Psychrometric Calculator
The Psychrometric Calculator determines all air properties from any two known parameters. This comprehensive tool is essential for HVAC design, air conditioning analysis, and building environmental control systems.
Understanding Psychrometrics
Psychrometrics is the study of the thermodynamic properties of moist air. It deals with the relationships between temperature, humidity, pressure, and energy content of air-water vapor mixtures.
Key Psychrometric Properties
Temperature Parameters
- Dry Bulb Temperature (DB): Actual air temperature measured by standard thermometer
- Wet Bulb Temperature (WB): Temperature of adiabatic saturation
- Dew Point Temperature (DP): Temperature at which condensation begins
Humidity Parameters
- Relative Humidity (RH): Ratio of actual to saturated vapor pressure (%)
- Humidity Ratio (W): Mass of water vapor per unit mass of dry air (kg/kg)
- Specific Humidity: Mass of water vapor per unit mass of moist air (kg/kg)
Energy Parameters
- Enthalpy (h): Total heat content of moist air (kJ/kg)
- Sensible Heat: Heat affecting temperature change
- Latent Heat: Heat of vaporization/condensation
Volume Parameters
- Specific Volume: Volume per unit mass of dry air (m³/kg)
- Density: Mass per unit volume (kg/m³)
Psychrometric Processes
Sensible Heating/Cooling
Temperature change with constant humidity ratio (horizontal line on psychrometric chart)
Humidification
Adding moisture at constant dry bulb temperature (vertical line)
Dehumidification
Removing moisture, often with cooling below dew point
Evaporative Cooling
Cooling with moisture addition at constant wet bulb temperature
Mixing
Combining two air streams with different properties
HVAC Applications
System Design
- Load Calculations: Determine sensible and latent cooling loads
- Equipment Sizing: Size air conditioning and dehumidification equipment
- Duct Design: Calculate air flow rates and properties
- Energy Analysis: Optimize system efficiency
Process Analysis
- Cooling Coil Performance: Analyze coil leaving conditions
- Mixing Box Calculations: Determine mixed air properties
- Economizer Analysis: Optimize outdoor air usage
- Heat Recovery: Calculate energy recovery potential
Industrial Applications
Manufacturing Processes
- Textile Industry: Control humidity for fiber processing
- Paper Production: Maintain moisture content
- Food Processing: Control drying and storage conditions
- Pharmaceutical: Maintain sterile environments
Environmental Control
- Museums: Preserve artifacts and artwork
- Data Centers: Maintain equipment operating conditions
- Laboratories: Control experimental conditions
- Cleanrooms: Maintain contamination control
Calculation Methods
Fundamental Equations
Humidity Ratio: W = 0.622 × (Pv / (P - Pv))
Enthalpy: h = 1.006 × T + W × (2501 + 1.86 × T)
Specific Volume: v = 0.287 × (T + 273.15) × (1 + 1.608 × W) / P
Relative Humidity: RH = (Pv / Pvs) × 100
Psychrometric Chart
The psychrometric chart is a graphical representation of air properties:
- X-axis: Dry bulb temperature
- Y-axis: Humidity ratio
- Curved lines: Relative humidity
- Diagonal lines: Wet bulb temperature and enthalpy
- Nearly vertical lines: Specific volume
Comfort Applications
Human Comfort Zone
- Temperature: 20-26°C (68-79°F)
- Relative Humidity: 30-60%
- Air Velocity: 0.1-0.2 m/s
- Clothing Insulation: 0.5-1.0 clo
Comfort Indices
- Effective Temperature: Combined effect of temperature and humidity
- Heat Index: Apparent temperature considering humidity
- PMV/PPD: Predicted Mean Vote and Percentage Dissatisfied
Energy Considerations
Cooling Load Components
- Sensible Load: Heat affecting temperature (kW)
- Latent Load: Heat from moisture removal (kW)
- Total Load: Sum of sensible and latent loads
- SHR: Sensible Heat Ratio = Sensible / Total
System Efficiency
- COP: Coefficient of Performance
- EER: Energy Efficiency Ratio
- SEER: Seasonal Energy Efficiency Ratio
- Part Load Performance: Efficiency at reduced loads
Measurement and Instrumentation
Temperature Measurement
- Thermocouples: Wide range, fast response
- RTDs: High accuracy, stable
- Thermistors: High sensitivity, limited range
Humidity Measurement
- Capacitive Sensors: Fast response, wide range
- Resistive Sensors: Low cost, moderate accuracy
- Psychrometers: Reference standard method
Note: Psychrometric calculations assume standard atmospheric pressure unless otherwise specified. For high altitude applications, pressure corrections are essential for accuracy.