Example Data Table
| Airflow |
Entering Air |
Leaving Air |
Pressure |
Expected Result |
| 1200 CFM |
27 °C, 60% RH |
13 °C, 95% RH |
101.325 kPa |
About 5.8 L/hr |
| 2500 CFM |
30 °C, 65% RH |
12 °C, 95% RH |
101.325 kPa |
Higher condensate rate |
| 800 CFM |
24 °C, 50% RH |
14 °C, 90% RH |
95 kPa |
Lower condensate rate |
Formula Used
The calculator estimates condensate from humidity ratio reduction across the coil.
W = 0.62198 × Pv / (P - Pv)
Pv = RH × Pws / 100
v = 0.287042 × T × (1 + 1.607858W) / P
ṁda = airflow / v
Condensate = ṁda × (Wentering - Wleaving) × drain efficiency
Optional latent load uses this relation:
Condensate kg/s = latent kW / 2450
The final design rate adds the selected safety factor.
How to Use This Calculator
Enter the cooling coil airflow first. Select the correct airflow unit.
Enter the entering dry bulb temperature and relative humidity.
Enter the leaving dry bulb temperature and relative humidity.
Use local barometric pressure when altitude is important.
Add runtime to estimate total collected condensate.
Set drain efficiency for pan loss or carryover allowance.
Add a safety factor for drain sizing and field variation.
Press Calculate. The result appears above the form.
Use CSV or PDF buttons to save the report.
Cooling Coil Condensate Calculation Guide
Why Condensate Forms
A cooling coil removes sensible heat from air.
It also removes moisture when the coil surface is cold.
Condensate appears when moist air is cooled below dew point.
The water vapor changes into liquid water.
This water must drain safely from the equipment.
What the Calculator Measures
This tool compares entering and leaving air conditions.
It uses dry bulb temperature, relative humidity, and pressure.
These values define the humidity ratio of the air.
The humidity ratio means water vapor per dry air mass.
The difference across the coil gives removed moisture.
Airflow and Pressure Matter
Airflow controls how much dry air crosses the coil.
More airflow can carry more moisture.
Pressure also affects humidity calculations.
High altitude lowers air pressure.
That changes specific volume and dry air flow.
Use local pressure for better results.
Drain Sizing Use
The hourly condensate rate helps size pans and drains.
The daily value helps estimate disposal volume.
The monthly value helps compare seasonal water production.
A safety factor is useful in humid climates.
It also helps when coil data is uncertain.
Advanced Options
Drain efficiency adjusts the collected water amount.
Coil bypass factor accounts for air not fully treated.
Optional latent load gives a second calculation path.
The calculator uses the larger moisture estimate.
This supports design checks and service review.
Practical Notes
Results depend on accurate field readings.
Measure temperatures after stable operation begins.
Place sensors away from direct water spray.
Use calibrated humidity instruments when possible.
Check blocked drains, dirty filters, and low airflow.
These problems can change the real condensate rate.
The result is an engineering estimate.
Final system design should follow local codes.
FAQs
What is cooling coil condensate?
It is liquid water formed when moist air passes over a cold coil. The coil cools air below dew point, so water vapor condenses on the surface.
Which input affects condensate most?
Entering humidity is very important. Airflow and leaving coil temperature also matter. High airflow with humid entering air usually creates more condensate.
Why do I need barometric pressure?
Pressure changes the humidity ratio and dry air volume. Sea level pressure works for many estimates, but local pressure improves accuracy at higher elevations.
What does coil bypass factor mean?
It estimates the portion of air that leaves without full contact with the cold coil surface. A higher bypass factor reduces predicted moisture removal.
Can this calculator size a drain line?
It helps estimate design flow. Use the design drain rate with plumbing rules, slope, trap needs, and local code before selecting a final drain size.
Why is my result zero?
The leaving air may not be drier than entering air. Check humidity values, temperature units, pressure, and sensor readings. The coil may be above dew point.
What is latent load?
Latent load is the cooling energy used to remove moisture. If known, it can estimate condensate from energy instead of psychrometric air conditions.
Are gallons and liters exact?
They are based on calculated mass and selected water density. Normal condensate is close to one kilogram per liter, so results are usually practical estimates.