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84 SCXG-SVX01B-EN
temperature is less than 58 F (15 C). This
option allows the compressor to operate
with entering fluid temperature down to
35 F (2 C). The minimum valve position to
maintain minimum condenser flow rates
is user-defined at the HI. This valve drives
closed if the unit shuts down or if a power
failure occurs.
• Water Flow Switch Option
A water flow switch is factory installed in
the condenser water pipe within the unit.
Whenever the flow switch detects a
water flow loss prior to or during
mechanical cooling, compressor
operation locks out and a diagnostic code
displays. If water flow is restored, the
compressor operation automatically
restores.
To prevent injury or death due to
instantaneous release of high
pressure water, provide relief
valves on system water piping.
This will also help prevent water
pump damage or stoppage due to
excessive system pressure.
Water-Cooled Condensers
Units that are set up for variable water
flow will modulate a water valve to
maintain a user-defined condensing
temperature setpoint. Condensing
temperature will be referenced utilizing
factory installed sensors located at each
condenser.
Table O-GI-8. Water Condenser Connection
Sizes
Unit Size Direct Factory
Condenser Piped
SXWG 20-35 1
1
/
2
NPT 2
1
/
2
NPT
Waterside Economizer Option
The waterside economizer option takes
advantage of cooling tower water to
either precool the entering air to aid the
mechanical cooling process or, if the
water temperature is low enough,
provide total system cooling. Waterside
economizing enables when the unit’s
entering water temperature is below the
Waterside Components
Waterside components consist of water
piping, water valves, water flow switch
option, water cooled condensers (SXWF
only), and the economizer option.
Water Purge
This user-definable feature allows the
user to select a purge schedule to
automatically circulate water through the
economizer and condensers periodically
during non-operational times. This allows
fresh chemicals to circulate in waterside
heat exchangers. This feature is on all
units and is defined at the HI.
Water Piping Options
Water piping is factory-installed with left-
hand connections. Units can be ordered
with either basic piping or intermediate
piping. Also, units with waterside
economizers can be set for either
variable or constant water flow at the HI.
See Figures O-GI-3, O-GI-4, and O-GI-5 for
detailed piping configuration information.
With compatible piping configurations,
the unit can be configured to provide:
1) Constant water flow with basic or
intermediate piping or 2) Variable water
flow (head pressure control) with
intermediate piping only.
Constant water flow is for condenser
pumping systems that are not capable of
unloading the water-pumping system.
Variable water flow maximizes energy
saving by unloading the water pumping
system.
• Basic Water Piping
This option is available on units without a
waterside economizer and with
condenser water applications above 54 F
(12.2 C) that do not require condensing
pressure control. Left hand water
connections and piping are extended to
the unit exterior. Manifold piping is
factory installed.
• Intermediate Water Piping
This option provides condensing
temperature control when the unit is
configured (user defined at the HI) for
variable water flow with or without a
waterside economizer. A two-way
modulating control valve is wired and
installed in the unit to maintains a specific
range of water temperature rise through
the condenser when entering fluid
Owner
General
Information
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WARNING
!
unit’s entering mixed air temperature by
a minimum of 4 F plus the economizer’s
approach temperature. The approach
temperature default is 4 F. Waterside
economizing disables when the unit’s
entering water temperature is not below
the unit’s entering mixed air temperature
by at least the water economizer
approach temperature. The approach
temperature defaults to 4 F. The
economizer acts as the first stage of
cooling. If the economizer is unable to
maintain the supply air setpoint, the unit
control module brings on compressors as
required to meet the setpoint.
The waterside economizer includes a coil,
modulating valves, controls, and piping
with cleanouts. The coil construction is ½-
inch (13 mm) OD seamless copper tubes
expanded into aluminum fins. The
evaporator and economizer coils share a
common sloped (IAQ) drain pan. Drain
pan options are either galvanized or
stainless steel, and are insulated and
internally trapped.
The waterside economizer coil is avail-
able with either a two or four row coil,
with no more than 12 fins per inch. The
tubes are arranged in a staggered
pattern to maximize heat transfer. The
coil has round copper supply and return
headers with removable cleanout and
vent plugs. The optional mechanical
cleanable economizer has removable
cast iron headers to allow easy mechani-
cal cleaning of the tubes. The waterside
working pressure is rated for 400 psig
(2758 kPa).
Waterside Economizer Flow Control
Units equipped with a waterside
economizer can be set from the human
interface panel for variable or constant
water flow.
• Constant Water Flow
Two-way modulating control shutoff
valves are wired, controlled, and installed
in the unit. One valve is located in the
economizer’s water inlet, and the other is
in the condenser bypass water inlet.
When the waterside economizer enables,
the two-way valves modulate to maintain
the discharge air temperature setpoint.
As the economizer valve opens, the