1. What is Humidity Ratio?

The humidity ratio (also called mixing ratio) is the mass of water vapor per unit mass of dry air. It's a fundamental parameter in psychrometric analysis and HVAC calculations.

2. How Does the Calculator Work?

The calculator uses the humidity ratio formula:

Where:

• \( W \) — Humidity ratio (kg/kg of dry air)
• \( P_w \) — Partial pressure of water vapor (kPa)
• \( P \) — Total pressure of the air-vapor mixture (kPa)
• 0.62198 — Ratio of molecular weights of water and dry air

Explanation: The equation relates the mass of water vapor to the mass of dry air in a given air sample.

3. Importance of Humidity Ratio

Details: Humidity ratio is crucial for designing HVAC systems, calculating cooling loads, and understanding psychrometric processes like heating, cooling, humidification, and dehumidification.

4. Using the Calculator

Tips: Enter partial pressure of water vapor and total pressure in kPa. Both values must be positive and P must be greater than P_w.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between humidity ratio and relative humidity?
A: Humidity ratio measures absolute moisture content, while relative humidity measures how close the air is to saturation at its current temperature.

Q2: What are typical humidity ratio values?
A: Typical values range from 0.005 to 0.030 kg/kg in most comfort applications, but can be higher in tropical climates.

Q3: How is partial pressure of water vapor determined?
A: It can be measured directly with specialized instruments or calculated from other psychrometric properties like dew point temperature.

Q4: Does humidity ratio change with temperature?
A: Not directly - it's a mass ratio. However, the maximum possible humidity ratio increases with temperature.

Q5: Why is 0.62198 used in the formula?
A: It's the ratio of the molecular weight of water (18.01528 g/mol) to dry air (28.9645 g/mol).