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Thermonics Low Temp. Chillers – Glossary


Syltherm XLT and Syltherm 800 are Silicone-based Heat Transfer Fluids (See Heat Transfer Fluid) commonly used in Chiller Technology. They have low fouling potential, a Low Freeze Point, and High Temperature Stability and are Non-Corrosive. They have low acute oral toxicity, and are Non-reportable under SARA Title III. Syltherm XLT has a recommended use range from -101°C to 260°C and is ideal for low temperature heat transfer and promotes pump ability. Syltherm 800 is designed for high temperature liquid-phase operation, and has a recommended operating range of -40°C to 400°C.

Thermal Engine

Thermal Engine is conceptual term which describes the Cooling Capacity of a particular system, typically expressed in a relationship between the amount of Heat Energy in Watts that needs to be removed from the process, and the operating temperature of the system, i.e. 55W at -55°C, 125W at -40°C.


Thermocouples are temperature sensing probes manufactured of a combination of metal oxides with varying conductive properties, encapsulated in epoxy or glass. Changes in temperature produce proportional changes in resistance, with resistance decreasing as temperature rises. Although RTDs are superior to Thermocouples in accuracy and durability, they are substantially more expensive than Thermocouples, therefore, a cost vs. accuracy/durability consideration is necessssary when choosing which type of temperature sensing device is appropriate for a particular chiller.

Ton (Tonnage)

Tonnage is a way of measuring a particular chiller's ability to cool. A 'ton' of cooling expresses the amount of heat transfer required to melt 1 short ton of pure ice at
0 °C (32 °F) in 24 hours.


UL typically refers to a broad set of Industrial and Scientific Standards, developed by the Safety Science company UL to provide guidelines and certification of industry practices and manufacturing. Many of these standards, particularly Electrical Standards, are applicable to the design, manufacture and documentation of state-of-the-art Chiller Equipment. These standards are developed based on a consensus of UL's voting industry-representative and scientific members worldwide. Two standards particularly applicable to the Chiller Industry is UL/IEC 61010, which governs Safety in Laboratory Test Equipment, and UL1995, which is concerned with Safety in Heating and Cooling Equipment.

Variable Frequency Drive

A variable-frequency drive (VFD) is an adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage. VFDs are used in Chiller Systems to control Heat Transfer Fluid Pumps and Compressors.

Water Cooled Chiller

Water Cooled Chillers use Water to remove Heat from the system, using Heat Exchangers (typically composed of touching and/or interlocking Conductive Coils and Heat Transfer Fins) to remove the Heat from the condensing Refrigerant and reject the heat to a separate water stream or source such as a Cooling Tower or natural body of water. Generally used for large applications requiring more than two hundred tons of cooling.


Window is a term used in temperature generation to describe the amount of leeway allowed, or degree of accuracy required, above/below the Set Point, in determining whether the system is 'At Temperature'. The 'Window' can be set in the programming of the system to be wider (in °C or °F) or narrower, according to the needs of the application.

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