Incubator chamber heating and cooling

Incubators, used in hospital and laboratory settings for cell and tissue culture, can cultivate and maintain cell and tissue samples under controlled conditions for periods ranging from several hours to several weeks or even months. By precisely regulating temperature, humidity, carbon dioxide levels, and oxygen levels, incubators create an ideal environment for the growth of cell and tissue samples. This precise control over these factors enables researchers in critical fields—such as zoology, microbiology, drug development, food science, and the cosmetics industry—to carry out essential research and experimental work.

Precise temperature control is particularly critical for cell growth. Even a deviation of just 6°C from the optimal mammalian body temperature of 37°C can negatively affect cell health: temperatures that are too low can slow down growth (and sometimes even cause permanent arrest), while temperatures that are too high can trigger the denaturation of sensitive proteins.

Adopting thermoelectric technology to replace traditional compressor-based refrigeration systems offers a more efficient and cost-effective solution. Moreover, with the introduction of new regulations by governments worldwide restricting the use of conventional refrigerants central to compressor-based refrigeration systems, thermoelectric technology has emerged as an environmentally superior solution for maintaining stable temperature control in incubators.
Incubator Performance Requirements

To ensure normal cell culture, the incubator must precisely maintain stable control of temperature, humidity, carbon dioxide, and oxygen levels. Depending on the size of the chamber, the thermal load requirement ranges from 30 to over 400 watts. For CO2 incubators, it is also necessary to maintain a relative humidity between 95% and 98% and a specific CO2 concentration range from 0.3% to 19.9%.

Design Challenge

Incubator manufacturers face numerous thermal management design challenges, involving multiple dimensions such as space constraints, airflow organization, humidity control, dust-proof characteristics, and ease of cleaning.
Depending on the differences in cabinet dimensions, the culture chamber requires specific cooling capacities to meet temperature-reduction demands under extreme operating conditions. The higher the cooling capacity required, the larger the volume of the cooling unit will be. However, the thermal management solution must incorporate lightweight, high-efficiency heat exchangers that can operate within limited spaces, thereby maximizing the usable volume of the culture chamber. Consequently, space-constrained incubators need to employ high-performance heat exchangers to satisfy the increased cooling capacity requirements.

Another challenge lies in ensuring uniform airflow within the chamber. The incubator achieves air circulation inside the chamber through a built-in fan and employs air duct baffles to distribute air evenly, thereby minimizing environmental variations among samples. However, when operating in high-humidity environments, components such as the fan must be protected against moisture to prevent corrosion and subsequent degradation of mechanical performance. The key difficulty lies in balancing the high humidity required for the incubator’s normal operation with the risk of condensation forming inside the device. By incorporating designs such as sealing gaskets, thermal insulation materials, encapsulation techniques, and condensate drainage systems, we can effectively mitigate the risk of humidity-induced damage.

From the perspective of the operating environment, laboratory dust is also an important influencing factor. Depending on the intensity of experimental activities in the area where the incubator is located, dust will gradually accumulate in the heat-exchanger components, leading to increased thermal resistance. This not only degrades system performance but also forces the thermoelectric components to operate under higher load in order to maintain the set temperature. To ensure long-term stable thermal performance, it is recommended to position the air intake away from the floor and install an air filter to block dust. In addition, the incubator design must comply with biosafety regulations and be equipped with an interior cavity and shelves that are easy to clean and disinfect. This implies that the cooling unit must be able to withstand the high-temperature conditions encountered during sterilization processes.

Traditional solution

In CO2 incubators, air-jacket or water-jacket structures are typically used to maintain a constant temperature environment. Since water has a much higher specific heat capacity than air, its temperature changes more slowly, thereby ensuring stable regulation of the internal temperature of the incubator. The water-jacket system consists of a circulating water layer that surrounds the incubator chamber; water flows through inlet and outlet ports, passing over the chamber walls and exchanging heat with external heating or cooling equipment. Through natural convection, the water exchanges heat with the inner cavity, providing a highly uniform internal temperature environment and effectively buffering against fluctuations in external ambient temperature. However, water-jacket systems carry the risk of leakage, and due to their large water storage capacity, they tend to be bulky and heavy, requiring the liquid to be drained before moving the unit. After relocation, the process of refilling and restarting the system takes about 24 hours to restore a stable operating temperature, resulting in significant downtime.

The system, featuring a shell structure similar to a water jacket, uses electric heating coils or a compressor to heat the air within the jacket and directly radiates heat onto the cell culture. Some air-jacket models rely exclusively on natural convection to achieve uniform temperature distribution inside the chamber, while others are equipped with fans to enhance convective airflow. However, forced convection can accelerate evaporation of the culture medium, and even with the addition of humidity-control plates, small samples may still become dehydrated. Moreover, air-jacket systems driven by compressors can introduce vibration disturbances and noise pollution into the laboratory environment, and they typically occupy a relatively large amount of space.

Recent government regulations—particularly in Europe—restricting certain refrigerants are prompting incubator manufacturers to adopt solid-state thermoelectric temperature-control systems as an alternative to compressor-based refrigeration solutions. Early compressor-based refrigeration systems relied on hydrofluorocarbon refrigerants with high global warming potentials, such as R134a and R404A; modern systems, by contrast, now utilize a variety of natural refrigerants: R744 (carbon dioxide), R717 (ammonia), R290 (propane), R600a (isobutene), and R1270 (propylene). However, each of these natural refrigerants presents unique design challenges, including increased pressure levels, high toxicity, flammability and explosivity risks, asphyxiation hazards, and relatively lower energy efficiency. Moreover, the flammable nature of certain natural refrigerants further increases transportation risks and imposes limitations on storage capacity.

Peltier heating/cooling technology

The eco-friendly thermoelectric temperature-control system achieves precise heating and cooling within the incubator through a compact design. Thermoelectric technology offers multiple advantages in thermal management: it allows seamless switching between cooling and heating modes, enables highly accurate temperature control, delivers rapid cooling and heating rates, and effectively protects samples from temperature fluctuations. All these functions can be realized without the use of any natural or synthetic refrigerants.

As a solid-state heat pump device, a thermoelectric cooler achieves heat transfer based on the Peltier effect. When direct current passes through the thermoelectric cooler, a temperature difference is generated across the module: one side becomes colder (absorbing heat), while the other side becomes hotter (releasing heat). Typically, the cold side of the thermoelectric cooler is connected to a forced-convection radiator to absorb heat from within the enclosure, while the hot side is equipped with a radiator that dissipates heat into the surrounding environment. By reversing the polarity of the thermoelectric cooler, it is also possible to heat the interior space of the enclosure. This bidirectional cooling and heating capability provides the technical foundation for precise temperature control.

Thermoelectric cooler manufacturers define two key parameters for their products: ΔTMax (maximum temperature difference) and QcMax (maximum heat flow rate). ΔTMax refers to the maximum temperature difference under zero-heat-flow conditions (Qc = 0), while QcMax represents the maximum heat flow rate under zero-temperature-difference conditions (ΔT = 0). For most single-stage thermoelectric coolers, the ΔTMax value is around 70°C; however, in practical applications, some of this temperature difference may be lost due to the thermal resistance of the heat sink. If a higher cooling capacity is required, the number of thermoelectric coolers must be increased—either by connecting them in series or in parallel to match a 12/24-volt DC power supply. In actual operation, both thermoelectric coolers and modules need to carefully balance the combined parameters of ΔT and Qc to meet the cooling and heating demands necessary for maintaining stable incubator temperatures.

The thermoelectric cooling module features a compact, integrated design, enabling engineers to quickly build systems by combining basic modules (fan + thermoelectric cooler + heat exchanger). Its cooling capacity ranges from 10 to 400 watts and supports various heat transfer mechanisms, including convection, conduction, and liquid-based heat transfer.

The following figure illustrates the temperature-control principle of a typical thermoelectric heating/cooling module installed within an incubator chamber: The thermoelectric module is positioned between two air heat exchangers. In cooling mode, air inside the chamber circulates through the cold-side heat exchanger, where it is cooled. The thermoelectric cooler absorbs the heat and pumps it to the hot-side heat exchanger, which then dissipates the heat into the ambient air. In heating mode, the process operates in reverse. To minimize heat loss to the environment, the hot-side fan is typically turned off during heating mode.

The combination of a closed-loop temperature controller and a thermoelectric cooling module enables the construction of a thermal management system with high response speed and high precision. The temperature controller, specially designed for thermoelectric cooling modules, dynamically adjusts the power output based on feedback signals from temperature sensors, thereby achieving precise temperature control in enclosed spaces. This controller supports multiple energy-saving control modes and features a safety alarm function. It provides I/O interfaces for connecting fans, thermoelectric coolers, alarm/status indicator lights, thermistors, fan speed sensors, and overheat protection thermostats.

Conclusion

Using thermoelectric technology to replace conventional solutions for incubator temperature control can provide an efficient, energy-saving, highly thermally stable, compact, highly reliable, low-maintenance, and cost-optimized solution for the thermal management of CO2 incubators.
BoSheng can customize thermoelectric solutions to meet specific application requirements. Typically, customers start with standard thermoelectric cooling modules and then optimize the heat sink structure, installation location, and airflow layout to overcome spatial constraints. The sealed protective design around the thermoelectric cooler’s cavity effectively prevents condensation from affecting module performance. We are highly skilled in enhancing performance and energy efficiency through structural optimization, precisely achieving the desired thermal management outcomes.