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Portable Chiller Systems Glossary

Cycle

In Programmed Temperature Control, a Cycle is one set of programmed tasks or events, called Segments. Typical Segments may be devoted to Running to (a) Set Point, Ramp (the amount of time the system takes to reach Set Point), Soak (the amount of time a setpoint is maintained) and Window (the amount of leeway allowed, or degree of accuracy required, above/below the Set Point, in determining whether the system is 'At Temperature). Any Cycle may, additionally, be programmed to 'Loop' or repeat a designated number of times (see 'Loop').

EN 61326

EN 61326 is the European Union’s EMC (Electromagnetic Compatibility) standard, determining EMC Emissions and Immunity requirements for electrical equipment operating from a supply, battery or circuit being measured. EN 61326 governs the design of electrical equipment involved in control, laboratory use, measurement and testing, and is therefore an important resource for Chiller manufacturers wishing to export to European countries.

Enthalpy

Enthalpy is a measurement of the energy in a thermodynamic system; equal to the internal energy of the system (the energy required to create the system) combined with the effects of pressure and volume; that is, the amount of energy required to make room for the system by displacing its environment and establishing its volume and pressure.

Entropy

Entropy is an expression of the disorder, or randomness of a system. In Thermodynamics, and discussions of Absolute Zero, it is a measure of the amount of a system's thermal energy per unit of temperature that is unavailable for accomplishing work.

Evaporator

Evaporator is a term ported over from traditional Mechanical Refrigeration, wherein the refrigerant is evaporated by evaporator coils to cool an area, substance or process. In Chiller Technology, the Evaporation process is generally achieved as part of the heat exchange process; as the refrigerant is evaporated in the Heat Exchanger as the Heat Transfer Fluid is cooled (see Heat Exchanger, below).

Flash Point

Flash Point is the temperature at which the vapors produced from Heat Transfer Fluid (HTF) will ignite (flash off) with the presence of an ignition source; the fluid itself will not burn at this temperature. Flash point is important from the viewpoint of safety, however, it is quite common for heat transfer systems to be operated at temperatures above the flash point of the fluid, as sufficient oxygen and an ignition source are not present in a closed HTF system. The danger lies in leakage, and emphasizes the inportance of regualr checks for leaks in a Chilling System, as external 'weeping' leaks from fixtures can oxidize and produce smoke (though not ignite), and internal leaking of HTF into the porous insulation of the chiller can actually cause the HTF to ignite, as the heat generated by oxidation is trapped in the insulation and can exceed the fluid's auto-ignition temperature.

Flow Rate

In fluid dynamics, the Volumetric Flow Rate, (usually referred to in Chiller systems as the Flow Rate) is the volume of fluid which passes a point per unit of time. The Flow Rate of the Heat Transfer Fluid is one of the parameters (along with Fluid Pressure) that regulates the speed and extent of transfer of heat from the load.

Fluid Bypass Circuit

A Fluid Bypass Circuit is a safety device similar to a Pressure Relief Valve, used in Fluid Systems to control or limit pressure in the system which could otherwise exceed the indicated or set level and result in the interruption of a process, damage to equipment, or a catastrophic event (fire, explosion, etc.). In the case of the Bypass Circuit, however, pressure is relieved as the pressurized fluid is allowed to recirculate in the system rather than continue its normal path until the condition is relieved. The Fluid Bypass Circuit is set or pre-designed to open at a predetermined pressure.

Fluid Chillers

The term Fluid Chiller refers to chillers which use Fluid Heat Transfer Mediums such as Ethylene and Propylene Glycol/Water mixture to carry heat away from the process, to be rejected in the refrigeration cycle of the chiller.

Freezing Point

Freezing point is the temperature below which a liquid turns into a solid. It is necessary to choose fluids, and design and program Chiller Systems, such that the fluids in the sytem do not reach the freezing point.

Gas Chillers

The term Gas Chiller refers to chillers which use Gaseous Heat Transfer Mediums such as Argon, Nitrogen Gas and Air to carry heat away from the process, to be rejected in the refrigeration cycle of the chiller.

Glycol (Ethylene Glycol) (Propylene Glycol)

Glycol Chillers use Heat Transfer Fluid with concentrations of Glycol (Ethylene Glycol or Propylene Glycol) to protect the Evaporator and lines from freezing. Glycol Chillers are used in applications that require rapid achievement of very low temperatures or involve the risk of low line loss, slow line flow or pressure drop. Achieving the correct percentage of glycol is key, as a concentration that is too high can cause significant drop in chiller efficiency and capacity. In applications characterized by contamination/toxicity concerns, Propylene Glycol is preferred for its non-toxicity.

Glycol Chiller

Glycol Chillers use Heat Transfer Fluid with concentrations of Glycol (Ethylene Glycol or Propylene Glycol) to protect the Evaporator and lines from freezing. Glycol Chillers are used in applications that require rapid achievement of very low temperatures or involve the risk of low line loss, slow line flow or pressure drop. Achieving the correct percentage of glycol is key, as a concentration that is too high can cause significant drop in chiller efficiency and capacity. In applications characterized by contamination/toxicity concerns, Propylene Glycol is preferred for its non-toxicity.

Heat Exchanger

A Heat Exchanger is a device used to transfer heat between substances, generally for the purpose of removing heat from a process, space or environment. In Chiller technology, the exchange is generally between two fluids, for the purpose of removing heat from a load or product. This process usually involves receiving a liquid vapor refrigerant mixture from the condensing function of the system, and passing it through an arrangement of coils, plates and/or fins wherein the liquid passes close to, and in the opposite direction from, the heat transfer fluid coming from the load, evaporating the liquid part of the cold refrigerant mixture, which cools the transfer fluid which is then returned to the load. The resulting evaporated refrigerant is then moved to the compressor to be recirculated in the process.

Heat Transfer

Heat Transfer is the process of thermal energy moving from one body to another - There are three types of Heat Transfer: Conduction is the transfer of heat from one particle of matter to another, Convection is the transfer of heat from one part of a particle to another by the mixing of the warmer particles with the cooler; and Radiant is the transfer of heat from one body to another as the result of the bodies emitting and absorbing radiation energy. The Heat Transfer in the Heat Exchanger of a typical Chiller is Conductive Transfer.
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