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Thermonics Low Temp. Chillers – Glossary

Absolute Zero

Absolute zero is the bottom limit of the thermodynamic temperature scale. It is the point at which all thermal motion ceases; a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum values. At this point, the fundamental particles of nature have minimal vibrational motion, retaining only quantum mechanical particle motion. It is the zero point on the Kelvin scale (-273.15°C or -459.67°F)


An actuator is the component of a system that is responsible for moving or controlling a mechanism in that system. Actuators uses a control signal (electric current, computer command, pneumatic or hydraulic pressure, human power) and a source of energy (electric current, hydraulic or pneumatic pressure). When the control signal is received, the actuator responds by converting that energy into mechanical motion.

Air-Cooled Chiller

Air Cooled Chillers use Ambient Air to remove heat from the system; typically using Fans or CDA (Clean Dry Air) streams to pass air over Condenser Coils; removing heat from the condensing Refrigerant and rejecting the Heat to the surrounding atmosphere. Generally used for small to medium applications requiring two hundred tons of cooling or less.

Ambient Temperature Range

Ambient Temperature is the Temperature of the Environment that surrounds, or is outside of the Process/Cooling Medium. Standard Ambient Temperature is generally considered to be 25 °C, (77 °F/298.15 K) at an absolute pressure of 1 atm.


The American National Standards Institute (ANSI) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, and systems in the United States. The organization also coordinates U.S. standards with International standards so that American products can be consumed worldwide. ANSI accredits standards that are developed by representatives of other standards organizations, many of which, whose standards are applicable to the design, manufacture and documentation of state-of-the-art Chiller Equipment, are discussed in this Glossary.


Argon is an inert gas naturally found in the atmosphere, and easily produced as a byproduct of cryogenic air separation. In the Chiller Industry, Argon is used as a Heat Transfer Medium in Gas Chillers.

Boiling Point

Boiling Point is the temperature at which a liquid (here, Heat Transfer Fluid and Refrigerant) begins to change from a liquid to a gaseous state, or boils. It is necessary to choose fluids, and design and program Chiller Systems, such that the fluids in the sytem do not reach the boiling point.


The British thermal unit (BTU) is a traditional unit of work equal to about 1055 joules. It represents the amount of work needed to raise the temperature of one pound of water by one degree Fahrenheit. In the Chiller Industry. The BTU is often used to describe or quantify a chiller's capacity to cool/remove heat.

Capillary Tube

A capillary tube is a very small tube or multiple tubes through which refrigerant is forced in order to reduce the pressure of the liquid in a controlled manner and maintain a desired temperature. The amount by which the pressure is reduced is determined by the length and diameter of the capillary tube.


Cascade Chiller Systems combine two separate refrigeration cycles that share one Heat Exchanger. One side of the heat exchanger is used for Evaporating the refrigerant of the First Cycle (High Stage) and the other side to Condense the refrigerant of the Second Cycle (Low Stage). Cascade systems are used in applications in which there is a wide temperature range between the low amd high side, and use two different type of refrigerants which are ideal for their stage and complement each other in the refrigeration process. Essentially, the first stage brings the system's temperature down to a point at which the second stage can rapidly bring the temperature of the Heat Transfer Fluid (and thereby the process) down to Set Point.


A Chiller is a machine, piece of equipment or device that circulates liquid (Heat Transfer Fluid) to a process or process stream in order to remove heat from that system, protect the process and facilitate the result. Cooling usually is achieved via a vapor-compression refrigeration cycle in which Heat Transfer Fluid is circulated through a Heat Exchanger in which the refrigerant stream removes the heat from the heat transfer fluid and thereby the process. There are two primary trypes of Chillers: Water Cooled Chillers, in which the heat is rejected via water flow (see Water Cooled Chillers) and Air cooled Chillers, in which a CDA (Clean Dry Air) stream rejects the heat to ambience (see Air Cooled Chillers). Cryogenic Chillers are also now available, in which the removal of Heat from the Heat Transfer Fluid is accomplished via an N2 supplied/filled chamber from which the rejected heat is expelled to ambience via fan systems.

Cold Trap

The cold trap is a device that condenses all vapors in a gaseous stream, with the exception the desired gas(es), into a liquid or solid in order to prevent the contamination of the next step of a process, or to protect a system component (typically Pumps) from contamination and/or damage. Chillers are employed as dedicated Cold Traps in specialized processes such as De-Vulcanization.


The Compressor is the central component of a refrigeration system, pumping Refrigerant at the required pressure and in sufficient quantities in order to meet the cooling requirements of the system. The compressor compresses the saturated vapor coming from the evaporator to a high pressure state, resulting in a superheated vapor which is then condensed (rejecting heat from the system) then evaporated, cooling the load.


In heat transfer technology, a condenser is a device used to condense a substance from a gaseous state into a liquid one, by cooling it. In Chiller Technology, circulating refrigerant leaves the compressor as saturated vapor in a high pressure state and enters the Condenser Coils where it is cooled, usually by air (or water in water-cooled systems) flowing across the coils, thereby rejecting the heat, which is then transferred to, or beyond, the surrounding environment.


In Chiller Technology, Controllers (small computer devices usually physically installed as part of the Chiller Unit) are used to control the Chiller's tasks, from simple ramping to and holding a chilled state in a process, to sophisticated programming such as Cycling and Looping with provisions for Multiple Set Points, Ramp, Soak and Window.
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