Understanding Your Pool's Evaporation Rate
Water evaporation is a natural process that contributes to a significant loss of water from your swimming pool. Several factors influence this rate, and understanding them can help you manage your pool's water levels more effectively, reduce chemical costs, and conserve water. The primary drivers of evaporation are:
- Water Temperature: Warmer water evaporates faster than cooler water.
- Air Temperature: Higher air temperatures increase the rate of evaporation.
- Humidity: Lower humidity in the surrounding air allows for more water to evaporate.
- Wind Speed: Wind blowing across the surface of the pool carries away moist air, replacing it with drier air, thus increasing evaporation.
- Surface Area: A larger water surface exposed to the air will naturally lose more water to evaporation.
- Pool Cover Usage: Using a pool cover significantly reduces evaporation by creating a barrier between the water and the air.
This calculator helps you estimate your pool's daily water loss due to evaporation. By inputting key environmental conditions and your pool's characteristics, you can gain a better understanding of how much water you might be losing and explore ways to mitigate it.
Estimated Daily Evaporation Loss:
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var calculateEvaporation = function() {
var surfaceArea = parseFloat(document.getElementById("poolSurfaceArea").value);
var waterTemp = parseFloat(document.getElementById("waterTemp").value);
var airTemp = parseFloat(document.getElementById("airTemp").value);
var humidity = parseFloat(document.getElementById("humidity").value);
var windSpeed = parseFloat(document.getElementById("windSpeed").value);
var isCovered = parseFloat(document.getElementById("isCovered").value);
var resultDiv = document.getElementById("result");
if (isNaN(surfaceArea) || isNaN(waterTemp) || isNaN(airTemp) || isNaN(humidity) || isNaN(windSpeed) || isNaN(isCovered)) {
resultDiv.innerHTML = "Please enter valid numbers for all fields.";
return;
}
if (humidity 100) {
resultDiv.innerHTML = "Humidity must be between 0 and 100.";
return;
}
if (isCovered !== 0 && isCovered !== 1) {
resultDiv.innerHTML = "For 'Is Pool Covered?', please enter 0 for No or 1 for Yes.";
return;
}
// Simplified evaporation calculation (empirical formula approximation)
// This is a simplified model for demonstration. Real-world calculations can be more complex.
// Formula based on general principles, not a single scientific standard.
// Evaporation rate (in inches per day) = (0.25 + 0.03*windSpeed + 0.001*surfaceArea^0.5) * (0.44 + 0.016*waterTemp – 0.0005*humidity^2)
var baseRate = 0.25 + (0.03 * windSpeed); // Base rate influenced by wind
var tempHumidityFactor = (0.44 + (0.016 * waterTemp) – (0.0005 * Math.pow(humidity, 2)));
// A very rough adjustment for surface area – a more complex formula would be needed for accuracy
// For simplicity, we'll use it more as a modifier on the overall rate rather than a primary driver here.
// In many simplified models, surface area is a direct multiplier after other factors are determined.
// Let's use a slightly different approach for better conceptual clarity:
// Evaporation (gallons/day) ≈ Surface Area (sq ft) * Evaporation Rate (inches/day) * 7.48 (gal/cu ft) / 12 (inches/ft) * Daily Hours
// Let's try a more common simplified approach based on Vapor Pressure Deficit (VPD) and wind.
// Evaporation rate is proportional to (Saturation Vapor Pressure at Water Temp – Actual Vapor Pressure at Air Temp) and Wind Speed.
// A very common simplified formula often cited for pools is:
// Daily Loss (gallons) = Surface Area (sq ft) * (Temp Diff + Wind Factor) * [Some Empirical Constant]
// Or, a simpler empirical method focusing on key variables:
var tempDiff = waterTemp – airTemp;
var windEffect = windSpeed * 0.2; // Rough multiplier for wind effect
// A simplified empirical formula often found:
// Evaporation inches/day = (Temp_Diff_Factor + Wind_Factor) * (Surface_Area_Factor) * (Humidity_Factor)
// These factors are highly simplified. A common approximation uses a coefficient based on the difference in vapor pressure.
// Let's use a widely cited simplified formula structure:
// Evaporation in inches per day = K * (Pw – Pa) * (1 + 0.03 * windSpeed)
// Where Pw is saturated vapor pressure at water temp, Pa is actual vapor pressure at air temp.
// This is complex to implement without a vapor pressure table or function.
// For a *practical calculator* that's understandable and demonstrates the concept, let's use a generalized empirical formula that combines factors:
// Daily Evaporation (inches) ≈ (C1 * (waterTemp – airTemp) + C2 * windSpeed) * (1 – humidity/100) * (surfaceArea_factor)
// Let's assume a base evaporation rate and modify it.
// A commonly used simplified pool evaporation formula structure:
// Evaporation (gallons/day) = 0.00023 * Area (sq ft) * (Vpd) * (1 + Wind_Factor)
// Vpd (Vapor Pressure Deficit) is roughly (Saturation VP at Air Temp – Actual VP at Air Temp).
// Saturation VP is a function of temperature.
// Given the constraints and need for a simple, functional calculator without external libraries for vapor pressure,
// we'll use a blend of common empirical influences.
// Simplified empirical approach:
var effectiveTempDiff = waterTemp – airTemp;
if (effectiveTempDiff < 0) effectiveTempDiff = 0; // Water temp shouldn't be colder than air temp for *increased* evaporation
var vaporPressureDeficitEstimate = effectiveTempDiff * 0.5 + windSpeed * 0.5; // Very rough VpD estimate
var baseEvaporationRateInchesPerDay = 0.03; // A typical daily base rate without other factors
var evaporationInchesPerDay = baseEvaporationRateInDay * (1 + (vaporPressureDeficitEstimate / 10)) * (1 + 0.03 * windSpeed);
// Let's try a different widely cited simplified formula that directly uses temperature and wind:
// A common simplification for pool evaporation:
// Evaporation in inches/day = (0.4 + 0.03 * Wind Speed) * (Water Temp – Air Temp) * 0.7
// This formula is often used but lacks direct humidity input.
// Let's try to incorporate humidity more directly using a common approach:
// Evaporation (inches/day) ≈ (A * windSpeed + B) * (C * waterTemp – D * airTemp – E) * (1 – humidity/100)
// Where A, B, C, D, E are empirical coefficients.
// Using a more robust simplified model that directly accounts for key factors and their interactions:
var windFactor = 1 + (windSpeed * 0.05); // Wind increases evaporation
var tempFactor = (waterTemp – airTemp) * 0.05; // Temperature difference drives evaporation
if (tempFactor < 0) tempFactor = 0; // Only positive temp diff drives evaporation
var humidityFactor = (1 – (humidity / 100)) * 0.8; // Lower humidity increases evaporation, scaled down
// A common simplified formula structure:
// Evaporation (inches/day) = (0.25 + 0.03 * windSpeed) * (1.07 * (waterTemp – airTemp) + 2.5) * (1 – humidity/100)
// Let's use this as it's reasonably comprehensive for a simplified model.
var factor1 = 0.25 + (0.03 * windSpeed);
var factor2 = (1.07 * (waterTemp – airTemp) + 2.5);
if (factor2 < 0) factor2 = 0; // Ensure temp difference doesn't lead to negative evaporation
var factor3 = (1 – (humidity / 100));
var dailyEvaporationInInches = factor1 * factor2 * factor3;
// Apply cover reduction
var coverReduction = 1.0; // No reduction if not covered
if (isCovered === 1) {
coverReduction = 0.25; // Assume a cover reduces evaporation by 75% (leaves 25%)
}
dailyEvaporationInInches *= coverReduction;
// Convert inches to gallons
var gallonsPerInchPerSqFt = 0.623; // Approximately 7.48 gallons/cubic foot / 12 inches/foot
var dailyEvaporationInGallons = surfaceArea * dailyEvaporationInInches * gallonsPerInchPerSqFt;
if (dailyEvaporationInGallons < 0) dailyEvaporationInGallons = 0; // Ensure non-negative result
resultDiv.innerHTML = dailyEvaporationInGallons.toFixed(2) + " gallons per day";
};