Cooling Systems: Air Cooling vs Liquid Cooling

The ongoing pandemic continues to impact the tech industry and automotive industries alike. At the dawn of the pandemic, tech spending increased by 12% as consumers adhered to the strict stay-at-home orders [1]. The drastic spending spree has led to the inevitable global semiconductor chip shortage. Now, as the new wave of the pandemic crashes, enterprises are missing critical opportunities for rapid revenue recovery as they scramble to find chips for their devices. While the industry is no stranger to turbulent supply and demand cycles, advanced cooling systems can provide alternative methods to deescalate demands.  

Ideally, manufacturers and enterprises would have a solution to make their chips work harder and last longer. Unfortunately, that is easier said than done. Semiconductor enterprises are constantly innovating chip architecture to pack more compute with less power. In fact, the NVIDIA Grace CPU boasts a 2X performance improvement over competitors at the same power envelope. This breakthrough will have a drastic impact on chip architecture moving forward as semiconductor enterprises continue to innovate performance sustainably. While data center innovations continue to develop, cooling solutions support innovation by combating thermal obstacles and supporting high power outputs. Simply put, the more energy used, the greater the heat byproduct. As a result, appropriate thermal management implementation is necessary to run devices harder. While there is no easy answer, cooling solutions offer potential opportunities to maximize chip usage and decrease mean time to failure. First, let’s dive into the two general types of cooling systems: air cooling and liquid cooling. 

The central processing unit (CPU) is the brain of most electronics systems. As a result, CPUs consume a lot of energy which produces large heat byproducts. If the heat went unmanaged, the CPU would fry itself in a matter of seconds. Consequently, CPUs need effective cooling systems in order to run efficiently and safely.

The two common methods of cooling electronics are air cooling and liquid cooling. In both methods, electronics are cooled by a cooling fluid (air or liquid) interacting with electronics and their associated heat sinks. These heat sinks are attached to CPUs with a thermal interface material, such as a thermal paste, that fill microscopic air gaps and thereby facilitates efficient thermal transmission between surfaces. The heat sink and TIM help improve heat transfer capabilities as the respective cooling medium (air or liquid) circulates. There are several CPU cooler options in the market, and each has its own advantages and disadvantages. Let’s compare liquid cooling vs. air cooling to understand the advantages and disadvantages of both and what applications they may fit best in.

Figure 1: Traditional Liquid Cooling Stackup

If you’ve ever used your laptop for hours on end, you’re probably familiar with the loud fan that starts when your device begins to overheat. While sometimes annoying, that fan cools your laptop before it damages the computer. Air cooled CPUs are a common thermal management solution for most laptops, computers, and gaming systems. As the pandemic pushed people to their devices for play, work and connecting, fans have been working overboard to manage increased heat byproducts. 

Simply put, air cooling is a traditional method of removing or dissipating heat with air flows to cool the intended object. This is typically done through the implementation of a fan to run cool air over the heated components. Air cooling techniques also include enhancing device surface area via large conductive heat sinks and cooling fins. In these approaches, the heat sink or fins maximize the surface area in contact with the cooling medium – the air. As a result, the air cools the heat sink and, by extension, the CPU. 

While these methods work well for most consumer electronics, if you were to take on a more computationally intensive task such as overclocking your computer, it would most likely fail by these cooling means. In order to augment cooling effectiveness using fans and heat sinks, you must increase the size or volume of the cooling hardware. However, even with hypothetically unlimited space, this method has a limit. As a result, hyperscale data centers or dense compute loads typically require a liquid cooling solution to manage the increased heat byproducts and energy output. 

In addition to their heat transfer limitations, air cooled CPUs are typically large and loud. However, if you aren’t looking for top-notch performance, air cooling is a viable option. Air cooled CPUs are almost always cost-effective, light on infrastructure, and easy to install, making it a sufficient system for most users. 

Unlike air cooling, liquid cooling solutions aren’t as popular for personal devices. Occasionally, the advanced gamer or bitcoin miner will use liquid cooling solutions to improve performance. Typically, enterprises that need to manage, store and compute dense workloads use liquid cooling solutions for thermal management. Large data centers and colocation services usually implement liquid cooling techniques to cut operating and energy costs.  

Liquid cooling, or water cooling, is a more innovative approach that utilizes liquid to remove heat from CPUs. In short, liquid cooling systems circulate liquid, usually water, to water blocks or cold plates that sit atop the CPU. The water then absorbs and removes the heat from CPU. This creates a liquid cooling loop. Typically, water can absorb more heat than air before it starts to increase in temperature. This means it can take on more heat from the CPU before needing to be recirculated and dissipate the heat. Specifically, water can absorb up to 4200 J/kg-°C of heat while air barely reaches 1000 J/kg-°C, a >4X improvement in specific heat capacity. When it comes to coolants, you want your medium to have a high heat transfer capacity. 

While sometimes called water cooling, not all liquid cooling uses standard water as the cooling medium. Deionized water, glycol/water solutions and dielectric fluids are common heat transfer fluids in high performance computing. Different heat transfer fluids work better for different industry needs. To learn more about what heat transfer fluid you should be using, check out our blog post here.  

Due to its efficiency, liquid cooling is typically more expensive. In addition, liquid cooling can also be more complicated to install and manage, and there’s always the possibility of leaks. However, long-term liquid cooling solutions lower operating costs by reducing electricity and energy usage. Many data center integrators with advanced devices opt to put extra money and effort into liquid cooling systems to offer peak performance and heat regulation, enabling new applications and innovative devices that would be impossible using air cooling.

The pandemic has completely changed consumer behavior and electronics usage. As people rely more heavily on their devices to complete daily tasks, compute density will need to increase to meet demands. With the semiconductor chip shortage also wreaking havoc, finding ways to run devices harder and cool them is quickly becoming a global priority. As a result, processors continue to densify, pushing traditional forms of air and liquid cooling to their limits. Innovative cooling solutions provide enterprises with more power per chip, enabling customers with exceptional device performance while using fewer chips. Check out our recent press release to learn more about how JetCool’s liquid cooling can help the global semiconductor chip shortage.

Some innovative liquid cooling solutions include microchannel, immersion and JetCool’s microconvective cooling. JetCool’s microconvective liquid cooling aims to further improve the current liquid cooling systems to produce improved performance for applications with densest compute profiles.

Microconvective liquid cooling uses arrays of small fluid jets within compact cooling modules, transforming cooling performance at the chip level. This direct-to-chip cooling solution efficiently removes heat from the processor as small cooling jets directly contact the device.

To learn more about innovative liquid cooling technologies, check out our 2021 Data Center Cooling Solutions blog post.

The battle over which cooling system is better will constantly be had. What’s important is that you find the best cooling solution for you and your company. For companies that need to stick hard and fast to your budget, go with air cooling. However, bear in mind that air cooling isn’t equipped to handle dense compute loads. While it may be cheaper to start, overall operating expenses will slowly eat away at any initial capital savings. For companies that need peak performance for heavy compute loads, liquid cooling solutions yield greater computational success.