Dry Bulb Wet Bulb Calculator

Relative Humidity Formula:

\[ RH = \frac{e_w - 0.00066 \times P \times (T_d - T_w)}{e_d} \times 100 \]

Saturation Vapor Pressure at Wet Bulb (e_w):

Atmospheric Pressure (P):

mbar

Dry Bulb Temperature (T_d):

°C

Wet Bulb Temperature (T_w):

°C

Saturation Vapor Pressure at Dry Bulb (e_d):

Relative Humidity (RH):

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1. What is the Dry Bulb Wet Bulb Method?

The dry bulb wet bulb method is a psychrometric technique for determining relative humidity by measuring the difference between dry air temperature (dry bulb) and the temperature cooled by evaporation (wet bulb). This method is widely used in meteorology, HVAC, and industrial applications.

2. How Does the Calculator Work?

The calculator uses the following psychrometric formula:

\[ RH = \frac{e_w - 0.00066 \times P \times (T_d - T_w)}{e_d} \times 100 \]

Where:

\( RH \) — Relative Humidity (%)
\( e_w \) — Saturation vapor pressure at wet bulb temperature (Pa)
\( P \) — Atmospheric pressure (mbar)
\( T_d \) — Dry bulb temperature (°C)
\( T_w \) — Wet bulb temperature (°C)
\( e_d \) — Saturation vapor pressure at dry bulb temperature (Pa)

Explanation: The formula accounts for the cooling effect of evaporation on the wet bulb thermometer and the relationship between temperature and saturation vapor pressure.

3. Importance of Relative Humidity Calculation

Details: Accurate relative humidity measurement is crucial for weather forecasting, indoor climate control, industrial processes, and preserving materials sensitive to moisture.

4. Using the Calculator

Tips: Enter all required parameters in the specified units. Ensure wet bulb temperature is always less than or equal to dry bulb temperature. For accurate results, use precise measurements from calibrated instruments.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between dry bulb and wet bulb temperature?
A: Dry bulb measures ambient air temperature, while wet bulb measures the lowest temperature achievable by evaporative cooling.

Q2: How does atmospheric pressure affect the calculation?
A: Higher pressure reduces the evaporation rate, affecting the wet bulb depression (T_d - T_w) for a given humidity.

Q3: What are typical RH values in different environments?
A: Comfortable indoor RH is 30-60%. Below 30% feels dry, above 60% feels humid and promotes mold growth.

Q4: How accurate is this method?
A: With precise temperature measurements (±0.1°C) and proper wet bulb conditions, accuracy of ±2% RH is achievable.

Q5: Can I use this for very high temperatures?
A: The formula works best below 60°C. At higher temperatures, more complex psychrometric relationships apply.