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DN-Series Integrated Programmable Controls
DOAS
SYSTEM MONITORING
13.9.5.5 Economizer Control
The economizer will be enabled when there is a call for cooling and the outdoor is more
favorable than the return air. In this case it will modulate the bypass damper to bypass the
enthalpic core and thus limit or inhibit the exchange of energy. The mechanical cooling is not
allowed until the bypass is open 100%. During this time the unit still uses 100% outdoor air.
Economizing is allowed when both of the following Are below their limit:
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Holding Register 30 “Economizer.Econ_Low_OA_Temp_Limit”
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Holding Register 42 “Economizer.Econ_Low_RA_Temp_Limit”
The damper will modulate using PI Control set in the controller when the OA is less than the
difference value specified as follows:
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If using the temperature economizer type, the value used is Holding Register 28
“Econ_Temp_Diff”
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If using the enthalpy economizer type, the value used is Holding Register 32
“Economizer.Econ_Hysteresis”
You can view the status through Discrete Input 14 “Econ_Active” to see if the economizer is
active. The bypass damper position is viewed at Input Register 38 “Bypass_Command.Val.”
13.9.5.6 Unoccupied Control
If optional recirculation dampers are present, the unit will operate in unoccupied mode
according to the following settings:
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Coil 3 “OnOffUnitMng.BMSUnocc” allows you to put the unit in unoccupied mode.
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The supply fan will either run continuous or on a call for heat or cooling as set in the
controller. It will run at a speed set in Holding Register 46 “SF_UnoccFlowSetP.Val.”
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It will maintain the Holding Register 48 “Unocc_CLG_SetP.Val” and Holding Register 50
“Unocc_HTG_SetP.Val.”
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The status of the recirculation damper is seen at Discrete Input 12 “Recirc_Damp.Val.”
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The unoccupied statuses can be viewed in Discrete Input 17 “Unocc_Mode,”
Discrete Input 18 “Unocc_HTG,” and Discrete Input 19 “Unocc_CLG.”
13.9.6 Frost Control
The frost control function utilizes the bypass to avoid frosting the enthalpic core. If bypass is
enabled, when the OA is lower than Holding Register 64 “Defrost_OA_SetP.Val” minus Holding
Register 66 “Defrost_OA_SetP.DBright,” and turns off again when the OA exceeds the HR66.
The frost control status can be viewed at Discrete Input 23 “DefrostOn.”
When frost control is on, the bypass damper will modulate to maintain a maximum Holding
Register 79 “Defrost_EA_High_SetP.Val.” The bypass damper position is viewed at Input
Register 59 “Bypass_Command.Val.”
13.9.7 Filter Monitoring
Filter pressures are read through Input Register 16 “RA_Flt_Press.Val” and Input Register 18
“OA_Flt_Press.Val.”
Filter alarm levels are set at Holding Register 0 (or 98) “RA_Flt_AlarmHigh” and Holding
Register 2 “OA_Flt_AlarmHigh.”
13.9.8 Exhaust Fan Only Mode
If BMS control is enabled, the unit can also be put in exhaust fan only mode in occupied
operation using Coil 1 “UnitOnOffMng.BMSEFOnly.”
