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DN-Series Integrated Programmable Controls
DOAS
68
SPECIAL FEATURES
The frost control function is locked out if the OA temperature is above 5°F (adjustable). This
is due to the fact that the core will typically not frost above 5°F if the RA humidity is not high
enough to result in a saturated condition in the EA airstream. If they are exhausting restrooms
with showers they may need to increase this value; if the RA is very dry they could decrease
this value. Frost control actually is not enabled until the OA falls below the OA minus the
hysteresis (1.1°F in this example) and is disabled when the OA temperature increases to 5°F.
If the OA is below 5°F the controller monitors the average EA temperature entering the exhaust
fan. If the RA is very warm the EA will be warm even at colder OA temperatures and frost
control is not required. The core has a “cold corner” in the exhaust (at the top in the DN as that
RA experiences unconditioned OA over the entire core length) that could freeze before the rest
of the exhaust portion of the core, thus the 35°F (adjustable) instead of 32°F for the default
value. If the average exhaust temperature falls below 35°F a PI loop drives the modulating face/
bypass damper to let a portion of the OA go around the core. Bypassing a portion of the OA will
increase the EA temperature and the damper modulates to hold the EA at 35°F.
In some cases the application may require that only one fan run. The single fan mode is initiated
by either closing the ID2 contact (terminals and 19) or a BMS command to BMSEFOnly variable.
It is BV11 for BACnet and Coil 1 for Modbus, where 0 = No and 1 = Yes. The default is Exhaust
Fan but it can be changed to Supply Fan here. If tracking the supply fan, also set a value for
exhaust fan in single fan mode.
8.2 SINGLE FAN MODE
The status can be viewed on this screen.
