Taco iWorx UCP-1 User guide

© 2014 Taco Electronic Solutions, Inc. 1
Application Guide 505-010-2
VPU2 Air Control – Pressure Independent Multi-Zone
Self-Contained Interoperable Controller Model UCP-1
SUPERSEDES: January 16, 2013 EFFECTIVE: April 29, 2014
Plant ID: 001-4026
Table of Contents
VPU2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Purpose of This Guide . . . . . . . . . . . . . . . . . . . . . . . . . 3
Representations and Warranties . . . . . . . . . . . . . . . . . 4
Applicable Documentation . . . . . . . . . . . . . . . . . . . . . . 4
Installation Instructions . . . . . . . . . . . . . . . . . . . . . . . . . 5
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Static Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
FCC Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Before Installing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
About this Document . . . . . . . . . . . . . . . . . . . . . . . . 5
Inspecting the Equipment . . . . . . . . . . . . . . . . . . . . 5
What is Not Included with this Equipment . . . . . . . . 6
Equipment Location . . . . . . . . . . . . . . . . . . . . . . . . . 6
Selecting a Power Source . . . . . . . . . . . . . . . . . . . . 6
Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Mounting the Device . . . . . . . . . . . . . . . . . . . . . . . . 6
Routing Cabling to the Device . . . . . . . . . . . . . . . . . 7
Grounding the Device . . . . . . . . . . . . . . . . . . . . . . . 7
Wiring Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Connecting Input Devices . . . . . . . . . . . . . . . . . . . 10
Connecting Output Devices . . . . . . . . . . . . . . . . . . 11
Other Connections . . . . . . . . . . . . . . . . . . . . . . . . . 12
Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Mechanical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Application Description . . . . . . . . . . . . . . . . . . . . . . . . 15
Sequence of Operation. . . . . . . . . . . . . . . . . . . . . . . . 17
Occupancy State . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Operational Mode . . . . . . . . . . . . . . . . . . . . . . . . . 18
Setpoint Calculations . . . . . . . . . . . . . . . . . . . . . . . 20
Supply Air Setpoint Reset Curve . . . . . . . . . . . . . . 20
Outside Air Temperature Lockouts . . . . . . . . . . . . 21
Heating Sequence . . . . . . . . . . . . . . . . . . . . . . . . . 22
Cooling Sequence . . . . . . . . . . . . . . . . . . . . . . . . . 25
Economizer Operation. . . . . . . . . . . . . . . . . . . . . . 29
Dehumidification . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Fan Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Static Pressure Control . . . . . . . . . . . . . . . . . . . . . 30
Soft Start Ramping . . . . . . . . . . . . . . . . . . . . . . . . 31
Fan Proof. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
VPU2 and VAVI Communications . . . . . . . . . . . . . 31
Power On/Reset Delay . . . . . . . . . . . . . . . . . . . . . 32
Supply Air Temperature Monitoring . . . . . . . . . . . . 32
Smoke Detection . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Mixed Air Low Limit Detection . . . . . . . . . . . . . . . . 32
Filter Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Indoor Air Quality. . . . . . . . . . . . . . . . . . . . . . . . . . 33
Real Time Clock (RTC) . . . . . . . . . . . . . . . . . . . . . 33
Local Backup Schedule . . . . . . . . . . . . . . . . . . . . . 33
Runtime Accumulation. . . . . . . . . . . . . . . . . . . . . . 34
Alarms and Events. . . . . . . . . . . . . . . . . . . . . . . . . 34
Automatic Configuration . . . . . . . . . . . . . . . . . . . . 34
Controller Identification . . . . . . . . . . . . . . . . . . . . . . . 34
Inputs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Diagnostic LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Troubleshooting Tips . . . . . . . . . . . . . . . . . . . . . . . 44

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VPU2
The VPU2 is a self-contained microprocessor-based controller for one Variable Air Volume (VAV) package unit. Appli-
cations include VAV package units with up to four stages of cooling, or a floating point control valve or a modulated out-
put (valve or variable speed circulator) two stages of heating, or a floating point control valve or a modulated output
(valve or variable speed circulator) an economizer, and a variable speed fan. The VPU2 is designed for integrated net-
worked operation with the iWorx® Local Control Interface (LCI) and up to 56 VAV terminal unit controllers.
Overview
Digital inputs are provided for fan status, mixed air low limit indication, smoke detector, and filter status. Analog inputs
are provided for mixed air temperature, return air humidity, supply air temperature and supply duct static pressure. An
indoor air quality (IAQ) input can be configured for analog or digital operation.
The VPU2 incorporates digital outputs in the form of triacs for fan start/stop, four cooling stages, two heating stages
and a two-position economizer. In addition, two analog outputs are provided to control a modulated economizer and
variable speed fan drive.
The controller is based on the LONWORKS®networking technology. The controller can be networked to a higher-level
control system for monitoring and control applications.
Features
• Four stages of cooling, or floating point valve control or a modulated output (valve or variable speed circulator)
• Two stages of heating, or floating-point valve control or a modulated output (valve or variable speed circulator)
• Dehumidification
• Modulated fan speed
• Digital or modulated economizer
• Economizer enabled based on enthalpy calculations or dry bulb
• Minimum cycle timers for stages
• Runtime accumulation for heating, cooling and fan
• Local backup schedule
• Maximum of 56 zones (VAV boxes)
• Supply air temperature safety limits
• Time proportioned control of the staged outputs to reduce cycling
• Proportional + Integral control of the modulated economizer, modulated heating, modulated cooling, and static
pressure
• Mixed air low limit protection, filter status, fan proof, freeze stat, and smoke detection inputs
• IAQ compensation based on IAQ alarm input or zone controller alarm
• Outside Air Temperature cutoffs
• Automatic morning warm-up sequence
•LONWORKS interface to building automation systems
• Automatic configuration with the LCI
• Alarm/Event reporting
PURPOSE OF THIS GUIDE
The iWorx® VPU2 Application Guide provides application information for the VPU2 Controller.
The reader should understand basic HVAC concepts, intelligent environmental control automation, and basic LON-
WORKS networking and communications. This Application Guide is written for:
• Users who engineer control logic

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• Users who set up hardware configuration
• Users who change hardware or control logic
• Technicians and field engineers of Taco Electronic Solutions, Inc.
REPRESENTATIONS AND WARRANTIES
This Document is subject to change from time to time at the sole discretion of Taco Electronic Solutions, Inc. All
updates to the Document are available at www.taco-hvac.com. When installing this product, it is the reader’s responsi-
bility to ensure that the latest version of the Document is being used.
iWorx® products shall only be used for the applications identified in the product specifications and for no other pur-
poses. For example, iWorx® products are not intended for use to support fire suppression systems, life support sys-
tems, critical care applications, commercial aviation, nuclear facilities or any other applications where product failure
could lead to injury to person, loss of life, or catastrophic property damage and should not be used for such purposes.
Taco Electronic Solutions, Inc. will not be responsible for any product or part not installed or operated in conformity with
the Document and instructions or which has been subject to accident, disaster, neglect, misuse, misapplication, inade-
quate operating environment, repair, attempted repair, modification or alteration, or other abuse. For further informa-
tion, please refer to the last page of this Document for the company’s Limited Warranty Statement, which is also issued
with the product or available at www.taco-hvac.com.
APPLICABLE DOCUMENTATION
See the table below for additional documentation that may be applicable to this controller.
Description Audience Purpose
iWorx® VPU2 Application Guide,
Document No. 505-010 (this docu-
ment)
– Application Engineers
– Installers
– Service Personnel
– Start-up Technicians
– End user
Provides instructions for setting up and using
the iWorx® VPU2 controller.
iWorx® LCI Application Guide, Docu-
ment No. 505-002
– Application Engineers
– Installers
– Service Personnel
– Start-up Technicians
– End user
Provides instructions for setting up and using
the iWorx® Local Control Interface.
iWorx® VAV Application Guide, Docu-
ment No. 505-011
– Application Engineers
– Installers
– Service Personnel
– Start-up Technicians
– End user
Provides instructions for setting up and using
the iWorx® VAV Series controller.
http://www.iWorxWizard.com – Application Engineers
– Wholesalers
– Contractors
An on-line configuration and submittal package
generator based on user input. Automatically
generates bill of materials, sequence of opera-
tions, flow diagrams, wiring diagrams, points
and specifications.
Additional
Documentation
LonWorks FTT-10A Free Topology Transceiver User’s Guide, published by Echelon Corpo-
ration. It provides specifications and user instructions for the FTT-10A Free Topology Trans-
ceiver. See also: www.echelon.com/support/documentation/manuals/transceivers.

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INSTALLATION INSTRUCTIONS
General
CAUTION: This symbol is intended to alert the user to the presence of important installation and mainte-
nance (servicing) instructions in the literature accompanying the equipment.
CAUTION: Risk of explosion if battery is replaced by an incorrect type. Contains lithium type battery; dis-
pose of properly.
WARNING: Electrical shock hazard. Disconnect ALL power sources when installing or servicing this
equipment to prevent electrical shock or equipment damage.
Make all wiring connections in accordance with these instructions and in accordance with pertinent national and local
electrical codes. Use only copper conductors that are suitable for 167 °F (75 °C).
Static Electricity
Static charges produce voltages that can damage this equipment. Follow these static electricity precautions when han-
dling this equipment.
• Work in a static free area.
• Touch a known, securely grounded object to discharge any charge you may have accumulated.
• Use a wrist strap when handling printed circuit boards. The strap must be secured to earth ground.
FCC Compliance
This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant to Part 15 of
the FCC rules. These limits are designed to provide reasonable protection against harmful interference. This equip-
ment can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause
harmful interference to radio communications. However, there is no guarantee that interference will not occur in a par-
ticular installation. If this equipment does cause harmful interference to radio or television reception, which can be
determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or
more of the following measures:
• Reorient or relocate the receiving antenna.
• Increase the separation between the equipment and the receiver.
• Connect the equipment to a power source different from that to which the receiver is connected.
• Consult the equipment supplier or an experienced radio/TV technician for help.
You are cautioned that any changes or modifications to this equipment not expressly approved in these instructions
could void your authority to operate this equipment in the United States.
BEFORE INSTALLING
About this Document
The instructions in this manual are for the VPU2 controller, which supporst one Variable Air Volume package unit.
Inspecting the Equipment
Inspect the shipping carton for damage. If damaged, notify the carrier immediately. Inspect the equipment for damage.
Return damaged equipment to the supplier.

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What is Not Included with this Equipment
• A power source for the equipment electronics and peripheral devices.
• Tools necessary to install, troubleshoot and service the equipment.
• The screws or DIN rail needed to mount the device.
• Peripheral devices, such as sensors, actuators, etc.
• Cabling, cabling raceway, and fittings necessary to connect this equipment to the power source, FTT-10A network
and peripheral devices.
Equipment Location
Abide by all warnings regarding equipment location provided earlier in this document.
Optimally, the equipment should be installed within a secure enclosure.
If the equipment is to be installed outdoors, it must be contained within a protective enclosure. The enclosure must
maintain internal temperature and humidity within the ranges specified for this equipment.
The equipment must be installed within 500 feet of all input peripherals (smoke detectors, sensors, etc.) that are con-
nected to the equipment.
Selecting a Power Source
This equipment requires a UL recognized Class 2 external power source (not supplied) to operate. The controller
power input requires a voltage of 24 Volts AC.
To calculate power source current requirements, add the power consumption of all peripheral devices to that of the
controller.
The controller and sensor power supplies can use the same power source. If both are using the same power source,
the loads must have EMF protection. This protection can be integral to the load, or installed in the 24 VAC wiring across
the load’s coil.
To provide necessary RFI and transient protection, the controller’s ground (GND) pin (T40) must be connected to earth
ground or the earth ground of the packaged unit’s enclosure ground. Failure to properly ground the controller may
cause it to exceed FCC limits. Excessive noise could also produce inaccurate sensor data. The power source must be
capable of operating with this connection to ground.
INSTALLATION
Warning: Electrical shock hazard. To prevent electrical shock or equipment damage, disconnect ALL
power sources to controllers and loads before installing or servicing this equipment or modifying any wir-
ing.
Mounting the Device
1.Select a mounting location. Enclosure mounting is recommended.
2.Hold the controller on the panel you wish to mount it on. With a marker or pencil mark the mounting locations on
the panel.
3.Using a small drill bit pre-drill the mounting holes.
4.Using two #6 pan head screws, mount the controller to the panel.
5.Wire the controller (See Routing Cabling to the Device).

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Figure 1: Mounting Dimensions
Routing Cabling to the Device
Cabling used to connect the power source and cabling used to connect the FTT-10A network must remain
separated within the control enclosure and wiring conduit.
Grounding the Device
The ground terminal (T40) must be securely connected to earth ground. Failure to properly ground this
equipment will result in improper operation. Improper grounding may also increase the risk of electrical
shock and may increase the possibility of interference with radio/TV reception.
For best performance, connect the power supply common terminal (T38) to the same external point as the
ground terminal (T40).

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WIRING INFORMATION
WARNING: Terminals 6, 9, 12, 15, and 18 are connected internally on all VPU2 controllers. Disconnect
ALL power sources when installing or servicing this equipment to prevent electrical shock or equipment
damage.
Figure 2: Typical VPU2 Wiring - Example A

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Figure 3: Typical VPU2 Wiring - Example B

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Figure 4: Typical VPU2 Wiring - Example C
Connecting Input Devices
Return Humidity (RAH)
To connect the Return Air Humidity sensor to the unit, connect the positive wire from the sensor to RAH (T19) and the
other wire to the adjacent common (T18). The sensor must be of the 0-10 Volt type.
If global indoor air humidity readings are being provided over the network, it is not necessary to attach a return air
humidity sensor directly to the VPU2.
Mixed Air (MAT)
To connect the Mixed Air thermistor to the unit, attach one wire from the thermistor to MAT (T17) and the other wire to
the adjacent common (T18). The thermistor used must be 10K Precon Type III.

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Supply Air (SAT)
To connect the Supply Air thermistor to the unit, attach one wire from the thermistor to SAT (T16) and the other wire to
the adjacent common (T15). The thermistor used must be 10K Precon Type III.
Smoke Detector (SMK)
To connect the smoke detector switch to the digital input, attach one wire of the contact to SMK (T14) and the other
wire to the adjacent common (T15). This must be a dry contact normally open switch. This input is for indication only. A
separate smoke detector should be wired into a fire alarm system if the generation of a fire alarm is required.
Filter Status (FIL)
To connect the filter switch to the digital input, attach one wire of the contact to FIL (T13) and the other wire to the adja-
cent common (T12).
Mixed Air Low Limit (MLL)
This must be a dry contact normally open switch. To connect the low limit indication switch to the digital input, attach
one wire of the contact to MLL (T11) and the other wire to the adjacent common (T12). This must be a dry contact nor-
mally open switch.
Indoor Air Quality (IAQ)
This must be a dry contact normally-open switch. To connect the digital CO2level sensor to the unit, attach one wire
from the sensor to IAQ (T10) and the other wire to the adjacent common (T9). For a digital sensor, this must be a dry
contact, normally closed switch. For an analog sensor, it must be of the 0-10V type.
Static Pressure (SPR)
To connect the static pressure sensor to the analog input, attach the positive wire from the sensor to SPR (T8) and the
other wire to the adjacent common (T9). The sensor must be analog, 0 to 10 volt type.
Return Air Temperature (RAT)
To connect the return air temperature thermistor to the analog input, attach one wire of the sensor to RAT (T7) and the
other wire to the adjacent common (T6).
Fan Proof (FNP)
To connect the fan proof switch to the digital input, attach one wire of the contact to FNP (T5) and the other wire to the
adjacent common (T6). This must be a dry contact, normally closed switch. If you are not providing a fan proof input, T5
and T6 must be shorted (jumpered) together.
Connecting Output Devices
Modulated Economizer (ECNM)
The modulated economizer output can be set to 0-10 V max through the control logic. Connect the positive wire from
the damper actuator to ECNM (T37) and the other wire to the adjacent common (T36). See preceding figures for
details.
Modulated Heating (HTGM)
The modulated heating output can be set to 0-10 V max through the control logic. Connect the positive wire from the
heating output to HTGM (T35) and the other wire to COM (T36). See preceding figures for details.
Modulated Cooling (CLGM)
The modulated cooling output can be set to 0-10 V max through the control logic. Connect the positive wire from the
cooling output to CLGM (T34) and the other wire to COM (T33). See preceding figures for details.

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Modulated Static Pressure Fan (SPF)
The modulated static pressure fan output can be set to 0-10 V max through the control logic. Connect the positive wire
from the fan output to SPF (T32) and the other wire to COM (T33). See preceding figures for details.
Cooling Stage 1 or Cooling Floating Point Valve Open (C1)
The cooling stage output must be connected to a 24 VAC pilot relay if the load is greater than 1 Amp. See preceding
figures for details. If the load is less than 1 Amp, connect cooling stage 1 to C1 (T31) and TC12 (T30). For control of a
floating point valve, connect C1 as the valve open signal.
Cooling Stage 2 or Cooling Floating Point Valve Close (C2)
The cooling stage output must be connected to a 24 VAC pilot relay if the load is greater than 1 Amp. See preceding
figures for details. If the load is less than 1 Amp, connect cooling stage 2 to C2 (T29) and TC12 (T30). For control of a
floating point valve, connect C2 as the valve close signal.
Cooling Stage 3 (C3)
The cooling stage output must be connected to a 24 VAC pilot relay if the load is greater than 1 Amp. See preceding
figures for details. If the load is less than 1 Amp, connect to C3 (T28) and TC34 (T27).
Cooling Stage 4 (C4)
The cooling stage output must be connected to a 24 VAC pilot relay if the load is greater than 1 Amp. See preceding
figures for details. If the load is less than 1 Amp, connect to C4 (T26) and TC34 (T27).
Heating Stage 1 or Heating Floating Point Valve Open (H1)
The heating stage output must be connected to a 24 VAC pilot relay if the load is greater than 1 Amp. See preceding
figures for details. If the load is less than 1 Amp, connect heating stage 1 to H1 (T25) and TC56 (T24). For control of a
floating point heating valve, connect H1 (T25) as the valve open signal. TC56 (T24) is the common.
Heating Stage 2 or Heating Floating Point Valve Close (H2)
The heating stage output must be connected to a 24 VAC pilot relay if the load is greater than 1 Amp. See preceding
figures for details. If the load is less than 1 Amp, connect heating stage 2 to H2 (T23) and TC56 (T24). For control of a
floating point heating valve, connect H2 (T23) as the valve close signal. TC56 (T24) is the common.
Fan (FAN)
The fan output must be connected to a 24 VAC pilot relay if the load is greater than 1 Amp. See preceding figures for
details. If the load is less than 1 Amp, connect the fan to FAN (T22) and TC78 (T21).
Two Position Economizer (ECD)
The two-position economizer output must be connected to a 24 VAC pilot relay if the load is greater than 1 Amp. See
preceding figures for details. If the load is less than 1 Amp, connect the economizer to ECD (T20) and TC78 (T21).
Other Connections
Network (LON)
Network wiring must be twisted pair. One network wire must be connected to terminal NETA (T1) and the other network
wire must be connected to terminal NETB (T2). Polarity is not an issue since an FTT-10A network is used for commu-
nications.
Power (PWR)
Connect one output wire from a 24 VAC power supply to PWR (T39) and the other output wire from the power supply to
the adjacent common terminal (T38). T38 must be connected to earth ground.

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Ground (GND)
Terminal GND (T40) must be connected to earth ground. Failure to properly ground this equipment will
result in improper operation. Improper grounding may also increase the risk of electrical shock, and may
increase the possibility of interference with radio and TV reception.
Protocol
The VPU2 is based on the LONWORKS®networking technology and can be networked to a higher-level control system
for monitoring and control applications. For additional information on the Protocol reference the LonWorks FTT-10A
Free Topology Transceiver User's Guide, published by the Echelon Corporation.
SPECIFICATIONS
Electrical
Inputs
• Cabling: twisted shielded pair, 18 AWG recommended—500 feet max. (152 meters)
• Resolution: 10 bit
Mixed Low Limit, Filter Status, Smoke Detect, Local IAQ Alarm
• Dry Contact
• Normally Open
•5Volts DC Max
Fan Proof
• Dry Contact
• Normally Closed
•5Volts DC Max
Return Air Humidity, Static Pressure
• 0 - 10 Volts DC
Mixed Air Temperature, Supply Air Temperature, Return Air Temperature
• Precon Type III 10K thermistor
Outputs
Cooling Stages 1, 2, 3, & 4; Heating Stages 1 & 2; Fan Start/Stop; Two-position Economizer
•24Volts AC
• 1A @ 50C, 0.5A @ 60C, limited by the Class 2 supply rating
Modulated Economizer, Modulated Static Pressure Fan
• 0-10 Volts DC
• 2K Ohm minimum load
• 8 bit resolution
Power
Power Requirements
• 24VAC (20VAC to 28VAC), requires an external Class 2 supply
Power Consumption
• 7.2W with no external loads, maximum limited by the Class 2 supply rating

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Recommended Sensor Wire
FTT-10A Network
• Speed: 78KBPS
• Cabling: Maximum node-to-node distance: 1312 feet (400 meters)
• Maximum total distance: 1640 feet (500 meters)
For detailed specifications, refer to the FTT-10A Free-Topology Transceiver User’s Guide published by Echelon Corpo-
ration (www.echelon.com/support/documentation/manuals/transceivers).
Mechanical
Housing
• Dimensions: 5.55” (141mm) high, 6.54” (166 mm) wide, 1.75” deep (44 mm)
• ABS
Weight
• Controller Weight: 0.70 pounds (0.32 kilograms)
• Shipping Weight: 1.0 pounds (0.46 kilograms)
Electronics
• Processor: 3150 Neuron 10 MHz
• Flash: 48 Kilobytes
• SRAM: 8 Kilobytes
• Termination: 0.197” (5.0 mm) Pluggable Terminal Blocks, 14-22 AWG
Environmental
• Temperature: 32 °F to 140 °F (0 °C to 60 °C)
• Humidity: 0 to 90%, non-condensing
Agency Listings
• UL Listed for US and Canada, Energy Management Equipment PAZX and PAZX7.
Agency Compliances
• FCC Part 15 Class A
Cable Type Pairs Details Taco Catalog No.
18AWG 1 Stranded Twisted Shielded Pair, Plenum WIR-018
Cable Type Pairs Details Taco Catalog No.
Level 4 22AWG (0.65mm) 1 Unshielded, Plenum, U.L. Type CMP WIR-022

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APPLICATION DESCRIPTION
The VPU2 is a Variable Air Volume (VAV) package unit controller for controlling supply air temperature and supply air
duct static pressure. Figure 5 and Figure 6 illustrate typical VPU2 applications. The VPU2 operates in conjunction with
up to 56 VAVI zone controllers. Control is achieved by modulating the economizer position and sequencing the heating
and cooling stages based on the current supply air temperature requirements. In addition, the VPU2 controls the sup-
ply fan speed to maintain a supply duct static pressure setpoint.
Figure 5: VPU2 Application with Staged Heating & Cooling and Modulated Economizer
The VPU2 controls the starting and stopping of the supply air fan. During the occupied and warm-up periods, the fan
runs continuously. The fan cycles on during the unoccupied periods when a zone is in extended occupancy or when
there is a call for emergency heating. The fan speed control operates to maintain a configurable system static pressure
setpoint. Fan speed is calculated by a Proportional + Integral (P+I) control loop based on the measured static pressure
and setpoint. As the pressure increases above the pressure setpoint, the fan speed output is throttled back. As the
pressure decreases below the pressure setpoint, the output is increased.
The enthalpies of the outside and inside air are calculated periodically. A comparison is performed to determine if “free
cooling” is available. If “free cooling” is available, the economizer is enabled. Free cooling can also be enabled based
on a dry-bulb comparison of the outdoor air temperature and indoor temperature. The system can use either a two-
position or modulated economizer. If a two-position economizer is employed, it is energized when there is a call for
cooling. It is used as the first stage of cooling to take advantage of the energy savings. The two-position economizer
output is off when the modulating economizer feature is disabled.

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If a modulated economizer is employed and “free cooling” is available the modulated economizer position is calculated
by a Proportional + Integral (P+I) control loop. The control is based on the mixed air temperature and setpoint. As the
temperature increases above the mixed air setpoint the economizer is modulated open. The economizer is modulated
closed as the temperature decreases below the mixed air setpoint. The economizer is modulated to its minimum posi-
tion when the economizer is disabled. The economizer can optionally be disabled during the unoccupied periods.
When free cooling is available, mechanical cooling will not be enabled until the economizer is fully open (100%) for
three minutes at which time mechanical cooling will be enabled. This will help in preventing low suction and icing of the
cooling coils.
Either type of economizer can be disabled during unoccupied periods.
The VPU2 operates in one of four states: morning warm-up/cool-down, occupied, unoccupied, or shutdown. A host
device on the network determines the active operating mode. An optional backup schedule is provided for cases when
the host device is not available. The operating state determines if the VPU2 is in heating mode or cooling mode.
Figure 6: VAV Zone Control System
Cooling is accomplished through control of up to four stages of cooling, or one floating point cooling valve or control of
one analog cooling output (valve or variable speed circulator).
When the operating mode is cooling (occupied and extended occupancy), the cooling stages are sequenced on and off
with a time-proportioned control algorithm to minimize excessive cycling. The sequencing is based on the supply air
temperature and cooling setpoint. The cooling stages are interlocked with the economizer control. If the economizer is
enabled, the cooling stages do not sequence on until the economizer has reached its open position.
If configured for modulated analog output the cooling output position is calculated by a P + I control loop based on the
supply temperature and the cooling setpoint. As the temperature increases above the cooling setpoint, the cooling out-
put will be modulated open. The cooling output will be modulated closed as the temperature decreases below the cool-
ing setpoint.
If configured for a floating point valve control the cooling valve is calculated by a P + I control loop based on the supply
temperature and cooling setpoint. As the temperature increases above the cooling setpoint, the valve will be modulated
open. The valve will be modulated closed as the temperature decreases below the cooling setpoint.
Heating is accomplished through control of up to two stages of electric heating, or control of one floating point heating
valve or control of one analog output.
When the operating mode is heating (morning warm-up), the heating stages are sequenced on and off with a time-pro-
portioned control algorithm to minimize excessive cycling. The sequencing is based on the supply air temperature and
heating setpoint. Heating can also be controlled with a floating-point control of a valve.
The heating output position is calculated by a P +I control loop based on the supply temperature and the heating set-
point. As the temperature decreases below the heating setpoint, the heating output will be modulated open. The heat-
ing output will be modulated closed as the temperature increases above the heating setpoint.

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If configured for a floating point valve control the heating valve is calculated by a P + I control loop based on the supply
temperature and cooling setpoint. As the temperature decreases below the heating setpoint, the valve will be modu-
lated open. The valve will be modulated closed as the temperature increases above the heating setpoint.
In both the heating and cooling modes the supply air temperature setpoint may be reset by the zone demand.
The VPU2 can also monitor the supply air temperature to determine if the heating and cooling are operating properly.
During the cooling mode, if the supply air temperature fails to drop below the cooling operational limit after a pre-deter-
mined time period, a cooling failed alarm is reported to the LCI.
During the heating mode, if the supply air temperature fails to rise above the heating operational limit after a pre-deter-
mined time period, a heating failed alarm is reported to the LCI.
As a safety device, the controller can optionally monitor the supply air temperature to determine if the heating stages
have failed on. If the supply air temperature rises above the heating high limit setpoint, the fan energizes. If the supply
air temperature does not drop below the setpoint after a pre-programmed time delay, the fan speed is overridden off. A
heating high limit exceeded alarm is reported to the LCI and all of the zone controllers.
An indoor air quality input is provided. If an indoor air quality alarm is detected, the supply air fan is energized and the
economizer is overridden to supply fresh air to the zones. In addition, an alarm condition can be signaled by one of the
zone controllers. When an alarm condition exists, the controller energizes the supply air fan and overrides the static
pressure setpoint to the IAQ alarm setpoint. The controller attempts to clear the IAQ condition by allowing the econo-
mizer to open more than usual. If the condition has not been cleared after a programmable delay, an alarm is sent to
the LCI.
The VPU2 monitors a digital input to determine the presence of smoke. When the input indicates smoke, the controller
immediately turns off the fan and all stages of heating and cooling. An alarm is reported to the LCI when this condition
exists. The VPU2 remains in the shutdown alarm state until it is reset.
A digital input is provided on the VPU2 to monitor the status of the air filter. An external pressure switch is wired to the
input to determine when the filter becomes dirty. An alarm is reported to the LCI when this condition exists.
Mixed air low limit protection is provided through a digital input. If a low limit condition exists, the VPU2 turns off all
stages of heating and cooling along with the supply air fan. If heating is controlled by a floating-point valve, the valve is
opened fully to prevent equipment damage. An alarm is reported to the LCI when this condition exists. The VPU2
remains in the shutdown alarm state until it is reset.
The VPU2 monitors an input to determine if the fan is operating properly. When the input indicates a fan failure, the
controller immediately turns off the fan and all stages of heating and cooling. An alarm is reported to the LCI when this
condition exists.
The VPU2 monitors the runtime of the cooling stages, heating stages and fan. When any one of the runtimes exceeds
a programmable limit, a maintenance alarm is reported to the LCI.
When the Return Air humidity rises above the humidity setpoint, dehumidification is enabled by enabling the cooling
stages, if modulated cooling is enabled; the cooling output goes to 100%. Dehumidification is disabled, when return air
humidity drops below the setpoint by 3%.
SEQUENCE OF OPERATION
This section describes the detailed sequence of operation for the VPU2 control algorithms.
Occupancy State
The VPU2 operates in one of three occupancy states: extended occupancy, occupied, or unoccupied. A host device on
the network determines the active operating mode. An optional backup schedule is provided for cases when the host
device is not available.

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In addition, the VPU2 polls each zone controller (VAVI) to determine if extended occupancy (bypass) has been
requested. During unoccupied periods when extended occupancy has been requested, the VPU2 enters the occupied
mode of operation. At least once every 5 seconds a different zone controller is polled.
Operational Mode
The VPU2 operates in one of three operating modes: primary heating, primary cooling, and primary off. The operating
mode determines whether warm or cool air is supplied to the zone controllers. The VPU2 determines the operating
mode based on its internal schedule state, which is determined based on the occupancy state and internal configura-
tion variables. The VPU2 can be in one of the following operational states: morning warm-up, occupied, extended
occupancy, emergency heating, shutdown, and emergency.
Morning Warm-up
The purpose of morning warm-up is to heat up the unoccupied zones to a comfortable level before the zones are occu-
pied. During morning warm-up, the VPU2 is in heating mode: the fan is energized, the static pressure is controlled, the
economizer is disabled, and the heating stages are controlled. The VPU2 enters the morning warm-up state from shut-
down, bypass, or emergency heating states.
The VPU2 must be configured at the LCI to perform morning warm-up; a reference VAV zone must be selected, and
the optimum start time for heating must be configured. If the reference zone requires heating, and morning warm-up is
configured, the LCI advances the occupancy start time of the VPU2 and passes the number of minutes the occupancy
has been advanced. The VPU2 remains in morning warm-up until the reference zone temperature is within 1 °F of the
heating setpoint, or until the optimum start time has expired.
The VPU2 informs all of its associated VAVI controllers, regardless of their occupancy state, that morning warm-up is
being performed, to allow all associated VAVIs to take advantage of the heating mode. During morning warm-up, all
VAVI controllers control to their occupied setpoints, regardless of their occupancy state. After morning warm-up, the
VPU2 enters the occupied state and delays the staging of cooling for one stage time.
Morning Cool Down
Similarly to morning warm-up, the VPU2 can perform morning cool-down, cooling the soon-to-be occupied zones to a
comfortable level before occupancy. Morning cool-down is exactly like the occupied state, but the occupancy time has
been advanced.
The VPU2 must be configured at the LCI to perform morning cool-down: a reference VAV zone must be selected and
the optimum start time for cooling must be configured. If the reference zone requires cooling, the VPU2 enters the
occupied state.
Unlike morning warm-up, the VPU2 does not inform its associated zone controllers that it is in morning cool-down. Only
the VAVI controllers that are in the same group take advantage of the cooling and control to their occupied setpoints.
Occupied
A remote device on the network (such as an LCI) provides the current occupancy mode. There are two modes of occu-
pancy; occupied and unoccupied. The VPU2 is in the occupied state if the VPU2 is scheduled for occupancy.
In addition, the current occupancy mode is periodically retrieved from each of the zone controllers. If at least one zone
controller is currently in occupancy or occupancy extension mode the occupancy mode is overridden to the occupied
state (See Extended Occupancy).
During the occupied state the controller is normally in the cooling mode. If the mixed air temperature is 7 °F colder than
the supply temperature (as can happen during cold winter weather), the controller enters the heating mode, and heats
the air to the cooling setpoint. Also, the fan is energized, the static pressure is controlled, and the economizer is
enabled. In heating mode, the controller compensates for the colder air being brought in by setting the economizer to
its minimum position.
The VPU2 enters the occupied state from shutdown, extended occupied, morning warm-up, and emergency heating
states. It remains in the occupied state until the VPU2 goes into the unoccupied state and no associated zone control-
lers are occupied.

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The current operational mode information is periodically transferred to the VAVI over the communications network. The
following information is transferred to the VAVI from the primary air source controller:
• Operational Mode (primary cool, primary heat, primary fan only, primary off)
• Alarm Conditions (IAQ Mode, Heat Failed On)
• Supply Air Temperature
Shutdown
When the space being controlled by the VPU2 is unoccupied, the controller operates in the shutdown state. The air
handler package unit is off, and there is no control of the static pressure or duct temperature.
The VPU2 is in the shutdown state when the occupancy status is “unoccupied,” and no associated controllers are occu-
pied or in extended occupancy. The VPU2 enters the shutdown state from Occupied, Extended Occupancy and Emer-
gency Heating Stages.
The controller can enter an unoccupied cooling state from shutdown when an associated VAVI zone controller's space
temperature is 1 °F warmer than its unoccupied cooling setpoint. During this cooling state, the controller is in cooling
mode; the fan is energized, the static pressure is controlled, the economizer is enabled provided it has been configured
to operate in the unoccupied mode, and the cooling stages are controlled. The controller remains in the cooling state
for thirty minutes or until no associated controllers are requiring cooling, after which the VPU2 reverts to the shutdown
state.
Extended Occupancy
When the VPU2 is in Shutdown state and a VAVI zone controller has indicated extended occupancy, the controller
enters the Extended Occupancy state (also known as Bypass). The Extended Occupancy state acts identically to the
Occupied State.
The VPU2 remains in the extended occupancy state until the VAVI's extended occupancy is over, the VPU2 enters
morning warm-up or cool-down, the VPU2 enters the occupied state, or the VPU2 enters the Shutdown state.
Emergency Heating
The VPU2 enters the emergency heating state from shutdown when an associated VAVI zone controller's space tem-
perature is 10 °F colder than its unoccupied heating setpoint. During the emergency heating state, the VPU2 is in heat-
ing mode: the fan is energized, the static pressure is controlled, the economizer is disabled, and the heating stages are
controlled. The VPU2 remains in the emergency heating state for thirty minutes, after which the VPU2 reverts to the
shutdown state.
Emergency
The VPU2 enters the emergency state (from any state) when there is an emergency condition. Emergency conditions
are:
• Mixed air low limit
• Heat stuck on
• Fan failure
• Smoke alarm
During the emergency state, the air handler package unit is off and there is no control of the static pressure or duct
temperature. The VPU2 remains in the emergency state until the controller is reset.

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Setpoint Calculations
The supply air heating and cooling setpoints are programmable values. The effective setpoint is a calculated value
based on the current operating mode. The effective setpoint is set to the heating setpoint when the operational mode is
heating. It is set to the cooling setpoint when the operational mode is cooling.
Additionally the heating and cooling setpoints may be reset based on the greatest zone demand.
Supply Air Setpoint Reset Curve
If the Supply Temperature Setpoint Reset Curve is enabled, the VPU2 keeps track of the differential between each
zone's space temperature and its temperature setpoint. The VPU2 selects the zone with the greatest differential and
uses that Temperature Differential to adjust the Supply Temperature Setpoint.
If the Temperature Differential is less than the Temperature Differential Minimum, then the Supply Temperature Set-
point Low will be used. If the Temperature Differential is greater than the Temperature Differential Maximum, then the
Supply Temperature Setpoint High is used.
When the Temperature Differential lies between the Temperature Differential Maximum and Temperature Differential
Minimum, the Supply Temperature Setpoint is linearly interpolated between the Supply Setpoint High and Supply Set-
point Low.