Data Center Cooling Systems – Benefits, Differences and Comparisons

IT hardware throws out a great deal of heat. When you stack hundreds or thousands of servers in a data center, things get very hot, very quickly. Data center cooling systems are therefore essential for infrastructure operations.

There are many different types of data center cooling systems, ranging from basic air conditioning to the latest and most advanced forms of liquid cooling. Below, we explore how various cooling systems for data centers work, how they are different, and how they compare.

What is Data Center Cooling?

Data center cooling is the process of reducing the temperature in a data center, typically by adding cool air or liquids to counteract the heat generated by servers, storage devices, and networking hardware.

The process dates back to the earliest days of computing, when mainframe computers ran inside air-conditioned “glass houses” that kept the machines’ vacuum tubes from overheating. We’ve come a long way from the glass-walled enclosures of the 1940s and ’50s, but the underlying challenges are still the same.

Computers, such as servers, generate heat because the transistor —the fundamental building block of microprocessors — is, in electrical terms, a resistor. Physically, it’s no different from the heating coils in a toaster. The millions of tiny electrical pulses that comprise computer instruction sets cause the transistors to heat up, much like a toaster. The faster the computer and the more transistors it uses, the more heat it generates.

The Importance of Cooling in Data Centers

The need for cooling solutions stems from the fact that heat impedes data center performance. You can’t achieve peak computing performance using an overheated processor. Additionally, if hardware gets hot enough, its circuitry can melt or even catch on fire, destroying itself and surrounding equipment. Data center cooling technologies mitigate this risk.

The choices of data center cooling methods matter. Cooling data centers is not a one-size-fits-all proposition, rather, each approach has its own optimal use case. Several factors affect the selection of data center cooling solutions. Cost is a major factor, as are concerns about sustainability. Typically, the more cooling required, the more energy consumed.

For organizations with sustainability goals, or those who don’t want to overspend on power, the more cost effective and power efficient the cooling system is, the more suitable it will be.

Hardware density is another reason cooling matters to data center operators. Data centers are extremely expensive to build, costing up to $13 million per megawatt, so owners want to pack as much hardware into the available floor space as possible. However, increasing processing power on racks raises heat, creating a greater need for effective cooling solutions.

Types of Data Center Cooling Systems

How are data centers cooled? Broadly speaking, there are two main approaches: air cooling and liquid cooling. Air cooling involves moving cold air past hot equipment to carry off the heat and exhaust it outside the data center. Liquid cooling is a process that reduces the heat of hardware using a flow of cold liquids.

Air cooling is the older and more established of the core data center cooling options. It’s more than just air conditioning, however. The choice of air cooling systems for data centers depends on several factors, including the age and design of the data center facility, as well as its size and location.

For instance, a data center located in Alaska can take advantage of naturally occurring cold air outside the building. In contrast, a data center in Arizona does not have this advantage.

For context, understand that there are two primary ways to generate cold air to cool down a data center: conventional air conditioning and chilled water plants. Conventional air conditioning is a process that pushes warm, outside air in front of refrigerated coils. It’s a ubiquitous technology that’s suitable for relatively small data centers.

A chilled water plant works by cooling water or other refrigerants. It then uses air handlers to move warm air through pipes that go past the cold liquid, cooling it down before pushing it out into a duct system. Chilled water plants are common in office buildings and data centers. They are more energy efficient for cooling large spaces than conventional air conditioners, but they represent a larger upfront capital investment to build.

1. Computer Room Air Conditioner

Computer room air conditioner (CRAC) is the most basic and common form of data center cooling options. It uses a standard air conditioner compressor to pull warm air from the outside, cool it, and flow it through the data center to reduce heat.

CRAC is not the most efficient data center cooling equipment, but it is economical and easy to service. For these reasons, a small data center may be best served by CRAC, while a larger facility might justify the investment in a chilled water plant.

2. Computer Room Air Handler

A computer room air handler (CRAH) is a unit that connects to a chilled water plant system. Chilled water flows into the CRAH unit’s cooling coil, enabling the CRAH to circulate cold air into the data center.

3. Raised Floor Cooling

Most modern data centers feature a raised floor that allows for wires and power cables. However, a raised floor can also enable cold air flow to help with cooling, for example with air ducts.

4. Hot Aisle/Cold Aisle Containment

With the cold aisle/hot aisle containment approach to data center cooling, data center designers designate rows of servers as either “hot” or “cold” aisles.

A cold aisle places cold air intakes in front of racks of servers. Hot aisles have exhausts for hot air in the back of the racks. The hot aisles push air into air conditioning intakes, where it is cooled and pumped back into the cold aisles.

5. Calibrated Vectored Cooling

Calibrated vectored cooling (CVC) is designed for blade-type servers. This approach optimizes airflow into the blade chassis, typically by directing cold air to the hottest parts of the hardware. This may involve using sensors to locate the heat and applying cooled air using hoses or comparable equipment. As a result, CVC enables efficient heat management.

6. Direct Expansion System

A direct expansion (DX) system is an air cooling refrigeration method in which the refrigerant directly absorbs the hot air and cools it. DX systems don’t control the environment temperature like CRAC systems do; instead they remove the hot air and exchange it for cold air.

Liquid cooling is considered more effective at cooling electronics than air. For years, however, using liquids—especially water—was neither practical nor safe to use in a data center environment.

Water, though plentiful and cheap, can ruin electronic equipment. Plus, piping liquids around data centers introduces a costly layer of plumbing infrastructure to be maintained. As cooling requirements and environmental impacts of data centers have intensified, new forms of liquid cooling in data centers became available on the market.

The predominant modes of liquid cooling today use non-conductive, non-flammable liquids, such as synthetic oils or glycol.

1. Immersion Cooling

Immersion cooling involves placing computer equipment in containers full of chilled liquids, such as glycol. It seems counterintuitive, because we’re conditioned to keep water away from electronics, but this process involves sinking a server safely into a bath of glycol chilled to around 13° C —about the same as a refrigerator —and allows it to work fine without overheating.

2. Single-Phase Direct-to-Chip Cooling

Single-phase direct-to-chip cooling directs the chill right at the source of heat within a server. This includes CPUs and GPUs, which often generate the most heat. Methods vary, but direct-to-chip cooling generally involves piping chilled water or other liquids directly around the processor.

3. Two-Phase Direct-to-Chip Cooling

Two-phase direct-to-chip cooling involves pumping a dielectric liquid across the cold plate attached to the processer chip (GPU/CPU). When the chip generates heat, the liquid absorbs the heat and boils, therefore becoming a vapor.

The vapor then travels to a condenser, where it is cooled back into a liquid and pumped back to the cold plate. From here, the cycle is repeated.

4. Rear Door Heat Exchanger

A rear door heat exchanger (RDHx) is a cooling system mounted onto the rear door of a server rack. The hot air from the server passes through the RDHx coils and the liquid in these coils cool the air before it re-enters the room or is removed entirely.

Unlike other liquid cooling solutions, RDHx cools the air expelled by the server, rather than the server components themselves.

Benefits of Different Data Center Cooling Solutions

Each approach to data center cooling equipment has its advantages and disadvantages. For any given data center architecture or workload, there will be an ideal cooling technology. Below, the overarching categories of liquid and air cooling are examined, followed by a closer look at their specific cooling technologies.

Data center liquid cooling is evolving at an astronomical rate, and there are a variety of reasons why it is a preferred cooling option:

• More energy efficient – Energy efficiency translates into less use of carbon-producing emissions, such as from electrical generation based on coal. This is advantageous in today’s environmentally conscious corporate landscape, especially in regions where businesses are committed to reducing their carbon footprints, either voluntarily or as required by law.
• More cost-effective on an operational basis – Compared to air cooling, liquid cooling leads to lower long-term operating costs. As a result, IT teams can therefore achieve a significant return on investment over time.
• High-density computing support – For instances where greater server rack density is required or where infrastructures employ emerging technologies such as AI, liquid cooling is the preferred cooling method, due to its ability to manage heat in confined spaces.
• Quieter cooling – Liquid cooling eliminates the need for large fans, which reduces the noise in data centers considerably.

Immersion Cooling

Submerging servers in liquid can seem daunting, however the payoffs are huge:

• Highly targeted energy efficiency – Instead of incurring the cost of air-conditioning an entire data center facility, which might comprise millions of cubic feet of air, with immersion cooling, you’re only cooling the actual heat-producing equipment itself.
• Space saving – Immersion cooling systems are compact and do not require space for airflow, unlike traditional air cooling methods. Setups can be densely configured and even integrated vertically to save additional space.
• Serviceability – Unlike air cooling, components in immersion cooling are not blocked by structures such as fans or ducts. This makes maintenance more straightforward, which leads to reduced downtime.
• Improved water-use effectiveness – Immersion cooling systems operate in closed-loop environments, which eliminates water waste.

Direct-to-Chip Cooling

By cooling hardware directly where it is generating the most heat —through both single-phase and two-phase direct-to-chip cooling —this can be advantageous for the following reasons:

• Enhanced liquid cooling efficiency – Direct-to-chip cooling is even more targeted than immersion cooling. It focuses cooling energy right where it needs to be, which reduces thermal resistance.
• Scalability with technology – As processors and GPUs becoming increasingly powerful, this also means they generate more heat. Direct-to-chip supports these higher thermal design power components effectively.
• Two-phased direct-to-chip heat transfer effectiveness – The two-phased approach to direct-to-chip cooling is more effective than single-phase systems, as the process not only removes more heat, but also performs better in high-density systems.

Rear Door Heat Exchanger Cooling

A rear door heat exchanger is different to other liquid cooling solutions in that it cools the air generated by the hardware, rather than the equipment itself. This comes with the following benefits:

• Non-invasive – Because RDHx attaches to the server separately and then cools the air, no modifications are required to the server components, making it a simpler approach.
• Optimizes existing infrastructures with airflow – If sufficient airflow management is already in place, such as hot/cold aisle containment, RDHx systems can leverage these systems and make them even more efficient.
• Easy Installation – Building on the non-invasive nature of RDHx, this cooling approach is also straightforward to install and maintain.

Air cooling is more commonplace in data centers as a cooling option. Here are some of its main benefits:

• Simplicity and pervasiveness – Air conditioning exists in almost every building in the industrialized world. There are thousands of firms that can install and repair air conditioners and chilled water plants. This widespread familiarity reduces risks and simplifies adoption.
• Lower up-front costs – Compared to liquid cooling, air cooling requires a smaller initial investment.
• Reliability – Due to its operating longevity, air cooling is a well-understood technology, which can lead to faster repairs if anything goes wrong. Additionally, features like air filters and fan redundancy ensure continued operation even during maintenance.

Computer Room Air Conditioner (CRAC) Systems

CRAC systems are perhaps the most widely used cooling solution for data centers. Though some aspects make them somewhat obsolete, there are still benefits to be had:

• Ease of installation – CRAC units have been around for a long time, offered by a range of providers. Due to this, installation expertise can be easily found.
• Ease of maintenance – Similarly to installation, if anything breaks in a CRAC unit, repairs can typically be made promptly and effectively, due to the widespread understanding of these systems.

Computer Room Air Handler (CRAH) Units

CRAH units are similar to CRAC, however they use a chilled water cooling medium rather than a refrigerant seen in CRAC. Two benefits of CRAH are:

• Scalability in large data centers – CRAH units use chilled water from centralized systems. This approach is practical and cost-effective, particularly in large-scale data centers.
• Improved air cooling efficiency – Though the initial cost for CRAH units is higher than that of CRAC, CRAH units are more energy-efficient in the long run.

Raised Floor System

Raised floor systems are another common data center cooling technology. Though it assists with cooling efficiency, other benefits are often indirect to lowering data center temperatures:

• Enhanced airflow – The space that is created beneath the raised floor allows cool air to flow evenly across many server racks. This is an improvement compared to cooling the room in its entirety.
• Adaptability – Reconfiguring cooling components is simpler with a raised floor, due to its accessibility. Not to mention it allows a hidden passage for improved cable management, which is useful for ongoing maintenance and nhancing the aesthetic appeal of the infrastructure.
• Greater structural integrity – When installed correctly, a raised floor provides a stable platform that can support the weight of heavy data center equipment. Expensive storage, server and network devices therefore have less risk of damage.

6 Comparisons of Data Center Cooling Methods

How do the different methods of cooling stack up against each other? We’ve compared some of the more common cooling technologies, as well as their relationships with each other.

Though most of the following are direct comparisons, some delve into different terminology covering the same cooling solution – liquid vs water cooling is an example of this.

Data Center Liquid Cooling vs Air Cooling

There is no single right answer in deciding between air cooled vs liquid cooled data centers. Instead, each has its best use in a given context. For example, in a data center where tenants rent racks, air cooling may be the default mode of cooling. Tenants may not want to install liquid cooling.

Liquid cooling offers a better economic outcome, though it requires a larger up-front investment. One data center cooling research study shows that liquid cooling reduces data center construction costs from 15% to 30% versus air cooling. However, the liquid cooling equipment can be from 40% to 60% more expensive to acquire and install than air cooling.

Ultimately, though, liquid cooling delivers cost savings on energy of between 10% to 20%. That is a significant number, and it is highly probable that the investment in liquid cooling will pay for itself in a relatively short time.

Liquid Cooling vs Water Cooling

There is no difference between liquid cooling and water cooling in the data center; both are the same thing with different terminologies, which are used interchangeably.

When comparing liquid cooled vs water cooled data centers, these are terms to describe cooling data center equipment using a fluid.

Liquid Cooling vs Immersion Cooling

It’s necessary to investigate immersion cooling vs liquid cooling because although immersion cooling is a subset of liquid cooling, the two terms can be confused.

Immersion cooling refers to a system where an entire piece of hardware, like a server, sits immersed in a container full of a non-conducting, non-flammable liquid. In contrast, liquid cooling refers to the general practice of using liquids to cool down data centers.

Immersion Cooling vs Direct-to-Chip

Assessing immersion cooling vs direct-to-chip, we see that they are different implementations of the same concept of liquid cooling.

Immersion cooling involves immersing hardware in liquid, while direct-to-chip cooling is more focused. It applies liquid cooling right on the processor, which is what generates the heat. It therefore applies liquid cooling direct to chip. An analysis of direct-to-chip vs immersion cooling should explore differences in cost, implementation, and support. These can differ based on parameters like workload and the type of chip involved.

CRAC vs CRAH

Regarding data center cooling, discussions are often had around CRAC vs CRAH units. Both are forms of air conditioning and both fall into the air cooling category.

A Computer Room Air Conditioner (CRAC) is a standard air conditioning system. It pulls in air from the outdoors, runs it past refrigeration coils, and blows it into a duct system that cools the data center. The system also removes hot air from the data center and pumps it outside. A Computer Room Air Handler (CRAH) cools air using a chilled water system.

CRAH vs CRAC processes are largely the same, just realized through two different mechanical systems. CRAHs are generally used in larger data centers that can justify the greater investment required to build a chilled water plant. Once in use, CRAC systems typically deliver improved energy efficiency, lower costs and better sustainability outcomes.

Cold Aisle Containment vs. Hot Aisle Containment

There is no comparison to be made when it comes to cold aisle containment vs hot aisle containment. There is no opposition between hot aisle vs cold aisle when it comes to data center cooling; in reality, you need both hot aisles and cold aisles working together to cool down your data center. Otherwise, the hot air generated by the cold aisle will have nowhere to go.

Cooling Data Centers with Park Place Technologies

Data center cooling technologies are no longer a “nice to have” —they are an essential part of a modern IT infrastructure, and with the growing emphasis on corporate sustainability, the need for efficient cooling systems has become even more critical.

Though air cooling has its benefits, advancements in liquid cooling technology have made it the leading cooling solution for data centers. With a lower operating cost, improved energy efficiency, and enhanced performance, it’s easy to see why many are turning to liquid.

Park Place Technologies provides two different data center liquid cooling solutions — immersion cooling and direct-to-chip.

We serve as a single vendor for the entire process, managing installation, hardware maintenance, and ongoing monitoring, to ensure your equipment operates at peak performance. We can also provide guidance on direct liquid cooling vs immersion cooling, and inform you on which approach is best suited for your business.

Revolutionize your data center cooling with Park Place Technologies today — contact us to find out more!