Chamber FAQ
How do test chambers get so cold?
What are the limitations of environmental chambers in achieving LOW temperatures?
20°C above ambient
This lower limit is common for chambers that don’t have any refrigeration. Because there is heat generated by the fan recirculating the air, we cannot guarantee temperatures close to the room ambient. So even if you just want a stable "ambient" temperature, you will need refrigeration. This low temperature is usually specified for ovens.
5 to -20°C
This is about as low as we can go with a standard refrigeration using R-134A refrigerant. This is the same refrigerant that is currently used in new air conditioning systems and refrigerators. This refrigerant is not widely used in the test chamber industry due to its limited range.
To learn more about refrigeration, see the following web site:
http://www.howstuffworks.com/refrigerator.htm
-35 to –40°C
This is the lowest range that chambers can achieve with R-404A or R-507 refrigerants. The type of refrigeration system they use is called "single stage", which basically means that there is one compressor.Chambers with this range are often only used to –20 or –25°C when cycling temperatures between hot and cold. Going to lower temperatures becomes a slow process. Higher performance systems may even limit the lower temperature more strictly in order to maximize the system to meet a desired test range in a specified time.
-65 to –73°C
Chambers that can get this low use "cascade" refrigeration. By using a "high stage" refrigeration circuit to cool the "low stage" circuit, these cold temperatures can be achieved. The low stage refrigerants (R-23 or R-508) would create too much pressure if they were used alone, which is why the high stage is added. The high stage ensures the low stage doesn’t overheat.
Cascade cooling is less efficient, so the actual pulling of heat from test samples is slower. Because the air is much cooler, it can make it appear that the chamber is going faster. It does take the samples longer to catch up.
-85 to -150°C
To get this cold, a triple cascade refrigeration system is used. This is rare in test chambers, although it is common for ultra-cool freezers.
-170°C
Chambers that can get this low use liquid nitrogen for cooling. Nitrogen is a cheap method for cooling a chamber, however long term use of liquid nitrogen can get expensive.
It is best suited for:
- Small or infrequently used chambers
- Chambers that especially need this low range
- Chambers that need temperature change rates greater than 30°C/m.
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