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SCXF-SVX01T-EN
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 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.
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 29. Condenser water piping connection sizes
Unit size
Inlet pipe Outlet pipe
SXWF 20, 22, 25, 29, 32, 35, 38
2 1/2 NPT 2 1/2 NPT
SXWF 42, 46, 52, 58, 65, 72, 80, 90,
100, 110
3 NPT 3 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 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 available 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 mechanical 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 with Intermediate
Piping
Two-way modulating control shutoff valves are wired,
controlled, and installed in unit. One valve is located in
economizer’s water inlet, and the other in condenser
bypass water inlet. When waterside economizer enables,
two-way valves modulate to maintain discharge air
temperature setpoint. As economizer valve opens,
condenser bypass valve closes, and vice versa. Full water
flow is always maintained through condensers. Both valves
will close in event of a power failure.
Variable Water Flow with Intermediate
Piping
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 water inlet. The economizer valve and the
condenser bypass valve modulate in- dependently of each
other. When the economizer valve is active, all the water
flowing through the economizer exits into the condensers.
The software reads the saturated condenser water
temperature for each circuit; trying to maintain 100 degrees
saturated condenser temperature. Whichever circuit is the
furthest away (either above 120 degrees or below 80
degrees) drives the software to modulate the condenser
Operating Principles
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