure in kilopascals, and optional elevation in metres.
Why do methods produce different values?
They represent different approximations and definitions. Empirical, psychrometer, and thermodynamic methods can differ slightly.
Can I calculate required humidity for a target wet bulb?
Yes. Select target-condition mode, enter dry bulb and target wet bulb, then solve for required relative humidity.
JSON endpoint
The same file exposes a simple read-only JSON endpoint for internal integrations.
?api=1&dry_bulb=30&relative_humidity=50&pressure=101.325&temperature_unit=cRate limiting should be added at the web-server or reverse-proxy layer for public deployments.