Most tests refer to either Air Temperature or Product Temperature (or both).   Therefore the following needs to be determined:

Air Temperature Inside Chamber - What is the Fastest  Ramp-Up in Temperature Required  (in degrees C or F per Minute)?
Air Temperature Inside Chamber - What is the Fastest Ramp-Down in Temperature Required (in degrees C or F per Minute)?

Actual Product Temperature - What is the Fastest  Ramp-Up in Temperature Required  (in degrees C or F per Minute)?
Actual Product Temperature - What is the Fastest Ramp-Down in Temperature Required (in degrees C or F per Minute)?

There are basically two ways to Cool a Temperature Chamber - Mechanical Refrigeration (compressors) or Cryogenic Gasses such as  Liquid Nitrogen (LN2) or Liquid Carbon Dioxide (CO2) which are injected into the chamber and controlled by solenoid valves which are programmed to open and close by the temperature controller.

Most standard mechanically refrigerated test chambers are designed for about a 2C/Minute average  ramp-down rate between  +170C and - 70C. However, by using extremely large mechanical compressors (2 x 30HP), ramp-down  rates of 15C/Minute and beyond are achievable.  However, these systems, often referred to as ESS chambers, can become relatively expensive.

In certain instances, where a fast temperature ramp-down  rate is required  (above 5C/Minute) utilizing relatively small mechanical compressors (2 x 2HP), Cryogenic Gas such as LN2 or CO2 can be used as a "boost" in conjunction with the compressors.  In this case, LN2 or CO2 boost is used only to achieve the fast temperature ramp down required  - Once the temperature has reached the set temperature,  the mechanical refrigeration is used to maintain the temperature for longer dwell times.

Note:  The Cryogenic Gas boost will only increase the ramp-down rate, not ramp-up rate.  While it is possible to increase ramp-up rates by adding additional  "heat boost" electric  heating elements, this is often limited by the the size of the circulation blower (used to dissipate the heat from the heating elements) and space available for extra heaters.  Should you require this option, our sales engineers will be pleased to assist you.

Thermal Shock Chambers
Another very severe temperature test, often referred to as Thermal Shock, utilizes two chambers (attached to one another), one hot and one cold, with a test basket which moves from one chamber to the other.  These chambers are also cooled using mechanical refrigeration, Cryogenic Gasses, or a combination.  Click here for more information on Thermal Shock Chambers