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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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4 VAV-PRC003-EN
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
Features andBenefits
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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VAV-PRC003-EN 9
Features andBenefits
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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Features andBenefits
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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Features andBenefits
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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Features andBenefits
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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VAV-PRC003-EN 13
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
ApplicationConsiderations
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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ApplicationConsiderations
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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ApplicationConsiderations
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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ApplicationConsiderations
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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ApplicationConsiderations
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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ApplicationConsiderations
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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22 VAV-PRC003-EN
ApplicationConsiderations
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
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VAV-PRC003-EN 23
ApplicationConsiderations
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
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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.
ApplicationConsiderations
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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
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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
08=8" (203 mm) round damper
10=10" (254 mm) round damper
12=12" (305 mm) round damper
14=14" (356 mm) round damper
16=16" (406 mm) round damper
1412=14 x 12 rectangular bypassdamper
1616=16 x 16 rectangular bypassdamper
2020=20 x 20 rectangular bypassdamper
3020=30 x 20 rectangular bypassdamper
0812=8 x 12 rectangular zone damper
0814=8 x 14 rectangular zone damper
0816=8 x 16 rectangular zone damper
1016=10 x 16 rectangular zone damper
1020=10 x 20 rectangular zone damper
1418=14 x 18 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.
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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
2R = 16 x 16 bypass damper
3R = 20 x 20 bypass damper
4R = 30 x 20 bypass damper
5R = 8 x 12 zone damper
6R = 8 x 14 zone damper
7R = 8 x 16 zone damper
8R = 10 x 16 zone damper
9R = 10 x 20 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
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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
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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
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VAV-PRC003-EN 31
Electrical Dataand Connections
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
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VAV-PRC003-EN 33
Electrical Dataand Connections
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
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34 VAV-PRC003-EN
Electrical Dataand Connections
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
OPTIONAL FIELD INSTALLEDPTIONAL FIELD INSTALLED
CO2 SENSORO SENSOR
OPTIONAL FIELD INSTALLEDPTIONAL FIELD INSTALLED
ONNOFF WATER VALVEFF WATER VALVE
OPTIONAL FIELD INSTALLEDPTIONAL FIELD INSTALLED
PROPORTIONAL WATER VALVEROPORTIONAL WATER VALVE
5.
OPTIONAL FIELD INSTALLEDPTIONAL FIELD INSTALLED
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
OPTIONAL FIELD INSTALLEDPTIONAL FIELD INSTALLED
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
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VAV-PRC003-EN 35
Electrical Dataand Connections
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
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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.
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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
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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(
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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
DischargeSize CFM ISP NC
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
DischargeSize CFM ISP NC
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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Figure 49.Communicating bypass control dimensions
Dimensions and Weights
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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VAV-PRC003-EN 45
Figure 51.Rectangular zone damper dimensions
Dimensions and Weights
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
Dimensions and Weights
Figure 53.Occupancy Sensor
Figure 55.Digital Zone Sensor
3.60"
1.90"
2.50"
Front View
SideView
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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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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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