Psychrometric Chart
The psychrometric chart is an interactive tool for visualizing and analyzing air conditions in HVAC systems.
Understanding the Chart
Section titled “Understanding the Chart”Axes and Lines
Section titled “Axes and Lines”Dry-Bulb Temperature
Section titled “Dry-Bulb Temperature”The horizontal axis shows dry-bulb temperature (°F or °C). This is the temperature measured by a standard thermometer.
Humidity Ratio
Section titled “Humidity Ratio”The vertical axis shows humidity ratio (grains/lb or g/kg). This is the mass of water vapor per mass of dry air.
Relative Humidity Lines
Section titled “Relative Humidity Lines”Curved lines showing constant relative humidity from 10% to 100% (saturation line).
Wet-Bulb Lines
Section titled “Wet-Bulb Lines”Diagonal lines showing constant wet-bulb temperature, used for evaporative cooling analysis.
Enthalpy Lines
Section titled “Enthalpy Lines”Lines of constant enthalpy (BTU/lb or kJ/kg), representing total heat content.
State Points
Section titled “State Points”A state point on the chart represents a specific air condition:
- Dry-bulb temperature
- Wet-bulb temperature
- Humidity ratio
- Relative humidity
- Enthalpy
- Specific volume
Using the Chart
Section titled “Using the Chart”Placing Points
Section titled “Placing Points”Click on the chart to place a state point, or enter values:
- Click Add Point
- Enter known properties (any two will define the state)
- The point appears with all properties calculated
Moving Points
Section titled “Moving Points”Drag points to see how properties change:
- Move horizontally for temperature change
- Move vertically for humidity change
- All properties update in real-time
Connecting Points
Section titled “Connecting Points”Draw process lines between points:
- Select two points
- Click Connect
- The process line shows the path
HVAC Processes
Section titled “HVAC Processes”Sensible Cooling
Section titled “Sensible Cooling”Horizontal line to the left:
- Temperature decreases
- Humidity ratio stays constant
- Common for cooling coils above dew point
Sensible Heating
Section titled “Sensible Heating”Horizontal line to the right:
- Temperature increases
- Humidity ratio stays constant
- Common for heating coils
Cooling with Dehumidification
Section titled “Cooling with Dehumidification”Line toward saturation then left:
- Air cools to dew point
- Moisture condenses
- Continues along saturation line
Humidification
Section titled “Humidification”Line upward (higher humidity ratio):
- Steam injection (isothermal)
- Evaporative (adiabatic)
Mixing
Section titled “Mixing”Straight line between two air streams:
- Mixed condition on the line
- Position based on airflow ratios
Elevation Adjustment
Section titled “Elevation Adjustment”Psychrometric properties vary with altitude:
- Set site elevation
- Chart adjusts automatically
- Sea-level vs. high altitude
Practical Applications
Section titled “Practical Applications”Coil Analysis
Section titled “Coil Analysis”Visualize cooling coil performance:
- Entering air condition
- Leaving air condition
- Sensible Heat Ratio
Economizer
Section titled “Economizer”Analyze mixed air conditions:
- Outdoor air point
- Return air point
- Mixed air result
Dehumidification
Section titled “Dehumidification”Evaluate moisture removal:
- Coil leaving condition
- Reheat requirements
- Latent capacity
Export Options
Section titled “Export Options”Screenshot
Section titled “Screenshot”Capture the chart image:
- Include state points
- Include process lines
- PNG format
Data Export
Section titled “Data Export”Export point data:
- All properties
- CSV format
- For further analysis