Trane ZN.520, Tracer Unit Ventilator User Manual

1.38 Mb

Installation

Owner

Diagnostics

Tracer® ZN.520 for Classroom

Unit Ventilator

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Start-up Procedures

Installation of New Units

1.Follow all instruction for installation of classroom unit

ventilators as detailed in UV- IOM-1 (Installation Operation Maintenance manual).

2.Disconnect power or disable the circuit breaker to unit.

3.Run communication link wire when required. (See wiring diagram in the unit).

4.Install zone sensor when

required. (See wiring diagram in the unit and zone sensor submittals).

5.Reapply power.

6.Check for GREEN Status LED

operation to ensure power has been made to the TracerTM ZN.520 unit controller.

7.Check for YELLOW Comm LED

operation to help ensure communication has been made to the Tracer ZN.520 unit controller when required.

Peel IDENTIFICATION TAG from

unit and place in the Appendix of this document, or on building plans for future location use. The

actual room location on the tag may be hand written.

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Start-up Procedures

Power Up Sequence

Manual output test can be initiated

at any time in the power up sequence or during normal operation.

When 24 VAC power is initially applied to the controller, the follow-

ing sequence occurs:

1.Green Status LED turns on.

2.All outputs are controlled Off.

3.The controller reads input values to determine initial values.

4.Standalone control is assumed unless occupancy data is communicated.

5.Random start timer expires (5 to 30 seconds, random).

6.Power-up control Wait feature is applied. When power up

control Wait is enabled, the controller waits 120 seconds to allow ample time for commu-

nicated control data to arrive. If, after 120 seconds, the controller does not receive a com-

municated occupancy request, the unit assumes standalone operation.

7.All modulating valves and

damper calibrate closed, face and bypass damper calibrate to bypass (when present).

8.Normal operation begins after

290 (potentially) seconds have passed.

Note: Manual output test can be initiated at any time.

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General Information

Tracer® ZN.520

Overview

The Trane® Tracer® ZN.520 controller is a factory-installed and

commissioned, direct-digital controller (DDC) offering for classroom unit ventilator sys-

tems. (See Figure 1: “Tracer ZN.520 Control Board”) The Tracer ZN.520 can also be applied to

other Trane® interoperable HVAC equipment, including the fan coil and blower coil products. (For

more information see,Table 1: Tracer™ ZN.520 Unit Controller features and coil availability, on

page 8 for more information.) For more information regarding the application of the Tracer ZN.520

to other Trane products, contact the appropriate local Trane sales office.

Trane offers a complete solution to space comfort control with the

flexibility of Integrated Comfort System (ICS) and stand-alone control packages. The ICS control

package combines HVAC equipment and building management into one environmental comfort

system.

Integrating the Tracer ZN.520 on

classroom unit ventilators, and tying them to a Tracer Summit® system will provide a complete

building management system. The stand-alone control package offers the features and function-

ality of the direct digital control without a front-end building automation system, while providing

future considerations for ICS.

Equipment problems can often be

diagnosed on each unit without having to access the unit componets. These diagnostics can be re-

ceived remotely via a modem with a Tracer Summit building automation system, thus reducing the

number of actual on-site service calls; through the Rover® service tool connected to a communica-

tion jack located inside the Trace zone sensor; or connected to the unit.

Figure 1: Tracer ZN.520 Control Board

The Tracer ZN.520 is factorymounted, tested, wired, config-

ured and commissioned for the selected application.

The Tracer ZN.520 configuration has flexible point and product configurations. For example, with

point configuration, a specific binary point can be configured to accept input from either a time clock

or some type of generic device.

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General Information

Table 1: Tracer™ ZN.520 Unit Controller features and coil availability
			Auto	Face and				Entering
	Multiple	Dehumid-	Auto	Face and	Valve	Economizer	Auxiliary	Water
Coil	Multiple	Dehumid-	Damper	Bypass	Valve	Economizer	Auxiliary	Water
Coil	Fan Speeds	ification	Damper	Bypass	Control	Damper	Heat2	Temperature
	Fan Speeds	ification	Adjust	Damper	Control	Damper	Heat2	Temperature
			Adjust	Damper				Sampling
								Sampling
2-pipe changeover	X		X	X	X	X	X	X
2-pipe hot water	X		X	X	X	X	X
only	X		X	X	X	X	X
only
2-pipe steam only	X		X	X		X	X
2-pipe changeover/	X	X	X		X	X	X	X
electric heat	X	X	X		X	X	X	X
electric heat
2-pipe cool only	X		X		X	X
2-pipe cool only/	X1		X1		X	X	X
electric heat	X1		X1		X	X	X
electric heat
4-pipe hot water/	X	X	X	X3	X	X	X
chilled water	X	X	X	X3	X	X	X
chilled water
4-pipe changeover	X	X	X	X3	X	X	X	X
4-pipe steam/chilled	X		X		X	X	X
water	X		X		X	X	X
water
Electric heat only						X	X
DX/hot water	X1		X1		X	X	X
DX/steam	X1		X1		X	X	X
DX/electric heat						X	X
DX cooling only						X

1.Multiple fan speeds are available in hydronic units only.

2.Auxiliary heat is designed to bring on baseboard heat as the second stage of heating. The baseboard heat must be the same type as the

unit heating coil.

3. Units with face bypass dampers cannot actively dehumidify.

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Controller Circuit Board

Features

Power

Generic

Auto Test Button

Status LED

Communications LED

Service Button and LED

Communications	Zone Sensor Connections

Figure 2: Tracer ZN.520 unit controller circuit board

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Controller Features

Each Tracer ZN.520 unit controller circuit board is equipped with enhancements to help facilitate ser-

vice, testing, and diagnosis. Each board has

qManual test button,

qStatus LED,

qCommunication status LED,

qService button,

qQuick terminal connectors, and

qEasy to read screen printing.

(See Figure 1: “Tracer ZN.520 Control Board”).

Service

The Trane Tracer ZN.520 unit con-

troller is serviced using Rover®, the ICS software service too. Rover is designed to support the Tracer

ZN.520 unit controller on the classroom unit ventilator.

For “remote” access to the communicating units, the zone sensors offered with the Tracer ZN.520

have a telephone style (RJ-11) connector allowing field connection between Rover and the zone sen-

sor; however, the RJ-11 connector must be connected to the terminals TB2-5 and TB2-6 on the Tracer

ZN.520 unit controller.(See Figure 3: “Rover service tool connected to the RJ-11 communication jack in a

zone sensor”)

The zone sensor may also be used when trying to locate a unit. By pressing the ON button on the zone

sensor for 5 seconds or using the “wink” command in Rover, the circuit board receives the signal caus-

ing the Communication LED to “wink”. Winking allows visual identifier on the board for service

technicians.

The Tracer ZN.520 also includes

features such as a test output to manually test all of the end devices and color coded wires (i.e. red for

heating valves and blue for cooling valves) to aid in the troubleshooting process.(See “Manual Output

Test” on page 48, for more information.)

Figure 3: Rover service tool connected to the RJ-11 communication jack in a zone sensor

Typical Components

A typical classroom unit ventilator

system with a DDC package consists of the following physical components, in addition to the

mechanical equipment:

qTracer ZN.520—contains the

sensor input circuits, service adjustments, microprocessor control electronics, and communications hardware.

Power is supplied by a separately mounted 24 VAC\90 VA transformer.

qSensor Modules—a variety of analog sensors that provide

temperature and optional

humidity sensing and CO2 sensor; and an operator interface to the Tracer ZN.520 for operating modes, status, and temperature setpoints.

qStandard End Devices—a variety of devices that help to gather information, control

capacity, and provide ventilation are used by the Tracer ZN.520 in its control

algorithm to condition the space to the desired temperature and relative

humidity level. (See “Standard End Devices” on page13, for more information.)

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Communication Configurations

Note: The Tracer ZN.520 is a	connect to a maximum of 120
configured controller. It will	Tracer ZN.520 controllers.
not operate without a valid
downloaded configuration
file.
The Tracer ZN.520 controller sup-
ports ICS and peer-to-peer com-
munications as well as stand-
alone operation. A number of con-
trol features may be configured at
the factory or by using the Rover
service tool. (See “Configuration”
on page32, for more information.)

Integrated Comfort

System

Note: The Tracer ZN.520

controller may only be used with Tracer Summit version 11.0 or greater with a Comm5

communications card.

Classroom unit ventilators can op-

erate as part of a large building automation system controlled by Tracer Summit. The Tracer ZN.520

is linked directly to the Tracer Summit via a twisted pair communication wire. Each Tracer Summit

building automation system can

Figure 4: Communications link wire

The ICS system allows for complete communication with the classroom unit ventilators via

Tracer ZN.520 unit controller. All points connected to the Tracer ZN.520 may be observed from the

Tracer Summit front-end controller. The Tracer Summit can also initiate an alarm on a loss of per-

formance or equipment malfunctions.

The ICS system also allows all of

the classroom unit ventilators to share information without the presence of hardwired sensors at

each unit. Some typical shared points include outside air temperature, entering water temperature,

and occupancy schedules.

Peer-to-Peer

Communications

On a peer-to-peer communication

system, multiple Tracer ZN.520 controllers may share data, via a twisted pair communication wire,

without the need for a Tracer Summit system. (See Figure 5: “Peer- to-peer communication connec-

tions”)

Peer-to-peer communications al-

lows features such as master/slave operation, in which multiple units operate off of a single zone sensor.

This is typically seen in large spaces requiring multiple units.

The Rover service tool is required to set up peer-to-peer communications.

Figure 5: Peer-to-peer communication connections

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Communication Configurations

Stand-Alone

In a stand-alone configuration,

commands for operation are determined based on input from the zone sensor, humidity sensor, and

factoryor field-mounted timeclock.(See Figure 6: “Typical classroom unit ventilator installation”)

qThe timeclock is wired to the Tracer ZN.520 to index the unit

between occupied and unoccupied modes.

qA unit-mounted, analog, outside-air temperature sensor is used to initiate the dry bulb

economizer and freeze avoidance routines.

qOn changeover units, a unitmounted, analog, entering water temperature sensor is

used to automatically control the system in the heat/cool mode.

These sensors are required for proper system operation and are

provided as standard on standalone units.

Figure 6: Typical classroom unit ventilator installation

Communication Interface

Important! To help ensure

optimal performance of the Rover service tool, please use the latest version. To obtain

the latest version contact your local Trane sales representtative or service technician.

Note: Refer to the Tracer system manuals for more

information on communications.

The Tracer ZN.520 communicates via Comm5 (LonTalk) to a building management system, the Rover

service tool, and other unit controllers on the communications link. Each Tracer ZN.520 requires a

unique address for the system to operate properly. Every Tracer ZN.520 has this address (Neuron

ID) embedded in the microprocessor, which eliminates the need for field-addressing of the units. Each

unit also ships from the factory with a unit identification tag. (See “Location Identifier” on page38,

for more information.)

Building automation system

Trane offers a state-of the art frontend building automation system designed to coordinate and moni-

tor Trane equipment and controllers: Tracer Summit.

The Tracer Summit system allows the user to monitor and/or change Tracer ZN.520:

qstatus, parameters, sensor data, diagnostics, and internal variables; and

qsetpoints, operating modes, and outputs.

Service tool

Trane also offers a service tool to work in conjunction with the Tracer Summit system or with peer-to-

peer and stand-alone systems: the Rover service tool.

Communication to the Tracer ZN.520, or multiple controllers, can also be accomplished by using the

ICS software service tool.

A personal computer running Rover may be directly connected to a standalone Tracer ZN.520; con-

nected to the communications jack in the Trane zone sensor; or connected to a communicating unit’s

Tracer ZN.520 unit controller, to access all of the units on a communicating link.

Rover allows the user to interface with the Tracer ZN.520, but will not

allow any advanced control (e.g. equipment scheduling or trending). To purchase a copy of the ICS

software service tool, contact the BAS department at your local Trane dealer.

Interoperability

Trane has lead the industry with BACnet interoperability and Trane

is now expanding the realm of interoperable solutions by offering LonMark certified unit controllers.

The Tracer ZN.520 controller conforms to the LonMark Space Comfort Controller profile. (See

“Appendix—Data Lists” on page64, for more information.)

This allows the ZN.520 to be used

as a unit controller on other control systems that support LonTalk and the SCC profile. Now building own-

ers have more choices and design engineers have more flexibility to meet the challenges of building au-

tomation.

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Standard End Devices

Table 2: End Device Specifications

Device

Fan Status Switch

Low Temperature Detection Switch (Freezestat)

OutsideAir Sensor/discharge AirSensor/Entering

Water Temperature Sensor/Unit Mounted, Zone

Return-air Temperature Sensor

Characteristic

Material

Operating Temperature Range

Contact Form

Preset

Trip Temperature:

Release Temperature

Rating—Auto Reset

Sensing Element

Description

Contact Blade—Pilot duty rated

-40°F/250°F (-40°C/120°C)

SPST-NO

Fan status - 0.07”

36°F ± 2°F (2°C + - 1.11°C)

44°F ± 3°F (6.67°C + - 1.67°C)

Pilot Duty	120	VAC	240	VAC
(24 VAC)	120	VAC	240	VAC
(24 VAC)
FLA	10.0		5.0
LRA	60.0		30.0

Thermistor 10 KOhms @ 77°F ± 1.8°F (25°C ±1°C)

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Standard End Devices

Table 2: End Device Specifications

Device	Characteristic	Description

Outside Air Actuator	Description	Three-point floating with spring return
	Ambient Temperature Rating	-25°F to 125°F
	Power Consumption	5 VA
	Torque	35 in-lbs.

Drive Time

90 seconds, 95 degree stroke

Face and Bypass Actuator	Description	Three-point floating
	Ambient Temperature Rating	32°F to 122°F
	Power Consumption	3 VA
	Torque	35 in-lbs.

Drive Time

80-110 seconds, 95 degree stroke

2-way Control Valve	Description	Three-point modulating
	Ambient Temperature Rating	140°F at 95% relative humidity
	Drive Time	50 seconds
	Max Pressure	400 psi water
	Close Off	Varied by size and Cv

Temperature

Water 200°F maximum

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Standard End Devices

Table 2: End Device Specifications

Device	Characteristic	Description

3-way Control Valve	Description	Three-point modulating
	Ambient Temperature Rating	140°F at 95% relative humidity
	Drive Time	50 seconds
	Max Pressure	400 psi water
	Close Off	Varied by size and Cv

Temperature

Water 200°F maximum

Time clock	Size	2.83'' x 4.0'' x 2.06''
	Power Consumption	4.4 VA
	Switch	SPDT dry contacts, silver cadmium oxide
	Switch Rating	16A 250V resistive, 1000 Watts tungsten
	Minimum Switching Current	100mA,230V
	Shortest Switching Time	1 minute
	Ambient Temperature Range	-14°F to 131°F
	Wiring Connections	Screw terminals suitable for #10 to #24 AWG
	Backup	Seven day capacitor backup

Zone sensor

	Zone Sensor Wiring Size And	16-22 AWG: up to 200 feet
	Maximum Lengths	16-22 AWG: up to 200 feet
	Maximum Lengths

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Standard End Devices

Table 2: End Device Specifications

Device	Characteristic	Description

Humidity Sensor	Sensing Element	Polymer capacitive
	Sensing Element	Accuracy: ± 5% over 20-95% RH @ 77ºF
	Range	0 to 99% RH
	Operating Temperature Range	0°F to 140ºF
	Max Supply Voltage	24VDC
	Output Characteristics	4 to 20 MA for 0-100% RH
	Drift Rate	Less than 1% per year
CO 2 Sensor	Sensing Element	Accuracy: ± 100ppm full scale
	Range	0-2000 ppm
	Operating Temperature Range	59°F to 95ºF
	Supply Voltage	24VAC
	Output Characteristics	0-10 VDC for 0-2000 ppm
	Power consumption	10 VA
	Drift Rate	±5% full scale over four years
Fan Relay		20 amps at 120/240 vac
Fan Relay		20 amps at 120/240 vac
		3/4 hp at 120 vac
	Contact Rating	1 1/2 hp at 240 vac
		20 amps @ 28 vdc
		DPDT
	Terminals	0.25 quick connect
	Contact material	Silver-Cadium Oxide
	Coil	24 vac 2.7 va

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Standard End Devices

Table 2: End Device Specifications

Device	Characteristic	Description

	Type	N.E.C. Class 2
	Primary Voltage	120 vac
Control Transformer		24 vac at 90 va
		24 vac at 90 va
	Secondary voltage	Manual reset
		4amp fuse in 24-volt circuit

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Installation and Wiring

Specifications

Dimensions

Tracer ZN.520 board and mounting hardware:

•Height: 5.25 inches (133 mm.)

•Width: 5.50 inches (140 mm)

•Depth: 2.25 inches (57 mm)

Power Requirements

•18 to 32 VAC (24 VAC nominal)

•50 or 60 Hz

•570 mA AC

Operating Environment

•32° to 140°F (0× to 60°C)

•5% to 95% relative humidity, non-condensing

Storage Environment

•-40° to 185°F (-40° to 85°C)

•5% to 95% relative humidity, non-condensing

Agency Listings

•UL and CUL 916 Energy Management System

•Agency Compliance IEC 1000- 4-2 (ESD), IEC 1000-4-4(EFT), IEC 1000-4-5 (Surge)

Figure 7: Tracer ZN.520 circuit board schematic

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Installation and Wiring

Binary Inputs

Each binary input associates an input signal of 0 VAC with open con-

tacts and 24 VAC with closed contacts.

Table 3: Binary inputs (typically 24 mA AC)

Description	Terminals	Terminal Function
Binary input 1	J2-1	24 VAC
(BI 1)	J2-1	24 VAC
(BI 1)
	J2-2	Input
Binary input 2	J2-3	24 VAC
(BI 2)	J2-3	24 VAC
(BI 2)
	J2-4	Input
Binary input 3	J2-5	24 VAC
(BI 3)	J2-5	24 VAC
(BI 3)
	J2-6	Input
Binary input 4	J2-7	24 VAC
(BI 4)	J2-7	24 VAC
(BI 4)
	J2-8	Input

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Installation and Wiring

Binary Outputs

Outputs are load side switching tri-

acs. The triac acts as a switch, either making or breaking the circuit between the load (valve, damper,

contactor, relay) and ground.

Table 4: Binary outputs

Description

Fan high

Fan medium,

Exhaust fan

Fan low

No connection

Cool open, face bypass cool valve DX, 2-position cooling valve, BI 5

Cool close

Face/bypass damper open

Face/bypass damper close

Heat open

Face bypass isolation valve, 2-position heating valve Electric heat 1st stage

Heat close

Electric heat 2nd stage

Economizer damper open

Economizer damper close

	Terminals	Output
	Terminals	Rating
		Rating
	J1-1	12 VA
	J1-2	12 VA
	J1-3	12 VA
	J1-4 (Key)	—
	J1-5	12 VA
	J1-6	12 VA
	J1-7	12 VA
	J1-8	12 VA
	J1-9	12 VA
	J1-10	12 VA
	J1-11	12 VA
	J1-12	12 VA

Load Energized	Load De-energized
1 VAC RMS	24 VAC RMS
(typical)	(typical)
1 VAC RMS	24 VAC RMS
(typical)	(typical)
1 VAC RMS	24 VAC RMS
(typical)	(typical)
—	—
1 VAC RMS	24 VAC RMS
(typical)	(typical)
1 VAC RMS	24 VAC RMS
(typical)	(typical)
1 VAC RMS	24 VAC RMS
(typical)	(typical)
1 VAC RMS	24 VAC RMS
(typical)	(typical)
1 VAC RMS	24 VAC RMS
(typical)	(typical)
1 VAC RMS	24 VAC RMS
(typical)	(typical)
1 VAC RMS	24 VAC RMS
(typical)	(typical)
1 VAC RMS	24 VAC RMS
(typical)	(typical)

Generic/baseboard Heat Binary Output

Table 5: Generic binary outputs
Description	Terminals	Output	Load Energized	Load De-energized
		Rating
Generic/ baseboard heat output	TB4-1	12 VA	1 VAC RMS	24 VAC RMS
			(typical)	(typical)
24VAC	TB4-2	12 VA	NA	NA

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Installation and Wiring

Analog Inputs

Table 6: Analog inputs
Description	Terminals	Function	Range
Zone	TB3-1	Space temperature input	5° to 122°F
			(-15° to 50°C)
Ground	TB3-2	Analog ground	NA
Set	TB3-3	Setpoint input	40 ° to 115 °F
			(4.4° to 46.1°C)
Fan	TB3-4	Fan switch input	4821 to 4919 Ω (Off)
			2297 to 2342 Ω (Auto)
			10593 to 10807 Ω (Low)
			13177 to 13443 Ω (Medium)
			15137 to 16463 Ω (High)
Ground	TB3-6	Analog ground	NA
Analog Input 1	J3-1	Entering water temperature	-40° to 212°F (-40° to 100° C)
	J3-2	Analog ground	NA
Analog Input 2	J3-3	Discharge air temperature	-40° to 212°F (-40° to 100° C)
	J3-4	Analog ground	NA
Analog Input 3	J3-5	Outdoor air temperature / Generic	-40° to 212°F (-40° to 100° C)
		temperature
	J3-6	Analog ground	NA
Analog Input 4	J3-7	Power port	4-20 mA
	J3-8	Universal input
		Generic 4-20ma	0 – 100%
		Humidity	0 – 100%
		CO2	0 – 2000ppm
	J3-9	Analog ground	NA

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Installation and Wiring

Mounting

The Tracer ZN.520 circuit board is

mounted in the left-hand end pocket for all classroom unit ventilator configurations. The sheet metal

mounting plate has raised embosses to accept the mounting feet on the circuit board. (See Figure 8:

“Classroom unit ventilator control box with close-up of horseshoe embosses and circuit board

mounting feet.”) This design allows the Tracer ZN.520 controller to be secured with a minimal num-

ber of sheet metal screws.

Figure 8: Classroom unit ventilator control box with close-up of horseshoe embosses and circuit board mounting feet.

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Installation and Wiring

The mounting position on the ver-

tical classroom unit ventilator configuration allows complete access to the Tracer ZN.520 by re-

moving the front panel. (See Figure 9: “Vertical classroom unit ventilator end pocket”) The

mounting plate swings out of the way with the removal of a single screw to allow access to the com-

ponents behind the control board.

The mounting plate on the hori-

zontal classroom unit ventilator configuration is designed to slide out with the removal of a sin-

gle screw for complete access to the Tracer ZN.520. (See Figure 10: “Horizontal classroom unit venti-

lator end pocket”) The location of the control board on this unit configuration allows complete access

to the other components in the end pocket when the front panel is removed.

For additional convenience, quick

connects and modular wire harnesses are used on the control board and mounting plate. (See

Figure 11: “Quick connects to control board in the classroom unit ventilator”) These quick connects

help facilitate ease of wiring devices (e.g., zone sensor) to the control board, and helps add accessibility

to major components.

Figure 11: Quick connects to control board in the classroom unit ventilator

Figure 9: Vertical classroom unit ventilator end pocket

Figure 10: Horizontal classroom unit ventilator end pocket

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Installation and Wiring

Wiring

! WARNING

Warning! Disconnect all electrical power before servicing unit to prevent injury or death due to electrical shock. Use copper conductors only. The use of aluminum or other incorrect types of wire may result in overheating and equipment damage.

! CAUTION

Caution: To prevent damage to the unit ventilator, refer to the diagram provided on the inside of the unit's access panel for specific wiring infor-

mation. All controls are wired at the factory. Single point power, zone sensor, and communication wiring is to be installed by the contractor.

Important! All wiring must comply with state, local, and federal guidelines. Contact the

appropriate local agency for furthur information.

Important! Wires for temperature sensors, communication lines, 24 VAC,

and contact closure sensing inputs should not be bundled with or run near high voltage

wiring.

qPower wiring must be

separated from the Tracer ZN.520 and all low voltage wires. External input wires

should be run in separate conduits from high voltage wires.

qWires connected to pin headers should be formed and routed

so as to cause minimum strain on the Tracer ZN.520 connector.

qA minimum of 1.5" clearance (from the pin centerline) for wires up to 16 AWG is

recommended for bending and forming wires.

qAll sensor and input circuits are at or near ground potential. Do not connect any sensor or input

circuit to an external ground connection.

qA close-coupled ground connection is required for the Tracer ZN.520. T

qTable 7: Tracer ZN.520 Wiring Requirements, shows Tracer ZN.520 wire types and lengths.

Table 7: Tracer ZN.520 Wiring

Requirements

Application	Wire Type	Length

Contact Closure	18 AWG	Up to
Contact Closure	18 AWG	1000 ft.
		1000 ft.
24 VAC	16-22 AWG	Up to
24 VAC	16-22 AWG	1000 ft.
		1000 ft.
Thermostat	16-22 AWG	Up to
Thermostat	16-22 AWG	1000 ft.
		1000 ft.
Zone	16-22 AWG	Up to
Sensor	16-22 AWG	200 ft.
Sensor		200 ft.
Communications	Belden 8760	Up to
	or equivalent	5000 ft.

Power

The Tracer ZN.520 controller is

quick-connect terminals are provided for 24 VAC connection to the board.

Figure 12: Power connection to the Tracer ZN.520 unit controller

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Installation and Wiring

Installing the WallMounted Zone Sensor (Optional)

Zone sensor location is an important element of effective room

control and comfort.

The best sensor location is typical-

ly on a wall, remote from the HVAC unit. Readings at this location assure that the desired set-

point is achieved across the space, not just near the unit itself.

Note: It may be necessary to

subdivide the zone with multiple units to ensure adequate control and comfort

throughout the space.

The following are typical areas

where the zone sensor should NOT be mounted:

qNear drafts or “dead spots” (e.g., behind doors or corners);

qNear hot or cold air ducts;

qNear radiant heat (e.g., heat

emitted from appliances or the sun);

qNear concealed pipes or chimneys;

qOn outside walls or other nonconditioned surfaces; or

qIn air flows from adjacent zones or other units.

Figure 13: Proper zone sensor placement

Note: All zone sensor wiring

will be done in the factory unless zone sensor options are selected to be wall mounted.

When a unit-mounted speed switch is selected with a wall-

mounted zone sensor, the contractor must disconnect the cooling setpoint on the unit mounted sen-

sor if the wall mounted cooling setpoint is used. The zone signal will be cut at the factory. The unit-

mounted speed switch cannot be used as a zone sensor.

THe communications link is not connected in the factory. Communications should be wired to the

wall-mounted sensor.

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Installation and Wiring

Humidity and CO2 Sensors

Humidity and CO2 sensors should be mounted in a similar location as the zone sensor.

Figure 14: Relative humidity sensor

Figure 15: CO 2 Sensor

26	UV-SVP01A-EN

Typical Wiring Diagram—Wall

Mounted Zone Sensor

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Typical Wiring Diagram—Unit

Mounted Zone Sensor

28	UV-SVP01A-EN

Typical Wiring Diagram—Unit

Mounted Switch, Wall Mounted Sensor

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Input/Output Summary

The following lists all possible bi-

nary and analog inputs and outputs available for the classroom unit ventilator applications. Some

of the points listed may be mutually exclusive and some are optional.

(See Table 8: Input and output summary)

Table 8: Input and output summary

Most binary inputs and outputs are wired from the factory based on unit configuration and options. If

the generic inputs and outputs are to be used, wiring connections are made at the 1/4” quick-connect ter-

minals provided.

Analog inputs from a wall-mount-

ed zone sensor, humidity sensor, CO2 sensor, or a generic device

Input	Description
	Freezestat
Binary Inputs	Fan Status
	Occupancy/Generic
	J1-1 Fan High Speed
	J1-3 Fan Low Speed
	J1-2 Exhaust Fan
	J1-5 Cooling Open
	(Modulating valve/DX/
	Isolation valve)
	J1-6 Cooling Close
	J1-7 Face and Bypass Damper
	Open
	J1-8 Face and Bypass Damper
	Close
Binary Outputs	J1-9 Heat Open (Modulating
	J1-9 Heat Open (Modulating
	valve/Isolation valve) or 1 st
	Stage Electric Heat
	J1-10 Heat Close or 2 nd Stage
	Electric Heat
	J1-11 Economizer Damper
	Open
	J1-12 Economizer Damper
	Close
	TB4-1 Generic/Baseboard
	Heat
	TB4-2 24 VAC

must be wired to the 1/4” quickconnect terminals provided. Most other analog inputs will be wired

from the factory.

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Input/Output Summary

Table 8: Input and output summary

Input

Description

Zone Temperature

Setpoint

Fan Speed

Entering Water Temperature

Analog Inputs

Discharge Air Temperature

Outdoor Air Temperature/

Generic

Generic/Humidity/CO2 (4-

20mA)

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Configuration

Note: The Tracer Zn.520 unit controller only supports cascade control by controlling

the discharge air temperature. Therefore, the controller requires both a space

temperature input and a discharge air temperature input.

Table 9: Typical applications supported

Configuration

2-pipe cooling only

2-pipe heating only

2-pipe changeover

4-pipe

4-pipe changeover

2-pipe face bypass heating only

2-pipe face bypass changeover

4-pipe face bypass DX cooling only

DX cooling, 2-pipe heating

DX cooling, electric heating

Electric heat only (1 or 2 stage)

1. Isolation valves are 2-position only.

Trane configures the Tracer® ZN.520 Unit Controller at the factory per the selected unit configu-

ration. The controller is applied classroom unit ventilator configurations that support modulating

valves, 2-position valves, economizer damper (modulating only), direct expansion (DX) cooling, 1-

and 2 -stage electric heat, face- and-bypass damper, baseboard heat, dehumidification, and ge-

neric I/O. The controller also supports HIGH and LOW fan speeds with exhaust fan output on 1- and

2-speed fan applications.

Type of valve			Options
		Electric Heat	Economizer	Baseboard
		Electric Heat	Economizer	Baseboard
Modulating	2 position	(1 or 2 stage)	Damper	Heat
ü	ü	ü	ü
ü	ü		ü	ü
ü	ü	ü	ü	ü
ü	ü		ü	ü
ü	ü		ü	ü
	ü1		ü	ü
	ü1		ü	ü
	ü1		ü	ü
NA	NA		ü
ü	ü		ü	ü
NA	NA	ü	ü	ü
NA	NA	ü	ü	ü

Configurable parameters

Rover service tool uses the unit type to determine and download

many other aspects of the unit configuration, such as the default analog input configuration, the default

binary input configuration, and the default binary output configuration.

Cooling source

qNone

qHydronic (main coil changeover)

qDedicated hydronic

qDX

Heating source

qNone

qHydronic

qDedicated hydronic

qSteam

qElectric heat

qHydronic (main coil changeover) + dedicated hydronic (auxiliary coil)

qHydronic (main coil changeover)

32	UV-SVP01A-EN

Configuration

Binary Outputs1

Table 10: Binary output summary

Binary output	Classroom unit ventilator		Valid range

J1-1	Fan high			NA
J1-2	Exhaust fan or none			NA
J1-3	Fan low			NA
J1-4	(Key)			NA
	Cooling valve open			NA
J1-5	Face bypass cool isolation valve		Normally open or normally closed2
	2-position cooling		Normally open or normally closed2

	DX			NA
J1-6	Cooling valve close			NA
J1-7	Face bypass damper open			NA
J1-8	Face bypass damper close			NA
	Heating valve open			NA
J1-9	Face bypass heat isolation valve		Normally open or normally closed2
	Electric heat stage 1			NA

	2-position heating		Normally open or normally closed 2
J1-10	Heating valve close			NA
	Electric heat stage 2			NA

J1-11	Outdoor air damper open			NA

J1-12	Outdoor air camper close			NA

TB4-1/TB4-2	Terminals	Output Rating	Load Energized		Load De-energized

Generic/baseboard heat output	TB4-1	12 VA	1 VAC RMS (typical)		24 VAC RMS (typical)
24 VAC	TB4-2

1.Trane’s Rover service tool uses the unit type to determine and download the proper default binary output configuration.

2.The normally open/closed configuration item refers to the inactive state of the controlled end device (such as an 2-position cooling valve output).

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Configuration

Binary Inputs1

Table 11: Binary input summary

Binary input	Configuration	Valid range

BI 1	Low coil temperature detection or not used	Normally open
BI 1	Low coil temperature detection or not used	Normally closed
		Normally closed
BI 2	Not used	Normally open
BI 2	Not used	Normally closed
		Normally closed
BI 3	Occupancy, generic, or not used	Normally open
BI 3	Occupancy, generic, or not used	Normally closed
		Normally closed
BI 4	Fan status or not used	Normally open
BI 4	Fan status or not used	Normally closed
		Normally closed

1. Trane Rover service tool uses the unit type to determine and download the proper default binary input configuration.

Analog Inputs1

Table 12: Analog input summary

	Analog input	Configuration

	Zone	Space temperature
	Set	Setpoint (hardwired)
	Fan	Fan switch
	AI 1	Entering water temperature
	AI 2	Discharge air temperature
	AI 3	Outdoor air temperature or generic temperature input
	AI 3	(Note 2)
		(Note 2)
	AI 4	Humidity, CO2 or generic
	AI 4	4-20mA input
		4-20mA input

Calibration range

+/- 10.0°F (0.1°F resolution)

1.Trane Rover service tool uses the unit type to determine and download the proper default analog input configuration.

2.Analog input 3 (AI 3) configured as generic temperature input does not affect unit operation. When configured, the Tracer™ ZN .520 Unit

Controller communicates the generic temperature value to Rover or Tracer Summit and displays it as generic temperature.

34	UV-SVP01A-EN

Configuration

Fan Configuration

Table 13: Fan configuration ranges

Fan configuration	Default

Fan operation in heating	Continuous
Fan operation in cooling	Continuous
Number of fan speeds	Varies 2
Configurable fan speed heating	Varies 2
Configurable fan speed cooling	Varies 2
Zone sensor fan switch	Enable

Valid range

Continuous (during occupied) Cycling with capacity (unoccupied)

1, 2

Off, low, high, auto

Disable or enable

End Device Configurations

Table 14: End device ranges

Main, cooling/changeover valve stroke time Entering water sampling

Auxiliary, heating valve stroke time

Outdoor air damper stroke time

Occupied outdoor air damper minimum position

Occupied standby outside air damper minimum position

Alternate minimum outside air damper position for low fan speed

Economizer enable temperature

Exhaust fan enable setpoint1

Face-and-bypass damper stroke time

	Default	Valid range

	Varies2	30 - 360 seconds
	Varies2	Disable or enable
	Varies2	30 to 360 seconds
	Varies2	30 to 360 seconds
	15%	0 to 100%
	15%	0 to 100%
	40%	0 to 100%
	55°F	30 to 70°F
	9%	0 to 100%, 101% disables the
	9%	exhaust fan
		exhaust fan
	65 seconds	30-360 seconds

1.The exhaust fan is energized when the outdoor air damper is equal to or greater than the exhaust fan enable point, and the exhaust fan is turned off when the outdoor air damper is 10% less than the exhaust fan enable point.

2.Varies with unit configuration.

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Configuration

Setpoints

Table 15: Setpoint defaults

Setpoint	Default	Valid range

Occupied heating setpoint	71°F	40 to 115° F
Occupied cooling setpoint	74°F	40 to 115° F
Occupied standby heating setpoint	67 °F	40 to 115° F
Occupied standby cooling setpoint	78 °F	40 to 115° F
Unoccupied heating setpoint	60°F	40 to 115° F
Unoccupied cooling setpoint	85°F	40 to 115° F
Heating setpoint low limit1	40°F	40 to 115° F
Cooling setpoint low limit1	40°F	40 to 115° F
Heating setpoint high limit 1	105°F	40 to 115° F
Cooling setpoint high limit 1	110°F	40 to 115° F
Thumbwheel setpoint	Enable	Disable or enable

1. The heating and cooling setpoint high and low limits only apply to the occupied and occupied standby setpoints and are never applied to the unoccupied setpoints.

Discharge Air Limits

Table 16: Discharge air limit ranges

	Default	Valid range

Low limit 1	38 °F	30 to 50°F
Control point high limit2	150 °F	38 to 150°F
Control point low limit2	45 °F	35 to 150°F

1.The low limit is the temperature at which the controller shuts down the unit to prevent the coil from freezing.

2.The control algorithm is limited to calculating this discharge air temperature based on capacity request.

Freeze Avoidance

Table 17: Freeze avoidance setpoint range

	Default	Valid range

Freeze avoidance setpoint1	40 °F	20 to 60° F

The controller disables freeze avoidance when the outdoor air temperature rises 3 °F above the freeze avoidance setpoint.

36	UV-SVP01A-EN

Configuration

Occupied Bypass Timer

Table 18: Bypass timer range

	Default	Valid range

Occupancy bypass timer1	120 Minutes	0 to 240 minutes
Occupancy bypass timer1	120 Minutes	(1 minute resolution)
		(1 minute resolution)
1. The occupied bypass timer is used for timed override applications.
Power-Up Control Wait
Table 19: Control wait timer

	Default	Valid range

Power up control wait (2 minutes)	120 seconds	Disable or enable
Maintenance Timers
Table 20: Maintenance timer range

	Default	Valid range

Maintenance timer	0	0 to 10,000 hours

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Location Identifier

Unit Identification Tag

The unit identification tag is factory mounted and provided for easy

identification of an installed unit. It contains model number, tagging, and location information.

The top portion of the unit identification tag remains permanently af-

fixed to the unit for identification purposes. The bottom portion of the tag provides pertinent informa-

tion that is removable to be placed on building plans or in “Appen- dix—Location Identifier” on

page68. This provides identification history about the unit’s location for quick reference.

These tags provide information about

q unit serial number;

qNID (neuron identification number)—The NID is similar to the serial number of the unit

but is specific to the identification of the Tracer ZN.520 unit controller circuit board; and

qunit location—The location identification is a customer defined, clear English description, of the unit’s

physical location. This is a 27 character description, including spaces, of the location. For

example, if the location identification for a unit is “Conference Room 101”, the

ZN.520, Rover (the Trane Comm 5 service tool), and Tracer Summit, will recognize this clear English description.

If location identification is not de-

fined, it will default to the unit serial number. This unit identification tag provides some information so

the user has multiple references to the unit. The blank location is provided for field modification in case

the unit is moved from the initial location.

Note: Fold and tear carefully along dashed removable line.

Figure 16: Unit identification tag

Winking

Winking a device causes the green

status LED on the device selected to blink at a rate of twice per second for approximately 10 seconds.

This feature is useful when a discrepancy in device location exists. As part of the troubleshooting pro-

cess, one person can WINK the device while another can observe the blinking and verify the device’s

physical location.

Important! If the status LED on

the ZN.520 does not blink, the device may not be communicating or it may not

be the device you selected according to the stored address.

A Tracer ZN.520 unit controller may be set to wink by

qholding the ON button on the zone sensor for 5 seconds

qusing Rover, Trane’s communication service tool

38	UV-SVP01A-EN

Unit Operation

Power-Up

When 24 VAC is initially applied to the controller, the following se-

quence of events occurs:

qGreen status LED turns ON.

qAll outputs are controlled OFF.

qThe controller reads input values to determine initial values.

qRandom-start timer expires (5 to 30 seconds).

qWhen POWER-UP CONTROL WAIT

is enabled, the controller waits

0-120 seconds (depending on configuration) to allow ample time for communicated control

data to input. If the controller does not receive communicated information, standalone control is assumed.

qAll modulating valves and dampers calibrate closed.

qNORMAL operation begins.

Occupancy

The valid occupancy modes for the Tracer ZN.520 controller are:

q OCCUPIED - Normal operating mode for occupied spaces or

daytime operation.

q UNOCCUPIED - Normal

operating mode for unoccupied spaces or nighttime operation.

q OCCUPIED STANDBY - Mode

used to reduce the heating and

cooling demands, while providing ventilation, during the occupied hours when the

space is vacant or unoccupied.

q OCCUPIED BYPASS -Used to

temporarily place the unit into the occupied operation.

The occupancy mode can be hardwired to the controller via the occupancy binary input or

communicated to the controller.

OCCUPIED mode

When the controller is in the OCCU- PIED mode, the unit attempts to

maintain the space temperature at the active occupied heating or cooling setpoint.

OCCUPIED mode is the default mode of the Tracer ZN.520 control-

ler.

UNOCCUPIED mode

When the controller is in the UN-

OCCUPIED mode, the unit attempts to maintain space temperature at the stored unoccupied heating or

cooling setpoint (i.e., configurable through Tracer Summit or the Rover service tool) regardless

of the presence of a hardwired or communicated setpoint. When the space temperature exceeds

the stored unoccupied setpoint, the controller brings on 100% of the primary heating or cooling ca-

pacity.

The UNOCCUPIED mode can be ini-

tiated through a hardwired signal to the occupancy binary input or by a communicated request.

OCCUPIED STANDBY mode

The OCCUPIED STANDBY mode al-

lows the unit to operate at a heat-

ing or cooling setpoint between the occupied and unoccupied setpoints to help maintain the envi-

ronment while decreasing energy consumption.

This mode decreases the ventilation for heating or cooling during brief periods of vacancy in the

space. Unit operation in this mode is similar to the occupied mode except for the different heating and

cooling setpoints and a different outside air damper position.

The OCCUPIED STANDBY mode is

initiated only when occupancy is communicated to the Tracer

ZN.520 controller and the hardwired signal to the occupancy input is calling for unoccupied

operation.

OCCUPIED BYPASS mode

The OCCUPIED BYPASS mode is

used to transition the unit from the

UNOCCUPIED mode to the OCCU-

PIED mode for a period of time from 0 to 4 hours (configurable

through Rover. Default=RUN). The controller can be placed in OCCU- PIED BYPASS mode by either com-

municating an occupancy request of BYPASS or by using the TIMED OVERRIDE (i.e., ON) button on the

Trane zone sensor.

ON and CANCEL Buttons

Some Trane zone sensors have ON and CANCEL buttons for timed override operation. Pressing the ON

button on the zone sensor when the unit is in the UNOCCUPIED mode initiates the OCCUPIED BY-

PASS mode and initializes the bypass timer. The CANCEL button is used to send the unit back into UN-

OCCUPIED mode before the bypass timer has expired.

The ON button may also be used for the unit identification or the “WINK” feature. (See “Winking”

on page38.for more information.)

When the Tracer ZN.520 controller is connected to a Tracer Summit

system or the Rover service tool, the ON button may be used in place of the service pin for easy unit

identification.

Heating And Cooling Changeover Logic

The Tracer™ ZN.520 Unit Control-

ler can receive communicated requests for heating or cooling operation. The communicated

variable nviApplicMode is used to communicate the requests for the controller's operating mode based

on the following values:

0 = Auto (mode determined by controller)

1 = Heat (uses heating setpoints)

2= Morning Warm-up

3= Cool (uses cooling setpoints)

UV-SVP01A-EN

Unit Operation

4 = Night Purge (air

changeover) not supported

5= Pre-cool (morning cool down)

6= Off (no unit operation allowed)

7= Test (special test mode)

8= Emergency Heat not supported

9 = Fan Only (no heating or cooling allowed)

All other enumerations will be interpreted as Auto.

As the controller automatically determines its heating or cooling mode, it changes from cool to heat

or from heat to cool, while the error (integrated over time between the active setpoint and the space tem-

perature) is (900°FhSec). Integration only begins once the heating and cooling capacity is equal to 0%

or the discharge air temperature is being limited by the discharge air temperature control limits.(See

Figure 17: “Heat/Cool Changeover logic”).

Figure 17: Heat/Cool Changeover logic

If the measured space temperature is 69 °F and the active cooling set-

point is 72 °F, the error between the space temperature and the setpoint is three degrees. If the same

error exists for one minute (60 seconds), the integration term is

(3 °Fh60 Sec) or (180 °Fh Sec).

The Tracer™ ZN.520 Unit Controller changes from heating to cool-

ing and cooling to heating when the integration term exceeds (900 °FhSec). Along with satisfy-

ing the integration for heating and cooling changeover, the measured space temperature must fall out-

side the setpoint range. This means the space temperature must be greater than the active

cooling setpoint or lower than the active heating setpoint.

Example: If the cooling setpoint is 75 °F and the heating setpoint

70 °F, any space temperature greater than 75 °F or less than 70 °F is outside the setpoint range.

Once the integration term is satisfied and the space temperature is

outside the setpoint range, the controller changes modes. However, before the unit's heating or

cooling capacity ramps up, the controller checks to make sure it is capable of heating or cooling.

For some units, heating and cooling capability exists with local re-

sources such as electric heat or

compressors. For these units, central heating or cooling plan opera-

tion is not required for heating or cooling because they are capable of providing their own local heat-

ing or cooling.

For 2-pipe changeover and 4-pipe

changeover units with hydronic capacity, heating and cooling is provided through hydronic. For those

hydronic, central heating or cooling plant operation is required for the unit to deliver heating or cool-

ing. To determine whether the central plant is providing the desired water temperature, an entering

water temperature sensor (either hardwired or communicated) must be present.

40	UV-SVP01A-EN

Unit Operation

The entering water must be five

degrees or more above the space temperature to allow hydronic heating, and five degrees or more

below the space temperature to allow hydronic cooling.

If the desired water temperature is available, the unit begins normal heating and cooling operation. If

the measured entering water temperature is not adequate for the desired heating or cooling, the

controller begins the entering water temperature sampling logic.

The Tracer™ ZN.520 Unit Controller operates the modulating valves and dampers based on a heating

or cooling capacity calculated by the control algorithm. The control algorithm calculates the heating or

cooling capacity based on the measured space temperature, the active setpoint and the discharge

air temperature. When the measured space temperature is within the active heating and cooling set-

points, the heating and cooling capacity approaches zero.

Cooling Operation

During the COOLING mode, the Tracer ZN.520 controller attempts

to maintain the space temperature at the active cooling setpoint. Based on the controller’s occupan-

cy mode, the active cooling setpoint is one of the following:

qOccupied cooling setpoint

qOccupied standby cooling setpoint

qUnoccupied cooling setpoint

The controller uses the measured space temperature, the active

cooling setpoint, and discharge air temperature along with the control algorithm to determine the re-

quested cooling capacity of the unit (0-100%). The outputs are controlled based on the unit configu-

ration and the requested cooling capacity.

Heating Operation

During the HEATING mode, the Tracer ZN.520 controller attempts

to maintain the space temperature at the active heating setpoint. Based on the controller’s occupan-

cy mode, the active heating setpoint is one of the following:

qOccupied heating setpoint

qOccupied standby heating setpoint

qUnoccupied heating setpoint

The controller uses the measured space temperature, the active

heating setpoint, and discharge air temperature along with the control algorithm to determine the re-

quested heating capacity of the unit (0-100%). The outputs are controlled based on the unit configu-

ration and the requested heating capacity.

Fan Operation

For multiple fan speed applications, the Tracer ZN.520 controller

allows separate default fan speeds to be configured for heating and cooling modes. When the fan

mode switch is in the AUTO position or no hardwired input exists, the fan operates at the configured

default fan speed (i.e, HIGH).

The Tracer ZN.520 controller also

allows the default fan speed to be configured as AUTO. When the fan speed switch is in the AUTO posi-

tion and the default fan speed is configured as AUTO, the unit may change fan speeds based on the

requested heating or cooling capacity. In this mode, the unit fan will operate at LOW speed until the

requested capacity requires HIGH fan speed operation to maintain space comfort.

The fan mode request can be either hardwired or communicated

to the Tracer ZN.520 controller. When both are present, the communicated request has priority

over the hardwired input. Additional flexibility in the controller al-

lows the fan speed switch to be

disabled. When this occurs, the unit will operate at the default fan speed unless a communicated re-

quest is present.

During OCCUPIED, OCCUPIED

STANDBY, and OCCUPIED BYPASS

modes, the fan will normally operate continuously at the appropri-

ate fan speed. The fan will only be OFF in these modes when the MAN- UAL OUTPUT TEST has been initiat-

ed, a latching diagnostic is present, or the communicated or hardwired fan speed is OFF. (See

“Manual Output Test” on page48.for more information.)

During the UNOCCUPIED mode, the unit fan is controlled OFF. When capacity is required to maintain the

unoccupied heating or cooling setpoint, the unit fan is controlled to high speed regardless of a hard-

wired or communicated fan speed.

Table 21: Absolute two-speed fan switch points

Fan Speed	Absolute
Change	Temperature Error
Low to High	2.00	°F
High to Low	1.25	°F

Fan Off Delay

When a heating output is controlled off, the Tracer™ ZN.520

Unit Controller automatically holds the fan on for an additional 30 seconds. This 30-second delay

gives the fan time to blow off any residual heat from the heating source, such as a steam coil. When

the unit is heating, the fan off delay is normally applied to control the fan; otherwise, the fan off de-

lay does not apply.

Fan Start On High Speed

On a transition from off to any oth-

er fan speed, the Tracer™ ZN.520 Unit Controller automatically starts the fan on high speed and

runs the fan at high speed for 0.5

UV-SVP01A-EN

Unit Operation

seconds. This provides the ample torque required to start all fan motors from the off position.

Exhaust fan/damper operation

This binary point is a shared point with medium fan speed. For this

point to be used for exhaust control, the controller must be configured for a 1- or 2-speed fan. The

exhaust fan/damper is coordinated with the unit fan and outdoor damper operation. The exhaust

output is energized only when the unit fan is operating and the outdoor damper position is greater

than or equal to the configurable exhaust enable point. The exhaust fan output is disabled when the

outdoor air damper position drops 10% below the exhaust enable point. If the enable point is less

than 10%, the unit turns on at the enable point and off at 0.

Valve Operation

Modulating Valves

The Tracer ZN.520 controller supports one or two modulating valves for hydronic heating and

cooling operation. The main valve/ coil is used for cooling only, heat/ cool changeover (2-pipe applica-

tions), or cooling (4-pipe applications). The auxiliary valve/coil provides heating in 4-pipe and

heating only applications.

At power-up, the Tracer ZN.520

controller drives the modulating valves to the closed position. The controller calibrates to the full

closed position by overdriving the actuator 135%. Whenever the controller requests a valve position of

zero or 100%, the controller overdrives the actuator 135% regardless of the current valve position.

Face-and-Bypass

Isolation Valves

Face-and-bypass units may use

isolation valves to prevent unwanted water flow in the coil. This eliminates problems such as radiant

heat or excessive condensate in 2- pipe systems.

In 4-pipe applications, the isolation valves are used to prevent conflicting capacities within the unit.

Face-and-Bypass

Damper Operation

Note: The Face-and-bypass actuator is located in the right-

hand end pocket of the classroom unit ventilator.

The Tracer ZN.520 controller actuates a face-and- bypass damper to modulate a percentage of air to the

face of the coil to maintain space comfort. When a requested capacity is present, the unit modulates

the damper to allow more air to the face of the coil. An averaging sensor is used on the discharge air to

provide accurate capacity control.

Figure 18: Horizontal unit with face-and-bypass damper option.

42	UV-SVP01A-EN

Unit Operation

Figure 19: Vertical unit with face-and- bypass damper operations

Upon power-up, the controller cal-

ibrates the face-and-bypass damper to the full bypass position by overdriving the damper actuator.

During normal operation, whenever the Tracer ZN.520 controller generates a face-and-bypass

damper position request of zero or 100%, the unit calibrates the actuator by overdriving the damper ac-

tuator 135%.

Entering Water

Temperature Sampling

Units with 4-pipe changeover and 2-pipe changeover require an en-

tering water temperature to determine if the appropriate water temperature is present for the re-

quested mode (heating or cooling). This temperature may be communicated in an ICS system or

hardwired to the Tracer ZN.520

controller for standalone applications.

When a unit uses 2-way modulat-

ing valves, it is possible for the water near the entering water temperature sensor to migrate to-

wards ambient temperature. The Tracer ZN.520 controller has a water sampling feature for these ap-

plications. When the sensed water temperature is not sufficient for the requested heat/cool mode

(5°F above the zone temperature for heating or 5°F below the zone temperature for cooling), the con-

troller drives the valve fully open. The controller then monitors the water temperature until the appro-

priate temperature is sensed or until the three minute time limit expires. If the water temperature is

acceptable for the requested capacity, the unit continues normal operation. If the three minute tim-

er expires and the water temperature is still unsuitable, the unit closes the valve and waits one

hour before invoking the sampling feature again.

Table 22: Water assumption chart

	Unit Configuration	Temperature
	Unit Configuration	Assumed1
		Assumed1
	2-pipe Heating valve	Hot
	2-pipe cooling valve	Cold

2-pipe H/C valve with

auto changeover enabled Hot

2-pipe H/C valve with

auto changeover Cold disabled

1. Assumption based on absence of a valid entering water temperature

Modulating Outdoor Air Operation

The Tracer ZN.520 controller oper-

ates a modulating (3-wire floating) outdoor air damper actuator according to the effective occupan-

cy, outdoor air temperature, space temperature, effective setpoint, discharge air temperature, and

discharge air temperature set-

point. Default minimum damper

positions are provided and can be changed for occupied and occupied standby modes, or for low

speed operation. The controller can also receive a communicated outdoor air damper minimum po-

sition from Tracer Summit. A communicated minimum position from Tracer Summit has priority

over all configured setpoints.

During the OCCUPIED mode the

outdoor air damper will always be controlled to the effective minimum position unless ASHRAE Cy-

cle I, ASHRAE Cycle II, or economizing modes are active.

Figure 20: OA/RA actuator mounting for the vertical unit ventilator

Figure 21: Figure 2: OA/RA actuator mounting for the horizontal unit ventilator

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Unit Operation

Automatic Outdoor Air

Damper Adjustment

The Tracer ZN.520 controller is ca-

pable of using different minimum outdoor air damper positions for high and low fan speeds, which are

configurable. This allows the ventilation rate to be maintained when switching between fan speeds.

Note: The typical reduction in airflow between high and low

fan speeds is 25%, however, if precise control is desired, an air balancer should be

consulted.

Economizer

Operation

Note: When there is a request

for 0% or 100% actuator position, the actuator will overdrive the actuator 135% to

help maintain calibration.

With a valid outdoor air tempera-

ture (hardwired or communicated), Tracer ZN.520 uses the modulating economizer damper as the highest

priority source of cooling.

The controller initiates the econo-

mizer function if the outdoor air temperature is cold enough to be used for free cooling capacity. If

the outdoor air temperature is less than the economizer enable setpoint (absolute dry bulb), the con-

troller modulates the outdoor air damper between the minimum position and 100% to control the

amount of cooling capacity. When the outdoor air temperature rises 5°F above the economizer enable

setpoint, the outdoor air damper returns to its minimum position and mechanical cooling is initiated.

ASHRAE Cycle I

ASHRAE Cycle I admits 100% outdoor air except during the warm up

cycle or the unoccupied mode. To set up the Tracer ZN.520 controller for ASHRAE Cycle I conformance,

set the occupied outdoor air damper minimum position to 100%.

ASHRAE Cycle II

The Tracer ZN.520 controller con-

forms to ASHRAE Cycle II by allowing the modulating outdoor air damper to maintain a minimum

position during the occupied mode unless economizing is enabled or the space temperature falls more

than 3°F below the effective setpoint.

If the space temperature falls more than 2°F below the setpoint, the outdoor air damper will begin to

close. When the space temperature hits 3°F below the setpoint, the outdoor air damper is completely

closed.

Figure 22: ASHRAE cycle 2

DX Operation

Tracer ZN.520 supports direct expansion (DX) compressor operation for cooling only.

The controller does not allow both the DX compressor and economiz-

er to operate at the same time. This prevents problems where the entering air temperature is too low

for the evaporator coil to operate as designed.

Tracer ZN.520 also includes a fixed minimum on/off time of 3 minutes for compressor operation to pre-

vent short cycling of the compressor.

Electric Heat Operation

The Tracer ZN.520 controller supports 1 or 2 stages of electric heat

control.

To control space temperature,

electric heat is cycled to control the discharge air temperature. The rate of cycling is dependent on the load

in the space and the temperature of the incoming fresh air.

Baseboard Heat Operation

The Tracer ZN.520 controller can be configured to support one stage of baseboard heat. A 2 position

valve or an electric heat contactor will be energized at 2.5°F below the effective heating setpoint. The

baseboard heat is de-energized at 1°F below the effective heating setpoint.

The unit will provide heating capacity as required regardless of the

presence of baseboard heat. If the unit can not maintain the space temperature, the baseboard heat

will come on as a secondary stage.

If baseboard heat is to be used as

the primary source of heating, the discharge air high limit should be set to a moderate temperature.

This will allow the ventilation air to be tempered and avoid a “drafty” feeling. The baseboard heat will

then operate as the heating capacity for the space.

In the UNOCCUPIED mode, the baseboard heat and unit heating capacity are brought on simulta-

neously as needed to maintain the unoccupied setpoint.

Exhaust Fan

Operation

The exhaust fan is coordinated with the unit fan and outdoor air damper operation. The exhaust fan

output is energized only when the unit fan is operating and the outdoor air damper position is greater

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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 enable 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 information see, Manual Output

Test, on page 48 for more information.)

Water Valve Override

To enable quicker water balancing, 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 remain 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 status 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 outputs 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 operation. If the device does not indicate fan operation after 1

minute, a unit shutdown is initiated, 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 controller compares the fan run time against an adjustable fan run hour

limit and recommends unit maintenance as required.

The Rover service tool is used to edit the maintenance required setpoint 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 diagnostic 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 reheat position; and the space rela-

tive humidity setpoint is valid.

The controller starts dehumidify-

ing the space when the space humidity exceeds the humidity setpoint. The controller continues

to dehumidify until the sensed humidity falls below the setpoint minus the relative humidity offset.

The controller uses the cooling and reheat coils simultaneously to

dehumidify the space. When dehumidifying, 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 operate as continuous. The unit will remain in the DEFROST mode until

the senor resets at 48°F. The unit will return to NORMAL operation after 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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Unit Operation

OFF due to a safety or command. The controller enters the FREEZE AVOIDANCE mode when an out-

door air temperature is present (communicated or hardwired) and it is below the freeze avoidance set-

point (configurable). The controller disables freeze avoidance when the outdoor air temperature rises

3°F above the freeze avoidance setpoint.

When the controller is in the freeze avoidance mode:

qAll water valves are driven open to allow water flow through the coil

qFan is OFF

qFace-and-bypass damper (when present) is in full BYPASS

qDX and electric heat are OFF

MORNING WARM-UP

The Tracer ZN.520 controller keeps

the modulating outdoor air damper closed anytime during the OCCU- PIED mode when the space

temperature is 3°F or more below the heating setpoint.

Figure 23: Simple data sharing application

The damper remains closed indefinitely during morning warm-up until the space temperature is with-

in 2°F of the effective heating setpoint. The unit runs at full capacity until setpoint is met.

COOL-DOWN

The Tracer ZN.520 controller keeps the modulating outdoor air damp-

er closed for up to one hour at every transition from UNOCCUPIED to OCCUPIED mode when the space

temperature is 3°F or more above the cooling setpoint.

The damper remains closed during cool-down until the space temperature is within 2°F of the effective

cooling setpoint. The unit runs at full capacity until setpoint is met.

Data Sharing—LonWorks

Tracer ZN.520 allows peer-to-peer data communication through the use of LonWork’s technology. Data

such as space temperature setpoint, occupancy, etc. can be shared from a master controller to

a peer controller over a twisted pair of communication wire with or without the presence of a front end

building management system.

(See Figure 23: “Simple data sharing application”) This ability al-

lows units to operate with the same data to prevent conflicting control.

Data sharing is established through the use of “bindings”.

Bindings are set up through the Rover service tool.

The Tracer ZN.520 controller includes a network variable for master/slave operation. This variable

includes all of the information required for the slave units to operate with master controller. (See

Figure 24: “More complex data sharing application”)

For more information on establishing bindings, see the Rover service tool manual. For a complete listing

on shared points see “Appendix— Data Lists” on page64.

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Unit Operation

Figure 24: More complex data sharing application

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Unit Operation

Power-Up

When 24 VAC is initially applied to the controller, the following se-

quence of events occurs:

qGreen status LED turns ON.

qAll outputs are controlled OFF.

qThe controller reads input values to determine initial values.

qRandom-start timer expires (5 to 30 seconds).

qWhen POWER-UP CONTROL WAIT

is enabled, the controller waits

0-120 seconds (depending on configuration) to allow ample time for communicated control

data to input. If the controller does not receive communicated information, standalone control is assumed.

qAll modulating valves and dampers calibrate closed.

qNORMAL operation begins.

Occupancy

The valid occupancy modes for the Tracer ZN.520 controller are:

q OCCUPIED - Normal operating mode for occupied spaces or

daytime operation.

q UNOCCUPIED - Normal

operating mode for unoccupied spaces or nighttime operation.

q OCCUPIED STANDBY - Mode

used to reduce the heating and

cooling demands, while providing ventilation, during the occupied hours when the

space is vacant or unoccupied.

q OCCUPIED BYPASS -Used to

temporarily place the unit into the occupied operation.

The occupancy mode can be hardwired to the controller via the occupancy binary input or

communicated to the controller.

OCCUPIED mode

When the controller is in the OCCU- PIED mode, the unit attempts to

maintain the space temperature at the active occupied heating or cooling setpoint.

OCCUPIED mode is the default mode of the Tracer ZN.520 control-

ler.

UNOCCUPIED mode

When the controller is in the UN-

OCCUPIED mode, the unit attempts to maintain space temperature at the stored unoccupied heating or

cooling setpoint (i.e., configurable through Tracer Summit or the Rover service tool) regardless

of the presence of a hardwired or communicated setpoint. When the space temperature exceeds

the stored unoccupied setpoint, the controller brings on 100% of the primary heating or cooling ca-

pacity.

The UNOCCUPIED mode can be ini-

tiated through a hardwired signal to the occupancy binary input or by a communicated request.

OCCUPIED STANDBY mode

The OCCUPIED STANDBY mode al-

lows the unit to operate at a heat-

ing or cooling setpoint between the occupied and unoccupied setpoints to help maintain the envi-

ronment while decreasing energy consumption.

This mode decreases the ventilation for heating or cooling during brief periods of vacancy in the

space. Unit operation in this mode is similar to the occupied mode except for the different heating and

cooling setpoints and a different outside air damper position.

The OCCUPIED STANDBY mode is

initiated only when occupancy is communicated to the Tracer

ZN.520 controller and the hardwired signal to the occupancy input is calling for unoccupied

operation.

OCCUPIED BYPASS mode

The OCCUPIED BYPASS mode is

used to transition the unit from the

UNOCCUPIED mode to the OCCU-

PIED mode for a period of time from 0 to 4 hours (configurable

through Rover. Default=RUN). The controller can be placed in OCCU- PIED BYPASS mode by either com-

municating an occupancy request of BYPASS or by using the TIMED OVERRIDE (i.e., ON) button on the

Trane zone sensor.

ON and CANCEL Buttons

Some Trane zone sensors have ON and CANCEL buttons for timed override operation. Pressing the ON

button on the zone sensor when the unit is in the UNOCCUPIED mode initiates the OCCUPIED BY-

PASS mode and initializes the bypass timer. The CANCEL button is used to send the unit back into UN-

OCCUPIED mode before the bypass timer has expired.

The ON button may also be used for the unit identification or the “WINK” feature. (See “Winking”

on page38.for more information.)

When the Tracer ZN.520 controller is connected to a Tracer Summit

system or the Rover service tool, the ON button may be used in place of the service pin for easy unit

identification.

Heating And Cooling Changeover Logic

The Tracer™ ZN.520 Unit Control-

ler can receive communicated requests for heating or cooling operation. The communicated

variable nviApplicMode is used to communicate the requests for the controller's operating mode based

on the following values:

0 = Auto (mode determined by controller)

1 = Heat (uses heating setpoints)

2= Morning Warm-up

3= Cool (uses cooling setpoints)

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Unit Operation

4 = Night Purge (air

changeover) not supported

5= Pre-cool (morning cool down)

6= Off (no unit operation allowed)

7= Test (special test mode)

8= Emergency Heat not supported

9 = Fan Only (no heating or cooling allowed)

All other enumerations will be interpreted as Auto.

As the controller automatically determines its heating or cooling mode, it changes from cool to heat

or from heat to cool, while the error (integrated over time between the active setpoint and the space tem-

perature) is (900°FhSec). Integration only begins once the heating and cooling capacity is equal to 0%

or the discharge air temperature is being limited by the discharge air temperature control limits.(See

Figure 17: “Heat/Cool Changeover logic”).

Figure 17: Heat/Cool Changeover logic

If the measured space temperature is 69 °F and the active cooling set-

point is 72 °F, the error between the space temperature and the setpoint is three degrees. If the same

error exists for one minute (60 seconds), the integration term is

(3 °Fh60 Sec) or (180 °Fh Sec).

The Tracer™ ZN.520 Unit Controller changes from heating to cool-

ing and cooling to heating when the integration term exceeds (900 °FhSec). Along with satisfy-

ing the integration for heating and cooling changeover, the measured space temperature must fall out-

side the setpoint range. This means the space temperature must be greater than the active

cooling setpoint or lower than the active heating setpoint.

Example: If the cooling setpoint is 75 °F and the heating setpoint

70 °F, any space temperature greater than 75 °F or less than 70 °F is outside the setpoint range.

Once the integration term is satisfied and the space temperature is

outside the setpoint range, the controller changes modes. However, before the unit's heating or

cooling capacity ramps up, the controller checks to make sure it is capable of heating or cooling.

For some units, heating and cooling capability exists with local re-

sources such as electric heat or

compressors. For these units, central heating or cooling plan opera-

tion is not required for heating or cooling because they are capable of providing their own local heat-

ing or cooling.

For 2-pipe changeover and 4-pipe

changeover units with hydronic capacity, heating and cooling is provided through hydronic. For those

hydronic, central heating or cooling plant operation is required for the unit to deliver heating or cool-

ing. To determine whether the central plant is providing the desired water temperature, an entering

water temperature sensor (either hardwired or communicated) must be present.

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Unit Operation

The entering water must be five

degrees or more above the space temperature to allow hydronic heating, and five degrees or more

below the space temperature to allow hydronic cooling.

If the desired water temperature is available, the unit begins normal heating and cooling operation. If

the measured entering water temperature is not adequate for the desired heating or cooling, the

controller begins the entering water temperature sampling logic.

The Tracer™ ZN.520 Unit Controller operates the modulating valves and dampers based on a heating

or cooling capacity calculated by the control algorithm. The control algorithm calculates the heating or

cooling capacity based on the measured space temperature, the active setpoint and the discharge

air temperature. When the measured space temperature is within the active heating and cooling set-

points, the heating and cooling capacity approaches zero.

Cooling Operation

During the COOLING mode, the Tracer ZN.520 controller attempts

to maintain the space temperature at the active cooling setpoint. Based on the controller’s occupan-

cy mode, the active cooling setpoint is one of the following:

qOccupied cooling setpoint

qOccupied standby cooling setpoint

qUnoccupied cooling setpoint

The controller uses the measured space temperature, the active

cooling setpoint, and discharge air temperature along with the control algorithm to determine the re-

quested cooling capacity of the unit (0-100%). The outputs are controlled based on the unit configu-

ration and the requested cooling capacity.

Heating Operation

During the HEATING mode, the Tracer ZN.520 controller attempts

to maintain the space temperature at the active heating setpoint. Based on the controller’s occupan-

cy mode, the active heating setpoint is one of the following:

qOccupied heating setpoint

qOccupied standby heating setpoint

qUnoccupied heating setpoint

The controller uses the measured space temperature, the active

heating setpoint, and discharge air temperature along with the control algorithm to determine the re-

quested heating capacity of the unit (0-100%). The outputs are controlled based on the unit configu-

ration and the requested heating capacity.

Fan Operation

For multiple fan speed applications, the Tracer ZN.520 controller

allows separate default fan speeds to be configured for heating and cooling modes. When the fan

mode switch is in the AUTO position or no hardwired input exists, the fan operates at the configured

default fan speed (i.e, HIGH).

The Tracer ZN.520 controller also

allows the default fan speed to be configured as AUTO. When the fan speed switch is in the AUTO posi-

tion and the default fan speed is configured as AUTO, the unit may change fan speeds based on the

requested heating or cooling capacity. In this mode, the unit fan will operate at LOW speed until the

requested capacity requires HIGH fan speed operation to maintain space comfort.

The fan mode request can be either hardwired or communicated

to the Tracer ZN.520 controller. When both are present, the communicated request has priority

over the hardwired input. Additional flexibility in the controller al-

lows the fan speed switch to be

disabled. When this occurs, the unit will operate at the default fan speed unless a communicated re-

quest is present.

During OCCUPIED, OCCUPIED

STANDBY, and OCCUPIED BYPASS

modes, the fan will normally operate continuously at the appropri-

ate fan speed. The fan will only be OFF in these modes when the MAN- UAL OUTPUT TEST has been initiat-

ed, a latching diagnostic is present, or the communicated or hardwired fan speed is OFF. (See

“Manual Output Test” on page48.for more information.)

During the UNOCCUPIED mode, the unit fan is controlled OFF. When capacity is required to maintain the

unoccupied heating or cooling setpoint, the unit fan is controlled to high speed regardless of a hard-

wired or communicated fan speed.

Table 21: Absolute two-speed fan switch points

Fan Speed	Absolute
Change	Temperature Error
Low to High	2.00	°F
High to Low	1.25	°F

Fan Off Delay

When a heating output is controlled off, the Tracer™ ZN.520

Unit Controller automatically holds the fan on for an additional 30 seconds. This 30-second delay

gives the fan time to blow off any residual heat from the heating source, such as a steam coil. When

the unit is heating, the fan off delay is normally applied to control the fan; otherwise, the fan off de-

lay does not apply.

Fan Start On High Speed

On a transition from off to any oth-

er fan speed, the Tracer™ ZN.520 Unit Controller automatically starts the fan on high speed and

runs the fan at high speed for 0.5

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Unit Operation

seconds. This provides the ample torque required to start all fan motors from the off position.

Exhaust fan/damper operation

This binary point is a shared point with medium fan speed. For this

point to be used for exhaust control, the controller must be configured for a 1- or 2-speed fan. The

exhaust fan/damper is coordinated with the unit fan and outdoor damper operation. The exhaust

output is energized only when the unit fan is operating and the outdoor damper position is greater

than or equal to the configurable exhaust enable point. The exhaust fan output is disabled when the

outdoor air damper position drops 10% below the exhaust enable point. If the enable point is less

than 10%, the unit turns on at the enable point and off at 0.

Valve Operation

Modulating Valves

The Tracer ZN.520 controller supports one or two modulating valves for hydronic heating and

cooling operation. The main valve/ coil is used for cooling only, heat/ cool changeover (2-pipe applica-

tions), or cooling (4-pipe applications). The auxiliary valve/coil provides heating in 4-pipe and

heating only applications.

At power-up, the Tracer ZN.520

controller drives the modulating valves to the closed position. The controller calibrates to the full

closed position by overdriving the actuator 135%. Whenever the controller requests a valve position of

zero or 100%, the controller overdrives the actuator 135% regardless of the current valve position.

Face-and-Bypass

Isolation Valves

Face-and-bypass units may use

isolation valves to prevent unwanted water flow in the coil. This eliminates problems such as radiant

heat or excessive condensate in 2- pipe systems.

In 4-pipe applications, the isolation valves are used to prevent conflicting capacities within the unit.

Face-and-Bypass

Damper Operation

Note: The Face-and-bypass actuator is located in the right-

hand end pocket of the classroom unit ventilator.

The Tracer ZN.520 controller actuates a face-and- bypass damper to modulate a percentage of air to the

face of the coil to maintain space comfort. When a requested capacity is present, the unit modulates

the damper to allow more air to the face of the coil. An averaging sensor is used on the discharge air to

provide accurate capacity control.

Figure 18: Horizontal unit with face-and-bypass damper option.

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