Taco Electronic Solutions iWorx HPU3 User guide

© 2015 Taco Electronic Solutions, Inc. 1
Application Guide 505-035
HPU3 Water Source Heat Pump Controller
Self-Contained Interoperable Controller Model UCP-1 for Software Version 2
SUPERSEDES: December 15, 2014 EFFECTIVE: June 30, 2015
Plant ID: 001-4056
Table of Contents
HPU3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . 9
Connecting Output Devices . . . . . . . . . . . . . . . . . . 10
Other Connections . . . . . . . . . . . . . . . . . . . . . . . . . 11
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Mechanical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Application Description . . . . . . . . . . . . . . . . . . . . . . . . 13
Sequence of Operation . . . . . . . . . . . . . . . . . . . . . . . 14
Setpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Heating Sequence . . . . . . . . . . . . . . . . . . . . . . . . . 16
Cooling Sequence . . . . . . . . . . . . . . . . . . . . . . . . . 18
Commissioning . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Fan Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Dehumidification with Reheat . . . . . . . . . . . . . . . . 20
Auxiliary Heat. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Global Unit Enable. . . . . . . . . . . . . . . . . . . . . . . . . 21
Humidification . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Thermostat. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Local Backup Schedule . . . . . . . . . . . . . . . . . . . . . 21
Runtime Accumulation. . . . . . . . . . . . . . . . . . . . . . 21
Reversing Valve. . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Supply Air Temperature Fan Modulated Output . . 22
Alarms and Events. . . . . . . . . . . . . . . . . . . . . . . . . 22
Hydronic Zone Interaction . . . . . . . . . . . . . . . . . . . 23
Automatic Configuration . . . . . . . . . . . . . . . . . . . . 23
Communication with Associated Controllers . . . . . 23
Controller Identification . . . . . . . . . . . . . . . . . . . . . . . 23
Network Inputs. . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Inputs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Diagnostic LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Troubleshooting Tips . . . . . . . . . . . . . . . . . . . . . . . 32

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HPU3
The HPU3 heat pump controller is a stand-alone microprocessor-based controller for liquid source heat pump units.
The application includes liquid source heat pump units with two-stage compressor, reversing valve, fan, dehumidifica-
tion (internal and external), humidification, and auxiliary (emergency) heat.
Overview
The HPU3 incorporates digital outputs in the form of triacs for digital fan fan start/stop, two compressor stages, dehu-
midification enable, humidification enable, reheat enable, auxiliary heat enable, and a reversing valve. An analog out-
put for modulated fan control is also provided. Digital inputs are provided to monitor equipment status and high and low
pressure alarms. A two-wire serial interface is provided for the thermostat. Analog inputs are available for optional
space temperature, power transducer, supply air temperature, and supply air humidity.
The controller is based on LONWORKS®networking technology. The controller can be networked to a higher-level control
system for monitoring and control applications.
Features
• Two stage compressor heating/cooling control
• Reversing valve control
• Auxiliary (Emergency) Heat enable
• Dehumidification with Reheat, both internal and external
• Humidification with SAT monitoring
• Local backup schedule
• Individual temperature setpoints for occupied/unoccupied heat and cool
•LONWORKS interface to building automation systems
• Equipment status input for additional safety interlocks
• High and Low Pressure Alarm inputs
• Thermostat with space temperature, humidity, temperature setpoint adjust, fan override, occupancy override
• Fan control energized on call for heating or cooling
• Automatic heat/cool changeover
• Global unit enable for main plant synchronization
• Remote sensor capabilities
• Automatic configuration with the LCI
• Real Time Clock
• Alarm/Event reporting
PURPOSE OF THIS GUIDE
The iWorx® HPU3 Application Guide provides application information for the HPU3 Controller.
The reader should understand basic HVAC concepts, intelligent environmental control automation, and basic LON-
WORKS networking and communications. This application manual is written for:
• Users who engineer control logic
• Users who set up hardware configuration
• Users who change hardware or control logic
• Technicians and field engineers

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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® 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® LHP2 Application Guide, Doc-
ument No. 505-024
– Application Engineers
– Installers
– Service Personnel
– Start-up Technicians
– End user
These controllers may operate in conjunction
with the LHP2. Application manuals provide
specific application information about these con-
trollers, including sequence of operation and
configuration information.
iWorx® CCU2 Application Guide,
Document No. 505-022
– Application Engineers
– Installers
– Service Personnel
– Start-up Technicians
– End user
These controllers may operate in conjunction
with the CCU2. Application manuals provide
specific application information about these con-
trollers, including sequence of operation and
configuration information.
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 HPU3 module which supports a liquid source heat pump.
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 outside, it must be contained within a protective enclosure. The enclosure must main-
tain 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, and 12 are connected internally on all HPU3 controllers. Disconnect ALL
power sources when installing or servicing this equipment to prevent electrical shock or equipment dam-
age.
Figure 2: HPU3 Wiring Example - Power Sourcing

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Figure 3: HPU3 Wiring Example - Power Isolated
Connecting Input Devices
Thermostat (STAT)
To connect the heat pump thermostat or an RH (humidity) sensor to the unit, attach one wire from the thermostat or
sensor to STAT (T3) and the other wire to the adjacent common (T4).
Equipment Status (EQS)
To connect the equipment switch to the digital input, attach one wire of the contact to EQS (T5) and the other wire to
the adjacent common (T6). This must be a dry contact switch.

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Low Pressure Alarm (LP)
To connect the Low Pressure alarm to the digital input, attach one wire of the contact to LP (T10) and the other wire to
the adjacent common (T9). This must be a dry contact switch.
High Pressure Alarm (HP)
To connect the High Pressure alarm to the digital input, attach one wire of the contact to HP(T8) and the other wire to
the adjacent common (T9). This must be a dry contact switch.
Heat Pump Power Transducer (POW, optional)
To connect the power transducer to the unit, connect the positive wire from the sensor to POW (T11) and the other wire
to the adjacent common (T12). The sensor must be provided and configured by Taco. It is required if the HPU3 needs
to report energy usage to a GHP1 for COP calculations.
Supply Air Humidity (SAH)
To connect a humidity sensor to the unit, connect one wire from the sensor to SAH (T14) and the other wire to the adja-
cent common (T15). This is required when humidifying to prevent saturating the air duct.
Space Temperature / Space Humidity (ST, optional)
To connect a thermistor (Precon III) or a humdity sensor to the analog input, attach one wire of the sensor to ST (T7)
and the other wire to the adjacent common (T6). The thermistor or humidity sensor can be used if no TS300 series
thermostat is being used.
Supply Air Temperature (SAT, optional)
To connect a thermistor (Precon III) to the analog input, attach one wire of the sensor to ST (T13) and the other wire to
the adjacent common (T12).
Connecting Output Devices
Stage 1 & Stage 2 (S1, S2)
The outputs for the stages must be connected to 24 VAC pilot relays if the loads are greater than 1 Amp for each pump.
If the loads are less than 1 Amp, connect stage 1 to S1 (T28) and adjacent COM (T27), and connect stage 2 to S2
(T26) and adjacent COM (T27).
Reversing Valve (RV)
The output for the reversing valve must be connected to a 24 VAC pilot relays if the load is greater than 1 Amp. If the
load is less than 1 Amp, connect the reversing valve input to RV (T29) and adjacent COM (T30).
Digital Fan (FAN)
The output for the fan must be connected to a 24 VAC pilot relay if the load is greater than 1 Amp. If the load is less
than 1 Amp, connect the fan input to FAN (T31) and adjacent COM (T30).
Dehumidification (DHUM)
The dehumidification mode output must be connected to a 24 VAC pilot relays if the load is greater than 1 Amp. If the
load is less than 1 Amp, connect the fan input to DHUM (T25) and adjacent COM (T24).
Humidification (HUM)
The humidification output must be connected to a 24 VAC pilot relay if the load is greater than 1 Amp. If the load is less
than 1 Amp, connect the external humidification signal to HUM (T23) and the adjacent COM (T24).
Reheat Valve (RH)
The reheat valve output must be connected to a 24 VAC pilot relay if the load is greater than 1 Amp. If the load is less
than 1 Amp, connect the reheat valve to RH (T22) and the adjacent COM (T21).

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Auxiliary Heat (AUX)
The auxiliary heat output must be connected to a 24 VAC pilot relay if the load is greater than 1 Amp. If the load is less
than 1 Amp, connect the auxiliary heat output to AUX (T20) and the adjacent COM (T21).
Modulated Fan (FANM)
The modulated fan output can be set to 0-10 V max through the control logic. Connect the positive wire from the fan to
FANM (T37) and the other wire to COM (T36).
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.
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.
SPECIFICATIONS
Electrical
Inputs
• Cabling: twisted shielded pair, 18 AWG recommended—500 feet max. (152 meters)
• Resolution: 10 bit
Stat
• Precon Type III 10K thermistor, or
• 12 Volt nominal, internally limited to 0.04 A (SLink)
Supply Air Temp
• Precon Type III 10K thermistor
Heat Pump Power Transducer
• 0 to 10 Volts DC
Equipment Status, High Pressure Alarm, Low Pressure Alarm
• Dry Contact
• Configurable as Disabled, Normally Open, or Normally Closed
• 5 Volts DC Max
Outputs
Stage 1, Stage 2, Reversing Valve, Fan, and Dehumidification
•24Volts AC

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• 1A @ 50C, 0.5A @ 60C, limited by the Class 2 supply rating
Modulated Fan (analog output)
• 0-10 Volt
• 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
Recommended Sensor Wire
FTT-10A Network
• Speed: 78KBPS
• 42.4 Volts DC max
• 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)
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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• 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
APPLICATION DESCRIPTION
The controller maintains the temperature of a space to a defined setpoint. The figure below illustrates a typical control-
ler application. The control is achieved by sequencing the reversing valve and compressor stages of a liquid source
heat pump based on the current space requirements.
Figure 4: HPU3 Application
The controller controls the starting and stopping of the supply air fan. If the unit enable input indicates plant synchroni-
zation, the fan is energized when there is call for heating or cooling. During the occupied periods, the fan can be config-
ured to run continuously. The fan can be overridden from the local thermostat. If overridden, the fan will run
continuously.
When the temperature increases above the cooling setpoint, the reversing valve cycles to the cooling position. The
compressor stages are sequenced on with a time proportioned control algorithm to minimize excessive cycling. As the
temperature decreases below the cooling setpoint, the compressor stages are sequenced off. When the unoccupied
mode is entered, the cooling setpoint is set up to a separate cooling setpoint for unoccupied mode.
When the temperature decreases below the heating setpoint, the reversing valve cycles to the heating position. The
compressor stages are sequenced on with a time proportioned control algorithm to minimize excessive cycling. As the
temperature increases above the heating setpoint, the compressor stages are sequenced off. When the unoccupied
mode is entered, the heating setpoint is set back to a separate heating setpoint for unoccupied mode.
Each controller interfaces to a local thermostat. The thermostat includes a space temperature sensor, space humidity
sensor, temperature setpoint adjustment, occupancy override, and a fan auto/on selection (depending on the model).
The controller operates in one of two states: occupied or unoccupied. The LCI determines the active operating mode.
The controller maintains the comfort level to a user-defined setpoint during the occupied period, and uses setup and
setback values during the unoccupied period to maintain the space temperature. An optional backup schedule is pro-
vided for cases when the LCI is not available.

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Three digital inputs are provided to monitor the status of the equipment within the unit. An external contact may be
wired to these input to provide additional equipment safety interlocks. When the contact closes, the controller shuts the
unit down. An alarm is reported to the LCI when this condition exists. For more detail on response and recovery to the
digital alarms, see the appropriate sections under “Sequence of Operation.”
The HPU3 can be synchronized to the main plant water supply through its global unit enable feature. The status of the
supply water flow is measured by an external device, and provided to the controller over the network.
The controller monitors the runtime of the fan. When the runtime exceeds a programmable limit, a maintenance alarm
is reported to the LCI.
When the space temperature exceeds a programmable limit, a high limit alarm is reported to the LCI. When the space
temperature drops below a programmable limit, a low limit alarm is reported to the LCI. When the space temperature
returns to the proper range, a return to normal alarm is reported to the LCI.
When the zone humidity rises above the humidity setpoint, dehumidification is enabled by activating the dehumidifica-
tion output (external dehumidification), and optionally, the cooling stages (internal dehumidification). Dehumidification
is disabled when zone air humidity drops below the setpoint by 3%.
An analog output is available to modulate a variable speed fan to maintain a consistent Supply Air Temperature. This
output is governed by a P+I loop with a thermistor based sensor to monitor the Supply Air Temperature.
SEQUENCE OF OPERATION
This section describes the detailed sequence of operation for the controller control algorithms.
Setpoints
The heating and cooling setpoint for both occupied and unoccupied periods are programmable values. The space set-
point is a calculated value based on the programmed heating setpoint, cooling setpoint and current operating mode
(i.e. occupied or unoccupied).
The space setpoint is derived by first calculating the zero energy band (ZEB) for the current operating mode.
Occupied Mode
Unoccupied Mode
Next, the space setpoint is calculated from the zero energy band and the heating setpoint.
Occupied Mode
Unoccupied Mode
ZebOcc OccupiedCoolSp OccupiedHeatSp–=
ZebUnocc UnoccupiedCoolSp UnoccupiedHeatSp–=
SpaceSp OccupiedHeatSp ZebOcc
2
--------------------+=
SpaceSp UnoccupiedHeatSp ZebUnocc
2
---------------------------+=

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Figure 5: Space Setpoint Calculation.
The effective setpoint is a calculated value based on the space setpoint and the thermostat setpoint offset value. The
setpoint offset is used to increase or decrease the space setpoint from the local thermostat. The offset value is limited
to plus or minus the programmed setpoint adjustment.
The setpoint offset also affects the calculated heating and calculated cooling setpoints by an equal amount. The set-
point offset only applies in the occupied mode of operation; it has no affect in the unoccupied mode. Note that the
actual programmed heating and cooling setpoints are not changed. The offset is added to the programmed setpoints to
derive the calculated values.
Occupied Mode
Unoccupied Mode
CalcCoolingSp OccupiedCoolingSp SpOffset=
CalcHeatingSp OccupiedHeatingSp SpOffset=
EffectiveSp SpaceSp SpOffset=
CalcCoolingSp UnoccupiedCoolingSp SpOffset=
CalcHeatingSp UnoccupiedHeatingSp SpOffset=
EffectiveSp SpaceSp=

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Figure 6: Setpoint Adjustment
Heating Sequence
The reversing valve and compressor stages are sequenced based on the space temperature and the calculated heat-
ing setpoint. When the space temperature drops below the calculated heating setpoint, the reversing valve is cycled to
the heating position. When the space temperature drops below the calculated heating setpoint minus the heating con-
trol band for a predefined time period, a compressor stage is turned on. If the space temperature remains below the
heating control band for an additional time period, the next available stage is turned on. This cycle continues until all
available stages have been energized.

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After the space temperature has risen above the heating setpoint for a predefined time-period, the last-energized stage
is turned off. (Note that the last stage that was turned on will be the first one to be turned off.) If the space temperature
remains above the heating setpoint for an additional time-period, the next previous stage will be turned off. This cycle
continues until all stages have been de-energized.
The configurable value "stage time" determines the duration of the stage. An absolute minimum stage ON time of 2
minutes, and an absolute minimum stage OFF time of 5 minutes are enforced when the space temperature is less than
the space setpoint. If the temperature rises above the space setpoint then the minimum on and off times are ignored.
When the space temperature rises above the space setpoint, all of the compressor stages turn off immediately; the
stage time and minimum on time are ignored.
During unoccupied periods, the heating setpoint is adjusted downwards through a separate unoccupied heating set-
point.
Figure 7:
T1 = Stage Cycle Time
Occupied
Heating
Setpoint
Heating
Control
Band
T2 = Stage Cycle Time x 2
Space
Setpoint
Temperature
Stage 2 On
Stage 1 On
Stage 2 Off
Stage 1 Off
T1 T2T1T2
Reversing Valve = HEAT
Heat Sequence - Occupied Mode
Figure 8: Heat Sequences – Unoccupied Mode
T1 = Stage Cycle Time
Unoccupied
Heating
Setpoint
Heating
Control
Band
T2 = Stage Cycle Time x 2
Space
Setpoint
Temperature
Stage 2 On
Stage 1 On
Stage 2 Off
Stage 1 Off
T1 T2T1T2
Reversing Valve = HEAT

iWorx® HPU3
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Cooling Sequence
The reversing valve and compressor stages are sequenced based on the space temperature and the calculated cool-
ing setpoint. When the space temperature rises above the calculated cooling setpoint, the reversing valve is cycled to
the cooling position. When the space temperature rises above the calculated cooling setpoint plus the cooling control
band for a predefined time period, a compressor stage is turned on. If the space temperature remains above the cool-
ing control band for an additional time period, the next available stage will be turned on. This cycle continues until all
available stages have been energized.
After the space temperature has dropped below the cooling setpoint for a predefined time period, the last-energized
stage is turned off. (Note that the last stage that was turned on will be the first one to be turned off.) If the space tem-
perature remains below the cooling setpoint for an additional time-period, the next previous stage will be turned off.
This cycle continues until all stages have been de-energized.
The configurable value "stage time" determines the duration of the stage. An absolute minimum stage ON time of 2
minutes, and an absolute minimum stage OFF time of 5 minutes are enforced when the space temperature is more
than the space setpoint. If the temperature falls below the space setpoint then the minimum on and off times are
ignored.
When the space temperature drops below the space setpoint, all of the compressor stages turn off immediately; the
stage time and minimum on time are ignored.
During unoccupied periods, the cooling setpoint is adjusted upwards through a separate unoccupied cooling setpoint.

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Figure 9:
T1 = Stage Cycle Time
Occupied
Cooling
Setpoint
Cooling
Control
Band
T2 = Stage Cycle Time x 2
Space
Setpoint
Temperature
Stage 2 Off
Stage 1 Off
Stage 2 On
Stage 1 On
T1 T2T1T2
Reversing Valve = COOL
Cooling Sequence - Occupied Mode
Figure 10:
T1 = Stage Cycle Time
Unoccupied
Cooling
Setpoint
Cooling
Control
Band
T2 = Stage Cycle Time x 2
Space
Setpoint
Temperature
Stage 2 Off
Stage 1 Off
Stage 2 On
Stage 1 On
T1 T2T1T2
Reversing Valve = COOL
Cooling Sequence – Unoccupied Mode
Commissioning
The controller has a Commissioning screen that allows any of the controller's outputs to be manually configured to any
valid value. The Commissioning screen is the last choice in the All Settings menu.
From the Commissioning screen, the following outputs can be configured:
• Modulated Fan
• Digital Fan
• Reversing Valve (independent of Valve Type configuration)
• Compressor Stage 1
• Compressor Stage 2
• Dehumidification
• Humidification
• Reheat
• Auxiliary Heat
To enable Commissioning, configure the Enabled parameter in the Commissioning screen to “Yes.” Note that when
commissioning is enabled, all values are overridden.

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To disable Commissioning, configure the Enabled parameter in the Commissioning screen to “No.”
Fan Operation
The Fan Type is configured for either “Auto” or “On.” This setting determines the fan operation when the Occupancy
Mode is “Occupied.” This configuration applies to both the digital and modulated fan outputs.
When the Fan Type is “Auto,” and the Occupancy Mode is “Occupied,” the fans are energized when there is a call for
heating or cooling and de-energized when there is no demand for heating or cooling. (i.e. when the space temperature
is in the zero energy band - between the heating and cooling setpoints).
When the Fan Type is "On," and the Occupancy Mode is “Occupied,” the fans are always energized regardless of heat-
ing or cooling demand; the modulated fan output is a minimum of 33%; when there is a heating or cooling demand, the
modulated fan may increase in speed to satisfy the demand.
Some thermostats allow the fan operation to be overridden. When a thermostat with a single speed fan override is
used, the fan override energizes the digital fan and the modulated fan output is 100%. When a thermostat with a three
speed fan override is used, all fan speed overrides energize the digital fan and the modulated fan output is 33%, 67%
or 100% corresponding to fan speed 1, 2 and 3.
When the Occupancy Mode is “Unoccupied,” the fans operate as they would when the Fan Type is “Auto.”
Dehumidification with Reheat
The controller may be configured for either “External” Dehumidification Mode or “Internal” Dehumidification Mode.
“External” Dehumidification Mode triggers dehumidification equipment using the DHUM digital output. In addition,
“Internal” Dehumidification Mode controls the reversing valve and compressor stages. The fan purges for two minutes
both before and after dehumidification occurs.
Dehumidification begins when the Space Humidity rises above the configured dehumidification setpoint, and stops
when the Space Humidity falls three percent below the dehumidification setpoint. The Reheat (RH) digital output may
energize during dehumidification.
Both dehumidification and reheat have valid temperature operating ranges. The valid dehumidification range is defined
as the configurable Shutoff Limit below the Cooling Setpoint. Reheat only occurs when dehumidifying and the space
temperature is below the cooling setpoint. Note that the dehumidification range and reheat range are subject to a hys-
teresis to prevent rapid cycling.
To enable dehumidification, configure the Dehumidification Type as either “Always” or “Occupied,” configure the Set-
point to a non-zero value (percent), configure the Shutoff Limit (°F), and configure the Dehumidification Mode to either
“External” or “Internal.” Configuration is not required for Reheat.
To disable dehumidification and reheat, configure the Dehumidification Setpoint to zero. This action disables all dehu-
midification and reheat regardless of other configured values.
Auxiliary Heat
When the Outdoor Temperature is provided by either an ASM or CSM controller, Auxiliary Heating is enabled. When
the Outdoor Temperature falls below the configured auxiliary heat setpoint, the auxiliary heat digital output (AUX) is
energized and the compressor stages are turned off. When the Outdoor Temperature rises above the auxiliary heat set-
point plus the configured temperature offset, the auxiliary heat output is deenergized and normal compressor operation
continues.
To enable auxiliary heat, insure that there is an ASM or CSM controller on the same network as the HPU3. No other
action is necessary.
To disable auxiliary heat without removing the ASM or CSM controllers from the network, configure the auxiliary heat
setpoint to a value well below any possible outdoor air temperature. The auxiliary heat setpoint may be configured as
low as -459.7°F (absolute zero).