Two situations that must be managed in low air temperature applications are cold downdrafts and condensation.

For cold downdrafts:
  • Use parallel fan-powered VAV boxes on the perimeter.
  • Use cooling-only DDC/VAV boxes on the interior.
  • Use linear slot diffusers with aspirating characteristics on both the interior and perimeter VAV boxes.
For condensation:
  • Cold surfaces must be kept inside the humidity-controlled envelope. Air-condition the equipment room and use nonducted returns where codes allow. If ducted returns are required, contact your cooling system representative for a recommendation on insulation thickness.
  • Control the system’s night setback and morning pulldown with the interior dewpoint sensor. Don’t pull the system down all at once; instead, pull it down in stages, following a planned process that is controlled with input from the sensor.
  • A positive plant pressure is critical for “no” condensation. Make sure your plant’s automation system has the ability to maintain a slightly positive pressure.
  • Design the “P” traps and pitch the condensate drains correctly. These systems will produce a good deal of condensation and must be designed and pitched correctly on all systems, but especially for draw-through fan applications.
  • Install a vapor barrier with reasonable construction. This is a basic item that is important to check.
By adhering to these basic principles, millions of square feet of refrigerated space in humid climates such as Florida are cooled successfully using low air temperature applications.

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