When we think of incubators, the first image that pops to mind is usually an incubator maintained between 30 and 37°C for bacterial and mammalian cell culture. However, there are also refrigerated incubators that can maintain a wider temperature range (between 5 and 70°C) with greater precision for applications such as temperature-dependent growth of microorganisms, quality testing of food products, and temperature-controlled storage and transport. In this article, we will discuss the different cooling mechanisms and what factors to consider when selecting refrigerated incubators for your lab.
Vapor compressors vs Peltier cooling
There are two main cooling mechanisms for refrigerated incubators. The conventional type is vapor compressor technology, which uses a circulating liquid refrigerant to cool the incubator. Circulating refrigerant first passes through the compressor where it is compressed to a higher temperature and pressure. The hot, compressed vapor then passes through a condenser where it is cooled by air or water, condensing into liquid refrigerant. The liquid refrigerant next flows into the thermal expansion valve where it experiences an abrupt drop in pressure, and thus temperature, making it colder than the temperature of the enclosed space to be refrigerated. Finally, the cold liquid refrigerant is circulated into the evaporator, where it absorbs heat from warm air and cools the enclosed space in the refrigerator to the desired temperature.
Alternatively, Peltier cooling utilizes the thermoelectric effect to create heated and cooled sides in a device, and does not require liquid refrigerant. Refrigerated incubators that operate by the Peltier effect make use of semiconductors to achieve cooling. When direct current is applied to the device, it flows through two different types of semiconductors in the Peltier module, causing the heat sink on one side to warm, and the other side to cool, which cools the circulating air and refrigerated space.
Key parameters to consider
Peltier cooling technology does not contain moving parts, which circumvents problems of mechanical wear and tear and reduces the probability of system failure. In general, it also extends the life of the refrigerated incubator and reduces the ongoing maintenance costs compared to vapor compression technology. The typical reasons for a vapor compressor failing are fouling such as algae growth, lubrication problems, and overheating that can reduce energy efficiency and disrupt the cooling system. Although the Peltier cooling method can also fail due to overheating, generally it is more reliable. The industrial standard for mean time between failures for a Peltier module is 200,000 hours.
Materials used in Peltier cooling technology are flexible and can be used to create refrigerated incubators that occupy less space and make cooling of small, enclosed areas more targeted. Additionally, with the use of direct current to generate heat flow, Peltier-cooled incubators offer better temperature control, as the direction and amount of electric current can be more precisely tuned. This is particularly important in applications such as monitoring the growth of microorganisms for safe product storage as well as transport of temperature-sensitive biological materials.
In summary, both vapor compression and Peltier cooling technology offer different advantages. Users should take into consideration these main parameters—energy efficiency, maintenance, physical footprint, temperature control, and environmental-friendliness—when selecting refrigerated incubators.