How to Calculate Condensation Rate of Cooling Coil

Cooling Coil Condensation Rate Calculator

Moisture content of air entering the coil.

Moisture content of air leaving the coil (after cooling).

Calculation Results:

function calculateCondensate() { var cfm = parseFloat(document.getElementById('airFlowCfm').value); var w1 = parseFloat(document.getElementById('inletHumidity').value); var w2 = parseFloat(document.getElementById('outletHumidity').value); var resultDiv = document.getElementById('condensationResult'); if (isNaN(cfm) || isNaN(w1) || isNaN(w2)) { alert("Please enter valid numeric values for all fields."); return; } if (w2 >= w1) { alert("Outlet humidity must be lower than inlet humidity for condensation to occur."); return; } // Formula: Condensate (lb/hr) = CFM * 4.5 * (w1 – w2) / 7000 // 4.5 is standard air density factor (0.075 lb/ft3 * 60 min/hr) // 7000 is the conversion factor from grains to pounds var moistureDiff = w1 – w2; var lbHr = (cfm * 4.5 * moistureDiff) / 7000; var gph = lbHr / 8.34; // 1 gallon of water weighs approx 8.34 lbs var lph = gph * 3.78541; // Conversion to liters document.getElementById('lbPerHour').innerHTML = "Moisture Removal: " + lbHr.toFixed(2) + " lbs/hr"; document.getElementById('galPerHour').innerHTML = "Condensation Rate: " + gph.toFixed(2) + " Gallons/hr"; document.getElementById('litersPerHour').innerHTML = "Metric Rate: " + lph.toFixed(2) + " Liters/hr"; resultDiv.style.display = 'block'; }

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Understanding Cooling Coil Condensation

In HVAC systems, the condensation rate of a cooling coil refers to the amount of water vapor that transitions from a gaseous state to a liquid state as air passes through the refrigerated fins. This process occurs when the surface temperature of the cooling coil is below the dew point of the entering air.

The Importance of Calculating Condensate

Accurately determining the condensation rate is vital for several engineering and maintenance reasons:

• Drainage Design: Ensuring condensate drain pans and piping are sized correctly to prevent overflow and water damage.
• Humidity Control: Measuring the latent cooling capacity of the system to ensure comfort and prevent mold growth.
• Pump Selection: If the unit requires a condensate pump, you must know the flow rate to select an appropriately sized model.

The Physics Behind the Calculation

The calculation relies on psychrometrics—the study of gas-vapor mixtures. The primary factors involved are:

1. Airflow (CFM): The volume of air moving across the coil per minute.
2. Specific Humidity (Grains/lb): The actual weight of water vapor in the air. 7,000 grains equal 1 pound of water.
3. Air Density: Standard air density is typically assumed to be 0.075 lb/ft³ for most HVAC calculations.

Example Calculation

If you have an AHU (Air Handling Unit) moving 2,000 CFM of air. The air enters the coil at 110 grains/lb and leaves at 60 grains/lb:

Rate (lb/hr) = [2,000 × 4.5 × (110 – 60)] / 7,000
Rate (lb/hr) = [2,000 × 4.5 × 50] / 7,000
Rate (lb/hr) = 450,000 / 7,000 = 64.28 lbs/hr
Rate (GPH) = 64.28 / 8.34 = 7.7 Gallons Per Hour

Frequently Asked Questions

What is a typical "Grain"?

A grain is a unit of mass. In HVAC, we use grains of moisture per pound of dry air to describe absolute humidity levels without temperature interference.

Why did I get zero condensation?

If the outlet humidity is the same as the inlet, no moisture was removed. This happens if the coil temperature is higher than the air's dew point (sensible cooling only).