Trane CG-PRC007-EN manual Low Ambient Operation, High Ambient Operation, Temperature Controller

Application Considerations

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 localTrane 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 localTrane 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-recycleTimer/Fixed-OffTimer

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 SolutionTemperature 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

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