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DN-Series Integrated Programmable Controls
DOAS
UNIT OPERATION
5.1.1.3 Optional Drain Overflow Switch
This is an optional accessory, ordered with the unit and factory-installed. The overflow switch
monitors condensate levels in the condensate pan and if unacceptable levels are detected,
it will cause the fans to switch OFF and the dampers will return to their Normally Closed
positions. When the condensate level drops, the unit will return to normal operation.
FIGURE 5.1.3 OVERFLOW SWITCH
5.1.2 Dampers
Inside the DN DOAS unit, OA and RA airstreams are directed based on operating modes. There
are three modes of operation: energy recovery, economizer/bypass, and recirculation.
In Energy Recovery Mode, OA and RA airflow is through the enthalpic cores. The isolation
dampers are open and both fans are operating. The economizer face damper is open, and
the bypass damper is closed, allowing OA to flow through the enthalpic cores only. Energy is
recovered between the OA and RA airstreams.
Economizer/Bypass Mode, a standard feature, is activated when the OA enthalpy is less
than the RA enthalpy and free cooling is desired. A portion or all of the OA passes through
the bypass compartment. The isolation dampers are open and both fans are operating. The
economizer face damper and bypass damper modulate to meter OA flow through the enthalpic
cores and bypass compartment for no or limited energy recovery. Modulation of the face and
bypass dampers allows the CA to maintain a desired air temperature without use of additional
cooling. In full bypass mode, all OA flows through the bypass compartment with the economizer
damper fully closed and the bypass damper fully open. RA continues to pass through the cores.
Recirculation Mode, an optional feature, is typically used during the Unoccupied Mode. OA
does not enter the unit and RA airflow bypasses the enthalpic cores. The isolation dampers are
closed and only the supply air fan is operating. The recirculation damper diverts RA through the
bypass compartment and to the supply air fan. Additional heating or cooling can be added to the
airstream before delivery back to the Occupied Space.
Refer to the unit IOM for more information on the dampers.
5.1.3 Fans
The fans may be driven by VFDs or may be ECM fans. The VFD fans get an enable signal and
both types of fans get a 0–10VDC signal which is proportional to 0–100% fan command.
Factory VFD settings should not be changed. The settings are available in the
Reference
section
of this manual.
5.1.4 Airflow Measurement
Two pressure transmitters that measure up to 20" w.g. are installed at the fan inlet cones and
are used to measure pressure drop across the fan inlet rings. The scaling screen can be found
in the
I/O Configuration
. The kfactor is factory set for the fans and should only be adjusted
during test and balance. The supply and exhaust flow values can be read in the
Unit
Status
screens.
