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.
- 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
- 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
- Install a vapor barrier with reasonable construction. This is a basic item that is important to check.