Catalogue

8 RLC-PRC029-EN
Application Considerations
Condenser Water Temperatures
With the model RTWD chiller, condenser head pressure control is necessary only if the unit starts
with entering condenser 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°C) is not possible.
When the application requires startup temperatures below the prescribed minimums, a variety of
system implementation options are available including the use of a 2- or 3-way valve or tower
bypass to maintain the required system refrigerant differential pressure.
• To control a 2-way or 3-way valve, select the Condenser Regulating Valve Control option for the
Trane CH530 controls. This option enables the CH530 controls to send a signal for opening and
closing the valve as necessary to maintain chiller differential refrigerant pressure. The 2-way
valves are available as a ship-with option.
• Tower bypass may also be a valid control method if the chiller temperature requirements can
be maintained and the loop is small.
The minimum acceptable refrigerant pressure differential between condenser and evaporator is 25
psid (1.7 bars) at all load conditions in order to ensure adequate oil circulation. Condenser leaving
water temperature must be 17°F (9.5°C) higher than evaporator leaving water temperature within
2 minutes of startup. A 25°F (13.9°C) temperature difference must be maintained thereafter [this
differential requirement is lessened by 0.25°F (0.14°C) for every 1°F (0.56°C) that the condenser
leaving water temperature is above 55°F (12.8°C)].
Trane Series R chillers start and operate successfully and reliably over a range of load conditions
with controlled condenser pressure. 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 local Trane systems
solution provider for more information on optimizing system performance.
Variable Evaporator Flow and Short Evaporator Water 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 superior unloading
compressor design and advanced Trane CH530 controls, the RTWD/RTUD has excellent capability
to maintain leaving water temperature control within +/-0.5°F (0.28°C), even for systems with
variable evaporator flow.
Some basic rules should be followed whenever using these system design and operational savings
methods with the RTWD/RTUD. 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.