How to Calculate Evaporation Rate of a Swimming Pool
by
Swimming Pool Evaporation Rate Calculator
.calculator-container {
font-family: sans-serif;
border: 1px solid #ccc;
padding: 20px;
border-radius: 8px;
max-width: 500px;
margin: 20px auto;
background-color: #f9f9f9;
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.calculator-container h2 {
text-align: center;
margin-bottom: 20px;
color: #333;
}
.input-section {
margin-bottom: 20px;
}
.input-section label {
display: block;
margin-bottom: 5px;
font-weight: bold;
color: #555;
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.input-section input[type="number"] {
width: calc(100% – 22px);
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#result {
margin-top: 20px;
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background-color: #e9ecef;
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border-radius: 4px;
text-align: center;
font-size: 18px;
color: #333;
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function calculateEvaporation() {
var poolSurfaceArea = parseFloat(document.getElementById("poolSurfaceArea").value);
var ambientTemperature = parseFloat(document.getElementById("ambientTemperature").value);
var waterTemperature = parseFloat(document.getElementById("waterTemperature").value);
var relativeHumidity = parseFloat(document.getElementById("relativeHumidity").value);
var windSpeed = parseFloat(document.getElementById("windSpeed").value);
var resultElement = document.getElementById("result");
resultElement.innerHTML = ""; // Clear previous result
if (isNaN(poolSurfaceArea) || isNaN(ambientTemperature) || isNaN(waterTemperature) || isNaN(relativeHumidity) || isNaN(windSpeed)) {
resultElement.innerHTML = "Please enter valid numbers for all fields.";
return;
}
if (poolSurfaceArea <= 0 || ambientTemperature 120 || waterTemperature 100 || relativeHumidity 100 || windSpeed < 0) {
resultElement.innerHTML = "Please enter realistic values.";
return;
}
// Simplified empirical formula for evaporation rate (inches per day)
// This is a common approximation, actual rates can vary due to many factors.
// Formula based on: Evaporation = (A * (Pw – Pa)) + (B * V * (Pw – Pa))
// Where:
// Pw is the saturation vapor pressure at the water surface temperature
// Pa is the saturation vapor pressure at the ambient air temperature
// V is the wind speed
// A and B are empirical coefficients.
// A more direct approximation often used is:
// Evaporation (inches/day) = 0.4 to 0.6 * (saturation vapor pressure at water temp – saturation vapor pressure at air temp) * (1 + wind speed factor)
// We'll use a common simplified model that incorporates temperature difference and wind.
// Constants for vapor pressure calculation (approximations for Fahrenheit)
var C1 = 17.27;
var C2 = 35.86; // Used in denominator for Fahrenheit
var C3 = 28.0; // Subtraction term for Fahrenheit
// Calculate saturation vapor pressure at water temperature (e_w)
var e_w = 6.112 * Math.exp((C1 * waterTemperature) / (waterTemperature + C2));
// Calculate saturation vapor pressure at ambient air temperature (e_a)
var e_a = 6.112 * Math.exp((C1 * ambientTemperature) / (ambientTemperature + C2));
// Calculate actual vapor pressure (e_p) using relative humidity
var e_p = (relativeHumidity / 100) * e_a;
// Factor for wind speed (simplified)
// Typical wind speed impact: 5 mph might be a base, higher speeds increase evaporation.
var windFactor = 1 + (windSpeed * 0.05); // Simple linear increase
// Evaporation rate in inches per day
// The factor 0.16 is an empirical coefficient to convert vapor pressure difference and wind into inches/day
var evaporationRateInchesPerDay = 0.16 * (e_w – e_p) * windFactor;
// Ensure the rate is not negative (though physics should prevent this with valid inputs)
if (evaporationRateInchesPerDay < 0) {
evaporationRateInchesPerDay = 0;
}
// Convert to gallons per day for a typical pool size
// 1 inch of water over 1 sq ft = 0.623 gallons
var evaporationGallonsPerDay = evaporationRateInchesPerDay * poolSurfaceArea * 0.623;
resultElement.innerHTML = "Estimated Evaporation Rate: " +
evaporationRateInchesPerDay.toFixed(2) + " inches per day" +
"Estimated Volume Loss: " + evaporationGallonsPerDay.toFixed(2) + " gallons per day";
}
Understanding Swimming Pool Evaporation
Swimming pool evaporation is a natural process where water transitions from a liquid state to a gaseous state and disappears into the atmosphere. This is influenced by several environmental factors. Accurately estimating this evaporation rate can help pool owners manage water loss, chemical levels, and heating costs more effectively.
Factors Affecting Evaporation:
Water Temperature: Warmer water evaporates faster because water molecules have more kinetic energy and are more likely to escape into the air.
Air Temperature: Higher ambient air temperatures can hold more moisture, increasing the rate of evaporation.
Relative Humidity: Low relative humidity means the air is dry and can accept more water vapor, thus increasing evaporation. High humidity has the opposite effect.
Wind Speed: Wind blows away the humid air directly above the water surface, replacing it with drier air and promoting continuous evaporation.
Pool Surface Area: A larger surface area exposed to the air will naturally lose more water through evaporation.
Sunlight/Solar Radiation: While not directly included in this simplified calculator, direct sunlight significantly heats the water and air, indirectly increasing evaporation.
How the Calculator Works:
This calculator uses a simplified empirical formula based on the principles of vapor pressure and wind effects. It estimates the difference in vapor pressure between the water surface and the ambient air. A higher vapor pressure difference, combined with lower humidity and higher wind speed, leads to increased evaporation. The output is given in inches of water depth lost per day and the corresponding volume loss in gallons, assuming a specific pool surface area.
Tips to Reduce Evaporation:
Use a Pool Cover: This is the most effective way to reduce evaporation, by creating a barrier between the water and the air.
Install Windbreaks: Fencing, hedges, or screens around the pool can reduce wind speed.
Maintain Water Temperature: Avoid unnecessarily high water temperatures.
Consider a Pool Enclosure: A permanent structure can significantly reduce losses.