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VariTrac

Changeover Bypass VAV

VAV-PRC003-ENJune 2004


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VAV-PRC003-EN 2004 American Standard, Inc. All rights reserved


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Comfort Made SimpleTrane has a long history of innovativeleadership in variable air volume (VAV)technology. Trane introduced the:

first fan-powered VAV unit

first factory-commissioned DDCcontroller

first preprogrammed VAV controllerdesigned specifically for VAVapplications

Trane is now the leading manufacturerof VAV terminal units and VAV-relatedproducts in the world.

The introduction of VariTrac in 1989brought VAV controls expertise into thechangeover bypass zoning market.

Trane is committed to continuousproduct improvement and nowintroduces a new generation of VariTraccontrols. This latest generation retainsthe functionality of the original VariTracsystem with exciting newenhancements, utilizing the best oftodays technology.

Figure 1. The VariTrac CCP maximizessystem efficiency and reliability bycoordinating the components of thechangeover-bypass system

Selected enhancements of the newVariTrac product are listed below.

A new central control panel (CCP) withimproved system temperature andpressure control functions

An optional touch-screen operatordisplay for the CCP with built-intime clock for easier system setup andcontrol

A communicating bypass controllerallows duct pressure and ducttemperature to communicate to thesystem via a twisted shielded wire pair,thus eliminating costly home-runwiring

The next generation UCM zonecontroller allows CO

2and occupancy

sensor inputs

A digital display zone sensor forsimplified occupant control

VariTrac ProductEnhancements

Advanced Control Options

Some of the VariTrac intelligent system

control features are listed below. CO

2-based demand control ventilation

resets the position of the HVAC unitventilation air damper when zone CO

2

levels rise

Zone-based HVAC unit control operatesheating and cooling only when zonedemand exists

Discharge air control to avoid extremesupply air conditions and maximizeequipment life and occupant comfort

A simplified system-balancing processis available via PC software or thetouch-screen interface

Global zone temperature setpoint limitssimplify startup, commissioning, andoperator control

Figure 2. The VariTrac CCP withoptional touch-screen interfacesimplifies system operation withintuitive icon-driven design

The Changeover BypassVAV Comfort Advantage

Packaged unitary systems offer apopular and cost-effective method ofsupplying conditioned air to lightcommercial buildings. These systemscommonly have a constant-volume fanwith a fixed outside air damper and asingle thermostat. While a constantvolume system may meet the overallthermal requirements of the space, onlya single thermostat is available. This

system may be insufficient in multiple-space applications with independentthermal load requirements.

Changeover bypass systems use thepracticality and cost effectiveness ofconstant volume unitary componentslike packaged rooftop units, splitsystems, or water-source heat pumps,and simply add dampers and a centralcontrol panel to coordinate thecomponents. This allows up to24 individual sensors (thermostats) forindependent temperature control.

Introduction


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Features andBenefits

OverviewChangeover-bypass VAV is a comfortsystem developed for light commercialapplications. A changeover-bypass VAVsystem responds to changing coolingor heating requirements by varying thequantity or volume of air delivered toeach zone. Each zone has a thermostatfor individual comfort control. AnHVAC unit delivers a constant volumeof air to the system. As the volume ofair required by the zone changes,

excess supply air is directed to thereturn duct via a bypass duct anddamper. (See Figure 3 for typicalsystem components.)

A changeover-bypass VAV systemcombines the comfort benefits of VAVwith the cost effectiveness andsimplicity of packaged, constant-volume unitary equipment.

How the System Works

A changeover-bypass VAV systemcommonly consists of an HVAC unitwith a constant-volume supply fan, anddirect-expansion (DX) cooling. Thiscombined system has the ability tochange to the heating mode orcooling mode, depending on individualzone comfort requirements. A heatingcoil or a gas-fired heater and an outsideair damper are possible options.

Atemperature sensor in each zone

communicates information to anelectronic controller on the VAVterminal unit. The controller thenmodulates the zone damper open orclosed, supplying heating or cooling airto the zone.

The HVAC unit delivers a constantvolume of supply air to the system. Inorder to maintain duct static pressure, abypass duct and damper are requiredto bypass (detour) air not required inthe zones.

The VAV terminal unit controllercommunicates zone temperatureinformation to a central control panel(CCP). The CCP also gathersinformation from the system, includingduct static pressure and supply-airtemperature. The CCP determines zoneheating or cooling needs using voting(or polling) logic, then requests heatingor cooling from the HVAC unit. The CCPdirects the HVAC unit to provideventilation air to high-occupancy areas(demand control ventilation) or free-

cooling when the outside airtemperature falls below thetemperature setpoint (economizercontrol).

Auto Changeover

Auto changeover refers to the abilityof the system to automatically changebetween the heating and coolingmodes.

In a changeover-bypass VAV system,the CCP determines whether the HVACunit should heat or cool by polling thetemperature of the individual zones. Itthen compares the zone temperatures

to the space temperature setpoints. Ifthe supply air does not meet the criteriafor the heat or cool mode called for, theCCP sends a signal to the HVAC unit tochange the system to the oppositemode.


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VAV-PRC003-EN 7

Figure 6. VariTrac central control panelwith optional operator display


Central Control Panel

The VariTrac central control panel (CCP)serves as the central source ofcommunications and decisionmakingbetween the individual zones and theHVAC unit. The CCP determines systemheating and cooling modes andcoordinates the system supply airtemperature and static pressure tosatisfy building thermal loadconditions. Inputs to the CCP include24VAC power and communication

wiring to the zone dampers and bypasscontrol.

Binary inputs consist of priorityshutdown and occupied/unoccupiedmodes. Heating, cooling, and the HVACunit fan on split systems and non-TraneHVAC units can be controlled throughbinary outputs on an accessory relayboard. If a Trane rooftop air conditionerwith factory-installed electroniccontrols is used, the CCP can controlheating, cooling, and the fan with a two-wire communication link tied to aninterface board mounted in the rooftop.It can also display status information

from the electronic controller in therooftop. (See Figure 4.)

Optional Operator DisplayThe optional operator display is abacklit, liquid crystal display with touch-screen programming capability.

The operator can access system andzone status through the display andperform basic setup of zone VAV UCMsand CCP system operating parameters.The display allows an installer tocommission a VariTrac system without

using a PC. The operator display has aseven-day time clock for stand-alonescheduling capability.

Operator Display Feature Summary

Backlit LCD touch-screen display foreasy operator interface

Combination of icon- and menu-basednavigation provides intuitive operation

Provides a level of control for the dailyoperator, and a second level forcommissioning and service

Three levels of security are available toprotect system settings

Seven-day time clock for stand-alone,time-of-day scheduling

CCP Feature Summary

Communicates with up to 24 VAV unitcontrol modules (UCMs)

Makes optimal heating and coolingdecisions based on setpoint andtemperature information received fromindividual zones

Automatically calibrates all dampers,significantly reducing labor-intensiveand costly field calibration

Windows-based PC software simplifiessetup and control

Provides diagnostic information for allsystem components via the operatordisplay or PC software

Provides status and diagnosticinformation for Trane HVAC unitsequipped with Trane ReliaTel or UCPelectronic controls

Figure 5.VariTrac central control panel

Figure 4. A screen representationfrom the central control panelillustrating system status


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VariTrac Bypass DampersBypass dampers are non-communicating VariTrac dampers andinclude an integrated fully-modulating24 VAC electric actuator.

Field wiring errors are reduced with aquick-connect harness that plugs intothe communicating bypass controller.

Dampers are nominally rated up to18002400 fpm at 1.75" of staticpressure, depending on size.

For damper performance information,see Table 2.

Round Bypass Damper Summary

Round bypass dampers are availablewith inlet diameters 6, 8, 10, or 12 inches

Heavy gage galvanized steel cylinderwith rolled bend for high structuralintegrity and corrosive resistance

Metal-to-metal blade seal provides tightshutoff for low leakage

Aerodynamic blade design provides aconstant torque for stable operation athigh velocity

Factory-installed, direct-coupled, fully-modulating 24 VAC actuator

Rated up to 2400 fpm at 1.75" of staticpressure

Rectangular Bypass Damper Summary

Rectangular bypass dampers areavailable in sizes 14 x 12, 16 x 16,20 x 20, and 30 x 20 inches

Formed heavy gage galvanized steelframe, mechanically joined with linkageconcealed in the side channel

Air linkage is minimized with anopposed blade design with stainlesssteel side seals

Damper casing is 16 inches long and

constructed of heavy gage galvanizedsheet metal with Scleats on the inletand outlet for easy installation

Blades are six-inch nominal width,heavy gage galvanized steel

A blade rotation stop feature preventsover-rotation of the blades in the fullyopen position

Factory-installed, direct-coupled, fully-modulating 24 VAC actuator

Rated up to 3000 fpm at 2" of staticpressure


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VariTrac Zone DampersVariTrac zone dampers are fully-modulating, pressure-dependent VAVdevices. The dampers control zonetemperature by varying the volume ofair flowing into a space. Each VariTracdamper has a control box with a VAVcontrol board and actuator enclosed.The dampers are designed to operate instatic pressures up to 1.75 in. wg.

Round Zone Damper

Round dampers are available in 6, 8, 10,12, 14, and 16 inch diameters

Heavy gage galvanized steel cylinderwith rolled bend for high structuralintegrity and corrosive resistance

Metal-to-metal seal provides tightshutoff

90 blade rotation for a wide controlrange and stable operation

Aerodynamic blade design providesconstant torque for stable operation athigh velocity

Rated up to 2000 fpm at 1.75" of staticpressure

Rectangular Zone Damper

Rectangular dampers are available insizes 8 x 12, 8 x 14, 8 x 16, 10 x 16,10 x 20, and 14 x 18 inches

Heavy gage G90 galvanized steelframe assembled by a mechanical

joining process

Single-ply, heavy gage G90 galvanizedsteel blades

Linkage has high impact ABS gears,and is 3" nominal diameter

Factory-installed 24 VAC direct-coupledactuator

Rated up to 2400 fpm at 2" of staticpressure

Figure 9.VariTrac rectangular and round zone dampers with UCMs

Unit Control ModuleA unit control module (UCM) is theindividual zone controller for theVariTrac air damper and is mounted oneach zone damper. The unit controllercontinually monitors the zonetemperature to maintain spacetemperature. The UCM varies thedamper position as needed to meetzone setpoints and communicatescurrent space requirements andsystem operating modes to the CCP.

The UCM can also control local heat.Local heat may be duct- or space-mounted, and can be staged electric,pulse-width modulating electric, andmodulating or two-position stagedhot water.


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Figure 10.DDC zone sensors Figure 11.DDC zone sensor with LCD

DDC Zone Sensor

The direct digital control (DDC) zonesensor is an uncomplicated, reliableelectro-mechanical room sensor. Noprogramming is required and mostsensors contain an internalcommunications jack.

Models are available with combinationsof features such as override (on-cancel)

buttons and space-mounted setpoint.Four sensor variations are available:

Sensor only (no communications jack)

Sensor with override buttons

Sensor with temperature setpoint only

Sensor with temperature setpoint andoverride buttons

DDC Zone Sensor with LCD

The DDC zone sensor with LCD (liquidcrystal display or digital) is compatiblewith VariTrane VAV and VariTraccontrollers.

Zone Sensors

Digital Zone Sensor Summary

Displays setpoint adjustment and spacetemperature in F or C

Simple, two-button control of spacesetpoint

Setpoint control and room temperaturedisplay can be optionally disabled

Includes button for timed override and

a cancel feature for after-hours systemoperation

An easily accessible communicationsjack is provided for Trane portable editterminal devices

Nonvolatile memory stores lastprogrammed setpoints

For field balancing, maximum andminimum airflow or position can beoverridden from the sensor


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Figure 14. Zone occupancy sensorFigure 12.Wall-mounted CO2sensor

CO2Sensor

Wall- and duct-mounted carbon dioxide(CO

2) sensors are designed for

demand-controlled ventilation zoneapplications. The sensor is compatiblewith VariTrane VAV and VariTraccontrollers. The Trane CO

2sensors

measure carbon dioxide in parts-per-million (ppm) in occupied buildingspaces. Carbon dioxide measurementsare used to identify under-ventilatedbuilding zones. Outdoor airflowincreases beyond design ventilationrates if the CO

2exceeds specified levels.

CO2 Zone Sensor Summary Use with the UCM CO2input for

demand control ventilation

Silicone-based NDIR sensor technologyfor long-term stability

Measurement range of 2000 ppm CO2

input with an output of 010 Vdc

Wall-mount transmitter is compact andaesthetic in appearance

Optional zone return duct-mounttransmitter is available

Zone Occupancy SensorThe energy-saving zone occupancysensor is ideal for zones havingintermittent use during the occupiedmode. The sensor sends a signal to theVAV controller upon detection ofmovement in the coverage area. TheVAV system then changes the zonefrom occupied standby mode tooccupied mode.

Occupancy Zone Sensor Summary

Compatible with VariTrane VAV andVariTrac controllers

Used with zone damper UCM forcontrolling the occupied standbyfunction

Ceiling-mount PIR occupancy sensordetects motion over an adjustablerange up to 360 degrees

Single detector covers up to 1200square feet. For areas larger than 1200square feet, multiple sensors can bewired in parallel

Adjustable time delay avoids nuisancechange of state on loss of detection

Adjustable sensitivity

SPDT isolated contacts connect to

UCM input

Figure 15. Auxiliary temperaturesensor

Figure 13. Duct-mounted CO2sensor

Auxiliary Temperature Sensor

The auxiliary temperature sensor isused with any UCM damper control.The sensor allows the operator tomonitor duct temperature or airtemperature leaving a reheat device atthe zone damper. This sensor is usedfor automatic changeover of a UCMdamper when not using a CCP. Theauxiliary temperature sensor is ideal forremote monitoring and diagnosticsfrom the CCP operator display.

Auxiliary Temperature Sensor Summary

Thermistor sensing element 10,000Ohms @ 77F

Wiring connection 8 feet, 18 awg

Sleeving for wire leads is acrylic #5 awggrade C rated @ 155C


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ApplicationConsiderations

IntroductionThe VariTrac system is a changeover-bypass VAV system. One fan supplieseither warm air for heating or cool airfor cooling. It is typically applied insmall buildings which use unitaryheating/cooling air conditioners. Thesebuildings need the simplicity and lowcost of unitary equipment, but morethan one comfort control zone (onezone temperature sensor) for each airconditioner.

When is VariTrac a good HVAC systemchoice? To help answer this question,several important application conceptsand considerations are discussedbelow.

Zoning ConsiderationsConsider the following two questionswhen evaluating your HVAC systemdesign:

Will the building occupants becomfortable? A system designedwith a single-zone HVAC unit and onezone sensor provides comfort tooccupants near the zone sensor.However, occupants in perimeter areasor interior rooms may be too hot or toocold.

Will comfort be consistent fromroom to room and area by area? Abuilding is normally divided intothermal zones for increased comfortcontrol and energy savings. Eachthermal zone should have a dedicatedHVAC unit. For optimum comfort, eachthermal zone should be further dividedinto comfort zones.

Choosing the number and location ofthermal and comfort zones is critical inplanning an effective system. Somethings to consider in the designprocess include:

Geographic location

Orientation of the building to the sun

Prevailing winds

Wall construction (glass, insulation,building materials)

Building layout, design, occupancy andoccupancy pattern throughout the dayand year

Activities in each zone

Zoned unitary systems, such aschangeover-bypass VAV, divide thermalzones into smaller comfort zones. Eachcomfort zone has a damper and zonesensor that controls the amount ofheated or cooled air delivered to thezone. A central system controllermonitors the status of each zonedamper and zone sensor. The controllerthen makes the decision to heat or coolfor the HVAC unit.

Individual comfort zones served by a

common HVAC unit (part of the samethermal zone) can require heating andcooling at the same time. In achangeover-bypass VAV system, theunit alternately provides warm and coolair in an attempt to satisfy the needs ofall comfort zones. This is effective if thesimultaneous calls for heating andcooling exist for short time periodsonly. Wide temperature variations mayoccur if some comfort zones needheating for extended periods of timewhile others need cooling.

Some comfort zones require specialconsideration because of their use or

location. An example is the foyer orreception area of an office building.These areas often have wide variationsin thermal load because of glass(relative to other areas of the building)and frequently-opened exterior doors.Another example is an interior storageroom with the need for ventilation butlittle or no heating or cooling. Thesezones can significantly influenceefficient operation and comfort levelsthroughout the building.

Preferably, areas such as these aredesigned as separate thermal zoneswith dedicated HVAC units. However,

this may be impractical or costly.Instead, use fan-powered variable-volume terminal units, or units withlocal reheat.

Figure 16.System design affects

occupancy comfort

Single Zone BuildingOne thermal and

one comfort zone

Thermal Zoned Building

Multiple thermal zoneseach with one

comfort zone

Thermal and

Comfort Zoned Building

Multiple thermal zones

each with multiplecomfort zones

Least

Most

EnergySavingsComfortFlexibility


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VAV-PRC003-EN 15


Cost vs. Comfort

First cost can be reduced by limitingthe number of thermal zones.Unfortunately, this may impact thethermal flexibility of the system, andresult in zone comfort issues. Lets takea closer look at this important systemdecision known as thermal zoning.

Characteristics of a building which caninfluence thermal load are:

Orientation of the building (North,

South, East, West) Amount and thermal resistance (R-

value) of glass (walls, skylights, etc.)

Expected occupancy within the area

Interior partitions and doors

Varying loads from equipment orprocesses

Lets examine a few building examplesand discuss the zoning criteria of each.

Building Example 1 (See Figure 18.)

Consider an existing single-story officebuilding which is small, poorlyinsulated, with many large windowsand few interior partitions. On a clear,cool spring day, the entire building iscool in the morning so heating isrequired. By afternoon, however, thesouth side of the building beinginfluenced by the solar load, is warmand requires cooling. The north sideremains shaded and continues to

require heating. This situation results ina simultaneous requirement for heatingand cooling for extended periods. Dueto the varying loads throughout thebuilding, controlling the building as asingle thermal zone (with a single HVACunit) cannot satisfy the comfort needs

of all areas. It also is not a goodcandidate for a zoning system becauseof the simultaneous need for heatingand cooling.

A similar building with good insulationand fewer shaded windows, on theother hand, may be a good candidatefor a single thermal zone with individualcomfort zones. The reduction in wallglass reduces the solar effect on thebuilding resulting in all areas of thebuilding having similar load profiles

throughout the day. In this case, thebuilding has a single thermal zone andis a good candidate for one HVAC unit.Individual comfort zones (zonedampers) will be needed to assurecomfortable conditions throughout thezone.

Figure 18. Building Example 1illustrates a small, poorly insulated office on the left, and improved design on the right.

Men'sRestroom

Women'sRestroom

ThermostatT

ShadedWindows

InsulatedWalls

Improved Design Elements Multiple zone thermostats

Shaded windows Insulated walls

ThermostatTThermostatT

Men'sRestroom

Women'sRestroom

ThermostatT

Glass windowswith no shading Minimal wall

insulation

Poor Design Elements One thermostat for space

Glass windows with no shading Minimal wall insulation


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Figure 19. Building Example 2illustrates a poorly insulated storedesign (above) and an improved design(below)

Building Example 2 (See Figure 19.)

Consider a strip mall in the spring or fallwith stores that face both east andwest. In the morning, the east side ofthe building gets full sun and warms upwhile the west side is shaded andrequires heating. In the afternoon, theeast side of the building may need heatand the west side cooling. Because ofthe thermal load variation throughoutthe day, this building will not remaincomfortable if designed with a single

heating and cooling unit.On the other hand, comfort in thisbuilding could be improved by dividingthe building into two thermal zones(two HVAC units), one serving the eastexposure and the other serving thewest. Even with the two systems,individual occupant comfort is notnecessarily assured. Interiorpartitioning, varying schedules andnumber of occupants within thethermal zone will drive differingamounts of heating and cooling. Theissues related to comfort zoning areaddressed in the next section.

Step 3. Define the Comfort Zones

A primary criteria for defining a thermalzone is that it will not requiresimultaneous heating and cooling. AnHVAC unit with one fan is limited tosupplying either heating or cooling.Most applications with larger thermalzones however will have varyingthermal needs throughout the zone.These small variations can easily beaddressed by properly defining comfortzones.

A comfort zone is an area within athermal zone that is controlled by azone damper. The amount ofconditioned (heated or cooled) airentering the space varies. This is inresponse to a space thermostat.ASHRAE Standard 55 recommendslimiting indoor temperature variations.Temperature variations of less than 2Fin 15 minutes or 4F in an hour.Deviations from this recommendationwill cause discomfort in 80 percent ofthe occupants. Zoning systems cangreatly reduce temperature variationscaused by shifting occupancy and solar

load conditions in large thermal zones.

JewelryStore

CoffeeShop

ElectronicsStore

ToyStore

ClothingStore

Pharmacy

OutsideDoors

N

Poor Design Elements One thermostat for entire space

One HVAC unit

JewelryStore

CoffeeShop

ElectronicsStore

ToyStore

ClothingStore

Pharmacy

OutsideDoors

N

Improved Design Elements Two thermal zones

Two HVAC units


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Table 1. Diversity example

Calculating thermal zone diversity:

1. Determine the instantaneous peak(or block) load for the thermal zone.This information is output from loadanalysis software such as TraneTRACEor manually calculated.

2. Calculate the sum of the peak loadsfor each of the comfort zones withinthe thermal zone.

3. The diversity factor is then calculatedby dividing the instantaneous peakload value by the sum of the peakloads.

The heating and cooling equipment willnever be called upon to provide morecapacity than was determined by theinstantaneous peak load value.Consequently, the equipment capacitycan be reduced by the diversity factor.

Step 4. Sizing HVAC Equipment

Once the building heating and coolingloads are known and the thermal zoneshave been determined, the heating andcooling equipment can be selected.Each thermal zone requires a separateheating and cooling unit. As discussedearlier, unitary zoning systems typicallyuse packaged DX rooftop units or DXsplit systems. These systems areoffered as heating and cooling units orheat pumps.

When selecting the heating and coolingunit for a thermal zone, load diversitywithin the zone should be considered tominimize equipment size and thereforereduce system first cost and operatingexpense. Load diversity is defined asthe ratio of the instantaneous peakloads (block load) to the sum of thepeak loads within the thermal zone. Inrecognizing load diversity, the designeracknowledges that all areas of thethermal zone will not require maximumcooling or heating at the same time.

While using diversity may reduce thesize of the HVAC unit, the zone

ductwork, dampers, and diffusers mustbe sized for the individual zone peakloads. The main trunk duct may be sizedbased on the HVAC unit airflow.

DiversityFactor =

InstantaneousPeak Load

Sum of Peaks

Zone Time Peak LoadInterior 3 p.m. in mid-July 7.5 tonsNorth 5 p.m. in mid-July 3.0 tonsEast 9 a.m. in June 2.5 tonsSouth 4 p.m. in November 4.0 tonsWest 5 p.m. in September 2.5 tons

Sum of Peak Loads 19.5 tons

Note:The sum of blocks loads = 17.5 tonsand occurs at 5 p.m. in mid-July.

______

19.5

Diversity = 17.5 = 90%

Figure 20. Diversity example

North Zone

East ZoneWest Zone Interior Zone

South Zone

Wedge ZoneBuilding Perimeter

Glass

Windows


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Step 5. Size Zone and BypassDamper Units

Sizing zone damper is relativelystraightforward. The volume of airflow(in cfm or L/s) for each comfort zoneshould be known from the loadanalysis. The designer must select theduct velocity to be used for the system.Recommended zone damper velocitiesare 1000 to 1600 feet per minute (fpm)when applied at the branch level.Sizing dampers in this range will

minimize damper cost, reduce the riskof excessive noise, and ensureadequate zone modulation/temperaturecontrol.

Dampers located immediately adjacentto the zone or diffuser may need to besized at a lower velocity to avoid soundand airflow delivery issues.

Bypass dampers are typically sized for80 percent of HVAC unit airflow.Recommended velocities are 1600 to2000 fpm. Bypass dampers should belocated as close to the HVAC unit aspossible. (See Bypass DamperOperation for additional details.)

Note: VariTrac systems are designed

for HVAC unit static pressures up to1.75" w.c.

Step 6. Designing the Duct System

Low pressure, low velocity airdistribution systems, such as zonedunitary systems, are usually designedusing the equal friction method.Although static regain is the ductdesign method of choice for mediumand high velocity variable air volumesystems, the added complexity isdifficult to justify with smaller unitarysystems. In addition, the low operatingvelocity of most unitary systems makes

the pressure available to regain, smalland inconsequential.

With the equal friction method, ductsare sized for a constant pressure lossper given length of duct and fitting(s).Where low noise levels are especiallycritical, the system velocity can bereduced by enlarging the entering andleaving ductwork, damper unit oradding duct liner. A characteristic of theequal friction method that must beconsidered however, is that there is nonatural provision for equalizingpressure drops in the branch sections.This results in each branch duct, and

thus the damper units, having differententering static pressure and airflowcharacteristics.

A robust system and zone unitcontroller, like the Trane VariTracsystem, will compensate for systemstatic changes. The use of manual (orhand) balancing dampers in thebranches will also ensure that airflow isappropriately distributed to eachdiffuser. (See Figure 21.) The overalleffect is improved acoustical andsystem performance.

Figure 21.Hand balancing dampersHand

BalancingDamper

VariTracDamper

SupplyDuct


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When the average glass plus wall heatloss is less than 250 Btuh/linear foot,the slot diffuser may be located inthe center of the room with one ormore slots blowing toward theperimeter wall.

With glass and wall heat loss between250 and 450 Btuh/linear foot, diffusersshould be positioned to blow towardthe window and the perimeter wall witha collision velocity of 75 to 150 fpm. Ifusing a continuous glass design,

position diffusers every four feet. If heat loss exceeds 450 Btuh/linear

foot, radiation or floor mounted heatedair will be required to offset the highwall heat loss.

Step 7. Air Diffuser Selection andPlacement

Supply Diffusers

Many types of supply air diffusers areused in variable air volume systems.Performance, and ultimately spacecomfort, can vary greatly depending onthe diffuser selected. Althoughconstant-volume diffusers will provideair to the space at full cfm, as airvolume delivered to the spacedecreases, so does performance.Linear slot diffusers are recommendedfor most VAV systems.

Linear supply air slot diffusers aredesigned to properly mix variable airdelivery of both heated and cooled air.Linear slot diffusers supply conditionedair which hugs the ceiling rather thandumps air downward on theoccupants. This airflow characteristic isknown as the coanda effect. Thethrow and aspiration characteristics ofslot diffusers help to evenly distributethe air throughout the room or space.

Locate linear slot diffusers in the center

of the room with the discharge airpattern perpendicular to a perimeterwall. To maximize diffuserperformance, placement in which airdischarge patterns converge at rightangles should be avoided. (See Diffusersection of the VariTrane catalog (VAV-PRC008-EN) for additional diffuserplacement and performancerecommendations.)

The throw characteristics of diffusers iswell-documented. Slot diffusers shouldbe positioned so that the velocity of theair striking an obstruction (such as awall or column) is 75 feet per minute

(fpm) or less. If airstreams from twodiffusers collide, the collision velocityshould not exceed 150 fpm. Highercollision velocities result inuncomfortable drafts in the lower levelsof the room.

In heating applications, linear slotdiffusers must be placed to offset heatloss and prevent downdraft problemsalong perimeter walls. The followingtechniques have been proven by testand experience:

Figure 22.Proper return diffuser orientation

Return Diffusers

Slot-style return diffusers offer someacoustical advantages over perforatedgrille styles. Perforated drop-in grillestypically offer little attenuation effectand thus allow sound in the plenum tobreak out into the occupied space. Thisis a problem in areas near the unitaryheating and cooling unit. Improvedceiling aesthetics is also an advantageof slot return diffusers in jobs whereslot supply diffusers are used. Within

the occupied space, they blend with theslot supply diffusers.

A general rule of thumb is for the returnair openings to equal the total area ofthe supply openings. If the ceiling is nottight, such as a drop-in ceiling, thereturn openings can be reduced by upto 50% of the supply air openings.

To promote good air distribution, returndiffusers should be positioned tominimize supply air short-circuiting tothe return slot. The returns should beeither perpendicular to the supplyairflow or parallel and offset from thesupply diffusers.


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Local Reheat CapabilitiesNon-VAV Options

The Trane VariTrac Zone Controller hasbuilt-in capabilities and logic to controla number of reheat sources. Theprevious page discussed how aVariTrane VAV unit with reheat cansolve application issues by providinglocal reheat.

Local Reheat

Lets investigate a few other alternatives

which will provide local reheat, andresult in exceptional zone temperaturecontrol.

Local reheat is particularly importantwhen an HVAC unit is in cooling mode.Cold air is delivered to all zoneswhether it is needed or not. Setting theminimum cooling position to zero maynot be practical based on ventilationand/or general airflow requirements. Inthis case, local reheat options whichcan be controlled by the standardVariTrac zone controller include:

hydronic wall fin or convector unit with

either modulating or two positioncontrol. (See trane.com for a full line ofwall fin and convector products.)

electric wall fin with multi-stage control

duct-mounted electric heater withmulti-stage control

duct-mounted hot water coil with eithermodulating or two-position control.(See trane.com for a full line of duct-mounted water coils.)

Figure 26. Trane hydronic wall fin

This is ideal for spaces with largewindows or perimeter heat losseswhich exceed 450 Btuh per linear foot.Trane wallfin is available with variousgrilles and paint options and can bepedestal or wall-mounted

Figure 27. Trane electric wall fin


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Figure 28.Changeover bypass variable-air-volume system

Bypass Damper OperationWhen zone dampers modulate airflowto the spaces, static pressure changesin the supply duct system. Highpressure in a duct system createsexcessive noise and causes poorcomfort control. Low pressure resultsin insufficient airflow to the spaces.

The HVAC unit in a changeover bypasssystem is constant volume and doesnot modulate supply airflow.Changeover-bypass VAV systems

support variable-air-volume operationin the zones by using a bypass ductwith a motorized damper and apressure-sensing device.

As duct pressure rises above the staticpressure setpoint, the bypass damperbegins to open. Conversely, when staticpressure falls below the static pressuresetpoint, the bypass damper begins toclose until the static pressure setpointis reached. The optimal static pressuresetpoint is automatically determinedupon system calibration.

Proper operation requiresconsideration of all aspects of bypassdesign and location. The bypassdampers and ductwork should be sizedand located according to the followinggeneral recommendations:

Avoid turbulence by locating thebypass two to three equivalent ductdiameters downstream of the HVACunit discharge.

Locate the static pressure and supplyair sensors in the main supply duct

upstream of the bypass. Locate the bypass before the zone

dampers (as close to the HVAC unit aspossible) to avoid comfort or noiseissues.

Size the bypass damper to maintain theminimum required airflow through theHVAC unit (usually 80 percent of thetotal design cfm)

Provide adequate access for servicingthe damper.

SupplyAir Duct

ReturnAirDuct

Ductwork

BypassDamper

ReturnAirDuct

Heating and

RooftopMicro Control

and SupplyTemperature Sensors


23/52

VAV-PRC003-EN 23


Building Pressure ControlComfortable, efficient buildingoperation requires that the air pressureinside the building be slightly higherthan the atmospheric pressure outsideof the building. That is, the building is ata positive pressure with respect tothe outside environment. If the indoorpressure is too low (negative), thedoors may be hard to open and cold airmay leak in through constructioncracks, causing drafts and cold floors.

On the other hand, if the indoorpressure is too high, the doors maystand open and the supply air flow tothe zones may decrease, decreasingcomfort.

Fixed Outside Air Dampers

Achieving appropriate buildingpressure is simple in a system with aconstant volume supply fan and fixedoutdoor air damper. To maintain aslightly positive building pressure, sizethe exhaust fans to remove slightlyless air than is introduced through theoutdoor air damper.

Outside Economizer or Demand-Controlled Ventilation Systems

If the system resets the quantity ofoutdoor air in response to occupancydemands (demand-controlledventilation), or uses an outdoor aireconomizer, undesirable changes inbuilding pressure may result. As thequantity of outdoor air intake varies,the system must exhaust a similarquantity of air to avoid over or underpressurizing the building.

When using an economizer in achangeover-bypass VAV system under

low cooling load conditions (reducedairflow to the zones), the bypassdamper opens to maintain the staticpressure setpoint and airflow throughthe supply fan. As the outside airdamper opens to provide economizercooling, the return air damper closes.In buildings with a ceiling plenumreturn, the bypass air dumps into theceiling plenum since it can no longerreturn to the fan. The plenum pressurerises and plenum air enters the zonesthrough the return air grilles.

In buildings that have a ducted return tothe fan, bypass air pressurizes thereturn air duct. As the return air ductpressure rises, the air flows out of thebuilding through the barometric reliefdamper in the rooftop unit. Excessbypass air flows into the zones throughthe return air grilles.

Using the following suggestions willhelp maintain building pressurizationcontrol:

Use an exhaust fan with a modulated

exhaust damper to remove air from thereturn air plenum or duct. Energize theexhaust fan as the outside air damperopens beyond the minimum position.Sense building static and maintainbuilding air pressure at a slightlypositive level by modulating theexhaust damper position.

Use an exhaust fan with no exhaustdamper. Energize the exhaust fan whenthe outdoor air damper opens beyond25 percent to remove excess outside airfrom the building. This method is usedwith some rooftop units and iseffective, affordable, and easy to install.

Use a back draft damper to preventairflow to the return air plenum orgrilles. When bypass airflowpressurizes the return duct, the backdraft damper closes. Pressure in the

HVAC unit return air inlet rises, causingthe rooftop barometric relief damper toopen. This method is less effectivebecause the rooftop barometric reliefdamper is sized for a portion of the totalairflow, not 100 percent of airflow whichmay be seen in economizer mode. Asthe economizer drives to the maximumposition, the building usually becomesover-pressurized.

Figure 29. Changeover bypass with an economizer. Without proper buildingpressurization, bypass air may be forced out of the return duct.

OutdoorAir Damper

Economizer Fan

Bypass

ReturnDamper

ReturnOpening


24/52

24 VAV-PRC003-EN

Application Tip Summary

Tip 1. Use comfort zones

Units serving thermal zones canprovide greater comfort by dividing thethermal zones into comfort zonesusing a changeover-bypass-VAVsystem.

Tip 2. Create thermal zones

Create thermal zones which minimizesimultaneous heating and coolingrequirements. This will avoidunnecessary changeover of the systemand maximize comfort. As an example,a computer room would be a poorcandidate for one comfort zone of achangeover-bypass-VAV systembecause it will rarely, if ever, requireheating.

Tip 3. Use local heat

Zones which vary thermally byrequiring more heat than the otherzones or require heat when the HVACunit is in cooling mode should use localheat. Local heat in the form of VariTrane

VAV units with electric or hot waterheat, or wallfin, or convectors, or duct-mounted coils. The standard VariTraccontroller is capable of controlling theheat based on zone temperaturedemands.

Tip 4. Place dampers properly

The bypass damper should be ductedbetween the supply and the return ofthe unit as close to the unit as possible,and should be sized to handle 80% ofthe total system CFM.

Tip 5. Control building pressure

It may be necessary to provide amodulating means to control building

pressure, especially when economizersor demand-controlled ventilation areused in conjunction with a changeover-bypass-VAV system.

Tip 6. Use fan-powered VAV boxes

Consider using fan-powered VAV boxesto provide local heat or to enhancecomfort levels in some of your zones.Conference rooms, or zones with highwall heat loss are ideal for either seriesor parallel units.



25/52


26/52

26 VAV-PRC003-EN

SelectionProceduress

Notes:1. Recommended velocity for zone dampers is between 1000 and 1600 fpm. Use

good standard design practices (such as location of duct).

2. Recommended velocity for bypass damper is between 1600 and 2000 fpm.

Table 2. Damper sizing charts

Recommended

Recommended

Recommended

Recommended

Round Bypass DamperCapacity (cfm), Dimensions, Blades, and Weights

Rectangular Zone DamperCapacity (cfm), Dimensions, Blades, and Weights

Rectangular Bypass DamperCapacity (cfm), Dimensions, Blades, and Weights

Velocity(fpm)

Velocity(fpm)

Velocity(fp

m)

Velocity(fpm)

Round Zone DamperCapacity (cfm), Dimensions, and Weights

Size 6" 8" 10" 12" 14" 16"

600 120 210 330 470 640 840

800 160 280 435 630 855 1115

1000 200 350 545 785 1070 1395

1200 235 420 655 940 1280 1675

1400 275 490 765 1100 1500 19551600 315 560 875 1255 1710 2235

Length 12" 12" 16" 16" 20" 20"

Ship Wt 11 lbs 12 lbs 17 lbs 18 lbs 27 lbs 31 lbs

Size 6" 8" 10" 12"

600 120 210 330 470

800 160 280 435 630

1000 200 350 545 785

1200 235 420 655 940

1400 275 490 765 1100

1600 315 560 875 1255

1800 350 630 980 1415

2000 390 700 1090 1570

Length 12" 12" 16" 16"

Ship Wt 11 lbs 12 lbs 17 lbs 18 lbs

Size 8 x 12 8 x 14 8 x 16 10 x 16 10 x 20 14 x 18

600 398 464 531 663 829 1045

800 531 619 707 884 1105 1393

1000 663 774 884 1105 1382 1741

1200 796 928 1061 1326 1658 2089

1400 928 1083 1238 1547 1934 2437

1600 1061 1238 1415 1769 2211 2785

Blades 2 2 2 3 3 4

Ship Wt 8 lbs 10 lbs 12 lbs 14 lbs 16 lbs 18 lbs

Size 14 x 12 16 x 16 20 x 20 30 x 20

600 696 1061 1658 2487

800 928 1415 2211 3316

1000 1161 1769 2763 4145

1200 1393 2122 3316 4974

1400 1625 2476 3869 5803

1600 1857 2830 4421 6632

1800 2089 3183 4974 7461

2000 2321 3537 5527 8290

Blades 2 3 3 3

Ship Wt 16 lbs 21 lbs 29 lbs 40 lbs


27/52

VAV-PRC003-EN 27

SelectionProcedures

VADA Product Coding Explanation

The features of VariTrac air dampersare described by valid productcategories (VPC). Options for each VPCare described by selectable items (SI).

The following describes VPCs and SIsfor ordering VariTrac air dampers.

MODL Unit Model

VADA=VariTrac Air DamperDevelopment Sequence A

VARA=VariTrac Rectangular AirDamper

DSEQ Design Sequence

(Factory Use)

DMPR VariTrac Damper Size

06=6" (152 mm) round damper






1412=14 x 12 rectangular bypassdamper




0812=8 x 12 rectangular zone damper






Model NumberDescriptions

CTRL Unit Control

BYPS=Bypass for round damper

CHGR=Changeover

ELEC=Electric, Three-State Heat-Disabled with Primary Heat

NCHW=Normally-closed Hot WaterValve, One-State Heat-Enabled w/Primary Heat

BYR=Bypass for rectangular damper

OPTN VariTrac Options

SNSR=Duct Temperature Sensor

Notes:

1. When the Unit Control, CTRL, isBypass, BYPS or BYR, the option of aZone Duct Temperature Sensor, SNSR,is not available.

2. Unit Control ELEC is typically used withelectric resistant duct heaters. Theauxiliary heat is disabled when theprimary heat is activated to protect theheating coils.

3. Unit Control NCHW is typically usedwith perimeter heating, hot water,

steam, or electric resistant perimeter. Itis always enabled, regardless ofwhether the primary system is heatingor cooling.


28/52

28 VAV-PRC003-EN

Digits 1, 2, 3, 4 Product Type

VADA = VariTrac Air Damper

VARA = Rectangular Air Damper

Digits 5, 6 VariTrac Damper Size

06 = 6" Damper

08 = 8" Damper

10 = 10" Damper

12 = 12" Damper

14 = 14" Damper

16 = 16" Damper

1R = 14 x 12 bypass damper




5R = 8 x 12 zone damper





AR = 14 x 18 zone damper

Digit 7 Controls (all factory downloadedand verified)

A = Bypass with actuator

B = Damper only control (Changeover)

C = Damper plus up to 3 stages ofElectric

D = Damper plus 1-stage Normally-open hot water

E = Damper plus 1-stage Normally-closed hot water

F = Not used

G = No controls (Actuator Only)

H = Not used

J = Bypass for rectangular damperwith actuator

Digits 8, 9, 10, 11

00P0 = Design sequence

SelectionProcedures

Service Model Numbers

V A D A 0 6 A 0 0 P 0

1 2 3 4 5 6 7 8 9 10 11


29/52

VAV-PRC003-EN 29

A & J

B

C

D

E

F

G

HFigure 31.Typicalcomponents in achangeover-bypassVAV system

Table 3.Typical VariTracchangeover-bypass VAVsystem components

SelectionProcedures

Typical Bill of Materials

Device Name Function in System Number Required

A Central control panelw/optional operator display

Controls the HVAC system and provides localoperator interface

One per HVAC unit/VariTrac system(thermal zone)

Communicating bypasscontroller

Sends supply duct temperature and pressure tothe central control panel

One per VariTrac system

Bypass damper(s) Supply air duct volume control to maintain

appropriate static pressure in the duct

One or two per system as needed to

bypass from supply to returnairstream

D VariTrac dampers Var ies a ir vo lume to the space to contro l comfor t One per comfort zone

Zone sensors Sends space temperature and setpoint

information to the zone damper controller

One per comfort zone (DDC sensor

w/ LCD requires 4 VA)

CCP power supply 24V power for the central control panel The CCP must have a dedicated 24Vpower supply

G Zone damper power supply(s) 24V power for the zone dampers Power suppl ies may be shared; eachzone requires 10VA (plus the load ofoptional outputs)

H Trane rooftop communicationsinterface

Allows the CCP and Trane rooftop controller to

communicate with each other via simple twistedshielded wire pair

One per controlled Trane rooftop

with ReliaTel controller

Opt ional relay board Provides 24V control of any non-communicatingHVAC unit

One per controlled non-communicating HVAC unit

B

C

J

FE


30/52

30 VAV-PRC003-EN

24 VacLine voltage

Comm5

link

omm

link

Comm5 UCMTracker

Splice

AA

BB

Twisted pair, shielded wireperTrane specifications

Shield termination

Earth ground

Contact points

rans ormer

Termination resistor

Shield ground

=

=

=

=

=

=

Termination Boar

Figure note

Comm4

link

omm

lin

omm4omm4

Splice

-

+

-

+

Legen Figure Notes:

1 All customer wiring must be in

accordance with national, state,

and local electrical codes.

2 Trane recommends a dedicated

transformer for 24 Vac power.

3 Do not apply voltage to the priority

shutdown and occupancy inputs.

4 Example of Comm5 communication

link wiring. See product-specific

literature for Comm5 wire connection

details.

Electrical Dataand Connections

Figure 32. Central control panel field wiring


31/52

VAV-PRC003-EN 31


Figure 34.Typical relay board wiring

Figure 33.Relay board wiring

1

3

2

9

12

15

R

5

13

4

8

10

11

14

6

7

TB1

Relay Board TB2

c

Rh

G

Y1

Y

2

W1

W2/0

AUX

NO

NC

NOTUSED

24 VAC CLASS 2 COOL UNIT

24 VAC CLASS 2 HEAT UNIT

COOL 1

COOL 2

HEAT 1

HEAT 2

SUPPLY FAN

SPARE OUTSIDE AIRHEAT/COOL

OR ICS

2 HEAT/2COOL HEAT PUMP

REV VALVE

AUX HEAT

COMP 2

COMP 1

HVAC Unit

24V Terminal Strip

R

G

Y1

Y2

W1

W2

Relay Board TB2

1

3

2

R

5

4

6

7

TB1

c

Rh

G

Y1

Y2

W1

W2/0


32/52


33/52

VAV-PRC003-EN 33


Figure 36.Communicating bypass controller wiring

CW

ACTUATOR

HOT

CLOSE

CCW OPEN

COM

SPARECONNECTOR

ACTUATOR

TB11

STATICPRESSURE

PORT

WHOT

BIP

BKOPEN

2. 24VAC

24VGNDACT

RCLOSE

TB12

TB41

TO NEC CLASS 224V TRANSFORMER

LOAD 8 VA(WITHOUT ACTUATOR){

HIGH

D.D.C.\U.C.M.CONTROL BOARD

PRESSURETRANSDUCER

ADDRESSSWITCH

COMMUNICATING SENSOR/BYPASS

CONTROL BOX

AIR SUPPLY TEMP SENSOR

SHIELDEDTWISTED PAIR

COMMUNICATIONSWIRING

D.D.C.\U.C.M.CONTROL BOARD

MALE PLUG ENDLOCATED ON DDC\UCM

CONTROL BOARD

FEMALE PLUG ENDOF BYPASS SENSOR

ASSEMBLY CABLE

{

TB23

TB24

TB25

J8

TB26

J11

J10

J9

J7 J1

YEL GRN

TB22

TB21

TB31 S

PRESS

TB26

TB32

TB36

TB35

TB33

GNDA/CO2SETGNDZONE

J3

1

VOUT

+++

R

BKG

+

OUT

OUTININ

ACT

WH

RBK


34/52

34 VAV-PRC003-EN


Figure 37.UCM Wiring

24 VAC 60 HZNEC CLASS2

CONTROL CIRCUIT

8.

W

GW

R

DAMPERACTUATOR

WIRING

D.D.C. \ U.CM.CONTROL BOARD

D.D.C. \ U.CM.CONTROL BOARD

ADDRESSSWITCH

SHIELDEDTWISTED PAIR

COMMUNICATIONSWIRING

}

}

J11

PRESS

TB21

TB22

TB23

TB24

TB25

TB26 S

TB36

TB35

TB33

TB32

TB31

TB11

TB12

TB41

J7

J8

J9

J10

A/CO2SETGNDZONE

J1

1

J3

24VGNDBIPACT

GRNYEL

GND

+++

1

7.

9.OUT

OUT

ININ

}6.

6.

OPTIONAL FIELD INSTALLEDPTIONAL FIELD INSTALLED

AUX TEMP SENSORUX TEMP SENSOR


CO2 SENSORO SENSOR


ONNOFF WATER VALVEFF WATER VALVE


PROPORTIONAL WATER VALVEROPORTIONAL WATER VALVE

5.


OCCUPANCY SENSORCCUPANCY SENSOR

R (HOT)

O (COMMON)

GR (NC CONTACT)

BK (RETURN)

Y

(TB41) BIP

(TB11) 24VAC

NOT CONNECTED

(TB11) 24VAC

(TB12) GND

ONOFF

WATER VALVE

24VAC

12 VA MAX

PROP. WATER

VALV

24VAC

12 VA MAX

TO J8

TO J8

TO J9

TO J9

TO J10


ELECTRIC HEATERLECTRIC HEATER

TO J11

TO J8

TO J9

TO J10

HOT

1ST STG.2ND STG.

3RD STG.HEATER STAGE

CONTACTOR(S)24 VAC, 12 VA

MAX/COIL

R (OPEN)

BK (CLOSE)

W (HOT)

CO2

SENSOR

24V

V

+

0

OUT

GND

WALL

MOUNTED

DUCT

MOUNTED

(TB35) A/CO2

(TB36) GND

(TB11) 24V

TB36TB35

TB11

22 1 3 211

TB3TB2TB1

TB26

TB25

TB33

TB32

TB31

TB12

DIGITALZONE SENSOR

OPTIONAL FIELDINSTALLED DIGITAL ZONE SENSOR

OPTIONAL FIELDINSTALLED DIGITAL ZONE SENSOR

ZONE SENSORW/ COMM. JACKREMOTE MTD.

TB26TB25

TB31TB32

TB33

4.

45 23

3.

1

1.

2. " quick connect required for all field connection.

3. Zone sensor terminals 4 and 5 require shielded twisted pair wiring for communications jack equipped zone sensor options

4. No additional wiring required for night setback override (on/cancel).

5. The optional binary input connects between TB41 (BIP) and 24VAC (HOT) from transformer. The binary input can be

reconfigured as an occupancy input via the communications interface.

6. As shipped, the aux input is configured as an AUX input. The AUX input can be reconfigured as a CO2 sensor input via

the communications interface.

7. S terminal not to be used with this applications.

8. If unit mounted transformer is not provided, polarity from unit to unit must be maintained to prevent permanent damage

to control board. If one leg of 24VAC supply is grounded, then ground leg must be connected to TB12.

9. Shields of communication wiring should be tied together and insulated.

NOTES:

Factory Wiring

Field Wiring

Optional or Alternate Wiring


35/52

VAV-PRC003-EN 35


Digital Sensor

Terminal Connection ChartSensor UCM

Field WireColor Code

TB11 TB11

TB21

TB12

TB26

TB22

TB25

TB31

TB33

TB31

TB23

TB32

TB12

TB32

Digital SensorBoard

TB11

TB31

TB21

GND

24V22

2

2

2

Temperature

Signal Common

Setpoint

Communications+ (High)

Communications (Low)

1

OptionalField Mounted

Aux. Temp. Sensor

J11

ACT

ADDRESS

SWITCH D.D.C.\U.C.M.CONTROL BOARD

J8J

7J9

J10

TB11

TB12

TB41

PRESS

TB21

TB22

TB23

TB24

TB25

TB26

TB36

TB35

TB33

TB32

TB31

1

J3

S

GNDA/CO2SETGNDZONE

GRNYEL

J1

GNDBIP

++ +

1

24V

Figure 38.DDC zone sensor with LCD

Figure 39.DDC zone sensor wiring

J11

ACT

ADDRESS

SWITCH D.D.C.\U.C.M.

CONTROL BOARD

J8J

7J9

J10

TB11

TB12

TB41

PRESS

TB21

TB22

TB23

TB24

TB25

TB26

TB36

TB35

TB33

TB32

TB31

1

J3

S

GNDA/CO2SETGNDZONE

GRNYEL

J1

GNDBIP

++ +

1

24V

OptionalField Mounted

Aux. Temp. Sensor

1

2

Mechanical Sensor

Terminal Connection Char t

Sensor UCMField Wire

Color Code

TB11 TB31

TB14

TB32

TB15

TB25

TB26

TB12

1

2

Figure Notes:

Shield must be spliced with othercommunication link shields

Shield must be cut back and tapedat sensor.

Temperature

Signal Common

Setpoint

Communications (Optional)+ (High)

Communications (Optional) (Low)

TB11

4

3

2

5CommunicationsJack

AdjustableSetpoint Option

Night SetbackOverride Option

Comm 1

Cooler

Warmer

Sensor

ON

PB1


36/52


37/52

VAV-PRC003-EN 37

Table 5.VariTrac control panel specifications

Specifications

Table 6.UCM damper specifications

Figure 41.VariTrac central controlpanel components

Figure 42.VariTrac UCM rounddamper

Power Requirements 2030 Vac, 60 Hz, single-phase, 30 VA minimum. Class 2 transformerrequired.

Operating Environment 32122F (050C), 1090% relative humidity, non-condensing

Storage Environment -40F122F (-4085C), 595% relative humidity, non-condensing

Control Enclosure NEMA 1 resin enclosure, plenum rated

Mounting Mount directly on wall surface or mount on recessed 4" x 4"(101.6 mm x 101.6 mm) conduit box.

Weight 2.5 lbs. (1.13 kg)

Communication Link Wiring Communication link wiring must be Level 4 22-AWG twisted shieldedpair wire with stranded tinned copper conductors. Maximum total wirelength is 3,500 ft (1066.8 m). Wire must meet Trane specifications.

Binary Input Voltage (provided by VariTrac CCP): 1014 Vdc

Current (provided by VariTrac CCP): 1014 mANote:Only dry contacts may be attached to binary inputs.

UL Approval The VariTrac Central Control Panel is UL approved.

Memory Backup Upon a power loss, all operator-edited data stored in the VariTrac CentralControl Panel is maintained permanently.

Power Requirements 2030 Vac, 60Hz, single-phase 10 VA minimum (plus load of optional heatoutputs). Class 2 transformer required.

Operating Environment 32120F (049C). 1090% relative humidity, non-condensing

Storage Environment -50200F (-4693C). 595% relative humidity, non-condensing

Control Enclosure NEMA 1 metal enclosure, plenum ratedCommunication Link Wiring Communication link wiring must be Level 4 22-AWG twisted shielded

pair wire with stranded tinned copper conductors. Maximum total wire is3,500 ft (1066.8 m). Wire must meet Trane specifications.


38/52


39/52

VAV-PRC003-EN 39

Table 10. CO2sensor specifications

Table 9. Digital zone sensor specifications

Specifications

Figure 45.DDC zone sensor withdigital display

Figure 46.CO2duct sensor

Figure 47.CO2wall sensor

Thermistor Resistance Rating 10kW at 77 (25C)

Accuracy at 77F (25C) 0.4F (0.2C)

Setpoint Resistance Rating 500 Ohms at 70F (21.2F)

Display Zone Temperature Range 4099F (10 to 35C)

Display Setpoint Range 5090F (10 to 32C)

Operating Temperature 0120F (18 to 49C)

Storage Temperature 20130F (29 to 54C)

Humidity Range 595% non-condensing

Power Supply 24 VAC

Maximum VA Load 4 VA

Housing Material Rigid vinyl

Duct Wall

Dimensions 3 1/8" 3 1/8" 7 3/4" 4 1/4" 3 1/8" 1 7/16"

Operating Temperature 23113F (545C) 5995F (1535C)

Accuracy at 77F (25C) < (30 ppm CO2+ 3% of reading) < (40 ppm CO2+ 3% of reading)

Measuring Range 0-2000 parts per million (ppm)

Recommended Calibration Interval 5 years

Response Time 1 minute (063%)

Storage Temperature 4158F (2070C)

Humidity Range 0 to 85% relative humidity (RH)

Output Signal (jumper selectable) 4-20 mA, 0-20 mA, 0-10 VDC

Resolution of Analog Outputs 10 ppm CO2

Power Supply Nominal 24 VACPower Consumption


40/52

40 VAV-PRC003-EN

Acoustics are tricky to define forspecific jobsites. To provide anacoustical overview of a typical officesystem with mineral glass fiberdropped ceiling, ARI standard 885-98has generated the transfer functions inTable 11.

Sound power data was collected inaccordance with ARI Standard 880.Applying the transfer function forsound reduction due to officefurnishings, materials, etc. generated

the NC data which follows. This is areference document only provided toaddress general acoustical issues.What you will find is that the sound inthe occupied spaces generated by theVariTrac dampers is minimal whencompared to the main HVAC unitsound generation.

Acoustics

Some general ideas to minimizeacoustical issues:

pay close attention to location of theHVAC unit. This will typically set theoverall acoustical quality of your job.

locate VariTrac dampers outside theoccupied space.

internally lined ductwork can be used toreduce the discharge sound generatedby the HVAC unit.

install flex duct with minimal sagging,

and turns. locate balancing dampers as far from

the diffuser as possible to limit airbornenoise.

Note: VariTrac dampers do not carry theARI seal.

Table 11. Acoustical transfer functions Table 12. Radiated sound data

NC Based on 885-98 Mineral TileSize Radiated NC Size

6 in. 33 4708 in. 26 840

10 in. 25 131012 in. 26 188514 in. 29 214016 in. 21 2515

NC based on maximum rated airflowconditions.

ARI 885-98 Discharge TransferFunction Assumptions

Octave Band2 3 4 5 6 7

Small Box -24 -28 -39 -53 -59 -40(


41/52

VAV-PRC003-EN 41

Acoustics

Table 13. Discharge sound data

Note: NC data based on ARI 885-98 Acoustical transfer functions in Table 11.

DischargeSize CFM ISP NC

6 in. 375 0.25 6 in. 375 0.5 6 in. 375 1 186 in. 375 2 22

6 in. 300 0.256 in. 300 0.5 6 in. 300 1 6 in. 300 2 19

6 in. 225 0.25 6 in. 225 0.5 6 in. 225 1

6 in. 225 2 166 in. 150 0.25 6 in. 150 0.5 6 in. 150 1 6 in. 150 2 16

6 in. 75 0.25 6 in. 75 0.5 6 in. 75 1 6 in. 75 2 16

6 in. 38 0.25 6 in. 38 0.5 6 in. 38 1 6 in. 38 2 15

8 in. 656 0.25 8 in. 656 0.5 168 in. 656 1 248 in. 656 2 30

8 in. 525 0.25 8 in. 525 0.5 8 in. 525 1 208 in. 525 2 25

8 in. 394 0.25 8 in. 394 0.5 8 in. 394 1 168 in. 394 2 22

8 in. 263 0.25 8 in. 263 0.5 8 in. 263 1 8 in. 263 2 23

8 in. 131 0.25 8 in. 131 0.5 8 in. 131 1 158 in. 131 2 24

8 in. 66 0.25 8 in. 66 0.5 8 in. 66 1

8 in. 66 2 20


10 in. 1031 0.25 10 in. 1031 0.5 1510 in. 1031 1 2110 in. 1031 2 27

10 in. 825 0.25 10 in. 825 0.5 10 in. 825 1 1710 in. 825 2 22

10 in. 619 0.25 10 in. 619 0.5 10 in. 619 1

10 in. 619 2 2010 in. 413 0.25 10 in. 413 0.5 10 in. 413 1 10 in. 413 2 19

10 in. 206 0.25 10 in. 206 0.5 10 in. 206 1 10 in. 206 2 19

10 in. 103 0.25 10 in. 103 0.5 10 in. 103 1 10 in. 103 2 18

12 in. 1500 0.25 12 in. 1500 0.5 1512 in. 1500 1 2112 in. 1500 2 29

12 in. 1200 0.25 12 in. 1200 0.5 12 in. 1200 1 1712 in. 1200 2 25

12 in. 900 0.25 12 in. 900 0.5 12 in. 900 1 12 in. 900 2 22

12 in. 600 0.25 12 in. 600 0.5 12 in. 600 1 12 in. 600 2 21

12 in. 300 0.25 12 in. 300 0.5 12 in. 300 1 12 in. 300 2 20

12 in. 150 0.25 12 in. 150 0.5 12 in. 150 1

12 in. 150 2 19


14 in. 2000 0.25 14 in. 2000 0.5 1714 in. 2000 1 2414 in. 2000 2 30

14 in. 1600 0.25 14 in. 1600 0.5 14 in. 1600 1 1914 in. 1600 2 26

14 in. 1200 0.25 14 in. 1200 0.5 14 in. 1200 1 15

14 in. 1200 2 2314 in. 800 0.25 14 in. 800 0.5 14 in. 800 1 14 in. 800 2 23

14 in. 400 0.25 14 in. 400 0.5 14 in. 400 1 14 in. 400 2 23

14 in. 200 0.25 14 in. 200 0.5 14 in. 200 1 14 in. 200 2 20

16 in. 2625 0.25 16 in. 2625 0.5 1716 in. 2625 1 2516 in. 2625 2 32

16 in. 2100 0.25 16 in. 2100 0.5 16 in. 2100 1 23

16 in. 2100 2 2916 in. 1575 0.25 16 in. 1575 0.5 16 in. 1575 1 2216 in. 1575 2 27

16 in. 1050 0.25 16 in. 1050 0.5 16 in. 1050 1 16 in. 1050 2 22

16 in. 525 0.25 16 in. 525 0.5 16 in. 525 1 16 in. 525 2 23

16 in. 263 0.25 16 in. 263 0.5 16 in. 263 1 16 in. 263 2 23


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Dimensions and Weights

Figure 48.Central control panel dimensions

Note:

1. Central control panel weight is 2.5 lbs.

Front view Side view

8.75 in.

(22.38 cm)

2.75 in.

(6.99 cm)

10.25 in.

(26.04 cm)

Top view

Bottom view


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VAV-PRC003-EN 43

Figure 49.Communicating bypass control dimensions


Mounting holesSee back view for dimensions

4 1/4"

1 15/16"

3 5/16"Side View

6 3/4"

5"

3 3/8"

3 7/8"4 5/16"

1.00" 1.00"

0.300"

Back View

Notes:

7/8" knockout1/2" conduitCustomer entry

Weight 3 1/4 lbs

Operating Temp 32 to 140Humidity 5 to 95% (non-condensing)Mounting Method Metal screws

Duct StaticPressure Sensor

Duct TempSensor


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Figure 51.Rectangular zone damper dimensions


X

Y

6.00" Ref.

Slip & DriveConnection

Seam

16.00" Ref.

Dimensions

X Y

8.00"

8.00"

8.00"

10.00"

10.00"

14.00"

12.00"

14.00"

16.00"

16.00"

20.00"

18.00"

Damper Frame Data

Frame

Blades

Blade Pin

Gear

16-gage galvanized steel16-gage galvanized steelAll blades are 3.19" nominal widthand 8" maximum

ABS plastic

3/8" rolled steel, zinc plated


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VAV-PRC003-EN 47

R

UNOCC SETPOINTOVERRIDE

CF

MAX

CANCEL

ON

4.5

2.8

1.1

1.0

4.25"

1.44"3.125"

Figure 54.CO2Sensor dimensions


Figure 53.Occupancy Sensor

Figure 55.Digital Zone Sensor

3.60"

1.90"

2.50"

Front View

SideView


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48 VAV-PRC003-EN

Glossary

ABS gears Gears formed of alightweight plastic known for itstoughness, impact strength, anddimensional stability.

Back draft damper A one-wayairflow damper in a parallel fanpowered unit prevents primary flowfrom exiting the plenem inlet.

Binary input A two-position signalindicating on/off status.

Binary output A control output thatis either on or off.

Built-in time clock The occupancytimer included in the CCP operatordisplay.

Bypass damper The motorizeddamper ducted between the systemsupply and return ducts used tocontrol static pressure in changeoverbypass VAV systems.

Central control panel (CCP) Thesystem level control device in a Tranechangeover bypass or delivered VAVsystem that gathers data from zonecontrollers and operates the HVAC unitto maintain the correct air flow and

temperature.

Changeover-bypass VAV A controlthat provides variable air volumefunctionality to a constant volume airhandling system.

CO2sensor An analog sensor that

detects and measures carbon dioxidesensor to determine occupancy level.

Commissioning The process ofstarting up and verifying correctoperation of a building system.

Conditioned air Air that is heated,cooled, humidified, or dehumidified to

maintain comfort in an interior space.Constant volume An airdistribution system that varies thetemperature of a fixed volume of air tomaintain space comfort.

Delivered VAV A self configuringsystem providing true pressureindependent VAV control to smallerbuilding applications. Delivered VAVrequires a CCP with operator display, a

Commercial Voyager VAV rooftop unitand VariTrane VAV boxes.

Demand control ventilation Amethod of maintaining indoor airquality through intelligent ventilationbased on occupancy. The quantity ofventilation is controlled based onindoor CO2 levels, which correlate tooccupancy levels. Demand controlledventilation saves money by reducingventilation during periods of lowoccupancy.

Direct-expansion (DX) When therefrigerant in the system is eithercondensed or evaporated directly bythe medium being heated or cooled.

Discharge air(DA) Air dischargedfrom the air handler into the ducts.

Discharge air control An airhandling system that provides fixedtemperature air (either fixed or variablevolume). Other control devices vary theactual volume of air delivered to thespace to maintain occupant comfort.

Economizer A damper arrangementand automatic control system that

allows a heating, ventilation and airconditioning (HVAC) system to supplyup to 100 percent outside air to satisfycooling demands, even if additionalmechanical cooling is required

Exception schedule A one timeonly time of day schedule in a systemthat is removed automatically after use

Free cooling Outdoor air introducedto a system under correct conditions toprovided cooling to a space. Also seealso Economizer

HVAC Unit An air moving devicethat conditions air. An HVAC unit may

provide cooling, or heating and cooling.Typical HVAC units include packagedrooftop units, split systems, and watersource heat pumps.

LCD Liquid crystal display

NDIR Non-dispersive infraredtechnology

Negative pressure The conditionthat exists when more air is exhaustedfrom a space than is supplied.

Non-volatile memory Systemmemory that retains programming withno battery or capacitor back uprequired

Normally closed (NC) Electricalcontacts that are closed (current flows)in the de-energized condition

Normally open (NO) Electricalcontacts that are open (no currentflows) in the de-energized condition

Occupancy sensor A binary sensorthat transmits a signal upon detectionof movement in the coverage area

Outdoor air (OA) This is fresh airdrawn in to provide space ventilation.Also see Ventilation air

Outdoor air damper The damperthat draws fresh air into the air handlingsystem for ventilation. Also referred toas the ventilation or fresh air damper

Override A manual or automaticaction taken to bypass normaloperation

Packaged unitary system An airhandling system with all the major

components contained in a singlecabinet or installed in a single location

PIR Passive infrared sensingtechnology (used in occupancy andmotion detection sensors)

Polling The method a VariTrac CCPuses to determine the need for heatingor cooling from the air handling systemby examining the zone requirements

Positive pressure The condition thatexists when more air is supplied to aspace than is exhausted.

Pressure-dependent VAV control AVAV unit with airflow quantity

dependent upon static pressure. Thereis no zone flow sensor in pressuredependent VAV boxes.

Pressure-independent VAVcontrol AVAV unit with airflowquantity independent of duct staticpressure. Actual airflow to the space ismeasured and controlled by an airflowsensor in the pressure independentVAV box.


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VAV-PRC003-EN 49

Glossary

Priority shutdown An immediateshutdown of the fan and heating orcooling stages in a VariTrac changeoverbypass or Delivered VAV systemcaused by either the loss of criticalsystem information or an externalpriority shutdown input

Pulse-width modulating reheat Reheat that operates duct mountedelectric coils on a 0-100% duty cycle inresponse to increased space heatingdemand.

Reheat device A source of heatlocated downstream from a controldevice such as a VAV box to add heat toair entering a space to provideoccupant comfort

ReliaTel (RTRM) The latestgeneration Trane factory mountedunitary controller.

Return air (RA) Air returned to theair handler from the conditioned space,to be reconditioned.

Setpoint The desired roomtemperature to be achieved andmaintained by an HVAC system.

Setpoint limit An electronic ormanual constraint imposed on asetpoint to prevent misadjustment

SPDT A relay with of one set ofnormally-open, normally-closedcontacts

Staged electric reheat Reheat thatoperates one or more duct mountedelectric coils in a series in response toincreased space heating demand.

Staged (or perimeter) hot waterreheat Reheat that operates duct-mounted hot water or space-mountedelectric or hot water reheat coils inresponse to increased space heatingdemand

Static pressure The differencebetween the air pressure on the inside

of the duct and outside of the duct.Static pressure is an indicator of howmuch pressure the fans are creatingand how effective they will be atdistributing the supply air through theducts.

Supply air(SA) air which blows outof the air handler into the ducts. Seealso Discharge air (DA)

Terminal unit HVAC equipment thatprovides comfort directly to a space.

Thermal requirements The heatingor cooling load requirements for aspecific area or space in a building.

Care must be taken to not control areaswith different thermal requirementsfrom one air handling system

Touch-screen operator display The LCD panel mounted onto a VariTracCCP to allow direct user interface andtime of day programming for thesystem

Unit control module UCM A Tranemicroelectronic circuit board thatcontrols individual HVAC equipment.May link to an Integrated ComfortSystem

Unitary one or more factory-madeassemblies which normally include anevaporator or cooling coil, an airmoving device, and a compressor andcondenser combination

Variable air volume (VAV) an airhandling system that varies the volume

(amount) of constant temperature air toa space to control comfort

VariTrac The Trane changeoverbypass VAV system

VariTrane The Trane pressureindependent VAV box

VAV box The damper or air valve(plus associated controller) thatcontrols the zone air volume in a VAVsystem. Also see Variable air volume

Ventilation air The outdoor airdrawn into the HVAC unit to providefresh air to the space. Also seeOutdoor air (OA)

Voting See Polling

Zone sensor The device thatmeasures a variable (usuallytemperature) in a space and sends it toa controller. Commonly referred to as athermostat.


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