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O O p p e e r r a a t t i i n n g g P P r r i i n n c c i i p p l l e e s s
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
64
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 bypass valve
either towards open or towards closed respectively.
Eventually a balance will be reached until the saturated
condenser temperatures change again. Both valves
close whenever mechanical cooling is not required,
and in the event of a power failure.
If the unit does not have a waterside economizer then
variable water flow is automatically active with
intermediate piping.
Figure 33. Basic water piping, constant water flow
Condenser 1
Condenser 2
Condenser 3
Condenser 4
Figure 34. Intermediate water piping, variable water
flow (L) and Intermediate piping with waterside
economizer, variable or constant water flow (R)
Condenser 1
Condenser 2
V2
Condenser 3
Condenser 4
Variable Water Flow
Condenser 1
Economizer
Condenser 2
V1
V2
Condenser 3
Condenser 4
Waterside Economizer
Variable or Constant Water Flow
SCXF-SVX01Q-EN
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