What is Forced Air Cooling, and Why Do You Need It?

Passive and active cooling are the two major weapons in the world of thermal management, which we have to fight this enemy. Passive means of approach are beautiful in their simplicity, but soon approach the limits. Once the thermal load becomes serious, forced air cooling must be called into the field: forced air cooling.

This paper will discuss the basics of this effective cooling system. We will discuss what it is, the difference between it and a passive system, its main elements (such as the air handler and the blower fan), and the urgent uses without which it just could not have existed. Above all, we will venture into the way to choose the most important part of this cooling system- the fan, and how to seek out a partner to make your design work.

What Is Forced Air Cooling?

Fundamentally, forced air cooling (also referred to as active air cooling or forced convection) is a thermal management method that involves a mechanical system forcing a fluid (in this case, air) to flow over a hot surface, regulating the air temperature.

This forced motion has a tremendous heat transfer effect. How? All that remains is a concept referred to as the convective heat transfer coefficient (h).

In a passive system, the air circulation is caused only under natural convection, that is, hot air has a lower density, hence it naturally rises and in the process pulls the cool air in to take its place. This is a slow process, and the coefficient of heat transfer is low.

A forced air system does not allow nature to take its course. It is a continuous process whereby pushing the high velocity air mechanically, it replaces the hot, stagnant, and therefore, the boundary layer of air on the surface with fresh, cooled air. Such a move may enhance the heat transfer coefficient 10-100 times greater than that of natural convection and enables a given system to cool a component of the same size by far more heat.

How Forced Air Cooling Differs From Passive Cooling Systems

One of the initial and most important decisions that an engineer makes is the one regarding passive or active cooling. Passive cooling is noise-free and not powered (requires no power), and very reliable (no moving parts). But it is only effective within a certain range of ambient temperature and a physical space that is huge.

Forced air cooling is used where passive cooling is no longer able to match the Thermal Design Power (TDP) – the maximum heat transfer a component (such as a CPU or GPU) is capable of.

The Must-Have Components of a Forced Air Cooling System

Although the idea is not complex, an effective system depends on a number of elements that have to be in concert. It applies to a huge home HVAC system and electronic enclosure.

Fans and Blowers

This is what is referred to as the engine of the air system, the working part.

• Axial Fans: They are the most widespread, which are propeller-like. They carry a great mass of air (high CFM, or Cubic Feet per Minute) sideways to the direction of the fan. They suit well in low-impedance applications where there is a clear, unobstructed passage of air.
• Blowers (Centrifugal Fans): They recirculate air in the center and discharge out at 90 degrees. They transport a smaller amount of air but at high pressure. They are necessary for high-impedance (high-resistance) tasks, such as forcing air through a very dense rack of server blades or a long, narrow duct.

To know more differences between axial fans and blowers, please check out our previous blog!

Ductwork and Air Filters

This is the “pathway” or air distribution system. The air has sluggish breathing; it can never pass through the path of least resistance.

• Ductwork (or Baffles): This is the network of ducts (or air ducts) that run in your walls in an HVAC system. These, in an electronics chassis, may be plastic or metal baffles, shrouds, and even the case walls themselves. They have the task of guiding the air so that it goes exactly where it is required without any form of bypass, where the cool air passes without even coming into contact with the hot part.
• Air Filters: Air filters in a house ensure your indoor air quality and would be able to eliminate indoor air pollutants. They cannot be more important in a data center or an industrial cabinet: they guard the hardware. Dust is an insulator and an electric conductor. A dust coating can severely limit the cooling and cause a short circuit. This is the reason why one of the major aspects of routine maintenance is air filtration.

The “Interface”: Heat Sinks (Radiators)

This is a heat exchanger that is commonly called the transfer point. A hot and small CPU chip does not have much surface area to dissipate its heat to the air. A passive block of high-heat-conductive metal (in most cases, aluminum or copper) containing numerous fins is referred to as a heat sink. It simply causes a massive amplification of the surface area, which gives the moving air a vast dock for harnessing the heat.

Heat sinks in a forced air system may be provided with far more dense finning, packed close together, since the fan has sufficient pressure to push air through the sinks–this natural convection could never do.

Why Do You Need It? Key Benefits and Advantages

This is mainly because forced air cooling is required by reason of power. The heat flux (heat/unit of area, or W/cm2) scales off the scale as we increase the performance of smaller devices.

1. Better Heat Dissipation: It is the primary benefit. The thermal load that a designed forced air system can handle is orders of magnitude greater than that of a passive-only solution; thus, powerful processors, FPGAs, and power supplies can be utilized.
2. Heightened Power Density and Miniaturization: Due to the efficiency of forced air, it is possible to fit the components far more tightly together. This enables the amazing power density of 1U “pizza box” servers, small 5G radio heads, and high-power medical equipment. In its absence, passive cooling of such devices would require 5-10 times the size.
3. Accurate Thermal Control: A Passive system is at the mercy of the surrounding environment, but the active system can be controlled. The use of smart fans with PWM (Pulse Width Modulation) control can allow a system to increase the fan speed when the load is high (such as during data processing) and reduce the speed when the load is low (such as at night). This enhances the energy efficiency, less noise, and increases the life of the fan.

Where You’ll Find forced air cooling

This is a two-sided term that is used to refer to two widely different, yet equally significant, worlds.

Home HVAC

This is the application that you are most likely used to. The most popular home heating and cooling system is a forced air system commonly referred to as central air. It relies on a central unit, typically a furnace (which may use natural gas to operate) or a heat pump, along with a blower fan pushing either warm air or cold air into a series of ducts that are run to various rooms so that the temperature can be precisely controlled. This kind of system is a sharp difference from the older radiant heating systems.

Servers and Data Centers

It is the typical instance of thermal management under high stakes. One server rack is capable of consuming in excess of 50kW of power, or more than 10 houses together, in a few square feet. This heat must be evacuated. In this case, forced air cooling works at several levels:

• Internally in the Server: There are several small high-pressure fans that push air in a very specific direction between CPUs and memory (front-to-back).
• Within the Rack: This airflow may be helped by the banks of bigger cooling fans.
• What is inside the Room: The CRAC (Computer Room Air Conditioner) units are what are known as the lungs of the data center, and cause cold air to circulate beneath the floor and the hot air to be taken out of the “hot aisle’s” hot air.

Telecommunications and 5G Infrastructure

This equipment (as with radio units and baseband units) will frequently be mounted in an outdoor cabinet or mounted on a cell tower at great height. These closures are isolated to the elements (rain, dust, snow) but roast in the dazzling sun.

Forced air cooling in this case is a challenge of reliability. The fans have to operate 24 hrs daily over a period of 10 years, and they have to work under high temperatures of -40 °C to 85 °C and supply high cooling power to the high process power chips of 5G.

New Energy and Industrial Automation

Imagine the brains of a modern factory (PLCs), the converters of power in a solar farm (inverters), or the controllers of the motor in a robotic arm (VFDs). These systems operate around the clock in dusty, moist, and shaking conditions. Downtime is not an option. In this case, forced air cooling fans are also chosen not only due to airflow, but because they are robust and have a long service life.

Choosing the Right Fan: The Heart of Your Forced Air Cooling System

You will find the same theme in all these high-tech applications: the heat sink is the interface, the chassis is the pathway, but the heart is the fan. It is the most important active component, which is critical, and its failure causes the failure of the entire system.

However, fans are a commodity in many engineering teams, where they are the final choice of fans that are based on a mere CFM (airflow) rating and price. This is a critical mistake. The actual functioning of a fan in the real world is so much more intricate than one number on a data sheet.

The spec sheet is a diagram illustrating the peak performance of a fan during a test done under zero resistance, in an open-air environment. But your application is resistant to the full–filters and heat sinks, and PCBs, and tight corners make “system impedance.” An inexpensive fan with claims of 100 CFM may actually only give 20 CFM when installed in your chassis, and this is what overheats and breaks.

It is on this basis that your supplier of fans is supposed to be a thermal partner. This is not the value of the component focused on, but your application-specific knowledge to assist you in choosing and testing, and putting it into practice.

How ACDCFAN Delivers Value for Your Application

This is where ACDCFAN is changed to a supplier to a thermal partner. We know that in telecom, industrial automation, and other mission-critical applications, failure is not a possibility. We address the real-life problem that engineers have:

• Extreme Reliability: Our high-precision ball bearing fans have an MTBF of more than 70,000 hours, which guarantees the long-term service life that your mission-critical system is expected to need.
• Surviving the Elements: Our advanced IP68-rated fans are completely dust-tight and waterproof, which guarantees maximum performance in high-altitude, high-humidity, or high-dust conditions.
• Smart, On-Demand Cooling: You do not require 100 percent cooling 100 percent of the time. Our smart-speed PWM digitals enable our customers to have on-demand cooling, which is silent at low loads, is energy saving, and is at its best when it counts.
• The Right Fan to the Job: We are not a one-size-fits-all manufacturer. A rich OEM/ODM support is supporting our full range of AC, DC, and EC fans. We do not cram your design into our fan; we make a fan to your design.

You do not just want a catalog when you are dealing with a complicated thermal problem. It can provide an initial thermal solution within a 10-day period.

Key Design Considerations for Engineers

When you are developing your forced air cooling strategy, you should make sure that you go beyond the fan. An effective design is a systemic design.

1. System Impedance (The P-Q Curve): This is the first concept to be learned. It only depends on the pressure differential, which can be established by the fan and against the opposition to the movement of air. Any chassis is resistant to airflow (impedance). Each fan has a performance curve (Pressure vs. Airflow or P-Q). The point where your system crosses the P-Q curve of your fan will be the actual performance of the fan. You have to choose a fan with a peak efficiency near that particular point.
2. Airflow Path: What is really happening to the air? Eliminate bypass paths, use baffles and shrouds. Make sure that you do not have dead zones where the hot air is stagnant and recirculates.
3. Noise and Vibration: Acoustic noise is a serious design issue in a medical or office setting. It can be controlled by larger and slower-turning fans, intelligent PWM systems, or complex bearing systems.
4. Inlet vs. Outlet: Do you force air into or out of the box (positive pressure or negative pressure)? Positive pressure is preferable since it is easier to filter the one-and-only inlet to ensure the chassis is clean.

Conclusion

The forced air cooling is not merely a feature; it is the essential facilitator of the modern high-performance technology. This technique is all that will stand between peak performance and a thermal meltdown, whether it is the data centers that empower our cloud or the industrial systems that create our world.

However, the weakest element is the most important part of a system. Selecting the appropriate fan- and the appropriate partner to assist you with its integration- is not the final step in your design. It is the heart of it.

When you are willing to go beyond the spec sheet and create a strong, stable, and intelligent thermal solution, our engineering team is willing to assist.