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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 temperature.

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.

Centrifugal Chiller

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.

Reciprocating Chiller

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 Chiller

Screw chillers are usually totally enclosed. They use R-22 refrigerant.



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