Chillers: Four Basic Types
A chiller is a machine used to produce chilled water for air conditioning or process cooling in large facilities. Most chillers operate using vapor compression, and there are four basic types: reciprocating, centrifugal, screw, and scroll.
Reciprocating chillers draw refrigerant into a compressor through an intake valve, and an internal piston compresses the refrigerant. Pressure forces it through an exhaust valve where it is released back into the system to absorb more heat. Reciprocating chillers can accommodate cooling loads between 30 and 150 tons, and multiple units can be used, allowing flexibility. They are the most affordable, but require a higher level of maintenance, and there is increased noise and vibration, and multiple chillers can consume more energy.
Rotary screw chillers employ helical rotors to compress the refrigerant. Refrigerant gas is forced into spaces created by meshing helical screws within a cylinder. The gas is forced along the length of the rotors and compressed refrigerant exits when the space reaches the other end. Screw chillers are mid-range units with capacities generally ranging from 20 to 1,000 tons. Screw chillers have a high compression ratio and few moving parts, which makes them smaller than reciprocating and centrifugal chillers of similar capacity. They are quiet, vibration-free, reliable, efficient, and require very little maintenance. The one main drawback is the higher initial cost.
Centrifugal chillers use an impeller wheel to force refrigerant against the sides of a cylindrical chamber, then exhausts the compressed refrigerant to continue the cycle. Centrifugal chillers can handle large volumes of refrigerant, and because their compressive force is relatively small, multiple impellers are often used. Centrifugal systems have the largest capacity – up to 2,000 tons – and are often used in applications requiring 300 tons and larger, where they are the least costly and most efficient design when operating at full load. At lower loads they can experience problems with surge.
Scroll chillers are the smallest in capacity of the four types, commonly ranging from 5 to 150 tons. Two offset spiral disks are nested together, one stationary and one rotating. Refrigerant is compressed into the center of the spiral where it is exhausted back into the system. They are compact, efficient, quiet, and low-maintenance. They are used in smaller applications and can be good candidates for spot cooling and make-up cooling.
There are many chiller option packages and accessories that can increase the efficiency, control and user-friendliness. To find out more about selecting chillers for your application, contact PJM Mechanical Contractors, Inc. at 609-921-1394
PJM Mechanical Contractors, Inc. is a multi-faceted mechanical contractor providing construction and installation, service and maintenance, and design/build services in a comprehensive range of mechanical disciplines that include HVAC, plumbing, controls, refrigeration, custom metal fabrication, piping, fire protection, and backflow preventer testing. PJM primarily serves clients in pharmaceuticals, manufacturing, healthcare, institutional, and other various commercial and industrial sectors. pharmaceuticals, manufacturing, healthcare, institutional, and commercial sectors.