BAC NEXUS NXF-0403N-CS2TS-H1 Manual

OPERATION & MAINTENANCE MANUAL

DANGER: Rotating equipment will cause severe personal injury or death to
persons who come in contact. Do not perform any service, maintenance, or
inspection on or near the fan(s), motor(s), or inside the unit without first ensuring
that the fans and pump motors are disconnected, locked out, and tagged out.
NOTE:
1. Recommended service intervals are the minimum for typical
installations. Different environmental conditions may dictate
more frequent servicing.
2. Clean the conductivity sensor two weeks after initial start-up.
Recommended Maintenance Intervals[1]
Inspect and clean as necessary: Start-Up Monthly Quarterly Annually Shutdown
Inspect general condition of the unit and check unit for unusual noise or vibration
Inspect and clean the fan guard
Inspect spray water basin and clean as required
Inspect and flush water distribution system as required
Check operation of solenoid make-up valve, mechanical make-up valve, and drain valve
Check and adjust water level in the spray water basin
Check operation of pump(s)
Inspect and clean conductivity sensor{2}
Check basin heater and stand alone BAC heater control panel (optional)
Drain spray water basin and connected piping
Inspect hCore® Heat Transfer Technology
Inspect and clean strainers in piping (by others)
Inspect unit finish
Mechanical equipment system: Start-Up Monthly Quarterly Annually Shutdown
Check motor voltage and current
Check general condition of EC Fan System and clean motor exterior when required
Check fan for rotation without obstruction
Check fan cycling for smooth operation
UV System:
Inspect and clean water circulation pump
Inspect and clean quartz sleeve
Inspect and clean UV intensity sensor
Check operation of solenoid drain valve, mechanical make-up valve, and drain valve
Replace UV bulb
Recommended Spare Parts
–Pump
–Nozzle/grommet kit
–Mechanical makeup valve
–Solenoid makeup valve
–Solenoid drain valve
–UV bulb for UV System (optional)
–EC Fan System
(for critical applications)

Table of Contents
Warnings and Cautions
2Safety Precautions
3Equipment Precautions
3General Maintenance Information
3Warranties
PART 1 Start-Up & Operation
6Start-Up
11 Operation
12 Spray Water Basin and Pump Water Control
13 Maintaining Water Quality
13 Fan Control
13 Cold Weather Operation
14 hCore®Heat Transfer Technology Freeze Protection
16 Emergency hCore®Heat Transfer Technology Drain
16 Spray Water Basin Protection
PART 2 Storage & Extended Shutdown
17 Prolonged Outdoor Storage
19 Extended Shutdown
PART 3 Detailed Component Maintenance Procedures
20 hCore®Heat Transfer Technology
21 EC Fan System
22 DiamondClear®Design
26 iPilot®Control System
30 Optional UV System
PART 4 Corrosion Protection
34 Water Treatment
35 Corrosion and Scale Control
36 Chemical Treatment Requirements
36 Passivation
36 Biological Control
37 Alternative Water Sources
37 Long Term Care of Stainless Steel
38 System Cleaning
PART 5 Bleed Rate
41 Example to Estimate Bleed Rate
PART 6 Operation Considerations for Accessories
42 Basin Heater and Stand Alone BAC Heater Control
Panel
44 Resonant Speed Identification Procedure
45 Positive Closure Dampers (PCDs)
PART 7 Troubleshooting Guide
46 Troubleshooting Guide
APPENDIX A iPilot®Control System
49 Menus
49 Software Menus
60 Controls Connections
OPERATION & MAINTENANCE »
NEXUS®MODULAR HYBRID COOLER
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WARNING
• WARNING: For basin and heater maintenance – switch off both of the control panels and lock and tag out the main disconnects.
• WARNING: The top horizontal surface of the unit is not intended to be used as a walking surface or working platform, and all
maintenance should be done in front of the equipment. If access to the top of the unit is desired, the purchaser/end-user is cautioned
to use appropriate means complying with applicable safety standards of governmental authorities.
• WARNING: Steps must be taken to avoid operation at or near system resonant frequency which could result in fan failure and possible
personal injury or damage. Refer to “Resonant Speed Identification Procedure” on page 40 for more details.
• WARNING: The recirculating water system may contain chemicals or biological contaminants, including Legionella, which could
be harmful if inhaled or ingested. Personnel exposed directly to the discharge airstream and the associated drift mists, generated
during operation of the water distribution system and/or fans, or mists produced by high pressure water jets or compressed air (if
used to clean components of the recirculating water system), must wear respiratory protection equipment approved for such use by
governmental occupational safety and health authorities.
• WARNING: Dangerous voltages are present in this equipment. To service the iPilot®Control System, disconnect the main electric power
supply to the control panel lock out and tag out the circuit. To service all other components on the unit, lock out and tag out the iPilot®
Control System. If ordered, the optional heater control panel should also be locked out and tagged out during service or maintenance.
• WARNING: The optional UV System contains a UV bulb. Do not operate the UV bulb when it is removed from the chamber. Unintended use or
damage of the system may result in the exposure of dangerous UV radiation. UV radiation may, even in little doses, cause harm to the eyes and skin.
• CAUTION: The operation, maintenance, and repair of this equipment shall be undertaken only by personnel authorized and qualified to
do so. All such personnel shall be thoroughly familiar with the equipment, the associated system and controls, and the procedures set
forth in this manual. Proper care, personal protective equipment, procedures, and tools must be used in handling, lifting, installing,
operating, maintaining, and repairing this equipment to prevent personal injury and/or property damage.
• CAUTION: Protect and secure this equipment and its premises against access by unauthorized personnel. Personal injury to members of
the public could result from interaction with the electrical and mechanical elements of this equipment.
• CAUTION: All electrical, mechanical, and rotating machinery are potential hazards, particularly for those not familiar with their design,
construction, and operation. Accordingly, use appropriate lockout procedures. Adequate safeguards (including the use of protective
enclosures where necessary) should be taken with this equipment both to safeguard the public from injury and to prevent damage to
the equipment, its associated system, and the premises.
• CAUTION: This equipment should never be operated without all access panels in place. For the protection of authorized service and
maintenance personnel, install a lockable disconnect switch located within sight of each equipment control panel.
DANGER: Rotating equipment will cause severe personal injury or death to persons who come in contact. Do not perform any service,
maintenance, or inspection on or near the fan(s), motor(s), or inside the unit without first ensuring that the fans and pump motors are
disconnected, locked out, and tagged out.
DANGER: To avoid possible electric shock, special care should be taken since water is present near the electrical equipment. Unless a situation is
encountered that is explicitly addressed by the provided maintenance and troubleshooting sections, DO NOT attempt repairs yourself.
DANGER
CAUTION
Safety Precautions

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• BAC units are typically installed immediately after shipment and many operate year round. However, if the unit is to be stored for a
prolonged period of time either before or after installation, certain precautions should be observed, as outlined in “Storage & extended
Shutdown” on page 17.
• Covering the unit with a clear plastic tarpaulin during storage can trap heat inside the unit and cause damage to the PVC components.
If units must be covered during storage, an opaque, reflective tarp should be used.
• Do not use steam or high pressure water to clean PVC eliminators, PVC water diverter, or materials other than steel.
• Do not use high pressure water exceeding 60 psi to clean the hCore®Heat Transfer Technology
• Do not use sharp or pointed objects, including screwdrivers and similar, for cleaning the hCore®Heat Transfer Technology.
• If noise or vibration persists, shut the unit down and correct the cause before continuing operation.
• Never use chloride or chlorine based solvents such as bleach or muriatic (hydrochloric) acid to clean stainless steel. It is important to
rinse the surface with warm water and wipe with a dry cloth after cleaning.
• The basin heater is not designed to prevent icing during unit operation.
General Maintenance Information
Equipment Precautions
NOTICE
The services required to maintain a piece of evaporative cooling equipment are primarily a function of the quality of the air and water in the
locality of the installation:
• AIR: The unit should be located such that unusual quantities of industrial smoke, chemical fumes, salt, or heavy dust do not enter the
equipment. Such airborne impurities entering into the equipment and absorbed by the recirculating water, which can form a corrosive
solution.
• WATER: As water evaporates from the equipment, dissolved solids are left behind, which were originally contained in the make-up water.
These dissolved solids may be either alkaline or acidic and as they are concentrated in the circulating water, they can cause scaling or
accelerated corrosion.
The extent of impurities in the air and water determines the frequency of most maintenance services and also governs the extent of water
treatment which can vary from a simple continuous bleed and biological control to a sophisticated treatment system. Refer to “Water
Treatment” on page 30 and “Biological Control” on page 32 for more details.
Warranties
Please refer to the Limitation of Warranties in the submittal package applicable to and in effect at the time of the sale/purchase of these
products. Described in this manual are the recommended services for start-up, operation, and shutdown, and the approximate frequency
of each.
• CAUTION: Steps must be taken to avoid operation at or near system resonant frequency which could result in fan failure and possible
personal injury or damage.
• CAUTION: The optional UV System includes a UV bulb that contains mercury. If the lamp breaks, avoid inhalation or ingestion of the
debris and avoid exposure to eyes and skin. Never use a vacuum cleaner to clean up a broken lamp as this may scatter the spilled
mercury. Obey local regulations and guidelines for the removal and disposal of mercury waste.

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Figure 1. Nexus®Modular Hybrid Cooler
NEXUS®MODULAR HYBRID COOLER
Start-Up & Operation
1
1
2
3
11
12
20
21
4
5
6
7+8
9
10
14
17

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NEXUS®MODULAR HYBRID COOLER
Start-Up & Operation
1. hCore®Heat Transfer Technology: Exclusive closed loop heat transfer section with
stainless steel construction that offers high corrosion-resistance.
2. Fluid Connections: Fewest field piping connections due to innovative, easy-to-install
manifold with grooved connections.
3. iPilot®Control System: Automatically controls equipment operation according to your
specific needs, including energy savings desired, water savings desired, and water
management.
4. EC Fan System: This Electronically Commutated (EC) Fan System includes a direct-
drive radial fan and a variable-speed EC motor.
5. Fan Guard: Protects operators and blocks large debris.
6. Hinged EC Fan System Access Panel: Allows for easy access to the EC Fan System.
7. Spray Water Basin: Small, workbench-height basin that collects recirculating spray
water.
8. Basin Access Cover: Allows easy access inside the spray water basin for inspection
and service.
9. Basin Interior Access Panels: Allows access to the water diverter and air baffle.
10. Spray Pump: Continuously circulates water through the system to meet cooling
demand. There is also an integral strainer to the spray pump which prevents large
debris from entering pump and spray distribution. Constructed of stainless steel for
corrosion-resistance.
11. Riser Pipe: Directs water to the spray distribution.
12. Water Distribution System: Evenly wets the hCore®Heat Transfer Technology for
optimal thermal performance and reliability.
13. Water Diverter: Creates water turbulence in basin to minimize maintenance.
14. High and Low Level Switches (Not Shown): Sends water level signals for monitoring
and control.
15. Mechanical Make-up Valve (Not Shown): Provides fresh water to the unit to replenish
water that evaporates through the evaporative cooling process and is bled from the
basin.
16. Solenoid Make-up Valve (Not Shown): Normally closed valve controls when water is
sent to the basin during wet operation.
17. Drain Valve: This motorized valve is conductivity-controlled and is used to periodically
drain water to maintain water quality. It is also used to fully drain the basin to
minimize maintenance.
18. Conductivity Sensor (Not Shown): Sends signal that controls drain valve based on
water conductivity.
19. Outside Air Temperature Sensor (Not Shown): Sends signal that controls fan and
pump operation based on user inputs.
20. High Efficiency Drift Eliminators: Ensures that recirculating water remains in the unit
during operation.
21. Spray Distribution Access Panel: Allows for access to spray branches, nozzles, and
drift eliminators
Start-Up and Operation
Nexus®Modular Hybrid Cooler
DANGER: Rotating equipment
will cause severe personal injury
or death to persons who come in
contact. Do not perform any service,
maintenance, or inspection on or
near the fan(s), motor(s), or inside
the unit without first ensuring
that the fans and pump motors
are disconnected, locked out, and
tagged out.

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Start-Up
General
• If the unit will be in storage prior to start-up, follow the “Prolonged Outdoor Storage”
instructions on page 17.
• It is strongly recommended to install a removable 1/16” mesh strainer upstream of
the process fluid inlet to prevent large debris from entering the hCore® Heat Transfer
Technology (closed loop heat transfer section).
• If the unit is mounted on vibration isolators (by others), refer to the vibration isolation
manufacturer’s guidelines before loading/unloading weight from the unit.
• Before opening the iPilot®Control System panel, follow the proper lockout / tagout
procedures.
• It is recommended to install a strainer or filter in the make-up water supply line as
close as possible to the solenoid valve as possible to protect the valve from debris
buildup and diminished operation.
• Before starting the system the first time, flush the make-up supply water piping to the
unit for at least 5 minutes, ensuring that the make-up and drain valves are free of dirt
and debris.
• Before starting system the first time, flush the hCore®Heat Transfer Technology and
spray water basin for at least 5 minutes to remove construction debris.
Cleaning and Inspection
• Ensure that the water diverter (see Figure 2) is free of dirt and debris.
• Flush the spray water basin interior to remove any accumulated dirt and debris. Use a
garden hose to remove any dirt and debris.
DANGER: Rotating equipment
will cause severe personal injury
or death to persons who come in
contact. Do not perform any service,
maintenance, or inspection on or
near the fan(s), motor(s), or inside
the unit without first ensuring
that the fans and pump motors
are disconnected, locked out, and
tagged out.
Figure 2. Water Diverter Figure 3. Spray Water Basin
Figure 4. Hinged Access Fan Panel
Water Diverter

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• Remove spray distribution access panels, and inspect and clean the spray branch,
nozzles, and drift eliminators as necessary.
• Remove all dirt and debris from the fan guard(s).
• Open hinged access fan panel (see Figure 4) to clean all mechanical components and
to remove dirt and debris from plenum area.
• The installation and manufacturing processes used for field assembly of steel-piped
systems may leave weld byproducts inside the hCore® Heat Transfer Technology and
connecting piping. It is common practice to install filters and/or strainers that remove
contaminants during initial system operation. Shortly after system start-up, the filters
and/or strainers should be cleaned or replaced.
• Conduct external inspection of the equipment, sensors and probes. Check for leaks,
corrosion, and any structural damage.
• Conduct internal inspection of the equipment. Check for anything unusual such as
structural or mechanical component damage.
• Inspect wiring and connections for all the components.
• Confirm that wiring and connections inside of the iPilot® Control System panel are
secured.
• Inspect riser pipe(s) and connections.
• Inspect process fluid manifold piping and connections.
• Thoroughly inspect the fan(s) and pump(s) for any mechanical or physical damage.
• Verify that fan(s) rotates freely.
• Inspect solenoid valves, make-up valves, drain valves, and level switches.
• Check that the mechanical make-up valve is operating freely.
Pre Start-up Checks
• Verify that the following items are turned off and the unit is locked
out/ tagged out:
–Supply power disconnect
–Fan motor(s)
–Pump motors
–iPilot®Control System (control panel)
–Basin heater control panel (optional)
–Basin heaters (optional)
–Positive closure dampers (optional)
• Verify that all panels are closed and secure, including the following:
–Fan access panel
–Spray distribution access panel
–Basin access cover
–iPilot®Control System panel door
–Heater control panel door (if ordered)
• Verify the following water connections:
–Solenoid make-up valve –
Incoming water pressure must
be between 20 and 75 psig
–Drain valve
–Overflow
Figure 5. Panels to Secure
DANGER: Rotating equipment
will cause severe personal injury
or death to persons who come in
contact. Do not perform any service,
maintenance, or inspection on or
near the fans, motors, and drives,
or inside the unit without first
ensuring that the fans and pump
motors are disconnected, locked
out, and tagged out.
Start-Up & Operation
Start-Up
General
Cleaning and Inspection
Pre-Start-up Checks

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• Remove excess and loose sealer tape from valves and connections, including flume
connections.
• Turn the water supply on.
• Set the make-up float valve so the water shuts off at the operating level, see Table 2
on page 22 and Figure 17 on page 23.
• Ensure proper water treatment. Refer to page 30 for details.
• Verify the voltage stated in the submittal package matches the incoming power at the
job site.
• Verify that the supply power is connected to the iPilot® Control System.
• Verify that Building Management System (BMS) interface is correctly wired to the
iPilot® Control System.
• Turn on all breakers inside the iPilot® Control System.
• Close the iPilot®Control System panel and ensure that all the locks have been fully
engaged and secured by rotating them 90° with a flathead screwdriver or coin.
• Turn on the main power supply to the unit.
• Verify wiring from each component to the iPilot® Control System.
• Verify component operation by entering the Main Menu of the user interface, select
Point Overview, and change Manual Mode to On. Refer to the “iPilot® Control System
Appendix” on page 45.
• On units that are powered with 230/460V three phase, the power must be connected
properly to ensure that the pumps rotate clockwise. The wiring should be installed to
have incoming power U phase connected to panel L1, V phase to L2, W phase to L2,
and E phase to ground. It is recommended that a rotation meter be used to confirm
the power is connected to allow clockwise operation. Failure to ensure correct phase
wiring will result in reduced spray pump water flow, reduced thermal performance, and
possible excessive scale buildup.
• Verify that fan(s) are rotating in the correct direction (clockwise when looking into the
unit from the outside) by operating each component in “Manual mode”.
• Check for unusual noise or vibration.
• To flush dirt, debris, and oils from the basin and from the heat exchanger exterior,
operate the fans at 350 rpm, per the instructions in Appendix screen V10, and
operate the pumps, per the instructions in Appendix screen V04.
• After verifying component operation, re-enter the Main Menu and change Manual
Mode to Off and ensure that operational system value (OSV) is Off so that the iPilot
Control System can cycle fans and pumps appropriately.
Start-Up
• For initial start-up, clean the conductivity sensor after two weeks of service.
• Ensure that main disconnect switch on the iPilot®Control System is turned On.
The iPilot® Control System will arrive onsite preconfigured with factory default values and
requires field setup. There are three methods of equipment control:
1. Local control without a Building Management System (BMS) interface
2. Local control with a BMS interface (See Table 15 on page 57 for the BMS
data points).
3. Customer Input: Control using analog input (0-10 VDC, 10-0 VDC,
or 4-20 mA) by others.
DANGER: Rotating equipment
will cause severe personal injury
or death to persons who come in
contact. Do not perform any service,
maintenance, or inspection on or
near the fans, motors, or inside
the unit without first ensuring
that the fans and pump motors
are disconnected, locked out, and
tagged out.
WARNING: Dangerous voltages
are present in this equipment.
Disconnect the electrical service
of the source and tag the circuit
out before servicing or replacing
components.

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• Ensure that Customer Input is set to “No”.
• Ensure that BMS On/Off Control is set to “No”.
• Select desired “Operating Mode” (see Selecting Your Operating Mode on page 50 for
details about which mode to select), set Run Authorize to On, and adjust setpoint
to desired leaving fluid temperature. Run Authorize may also be toggled by remote
contacts by others; see wiring diagram for details.
• Navigate to User Menu and press enter.
For Local Control without a Building Management System (BMS) Interface
Start-Up & Operation
Start-Up
Pre-Start-up Checks
Start-up
• Refer to “iPilot®Control System Appendix” on page 45 for more information
including for controls connections.
• Anytime equipment operation is required, Run Enable must be turned On
either locally through the iPilot®Control System interface or remotely with a
signal by others. When positive closure dampers are included, the run state
commands the dampers to open (On) and close (Off).

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Unit Run Authorization Enabled
• To enable unit access via BMS, change “Enable Unit Run Access via BMS” to “Yes”.
• Do Not enable “Yes” unless unit run authorization access via BMS is required.
Optional Controls Settings
For optimal control setup based on your system needs, you may select the following
optional controls settings (refer to the “iPilot®Control System Appendix” on page 45 for
more details):
• Water Management
–Time-based Bleed: Frequency and duration of bleed
• On the following screen, adjust your BMS configuration as required.
After 24 hours of operation
under thermal load, perform the
following services:
9Check the unit for any unusual
noises or vibrations.
9Check the operating water
level in the cold water basins.
9Adjust the mechanical make-
up valve if necessary.
9Inspect the spray nozzles and
the hCore® Heat Transfer
Technology.
For Local Control with a BMS Interface
Unit Run Authorization Disabled
• Ensure that the BMS is wired properly per wiring diagram located in the iPilot®Control
System.
• Navigate to BMS Communication screen and select your communication type (Modbus
or BACnet).
For Control Using Customer Input
• Ensure that analog input is wired
properly per the wiring diagram located
in the iPilot®Control System.
• Navigate to User Menu.
• Change Customer Input to Yes, then
select signal type.

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Operation
The Nexus®Modular Hybrid Cooler balances energy and water savings by operating each
module wet or dry. One of the following operating modes can be selected (see page 40) to
best fit your system needs:
Energy Saver Mode
Maximum Energy Savings
In Energy Saver Mode, energy savings are
maximized by leveraging the full power of
evaporative cooling. During periods when
ambient temperatures or loads from the building
or process are relatively high, the Nexus®Modular
Hybrid Cooler operates with all spray systems
active across all modules. During off-design
conditions, the EC Fan System will automatically
and intelligently reduce speed whenever possible.
As the load is satisfied, the fans and spray pumps
will cycle off.
When demand increases and calls for heat rejection, each module turns on in sequence.
Once all modules are turned on, all fans operate at a synchronized speed.
Nexus Mode
Balanced Energy and Water Savings
In the revolutionary Nexus Mode, you can
prioritize water and energy savings to achieve the
right balance of both. Your climate, cooling load
profile and the rates you pay for water and energy
will determine your specific settings, which can
easily be re-adjusted as needed. You can specify
the importance of water versus energy savings to
automatically achieve the right balance for your
specific situation.
When demand increases and calls for heat rejection, all fans ramp up simultaneously.
Once all fans reach 100% fan speed, each pump turns on one module at a time to meet
building demand. In Nexus mode, the user can choose how to balance energy savings and
water savings by adjusting the iPilot®Control System by selecting a program setting from
1-7 with 1 being maximum energy savings while dry and 7 being maximum water saving.
EVAPORATIVE
MAXIMUM ENERGY SAVINGS
Figure 6. Energy Saver Mode
HYBRID
EVAPORATIVE
Figure 7. Nexus Mode
Start-Up & Operation
Start-Up
Start-up
Operation
Energy Saver Mode
Nexus Mode
–Conductivity-based Bleed: Conductivity threshold value for bleed (recommended)
–Time-based Drain: Time and frequency of complete basin drain (optional)
• PI-Parameters
–Prop. Band – Proportional band of PI controller
–Integr. Time – Integration time of PI controller
–For addition parameters, see the “iPilot®Control System Appendix” on page 45.

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Water Saver Mode
Maximum Water Savings
In Water Saver Mode, water savings are
maximized by leveraging the dry efficiency of the
hCore®Heat Transfer Technology and operating
without spray water. To meet increasing loads, the
EC Fan System will automatically and intelligently
increase speed and the spray pumps will activate
only when necessary (Winter Guard Disabled).
Within Water Saver Mode, there are two options:
1. Winter Guard Disabled (Recommended):
When demand increases and calls for heat
rejection, each pump will turn on when
demand exceeds the capacity of the unit
while running dry. This mode is recommended to ensure that heat load can be rejected
by evaporative cooling when required.
2. Winter Guard Enabled: When demand increases and calls for heat rejection, all fans
ramp up simultaneously, and all modules will only run dry. This mode is typically
utilized when the make-up water line has been winterized / shutoff to the unit during
cold weather and / or the load is greatly reduced during winter months.
Spray Water Basin and Pump Water Control
• Verify that incoming water pressure is between 20 and 75 psig.
• When the iPilot®Control System calls for evaporative cooling, the solenoid make-up
valve will open, the mechanical make-up valve will open, the drain valve will close,
and water will fill the basin.
• Once the water reaches operating level, the mechanical make-up valve will close, there
will be a brief delay, and the pump(s) will cycle on in a staged operation to recirculate
water.
• As water evaporates, the mechanical make-up valve will open to ensure that the water
level is maintained.
• If the pump receives a signal to operate and the water level is too low, the iPilot®
Control System will indicate a corresponding fault and the system will switch to Water
Saver Mode with Winter Guard enabled. To re-enable evaporative cooling, correct the
issue and reset the alarm on the user interface.
DRY
MAXIMUM WATER SAVINGS
Figure 8. Water Saver Mode
Figure 9. Spray Water Basin
Drain Valve
Water Diverter
Access Panel
Overflow
Mechanical Make-up
Valve
Spray Pump
Solenoid Make-up Valve
High/Low Level Switches
NOTE: Be sure to open make-up
supply line before Winter Guard is
disabled and confirm that the spray
water basin is filled. .

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Maintaining Water Quality
The iPilot®Control System is preset at the factory in accordance with BAC’s Water Quality
Guidelines. Water quality can be controlled as follows:
• A conductivity sensor is included to constantly measure water conductivity. During
operation, the drain valve will slowly open to control conductivity by draining water
from the spray water basin to meet the setpoint (the default setpoint is set at 3300
micro ohms/cm).
• BAC recommends adjusting the conductivity setpoint in the iPilot®Control System to
to best minimize water consumption and keep heat transfer surfaces scale-free. Refer
to “Corrosion Protection” on page 30 for more details.
• A time-based bleed can be enabled by entering frequency and duration.
• An optional time-based drain can be enabled during periods of inactivity, and the
basin will not refill until building demand requires evaporative cooling. Refer to the
“iPilot®Control System Appendix” on page 45.
Fan Control
The fans are controlled by the iPilot®Control System by each of the following methods:
• The included temperature sensor at the outlet of the hCore® Heat Transfer Technology
is a negative temperature coefficient (NTC) sensor and sends a signal to the controller
in the iPilot®Control System, which modulates the fan speed accordingly.
• If the temperature signal is lost, an alarm will occur and the fans will continue to
operate at the most recent fan speed prior to loss of signal.
• If required, an analog signal (0-10V, 10-0V and 4-20mA) can be provided by the user
to control the fan. It is recommended to have the iPilot®Control System automatically
modulate the fan speed for optimal energy and water savings. This method of fan
control is only available in Energy Saver Mode, and Water Saver Mode with Winter
Guard enabled.
• For 2-fan modules (NXF-0603), ensure that both fans are operating simultaneously for
proper air and water management.
Cold Weather Operation
The iPilot®Control System has been designed to protect the equipment during freezing
conditions.
• All spray pumps will turn off below 35°F (1.7°C) ambient temperature, and the
equipment will automatically operate in Water Saver Mode with (Winter Guard
enabled).
Start-Up & Operation
Operation
Water Saver Mode
Spray Water Basin and Pump
Water Control
Maintaining Water Quality
Fan Control
Cold Weather Operation

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• When the optional basin heaters are not included:
–Once ambient temperature drops below 35°F (1.7°C), water will remain in the basin
for 1 hour and then the water will be drained.
–The solenoid make-up valve will remain closed until the ambient temperature is
above 35°F (1.7°C) and when evaporative cooling is required.
• When optional basin heater(s) are included, the basin heater(s) turn on when the
Figure 10. Optional Basin Heater(s)
following conditions are met:
–Spray water basin temperature drops below 40°F (4.4°C).
–Spray pumps are off.
–Sufficient water level in the basin.
• When the ambient temperature remains below 40°F (4.4°C), water will remain in the
basin for the duration of the user-defined time-based drain.
hCore®Heat Transfer Technology Freeze Protection
For protection against freezing of the hCore®Heat Transfer Technology (closed loop heat
transfer section), recommended methods are an industrial grade inhibited ethylene glycol
or propylene glycol solution. When the use of glycol is not practical, the system must be
designed to meet both minimum flow and minimum temperature requirements.
• See Table 1, for hCore®Heat Transfer Technology volumes for Nexus®Modular Hybrid
Cooler models.
• When a glycol solution is not utilized, operate the system to meet the following
conditions.
–Maintain the minimum recommended flow through the hCore®Heat Transfer
Technology at all times (see Table 1).
• Maintain a minimum heat load on the circulating fluid so that the temperature of the
fluid leaving the coil is not less than 45°F (7.2°C).
• To maintain the leaving fluid temperature at 50°F (10°C) when the process load is
extremely light or shut off, apply an auxiliary heat load to the circulating fluid and
adjust the flow to ensure that fluid leaving the coil maintains the minimum required
temperature.
NOTE: For the units with the heater
option installed, units are shipped
with two separate control panels –
one iPilot®Control System and one
heater control panel (which must be
interconnected).
WARNING: For basin and heater
maintenance – switch off both of
the control panels and lock and tag
out the main disconnects.

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Table 1. Internal Volume and Minimum Recommended Flow and Heat Loss
Model
Total Internal
hCore®Heat
Transfer Technol-
ogy Volume (gal)
Minimum Flow
(GPM)
Equipment Heat
Loss (BTU/hour)
Equipment Heat
Loss with Op-
tional PCDs (BTU/
hour)
NXF-0403N-CS2TS-H1 27 24 52,706 24,402
NXF-0403N-CS2TS-H2 53 48 104,413 47,961
NXF-0403N-CS2TS-H3 79 72 155,120 70,693
NXF-0403N-CS2TS-H4 105 96 204,828 92,614
NXF-0403N-CS2TS-H5 131 120 253,537 113,741
NXF-0403N-CS2TS-H6 157 144 301,249 134,090
NXF-0403N-CS2TT-H1 27 12 52,706 24,402
NXF-0403N-CS2TT-H2 53 24 104,413 47,961
NXF-0403N-CS2TT-H3 79 36 155,120 70,693
NXF-0403N-CS2TT-H4 105 48 204,828 92,614
NXF-0403N-CS2TT-H5 131 60 253,537 113,741
NXF-0403N-CS2TT-H6 157 72 301,249 134,090
NXF-0603N-CS2TS-J1 39 36 86,654 31,244
NXF-0603N-CS2TS-J2 78 72 170,307 60,537
NXF-0603N-CS2TS-J3 117 108 250,992 87,955
NXF-0603N-CS2TS-J4 156 144 328,749 113,578
NXF-0603N-CS2TS-J5 165 180 403,623 137,484
NXF-0603N-CS2TS-J6 234 216 475,666 159,753
NXF-0603N-CS2TT-J1 39 18 86,654 31,244
NXF-0603N-CS2TT-J2 78 36 170,307 60,537
NXF-0603N-CS2TT-J3 117 54 250,992 87,955
NXF-0603N-CS2TT-J4 156 72 328,749 113,578
NXF-0603N-CS2TT-J5 165 90 403,623 137,484
NXF-0603N-CS2TT-J6 234 108 475,666 159,753
Figure 11. Optional Positive Closure Dampers (PCDs)
Start-Up & Operation
Cold Weather Operation
hCore®Heat Transfer
Technology Freeze Protection
Positive Closure Dampers (PCDs) (Optional)
The amount of auxiliary heat required can be substantially reduced by the use of positive
closure dampers at the unit air discharge (see Figure 11). The dampers remain open as
long as the unit run state is active and remain closed whenever run state is inactive. The
heat loss data can be found in Table 1.

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Emergency hCore®Heat Transfer Technology Drain
The hCore®Heat Transfer Technology (closed loop heat transfer section) is constructed
of corrosion-resistant stainless steel, so it may be drained frequently. However, frequent
draining of any piping constructed of carbon steel, including the header piping, promotes
corrosion inside the pipes. Therefore, if frequent draining is required, ensure that the
header and system piping are constructed of corrosion-resistant materials before draining
regularly.
Draining is acceptable as an emergency method of freeze protection if the hCore®Heat
Transfer Technology is not protected by a glycol solution. If frequent draining is required
for freeze protection, an automatic drain valve and vacuum breaker are recommended to
drain the hCore®Heat Transfer Technology if flow stops or the fluid temperature drops
below 45°F (7.2°C) when the ambient temperature is below freezing. Further protection
against hCore® Heat Transfer Technology freeze-up is possible with the installation of an
alarm to alert personnel when the temperature of the fluid leaving the section falls below
45ºF (7.2°C). For more information, see “Detailed Component Maintenance Procedures”
on page 20.
Contact your local BAC Representative for guidelines on the installation of an emergency
hCore®Heat Transfer Technology drain system.
Spray Water Basin Protection
It is important to protect the basin and internal piping. The spray water basin could
freeze when the unit is shutdown and be exposed to subfreezing ambient temperatures.
When optional basin heaters are not included, the spray water basin will drain after the
temperature remains below 35°F (1.7°C) for one hour.
• Heat Tracing: Heat trace the make-up water lines and the drains with electrical heater
tape.
• Basin Heaters (Optional): For buildings that benefit from keeping water in the spray
water basin, basin heaters can be inclued in the spray water basin for freeze protection
duing subfrezing ambient temperature.
Contact your local BAC Representative for more details.

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NEXUS®MODULAR HYBRID COOLER
Storage & Extended
Shutdown 2
Prolonged Outdoor Storage
• Conduct the “Extended Shutdown” procedure on page 19 if the unit is installed.
• For storage prior to installation, all components and accessories that ship loose should
be removed and stored indoors.
• Ensure the spray water basin is fully drained and the drain is open.
• If the manifold is constructed of carbon steel, then the hCore®Heat Transfer
Technology should be capped and charged with nitrogen at 15 psig in the field and
capped.
• Insert desiccant bags into the control panel(s) to absorb moisture. Seal the control
panel for storage.
• Inspect the protective finish on the unit. Clean and refinish as required. Refer to
“Corrosion Protection” on page 30 for more details.
Motor Recommendation
BAC standard motors are designed for storage at ambient temperatures of -13ºF to 104ºF
(-28.9ºC to 40ºC). Prolonged periods of exposure above or below these specified conditions
could degrade components of the motor and cause malfunction or premature failure.
• EC Fan System should be removed and stored inside whenever possible. When indoor
storage is not possible the motor must be covered with a loose fitting tarpaulin. Do
not use plastic/plastic film. This cover should extend below the motor and be secured;
however, it should not tightly wrap the motor. This will allow the captive air space to
breathe, minimizing formation of condensation.
• Care must also be taken to protect the motor from flooding or from harmful chemical
vapors.
• The storage area should be free from ambient vibration. Excessive vibration can cause
bearing damage. Motors that must be stored in areas with high ambient vibration,
such as from heavy construction equipment or other sources, must have the fan
secured to prevent any movement.
• Precautions should be taken to prevent rodents, snakes, birds, or other small animals
from nesting inside the unit. In areas where they are prevalent, precautions must also
be taken to prevent insects from gaining access to the interior of the unit.
NOTICE: Covering the unit with
a clear plastic tarpaulin during
storage can trap heat inside the
unit and cause damage to the
PVC components. If units must be
covered during storage, an opaque,
reflective tarp should be used.
DANGER: Rotating equipment
will cause severe personal injury
or death to persons who come in
contact. Do not perform any service
on or near the fans or motors
or inside the unit without first
ensuring that the fans and pump
motors are disconnected, locked
out, and tagged out.

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• If not stored indoors in a controlled environment, some form of heating must be
utilized to prevent condensation from accumulating in the motor. This heating should
maintain temperature at a minimum of 9ºF (5ºC) above the ambient temperature of
the room, keeping it from dropping below the dew point where condensation could
form inside the motor.
• Rotate the motor shaft monthly to redistribute bearing grease.
Start-Up Preparation After Prolonged Storage
Keep in mind that start-up procedures after long periods of storage are just as important as
pre-shutdown procedures.
• Fans and motors should be thoroughly inspected and cleaned to restore them to pre-
storage condition.
• Reinstall all components, panels, and drain plugs (as applicable), and remove all
protective coverings.
• For units stored prior to installation, conduct rigging procedures as directed
in the unit’s Rigging and Assembly Instructions, by contacting your local BAC
Representative.
• Perform an insulation test to ensure satisfactory insulation resistance.
• Conduct full start-up procedure as stated in “Start-Up” on page 8. Be especially
thorough for cleaning and inspection prior to start-up.
DANGER: Rotating equipment
will cause severe personal injury
or death to persons who come in
contact. Do not perform any service,
maintenance, or inspection on or
near the fan(s), motor(s), or inside
the unit without first ensuring
that the fans and pump motors
are disconnected, locked out, and
tagged out.