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What Causes Condensate Carryover on Cooling Coils?

Condensate carryover happens when dehumidification takes place on chilled water or DX coils. Typically drain pans are placed under air cooling coils to take care of any water that is generated when cooling air below its dew point. But there are situations when water is carried past the drain pan, which can be an issue when you have it running down duct work. The amount and distance of water carryover is influenced by the following:

  • Sometimes localized or general air velocity across a coil exceeds 500 ft./minute. This is usually the result of bad design and will almost always cause a problem.
  • Outside air usually carries a lot more moisture than re-circulated air. Some areas, like the Gulf states, need larger and wider drain pans just to handle normal conditions. However, that can be the case even during high humidity months in Minnesota as well.
  • Multiple coils in a bank stacked 3 or 4 high. These systems often require intermediate drain pans under each coil since carryover at the top of the bank would travel a long distance.
  • New coils have less air resistance than older, dirty coils so face velocity is higher and this can increase the possibility for carryover. When installing new coils one sometimes has to you rebalance fan drives to maintain proper air velocities.

The most important design attribute for preventing condensate carryover is ensuring that air velocities don’t exceed 500 feet/minute across the face area of any cooling coil.

If you want more tips on coils, steam system maintenance, or how to maximize energy efficiency, contact the team at Campbell-Sevey.

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