A Chiller is a machine that produces chilled water (usually mixed
with ~20% glycol and corrosion inhibitors) which is used to cool
and dehumidify air in commercial and industrial facilities (see
air conditioning). A typical chiller is rated between 15 to 1000
tons (180,000 to 12,000,000 BTU/h or 53 to 3,500 kW) in cooling
power. There are basically four different types of chillers: Reciprocating,
centrifugal, or screw-driven chillers are mechanical machines
that can be powered by electric motors, steam, or gas turbines.
Absorption chillers are powered by a heat source (such as steam
or hot water). They have very low electrical power requirements
- very rarely above 15 kW combined consumption for both the solution
pump and the refrigerant pump.
Chilled water is then distributed to air handling units as a
refrigerant. The air handling unit is a heat exchanger consisting
basically of a fan, a filter bank, and heating/cooling coil, inlet/outlet
chilled water port, and air inlet port. These air handling units
provide air conditioning to the building by running the incomming
warm air through the coil of chilled water, transferring the heat
from the air to the chilled water, thus, cooling the air.
Chillers can be air-cooled or water-cooled. Water-cooled chillers
incorporate the use of cooling towers which improve heat rejection
more efficiently at the condenser than air-cooled chillers.
Industrial Chillers cool water using refrigeration cycles to
provide a constant stream of coolant for manufacturing and laboratory
processes. Industrial chillers use refrigeration to cool water
that is then pumped through process or laboratory equipment. Industrial
chillers are used in the controlled cooling of plastics during
fabrication, manufacturing elements such as printer rollers, and
high-heat specialized items such as MRI machines and lasers. Industrial
chillers typically come as complete packaged closed-loop systems,
including the chiller unit, condenser, and pump station with recirculating
pump, expansion tank, no-flow shutdown, and temperature control.
Closed loop industrial chillers recirculate a clean coolant at
a constant temperature and pressure to increase the stability
and reproducibility of water-cooled machines and instruments.
Open loop industrial chiller systems are also available. Open
loop industrial chillers control the temperature of a liquid in
an open tank or sump by constantly recirculating it. The liquid
is drawn from the tank, pumped through the chiller and back to
the tank. An adjustable thermostat senses the makeup liquid temperature,
cycling the chiller to maintain a constant temperature in the
tank. Most industrial chillers use refrigeration as the media
for cooling, but some rely on simpler techniques such as air or
water flowing over coils containing the coolant to regulate temperature.
Water is the most commonly used coolant within process chillers,
although coolant mixtures (mostly water with a coolant additive
to enhance heat dissipation) are frequently employed. Industrial
chillers are used for controlled cooling of products, mechanisms
and factory machinery in a wide range of industries. They are
often used in injection and blow molding, metal working cutting
oils, welding equipment, die-casting and machine tooling, chemical
processing, pharmaceutical formulation, food and beverage processing,
lasers, vacuum systems, X-ray diffraction, power supplies and
power generation stations, analytical equipment, semiconductors,
compressed air and gas cooling.
Important specifications to consider when searching for industrial
chillers include the power source, cooling capacity, fluid discharge
temperature, and compressor motor horsepower. Process pump specifications
that are important to consider include the process flow, process
pressure, and pump rating. Other important specifications include
the reservoir capacity full load amperage. Control panel features
that should be considered when selecting between industrial chillers
include the local control panel, remote control panel, temperature
indicators, and pressure indicators. Additional features include
emergency alarms, hot gas bypass, city water switchover, and casters.
An important environmental parameter to consider is the operating
To cool down a large building, it is often better to have a central
air conditioning system. It is simpler to have the refrigerant
unit located at one place, and distributing the coolness using
water. Chilled water is easily pumped and it is able to reach
all floors in the building. The heart of the central air conditioning
system is the chiller.
Chillers make use of the refrigeration principles to work. A
compressor is used to compress the refrigerant gas to a higher
temperature. The hot gas is then cooled by a heat exchanger. The
heat from the hot gas is dissipated to the outdoors through cooling
towers or fans. The hot gas, after being cooled, reverts back
to a liquid state. This is the property of most refrigerants,
to be liquid at normal room temperatures and pressures. This liquid
is then led through a valve or orifice. The liquid becomes expanded
in volume after passing through this restriction. The expansion
of volume through the expansion valve or orifice brings about
a cooling effect. Heat is absorbed when the liquid becomes a gas.
The cooling effect is used to cool chilled water through a heat
exchanger. The chilled water system is then pumped and distributed
to all the air handling units at various floors in the building.
The air handling units contain fans for moving air through cooling
coils. The indoor air is thus cooled.
The flow of the heat in central air conditioning system can be
summarized as follows:
Heat is transferred from the air in the rooms to chilled water
at the air handling units.
The chilled water is pumped through the chiller and the heat is
transferred to the refrigerant.
The refrigerant is cooled by cooling water circulating in the
condenser of the chiller.
The heated cooling water is passed through cooling towers where
the heat is dissipated to the atmosphere by fans.
Types of Chillers
Chillers are a general term for air conditioning units using
chilled water as a distributing agent. They are named according
to the type of compressors they use. Centrifugal chillers use
centrifugal impellers and high rotational speeds to work. Reciprocating
chillers contain pistons, crankshafts, suction valves and discharge
valves. Screw chillers use screw shafts to compress the refrigerant
gas. Different manufacturers produce their own designs based on
these basic ideas of compression. Some manufacturer design for
multistage compression, some have enclosed electrical motors in
the refrigerant circuit, while others have external motors. Many
of the control systems are designed to suit the different manufacturers.
The settings of controls and machine design also depend on the
refrigerant they use. There are also different configurations
for air or water cooled condensers.
The lubrication oil for chillers is special oil that is compatible
and able to mix freely with the refrigerant. All manufacturers
have their own arrangements to suit their own designs, with oil
heaters, oil bath, oil pumps, and others.
Large sized chillers have centrifugal fans to compress the refrigerant
gas. As with any high-speed centrifugal fans, these chillers are
susceptible to surging if the system is not matched properly.
Whenever there is a sudden change in the heat loads or speeds,
there is a possibility of surging. Many manufacturers design their
machines to cater for these sudden changes. For normal usage,
there is almost no problem in this area. Normally the condensers
are water cooled, and they work in conjunction with cooling towers.
The motors of reciprocating chillers are usually totally enclosed
inside the refrigerant circuit. The pistons are made small in
size. Because of the reciprocating movements of the several pistons
(6 to 8 pieces), these chillers are usually noisy. They commonly
use R-22 refrigerant. Very often the condensers are air-cooled.
Screw chillers are usually totally enclosed. They use R-22 refrigerant.