Performance
Condensate flow from a cooling coil
- where
- condensate flow (kg/h)
- latent cooling load (kW)
- latent heat of vaporisation of water (kJ/kg)
Explain this equation
Estimates how much water a cooling coil produces from its latent load. Use it for sizing condensate drains and pumps.
Q_L is the part of the coil duty spent condensing moisture out of the air, in kW, which is kJ per second. Each kilogram of water condensed gives up h_fg. Dividing gives kilograms per second, and 3600 converts to per hour. One kilogram of water is about one litre.
An energy balance: latent heat removed equals water condensed times its latent heat.
Sense check: 3 kW of latent load produces about 4.4 litres an hour, roughly 105 litres in 24 hours of running.
Watch out: latent load varies hugely with the weather and room use, so size pumps for the peak, not the average.
Estimates how much water a cooling coil produces from its latent load, for sizing condensate drains and pumps.
Enter your values to see the result.
Good to know
hfg is 2489 kJ/kg at 5 °C, 2477 kJ/kg at 10 °C and 2454 kJ/kg at 20 °C (NIST); the default 2477 suits a typical coil surface temperature of about 10 °C. One kg of water is about one litre. Get the latent load from the load calculation or the unit’s sensible/total capacity split.
Common mistake
Using the total cooling load instead of the latent part, which overstates the water by two to four times.
Limits
Steady-state; ignores re-evaporation and start-up. Size pumps with a margin as the manufacturer advises.
Sources
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow the equipment manufacturer’s data, CIBSE guidance, BS EN 378, the F-gas Regulations and your company procedures. Refrigerant work needs the correct F-gas certification.