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32 TRG-TRC012-EN
notes
period five
Application Considerations
is the elimination of the cooling tower. This eliminates the concerns and
maintenance requirements associated with water treatment, makeup water
availability and quality, tower mechanical maintenance, freeze protection, and
chiller condenser tube cleaning. This reduced maintenance requirement is
particularly attractive since it can substantially reduce operating costs.
Another advantage of an air-cooled chiller is its delivery as a “packaged
system.” Reduced design time, simplified installation, higher reliability, and
single-source responsibility are all factors that make the factory packaging of
the condenser, compressor, and evaporator a major benefit. A water-cooled
chiller has the additional requirement of condenser water piping, pump,
cooling tower, and controls.
Air-cooled chillers are often selected in buildings with a requirement for year-
round cooling that cannot be met with an air-side economizer. Air-cooled
condensers have the ability to operate in below-freezing weather without the
problems associated with operating the cooling tower in low-ambient
conditions. Cooling towers may require special sequences of operation, basin
heaters, or even an indoor sump for safe operation in freezing weather.
Water-cooled chillers are generally more energy efficient. The efficiency
advantage of a water-cooled chiller, however, is much less when the additional
cooling tower and condenser pump energy costs are considered. Additionally,
this efficiency advantage may lessen at part-load conditions since the dry bulb
temperature tends to drop faster than the wet bulb temperature and the air-
cooled chiller benefits from greater condenser relief.
Performing a comprehensive energy analysis is the best method of estimating
the system operating cost difference between air-cooled and water-cooled
systems.
Water-cooled chillers typically last longer than air-cooled chillers. This
difference is due to the fact that the air-cooled chiller is installed outdoors,
whereas the water-cooled chiller is installed indoors. Also, using water as the
condensing fluid allows the water-cooled chiller to operate at lower pressures
water-cooled
▲ Greater energy efficiency
▲ Longer equipment life
air-cooled or water-cooled
Comparison
air-cooled
▲ Lower maintenance
▲ Packaged system
▲ Better low ambient
operation
Figure 47