Humidity Change With Temperature Calculator Formula

Humidity Change With Temperature Formula:

\[ \text{New RH} = \text{Old RH} \times \frac{\text{Psat\_old}}{\text{Psat\_new}} \]

Old Relative Humidity (RH):

Saturation Pressure at Old Temperature (Psat_old):

Saturation Pressure at New Temperature (Psat_new):

New Relative Humidity (RH):

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1. What is the Humidity Change With Temperature Formula?

The Humidity Change With Temperature formula calculates how relative humidity changes when air temperature changes while keeping the absolute moisture content constant. It's based on the relationship between temperature and saturation vapor pressure.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ \text{New RH} = \text{Old RH} \times \frac{\text{Psat\_old}}{\text{Psat\_new}} \]

Where:

\( \text{Old RH} \) — Original relative humidity (%)
\( \text{Psat\_old} \) — Saturation vapor pressure at original temperature (Pa)
\( \text{Psat\_new} \) — Saturation vapor pressure at new temperature (Pa)
\( \text{New RH} \) — Calculated relative humidity at new temperature (%)

Explanation: The formula shows that relative humidity decreases when temperature increases (if moisture content remains constant), and increases when temperature decreases.

3. Importance of Humidity Calculation

Details: Understanding how humidity changes with temperature is crucial for HVAC system design, weather forecasting, industrial processes, and maintaining comfortable indoor environments.

4. Using the Calculator

Tips: Enter the original relative humidity percentage, and the saturation vapor pressures at both the original and new temperatures. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why does relative humidity change with temperature?
A: Warmer air can hold more moisture, so when temperature increases without adding moisture, the relative humidity decreases.

Q2: How do I find saturation vapor pressure values?
A: Saturation vapor pressure can be calculated using various formulas (like Magnus formula) or found in thermodynamic tables for specific temperatures.

Q3: Does this formula account for pressure changes?
A: This formula assumes constant atmospheric pressure. For significant pressure changes, additional corrections may be needed.

Q4: What's the typical range for saturation vapor pressure?
A: At room temperature (20°C), it's about 2330 Pa; at 0°C it's about 611 Pa; and at 40°C it's about 7380 Pa.

Q5: Can relative humidity exceed 100%?
A: While the formula can mathematically produce values above 100%, in reality, relative humidity cannot exceed 100% as condensation would occur.