Trane Recording Equipment 3VAV PRC003 EN User Manual
™
VariTrac Changeover  
BypassVAV  
(Tracker System CB)  
VAV-PRC003-EN  
June 2004  
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Contents  
Introduction ............................................................. 4  
Comfort Made Simple ................................................................ 4  
The Changeover BypassVAV Comfort Advantage ....................... 4  
VariTrac Product Enhancements ................................................. 4  
Features and Benefits........................................... 5–12  
Overview ................................................................................... 6  
Central Control Panel ................................................................. 7  
Optional Operator Display .......................................................... 7  
Communicating Bypass Controller ............................................. 8  
Tracker System Integration ......................................................... 8  
VariTrac Bypass Dampers ........................................................... 9  
VariTrac Zone Dampers ............................................................ 10  
Unit Control Module ................................................................ 10  
Zone Sensors ...................................................................... 11–12  
Application Considerations ................................ 13–24  
Introduction .............................................................................. 13  
Zoning Considerations.............................................................. 13  
Effective Changeover BypassVAV System Design ................ 14–19  
Pressure Dependent vs. Pressure Independent .......................... 20  
Local Reheat Capabilities UsingVariTraneVAV Units ............. 20–21  
Bypass Damper Operation ........................................................ 22  
Building Pressure Control ......................................................... 23  
ApplicationTip Summary .......................................................... 24  
Selection Procedures ......................................... 25–28  
VariTrac Dampers ................................................................25–26  
Service Model Numbers........................................................... 27  
Typical Bill of Materials ............................................................. 28  
Electrical Data and Connections ......................... 29–34  
Specifications ................................................... 35–38  
Acoustics.......................................................... 39–40  
Dimensions and Weights .................................... 41–46  
Glossary ........................................................... 47–48  
™ ® The following are trademarks or  
registered trademarks of their respective  
companies: Precedent, ReliaTel, Trace, Tracker,  
VariTrac, VariTrane, Voyager.  
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Introduction  
Comfort Made Simple  
Trane has a long history of innovative  
leadership in variable air volume (VAV)  
technology.Trane introduced the:  
The Changeover Bypass  
VAV Comfort Advantage  
VariTrac Product  
Enhancements  
Selected enhancements of the new  
VariTrac product are listed below.  
Packaged unitary systems offer a  
popular and cost-effective method of  
supplying conditioned air to light  
commercial buildings.These systems  
commonly have a constant-volume fan  
with a fixed outside air damper and a  
single thermostat.While a constant  
volume system may meet the overall  
thermal requirements of the space, only  
a single thermostat is available.This  
system may be insufficient in multiple-  
space applications with independent  
thermal load requirements.  
• first fan-poweredVAV unit  
• A new central control panel (CCP) with  
improved system temperature and  
pressure control functions  
• first factory-commissioned DDC  
controller  
• An optional touch-screen operator  
display for the CCP with built-in  
time clock for easier system setup and  
control  
• first preprogrammedVAV controller  
designed specifically for VAV  
applications  
Trane is now the leading manufacturer  
ofVAV terminal units andVAV-related  
products in the world.  
• A communicating bypass controller  
allows duct pressure and duct  
temperature to communicate to the  
system via a twisted shielded wire pair,  
thus eliminating costly “home-run”  
wiring  
The introduction ofVariTrac™ in 1989  
broughtVAV controls expertise into the  
changeover bypass zoning market.  
Changeover bypass systems use the  
practicality and cost effectiveness of  
constant volume unitary components  
like packaged rooftop units, split  
systems, or water-source heat pumps,  
and simply add dampers and a central  
control panel to coordinate the  
components.This allows up to  
24 individual sensors (thermostats) for  
independent temperature control.  
Trane is committed to continuous  
product improvement and now  
introduces a new generation ofVariTrac  
controls.This latest generation retains  
the functionality of the originalVariTrac  
system with exciting new  
• The next generation UCM zone  
controller allows CO2 and occupancy  
sensor inputs  
• A digital display zone sensor for  
simplified occupant control  
enhancements, utilizing the best of  
today’s technology.  
Advanced Control Options  
Some of theVariTrac intelligent system  
control features are listed below.  
• CO2-based demand control ventilation  
resets the position of the HVAC unit  
ventilation air damper when zone CO2  
levels rise  
Figure 1. TheVariTrac CCP maximizes  
system efficiency and reliability by  
coordinating the components of the  
changeover-bypass system  
Figure 2. TheVariTrac CCP with  
optional touch-screen interface  
simplifies system operation with  
intuitive icon-driven design  
• Zone-based HVAC unit control operates  
heating and cooling only when zone  
demand exists  
• Discharge air control to avoid extreme  
supply air conditions and maximize  
equipment life and occupant comfort  
• A simplified system-balancing process  
is available via PC software or the  
touch-screen interface  
• Global zone temperature setpoint limits  
simplify startup, commissioning, and  
operator control  
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Features and  
Benefits  
Figure 3. VariTrac changeover-bypass VAV system components  
VariTrac Central Control  
Panel with touchscreen  
interface  
HVAC  
Unit  
Bypass  
Damper  
Communicating  
Bypass  
Controller  
VariTrac Zone  
Damper  
Zone Sensor  
VariTrac Central Control Panel (CCP)  
The CCP is the system level controller which  
coordinates and monitorsVariTrac system  
Bypass Damper w/Wire and Quick Connect  
A round or rectangular damper ducted  
between the HVAC supply and return ducts. It  
is easily connected via a “quick-connector”  
which provides quick and consistent field wiring.The bypass  
damper is modulated by the CCP to maintain required system  
static pressure.  
operation, including HVAC system supply  
pressure and airflow, heating/cooling mode,  
supply air temperature, all zone temperatures and setpoints,  
fan mode, economizer position (when paired with CO2  
demand controlled ventilation), time-of-day scheduling, zone  
grouping logic, system override mode (after hours  
operation), and much more.  
Communicating Bypass Controller  
A single enclosure with duct temperature sensor,  
static pressure sensor, and communicating  
controller (UCM) which easily mounts on the  
supply ductwork.The UCM provides power to  
drive the bypass damper actuator.  
HVAC Unit  
VariTrac changeover bypass systems  
Rooftop  
operate withTrane and non-Trane products,  
including split systems, packaged rooftop  
units, and water-source heat pumps.These  
systems are generically referred to as HVAC  
(heating, ventilating, and air conditioning)  
units.When combined with aTrane  
packaged rooftop with ReliaTel™ controller,  
wiring, installation, and system startup  
efficiency is maximized by connecting with a  
simple twisted shielded wire pair.  
Zone Sensor  
Zone sensors (sometimes referred to as  
thermostats) measure space temperature and  
report it to the zone damper controller (UCM).  
Five models are available to satisfy varied aesthetic and  
application preferences.  
Split System  
WSHP  
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Features and  
Benefits  
How the System Works  
TheVAV terminal unit controller  
communicates zone temperature  
information to a central control panel  
(CCP). The CCP also gathers  
information from the system, including  
duct static pressure and supply-air  
temperature.The CCP determines zone  
heating or cooling needs using voting  
(or polling) logic, then requests heating  
or cooling from the HVAC unit.The CCP  
directs the HVAC unit to provide  
ventilation air to high-occupancy areas  
(demand control ventilation) or free-  
cooling when the outside air  
Overview  
A changeover-bypassVAV system  
commonly consists of an HVAC unit  
with a constant-volume supply fan, and  
direct-expansion (DX) cooling.This  
combined system has the ability to  
“change” to the heating mode or  
cooling mode, depending on individual  
zone comfort requirements. A heating  
coil or a gas-fired heater and an outside  
air damper are possible options.  
Changeover-bypassVAV is a comfort  
system developed for light commercial  
applications. A changeover-bypassVAV  
system responds to changing cooling  
or heating requirements by varying the  
quantity or volume of air delivered to  
each zone. Each zone has a thermostat  
for individual comfort control. An  
HVAC unit delivers a constant volume  
of air to the system. As the volume of  
air required by the zone changes,  
excess supply air is directed to the  
return duct via a bypass duct and  
damper. (See Figure 3 for typical  
A temperature sensor in each zone  
communicates information to an  
electronic controller on theVAV  
terminal unit.The controller then  
modulates the zone damper open or  
closed, supplying heating or cooling air  
to the zone.  
temperature falls below the  
temperature setpoint (economizer  
control).  
system components.)  
A changeover-bypassVAV system  
combines the comfort benefits ofVAV  
with the cost effectiveness and  
simplicity of packaged, constant-  
volume unitary equipment.  
Auto Changeover  
“Auto changeover” refers to the ability  
of the system to automatically change  
between the heating and cooling  
modes.  
The HVAC unit delivers a constant  
volume of supply air to the system. In  
order to maintain duct static pressure, a  
bypass duct and damper are required  
to bypass (detour) air not required in  
the zones.  
In a changeover-bypassVAV system,  
the CCP determines whether the HVAC  
unit should heat or cool by polling the  
temperature of the individual zones. It  
then compares the zone temperatures  
to the space temperature setpoints. If  
the supply air does not meet the criteria  
for the heat or cool mode called for, the  
CCP sends a signal to the HVAC unit to  
change the system to the opposite  
mode.  
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Features and  
Benefits  
Figure 5.VariTrac central control panel  
Figure 6.VariTrac central control panel  
with optional operator display  
Central Control Panel  
TheVariTrac central control panel (CCP)  
serves as the central source of  
communications and decisionmaking  
between the individual zones and the  
HVAC unit.The CCP determines system  
heating and cooling modes and  
coordinates the system supply air  
temperature and static pressure to  
satisfy building thermal load  
conditions. Inputs to the CCP include  
24VAC power and communication  
wiring to the zone dampers and bypass  
control.  
Binary inputs consist of priority  
shutdown and occupied/unoccupied  
modes. Heating, cooling, and the HVAC  
unit fan on split systems and non-Trane  
HVAC units can be controlled through  
binary outputs on an accessory relay  
board. If aTrane rooftop air conditioner  
with factory-installed electronic  
controls is used, the CCP can control  
heating, cooling, and the fan with a two-  
wire communication link tied to an  
interface board mounted in the rooftop.  
It can also display status information  
from the electronic controller in the  
rooftop. (See Figure 4.)  
CCP Feature Summary  
• Communicates with up to 24VAV unit  
control modules (UCMs)  
Optional Operator Display  
The optional operator display is a  
backlit, liquid crystal display with touch-  
screen programming capability.  
• Makes optimal heating and cooling  
decisions based on setpoint and  
temperature information received from  
individual zones  
The operator can access system and  
zone status through the display and  
perform basic setup of zoneVAV UCMs  
and CCP system operating parameters.  
The display allows an installer to  
commission aVariTrac system without  
using a PC. The operator display has a  
seven-day time clock for stand-alone  
scheduling capability.  
• Automatically calibrates all dampers,  
significantly reducing labor-intensive  
and costly field calibration  
• Windows-based PC software simplifies  
setup and control  
• Provides diagnostic information for all  
system components via the operator  
display or PC software  
Operator Display Feature Summary  
Figure 4. A screen representation  
from the central control panel  
illustrating system status  
• Backlit LCD touch-screen display for  
easy operator interface  
• Provides status and diagnostic  
information forTrane HVAC units  
equipped withTrane ReliaTel or UCP  
electronic controls  
• Combination of icon- and menu-based  
navigation provides intuitive operation  
• Provides a level of control for the daily  
operator, and a second level for  
commissioning and service  
• Three levels of security are available to  
protect system settings  
• Seven-day time clock for stand-alone,  
time-of-day scheduling  
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Features and  
Benefits  
• 365-day scheduling function and the  
flexibility of up to 10 schedules  
Communicating Bypass  
Controller  
The communicating bypass controller  
is a single control enclosure with the  
following integrated devices included:  
Tracker System Integration  
TheVariTrac system can be fully  
integrated with the new family of  
Tracker building controls. ATracker  
building management system can  
manage multipleVariTrac systems from  
a single control point.  
• Assign all systems to a single  
schedule, if desired, for simplified  
schedule changes  
• Exception scheduling feature for easy  
management of vacations and holidays  
• integrated UCM board  
• static pressure sensor  
Tracker System Summary  
• Automatically adjusts for daylight  
savings time and leap year  
• discharge air temperature sensor  
• Controls up to 10VariTrac systems  
from a singleTracker panel for easy  
building operation  
The communicating bypass controller  
directly controls the bypass damper  
and communicates duct conditions to  
the central control panel via a simple  
twisted shielded wire pair.  
• Remote communications capability  
via modem for system programming  
and control  
• LCD touch-screen operator display or  
Tracker PC software interface provides  
single-point building management by a  
local operator  
Quick Connect  
Minimizes field wiring labor and  
assures wiring consistency  
Figure 8.Tracker System Architecture  
DuctTemperature Sensor  
The supply air temperature sensor  
allows the CCP to control heating and  
cooling stages to maintain the supply  
air temperature. Supply air  
temperature setpoints can be edited  
through the operator display or  
PC software.  
Static Pressure Sensor  
The static pressure sensor measures  
duct static pressure and positions the  
bypass damper(s) to maintain the static  
pressure setpoint.  
Figure 7. Communicating bypass  
controller side view and 3-D view  
Up to 24  
VariTrac or  
VariTrane  
Dampers  
DuctTemperature  
Sensor  
Static Pressure  
Sensor  
Quick  
Connect  
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Features and  
Benefits  
Rectangular Bypass Damper Summary  
Round Bypass Damper Summary  
VariTrac Bypass Dampers  
• Rectangular bypass dampers are  
available in sizes 14 x 12, 16 x 16,  
20 x 20, and 30 x 20 inches  
• Round bypass dampers are available  
with inlet diameters 6, 8, 10, or 12 inches  
Bypass dampers are non-  
communicatingVariTrac dampers and  
include an integrated fully-modulating  
24VAC electric actuator.  
• Heavy gage galvanized steel cylinder  
with rolled bend for high structural  
integrity and corrosive resistance  
• Formed heavy gage galvanized steel  
frame, mechanically joined with linkage  
concealed in the side channel  
Field wiring errors are reduced with a  
quick-connect harness that plugs into  
the communicating bypass controller.  
• Metal-to-metal blade seal provides tight  
shutoff for low leakage  
• Air linkage is minimized with an  
opposed blade design with stainless  
steel side seals  
Dampers are nominally rated up to  
1800–2400 fpm at 1.75" of static  
pressure, depending on size.  
• Aerodynamic blade design provides a  
constant torque for stable operation at  
high velocity  
• Damper casing is 16 inches long and  
constructed of heavy gage galvanized  
sheet metal with S cleats on the inlet  
and outlet for easy installation  
For damper performance information,  
seeTable 2.  
• Factory-installed, direct-coupled, fully-  
modulating 24VAC actuator  
• Rated up to 2400 fpm at 1.75" of static  
pressure  
• Blades are six-inch nominal width,  
heavy gage galvanized steel  
• A blade rotation stop feature prevents  
over-rotation of the blades in the fully  
open position  
• Factory-installed, direct-coupled, fully-  
modulating 24VAC actuator  
• Rated up to 3000 fpm at 2" of static  
pressure  
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Features and  
Benefits  
Rectangular Zone Damper  
VariTrac Zone Dampers  
Unit Control Module  
• Rectangular dampers are available in  
sizes 8 x 12, 8 x 14, 8 x 16, 10 x 16,  
10 x 20, and 14 x 18 inches  
VariTrac zone dampers are fully-  
A unit control module (UCM) is the  
individual zone controller for the  
VariTrac air damper and is mounted on  
each zone damper.The unit controller  
continually monitors the zone  
modulating, pressure-dependentVAV  
devices. The dampers control zone  
temperature by varying the volume of  
air flowing into a space. EachVariTrac  
damper has a control box with aVAV  
control board and actuator enclosed.  
The dampers are designed to operate in  
static pressures up to 1.75 in. wg.  
• Heavy gage G90 galvanized steel  
frame assembled by a mechanical  
joining process  
temperature to maintain space  
temperature.The UCM varies the  
damper position as needed to meet  
zone setpoints and communicates  
current space requirements and  
system operating modes to the CCP.  
• Single-ply, heavy gage G90 galvanized  
steel blades  
• Linkage has high impact ABS gears,  
and is 3" nominal diameter  
Round Zone Damper  
• Round dampers are available in 6, 8, 10,  
12, 14, and 16 inch diameters  
The UCM can also control local heat.  
Local heat may be duct- or space-  
mounted, and can be staged electric,  
pulse-width modulating electric, and  
modulating or two-position staged  
hot water.  
• Factory-installed 24VAC direct-coupled  
actuator  
• Heavy gage galvanized steel cylinder  
with rolled bend for high structural  
integrity and corrosive resistance  
• Rated up to 2400 fpm at 2" of static  
pressure  
• Metal-to-metal seal provides tight  
shutoff  
• 90° blade rotation for a wide control  
range and stable operation  
• Aerodynamic blade design provides  
constant torque for stable operation at  
high velocity  
• Rated up to 2000 fpm at 1.75" of static  
pressure  
Figure 9.VariTrac rectangular and round zone dampers with UCMs  
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Features and  
Benefits  
Zone Sensors  
Figure 10. DDC zone sensors  
Figure 11. DDC zone sensor with LCD  
DDC Zone Sensor  
Digital Zone Sensor Summary  
DDC Zone Sensor with LCD  
The direct digital control (DDC) zone  
sensor is an uncomplicated, reliable  
electro-mechanical room sensor. No  
programming is required and most  
sensors contain an internal  
• Displays setpoint adjustment and space  
temperature in °F or °C  
The DDC zone sensor with LCD (liquid  
crystal display or digital) is compatible  
withVariTraneVAV andVariTrac  
controllers.  
• Simple, two-button control of space  
setpoint  
• Setpoint control and room temperature  
display can be optionally disabled  
communications jack.  
Models are available with combinations  
of features such as override (on-cancel)  
buttons and space-mounted setpoint.  
• Includes button for timed override and  
a cancel feature for after-hours system  
operation  
Four sensor variations are available:  
• Sensor only (no communications jack)  
• Sensor with override buttons  
• An easily accessible communications  
jack is provided forTrane portable edit  
terminal devices  
• Sensor with temperature setpoint only  
• Nonvolatile memory stores last  
programmed setpoints  
• Sensor with temperature setpoint and  
override buttons  
• For field balancing, maximum and  
minimum airflow or position can be  
overridden from the sensor  
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Features and  
Benefits  
Figure 12. Wall-mounted CO2 sensor  
Figure 15. Auxiliary temperature  
sensor  
Figure 14. Zone occupancy sensor  
Zone Occupancy Sensor  
AuxiliaryTemperature Sensor  
The energy-saving zone occupancy  
sensor is ideal for zones having  
intermittent use during the occupied  
mode.The sensor sends a signal to the  
VAV controller upon detection of  
movement in the coverage area.The  
VAV system then changes the zone  
from occupied standby mode to  
occupied mode.  
The auxiliary temperature sensor is  
used with any UCM damper control.  
The sensor allows the operator to  
monitor duct temperature or air  
temperature leaving a reheat device at  
the zone damper.This sensor is used  
for automatic changeover of a UCM  
damper when not using a CCP.The  
auxiliary temperature sensor is ideal for  
remote monitoring and diagnostics  
from the CCP operator display.  
Figure 13. Duct-mounted CO2 sensor  
Occupancy Zone Sensor Summary  
• Compatible withVariTraneVAV and  
VariTrac controllers  
AuxiliaryTemperature Sensor Summary  
• Thermistor sensing element 10,000  
Ohms @ 77°F  
• Used with zone damper UCM for  
controlling the occupied standby  
function  
CO2 Sensor  
Wall- and duct-mounted carbon dioxide  
(CO2) sensors are designed for  
demand-controlled ventilation zone  
applications.The sensor is compatible  
withVariTraneVAV andVariTrac  
controllers. TheTrane CO2 sensors  
measure carbon dioxide in parts-per-  
million (ppm) in occupied building  
spaces. Carbon dioxide measurements  
are used to identify under-ventilated  
building zones. Outdoor airflow  
• Wiring connection 8 feet, 18 awg  
• Ceiling-mount PIR occupancy sensor  
detects motion over an adjustable  
range up to 360 degrees  
• Sleeving for wire leads is acrylic #5 awg  
grade C rated @ 155C  
• Single detector covers up to 1200  
square feet. For areas larger than 1200  
square feet, multiple sensors can be  
wired in parallel  
• Adjustable time delay avoids nuisance  
change of state on loss of detection  
increases beyond design ventilation  
rates if the CO2 exceeds specified levels.  
• Adjustable sensitivity  
• SPDT isolated contacts connect to  
UCM input  
CO2 Zone Sensor Summary  
• Use with the UCM CO2 input for  
demand control ventilation  
• Silicone-based NDIR sensor technology  
for long-term stability  
• Measurement range of 2000 ppm CO2  
input with an output of 0–10Vdc  
• Wall-mount transmitter is compact and  
aesthetic in appearance  
• Optional zone return duct-mount  
transmitter is available  
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Application  
Considerations  
Zoned unitary systems, such as  
changeover-bypassVAV, divide thermal  
zones into smaller comfort zones. Each  
comfort zone has a damper and zone  
sensor that controls the amount of  
heated or cooled air delivered to the  
zone. A central system controller  
monitors the status of each zone  
damper and zone sensor.The controller  
then makes the decision to heat or cool  
for the HVAC unit.  
Zoning Considerations  
Consider the following two questions  
when evaluating your HVAC system  
design:  
Introduction  
TheVariTrac system is a changeover-  
bypassVAV system. One fan supplies  
either warm air for heating or cool air  
for cooling. It is typically applied in  
small buildings which use unitary  
heating/cooling air conditioners.These  
buildings need the simplicity and low  
cost of unitary equipment, but more  
than one comfort control zone (one  
zone temperature sensor) for each air  
conditioner.  
Will the building occupants be  
comfortable? A system designed  
with a single-zone HVAC unit and one  
zone sensor provides comfort to  
occupants near the zone sensor.  
However, occupants in perimeter areas  
or interior rooms may be too hot or too  
cold.  
Individual comfort zones served by a  
common HVAC unit (part of the same  
thermal zone) can require heating and  
cooling at the same time. In a  
changeover-bypassVAV system, the  
unit alternately provides warm and cool  
air in an attempt to satisfy the needs of  
all comfort zones.This is effective if the  
simultaneous calls for heating and  
cooling exist for short time periods  
only. Wide temperature variations may  
occur if some comfort zones need  
heating for extended periods of time  
while others need cooling.  
When isVariTrac a good HVAC system  
choice?To help answer this question,  
several important application concepts  
and considerations are discussed  
below.  
Will comfort be consistent from  
room to room and area by area? A  
building is normally divided into  
thermal zones for increased comfort  
control and energy savings. Each  
thermal zone should have a dedicated  
HVAC unit. For optimum comfort, each  
thermal zone should be further divided  
into comfort zones.  
Figure 16. System design affects  
occupancy comfort  
Choosing the number and location of  
thermal and comfort zones is critical in  
planning an effective system. Some  
things to consider in the design  
process include:  
Least  
Single Zone Building  
One thermal and  
one comfort zone  
Some comfort zones require special  
consideration because of their use or  
location. An example is the foyer or  
reception area of an office building.  
These areas often have wide variations  
in thermal load because of glass  
(relative to other areas of the building)  
and frequently-opened exterior doors.  
Another example is an interior storage  
room with the need for ventilation but  
little or no heating or cooling.These  
zones can significantly influence  
efficient operation and comfort levels  
throughout the building.  
• Geographic location  
• Orientation of the building to the sun  
• Prevailing winds  
Thermal Zoned Building  
Multiple thermal zones  
each with one  
• Wall construction (glass, insulation,  
building materials)  
comfort zone  
• Building layout, design, occupancy and  
occupancy pattern throughout the day  
and year  
Thermal and  
Comfort Zoned Building  
Multiple thermal zones  
each with multiple  
• Activities in each zone  
Preferably, areas such as these are  
designed as separate thermal zones  
with dedicated HVAC units. However,  
this may be impractical or costly.  
Instead, use fan-powered variable-  
volume terminal units, or units with  
local reheat.  
comfort zones  
Most  
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Application  
Considerations  
cooler, casual attire, such as golf shirts,  
light slacks, skirts, or shorts?  
Figure 17. Design process steps  
Effective Changeover  
Bypass VAV System Design  
Gather as much usage information as  
possible before designing a system.  
This can be challenging, particularly  
when finishing out tenant spaces.  
However, usage information is crucial  
to the selection of heating and cooling  
equipment, building zoning, and duct  
layout.  
Step 1. Define Occupant  
Comfort Needs  
Involves architect,  
engineer(s), and building owner  
Unitary zoning systems feature low  
first cost and quick, easy system design  
and equipment selection. The system is  
simple, but it is essential that key  
elements are considered during the  
design process.  
This section offers a system design  
sequence and discusses application  
considerations that, when followed,  
help avoid system control and  
operational instabilities.  
Step 2. Define Thermal Zones  
Involves engineers  
Several publications provide guidance  
for properly assessing indoor space  
comfort. An example is ASHRAE  
(American Society of Heating,  
and contractors  
Refrigerating and Air Conditioning  
Engineers) Standard 55,Thermal  
Environmental Conditions for Human  
Occupancy. This standard specifies the  
combinations of indoor space  
environments and personal factors  
(activity and clothing) that will produce  
thermal environmental conditions  
acceptable to 80 percent or more of the  
occupants within a space. Standard 55  
addresses temperature, thermal  
radiation, humidity, and air speed.  
Suggested design steps for unitary  
zoning systems are summarized in  
Figure 17.  
Step 3. Determine  
Comfort Zones  
Step 1. Define occupant comfort needs  
Involves engineers,  
The design process begins by  
considering the needs of building  
occupants and intended building use.  
contractors, and building owner  
y What is the intended use of the  
building? Is the building usage  
primarily office space? Is there a  
manufacturing operation? Are there  
areas that have special requirements  
such as computer or electronic rooms,  
video/television production, training  
facilities, etc.?  
Step 4. Size Heating/  
Cooling Equipment  
Involves engineer(s) and contractors  
ASHRAE Standard 62,Ventilation for  
Acceptable Indoor Air Quality, is  
another source for occupant comfort  
and safety issues regarding indoor air  
quality. The standard recommends that  
relative humidity be maintained  
between 30 and 60 percent.This  
maximizes comfort and reduces the  
potential for microbial growth.  
y What physical activity level is  
expected of the occupants? Seated  
occupants require different indoor  
temperatures for comfort than  
continuously moving occupants. An  
example may be a building with a mix  
of office space and light assembly or  
manufacturing.  
Step 5. Size Zone and  
Bypass Damper Units  
Involves engineer(s) and contractors  
Step 2. Define theThermal Zones  
A thermal zone is an area with similar  
load profiles and occupant comfort  
requirements. A thermal zone can be a  
single room, an area, a group of rooms  
or an entire building. Defining the  
thermal zones within a building is  
crucial to designing a comfortable  
indoor environment. Each thermal zone  
is conditioned by a single heating and/  
or cooling unit.The load of the thermal  
zone determines the size of the heating  
and cooling unit.  
Step 6. Design the Duct system  
Involves engineer(s) and contractors  
y Where will the occupants be  
located and at what times? Pay  
particular attention to areas with  
intermittent use, such as conference,  
training, and lunchrooms.  
Step 7. Air Diffuser  
Selection and Placement  
Involves engineer(s) and contractors  
y How are the occupants expected  
to dress? Give consideration to how  
the building occupants will dress.Will  
they dress in traditional business attire,  
such as long-sleeved shirts or blouses,  
ties, and jackets? Or, will they dress in  
14  
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Application  
Considerations  
Cost vs. Comfort  
Building Example 1 (See Figure 18.)  
of all areas. It also is not a good  
candidate for a zoning system because  
of the simultaneous need for heating  
and cooling.  
First cost can be reduced by limiting  
the number of thermal zones.  
Unfortunately, this may impact the  
thermal flexibility of the system, and  
result in zone comfort issues. Let’s take  
a closer look at this important system  
decision known as “thermal zoning.”  
Consider an existing single-story office  
building which is small, poorly  
insulated, with many large windows  
and few interior partitions. On a clear,  
cool spring day, the entire building is  
cool in the morning so heating is  
A similar building with good insulation  
and fewer shaded windows, on the  
other hand, may be a good candidate  
for a single thermal zone with individual  
comfort zones. The reduction in wall  
glass reduces the solar effect on the  
building resulting in all areas of the  
building having similar load profiles  
throughout the day. In this case, the  
building has a single thermal zone and  
is a good candidate for one HVAC unit.  
Individual comfort zones (zone  
required. By afternoon, however, the  
south side of the building being  
Characteristics of a building which can  
influence thermal load are:  
influenced by the solar load, is warm  
and requires cooling. The north side  
remains shaded and continues to  
require heating. This situation results in  
a simultaneous requirement for heating  
and cooling for extended periods. Due  
to the varying loads throughout the  
building, controlling the building as a  
single thermal zone (with a single HVAC  
unit) cannot satisfy the comfort needs  
• 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  
dampers) will be needed to assure  
comfortable conditions throughout the  
zone.  
• Varying loads from equipment or  
processes  
Let’s examine a few building examples  
and discuss the zoning criteria of each.  
Figure 18. Building Example 1 illustrates a small, poorly insulated office on the left, and improved design on the right.  
Men's  
Restroom  
Women's  
Restroom  
Men's  
Restroom  
Women's  
Restroom  
T
Thermostat  
T
Thermostat  
Poor Design Elements  
Improved Design Elements  
• Multiple zone thermostats  
• Shaded windows  
• One thermostat for space  
T
Thermostat  
T
Thermostat  
• Glass windows with no shading  
• Minimal wall insulation  
• Insulated walls  
Shaded  
Windows  
Glass windows  
with no shading  
Insulated  
Walls  
Minimal wall  
insulation  
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Application  
Considerations  
Building Example 2 (See Figure 19.)  
Step 3. Define the Comfort Zones  
Consider a strip mall in the spring or fall  
with stores that face both east and  
west. In the morning, the east side of  
the building gets full sun and warms up  
while the west side is shaded and  
requires heating. In the afternoon, the  
east side of the building may need heat  
and the west side cooling. Because of  
the thermal load variation throughout  
the day, this building will not remain  
comfortable if designed with a single  
heating and cooling unit.  
A primary criteria for defining a thermal  
zone is that it will not require  
Outside  
Doors  
Coffee  
Shop  
simultaneous heating and cooling. An  
HVAC unit with one fan is limited to  
supplying either heating or cooling.  
Most applications with larger thermal  
zones however will have varying  
thermal needs throughout the zone.  
These small variations can easily be  
addressed by properly defining comfort  
zones.  
Jewelry  
Store  
Poor Design Elements  
• One thermostat for entire space  
• One HVAC unit  
Electronics  
Store  
Pharmacy  
A comfort zone is an area within a  
thermal zone that is controlled by a  
zone damper.The amount of  
conditioned (heated or cooled) air  
entering the space varies. This is in  
response to a space thermostat.  
ASHRAE Standard 55 recommends  
limiting indoor temperature variations.  
Temperature variations of less than 2°F  
in 15 minutes or 4°F in an hour.  
Deviations from this recommendation  
will cause discomfort in 80 percent of  
the occupants. Zoning systems can  
greatly reduce temperature variations  
caused by shifting occupancy and solar  
load conditions in large thermal zones.  
Toy  
Store  
On the other hand, comfort in this  
building could be improved by dividing  
the building into two thermal zones  
(two HVAC units), one serving the east  
exposure and the other serving the  
west. Even with the two systems,  
individual occupant comfort is not  
necessarily assured. Interior  
partitioning, varying schedules and  
number of occupants within the  
thermal zone will drive differing  
amounts of heating and cooling. The  
issues related to comfort zoning are  
addressed in the next section.  
Clothing  
Store  
N
Figure 19. Building Example 2  
illustrates a poorly insulated store  
design (above) and an improved design  
(below)  
Coffee  
Shop  
Jewelry  
Store  
Outside  
Doors  
Improved Design Elements  
• Two thermal zones  
• Two HVAC units  
Electronics  
Store  
Pharmacy  
Toy  
Store  
Clothing  
Store  
N
16  
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Application  
Considerations  
Step 4. Sizing HVAC Equipment  
Calculating thermal zone diversity:  
1. Determine the instantaneous peak  
(or block) load for the thermal zone.  
This information is output from load  
analysis software such asTrane  
TRACE® or manually calculated.  
Once the building heating and cooling  
loads are known and the thermal zones  
have been determined, the heating and  
cooling equipment can be selected.  
Each thermal zone requires a separate  
heating and cooling unit. As discussed  
earlier, unitary zoning systems typically  
use packaged DX rooftop units or DX  
split systems. These systems are  
offered as heating and cooling units or  
heat pumps.  
2. Calculate the sum of the peak loads  
for each of the comfort zones within  
the thermal zone.  
3. The diversity factor is then calculated  
by dividing the instantaneous peak  
load value by the sum of the peak  
loads.  
When selecting the heating and cooling  
unit for a thermal zone, load diversity  
within the zone should be considered to  
minimize equipment size and therefore  
reduce system first cost and operating  
expense. Load diversity is defined as  
the ratio of the instantaneous peak  
loads (block load) to the sum of the  
peak loads within the thermal zone. In  
recognizing load diversity, the designer  
acknowledges that all areas of the  
Instantaneous  
Diversity  
Factor  
Peak Load  
=
Sum of Peaks  
The heating and cooling equipment will  
never be called upon to provide more  
capacity than was determined by the  
instantaneous peak load value.  
Consequently, the equipment capacity  
can be reduced by the diversity factor.  
thermal zone will not require maximum  
cooling or heating at the same time.  
Table 1. Diversity example  
While using diversity may reduce the  
size of the HVAC unit, the zone  
ductwork, dampers, and diffusers must  
be sized for the individual zone peak  
loads.The main trunk duct may be sized  
based on the HVAC unit airflow.  
Zone  
Time  
Peak Load  
Interior 3 p.m. in mid-July  
7.5 tons  
3.0 tons  
2.5 tons  
4.0 tons  
2.5 tons  
19.5 tons  
North  
East  
South  
West  
5 p.m. in mid-July  
9 a.m. in June  
4 p.m. in November  
5 p.m. in September  
Sum of Peak Loads  
Figure 20. Diversity example  
Note:The sum of blocks loads = 17.5 tons  
and occurs at 5 p.m. in mid-July.  
Wedge Zone  
Building Perimeter  
Diversity = 17.5 = 90%  
______  
19.5  
North Zone  
Glass  
East Zone  
West Zone  
Windows  
Interior Zone  
South Zone  
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Application  
Considerations  
Step 6. Designing the Duct System  
Dampers located immediately adjacent  
to the zone or diffuser may need to be  
sized at a lower velocity to avoid sound  
and airflow delivery issues.  
Step 5. Size Zone and Bypass  
Damper Units  
Low pressure, low velocity air  
distribution systems, such as zoned  
unitary systems, are usually designed  
using the equal friction method.  
Although static regain is the duct  
design method of choice for medium  
and high velocity variable air volume  
systems, the added complexity is  
difficult to justify with smaller unitary  
systems. In addition, the low operating  
velocity of most unitary systems makes  
the pressure available to “regain”, small  
and inconsequential.  
Sizing zone damper is relatively  
straightforward. The volume of airflow  
(in cfm or L/s) for each comfort zone  
should be known from the load  
analysis. The designer must select the  
duct velocity to be used for the system.  
Recommended zone damper velocities  
are 1000 to 1600 feet per minute (fpm)  
when applied at the branch level.  
Sizing dampers in this range will  
minimize damper cost, reduce the risk  
of excessive noise, and ensure  
Bypass dampers are typically sized for  
80 percent of HVAC unit airflow.  
Recommended velocities are 1600 to  
2000 fpm. Bypass dampers should be  
located as close to the HVAC unit as  
possible. (See Bypass Damper  
Operation for additional details.)  
Note:VariTrac systems are designed  
for HVAC unit static pressures up to  
1.75" w.c.  
adequate zone modulation/temperature  
control.  
With the equal friction method, ducts  
are sized for a constant pressure loss  
per given length of duct and fitting(s).  
Where low noise levels are especially  
critical, the system velocity can be  
reduced by enlarging the entering and  
leaving ductwork, damper unit or  
adding duct liner. A characteristic of the  
equal friction method that must be  
considered however, is that there is no  
natural provision for equalizing  
pressure drops in the branch sections.  
This results in each branch duct, and  
thus the damper units, having different  
entering static pressure and airflow  
characteristics.  
Figure 21. Hand balancing dampers  
Hand  
Balancing  
Damper  
A robust system and zone unit  
controller, like theTraneVariTrac  
system, will compensate for system  
static changes.The use of manual (or  
hand) balancing dampers in the  
branches will also ensure that airflow is  
appropriately distributed to each  
diffuser. (See Figure 21.)The overall  
effect is improved acoustical and  
system performance.  
VariTrac  
Damper  
Supply  
Duct  
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Application  
Considerations  
Step 7. Air Diffuser Selection and  
Placement  
• When the average glass plus wall heat  
loss is less than 250 Btuh/linear foot,  
the slot diffuser may be located in  
the center of the room with one or  
more slots blowing toward the  
perimeter wall.  
Return Diffusers  
Slot-style return diffusers offer some  
acoustical advantages over perforated  
grille styles. Perforated drop-in grilles  
typically offer little attenuation effect  
and thus allow sound in the plenum to  
break out into the occupied space. This  
is a problem in areas near the unitary  
heating and cooling unit. Improved  
ceiling aesthetics is also an advantage  
of slot return diffusers in jobs where  
slot supply diffusers are used. Within  
the occupied space, they blend with the  
slot supply diffusers.  
Supply Diffusers  
Many types of supply air diffusers are  
used in variable air volume systems.  
Performance, and ultimately space  
comfort, can vary greatly depending on  
the diffuser selected. Although  
constant-volume diffusers will provide  
air to the space at full cfm, as air  
volume delivered to the space  
• With glass and wall heat loss between  
250 and 450 Btuh/linear foot, diffusers  
should be positioned to blow toward  
the window and the perimeter wall with  
a collision velocity of 75 to 150 fpm. If  
using a continuous glass design,  
decreases, so does performance.  
Linear slot diffusers are recommended  
for mostVAV systems.  
position diffusers every four feet.  
• If heat loss exceeds 450 Btuh/linear  
foot, radiation or floor mounted heated  
air will be required to offset the high  
wall heat loss.  
A general rule of thumb is for the return  
air openings to equal the total area of  
the supply openings. If the ceiling is not  
tight, such as a drop-in ceiling, the  
return openings can be reduced by up  
to 50% of the supply air openings.  
Linear supply air slot diffusers are  
designed to properly mix variable air  
delivery of both heated and cooled air.  
Linear slot diffusers supply conditioned  
air which “hugs” the ceiling rather than  
“dumps” air downward on the  
To promote good air distribution, return  
diffusers should be positioned to  
minimize supply air short-circuiting to  
the return slot. The returns should be  
either perpendicular to the supply  
airflow or parallel and offset from the  
supply diffusers.  
occupants.This airflow characteristic is  
known as the “coanda effect”. The  
throw and aspiration characteristics of  
slot diffusers help to evenly distribute  
the air throughout the room or space.  
Locate linear slot diffusers in the center  
of the room with the discharge air  
pattern perpendicular to a perimeter  
wall. To maximize diffuser  
performance, placement in which air  
discharge patterns converge at right  
angles should be avoided. (See Diffuser  
section of theVariTrane catalog (VAV-  
PRC008-EN) for additional diffuser  
placement and performance  
Figure 22. Proper return diffuser orientation  
recommendations.)  
The throw characteristics of diffusers is  
well-documented. Slot diffusers should  
be positioned so that the velocity of the  
air striking an obstruction (such as a  
wall or column) is 75 feet per minute  
(fpm) or less. If airstreams from two  
diffusers collide, the collision velocity  
should not exceed 150 fpm. Higher  
collision velocities result in  
uncomfortable drafts in the lower levels  
of the room.  
In heating applications, linear slot  
diffusers must be placed to offset heat  
loss and prevent downdraft problems  
along perimeter walls. The following  
techniques have been proven by test  
and experience:  
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Application  
Considerations  
Example 2  
Local Reheat Capabilities  
Using VariTrane VAV Units  
Pressure Dependent vs.  
Pressure Independent  
Pressure-Dependent  
Parallel fan powered units with  
local heat applied help solve  
VariTrane pressure independentVAV  
units are a simple way to upgrade the  
zoneVAV capabilities on aVariTrac  
system.The main advantage is the  
ability to integrate units with either hot  
water or electric reheat. Here are  
application examples whereVAV units  
may enhance your design:  
problems in difficult areas to control  
like lobbies and vestibules. The parallel  
fan provides local heat to an individual  
zone without relying on the main HVAC  
unit’s heat or supply fan. This allows  
greater flexibility for mixing zones on a  
VariTrac system.  
A pressure-dependentVAV control  
sequence uses the space temperature  
sensor to directly control the position  
of the zone damper.The actual airflow  
delivered to the space is a by-product of  
this damper position and the static  
pressure in the duct upstream of the  
zone damper.  
VariTrane units with integral electric or  
hot water heat are available as:  
Example 1  
Series fan-powered VAV units  
work well in conference rooms and  
training rooms. Series fan-powered  
units supply constant air volume to the  
space.This provides excellent air  
movement in the space regardless of  
the internal load requirements. Hot  
water or electric heat are integral to the  
unit and optionally available to temper  
the air at partial load conditions.  
Ventilation air is a fixed-damper  
position and must be measured and set  
during the commissioning process.  
• single-duct  
• parallel fan-powered  
• series fan-powered  
Pressure-Independent  
A pressure-independentVAV control  
scheme directly controls the actual  
volume of primary air that flows to the  
space. An airflow-measuring device in  
theVAV terminal unit makes this  
possible.The position of the modulating  
device is not directly controlled and is a  
by-product of regulating the airflow  
through the unit. Because the airflow  
delivered to the space is directly  
controlled, it is independent of inlet  
static pressure.  
Figure 25. Parallel fan-poweredVAV  
terminal unit  
Figure 24. Series fan-poweredVAV  
terminal unit  
Figure 23. Single-ductVAV unit is  
available with integral electric or hot  
water heat  
20  
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Application  
Considerations  
Local Reheat Capabilities  
Non-VAV Options  
Figure 26. Trane hydronic wall fin  
This is ideal for spaces with large  
windows or perimeter heat losses  
which exceed 450 Btuh per linear foot.  
Trane wallfin is available with various  
grilles and paint options and can be  
pedestal or wall-mounted  
TheTraneVariTrac Zone Controller has  
built-in capabilities and logic to control  
a number of reheat sources.The  
previous page discussed how a  
VariTraneVAV unit with reheat can  
solve application issues by providing  
local reheat.  
Local Reheat  
Let’s investigate a few other alternatives  
which will provide local reheat, and  
result in exceptional zone temperature  
control.  
Local reheat is particularly important  
when an HVAC unit is in cooling mode.  
Cold air is delivered to all zones  
whether it is needed or not. Setting the  
minimum cooling position to zero may  
not be practical based on ventilation  
and/or general airflow requirements. In  
this case, local reheat options which  
can be controlled by the standard  
VariTrac zone controller include:  
Figure 27. Trane electric wall fin  
• hydronic wall fin or convector unit with  
either modulating or two position  
control. (See trane.com for a full line of  
wall fin and convector products.)  
• electric wall fin with multi-stage control  
• duct-mounted electric heater with  
multi-stage control  
• duct-mounted hot water coil with either  
modulating or two-position control.  
(See trane.com for a full line of duct-  
mounted water coils.)  
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Application  
Considerations  
Proper operation requires  
Bypass Damper Operation  
When zone dampers modulate airflow  
to the spaces, static pressure changes  
in the supply duct system. High  
pressure in a duct system creates  
excessive noise and causes poor  
comfort control. Low pressure results  
in insufficient airflow to the spaces.  
consideration of all aspects of bypass  
design and location.The bypass  
dampers and ductwork should be sized  
and located according to the following  
general recommendations:  
y Avoid turbulence by locating the  
bypass two to three equivalent duct  
diameters downstream of the HVAC  
unit discharge.  
The HVAC unit in a changeover bypass  
system is constant volume and does  
not modulate supply airflow.  
Changeover-bypassVAV systems  
support variable-air-volume operation  
in the zones by using a bypass duct  
with a motorized damper and a  
pressure-sensing device.  
y Locate the static pressure and supply  
air sensors in the main supply duct  
upstream of the bypass.  
y Locate the bypass before the zone  
dampers (as close to the HVAC unit as  
possible) to avoid comfort or noise  
issues.  
As duct pressure rises above the static  
pressure setpoint, the bypass damper  
begins to open. Conversely, when static  
pressure falls below the static pressure  
setpoint, the bypass damper begins to  
close until the static pressure setpoint  
is reached.The optimal static pressure  
setpoint is automatically determined  
upon system calibration.  
y Size the bypass damper to maintain the  
minimum required airflow through the  
HVAC unit (usually 80 percent of the  
total design cfm)  
y Provide adequate access for servicing  
the damper.  
Figure 28. Changeover bypass variable-air-volume system  
Rooftop  
Micro Control  
Heating and  
and Supply  
Temperature Sensors  
Return  
Air  
Duct  
Bypass  
Damper  
Supply  
Air Duct  
22  
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Application  
Considerations  
In buildings that have a ducted return to  
the fan, bypass air pressurizes the  
return air duct. As the return air duct  
pressure rises, the air flows out of the  
building through the barometric relief  
damper in the rooftop unit. Excess  
bypass air flows into the zones through  
the return air grilles.  
• Use an exhaust fan with no exhaust  
damper. Energize the exhaust fan when  
the outdoor air damper opens beyond  
25 percent to remove excess outside air  
from the building. This method is used  
with some rooftop units and is  
Building Pressure Control  
Comfortable, efficient building  
operation requires that the air pressure  
inside the building be slightly higher  
than the atmospheric pressure outside  
of the building.That is, the building is at  
a “positive” pressure with respect to  
the outside environment. If the indoor  
pressure is too low (negative), the  
doors may be hard to open and cold air  
may leak in through construction  
cracks, causing drafts and cold floors.  
On the other hand, if the indoor  
pressure is too high, the doors may  
stand open and the supply air flow to  
the zones may decrease, decreasing  
comfort.  
effective, affordable, and easy to install.  
• Use a back draft damper to prevent  
airflow to the return air plenum or  
grilles. When bypass airflow  
Using the following suggestions will  
help maintain building pressurization  
control:  
pressurizes the return duct, the back  
draft damper closes. Pressure in the  
HVAC unit return air inlet rises, causing  
the rooftop barometric relief damper to  
open.This method is less effective  
because the rooftop barometric relief  
damper is sized for a portion of the total  
airflow, not 100 percent of airflow which  
may be seen in economizer mode. As  
the economizer drives to the maximum  
position, the building usually becomes  
over-pressurized.  
• Use an exhaust fan with a modulated  
exhaust damper to remove air from the  
return air plenum or duct. Energize the  
exhaust fan as the outside air damper  
opens beyond the minimum position.  
Sense building static and maintain  
building air pressure at a slightly  
positive level by modulating the  
Fixed Outside Air Dampers  
Achieving appropriate building  
pressure is simple in a system with a  
constant volume supply fan and fixed  
outdoor air damper.To maintain a  
slightly positive building pressure, size  
the exhaust fans to remove slightly  
less air than is introduced through the  
outdoor air damper.  
exhaust damper position.  
Figure 29. Changeover bypass with an economizer.Without proper building  
pressurization, bypass air may be forced out of the return duct.  
Outside Economizer or Demand-  
ControlledVentilation Systems  
Fan  
Economizer  
If the system resets the quantity of  
outdoor air in response to occupancy  
demands (demand-controlled  
Outdoor  
ventilation), or uses an outdoor air  
economizer, undesirable changes in  
building pressure may result. As the  
quantity of outdoor air intake varies,  
the system must exhaust a similar  
quantity of air to avoid over or under  
pressurizing the building.  
Air Damper  
Return  
Damper  
Bypass  
Return  
Opening  
When using an economizer in a  
changeover-bypassVAV system under  
low cooling load conditions (reduced  
airflow to the zones), the bypass  
damper opens to maintain the static  
pressure setpoint and airflow through  
the supply fan. As the outside air  
damper opens to provide economizer  
cooling, the return air damper closes.  
In buildings with a ceiling plenum  
return, the bypass air dumps into the  
ceiling plenum since it can no longer  
return to the fan. The plenum pressure  
rises and plenum air enters the zones  
through the return air grilles.  
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Application  
Considerations  
ApplicationTip Summary  
Tip 1. Use comfort zones  
Tip 4. Place dampers properly  
Units serving thermal zones can  
provide greater comfort by dividing the  
thermal zones into “comfort zones”  
using a changeover-bypass-VAV  
system.  
The bypass damper should be ducted  
between the supply and the return of  
the unit as close to the unit as possible,  
and should be sized to handle 80% of  
the total system CFM.  
Tip 2. Create thermal zones  
Tip 5. Control building pressure  
Create thermal zones which minimize  
simultaneous heating and cooling  
requirements.This will avoid  
unnecessary changeover of the system  
and maximize comfort. As an example,  
a computer room would be a poor  
candidate for one comfort zone of a  
changeover-bypass-VAV system  
because it will rarely, if ever, require  
heating.  
It may be necessary to provide a  
modulating means to control building  
pressure, especially when economizers  
or demand-controlled ventilation are  
used in conjunction with a changeover-  
bypass-VAV system.  
Tip 6. Use fan-poweredVAV boxes  
Consider using fan-poweredVAV boxes  
to provide local heat or to enhance  
comfort levels in some of your zones.  
Conference rooms, or zones with high  
wall heat loss are ideal for either series  
or parallel units.  
Tip 3. Use local heat  
Zones which vary thermally by  
requiring more heat than the other  
zones or require heat when the HVAC  
unit is in cooling mode should use local  
heat. Local heat in the form ofVariTrane  
VAV units with electric or hot water  
heat, or wallfin, or convectors, or duct-  
mounted coils.The standardVariTrac  
controller is capable of controlling the  
heat based on zone temperature  
demands.  
24  
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Selection  
Procedures  
Zone Damper Selection Procedures  
VariTrac Dampers  
Refer to the sizing chart inTable 2 for  
zone dampers. Follow down the first  
column in the table for the desired  
velocity.Then follow across for the cfm  
(air volume) of a givenVariTrac damper  
based on that velocity.  
VariTrac dampers are typically installed  
onVariTrac changeover bypass variable  
air volume (VAV) systems.VariTrac is  
ideal when applied to buildings which  
use unitary HVAC units.The damper  
units have controls, which vary air  
volume and maintain appropriate duct  
static pressure in the system to make  
sure that all zones receive the right  
amount of airflow.  
Note: If the cfm exceeds the damper  
range, increase the damper size.  
Minimum airflow damper position  
should be set to10 percent in heating or  
cooling when a zone duct temperature  
sensor is used for stand-alone control.  
In addition, when controlling duct-  
mounted electric reheat coils, cooling  
minimum airflow should meet the  
heating unit manufacturer’s guidelines.  
(See Application Considerations,  
Maximum System Effectiveness for  
more details.)  
Trane offers fourVariTrac dampers:  
• Round zone dampers with DDC  
controls  
• Rectangular zone dampers with DDC  
controls  
• Round bypass dampers  
• Rectangular bypass dampers  
Figure 30. Round and rectangular zone and bypass dampers  
Bypass Damper Selection Procedures  
To determine the cfm capacity required  
for a bypass damper, calculate  
80 percent of the cfm capacity of  
the heating/cooling unit.  
Example: If the rooftop capacity is 1200  
cfm, the bypass damper should be  
sized for 1200 x .8 = 960 cfm.  
To determine the size of the damper,  
locate the recommended velocity and  
cfm for the bypass damper.  
Since a 10" round bypass damper at  
1800 fpm provides 980 cfm, a 10"  
damper at 960 cfm would be slightly  
less than 1800 fpm, but still within the  
1600 to 2000 fpm recommended  
velocity. A 10" bypass damper is  
selected.  
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Selection  
Procedures  
Table 2. Damper sizing charts  
Round Zone Damper  
Capacity (cfm), Dimensions, and Weights  
Round Bypass Damper  
Capacity (cfm), Dimensions, Blades, andWeights  
Size  
600  
6"  
120  
8"  
210  
10"  
330  
12"  
470  
14"  
640  
16"  
840  
Size  
600  
6"  
120  
8"  
210  
10"  
330  
12"  
470  
800  
160  
280  
435  
630  
800  
160  
280  
435  
630  
855  
1115  
1000  
200  
235  
350  
545  
785  
1000  
200  
235  
350  
545  
785  
1070  
1280  
1500  
1710  
20"  
1395  
1675  
1955  
2235  
20"  
1200  
420  
655  
940  
1200  
420  
655  
940  
1400  
275  
490  
765  
1100  
1255  
1415  
1570  
16"  
1400  
275  
490  
765  
1100  
1255  
16"  
1600  
315  
560  
875  
1600  
315  
560  
875  
1800  
350  
630  
980  
Length  
Ship Wt  
12"  
12"  
16"  
2000  
Length  
ShipWt  
390  
700  
12"  
1090  
16"  
11 lbs  
12 lbs  
17 lbs  
18 lbs  
27 lbs  
31 lbs  
12"  
11 lbs  
12 lbs  
17 lbs  
18 lbs  
Rectangular Zone Damper  
Capacity (cfm), Dimensions, Blades, andWeights  
Rectangular Bypass Damper  
Capacity (cfm), Dimensions, Blades, andWeights  
Size  
600  
8 x 12  
398  
531  
663  
796  
928  
1061  
2
8 x 14  
464  
8 x 16  
531  
10 x 16  
663  
10 x 20  
829  
14 x 18  
1045  
1393  
1741  
2089  
2437  
2785  
4
Size 14 x 12 16 x 16 20 x 20 30 x 20  
600  
800  
696  
928  
1061  
1415  
1769  
2122  
2476  
2830  
3183  
3537  
3
1658  
2211  
2763  
3316  
3869  
4421  
4974  
5527  
3
2487  
3316  
4145  
4974  
5803  
6632  
7461  
8290  
3
800  
619  
707  
884  
1105  
1382  
1658  
1934  
2211  
3
1000  
1161  
1393  
1625  
1857  
2089  
2321  
2
1000  
774  
884  
1105  
1326  
1547  
1769  
3
1200  
1200  
928  
1061  
1238  
1415  
2
1400  
1400  
1083  
1238  
2
1600  
1600  
1800  
Blades  
ShipWt  
2000  
8 lbs  
10 lbs  
12 lbs  
14 lbs  
16 lbs  
18 lbs  
Blades  
ShipWt  
16 lbs  
21 lbs  
29 lbs  
40 lbs  
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.  
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Selection  
Procedures  
Service Model Numbers  
V
1
A
2
D
3
A
4
0
5
6
6
A
7
0
8
0
9
P
0
10  
11  
Digits 1, 2, 3, 4 – ProductType  
Digit 7 – Controls (all factory downloaded  
and verified)  
VADA =VariTrac Air Damper  
A = Bypass with actuator  
VARA = Rectangular Air Damper  
B = Damper only control (Changeover)  
Digits 5, 6 –VariTrac Damper Size  
C = Damper plus up to 3 stages of  
Electric  
06 = 6" Damper  
08 = 8" Damper  
D = Damper plus 1-stage Normally-  
open hot water  
10 = 10" Damper  
12 = 12" Damper  
E = Damper plus 1-stage Normally-  
closed hot water  
14 = 14" Damper  
F = Not used  
16 = 16" Damper  
G = No controls (Actuator Only)  
H = Not used  
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  
J = Bypass for rectangular damper  
with actuator  
Digits 8, 9, 10, 11  
00P0 = Design sequence  
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Selection  
Procedures  
Typical Bill of Materials  
Device Name  
Function in System  
Number Required  
Central control panel  
w/optional operator display  
Controls the HVAC system and provides local  
operator interface  
One per HVAC unit/VariTrac system  
(thermal zone)  
A
B
C
Table 3. TypicalVariTrac  
changeover-bypassVAV  
system components  
Communicating bypass  
controller  
Sends supply duct temperature and pressure to  
the 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 return  
airstream  
VariTrac dampers  
Zone sensors  
Varies air volume to the space to control comfort  
One per comfort zone  
D
E
F
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 24V  
power supply  
Zone damper power supply(s)  
24V power for the zone dampers  
Power supplies may be shared; each  
zone requires 10VA (plus the load of  
optional outputs)  
G
H
J
Trane rooftop communications  
interface  
Allows the CCP and Trane rooftop controller to  
communicate with each other via simple twisted  
shielded wire pair  
One per controlled Trane rooftop  
with ReliaTel controller  
Optional relay board  
Provides 24V control of any non-communicating  
HVAC unit  
One per controlled non-  
communicating HVAC unit  
H
Figure 31. Typical  
components in a  
changeover-bypass  
VAV system  
B
C
G
D
F
E
A
&
J
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Electrical Data  
and Connections  
Figure 32. Central control panel field wiring  
Termination Board TB2  
Line voltage  
24 Vac  
Comm4 UCM  
Comm4 UCM  
+
+
Comm4  
link  
Comm4  
link  
-
-
Splice  
Comm5 UCM  
Tracker  
A
A
Comm5  
link  
Comm5  
link  
B
B
Splice  
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.  
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Electrical Data  
and Connections  
Figure 33. Relay board wiring  
Relay Board TB2  
TB1  
1
24 VAC CLASS 2 COOL UNIT  
24 VAC CLASS 2 HEAT UNIT  
SUPPLY FAN  
2
3
4
2 HEAT/2COOL  
COOL 1  
HEAT PUMP  
COMP 1  
COOL 2  
HEAT 1  
HEAT 2  
COMP 2  
5
6
AUX HEAT  
REV VALVE  
7
8
9
SPARE  
OUTSIDE AIR  
HEAT/COOL  
OR ICS  
10  
11  
12  
13  
14  
15  
Figure 34.Typical relay board wiring  
Relay Board TB2  
HVAC Unit  
TB1  
24V Terminal Strip  
1
2
3
4
5
R
G
Y1  
Y2  
W1  
W2  
6
7
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Electrical Data  
and Connections  
Figure 35. UCM Comm LinkWiring  
C O M M 4  
C O M M 5  
P R E S S  
P R E S S  
P R E S S  
T B 3 – 6  
T B 3 – 5  
T B 3 – 3  
T B 3 – 2  
T B 3 – 1  
T B 1 – 1  
T B 1 – 2  
T B 4 – 1  
T B 2 – 6  
T B 2 – 5  
J 8  
T B 2 – 4  
T B 2 – 3  
J 7  
J 9  
T B 2 – 2  
T B 2 – 1  
J 1 0  
J 1 1  
T B 3 – 6  
T B 3 – 5  
T B 3 – 3  
T B 3 – 2  
T B 3 – 1  
T B 1 – 1  
T B 1 – 2  
T B 4 – 1  
T B 2 – 6  
T B 2 – 5  
J 8  
T B 2 – 4  
T B 2 – 3  
J 7  
J 9  
T B 2 – 2  
T B 2 – 1  
J 1 0  
J 1 1  
T B 3 – 6  
T B 3 – 5  
T B 3 – 3  
T B 3 – 2  
T B 3 – 1  
T B 1 – 1  
T B 1 – 2  
T B 4 – 1  
T B 2 – 6  
T B 2 – 5  
J 8  
T B 2 – 4  
T B 2 – 3  
J 7  
J 9  
T B 2 – 2  
T B 2 – 1  
J 1 0  
J 1 1  
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Electrical Data  
and Connections  
Figure 36. Communicating bypass controller wiring  
CLOSE  
CCW OPEN  
COM HOT  
CW  
TO NEC CLASS 2  
24V TRANSFORMER  
LOAD 8 VA  
ACTUATOR  
(WITHOUT ACTUATOR)  
ACTUATOR  
W–HOT  
SPARE  
BK–OPEN  
CONNECTOR  
R–CLOSE  
STATIC  
PRESSURE  
2.  
24VAC  
PORT  
GND 24V  
ACT  
BIP  
FEMALE PLUG END  
OF BYPASS SENSOR  
ASSEMBLY CABLE  
J1  
1
HIGH  
ADDRESS  
SWITCH  
J3  
R
MALE PLUG END  
LOCATED ON DDC\UCM  
CONTROL BOARD  
+
D.D.C.\U.C.M.  
CONTROL BOARD  
BK  
VOUT  
–
G
1
+
–
–
+
+
–
PRESSURE  
TRANSDUCER  
YEL  
GRN  
ZONE GND SET A/CO2  
GND  
D.D.C.\U.C.M.  
CONTROL BOARD  
AIR SUPPLY TEMP SENSOR  
COMMUNICATING SENSOR/BYPASS  
CONTROL BOX  
SHIELDED  
TWISTED PAIR  
COMMUNICATIONS  
WIRING  
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Electrical Data  
and Connections  
Figure 37. UCMWiring  
24 VAC 60 HZ  
NEC CLASS–2  
8.  
CONTROL CIRCUIT  
R (HOT)  
5.  
(TB1–1) 24VAC  
O (COMMON)  
(TB4–1) BIP  
R
G
W
GR (NC CONTACT)  
(TB1–1) 24VAC  
BK (RETURN)  
(TB1–2) GND  
Y
NOT CONNECTED  
W
OPTIONAL FIELD INSTALLED  
OCCUPANCY SENSOR  
DAMPER  
ACTUATOR  
WIRING  
3RD STG.  
TO J11  
HEATER STAGE  
2ND STG.  
CONTACTOR(S)  
24 VAC, 12 VA  
MAX/COIL  
TO J10  
TO J9  
TO J8  
1ST STG.  
HOT  
OPTIONALL FIELD INSTALLED  
ELECTRIC HEATER  
ACT  
BIP  
GND 24V  
J1  
1
W (HOT)  
PROP. WATER  
VALV  
24VAC  
TO J8  
TO J9  
BK (CLOSE)  
R (OPEN)  
TB3–2  
TB3–1  
TB1–2  
TB3–3  
TB2–5  
TO J10  
12 VA MAX  
ADDRESS  
SWITCH  
J3  
1
D.D.C. \ U.CM.  
CONTROL BOARD  
TB1–1  
TB2–6  
OPTIONAL FIELD INSTALLED  
PROPORTIONAL WATER VALVE  
1
2
1
2
3
1
2
+
+
+
–
–
–
ON–OFF  
WATER VALVE  
24VAC  
TB1  
TB2  
TB3  
7.  
YEL  
GRN  
TO J9  
TO J8  
DIGITAL  
ZONE SENSOR  
OPTIONAL FIELD  
12 VA MAX  
A/CO2  
ZONE GND SET  
GND  
INSTALLED DIGITAL ZONE SENSOR  
OPTIONAL FIELD INSTALLED  
ON–OFF WATER VALVE  
TB2–6  
TB3–1  
TB2–5  
TB3–2  
TB3–3  
D.D.C. \ U.CM.  
CONTROL BOARD  
6.  
9.  
(TB1–1) 24V  
24V  
GND  
OUT  
+
0
V
5
4
3
2
1
CO2  
SENSOR  
(TB3–6) GND  
ZONE SENSOR  
W/ COMM. JACK  
REMOTE MTD.  
SHIELDED  
TWISTED PAIR  
(TB3–5) A/CO2  
OPTIONAL FIELD INSTALLED  
CO2 SENSOR  
3.  
4.  
COMMUNICATIONS  
WIRING  
OPTIONAL FIELD  
INSTALLED DIGITAL ZONE SENSOR  
TB3–5  
TB3–6  
NOTES:  
Factory Wiring  
Field Wiring  
Optional or Alternate Wiring  
1.  
6.  
OPTIONAL FIELD INSTALLED  
AUX TEMP SENSOR  
2. ¼" 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 TB4–1 (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 TB1–2.  
9. Shields of communication wiring should be tied together and insulated.  
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Electrical Data  
and Connections  
Figure 38. DDC zone sensor with LCD  
Digital Sensor  
Board  
TB1–1  
24V  
–2  
GND  
J1  
1
ACT  
BIP  
GND 24V  
TB2–1  
ADDRESS  
SWITCH  
Digital Sensor  
J3  
1
Temperature  
–2  
D.D.C.\U.C.M.  
CONTROL BOARD  
Terminal Connection Chart  
Field Wire  
Color Code  
Sensor  
UCM  
Signal Common  
–2  
TB1–1 TB1–1  
TB1–2 TB1–2  
TB2–1 TB3–1  
TB2–2 TB3–2  
TB2–3 TB3–3  
+
–
+
–
+
–
Setpoint  
S
YEL  
GRN  
ZONE GND SET A/CO2  
GND  
TB3–1  
1
Communications  
+ (High)  
–2  
TB3–1  
TB2–5  
TB3–2 TB2–6  
Communications  
– (Low)  
Optional  
Field Mounted  
Aux. Temp. Sensor  
Figure 39. DDC zone sensor wiring  
J1  
1
ACT  
BIP  
GND 24V  
ADDRESS  
SWITCH  
J3  
1
D.D.C.\U.C.M.  
CONTROL BOARD  
+
–
+
–
+
–
S
YEL  
GRN  
ZONE GND SET A/CO2 GND  
1
Night Setback  
Override Option  
TB1–1  
Sensor  
Optional  
Field Mounted  
Aux. Temp. Sensor  
Temperature  
–2  
PB1  
ON  
Mechanical Sensor  
Terminal Connection Chart  
Signal Common  
–3  
Field Wire  
Warmer  
Cooler  
Sensor  
Adjustable  
Setpoint Option  
UCM  
Color Code  
Setpoint  
–4  
2
TB1–1 TB3–1  
TB1–2 TB3–2  
TB1–4 TB2–5  
TB1–5 TB2–6  
Comm 1  
Communications (Optional)  
Figure Notes:  
+ (High)  
Communications  
Jack  
–5  
Shield must be spliced with other  
communication link shields  
1
2
Communications (Optional)  
– (Low)  
Shield must be cut back and taped  
at sensor.  
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Specifications  
Table 4. Zone sensor options  
Figure 40.VariTrac DDC zone  
sensors  
Number of  
Zone Sensor Options  
RequiredWires1  
Sensor only (no communications jack available)  
Sensor with adjustable setpoint  
Sensor with night setback override and cancel buttons  
2
3
2
Sensor with adjustable setpoint and night setback  
override and cancel buttons  
3
Sensor with digital display and adjustable setpoint and  
night setback override and cancel buttons  
52  
Notes:  
1 Most sensors have a communication jack available as an option. If these jacks are used, they must be  
wired to the UCM using an approved two-conductor, shielded cable.The communication jacks do not  
need to be wired for the system to operate properly.  
2 Three wires are required for sensor connections.Two wires are required for 24-Vac power connection.  
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Specifications  
Figure 41.VariTrac central control  
panel components  
Table 5.VariTrac control panel specifications  
Power Requirements  
20–30 Vac, 60 Hz, single-phase, 30 VA minimum. Class 2 transformer  
required.  
Operating Environment  
Storage Environment  
Control Enclosure  
Mounting  
32°–122°F (0°–50°C), 10–90% relative humidity, non-condensing  
-40°F–122°F (-40°–85°C), 5–95% relative humidity, non-condensing  
NEMA 1 resin enclosure, plenum rated  
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 shielded  
pair wire with stranded tinned copper conductors. Maximum total wire  
length is 3,500 ft (1066.8 m). Wire must meetTrane specifications.  
Binary Input  
Voltage (provided by VariTrac CCP): 10–14 Vdc  
Current (provided by VariTrac CCP): 10–14 mA  
Note: 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 Central  
Control Panel is maintained permanently.  
Figure 42.VariTrac UCM round  
damper  
Table 6. UCM damper specifications  
Power Requirements  
20–30Vac, 60Hz, single-phase 10VA minimum (plus load of optional heat  
outputs). Class 2 transformer required.  
Operating Environment  
Storage Environment  
Control Enclosure  
32°–120°F (0°–49°C). 10–90% relative humidity, non-condensing  
-50°–200°F (-46°–93°C). 5–95% relative humidity, non-condensing  
NEMA 1 metal enclosure, plenum rated  
Communication Link Wiring Communication link wiring must be Level 4 22-AWG twisted shielded  
pair wire with stranded tinned copper conductors. Maximum total wire is  
3,500 ft (1066.8 m). Wire must meetTrane specifications.  
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Specifications  
Figure 43. Communicating bypass  
controller  
Table 7. Communicating bypass control assembly specifications  
Power Requirements  
20–30 Vac, 60Hz, single-phase 15 VA minimum. Class 2 transformer  
required.  
Operating Environment  
Storage Environment  
Control Enclosure  
32°–120°F (0°–49°C). 10–90% relative humidity, non-condensing  
-50°–200°F (-46°–93°C). 5–95% relative humidity, non-condensing  
NEMA 1 metal enclosure, plenum rated  
Communication Link Wiring Communication link wiring must be Level 4 22-AWG twisted shielded  
pair wire with stranded tinned copper conductors. Maximum total wire is  
3,500 ft (1066.8 m). Wire must meetTrane specifications.  
Table 8. Zone occupancy sensor specifications  
Figure 44. Zone occupancy sensor  
Power Supply  
24 Vac or 24 Vdc, 10%  
0.88 VA @ 24 Vac, 0.722 VA @ 24 Vdc  
1 A @ 24 Vac or 24 Vdc  
32°–131°F (0°–55°C)  
-22°–176°F (-30°–80°C)  
0–95% non-condensing  
1200 sq. ft (365.8 m)  
22 ft (6.7 m)  
Maximum VA Load  
Isolated Relay Rating  
OperatingTemperature  
StorageTemperature  
Humidity Range  
Effective Coverage Area  
Effective Coverage Radius  
Housing Material  
ABS plastic  
Ideal for zones with intermittent  
occupancy like conference rooms).  
When occupied, the zone reverts to  
unoccupied setpoints to save energy.  
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Specifications  
Figure 45. DDC zone sensor with  
digital display  
Table 9. Digital zone sensor specifications  
Thermistor Resistance Rating  
Accuracy at 77°F (25°C)  
Setpoint Resistance Rating  
Display ZoneTemperature Range  
Display Setpoint Range  
OperatingTemperature  
StorageTemperature  
Humidity Range  
10kW at 77° (25°C)  
0.4°F (0.2°C)  
500 Ohms at 70°F (21.2°F)  
40°–99°F (10° to 35°C)  
50°–90°F (10° to 32°C)  
0°–120°F (–18° to 49°C)  
–20°–130°F (–29° to 54°C)  
5–95% non-condensing  
24 VAC  
Power Supply  
Maximum VA Load  
4 VA  
Housing Material  
Rigid vinyl  
Figure 46. CO2 duct sensor  
Table 10. CO2 sensor specifications  
Duct  
Wall  
Dimensions  
3 1/8" × 3 1/8" × 7 3/4"  
4 1/4" × 3 1/8" × 1 7/16"  
OperatingTemperature  
Accuracy at 77°F (25°C)  
Measuring Range  
23°–113°F (–5°–45°C)  
59°–95°F (15°–35°C)  
<
(30 ppm CO2 + 3% of reading)  
<
(40 ppm CO2 + 3% of reading)  
0-2000 parts per million (ppm)  
Recommended Calibration Interval 5 years  
Response Time  
1 minute (0–63%)  
StorageTemperature  
Humidity Range  
Output Signal (jumper selectable)  
Resolution of Analog Outputs  
Power Supply  
–4°–158°F (–20°–70°C)  
0 to 85% relative humidity (RH)  
4-20 mA, 0-20 mA, 0-10 VDC  
10 ppm CO2  
Figure 47. CO2 wall sensor  
Nominal 24 VAC  
Power Consumption  
Housing Material  
<5 VA  
ABS plastic  
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Acoustics  
Acoustics are tricky to define for  
specific jobsites. To provide an  
acoustical overview of a typical office  
system with mineral glass fiber  
dropped ceiling, ARI standard 885-98  
has generated the transfer functions in  
Table 11.  
Table 11. Acoustical transfer functions  
Some general ideas to minimize  
acoustical issues:  
ARI 885-98 DischargeTransfer  
Function Assumptions  
Octave Band  
• pay close attention to location of the  
HVAC unit. This will typically set the  
overall acoustical quality of your job.  
2
3
4
5
6
7
Small Box  
-24 -28 -39 -53 -59 -40  
-27 -29 240 -51 -53 -39  
-29 -30 -41 -51 -52 -39  
• locateVariTrac dampers outside the  
occupied space.  
(<300 cfm)  
Medium Box  
(<300–700 cfm)  
Large Box  
Sound power data was collected in  
accordance with ARI Standard 880.  
Applying the transfer function for  
sound reduction due to office  
furnishings, materials, etc. generated  
the NC data which follows. This is a  
reference document only provided to  
address general acoustical issues.  
What you will find is that the sound in  
the occupied spaces generated by the  
VariTrac dampers is minimal when  
compared to the main HVAC unit  
sound generation.  
• internally lined ductwork can be used to  
reduce the discharge sound generated  
by the HVAC unit.  
(>700 cfm)  
Note:Add to terminal unit sound power to  
determine discharge sound pressure in the space.  
• install flex duct with minimal sagging,  
and turns.  
ARI 885-98 RadiatedTransfer  
Function Assumptions  
Octave Band  
• locate balancing dampers as far from  
the diffuser as possible to limit airborne  
noise.  
2
3
4
5
6
7
Type 2 Mineral  
Fiber Insulation  
-18 -19 -20 -26 -31 -36  
Note:VariTrac dampers do not carry the  
ARI seal.  
Table 12. Radiated sound data  
NC Based on 885-98 MineralTile  
Size  
Radiated NC  
Size  
6 in.  
8 in.  
10 in.  
12 in.  
14 in.  
16 in.  
33  
26  
25  
26  
29  
21  
470  
840  
1310  
1885  
2140  
2515  
NC based on maximum rated airflow  
conditions.  
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Acoustics  
Table 13. Discharge sound data  
Discharge  
Discharge  
Discharge  
NC  
Size  
CFM  
ISP  
NC  
Size  
CFM  
ISP  
NC  
Size  
CFM  
ISP  
6 in.  
6 in.  
6 in.  
6 in.  
375  
375  
375  
375  
0.25  
0.5  
1
—
—
18  
22  
10 in.  
10 in.  
10 in.  
10 in.  
1031  
1031  
1031  
1031  
0.25  
0.5  
1
—
15  
21  
27  
14 in.  
14 in.  
14 in.  
14 in.  
2000  
2000  
2000  
2000  
0.25  
0.5  
1
—
17  
24  
30  
2
2
2
6 in.  
6 in.  
6 in.  
6 in.  
300  
300  
300  
300  
0.25  
0.5  
1
10 in.  
10 in.  
10 in.  
10 in.  
825  
825  
825  
825  
0.25  
0.5  
1
—
—
17  
22  
14 in.  
14 in.  
14 in.  
14 in.  
1600  
1600  
1600  
1600  
0.25  
0.5  
1
—
—
19  
26  
—
—
19  
2
2
2
6 in.  
6 in.  
6 in.  
6 in.  
6 in.  
6 in.  
6 in.  
6 in.  
6 in.  
6 in.  
6 in.  
6 in.  
6 in.  
6 in.  
6 in.  
6 in.  
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
225  
225  
225  
225  
150  
150  
150  
150  
75  
75  
75  
75  
38  
38  
38  
38  
656  
656  
656  
656  
525  
525  
525  
525  
394  
394  
394  
394  
263  
263  
263  
263  
0.25  
0.5  
1
—
—
—
16  
—
—
—
16  
—
—
—
16  
—
—
—
15  
—
16  
24  
30  
—
—
20  
25  
—
—
10 in.  
10 in.  
10 in.  
10 in.  
10 in.  
10 in.  
10 in.  
10 in.  
10 in.  
10 in.  
10 in.  
10 in.  
10 in.  
10 in.  
10 in.  
10 in.  
12 in. 1500  
12 in. 1500  
12 in. 1500  
12 in. 1500  
12 in. 1200  
12 in. 1200  
12 in. 1200  
12 in. 1200  
12 in.  
12 in.  
12 in.  
12 in.  
12 in.  
12 in.  
12 in.  
12 in.  
619  
619  
619  
619  
413  
413  
413  
413  
206  
206  
206  
206  
103  
103  
103  
103  
0.25  
0.5  
1
—
—
—
20  
—
—
—
19  
—
—
—
19  
—
—
—
18  
—
15  
21  
29  
—
—
17  
25  
—
—
—
22  
—
—
—
21  
—
—
—
20  
—
—
—
19  
14 in.  
14 in.  
14 in.  
14 in.  
1200  
1200  
1200  
1200  
0.25  
0.5  
1
—
—
15  
23  
2
2
2
14 in.  
14 in.  
14 in.  
14 in.  
800  
800  
800  
800  
0.25  
0.5  
1
—
—
—
23  
0.25  
0.5  
1
0.25  
0.5  
1
2
2
2
14 in.  
14 in.  
14 in.  
14 in.  
400  
400  
400  
400  
0.25  
0.5  
1
—
—
—
23  
0.25  
0.5  
1
0.25  
0.5  
1
2
2
2
14 in.  
14 in.  
14 in.  
14 in.  
200  
200  
200  
200  
0.25  
0.5  
1
—
—
—
20  
0.25  
0.5  
1
0.25  
0.5  
1
2
16 in.  
16 in.  
16 in.  
16 in.  
2625  
2625  
2625  
2625  
0.25  
0.5  
1
—
17  
25  
32  
2
2
0.25  
0.5  
1
0.25  
0.5  
1
2
16 in.  
16 in.  
16 in.  
16 in.  
2100  
2100  
2100  
2100  
0.25  
0.5  
1
—
—
23  
29  
2
2
0.25  
0.5  
1
0.25  
0.5  
1
2
16 in.  
16 in.  
16 in.  
1575  
1575  
1575  
0.25  
0.5  
1
—
—
22  
2
2
0.25  
0.5  
1
900  
900  
900  
900  
600  
600  
600  
600  
300  
300  
300  
300  
150  
150  
150  
150  
0.25  
0.5  
1
16 in.  
1575  
2
27  
16 in.  
16 in.  
16 in.  
16 in.  
16 in.  
16 in.  
16 in.  
16 in.  
16 in.  
16 in.  
16 in.  
16 in.  
1050  
1050  
1050  
1050  
525  
525  
525  
525  
263  
263  
263  
263  
0.25  
0.5  
1
—
—
—
22  
—
—
—
23  
—
—
—
23  
16  
22  
—
—
—
23  
—
—
15  
24  
2
2
0.25  
0.5  
1
0.25  
0.5  
1
2
0.25  
0.5  
1
2
2
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
8 in.  
131  
131  
131  
131  
66  
66  
66  
66  
0.25  
0.5  
1
12 in.  
12 in.  
12 in.  
12 in.  
12 in.  
12 in.  
12 in.  
12 in.  
0.25  
0.5  
1
2
0.25  
0.5  
1
2
2
0.25  
0.5  
1
—
—
—
20  
0.25  
0.5  
1
2
2
2
Note: NC data based on ARI 885-98Acoustical transfer functions inTable 11.  
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Dimensions and Weights  
Figure 48. Central control panel dimensions  
Top view  
10.25 in.  
2.75 in.  
(26.04 cm)  
(6.99 cm)  
8.75 in.  
(22.38 cm)  
Front view  
Side view  
Bottom view  
Note:  
1. Central control panel weight is 2.5 lbs.  
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Dimensions and Weights  
Figure 49. Communicating bypass control dimensions  
Mounting holes  
See back view for dimensions  
6 3/4"  
5"  
4 1/4"  
3 3/8"  
Duct Static  
Pressure Sensor  
3 7/8"  
Duct Temp  
Sensor  
4 5/16"  
0.300"  
1 15/16"  
3 5/16"  
1.00"  
1.00"  
7/8" knockout  
1/2" conduit  
Back View  
Side View  
Customer entry  
Notes:  
Weight  
3 1/4 lbs  
Operating Temp  
Humidity  
Mounting Method  
32˚ to 140˚  
5 to 95% (non-condensing)  
Metal screws  
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Dimensions and Weights  
Figure 50. Round zone and bypass damper dimensions  
Airflow  
6.625"  
8.875"  
Controls Area  
4.375"  
0.50"  
2.125"  
C
Airflow  
2.00"  
Duct Temp Sensor (Optional)  
N/A on Bypass Control  
3.625"  
Center of Bead  
A
DIA  
B
Damper  
Size  
Nominal  
CFM  
Weight  
C
A
B
6"  
12.00"  
12.00"  
16.00"  
11.125"  
13.125"  
15.125"  
17.125"  
300  
500  
800  
6 lbs  
7 lbs  
6.375"  
8"  
8.375"  
8 lbs  
10"  
10.375"  
1100  
1600  
2000  
9 lbs  
12"  
14"  
16"  
12.375"  
14.375"  
16.375"  
16.00"  
20.00"  
20.00"  
19.125"  
21.125"  
11 lbs  
12 lbs  
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Dimensions and Weights  
Figure 51. Rectangular zone damper dimensions  
X
16.00" Ref.  
Y
Seam  
Slip & Drive  
Connection  
6.00" Ref.  
Dimensions  
Damper Frame Data  
Frame  
Blades  
16-gage galvanized steel  
16-gage galvanized steel  
X
Y
All blades are 3.19" nominal width  
12.00"  
14.00"  
16.00"  
16.00"  
20.00"  
18.00"  
8.00"  
8.00"  
and 8" maximum  
ABS plastic  
3/8" rolled steel, zinc plated  
Gear  
Blade Pin  
8.00"  
10.00"  
10.00"  
14.00"  
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Dimensions and Weights  
Figure 52 Rectangular bypass damper dimensions  
Hub  
1.20"  
6"  
X
16" Ref  
.70"  
2"  
1.10"  
4"  
Actuator Dimensions  
Seam  
Dimensions  
Y
X
14"  
12"  
Y
16"  
20"  
16"  
20"  
30"  
20"  
Seam  
Actuator  
CCP  
Wiring  
Red  
Close  
Com  
CCW  
COM  
CW  
White  
Black  
Open  
Factory Installed  
Cable Provided  
Damper Frame Data  
13 gage galvanized steel  
Frame  
Blades  
16 gage galvanized steel; blades are  
6" nominal width and 8" maximum  
Actuator  
5"  
1/8" rolled steel, zinc plated  
3/8" square steel, zinc plated  
Linkage  
Blade Pin  
Blade Pin  
Extension  
7/16" diameter, 7" long  
Included with all dampers  
Bearings  
Self-lubricating acetol  
None  
None  
10"  
Blade Seals  
Side Seals  
Cable  
Weight  
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Dimensions and Weights  
Figure 53. Occupancy Sensor  
Figure 54. CO2 Sensor dimensions  
3.125"  
1.44"  
4.25"  
Figure 55. Digital Zone Sensor  
1.1  
1.0  
3.60"  
2.8  
Front View  
˚F  
˚C  
MAX  
UNOCC SETPOINT OVERRIDE  
2.50"  
4.5  
ON  
Side  
View  
CANCEL  
1.90"  
R
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Glossary  
ABS gears – Gears formed of a  
lightweight plastic known for its  
toughness, impact strength, and  
dimensional stability.  
Non-volatile memory – System  
memory that retains programming with  
no battery or capacitor back up  
required  
CommercialVoyagerVAV rooftop unit  
andVariTraneVAV boxes.  
Demand control ventilation – A  
method of maintaining indoor air  
quality through intelligent ventilation  
based on occupancy.The quantity of  
ventilation is controlled based on  
indoor CO2 levels, which correlate to  
occupancy levels. Demand controlled  
ventilation saves money by reducing  
ventilation during periods of low  
occupancy.  
Back draft damper – A one-way  
airflow damper in a parallel fan  
powered unit prevents primary flow  
from exiting the plenem inlet.  
Normally closed (NC) – Electrical  
contacts that are closed (current flows)  
in the de-energized condition  
Normally open (NO) – Electrical  
contacts that are open (no current  
flows) in the de-energized condition  
Binary input – A two-position signal  
indicating on/off status.  
Binary output – A control output that  
is either on or off.  
Occupancy sensor – A binary sensor  
that transmits a signal upon detection  
of movement in the coverage area  
Direct-expansion (DX) –When the  
refrigerant in the system is either  
condensed or evaporated directly by  
the medium being heated or cooled.  
Built-in time clock –The occupancy  
timer included in the CCP operator  
display.  
Outdoor air (OA) –This is fresh air  
drawn in to provide space ventilation.  
Also see ‘Ventilation air”  
Bypass damper – The motorized  
damper ducted between the system  
supply and return ducts used to  
control static pressure in changeover  
bypass VAV systems.  
Discharge air (DA) – Air discharged  
from the air handler into the ducts.  
Outdoor air damper –The damper  
that draws fresh air into the air handling  
system for ventilation. Also referred to  
as the ventilation or fresh air damper  
Discharge air control – An air  
handling system that provides fixed  
temperature air (either fixed or variable  
volume). Other control devices vary the  
actual volume of air delivered to the  
space to maintain occupant comfort.  
Central control panel (CCP) –The  
system level control device in aTrane  
changeover bypass or deliveredVAV  
system that gathers data from zone  
controllers and operates the HVAC unit  
to maintain the correct air flow and  
temperature.  
Override – A manual or automatic  
action taken to bypass normal  
operation  
Packaged unitary system – An air  
handling system with all the major  
components contained in a single  
cabinet or installed in a single location  
Economizer – A damper arrangement  
and automatic control system that  
allows a heating, ventilation and air  
conditioning (HVAC) system to supply  
up to 100 percent outside air to satisfy  
cooling demands, even if additional  
mechanical cooling is required  
Changeover-bypass VAV – A control  
that provides variable air volume  
functionality to a constant volume air  
handling system.  
PIR – Passive infrared sensing  
technology (used in occupancy and  
motion detection sensors)  
Exception schedule – A one time  
only time of day schedule in a system  
that is removed automatically after use  
Polling –The method aVariTrac CCP  
uses to determine the need for heating  
or cooling from the air handling system  
by examining the zone requirements  
CO2 sensor – An analog sensor that  
detects and measures carbon dioxide  
sensor to determine occupancy level.  
Free cooling – Outdoor air introduced  
to a system under correct conditions to  
provided cooling to a space. Also see  
also “Economizer”  
Commissioning –The process of  
starting up and verifying correct  
operation of a building system.  
Positive pressure –The condition that  
exists when more air is supplied to a  
space than is exhausted.  
Conditioned air – Air that is heated,  
cooled, humidified, or dehumidified to  
maintain comfort in an interior space.  
HVAC Unit – An air moving device  
that conditions air. An HVAC unit may  
provide cooling, or heating and cooling.  
Typical HVAC units include packaged  
rooftop units, split systems, and water  
source heat pumps.  
Pressure-dependent VAV control –  
A VAV unit with airflow quantity  
dependent upon static pressure.There  
is no zone flow sensor in pressure  
dependentVAV boxes.  
Constant volume – An air  
distribution system that varies the  
temperature of a fixed volume of air to  
maintain space comfort.  
Pressure-independent VAV  
control – A VAV unit with airflow  
quantity independent of duct static  
pressure. Actual airflow to the space is  
measured and controlled by an airflow  
sensor in the pressure independent  
VAV box.  
LCD – Liquid crystal display  
Delivered VAV – A self configuring  
system providing true pressure  
independentVAV control to smaller  
building applications. DeliveredVAV  
requires a CCP with operator display, a  
NDIR – Non-dispersive infrared  
technology  
Negative pressure –The condition  
that exists when more air is exhausted  
from a space than is supplied.  
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Glossary  
Priority shutdown – An immediate  
shutdown of the fan and heating or  
cooling stages in aVariTrac changeover  
bypass or DeliveredVAV system  
caused by either the loss of critical  
system information or an external  
priority shutdown input  
Staged electric reheat – Reheat that  
operates one or more duct mounted  
electric coils in a series in response to  
increased space heating demand.  
Unit control module UCM – ATrane  
microelectronic circuit board that  
controls individual HVAC equipment.  
May link to an Integrated Comfort  
System  
Staged (or perimeter) hot water  
reheat – Reheat that operates duct-  
mounted hot water or space-mounted  
electric or hot water reheat coils in  
response to increased space heating  
demand  
Unitary – one or more factory-made  
assemblies which normally include an  
evaporator or cooling coil, an air  
moving device, and a compressor and  
condenser combination  
Pulse-width modulating reheat –  
Reheat that operates duct mounted  
electric coils on a 0-100% duty cycle in  
response to increased space heating  
demand.  
Static pressure –The difference  
between the air pressure on the inside  
of the duct and outside of the duct.  
Static pressure is an indicator of how  
much pressure the fans are creating  
and how effective they will be at  
distributing the supply air through the  
ducts.  
Variable air volume (VAV) – an air  
handling system that varies the volume  
(amount) of constant temperature air to  
a space to control comfort  
Reheat device – A source of heat  
located downstream from a control  
device such as aVAV box to add heat to  
air entering a space to provide  
occupant comfort  
VariTrac –TheTrane changeover  
bypassVAV system  
VariTrane –TheTrane pressure  
independentVAV box  
ReliaTel (RTRM) – The latest  
generationTrane factory mounted  
unitary controller.  
Supply air (SA) – air which blows out  
of the air handler into the ducts. See  
also “Discharge air (DA)”  
VAV box – The damper or air valve  
(plus associated controller) that  
controls the zone air volume in aVAV  
system. Also see “Variable air volume”  
Return air (RA) – Air returned to the  
air handler from the conditioned space,  
to be reconditioned.  
Terminal unit – HVAC equipment that  
provides comfort directly to a space.  
Ventilation air –The outdoor air  
drawn into the HVAC unit to provide  
fresh air to the space. Also see  
“Outdoor air (OA)”  
Setpoint –The desired room  
temperature to be achieved and  
maintained by an HVAC system.  
Thermal requirements –The heating  
or cooling load requirements for a  
specific area or space in a building.  
Care must be taken to not control areas  
with different thermal requirements  
from one air handling system  
Setpoint limit – An electronic or  
manual constraint imposed on a  
setpoint to prevent misadjustment  
Voting – See “Polling”  
Zone sensor –The device that  
measures a variable (usually  
temperature) in a space and sends it to  
a controller. Commonly referred to as a  
thermostat.  
Touch-screen operator display –  
The LCD panel mounted onto aVariTrac  
CCP to allow direct user interface and  
time of day programming for the  
system  
SPDT – A relay with of one set of  
normally-open, normally-closed  
contacts  
48  
VAV-PRC003-EN  
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VAV-PRC003-EN  
49  
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50  
VAV-PRC003-EN  
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VAV-PRC003-EN  
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Literature Order Number  
File Number  
VAV-PRC003-EN  
PL-TD-VAV-000-PRC003-EN-0604  
VAV-DS-12  
Trane  
Supersedes  
A business of American Standard Companies  
www.trane.com  
Stocking Location  
La Crosse  
For more information contact your local district office  
or email us at [email protected]  
Trane has a policy of continuous product and product data improvement and reserves the right to change  
design and specifications without notice.  
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