Catalogue

RLC-PRC029-EN 9
Application Considerations
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 change in flow per minute are possible. Flow rates
should be maintained between the minimum and maximum allowed for any particular chiller
configuration.
For applications designed to operate with changes in the water flow rate, the new evaporator water-
flow compensation improves the ability of the chiller to respond to increasing or decreasing water
flow. This new standard control feature works by varying the leaving evaporator temperature
control gains in response to changes in evaporator water flow. By measuring the refrigerant flow
in each circuit and using this value to calculate the resulting waterside temperature drop, the CH530
can estimate the water flow rate through the evaporator.
Series Chiller Arrangements
Another energy-saving strategy is to design the system around chillers arranged in series, on the
evaporator, condenser, or both. It is possible to operate a pair of chillers more efficiently in a series
chiller arrangement than in a parallel arrangement. It is also possible to achieve higher entering-
to-leaving chiller differentials, which may, in turn, provide the opportunity for lower chilled water
design temperature, lower design flow, and resulting installation and operational cost savings
(including downsizing a chiller).
The Trane screw compressor also has excellent “lift” capabilities which afford an opportunity for
savings on the evaporator and condenser water loops. Like series arrangements on the evaporator,
series arrangements on the condenser may enable savings. This approach may allow reductions
in pump and tower installation and operating costs.
Maximizing system efficiency requires that the designer balance performance considerations for
all system components; the best approach may or may not involve multiple chillers, or series
arrangement of the evaporators and/or condensers. This ideal balance of design integrity with
installation and operating cost considerations should be researched by consulting a Trane systems
solutions provider and applying the Trace™ building energy and economic analysis program.
Water-to-Water Heat Pump
The RTWD can be used as a water side heat pump by using ground or surface water as a heat
source. Leaving condenser water control option provides the ability to control the heating setpoint.
Local regulation concerning limitation on minimum/maximum rejected water temperature needs
to be checked before using this method.
Dry Cooler
The RTWD can be used with dry coolers. Generally this application is selected to minimize the
spread of airborne contaminates associated with open tower systems. In addition, other drawbacks
of cooling towers are avoided: water consumption, production of vapor, need of water treatment,
etc. Another benefit of dry coolers is the ability to operate in low ambient conditions. With the use
of a third party heat exchanger this design can also be used to provide free cooling to the chilled
water loop during cold weather.