Unit Operation
than or equal to the configurable exhaust enable setpoint. This is useful for exhaust fans designed to offset the added economizer ventilation.
The exhaust fan is disabled when the outdoor air damper position drops 10% below the exhaust en- able point. If the exhaust fan en- able setpoint is less than 10%, the Tracer ZN.520 controller energizes the exhaust fan at the enable point and disables it when the outdoor air damper closes.
Output Overrides
Manual Output Test
Manual output test allows the bi- nary outputs to be energized in a predefined sequence.(For more in- formation see, Manual Output
Test, on page 48 for more informa- tion.)
Water Valve Override
To enable quicker water balanc- ing, the controller allows a user to specify the desired state of all wa- ter valves. The values supported are:
qOpen all valves
qClose all valves
The valves in the system will re- main open for two hours or until normal operation is resumed.
The Tracer Summit or the Rover service tool is required to access this feature.
Fan Status
There are two ways to do fan sta- tus monitoring:
1.The status of the fan is reported based on the state of the binary output(s) dedicated to fan control. The fan status is reported as HIGH or LOW whenever the corresponding binary output is directed ON.
The fan status is reported as OFF when none of the fan out- puts are directed ON.
2.The Tracer ZN.520 controller has a binary input available for a fan status device (current sensing relay or differential pressure switch) which can provide feedback of fan opera- tion. If the device does not indicate fan operation after 1
minute, a unit shutdown is ini- tiated, and the unit is latched
OFF.
Filter Status/ Maintenance Timer
The unit filter status\maintenance timer is based on the cumulative run hours of the unit fan. The con- troller compares the fan run time against an adjustable fan run hour limit and recommends unit main- tenance as required.
The Rover service tool is used to edit the maintenance required set- point time. Once the setpoint limit is exceeded, the controller gener-
ates a MAINTENANCE REQUIRED infor-
mational diagnostic. When the maintenance required setpoint time is set to zero, the controller disables this feature.
You can use the Trace Summit or the Rover service tool to clear the
MAINTENANCE REQUIRED informa-
tional diagnostic. Once the diag- nostic is cleared, the controller resets the fan run time to zero and begins accumulating fan run hours again.
Note: If at any time the unit loses power, the timer is reset to zero.
Other Modes
DEHUMIDIFICATION
Note: If the unit is in the unoccupied mode, the dehumidification routine will not operate
Dehumidification is possible when mechanical cooling is available; the heating capacity is in the re- heat position; and the space rela- tive humidity setpoint is valid.
The controller starts dehumidify- ing the space when the space hu- midity exceeds the humidity setpoint. The controller continues to dehumidify until the sensed hu- midity falls below the setpoint mi- nus the relative humidity offset.
The controller uses the cooling and reheat coils simultaneously to dehumidify the space. When de- humidifying, the discharge air temperature is controlled to main- tain the space temperature at the current setpoint.
Economizing is disabled during the dehumidification mode.
Note: While in the dehumidification mode, if there is a call for capacity by the unit, the zone temperature setpoint will take priority over the relative humidity setpoints.
DEFROST
For defrost operation, a sensor is wired in series with the DX cooling relay. When a defrost condition is detected, the condensing unit is disabled, and the unit is placed in the DEFROST mode.
During DEFROST the condensing unit is OFF the outside air damper is set to the minimum positions, and the fan will continue to oper- ate as continuous. The unit will re- main in the DEFROST mode until the senor resets at 48°F. The unit will return to NORMAL operation af- ter the mode is discontinued.
FREEZE AVOIDANCE
FREEZE AVOIDANCE is used as low
ambient temperature protection, and is only invoked when the fan is OFF. This includes the UNOCCUPIED mode when there is no call for ca- pacity, or any other time the fan is
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