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SYS-APM001-EN Chiller System Design and Control 7
Figure 4. Air-cooled or water-cooled efficiency
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 requirements of condenser-water piping, pump,
cooling tower, and associated controls.
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
than the air-cooled chiller. In general, air-cooled chillers last 15 to 20 years,
while water-cooled chillers last 20 to 30 years.
To summarize the comparison of air-cooled and water-cooled chillers, air-
cooled chiller advantages include lower maintenance costs, a pre-packaged
system for easier design and installation, and better low-ambient operation.
Water-cooled chiller advantages include greater energy efficiency (at least at
design conditions) and longer equipment life.
Loads
In comfort-cooling applications, cooling loads are often satisfied by air
handlers equipped with coils to transfer heat from the conditioned space air
to circulating chilled-water. Air is cooled and dehumidified as it passes across
the finned surface of the cooling coils. Since the psychrometric process of
conditioning air takes place at the coils, selection of the optimum coil size
and type from the wide variety available is important for proper system
performance.
Some specialized process loads do not involve cooling air. Instead, they may
involve heat transfer directly within a piece of process equipment, such as the
cooling jacket of an injection-molding machine.
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