Taco iWorx MPU2 User guide

© 2014 Taco Electronic Solutions, Inc. 1
Application Guide 505-009-2
MPU2 Air Control – Pressure Dependent Multi-Zone
Self-Contained Interoperable Controller Model UCP-1
SUPERSEDES: January 16, 2013 EFFECTIVE: April 28, 2014
Table of Contents
MPU2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Mechanical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Application Description . . . . . . . . . . . . . . . . . . . . . . . . 15
Sequence of Operation. . . . . . . . . . . . . . . . . . . . . . . . 18
Operational Mode . . . . . . . . . . . . . . . . . . . . . . . . . 18
Occupancy Mode . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Setpoint Calculations . . . . . . . . . . . . . . . . . . . . . . . 19
Supply Air Setpoint Reset Curve . . . . . . . . . . . . . . 19
Heating Sequence . . . . . . . . . . . . . . . . . . . . . . . . . 20
Cooling Sequence . . . . . . . . . . . . . . . . . . . . . . . . . 24
Economizer Operation. . . . . . . . . . . . . . . . . . . . . . 27
Cutoff Temperatures . . . . . . . . . . . . . . . . . . . . . . . 28
Dehumidification . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Bypass Damper . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Analog Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Fan Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Fan Proof. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
MPU2 and VAVD Communications . . . . . . . . . . . . 30
Associating VAVDs . . . . . . . . . . . . . . . . . . . . . . . . 30
Supply Air Temperature Monitoring . . . . . . . . . . . . 30
Indoor Air Quality. . . . . . . . . . . . . . . . . . . . . . . . . . 31
Smoke Detection . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Mixed Air Low Limit Detection . . . . . . . . . . . . . . . . 31
Filter Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Real Time Clock (RTC) . . . . . . . . . . . . . . . . . . . . . 32
Local Backup Schedule . . . . . . . . . . . . . . . . . . . . . 32
Runtime Accumulations. . . . . . . . . . . . . . . . . . . . . 32
Alarms and Events. . . . . . . . . . . . . . . . . . . . . . . . . 32
Automatic Configuration . . . . . . . . . . . . . . . . . . . . 33
Controller Identification . . . . . . . . . . . . . . . . . . . . . . . 33
Inputs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Diagnostic LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Troubleshooting Tips . . . . . . . . . . . . . . . . . . . . . . . 42

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MPU2
The MPU2 is a self-contained microprocessor-based controller for multiplexed zone package units. Applications
include packaged rooftop DX units with up to four stages of cooling, or a floating point control valve, or a modulated
output (valve or variable speed circulator) two stages of heating, or a floating point control valve, or a modulated output
(valve or variable speed circulator) economizer, and bypass damper.
Overview
Digital inputs are provided for fan status, mixed air low limit indication, smoke detector, filter status and indoor air qual-
ity (IAQ). Analog inputs are provided for mixed air temperature, return air humidity, supply air temperature, and supply
duct static pressure. The MPU2 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, four analog outputs are provided to control cooling and
heating outputs, a modulated economizer, and bypass damper.
The MPU2 is based on the LONWORKS®networking technology. The controller can be networked to a higher-level con-
trol system for monitoring and control applications.
Features
• Four stages of cooling, or a floating point control valve, or a modulated output (valve or variable speed circulator)
• Two stages of heating, or a floating point control valve, or a modulated output (valve or variable speed circulator)
• Modulated bypass damper
• 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
• Dehumidification
• Multiplexed control of 32 zones based on zone demand
• Supply air temperature safety limits
• Supply air temperature setpoint reset based on greatest zone demand
• Time proportioned control of the staged outputs to reduce cycling
• Proportional+Integral control of the modulated economizer, modulated heating modulated cooling and static pres-
sure
• Local backup schedule
• Mixed air low limit protection
• Filter status, fan proof, freeze stat and smoke detection inputs
• Fan control energized on a call for heating, cooling or ventilation
• Automatic Heat/Cool changeover
• IAQ compensation based on the IAQ input or zone controller alarm
• Outside Air Temperature cutoffs
• Real Time Clock
•LONWORKS®interface to building automation systems
• Automatic configuration with the LCI
• Alarm/Event reporting
PURPOSE OF THIS GUIDE
The iWorx® MPU2 Application Guide provides application information for the MPU2 Controller.

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The reader should understand basic HVAC concepts, intelligent environmental control automation, and basic LON-
WORKS networking and communications. This Guide 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
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
Table 1: Applicable Documentation
Description Audience Purpose
iWorx® MPU2 Application Guide,
Document No. 505-009 (this docu-
ment)
– Application Engineers
– Wholesalers
– Contractors
– Start-up Technicians
– End user
Provides instructions for setting up and using the iWorx®
MPU2.
iWorx® VAV Application Guide,
Document No. 505-010
– Application Engineers
– Installers
– Service Personnel
– Start-up Technicians
– End user
Provides instructions for setting up and using the iWorx® VAV
controller.
iWorx® LCI Application Guide, Doc-
ument 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.
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 operations, flow diagrams, wiring diagrams,
points and specifications.
Additional Documentation LonWorks FTT-10A Free Topology Transceiver User’s Guide, published by Echelon Cor-
poration. It provides specifications and user instructions for the FTT-10A Free Topology
Transceiver. 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 MPU2 controller, which supports one multiplexed 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 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, 12, 15, 18, and 38 are connected internally on all MPU2 controllers. Disconnect
ALL power sources when installing or servicing this equipment to prevent electrical shock or equipment
damage.
Figure 2: Typical MPU2 Wiring - Example A

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Figure 3: Typical MPU2 Wiring - Example B

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Figure 4: Typical MPU2 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 MPU2.

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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.
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 (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). This must be a dry contact normally open switch.
Mixed Air Low Limit Indication (MLL)
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 normally open switch.
Indoor Air Quality (IAQ)
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). The sensor must provide a contact closure when the CO2limit is exceeded. For a digital
sensor, this must be a dry contact normally open switch. For an analog sensor, it must be of the 0-10V type.
Static Pressure (SPR)
To connect the static pressure transducer to the analog input, connect the positive wire from the sensor to SPR (T8)
and the other wire to the adjacent common (T9). The sensor must be of the 0 to 10 V 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 ECNM (T35) and the other wire to COM (T36). See preceding figures for details.

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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.
Bypass Damper (BYP)
The bypass damper output can be set to 0-10 VDC max through the control logic. Connect the positive wire from the
damper actuator to BYP (T32) and the other wire to the adjacent common (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 (31) and TC12 (30). 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 (29) and TC12 (30). 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 (24). 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 H1 (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).
Digital Economizer (ECD)
The digital economizer output must be connected to a 24 VAC pilot relay if the load is greater than 1 Amp. See preced-
ing 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.

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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
Mixed Air Low Limit, Filter Status, Smoke Detect, Local IAQ Alarm
• Dry Contact
• Normally Open
•5Volts DC Max
Fan Proof
• Dry Contact
• Normally Closed
Return Air Humidity, Static Pressure
• 0 - 10 Volts DC
Mixed Air Temperature, Supply Air Temperature, Return Air Temperature
• Precon Type III 10K thermistor
Outputs
Fan Start/Stop, Heating Stage 1, Heating Stage 2, Cooling Stage 1, Cooling Stage 2, Cooling Stage 3, Cool-
ing Stage 4, Digital Economizer
•24Volts AC
• 1A @ 50C, 0.5A @ 60C, limited by the Class 2 supply rating
Modulated Economizer, Bypass Damper
• 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 MPU2 is a multiplexed package unit controller that permits a single zone package unit to operate multiple zones.
Figure 5 and Figure 6 illustrate typical MPU2 applications. The MPU2 operates in conjunction with up to 32 multiplexed
zone controllers. The control is achieved by multiplexing the primary supply air between cooling and heating based on
the various demands from the Zone Controllers. In addition to multiplexing, the MPU2 controls an economizer and
bypass damper.
Figure 5: Multiplexed Package Unit - Staged Heating & Cooling, Modulated Economizer
The starting and stopping of the supply air fan is controlled by the MPU2. The fan is energized when the there is a call
for heating or cooling from the Zone Controllers. During the occupied periods, the fan can be configured to run continu-
ously.
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. Optionally, free cooling can be determined
by a dry bulb comparison of the outside air temperature and average zone temperature.
The economizer can be configured as two-position (digital) or modulated (analog). If enabled, the two position econo-
mizer output 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 economizer is disabled.

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When “free cooling” is available, the modulated economizer position is calculated by a Proportional + Integral (P+I)
control loop based on the mixed air temperature and setpoint. As the temperature increases above the mixed air set-
point, the economizer damper is modulated open. The economizer is modulated closed as the temperature decreases
below the mixed air setpoint. The economizer is modulated to its minimum position when the economizer is disabled.
The economizer can optionally be disabled during unoccupied periods.
The bypass damper operates to maintain a configurable system static pressure setpoint. The bypass damper position
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 bypass damper is modulated open. The bypass damper is modu-
lated closed as the pressure decreases below the pressure setpoint.
Heating and cooling changeover setpoints are provided to prevent zone thermal shock during mode changes.
Figure 6: Multiplexed Zone Control System
An indoor air quality input is provided to monitor the Indoor Air Quality (IAQ). It can accept a digital CO2 sensor provid-
ing a contact closure, or an analog CO2 sensor. In addition, an alarm condition can be signaled by one of the Zone
Controllers. When an alarm condition exists, the MPU2 energizes the supply air fan and override the static pressure
setpoint to the IAQ alarm setpoint. The controller attempts to clear the IAQ condition by allowing the economizer to
open more than usual. If the condition has not been cleared after a programmable delay, an alarm is sent to the LCI.
The MPU2 scans all associated Zone Controllers to collect system demand data. The total heating and cooling
demands are accumulated. The greatest demand determines the control mode.
When the system cooling demand is greater than the system heating demand, the system enters the cooling mode.
When the system heating demand is greater than the system cooling demand, the system enters the heating mode.
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 (valve or variable speed circulator). 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).
The cooling stages are sequenced with a timed-proportioned control algorithm to minimize excessive cycling. The
sequencing is based on the measured supply air temperature, and the cooling setpoint. The cooling and heating
demands are continually re-evaluated during the cooling mode of operation. The controller is capable of switching to
the heating mode when the temperature demand is greater for heating. The cooling stages are interlocked with the
economizer control. If the two-position economizer is employed, the stages sequence on after the economizer.
The heating stages are sequenced with a timed-proportioned control algorithm to minimize excessive cycling. The
sequencing is based on the measured supply air temperature, and the heating setpoint. The cooling and heating
demands are continually re-evaluated during the heating mode of operation. The controller is capable of switching to
the cooling mode when the temperature demand is greater for cooling.

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If configured for modulated analog output (valve or variable speed circulator) 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 output will be modulated open. The cooling output will be modulated closed as the
temperature decreases below the cooling setpoint.
The heating output (valve or variable speed circulator) position is calculated by a P +I control loop based on the supply
temperature and the heating setpoint. As the temperature decreases below the heating setpoint, the heating output will
be modulated open. The heating output will be modulated closed as the temperature increases above the heating set-
point.
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.
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 greatest zone temper-
ature.
The controller optionally has the capability of monitoring 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-determined time period, the cooling stages shut down and 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, the heating stages shut down and 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 bypass damper is overridden
closed. A heating high limit exceeded alarm is reported to the LCI and all of the zone controllers.
The controller operates in one of two states: occupied or unoccupied. The LCI determines the active operating mode.
An optional backup schedule is provided for cases when the LCI is not available.
A digital input is provided to monitor the fan proof. If the fan is energized and no air flow is detected after 30 seconds,
the controller turns off all stages of heating and cooling along with the supply air fan. The controller returns to normal
operation after it is reset. An alarm is reported to the LCI when this condition exists.
A digital input is provided on the controller 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 controller turns off all
stages of heating and cooling along with the supply air fan. An alarm is reported to the LCI when this condition exists. If
configured for either analog or floating point valve, the output will open 100% to prevent freezing of the coils. The con-
troller returns to normal operation after it is reset. Following the reset there is a 10 minute delay before the mixed air
low limit is checked again.
The controller monitors the runtime of the cooling stages, heating stages, and fan. When any of the runtimes exceeds
the 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%.

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SEQUENCE OF OPERATION
This section describes the detailed sequence of operation for the MPU2 control algorithms.
Operational Mode
The MPU2 operates in one of four operating modes: primary heating, primary cooling, primary fan only, and primary off.
The operating mode determines whether warm or cool air is supplied to the zone controllers. The MPU2 determines
the operational mode based on the zone demand information supplied by each of the associated zone controllers. At
least once every 5 seconds, a different zone controller is polled. Each zone controller transfers its zone demand infor-
mation to the MPU2 over the communications network. The following information is transferred to the MPU2 controller:
• Zone temperature
• Calculated Heating Setpoint
• Calculated Cooling Setpoint
• IAQ Sensor Status (safe, alarm)
• Local Alarm (VAVD shutdown)
• Occupancy Mode (occupied, unoccupied, occupied extension)
• Supplemental heat status (on, off)
A zone heating demand is recognized when the zone temperature of a zone is at least 1.0 ° F below the calculated
heating setpoint. The total heating demand is the sum of all zones requiring heating.
A zone cooling demand is recognized when the zone temperature of a zone is at least 1.0 ° F above the calculated
cooling setpoint. The total cooling demand is the sum of all zones requiring cooling.
The system operational mode is determined by the greatest total demand value. When there is demand for both heat-
ing and cooling, the system switches between heating and cooling based on a configurable changeover time. Note that
minimum cycle times for the heating and cooling stages are enforced before an operational mode change can take
place. Also, a minimum 5-minute off-cycle is enforced before switching modes and following controller startup or reset.
When all zone demands have been satisfied (zone demand = 0), the operational mode is set to primary off indicating
no heating or cooling is being provided. When there is neither heating nor cooling, but the supply fan is on, the opera-
tional mode is set to primary fan only.
The heating mode can be disabled during warm weather by setting the outdoor air temperature heating lockout Max
OAT Heat. If the OAT is above the heating lockout temperature, the primary heating mode is disabled and the MPU2
can only be in the primary off or primary cooling modes. This feature requires that a controller that broadcasts the OAT,
such as an iWorx® ASM2, be installed on the network.
The cooling mode can be disabled during cold weather by setting the outdoor air temperature cooling lockout Min OAT
Cool. If the OAT is below the cooling lockout temperature, the primary cooling mode is disabled and the controller can
only be in the primary off or primary heating modes. This feature requires that a controller that broadcasts the OAT,
such as an ASM2 be installed on the network.
The economizer can be disabled during warm or cold weather by setting the outdoor air temperature economizer Max
and Min OAT Econ settings. If the OAT is above the Max lockout temperature or below the Min OAT temperature, the
economizer is disabled and forced to its minimum fresh air position. The controller can only be in the primary off, pri-
mary heating or primary cooling modes. This feature requires that a controller that broadcasts the OAT, such as an
ASM2 be installed on the network.
The MPU2 can also be configured to only enter primary cooling or primary heating mode when a minimum number of
zones require cooling or heating. Setting the Zone Limit to a higher number prevents a small number of zones from
affecting the desired operating mode of the whole space by instructing the MPU2 to not change operating modes until
at least that number of zones require heating or cooling.
The current operational mode information is periodically transferred to the VAVD over the communications network.
The following information is transferred to the VAVD from the primary air source controller:
• Operational Mode (primary cool, primary heat, primary fan only, primary off)

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• Alarm Conditions (IAQ Mode, Heat Failed On)
• Supply Air Temperature
Occupancy Mode
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.
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 extension mode the occupancy mode is overridden to the occupied state.
The current occupancy mode can affect the operation of the economizer, fan and bypass damper.
Additionally the heating and cooling setpoints may be reset based on the greatest zone demand.
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.
Supply Air Setpoint Reset Curve
If the Supply Temperature Setpoint Reset Curve is enabled, the MPU2 keeps track of the differential between each
zone's space temperature and its temperature setpoint. The MPU2 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 is 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.

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When the Temperature Differential Maximum is set to 0, the Supply Temperature Setpoint Reset Curve is disabled and
the MPU2 operates with the usual heating and cooling supply air temperature setpoints.
Figure 7: Supply Air Setpoint Reset Curves
Heating Sequence
The controller provides support for either two stages of electric heating or one floating point or 0-10V modulating heat-
ing output (valve or variable speed circulator). You can specify which type of heat you are using through configuration
parameters.