Climatic chambers have the ability to control both positive and negative temperatures. For positive temperature control, the chambers have electrical heating elements for heating, but in the case of negative temperatures there are different cooling options, but most climatic chambers have a mechanical system based on refrigerant gas compressors for cooling.
There are several negative temperature ranges, but it will be the standard to be used and the type of material or sample to be tested that will define the negative range. You have to take into account: the negative temperature range indicated in the standard, the energy dissipation, the amount of mass and the type of material, to be able to make a calculation of the cooling unit and to know if it is the most suitable or not. For example, if you want to lower the temperature of a test to -40°C with a lot of mass and a lot of dissipation, a single compressor chamber will not be sufficient and you will have to select a two-compressor system with a higher negative temperature range.
There are several alternatives for the lower temperature ranges, based on either mechanical cooling or expandable refrigerant.
• Ambient +10ºC. This lower limit is common for chambers without refrigeration. Since the fan generates its own heat, temperatures close to ambient cannot be guaranteed. If a temperature close to ambient is desired, a cooling system will be necessary.
• -25 °C. This is a considerably low range that can be reached by refrigerants commonly used in refrigerators or air conditioners, via a refrigerant gas.
• -40 °C, These types of refrigeration systems are commonly referred to as single-stage systems, as there is only one compressor in the cooling system.
• -70 ºC, Cascade or dual-stage systems. The high stage will be used to cool the low stage, allowing lower temperature limits. The high stage will ensure that there is no overpressure or overheating.
• -86 °C. To achieve this cooling, a triple cascade cooling system is used. This is rare in climatic chambers, however, it is common for ultra-freezers.
• -170 ºC Chambers that reach these limits use liquid nitrogen for cooling. Nitrogen is an inexpensive method of cooling a chamber, however, prolonged use can be costly. It is often used for tests requiring gradients close to 30ºC/min with small volume.
Remember, provide as much information as possible to DYCOMETAL’s technical department, so that they can configure the most suitable equipment for your solution.
