Trane RTHD manual Application Considerations

Application Considerations

Condenser Water Temperatures Reduced sensitivity to condenser water startup temperatures is one major enhancement in the newest-generationwater-cooled Series R chiller.With the model RTHD chiller, a condenser water control method is necessary only if the unit starts with entering water temperatures below 55°F (12.8°C), or between 45°F (7.2°C) and 55°F (12.8°C), when a temperature increase of 1°F (0.56°C) per minute to 55°F (12.8°) is not possible.

When the application requires startup temperatures below the prescribed minimums, a variety of options are available.To control a 2-way or 3-way valve,Trane offers a Condenser RegulatingValve Control option for the CH530 controls.This option enables the CH530 controls to send a signal for opening and closing the valve as necessary to maintain chiller differential pressure.The 2-way valves are available as a ship-with option.Tower bypass is also a valid control method if the chiller temperature requirements can be maintained.

Trane Series R chillers start and operate successfully and reliably over a range of load conditions with controlled entering condenser water temperature. Reducing the condenser water temperature is an effective method of lowering chiller

power input required, but the ideal temperature for optimizing total system power consumption will depend on the overall system dynamics. From a system perspective, some improvements in chiller efficiency may be offset by the increased tower fan and pumping costs required to achieve the lower tower temperatures. Contact your localTrane systems solution provider for more information on optimizing system performance.

The minimum acceptable refrigerant pressure differential between condenser and evaporator is 23 psid.The chiller control system will attempt to obtain and maintain this differential at startup, but for continuous operation a design should maintain a 25°F (13.9°C) differential from evaporator leaving water temperature to condenser leaving water temperature.

Variable Evaporator Flow and Short EvaporatorWater Loops

Variable evaporator flow is an energy- saving design strategy which has quickly gained acceptance as advances in chiller and controls technology have made it possible.With its linear unloading compressor design and advanced CH530 controls, the RTHD has excellent capability to maintain leaving water temperature control within +/-0.5°F (0.28°C) , even for systems with variable evaporator flow and small chilled water volumes.

Some basic rules should be followed whenever using these system design and operational savings methods with the RTHD.The proper location of the chilled water temperature control sensor is in the supply (outlet) water.This location allows the building to act as a buffer, and it assures a slowly changing return water temperature. If there is insufficient water volume in the system to provide an adequate buffer, temperature control can be lost, resulting in erratic system operation and excessive compressor cycling.To ensure consistent operation and tight temperature control, the chilled water loop should be at least two minutes. If this recommendation cannot be followed, and tight leaving water temperature control is necessary, a storage tank or larger header pipe should be installed to increase the volume of water in the system.

For variable primary flow applications, the rate of chilled water flow change should not exceed 10 percent of design per minute to maintain +/-0.5°F (0.28°C) leaving evaporator temperature control. For applications in which system energy savings is most important and tight temperature control is classified as +/-2°F (1.1°C), up to 30 percent changes in flow per minute are possible. Flow rates should be maintained between the minimum and maximum allowed for any particular chiller configuration.

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