In a large building or plant, it is more efficient to make cold water in one central machine and pipe it everywhere than to put a refrigeration unit at every point of use. That central machine is the chiller. This guide explains what a chiller is, how vapor-compression and absorption chillers produce chilled water, the difference between air-cooled and water-cooled designs, and where chillers fit in oil and gas facility cooling.
Chiller in one line: A chiller is a machine that removes heat from water (or a water/glycol mix) to produce chilled water, which is then pumped to cooling coils in air handlers, process coolers, or equipment across a facility. Most chillers use a vapor-compression refrigeration cycle - a compressor, condenser, expansion device, and evaporator - to draw heat out of the water; the heat is then rejected to the air or to a water loop. Chillers are the heart of a central chilled-water cooling plant.
A vapor-compression chiller runs a refrigerant around a closed loop. In the evaporator, the refrigerant absorbs heat from the building's chilled-water loop, boiling into a low-pressure vapor and chilling the water (typically to around 6 to 7 C / 44 F supply). A compressor raises that vapor to high pressure and temperature; in the condenser the refrigerant rejects its heat and condenses back to a liquid; an expansion device drops it back to low pressure, and the cycle repeats. The chilled water is pumped out to cooling loads and returns warmer to be chilled again.
Chillers are classified by compressor type - reciprocating, scroll, screw, and centrifugal - each suited to a capacity range, with large centrifugal units serving the biggest plants. An absorption chiller works differently: instead of a mechanical compressor it uses a heat source (steam, hot water, or waste heat) and an absorbent such as lithium bromide to drive the refrigeration cycle, which makes it attractive where cheap waste heat is available and electrical demand is a concern.
The heat a chiller pulls out of the water has to go somewhere. An air-cooled chiller rejects it directly to the outside air through a finned condenser and fans, usually sitting outdoors as a self-contained package. It is simpler to install and needs no separate heat-rejection equipment, but is less efficient in hot climates and limited in size.
A water-cooled chiller rejects heat into a condenser-water loop, which then carries it to a cooling tower where it is dissipated by evaporation. This is more efficient, especially at large capacity, because water rejects heat better than air, but it requires the added condenser-water pumps, piping, cooling tower, and water treatment. Large central plants are almost always water-cooled; smaller or remote installations often use air-cooled packages for simplicity.
Chillers serve the facility side of oil and gas operations - central chilled water feeds air handlers and CRAH units that cool control rooms, server rooms, laboratories, and office buildings at gas plants, terminals, and processing facilities. Some also provide process cooling where a plant needs chilled water for a cooling duty. Because so much critical equipment depends on that cooling, chiller reliability and redundancy (often multiple chillers with a spare) are treated seriously.
A chiller's controller reports supply and return water temperature, flow, compressor and stage status, load, and alarms, typically over BACnet or Modbus through the building controls. A cloud SCADA such as Merobix can read those points, so operators can watch chilled-water temperature and chiller health remotely and get an early alarm on a cooling fault that could threaten the equipment the plant depends on.
An air-cooled chiller rejects its heat straight to the outside air through a finned condenser and fans, so it is self-contained and simple to install but less efficient in hot weather. A water-cooled chiller rejects heat into a condenser-water loop that carries it to a cooling tower, which is more efficient - especially at large capacity - but adds condenser pumps, a cooling tower, and water treatment. Large central plants are usually water-cooled.
A chiller produces chilled water that is pumped to many cooling coils across a facility - it is a central heat-removal machine. A CRAC unit is a room-level cooling device; a direct-expansion CRAC does its own refrigeration, while a CRAH cools by passing room air over a coil supplied with chilled water from the chiller. In short, the chiller makes cold water, and CRAH units and air handlers use it to cool the spaces.
An absorption chiller produces chilled water using a heat source - steam, hot water, or waste heat - and an absorbent such as lithium bromide instead of a mechanical compressor. It draws very little electrical power, which makes it attractive where waste heat is available or where reducing electrical demand matters, at the cost of lower efficiency than a modern electric vapor-compression chiller.
This page references the protocol specifications published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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