Fan-powered units offer energy savings due to intermittent fan control.The fan energizes only in
heating mode when the space needs heat. Additional energy savings are obtained by using warm
plenum air forfree reheat. Motor heat is never wasted in parallel units.Theyare an excellent choice
when minimal zone heating is needed.
Figure 1. Parallel fan-powered terminal unit (L) & series fan-powered terminal units (R)
VAV-PRC012-EN (16 Jul 2013). Updated proportional water valve design.
VAV-PRC012-EN (27 June 2013). Updated controls information. Updated dimensions for units
with attenuators.
Trademarks
Earthwise, VariTrane, VariTrac,Trane and theTrane logo are trademarks of Trane in the United
States and other countries. All trademarks referenced in this document are the trademarks of their
respective owners.
BACnet is a registered trademark of American Society of Heating, Refrigerating and AirConditioning Engineers (ASHRAE); LONMARK and LonTalk are registered trademarks of Echelon
Corporation.
Best Practices ................................................. 231
Unit Conversions .............................................. 232
Additional VAV System and Product References .................... 233
4VAV-PRC012-EN
Features and Benefits
VariTrane™– VAV Leadership
VariTrane variable-air-volume (VAV) units lead the industry in quality and reliability and are
designed to meet the specific needs of today’s applications.This generation of VariTrane units
builds upon the history of quality and reliability and expands the products into the most complete
VAV offering in the industry.
Parallel Fan-powered units offer energy savings due to intermittent fan control.The fan
energizes only inheating mode when the space needsheat. Additional energysavings are obtained
by using warm plenum air for free reheat. Motor heat is never wasted in parallel units.They are
an excellent choice when minimal zone heating is needed.
Series fan-powered units have fans which are always energized in occupied mode.They are
common in applications such as conference rooms, cafeterias, etc., that desire constant airflow
rates at all conditions.
Low-height parallel units provide the energy savings of an intermittent fan with the flexibility
of an 11"–11.5” casing height.This is a good choice for tight plenum spaces.
Low-height series units have been used for years in projects with strict plenum height
requirements. Units
are available in 11.0" height.
Energy Efficient Earthwise™ Systems
Figure 5. Rooftop VAV (office building)
A significant consumer of energy in commercial buildings is heating and air conditioning. One of
the most energy-efficient HVAC solutions is theVAV system.This inherent system efficiency, along
with high-quality, affordable DDC controls, has steadily increased demand forVAV systems over
the years. VAV systems save significant energy, are able to deliver the required amount of
ventilation air, and provide reliable occupant comfort.
Energy saving featuresmust go beyond a simple VAV unit to incorporate VAV unit level and system
level control strategies like:
•Ventilation Optimization-Combines demand-controlled ventilation (using either a time-of-day
schedule, an occupancy sensor, or a carbon dioxide sensor) at the zone level with ventilation
reset at the system level to deliver the required amount of outdoor air to each zone, while
minimizing costly over-ventilation.
VAV-PRC012-EN5
Features and Benefits
S
Q
s
r
y
u
g
l
•Fan Pressure Optimization- reduces supply fan energy by as much as 40% by intelligently
•Night setback reduces energy consumption during unoccupied periods by raising or lowering
•Supply AirTemperature Reset-reduces overall system energy use (balancing reduced cooling
•Electrically Commutated Motors (ECM) improve the efficiency of fan-powered VAV units.
•LowTemperatureAir Distribution can decrease overall system energy use by reducing airflows
To determine the potential energy savings a VAV system can bring to your applications,Trane
offers energy-modeling software like System Analyzer™ andTRACE 700
introduced into the HVAC industry in 1972, the HVAC design and analysis program was the first of
its kind and quickly became a defacto industry standard. It continues to grow with the industry
meeting requirements for ASHRAE Standard 140, ASHRAE 90.1, and the LEED® Green Building
Rating System and has now been approved by the IRS to certify energy savings for building
owners. Contact your localTrane Sales Engineer for additional information.
reducing the pressure in the air distribution system to the lowest possible level without
impacting occupant comfort.
space temperature setpoints.
and reheat energy with increasedfan energy)by raising thesupply airtemperature at part load,
while avoiding elevated space humidity levels.
and the fan energy needed to move that air through the system.
®
. WhenTRACE™ was
Control Flexibility—Trane
factory installs more VAV
controllers than any other
manufacturer in the
industry. In addition to
Trane DDC controls and
simple factory-mounting
of non-Trane VAV controllers,
Trane now offers a LonMark™
controller that is completely
factory-commissioned to
maximize installation quality
and system reliability. Labor
savings are maximized with
Trane factory-commissioned
controllers.
Service Friendly:
* Internal shaft visible
through control box
cover sight hole for
blade orientation
verification.
* Same-side NEC jumpback clearance—
provides all high- and low-voltage
components on the same side
to minimize field labor.
* SQ fan-powered units have
improved accessability to
internal components. Sliding
panels are standard which
improve safety and allow
servicing with a single
technician.
Accurate Flow Ring—Housed
and recessed within the air
valve to provide flow ring
handling/shipping protection.
The patented flow ring provides
unmatched airflow measurement
accuracy.
Optional Narrow Corridor unit
configuration — designed to minimize building
material expenses by squeezing more into less space.
Meets all NEC jumpback clearance requirements
for these extra-tight areas. Narrow Corridor
Configuration not pictured here. Refer to Series
Fan-Powered dimensional data for reference drawings.
Rugged Air Valve—Trane air
valves are heavy gage steel
with a continuously welded
seam to limit inlet deformation.
This provides consistent and
repeatable airflow across
the flow ring with performance you
can count on.
Full Range of Insulation—Whether seeking optimal acoustical perf
or cleanability, Trane has a complete line of insulation options, inc
double-wall, matte-faced, foil-faced, closed cell, etc.
Technologically Advanced "
Units— New super-quiet (S
fan/motor/wheel assemblie
engineered as an air delive
system to provide the most
efficient design available in
industry. For quiet comfort
can trust, rely on Trane SQ
Tough Interlocking Panels— Ru
and rigidity are assured with Tra
patent-pending interlocking pan
Superior Metal Encapsulated
VariTrane Units are complete
encapsulated edges to arrest
fibers and prevent erosion in
6VAV-PRC012-EN
Construction
Features and Benefits
UL-listed products—
Safety and reliability are vital in commercial construction. AllVariTrane units are completely listed
in accordance with UL -1995 as terminal units.This listing includes the VAV terminal with electric
heaters. Additionally, all insulation materials pass UL 25/50 smoke and flame safety standards.
AHRI Certified Performance—
All VariTrane units are AHRI certified. AHRI 880 guarantees the pressure drop, flow performance,
and acoustical performance provided is reliable and has been tested in accordance with industry
accepted standards. AHRI 885 uses AHRI 880 performance and applies accepted industry methods
to estimate expected “NC” sound levels within the occupied space.
Casing Design—
Interlocking Panels—VariTrane products are manufactured in the most state-of-the-art VAV facility
in the world.The patent-pending interlocking panels are designed using integral I-beam
construction technology.This limits deformation and creates tremendous product rigidity. An
additional benefit is a smooth unit exterior with few exposed screws—ideal for exposed ceiling
applications. VariTrane units are designed for use in systems that operate up to 5" w.c. of inlet
pressure.
Metal Encapsulated Edges—AllVariTrane unitsare complete
with encapsulated edges to arrest cut fibers and prevent
insulation erosion into the airstream.This is the standard of
care in applications concerned with fiberglass erosion or
projects with either double-wall or externally wrapped duct
work.
TheTrane Air Valve—is at the heart of VariTrane terminal
units.This is where airflow is measured and controlled.
Repeatability and ruggedness is vital.VariTrane products are
the most rugged and reliable available.
18-gage Cylinder—limits deformation or damage during shipment and job site handling, and
provides even airflow distribution across the flow ring for unmatched airflow measurement
accuracy.
Continuously Welded Seam — an automated weld process creates the highest quality continuous
seam, which is “right” every time.The welded seam improves air valve rigidity and creates
consistent and repeatable airflow across the flow measurement device.The result is a truly round
cylinder every time, with no flat spots caused by lower quality crimping and riviting technologies.
Flow Ring—TheTrane flow ring is time tested to perform under the
most demanding conditions. Additionally,Trane’s patented flow ring
is recessed within the air valve cylinder to reduce the potential for
damage during job site handling and installation.
VAV-PRC012-EN7
Features and Benefits
External Shaft—The simple design provides controller flexibility and is designed to facilitate
actuator field replacement.
Position Indicator—The position indicator shows current air valve position to aid in system
commissioning. Many times this can be seen from the floor without climbing a ladder.
ExternalActuator—This feature increases serviceability,control system compatibility,and actuator
clutch access for simplified commissioning.
Indoor Air Quality (IAQ) Features
The oil embargo ofthe early1970s created an energy crisis,which resulted in tighter buildings,and
reduced ventilation rates. A fallout issue of tighter building construction was poor indoor air
quality.This heightened IAQ awareness. IAQ issues have been featured in publications from the
smallest towns to the largest cities. System design should consider applicable ventilation and IAQ
standards.(See your localTrane Sales Engineer or visit
Good indoor air quality results from units and systems which:
•Provide the required amount of ventilation air to each zone during all operating conditions
•Limit particulates from entering occupied spaces
•Allow proper access for periodic cleaning.
www.trane.com for additional information).
Note: Access made easy on new VariTrane units, as shown on this Series Fan-Powered unit.
VariTrane units are designed with simplified access and a full line of insulation options including:
Matte-faced—Typical industry standard with reduced first cost.
Closed-cell—This insulation has anR-value andperformance equivalent to matte-faced insulation.
The main difference is the reduction of water vapor transmission. Closed-cell is designed for use
in installations with a high chance of waterformation. (It has been usedto coat the exterior of chiller
evaporator barrels for many years.)
Foil-faced—A fiberglass insulation with a thin aluminum coating on the air stream side to prevent
fibers frombecoming airborne.The aluminum lining is acceptable for many applications, however
it is not as rugged as double-wall
Double-wall—Premium insulation often used in many health care applications with insulation
locked between metal liners.This eliminates the possibility for insulation entering the airstream
and allows for unit interior wipe-down as needed.
VariTrane VAV units are the most prepared IAQ units in the industry.
The end result is areliable product designed for peak performance, regardless of jobsite conditions
or handling.
8VAV-PRC012-EN
Tracer™ Building Automation System
Tracer Building Automation System assures comfort within your building. Building controls have
a bigger job descriptionthan theydid afew years ago. It’s no longer enough tocontrol heatingand
cooling systems and equipment. Sophisticated buildings require smarter technology that will
carry into the future. Tracer™ controls provide the technology platform – mobile, easy-to-use,
cloud-based, scalable and open - for the next generation of data-driven, technology-enabled
services that are creating high performance buildings. With aTraneTracer Building Automation
System, you’ll:
•Reduce operating costs through energy management strategies
•Consistently provide occupant comfort
•Enjoy reliable operation with standard, pre-engineered and pretested applications
•Easily troubleshoot and monitor either on site or from a remote location
•Reduce installation time and simplify troubleshooting
Whether factory-mounted or field-installed,Trane offers a wide range of controllers to suit virtually
any application.These unitsare compatible witha variety of building typesand can be usedfor new
construction or renovation.Through extensive usability testing internally and with building
operators, we’ve designed our controls for real world ease of use.
(Additional control options and sequence-of-operations are located in the “Controls” section.)
Trane VAV UCM DDC Controller
Features and Benefits
DDC (communicating electronic)—DDC
controllers are today’s industrystandard. DDC
controllers provide system-level data used to
optimize overall SYSTEM performance.
Variables such as occupied/unoccupied,
minimum and maximum cfm and
temperature, valve position, ventilation
fraction, etc. are available on a simple twistedshielded wire pair. For additional information,
see “Industry Issues: Energy Efficiency”.
Note: One of many Trane DDC Control Options which are factory-installed, wired, calibrated, and fully tested before shipment.
temperature control in space comfort applications. DDC control capabilities include:
•Pressure-independent (PI) operation—Provides airflow required by the room thermostat to
maintain occupant comfort.The controller automatically adjusts valve position to maintain
required airflow. Minimum and maximum airflow is factory-set and field-adjustable.
•Factory-set airflow and temperature setpoints
•Most advanced system integration in the industry.
Tracer VV550 LonTalk™ Controllers
LonTalk™ Controller
Trane now offers a full line of LonTalk™
controllers designed for simple integration
into ANY system which can communicate via
the LonMark Space Comfort Control (SCC)
protocol.These controllers are also
completely factory-commissioned.
VAV-PRC012-EN9
Features and Benefits
Tracer BACnet™ Controllers
Trane now offers a full line of BACnet controllers designed for simple integration into any system
which can communicate via the BACnet protocol.These controllers are factory-commissioned and
shipped ready to be installed.
UC210 BACnet Controller
Trane Wireless Comm Interface (WCI)
WCI controller
Provides wireless communication between theTracer SC,
Tracer Unit Controllers, and BACnet™ Communication
Interface (BCI) modules.
TheTrane WCI is the perfect alternative to Trane’s BACnet
wired communication links (for example – Comm links
between aTracer SC andTracer UC400).
Eliminating communication wire used between terminal
products, zone sensors, and system controllers has substantial
benefits.
•Installation time and associated risks are reduced.
•Projects are completed with fewer disruptions.
•Future re-configurations, expansions, and upgrades are
easier and more cost effective.
UC400 BACnet Controller
Trane Wireless Zone Sensor
Wireless Zone Sensor
Provides wireless communication between theUnit Controller
and the zone sensor.This is an alterntive to the wired zone
sensor when access and routing of communicaiton cable is an
issue. It also allows very flexible mounting and relocation of
zone sensors
10VAV-PRC012-EN
Pneumatic Controller
Pneumatic Controller
Binary Input Controller
Features and Benefits
Pneumatic—Pneumatic controllers provide
proven reliability and performance. A full line
of options provide:
•Highest quality PVR available, which
maximizes zone temperature control.
Pressure-independent operation
•AllVariTrane pneumatic controllers use the
patented flow sensor input to provide the
most accurate performance available.
Integration Options (Interfacing with other control systems) - Trane offers three ways to
interface with other control systems.
2. UseTrane Binary Input Controller (BIC). BIC allows system control through binary logic.This
means that a control system on an existing campus, or those seeking “Analog noncommunicating control” can control aTrane DDCVAV unit viabasic binarycontact closures, like
relays, etc.This can be a cost effective interface option where a fullTrane DDC VAV System is
not available.
The terms factory-installedand factory-commissioned are often used interchangeably.Trane takes
great pride in being the industry leader in factory-commissioned DDC controllers. Table
differentiates these concepts.
Factory-commissioned controllers provide thehighest quality and most reliable units for your VAV
system. Additional testing verifies proper unit operation including occupied/unoccupied airflow,
temperature setpoints, communication link functionality, and output device functionality.The
benefits of factory-commissioning are standard on VariTrane terminal units withTrane DDC
controls.This means that factory-commissioned quality on VariTrane VAV units is now available
on ANY manufacturer’s control system that can communicate using the LonMark Space Comfort
Control (SCC) protocol. (See Controls section for complete listing of variables which are
communicated.
Table 1.Factory-installed vs. factory-commissioned
Factory-installedFactory-commissioned
Transformer installed (option)XX
Wires terminated in reliable/consistent settingXX
Controller mountedXX
Electric heat contactors and fan relay wiredXX
VAV-PRC012-EN11
Features and Benefits
Table 1.Factory-installed vs. factory-commissioned
Factory-installedFactory-commissioned
Testing of electric heat contactors and fan relayX
Controller addressing and associated testingX
Minimum & Maximum airflows settings (occupied/unoccupied)X
Minimum & Maximum temperature setpoints (occupied/unoccupied)X
Minimum ventilation requirementsX
Thumbwheel enable/disableX
Heating offsetX
Wireless communications modules (WCI)XX
Wireless zone sensorX
Indoor Air Quality Management During Construction
LEED wrap option is a pressure sensitive
covering that prevents contamination of the
VAV box during the construction phase. It is
utilized to seal all openings without
constraining the installation process.
Trane VAV Systems - Proven Performance
Trane is the industry leader in VAV systems, including factory-commissioned controls and
integration with other control systems.This leadership began with customers seeking the most
reliable VAV products in the industry.The solution was factory-commissioned controls (see
Factory-installed vs. Factory-commissioned). Since then, it has blossomed to include optimized
system control strategies.
Control strategies are often made more complicated than necessary. VariTrane DDC controls
simplify control strategies by pre-engineeringcontrol logic and sequencinginto the controller.This
information is available via a twisted-shielded wire pair, and accessible via aTraneTracer™ SC
building automation system. Data is easily accessed via a computer workstation.
Optimized system control strategies, such as ventilation optimization, fan-pressure optimization,
and optimal start/stop, are pre-engineered in VariTrane™ unit-level DDC controllers and theTracer
SC building automation system.
This allows aTrane VAV system to meet or exceed the latest ASHRAE 90.1 Energy Efficiency
standards. Pre-engineered controls allow consistent, high quality installations which are very
repeatable.The end result is PROVEN control strategies you can rely on to perform. For more
information on these and other control strategies, contact your localTrane Sales Office, or visit
www.trane.com.
PurchasingVAV controllers and VAV hardware from a single manufacturer provides a single
contact for all HVAC system related questions.
12VAV-PRC012-EN
Agency Certifications
There are numerous regulationsand standardsin theindustry thatdetermine theconstruction and
performance parameters for VAV terminal units. Some of the more important of those standards
and regulations are listed below, along with a brief description of what each one addresses.
American Society of Heating, Refrigerating and Air-conditioning Engineers
(ASHRAE) - 41.1
ASHRAE - 41.2
ASHRAE - 41.3
These standards specify methods for temperature measurement (41.1), laboratory airflow
measurement (41.2), and pressure measurement (41.3).While none of these standards specifically
discusses VAV air terminals, they discuss topics that are aspects of terminal box systems.
Therefore, some engineers will include these standards in their specifications as a primer on
accepted measurement techniques.
ASHRAE - 62
This standard specifies theminimum ventilationrates andindoor air qualitythat areacceptable for
occupied spaces.
ASHRAE - 111
This standard calls out procedures to be followed for testing and balancing HVAC systems. It
includes descriptions of the equipment used, procedures followed, and field changes that must be
made when a system is balanced.
Air-Conditioning, Heating and Refrigeration Institute (AHRI)
AHRI 880
This standard sets forth classifications, performance testing requirements, and test results
reporting requirements for air terminal units.The standard contains very detailed procedures that
are to be followed for the testing and certification program associated with this standard.This is
one of the most commonly referenced standards in the VAV terminal unit industry.The AHRI-880
certification program is designed to police the accuracy of documented performance for terminal
units.The certification program requires a sampling of at least four units be tested annually.The
tested units are chosen at random by AHRI and sent to an independent laboratory for the testing.
The performance is tested at one specific operating condition.The operating characteristics tested
include discharge and radiated sound power (for the damper and, in the case of fan-powered
boxes, the fan), wide-open damper pressure drop, and fan motor amp draw. VariTrane terminal
units are certified according to AHRI-880.
AHRI 885
This document provides a procedure to estimate sound pressure levels in an occupied space.The
standard accounts for the amount of sound pressure in the space due to the VAV air terminal,
diffusers and their connecting low pressure ductwork. While sound generated from the central
system fan andductwork may be a significant factor in determining thesound pressure level in the
room, this standarddoes not address those factors. It focusessolely onthe VAVterminal and items
downstream of it.This standard is related to AHRI-880 by using sound power determined using
AHRI-880 methodology as a starting point for the AHRI-885 procedure.
Underwriter’s Laboratory (UL) 1995
Underwriter’s Laboratory is an independent testing agency that examines products and
determines if those products meet safety requirements. Equipment manufacturers strive to meet
UL guidelines and obtain listing and classifications for their products because customers recognize
UL approval as a measure of a safely designed product. VariTrane VAV air terminals are listedper UL-1995, Heating and Cooling Equipment.The terminals are listed as an entire assembly.
VAV-PRC012-EN13
Agency Certifications
National Fire Protection Association
NFPA 70
This standard is also known as the National Electrical Code (NEC).The Code gives standards for
installation of wiring and electrical equipment for most types of commercial and residential
buildings. It is often referred to inVAV air terminal specifications when fan-powered boxes, electric
heat or electric controls are included.
NFPA 90A
This standard does not speak directly to VAV air terminals but does discuss central system
considerations pertaining to a fire and/or smoke condition.The standard discusses safety
requirements in design and construction that should be followed to keep the air-handling system
from spreading a fire or smoke.The standard specifies practices that are intended to stop fire and
smoke from spreading through a duct system, keep the fire-resistive properties of certain building
structures (fire walls, etc.) intact, and minimize fire ignition sources and combustible materials.
14VAV-PRC012-EN
Model Number Descriptions
Digit 1, 2—Unit Type
VP = VariTrane™ Fan-Powered Parallel
VS = VariTrane Fan-Powered Series
LP = VariTrane Fan-Powered
Low-Height Parallel
LS =VariTrane Fan-Powered
Low-Height Series
Digit 3—Reheat
C =Cooling Only
E=Electric Heat
W =Hot Water Heat
Digit 4—Development Sequence
F=Sixth
Digit 5, 6—Primary Air Valve
05 =5" inlet (350 max cfm)
06 =6" inlet (500 max cfm)
08 =8" inlet (900 max cfm)
10 =10" inlet (1400 max cfm)
12 =12" inlet (2000 max cfm)
14 =14" inlet (3000 max cfm)
16 =16" inlet (4000 max cfm)
RT =8" x 14" inlet (1800 max CFM)
Note: 10, 12, 14, 16 Not Available on Low-
Height
Digit 7, 8—Secondary Air Valve
00 =N/A
Digit 9—Fan
P=02SQ fan (500 nominal cfm)
Q = 03SQ fan (1100 nominal cfm)
R =04SQ fan (1350 nominal cfm)
S =05SQ fan (1550 nominal cfm)
T=06SQ fan (1850 nominal cfm)
U = 07SQ fan (2000 nominal cfm)
V=08SQ Fan (500 nominal cfm)
W =09SQ Fan (900 nominal cfm)
Heat
DD00= Trane Actuator Only
ENCL= Shaft Only in Enclosure
ENON= Shaft Out Side for Electric Units
FM00= Other Actuator and Control
FM01= Trane supplied actuator,
other control
PN00= N.O. Actuator and Linkage Only
PN05= N.O. 3000 Series, RA Stat
PN51= Pneumatic normally open
w/3011,DPS fan
PN52= Pneumatic normally open
w/3011, DPM fan
PNON= Shaft Out Side for Pneumatic
Units
N.C. = Normally-closed
N.O. = Normally-opened
DA Stat = Direct-acting pneumatic t-stat
(by others)
RA Stat = Reverse-acting pneumatic
t-stat (by others)
PN = Pneumatic
FM = Factory installation of customer-
This section describes elements and process required to properly select fan-powered VAV
terminals, and includes a specificexamples. Selection procedure is iterativein naturewhich makes
computer selection desirable. Selection of fan-powered VAV terminals involves four elements:
•Air valve selection
•Heating coil selection
•Fan size and selection
•Acoustics
Note: Use the same procedures for selecting Low-Height Fan-Powered Units.
Air Valve Selection
Provided in the Performance Data—Air Pressure Requirements section of the catalog is the unit air
pressure drop at varying airflows.To select an air valve, determine the airflow required at design
cooling. Next, select an air valve diameter that will allow proper airflow modulation, (a velocity of
1600 – 2000 FPM is recommended). Keep in mind that modulation below 300 FPM is notrecommended. Proper selection requires defining the minimum valve airflow (in either heating
or cooling) and maintaining at least 300 FPM through the air valve.The minimum is typically set
based on ventilation requirements. If zone ventilation does not come through the VAV unit, a
minimum valve position can also be zero.
Heating Coil Selection
Supply Air Temperature
The first step required when selecting a heating coil is to determine the heating supply air
temperature to the space, calculated using the heat transfer equation. A recommended value is
90°F, although values between 85°F and 95°F are common. Discharge air temperatures that exceed
20 degrees above space temperature are not recommended for proper diffuser operation. Air
temperature difference is defined as the heating supply air temperature to the space minus the
winter room design temperature.The zone design heat loss rate is denoted by the letter Q. Supply
air temperature to the space equals the leaving air temperature (LAT) for the terminal unit.
Coil Leaving Air Temperature
Once the terminal unit LAT is determined, the heating requirements for the coil can be calculated.
The leaving air temperature for the coil of a parallel fan-powered terminal unit varies based on the
type of unit installed heat being selected. Series unit leaving air temperatures do not vary because
in each case the coil is located on the unit discharge.
Electric coil LAT equals terminal unitLATbecause the coil is located on the unit discharge.Hot water
coils can be located on either the discharge or, for maximum system efficiency, the plenum inlet
when located on the entering air side of the fan. Coil LAT is calculated using a mixing equation.
Given the unitheating airflow and LAT, minimum primary airflow atits supplyair temperature,and
the volume of heated plenum air, the leaving air temperature for the hot water coil can be
determined (see the unit selection example that follows for more details).
Coil Entering Air Temperature
The entering air temperature (EAT) to the coil also varies based on the coil position on the unit for
parallel units.The unit heat is mounted on the discharge of a series unit.Therefore the EAT equals
the temperature of blended primary and plenum air.
Parallel electric coils are mounted on the unit discharge. Hot water coils can be mounted on the
discharge or on the plenum inlet. Plenum inlet mounting creates a more efficientVAV system.This
is because the parallel fan is energized only when in heating mode, and thus, when in cooling
mode, the water coil is not in the airstream.
The EAT for discharge mounted coils equals the temperature of blended primary air and plenum
air. For plenum inlet mounted water coils, the EAT equals the plenum air temperature.
VAV-PRC012-EN17
Selection Procedure
Capacity Requirement
Once both coil EAT and LAT are determined, the heat transfer (Q) for the coil must be calculated
using the heat transfer equation. For electric heat units, the Q value must be converted from Btu
to kW for heater selection.The required kW should be compared to availability charts in the
performance data section for the unit selected. For hot water heat units, reference the capacity
charts in the performance data section for the required heat transfer Q and airflow to pick the
appropriate coil.
Fan Size and Selection
Fan Airflow
Fan airflow is determined by calculating thedifference between the unitdesign heating airflowand
minimum primary airflow.
Fan External Static Pressure
Fan external static pressure is the total resistance experienced by the fan, which may include
downstream ductwork and diffusers, heating coils, and sound attenuators. As total airflow varies
so will static pressure, making calculation of external static pressure dependent on unit type.
In many applications of parallel terminals,a minimumprimary airflow mustbe maintainedto meet
ventilation requirements.This primary airflow contributes to the total resistance experienced by
the fan and should be accounted for in all components downstream of the fan itself, including
electric coils. Hot water coils positioned on the fan inlet are not affected by the additional primary
airflow.The static pressure resistance experienced by the fan due to the hot water coil is based on
fan airflow only, not the total heating airflow.
With series fan-powered terminal units, all airflowpasses through the fan. External static pressure
requirements are the sum of the individual component pressure retirements at the design airflow
of the unit.
Acoustics
Fan Motor Type
The fan motor type that will be used for the unit will need to be known before fan selection can
begin.The ECM motor offers more efficient operation than the standard single-speed PSC motor
and will use different fan curves. Because series fans operate in both heating and cooling mode,
payback is typically 2–3 years for the premium ECM option. Refer to the Features and Benefits
section to determine which motor is more appropriate for the unit
Selection
Once fan airflow and external static pressure are determined, reference the fan curves in the
performance data section. Cross plot both airflow and external static pressure on each applicable
graph. A selection between the minimum and maximum airflow ranges for the fan is required.
It is common to identify more than one fan that can meet the design requirements.Typically,
selection begins with the smallest fan available to meet capacity. If this selection does not meet
acoustical requirements, upsizing the fan andoperating it at aslower speed can be donefor quieter
operation.
Air Valve Generated Noise
To determine the noise generated by the air valve, two pieces of information are required; design
airflow and design air pressure drop.The design air pressure drop is determined by taking the
difference between design inlet and static pressure (the valve’s most over-pressurized condition)
and external static pressure at design cooling flow.This represents a worst-case operating
condition for the valve.
18VAV-PRC012-EN
Fan Generated Noise
To determine fan noise levels, fan airflow, external static pressure and speed information is
required.
Evaluation Elements
For parallel fan-powered terminal units, the air valve and fan operation must be evaluated
separately because these operations are not simultaneous. For Series fan-powered units, the air
valve and fan are evaluated together because they have simultaneous operation. Access the
appropriate acoustics table(s)of the catalog and determine the sound power and NC predictionfor
both the discharge and radiated paths. It is important to understand that discharge air noise is
generally not a concern with fan-powered terminals. Radiated noise from the unit casing typically
dictates the noise level of the space. If the entire unit or any element of it is generating noise in
excess of the NoiseCriteria requirements, thesize of theappropriate portion of theterminal should
be increased. Because the selection procedure is iterative, care should be taken by the designer to
confirm that the change in selection does not affect other elements of the unit or system design.
Selection Example—ParallelWith Hot Water Heat
Air Valve Selection
Design Cooling Airflow:1000 cfm
Minimum Ventilation Airflow: 200 cfm
Maximum Unit APD: 0.25 in. wg
Choose 10" air valve
Check – Is minimum airflow above 300 FPM? Guidelines, FPP 8)
A 10" air valve is selected with unit pressure drop = 0.01 in. wg
Selection Procedure
Heating Coil Selection
Required Information:
Zone design heat loss: 20000 Btu
Unit heating airflow: 600 cfm
Winter room design temp.: 68ºF
Coil entering water temp.: 180ºF
Minimum primary airflow: 200 cfm
Fan Airflow: 400 cfm
Plenum temperature: 70ºF
Coil flow rate: 2 gpm
Primary air temperature: 55ºF
Heat Transfer Equation (Btu)
Q = 1.085 x Cfm x DTemperature
For the heating zone, the temperature difference is the zone supply air temperature (SAT) minus
the winter room design temperature.
18000 Btu = 1.085 x 600 x (SAT - 68ºF)
SAT = 95.6ºF
Because the designer chose to maximize system efficiency by having the hot water coil on the
plenum inlet, the unit supply air temperature is equal to the mix of the heated plenum air from the
fan and the minimum primary airflow.
600 cfm x 95.6ºF =
200 cfm x 55ºF +
(600 cfm - 200 cfm) x Coil LAT
Coil LAT = 116ºF
VAV-PRC012-EN19
Selection Procedure
For the heating coil, the temperature difference is the calculated coil LAT minus the coil EAT
(Plenum AirTemperature).
CoilQ=1.085 x 400 x (116-70) = 19,964 Btu = 19.96 Mbh
Design airflow: 400 cfm
Downstream static pressure at design airflow: 0.25 in. wg
Fan external static pressure equals downstream static pressure (ductwork and diffusers) plus coil
static pressure.The coil static pressure that the fan experiences is at the fan airflow (400 cfm).The
downstream static pressure the fan experiences is at fan airflow plus minimum primary airflow.
The sum of fan airflow and minimum primary airflow (600 cfm) is less than design airflow (1000
cfm) and therefore the 0.25 in. wg downstream static pressure at design airflow must be adjusted
for the lower heating airflow.
Parallel Fan-Powered Unit with Water Coil (2 Options)
Plenum Inlet Mounted
Using Fan LawTwo:
Heating Downstream Static Pressure = (600/1000)2 x 0.25 = .09 in. wg
A size 02SQ fan has the capability to deliver approximately 650 cfm at 0.09 downstream static
pressure. If an attenuator is required, use the attenuator air pressure drop tables to define
additional fan static pressure.
Acoustics
Required Information:
Design inlet static press.: 1.0 in. wg
NC criteria: NC-35
The selection is a VPWF Parallel Fan-poweredTerminal Unit, 10" primary, parallel fan size 02SQ,
with a 1-row hot water coil.
Determine the casing radiated noise level because it typically dictates the sound level (NC) of the
space. With a parallel unit, two operating conditions must be considered, design cooling and
design heating.
Discharge Mounted
20VAV-PRC012-EN
Selection Procedure
Design Cooling (1000 cfm). Radiated valve typically sets the NC for parallel units incooling mode.
The closest tabulated condition (1100 cfm at 1.0 in. wg ISP) has an NC=31. (A more accurate
selection can be done viaTOPSS electronic selection program.):
Table 2.Selection Program Output (Radiated Valve):
Octave Band 234567 NC
Sound Power65 60 53 48 41 32 30
Design Heating (200 cfm valve, 400 cfm fan, 0.25 in. wg DSP). Radiated fan typically sets the NC
for parallel units in heating mode.The closest cataloged condition (430 fan cfm , 0.25 in. wg DSP)
has an NC=32. (A more accurate selection can be done viaTOPSS electronic selection program.)
Table 3.Selection Program Output (Radiated Fan):
Octave Band 234567 NC
Sound Power66 58 56 52 48 41 31
The predicted NC level for design cooling is NC-30 and for design heating is NC-31. If the catalog
path attenuation assumptions are acceptable, this unit meets all of the design requirements and
the selection process is complete.
Computer Selection
The advent of personal computers has served to automate many processes that were previously
repetitive and time-consuming. One of those tasks is the proper scheduling, sizing, and selection
of VAV terminal units.Trane has developed a computer program to perform these tasks.The
software is called theTrane Official Product Selection System (TOPSS).
TheTOPSS program will take the input specifications and output the properly sizedVariTrane VAV
terminal unit along with the specific performance for that size unit.
The program has several required fields, denoted by red shading in theTOPSS screen, and many
other optional fields to meet the criteria you have. Required values include maximum and
minimum airflows, control type, and model. If selecting models with reheat, you will be required
to enter information to make that selection also.The user is given the option to look at all the
information for one selection on one screen or as a schedule with the other VAV units on the job.
The user can select single-duct, dual-duct, and fan-poweredVAV boxes with the program, as well
as most otherTrane products, allowing you to select all yourTrane equipment with one software
program.
The program will also calculate sound power datafor the selected terminal unit.The usercan enter
a maximum individual sound level for each octave bandor a maximum NC value.The program will
calculate acoustical data subject to default or user supplied sound attenuation data.
Schedule View
The program has many time-saving features such as:
•Copy/Paste from spreadsheets like Microsoft® Excel
•Easily arranged fields to match your schedule
•Time-saving templates to store default settings
The user can also export the Schedule View to Excel to modify and put into a CAD drawing as a
schedule.
Specific details regarding the program, its operation, and how to obtain a copy of it are available
from your localTrane sales office.
VAV-PRC012-EN21
Selection Procedure
Selection Example—Series With Hot Water Heat and ECM
Minimum ventilation airflow: 200 cfm
Maximum unit APD: 0.40 in. wg
A 10" air valve is selected.
Check–is minimum airflow above 300 FPM?
Answer–Yes. Minimum cfm allowable = 165 cfm. (See
General Data—Valve/Controller Guidelines pp FPS 8).
The 03SQ fan will be used in this instance. By interpolating,
you can choose a 10" air valve with wide-open air pressure
drop of 0.32 in. wg.
Heating Coil Selection
Required Information: Zone design heat loss: 30000 Btu
Design heating airflow: 1000 cfm
Winter room design temp.: 68ºF
Coil entering water temp.: 180ºF
Minimum primary airflow: 200 cfm
Plenum temperature: 70ºF
Primary air temperature: 55ºF
Coil flow rate: 2 gpm
HeatTransfer Equation (Btu)Q=1.085 x Cfm x Temperature
For the heating zone, the temperature difference is the zone supply air temperature (SAT) minus
the winter room design temperature.
30000 Btu = 1.085 x 1000 x (SAT-68°F)
SAT = 96ºF
Because the hot water coil is on the unit discharge of a series fan-powered unit, the unit supply air
temperature is equal to the coil LAT. Coil entering air temperature (EAT) is a mix of plenum air and
the minimum primary airflow.
1000 cfm x Coil EAT = 200 cfm x 55ºF + (1000 cfm - 200 cfm) x 70ºF
Coil EAT = 67ºF
For the heating coil, the temperature difference is the calculated coil LAT minus the coil EAT
(Plenum AirTemperature).
Coil Q =1.085 x 1000 x (96-70) = 31,465 Btu
On a series unitthe hot water coilis locatedon thedischarge, so the totalheating airflow, 1000 cfm,
passes through the coil.
Coil Performance Table
Selection:
Performance:
Size 03SQ fan, 1-row coil at 2 gpm = 32.23 MBh
1-row Coil at 2 gpm= 0.83 ftWPD
Fan Selection
Required Information. Fan airflow: 1000 cfm
Downstream static pressure at design airflow: 0.25 in. wg
A size 03SQ fan can operateat upto 1150 cfm (1-row coil) or 1100 (2-row coil) and 0.25" downstream
static pressure. Inlet and coil selections should be verified withTOPSS electronic selections.
22VAV-PRC012-EN
Selection Procedure
If an attenuator is required, use attenuator air pressure drop tables to define additional fan static
pressure.
Acoustics
Required Information. Design inlet static press: 0.75 in. wg
NC criteria (general office space): NC-40
The selection is aVSWF Series Fan-PoweredTerminal Unit, 10" primary, series fan size 03SQ, with
a 1-row hot water coil.
Determine the casing radiated noise level because it typically dictates the sound level
(NC) of the space. With a series unit, the air valve and fan operate simultaneously, so the chart
for air valve and fan sound data must be consulted.
The results in the below table are for the acoustics value of a size 10" air valve with a size 03SQ fan.
The predicted NC level for design conditions is NC-38.
Octave Band234567NC
Sound Power70656361595938
Note: Ensure water coil acoustical impact is considered. For this example, the appurtenance effect
adds one (1) NC to fan-only radiated sound. Because this does not set NC for this selection,
it can be overlooked.The addition of an attenuator (see same appurtenance effect tables
reduces the NC four (4) points, resulting in a final selection NC = 30 (if required).
Note: Do not overlook the water coil impact on acoustics. A good rule of thumb is that it will add
1 to 2 NC to “fan only” radiated sound for most applications.
Computer Selection
The advent of personal computers has served to automate many processes that were previously
repetitive and time-consuming. One of those tasks is the proper scheduling, sizing, and selection
of VAV terminal units.Trane has developed a computer program to perform these tasks.The
software is called theTrane Official Product Selection System (TOPSS).
TheTOPSS program will take the input specifications and output the properly sizedVariTrane VAV
terminal unit along with the specific performance for that size unit.
The program has several required fields, denoted by red shading in theTOPSS screen, and many
other optional fields to meet the criteria you have. Required values include maximum and
minimum airflows, control type, and model. If selecting models with reheat, you will be required
to enter information to make that selection also.The user is given the option to look at all the
information for one selection on one screen or as a schedule with the other VAV units on the job.
User can select single-duct, dual-duct, and fan-powered VAV boxes with the program, as well as
most otherTrane products, allowing selection of allTrane equipment with one software program.
The program will also calculate sound power datafor the selected terminal unit.The usercan enter
a maximum individual sound level for each octave bandor a maximum NC value.The program will
calculate acoustical data subject to default or user supplied sound attenuation data.
Schedule View
The program has many time-saving features such as:
•Copy/Paste from spreadsheets like Microsoft® Excel
•Easily arranged fields to match your schedule
•Time-saving templates to store default settings
User can also export Schedule View to Excel to modify and put into a CAD drawing as a schedule.
Specific details regarding program, its operation, and how to obtain a copy of it are available from
your localTrane sales office.
VAV-PRC012-EN23
Performance Data
Parallel Fan-PoweredTerminal Units
Table 4.Primary airflow control factory setting-I-P
Control Type
Direct Digital
Control/ UCM
Pneumatic with
Volume
Regulator
Note: Maximum airflow must be greater than or equal to minimum airflow.
Size (in.)
5
6
8
10
12
14
16
5
6
8
10
12
14
16
Table 5.Primary airflow control factory settings – SI
Air Valve
Control Type
Direct Digital
Control/ UCM
Pneumatic with
Volume
Regulator
Note: Maximum airflow must be greater than or equal to minimum airflow.