Chiller

Centrifugal chiller

Centrifugal chiller

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.

Centrifugal chiller

Centrifugal 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

Air cooled reciprocating chiller

Air cooled reciprocating chiller

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.

centrifugal chiller with insulation

centrifugal chiller with insulation

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

centrifugal chiller dismantled

centrifugal chiller dismantled

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

centrifugal chiller

centrifugal 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

reciprocating chiller compressor dismantled

reciprocating chiller compressor dismantled

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