Trane Zone Controller Zone temperature control, Cascade zone control, Simplified zone control

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Chapter 5 Sequence of operations

Zone temperature control

The Tracer ZN521 zone controller uses two methods of zone temperature control:

Cascade zone control—used in the occupied, occupied bypass, and occupied standby modes

Simplified zone control—used in the unoccupied mode

Cascade zone control

Cascade zone control maintains zone temperature by controlling the dis- charge air temperature to control the zone temperature. The controller uses the difference between the measured zone temperature and the active zone temperature setpoint to produce a discharge air temperature setpoint. The controller compares the discharge air temperature setpoint with the discharge air temperature and calculates a unit heating/cooling capacity accordingly (see Figure 18). The end devices (outdoor air damper, valves, etc.) operate in sequence based on the unit heating/cooling capac- ity (0–100%).

Figure 18. Cascade zone control

Active zone

 

temperature

 

setpoint

Difference

 

Calculated discharge air temperature setpoint

Difference

Calculated unit heating/cooling capacity

Measured

zone

temperature

Measured

discharge air temperature

If the discharge air temperature falls below the Discharge Air Control Point Low Limit (configurable using the Rover service tool) and cooling capacity is at a minimum, available heating capacity will be used to raise the discharge air temperature to the low limit (see “Discharge air temper- ing” on page 39).

Simplified zone control

In the unoccupied mode, the controller maintains the zone temperature by calculating the required heating or cooling capacity (0–100%) accord- ing to the measured zone temperature and the active zone temperature setpoint. The active zone temperature setpoint is determined by the cur- rent operating modes, which include occupancy and heat/cool modes.

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Contents Installation and Operation Tracer ZN521 Zone Controller Page CNT-SVX07C-EN April CNT-SVX07C-EN Tracer ZN521 Zone Controller Installation and Operation CNT-SVX07C-EN Contents Sequence of operations Status indicators for operation and communication Troubleshooting Index Overview and specifications Product descriptionDimensions Storage environmentClearances Plastic-cover model dimensions and clearances Agency listing/compliance Additional componentsTracer zone temperature sensor options Damper actuatorsZone humidity sensor CO2 sensorOverview and specifications Input/output terminal wiring AC-power wiringGeneral wiring information Communication-link wiring and addressing General wiring information Location recommendations Operating environment requirementsMounting recommendations Mounting the Tracer ZN521 zone controllerTypical applications for the Tracer ZN521 zone controller Application SpeedfanMultiple DehumidificationControlValve Economizing HeatElectricBI1 Low-coil-temperature detection Binary inputsBI2 Condensate overflow Binary inputsBI3 Occupancy or generic binary input BI4 Fan statusZN Zone temperature Analog inputsGND Ground terminals Analog inputsFAN Fan mode input AI1 Entering water temperatureSET Local setpoint AI2 Discharge air temperature AI3 Outdoor air temperature or generic temperatureAI4 configuration options and associated measurement ranges Configuration Measurement rangeAI4 Universal 4-20 mA AI4 terminal wiring CO2 measurement Binary outputs Generic binary outputBinary output functions Binary output FunctionsWiring requirements and options Overriding binary outputsRequired controller inputs for proper operation Function Input source For more information SeeTwo-pipe hydronic-cooling unit Two-pipe hydronic-heating unit Two-pipe hydronic heating/cooling unit with auto changeover Four-pipe hydronic heating/cooling unit Four-pipe heating/cooling unit with auto changeover Two-pipe heating unit with DX cooling Electric heat unit with DX cooling Electric heat unit Two-pipe heating unit with face-and-bypass damper Two-pipe heating/cooling unit with face-and-bypass damper Four-pipe heating/cooling unit with face-and-bypass damper Input/output functions and wiring for typical applications Power-up sequence Random startOccupied mode Unoccupied modeOccupied standby mode Occupancy modesOccupied bypass mode Timed override controlZone temperature control Cascade zone controlSimplified zone control Heating or cooling mode Discharge air temperingMorning warm-up Morning cool-downEntering water temperature sampling function Fan operationExhaust control Exhaust controlValve operation Modulating valve operationModulating valve calibration Valve control optionsModulating outdoor/return air dampers Two-position valve operationIsolation-valve operation Two-pipe operationModulating outdoor air damper position Ashrae Cycle 1 conformance Ashrae Cycle 2 conformanceEconomizing free cooling Two-position control of a modulating outdoor air damper Face-and-bypass damper operationDX cooling operation Face-and-bypass, isolation-valve operationElectric heat operation Baseboard heat operationDehumidification Peer-to-peer communication Unit protection strategiesSmart reset Low-coil-temperature protectionFan off delay Condensate overflowFilter-maintenance timer Freeze protection discharge air temperature low limitFreeze avoidance Test button Tracer ZN521 zone controller circuit boardManual output test For non OutputClose damper, air Outdoor Open damper, air Outdoor Step Result BOP1 BOP2 BOP3 BOP4 BOP5 BOP6 BOP7 BOP8 BOP9Service pin button Red LED Service indicatorInterpreting LEDs LED activity ExplanationGreen LED Status indicator Yellow LED Communications indicatorDiagnostics Types of diagnosticsTable of diagnostics DiagnosticsDiagnostic Probable cause Consequences Type Fan unaffectedValved unaffected PositionDamper unaffected Status indicators for operation and communication Fan does not energize Probable cause ExplanationTroubleshooting Valves remain closedValves remain open DX or electric heat does not energizeOutdoor air damper remains closed Outdoor air damper remains openOutdoor air damper remains open Troubleshooting Index NumericsIndex Index Index Page Trane