Evaporation Rate Calculator
The Evaporation Rate Calculator determines water evaporation rates for various applications including swimming pools, ponds, reservoirs, and industrial processes. This tool helps in water management, HVAC design, and process optimization.
Understanding Evaporation
Evaporation is the process by which water changes from liquid to vapor at temperatures below the boiling point. The rate depends on temperature, humidity, air movement, and surface area.
Factors Affecting Evaporation Rate
Primary Factors
- Temperature Difference: Higher water temperature increases evaporation
- Humidity: Lower air humidity increases evaporation rate
- Air Movement: Wind or air circulation removes vapor and increases rate
- Surface Area: Larger surface area provides more evaporation
Secondary Factors
- Atmospheric Pressure: Lower pressure increases evaporation
- Water Quality: Dissolved substances affect evaporation rate
- Surface Conditions: Roughness and contamination effects
- Solar Radiation: Direct heating increases water temperature
Calculation Methods
Dalton's Law Method
Formula: E = A × K × (es - ea)
Where:
- E = Evaporation rate (kg/h)
- A = Surface area (m²)
- K = Mass transfer coefficient
- es = Saturated vapor pressure at water temperature
- ea = Actual vapor pressure of air
Penman Equation
Application: Meteorological and agricultural use
Considers: Solar radiation, wind speed, temperature, humidity
Accuracy: High for outdoor applications
Pool-Specific Methods
ASHRAE Method: E = A × (pw - pa) × (0.1 + 0.046 × V)
Where: V = air velocity over water surface
Units: E in kg/h, pressures in kPa, V in m/s
Applications
Swimming Pools
- HVAC Design: Size dehumidification equipment
- Energy Calculations: Determine heating and cooling loads
- Water Management: Plan water replacement schedules
- Indoor Air Quality: Control humidity levels
Industrial Applications
- Cooling Towers: Calculate water loss and makeup requirements
- Process Tanks: Monitor water levels and concentrations
- Waste Treatment: Design evaporation ponds
- Chemical Processing: Control solution concentrations
Environmental and Agricultural
- Water Resources: Estimate reservoir losses
- Irrigation: Calculate water requirements
- Climate Studies: Assess regional water balance
- Wetland Management: Monitor water levels
Typical Evaporation Rates
| Application | Conditions | Rate (mm/day) | Rate (kg/m²/day) |
|---|---|---|---|
| Indoor Pool | 26°C water, 24°C air, 60% RH | 3-5 | 3-5 |
| Outdoor Pool | Summer conditions | 5-8 | 5-8 |
| Lake/Reservoir | Temperate climate | 2-6 | 2-6 |
| Cooling Tower | Industrial operation | 10-20 | 10-20 |
Control and Reduction Methods
Reducing Evaporation
- Pool Covers: Can reduce evaporation by 90-95%
- Windbreaks: Reduce air movement over water surface
- Lower Water Temperature: Reduce driving force for evaporation
- Increase Humidity: Reduce vapor pressure difference
Managing Evaporation
- Automatic Water Levelers: Maintain constant water levels
- Humidity Control: Manage indoor air conditions
- Ventilation Design: Control air movement patterns
- Energy Recovery: Capture latent heat from evaporation
Energy Considerations
Latent Heat of Vaporization
- Energy Required: 2.45 MJ/kg at 20°C
- Cooling Effect: Evaporation cools remaining water
- HVAC Impact: Adds latent load to air conditioning
- Heat Recovery: Potential for energy recovery systems
Economic Impact
- Water Costs: Replacement water and treatment
- Energy Costs: Heating replacement water
- Chemical Costs: Rebalancing water chemistry
- Equipment Sizing: Larger HVAC systems needed
Measurement and Monitoring
Direct Measurement
- Water Level Monitoring: Track water loss over time
- Flow Meters: Measure makeup water requirements
- Evaporation Pans: Standard meteorological method
- Lysimeters: Precise measurement for research
Calculation Verification
- Mass Balance: Account for all water inputs and outputs
- Energy Balance: Verify with heat transfer calculations
- Comparative Methods: Use multiple calculation approaches
- Calibration: Adjust coefficients based on measurements
Design Considerations
HVAC System Design
- Size dehumidification equipment for peak evaporation
- Consider seasonal variations in evaporation rate
- Design for both sensible and latent loads
- Plan for humidity control strategies
Water Management
- Size water storage and treatment systems
- Plan for peak makeup water demands
- Consider water quality changes due to evaporation
- Design overflow and drainage systems
Note: Evaporation rate calculations provide estimates based on simplified models. Actual rates may vary due to local conditions, water quality, and other factors. For critical applications, verify calculations with measurements and consider safety factors in design.