Outdoor air flow rate is controlled primarily by the relief and coil path return dampers, and in the event that adequate outdoor air cannot be provided by manipulating these dampers (only in the event that that the relief air damper is fully open and the coil path return damper is fully closed), then the bypass damper can be incrementally closed to force more air out through the relief damper
, causing more air to enter through the outdoor air inlet.
These included resetting supply air temperature based on maximum VAV box damper position to reduce reheat energy; controlling the return fan off of return plenum pressure rather than tracking the supply fan; controlling the relief damper
in response to measured building pressure; and controlling the outdoor air damper based on supply fan speed to ensure design outdoor airflow rates are maintained.
Even when the cleanroom is at positive 20 Pa as the initial condition, the area near the relief damper
is dirtier than the area behind the door because the damper remains open when the door is closed.
If the return fan has direct building pressure control, disable this control so the relief damper
Not only does it increase pressure drop and supply fan energy, it can cause reverse outdoor airflow through the relief damper
when Airflow Tracking control is used.
The relief damper
was modulated according to the relief fan VFD speed.
The relief damper
is controlled to maintain building pressure directly using a pressure sensor located in a representative space inside the building.
Dampers were checked to see how well they closed, and all but one relief damper
were tightly closed.
The loop output is applied to first open the relief dampers
with the low constant plenum pressure set point, 25 Pa (0.1 in.
Another option is to install expensive and architecturally unattractive pressure relief dampers
to the outdoors.