Calculate Specific Humidity From Relative

Specific Humidity Formula:

\[ SH = 0.622 \times \frac{RH \times P_{sat}}{P - RH \times P_{sat}} \]

Specific Humidity (SH):

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1. What is Specific Humidity?

Specific Humidity (SH) is the ratio of the mass of water vapor to the total mass of the air parcel. It's a fundamental parameter in meteorology and HVAC calculations, representing the actual amount of moisture present in the air.

2. How Does the Calculator Work?

The calculator uses the specific humidity formula:

\[ SH = 0.622 \times \frac{RH \times P_{sat}}{P - RH \times P_{sat}} \]

Where:

\( SH \) — Specific Humidity (kg water/kg air)
\( RH \) — Relative Humidity (%)
\( P_{sat} \) — Saturation Pressure (Pa)
\( P \) — Total Pressure (Pa)
0.622 — Ratio of molecular weights of water vapor and dry air

Explanation: The formula calculates the mass of water vapor per unit mass of moist air, considering the current humidity conditions and atmospheric pressure.

3. Importance of Specific Humidity Calculation

Details: Specific humidity is crucial for weather forecasting, climate studies, and designing HVAC systems. It helps determine the actual moisture content in air, which affects human comfort, agricultural processes, and industrial applications.

4. Using the Calculator

Tips: Enter relative humidity as a percentage (0-100%), saturation pressure in Pascals (Pa), and total pressure in Pascals (Pa). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between specific humidity and relative humidity?
A: Relative humidity is the ratio of current moisture to maximum possible moisture at a given temperature, while specific humidity is the actual mass of water vapor per mass of air.

Q2: What are typical specific humidity values?
A: Values range from near 0 in dry deserts to about 0.02-0.03 kg/kg in very humid tropical regions.

Q3: How does pressure affect specific humidity?
A: Specific humidity decreases with increasing pressure if the moisture content remains constant, as the formula denominator increases.

Q4: Why is the constant 0.622 used?
A: This represents the ratio of the molecular weight of water vapor (18.015 g/mol) to the effective molecular weight of dry air (28.964 g/mol).

Q5: Can specific humidity exceed 100%?
A: No, specific humidity is an absolute measure of moisture content and doesn't have a percentage scale like relative humidity.