How to achieve low temperature in the laboratory?

What are the limitations of environmental chambers in achieving low temperatures?

How can Haida get temperatures down to -94°F (-70°C)?

To help you understand the different ways to cool a chamber and how cold they can get, take a look below: 

Here’s a quick review of every confinement platform for cooling a test chamber, from room temperature to as low as -170°C.

20℃ above ambient temperature

This lower limit is common in rooms without any cooling equipment. Since the fan circulates the air to generate heat, we cannot guarantee a temperature close to the indoor environment. So even if you just want a stable "ambient" temperature, you need cooling. This low temperature is usually achieved by ovens.

5 ~ -20℃

This is the lowest level we can achieve with our standard refrigeration system using R-134A refrigerant. This refrigerant is currently used in new air conditioning systems and refrigerators. Due to its limited range of use, this refrigerant is not widely used in the test chamber industry.

-35 ~ -40°C

This is the lowest range that chambers using R-404A or R-507 refrigerants can achieve. The type of refrigeration system they use is called "single-stage", which basically means there is one compressor. Chambers with this range are usually only used to -20 or -25°C as the temperature cycles between hot and cold. The temperature reduction is a slow process. Higher performance systems can have even tighter limits on the lower temperatures in order to maximize the system's ability to meet the required test range within the specified time.

-65 to -73°C

The test chamber can get this low using "cascade" refrigeration. These low temperatures are achieved by using a "high-stage" refrigeration circuit to cool the "low-stage" circuit. If the low-stage refrigerant (R-23 or R-508) was used alone it would create too much pressure (which would burst the pipes), which is why the high-stage refrigerant is added. The high-stage ensures that the low-stage does not reach too high a pressure by cooling it.

Cascade cooling is less efficient...even with two compressors you have the cooling capacity of only one. Plus there are the losses due to inefficient heat transfer between stages.

-85 to -150°C

To achieve such low temperatures, a three-stage refrigeration system is used. This is rare in test laboratories, although it is common in ultra-low temperature freezers.

-170°C

Chambers that can reach this low temperature use liquid nitrogen for cooling. Nitrogen is a cheap way to cool a chamber, however long-term use of liquid nitrogen can become expensive. It is best suited for:

1. Small or infrequently used test chambers

2. Test conditions that specifically require this low temperature range

3. Test chambers with a temperature change rate greater than 30°C/m.