Pool evaporation is a natural process where water turns into vapor and escapes from your pool surface into the atmosphere. This can lead to a significant loss of water, increased chemical usage, and higher heating costs. Understanding the factors that influence evaporation can help pool owners take measures to minimize it.
Factors Affecting Evaporation:
Surface Area: The larger the surface area of your pool, the more water is exposed to the air, leading to higher evaporation rates.
Temperature: Higher water and air temperatures increase the rate of evaporation. Warm water molecules have more energy and are more likely to become vapor.
Humidity: Lower relative humidity in the air allows more water vapor to be absorbed from the pool surface. When the air is dry, it can hold more moisture.
Wind Speed: Wind blowing across the pool surface removes humid air and replaces it with drier air, accelerating evaporation. Think of it like fanning a fire – it makes it burn hotter and faster.
Water Treatment: While not a direct calculation factor in many simplified models, certain pool treatments can slightly affect evaporation.
Why Calculate Evaporation?
Regularly calculating your pool's evaporation rate can help you:
Monitor Water Loss: Identify if your water loss is within the normal range or if there might be a leak.
Optimize Chemical Use: Predict how quickly chemicals will become diluted or lost, allowing for better management.
Improve Heating Efficiency: Evaporation is a major source of heat loss from a pool. Understanding this can help you decide on heating strategies and pool covers.
Water Conservation: Be mindful of water usage, especially in drought-prone areas.
The Calculation
This calculator uses a common approximation for pool evaporation. A widely cited formula is based on the work of the American Society of Civil Engineers (ASCE) and the National Swimming Pool Foundation (NSPF). While precise calculations can be complex, this calculator provides a good estimate:
Evaporation (gallons) = Surface Area (sq ft) * Evaporation Rate (inches/day) * 0.623 * Number of Days
The Evaporation Rate (inches/day) is estimated using factors like temperature, humidity, and wind speed. A simplified estimation often used is:
This calculator implements a variation of this approach to provide an estimated volume of water lost in gallons over a specified period.
function calculateEvaporation() {
var poolSurfaceArea = parseFloat(document.getElementById("poolSurfaceArea").value);
var averageDailyTemperature = parseFloat(document.getElementById("averageDailyTemperature").value);
var averageRelativeHumidity = parseFloat(document.getElementById("averageRelativeHumidity").value);
var averageWindSpeed = parseFloat(document.getElementById("averageWindSpeed").value);
var dayCount = parseFloat(document.getElementById("dayCount").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
if (isNaN(poolSurfaceArea) || isNaN(averageDailyTemperature) || isNaN(averageRelativeHumidity) || isNaN(averageWindSpeed) || isNaN(dayCount)) {
resultDiv.innerHTML = "Please enter valid numbers for all fields.";
return;
}
if (poolSurfaceArea <= 0 || averageDailyTemperature < 0 || averageRelativeHumidity 100 || averageWindSpeed < 0 || dayCount <= 0) {
resultDiv.innerHTML = "Please enter realistic values. Temperature and wind speed cannot be negative. Humidity must be between 0 and 100%. Surface area and day count must be positive.";
return;
}
// Simplified Evaporation Rate calculation (inches per day)
// This is a common approximation. Real-world models can be more complex.
var tempFactor = (averageDailyTemperature – 32) * 0.008;
var windFactor = averageWindSpeed * 0.003;
var humidityFactor = (1 – (averageRelativeHumidity / 100)); // Convert % to decimal
// A baseline factor for evaporation (can be adjusted based on specific models)
// A common base evaporation rate for still air and 70F without humidity considered might be around 0.15-0.2 inches/day
// We'll adjust the formula slightly to incorporate a general rate and then modify by temp, wind, humidity
var baseEvaporationRate = 0.15; // Inches per day as a baseline
var estimatedEvaporationRateInchesPerDay = (baseEvaporationRate + tempFactor + windFactor) * humidityFactor;
// Ensure rate doesn't become negative due to very high humidity
if (estimatedEvaporationRateInchesPerDay < 0) {
estimatedEvaporationRateInchesPerDay = 0;
}
// Convert inches per day to gallons per day for the pool surface area
// 1 inch of water over 1 sq ft is approximately 0.623 gallons
var gallonsPerSqFtPerInch = 0.623;
var dailyEvaporationGallons = poolSurfaceArea * estimatedEvaporationRateInchesPerDay * gallonsPerSqFtPerInch;
// Calculate total evaporation over the specified number of days
var totalEvaporationGallons = dailyEvaporationGallons * dayCount;
resultDiv.innerHTML = "Estimated Total Evaporation: " + totalEvaporationGallons.toFixed(2) + " gallons over " + dayCount + " days.";
}