Catalogue

UNT-PRC001-EN 51
Controls
Tracer ZN520 and UC400 Additional Features
Automatic Fan Speed Adjustment
When configured in the AUTO mode, the fan operates at the lowest speed possible (high, medium,
or low) to maintain space temperature. As the cooling load decreases, the controller switches the
fan to operate at the next lower speed, and the control valve modulates the unit’s cooling capacity
as required. This results in less fan energy use, improved dehumidification performance, and lower
sound levels.
Automatic Ventilation Reset
To ensure proper ventilation rates, the controller is configured with two fresh air damper minimum
position setpoints for occupied operation. As the fan speed changes to low or high, the damper
adjusts to maintain the correct ventilation rate for the space. The damper position does not adjust
when the fan speed changes to medium.
Fan Status
Tracer ZN520 and UC400 monitors the fan output status to determine if the fan is operating.
Filter Maintenance Status
The controller has an adjustable timer that indicates through Summit, Rover (ZN520) or TU (UC400)
when filter maintenance is necessary. Filter maintenance status is based on cumulative fan run
hours.
Dehumidification
When the fan-coil unit is equipped with a reheat coil and humidity sensor, the controller will
independently control both space temperature and humidity. If the space humidity level rises
above the upper limit, the capacity of the cooling coil is increased, overcooling the air to maintain
the space humidity below the upper limit. Then, the capacity of the heating coil modulates, adding
a small amount of heat to temper (reheat) the air and avoid overcooling the space.
Water Valve Override
The water valve override function drives all water valves in every unit fully open simultaneously.
This helps reduce the time required for waterside balancing.
Cascade Control
The controller maintains discharge air temperature using a cascade control algorithm. The
discharge air temperature is based on the difference between the space temperature and setpoint.
Unit capacity modulates to achieve the discharge air temperature.
Interoperability
Tracer ZN520 can be used with a Tracer Summit system or on other control systems that support
LonTalk and the SCC profile. For more information on specific inputs and outputs, see the
Installation, Owner, and Maintenance Manual, UNT-IOM-6. UC400 can be used with a Tracer
Summit system or other control systems that support BACnet. For more information on specific
inputs and outputs, see the Installation, Owner, and Maintenance Manual, UNT-SVX07D-EN.
Tracer ZN520 and UC400 Additional Features
UNT-PRC001-EN.book Page 51 Tuesday, May 8, 2012 10:54 AM