Enclosure Air Circulation:
The Importance Of Airflow

Understanding Airflow in Electronics Enclosures

Thermal management for sophisticated electronics in protective enclosures starts with one fundamental element: airflow. Proper airflow within and throughout the enclosure can mean the difference between successfully maintaining and cooling your sensitive electronics and risking costly downtime associated with failures.

Airflow in cabinets and enclosures can occur in a few different ways.

Natural Convection

This is the most basic form of airflow. Naturally, when heat rises, cold air is pushed to the bottom of a space. Engineers should keep this in mind when laying out equipment within an enclosure. If convection isn’t properly addressed, a hot spot will form at the top of the enclosure. A solution to manage heat using natural convection is Passive Ventilation or more specifically, Louvres.

Passive Ventilation (can be filtered or not) only use the natural convection of air to move air in through a lower vent and out through a higher vent.
Louvres are open, unfiltered vents positioned to allow ambient air to be drawn into the enclosure through openings positioned low on the enclosure surface, and to exit through similar openings positioned high on the same surface.

Forced Convection

Using the same principle as natural convection, forced convection adds a fan, blower, or compressed air to force the warmed air through the enclosure and out through the upper vent (Ventilation Fan Filter Systems). Air moving devices include Fans and Blowers.

Fans are commonly used in enclosures to move the air more quickly than natural convection. Axial fans use multiple fan blades equally spaced around a center axle, drawing air from one side of the fan, moving it to the other as the blades spin on the axle. These types of fans are typically capable of delivering high volumes of air at medium to low pressure.
Blowers (or centrifugal fans) can also be used to move air through a space. Blowers change the direction of the air, typically 90 degrees, and push the air out through a ducted system. They are constructed of several fan blades mounted perpendicular to a central wheel hub. These devices commonly offer higher pressure with a lower flow when compared to axial fans of equal size.
Pressure is the force at which the air is moving; fans create a pressure differential to move the air. More obstructions within a space will require more pressure to move the air through and around them. Pressure is measured in pascals, psi, inH2O, or mmH2O.
Flow (or airflow) refers to the speed at which the air moves - this is typically measured in Cubic Feet per Minute (CFM) or Cubic Meter per Hour (CMH).

PRO TIP: When choosing a device to achieve forced convection, it is important to consider pressure vs. flow.

Protecting your Sensitive Electronics from Thermal Damage

Hotspots are a common problem within electrical equipment enclosures. They can be created when heat sources within the enclosure have a lack of airflow around them. Proper spacing of equipment to provide adequate airflow and to allow for natural convection within the cabinet is crucial to the successful operation of equipment housed within. In an air-conditioned enclosure, hotspots can have a negative effect on transfer of heat through enclosure walls. When cooling the temperature within the enclosure below ambient conditions, improper airflow can allow for the formation of both hot and cold spots. The hot spots can create a dangerous environment for the equipment, whereas a cold spot will cause heat transfer through the external walls at a much faster rate. Ideally, the air temperature needs to be even throughout the enclosure to maximize the performance of the air conditioner. This is achieved through proper airflow. Insufficient airflow can have negative impacts on both housed components AND on AC performance.

When the air temperature is uneven, the AC can’t perform optimally.
The cooling potential of the AC will be maximized by moving the warmer air throughout the enclosure to create an even temperature.
The AC can transfer more energy (watts of heat generated by the housed equipment) out of the enclosure with a homogenous internal temperature that is not necessarily cool at the AC’s air inlet.

Proper Designs for Thermal Management in Electronics Enclosures

There are three solutions to consider when thinking about designing enclosures to manage heat and prevent damage. These include air conditioner and component placements, along with airflow modification.

Air Conditioner Placement

When choosing the BTU output of the AC, it is equally important to choose the proper placement of the AC on the enclosure. Placing the AC in a high position on the enclosure will take advantage of natural convection and cool the warmer air within the space as it rises. It is also imperative to keep both the intake and exhaust of the air conditioner clear of obstructions to allow for proper airflow. EIC’s ThemoTEC series Thermoelectric Air Conditioners require a minimum of two inches of clearance around any intake or exhaust; the exhaust will be better served if there are no obstructions around it.

Component Placement

Similar to choosing your air conditioner placement, close care should be taken when considering the placement of components within the enclosure:

Components with significant heat generation should be given extra space to exhaust the heat and allow for proper airflow around them - this will help move heat away from the component and towards the AC. Place these items closer to the intake of the AC.
Components that run cooler can be stacked closer together. Airflow is less of a requirement with these pieces, as these cooler items have minimal effect on overall heat within the enclosure.
There should be clearance to walls and doors; keeping the hotter components away from walls of the enclosure allows for better circulation of air within the space.
Component airflow direction to complement AC is also important to consider. When a component has an active airflow through internal fans, directing the airflow towards the AC intakes will help the cooler to perform more efficiently. When designing an air-conditioned enclosure, it is more beneficial to get the hot air from the equipment into the AC, than it is to get the cold from the AC to the equipment.

Airflow Modification

Placement of the equipment within the enclosure is not always flexible enough to allow for ideal airflow. In cases where equipment with higher heat generating potential are not close to the AC, diverting the air may be an option. Diverting will help prevent recirculating and help the equipment exhaust to enter the intake of the AC. EIC does not recommend ducting air from its Thermoelectric AC’s as the fan output is very conical and ducting can produce too much pressure restriction. The flow at the intake is more linear, nevertheless ducting needs to be large enough to prevent restriction. Circulation fans can be added to the design to adequately move air throughout the enclosure and reduce or eliminate hotspots. EIC’s ThermoTEC series Thermoelectric Air Conditioners use constantly running internal fans to aid in the air circulation process even when the unit is not actively cooling. When adding circulation fans, be mindful of the heat generated by the fan motor. While typically a small value, this will add to the overall heat load being generated within the enclosure. Additionally, consider rotating or adjusting the internal components to create an adequate flow pattern.

Engineering a Solution for Heat Dissipation in Electronics Enclosures

EIC Solutions strives to provide innovative solutions and superior service, helping engineer a solution for your electronic enclosure needs. Our team specializes in the design and manufacturing of air-conditioned electronic enclosures, in addition to thermoelectric cooling systems and transit cases for a wide range of industries. Our products have been used in a variety of enclosure cooling applications involving the protection of electronic equipment both indoors and outdoors. We are committed to providing the highest quality products and serving our customer’s needs quickly and efficiently. If you need help with your electronic enclosures or have questions regarding any of our products, please contact us online or call us at 800-497-4524.

Enclosure Air Circulation:The Importance Of Airflow