Types of Test Chamber Cooling System

There are two major types of chamber cooling systems, expendable refrigerants and mechanically cooled.

Expendable Refrigerants

Expendable refrigerants are liquid/gases that can be injected directly into the space being cooled or into heat

exchangers, similar to mechanical systems. As the liquid enters the chamber (directly or through a fin coil) it

absorbs heat and flashes to a gas. The gas is then vented out of the chamber and should be ducted outdoors.

The two most popular refrigerants are liquid nitrogen (LN2) and liquid carbon dioxide (CO2). Cryogenic

temperatures down to - 184˚C can be achieved with LN2. CO2 on the other hand can only achieve

temperature down to -68˚C. Both of these gases are environmental safe and

can be vented to the atmosphere. Note: it is imperative that the gases be vented

outdoors. These gases displace oxygen and asphyxia can occur if the chamber is not

properly vented.

Mechanically cooled

Mechanically-cooled refrigeration systems are fundamentally the same as those used

in home refrigerators. They utilize a compressor and circulate a refrigerant around a

closed loop system. The ultimate low temperature required by your testing

determines the type of refrigeration system needed.

Single Stage

Single-stage refrigeration systems typically can pull the temperature in the chamber down to - 34˚C.

Some manufacturers rate their single stage systems down to -40˚C. However, due to the refrigerant used

there is very little cooling capacity available at -40˚C and can be difficult to achieve. For continuous operation at

-40˚C and below most manufacturers recommend a cascade refrigeration system.

Cascade

Cascade refrigeration systems have two separate refrigeration systems working to cool the chamber down to an

ultimate low of -73˚C and -85˚C on industrial freezer models. The first stage refrigeration system cools

and condenses the refrigerant in the second stage. The second stage refrigerant flows through an evaporator

located in the chamber which cools the air. These systems can become very complex depending on your

application.