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11CG-PRC007-EN
CONTROLS
1
Temperature Controller
In order to provide stable system
operation and to prevent excessive
compressor cycling, the temperature
control sensor in all 20-60 ton chillers is
located in the supply (outlet) solution.
The temperature sensor in all 10 and 15
ton chillers is located in the return (inlet)
solution. This sensor cannot be
relocated. Doing so would result in
improper unit operation.
2
Anti-recycle Timer/Fixed-Off Timer
All IntelliPak air-cooled chillers come
standard with Anti-recycle/Fixed Off
Timers. This function prevents rapid
cycling of the compressors due to low
load conditions or short water loops.
3
Pumpdown
CGAF air-cooled chillers will pumpdown,
if function is enabled, when a refrigerant
circuit is turned off. All of the refrigerant
is pumped into the condenser. A
solenoid valve provides a positive shut
off between the condenser and the
evaporator, allowing little or no
refrigerant migration to the evaporator
during “off” periods.
4
Hot Gas Bypass
Hot gas bypass provides more stable
leaving solution temperature control at
light load conditions. The compressor
runs continuously for a user-defined run
time. Minimum starting and operating
ambients with hot gas bypass are shown
in the “General Data” section of this
catalog. The hot gas bypass reduces the
unit head pressure, thereby increasing
the minimum operating ambient.
5
Loss of Flow Protection
Loss of flow may result in evaporator
freeze up. Full chilled solution flow must
be maintained through the evaporator
while compressors are operating.
A flow switch used as a safety interlock is
always recommended for CGA units.
The CGAF air-cooled chiller has a system
which senses a loss of flow condition
and shuts the unit down. A flow switch
used as a safety interlock is required for
CGAF units. A set of contacts is available
for externally starting and stopping the
pump.
WATERFLOW LIMITS
The minimum water flow rates are given
in the “General Data” section of this
catalog. Evaporator flow rates below the
tabulated values will result in laminar
flow causing scaling, stratification,
freeze-up problems, and poor
temperature control.
The maximum evaporator water flow
rate is given in the “General Data”
section. Flow rates exceeding those
listed will result in excessive tube
erosion and very high pressure drop
across the evaporator.
Trane recommends that constant water
flow be maintained at all times through
the evaporator. Because the
temperature controller strictly senses
temperature, variable flow through the
evaporator may result in loss of control
and localized freezing or nuisance low
temperature cutouts. Consult your local
Trane sales engineer if your application
requires varying flows.
TEMPERATURE LIMITS
1
Leaving Solution Temperature range
The minimum leaving solution
temperature set point is dependent on
the number of capacity stages and the
temperature difference across the
evaporator. Water supply temperature
set points less than these values result in
suction temperatures at or below the
freezing point of cold water.
A glycol solution is required for
operation below the recommended
minimum set points. Refer to the
“Performance Adjustment Factors”
section of this catalog to determine the
minimum leaving chilled solution set
AMBIENT LIMITATIONS
Trane chillers are designed for year-
round applications in ambients from 0°F
to 115°F. For operation below 0°F or
above 115°F, contact the local Trane sales
office. If hot gas bypass is used,
operating ambients vary depending
upon unit size (see the “General Data”
section of this catalog).
1
Low Ambient Operation
Start-up and operation of Trane chillers at
lower ambient temperatures require that
sufficient head pressure be maintained
for proper expansion valve operation.
Minimum operating ambient
temperatures for standard unit selections
and units with hot gas bypass are shown
in the “General Data” section of this
catalog.
Minimum ambient temperatures are
based on still conditions (winds not
exceeding five mph). Greater wind
velocities will result in a drop in head
pressure, therefore increasing the
minimum starting and operating
ambient temperatures.
Optional low ambient units use a
electronic low ambient damper control
(20-60 tons) or a variable speed fan
motor (10-15 tons) arrangement to
control condenser capacity by
modulating condenser fans in response
to refrigerant pressure.
2
High Ambient Operation
Maximum cataloged ambient
temperature operation of a standard
Trane chiller is 115°F. Operation at design
ambients above 115°F can result in
excessive head pressures. For operation
above 115°F, contact your local Trane
sales office.
Application
Considerations