| Application Considerations 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.
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 shutoff 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. The CGAF’s microcomputer is automatically reset for the unit to resume operation. 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 setpoint is dependent on the
number of capacity stages and the temperature
difference across the evaporator. Water supply
temperature setpoints 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
setpoints. Refer to the "Performance
Adjustment Factors" section of this catalog to
determine the minimum leaving chilled solution setpoint and adequate ethylene glycol concentration for safe operation.
The maximum catalog leaving solution temperature from the evaporator is 65°F for outdoor ambients up to 115°F. High leaving
water temperatures exceeding this may result in
excessive suction temperatures and, therefore, inadequate motor cooling. For applications
requiring high leaving water temperatures, contact your
local Trane sales office for suggested alternatives.
The maximum water temperature that can be circulated through an evaporator,
when the unit is not operating, is 108°F
(100°F for CGA 8, 10, 12½ and 15 ton chillers). The
evaporator becomes thermal stress limited at these temperatures. |
