Mar. 17, 2025
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.
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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.
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 s 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 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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:
Submerging servers in liquid can seem daunting, however the payoffs are huge:
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:
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:
Air cooling is more commonplace in data centers as a cooling option. Here are some of its main benefits:
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:
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:
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Related links: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:
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.
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.
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.
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.
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.
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.
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.
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.
Most generators have numerous conductors, all of which produce heat as current flows through them. That heat can build up quickly within the system and it must be properly removed to reduce the risk of damage.
If heat is not properly removed from the system, damage to the windings occurs rather quickly. A number of issues can occur including clearance and balance problems. But, it is possible to reduce this heat significantly through various cooling systems. By consistently cooling the generator, it is possible to minimize the risk of any damage to the generator itself. Ultimately, this reduces frustration and prevents the need for repairs.
Knowing the value of cooling generators, it is then important to understand how the best air-cooled systems work. For air-cooled systems, there are two main methods of cooling available.
The first is open-ventilated systems. Here, the air in the atmosphere is used with a type of exhaust system. This allows for the air to be released right back into the atmosphere. It pulls in the air and pushes it back out into the surrounding area.
The second type is an enclosed system. An enclosed system, as the name implies, keeps the air in place. It works to then recirculate the air. As it does, the air is cooled which, in turn, keeps the generator cool.
Air cooled systems have some limits including the risk of overheating. However, air cooled systems are mostly restricted to small standby and portable generators that produce up to 22 kilowatts of power per unit.
Liquid-cooled systems, sometimes referred to as water-cooled systems, are another option. There are numerous types of liquid-cooled systems. Some operate using oil while others use coolants. Hydrogen is another cooling element.
A liquid-cooled system features a water pump that moves the coolant around the engine using a number of hoses. The heat from the generator transfers naturally to the coolant, cooling the unit. This type of system is best for larger generators in particular. They require more heavy duty components to keep the generator cool. This does increase the cost, but these are the most common option for commercial and industrial use.
One key option is the hydrogen-cooled system. These are also used for large generators. The hydrogen used in them has a high thermal conductivity. This allows these systems to pull out heat at a faster rate. As a result, they work well for larger systems that cannot be efficiently cooled using other coolants.
When choosing the right cooling solution for a generator, the size and use of the generator plays a significant role in the decision process. For systems that are larger, usually all of those over 22 kilowatts of power, air-cooled systems are simply not effective. They cannot pull enough of the heat from the system, allowing them to overheat quickly. Liquid-cooled systems are the most common option for commercial and industrial spaces.
Air-cooled systems are best for portable generators and those used in residential settings. Here, there is less power and less demand, creating less heat. Air-cooled systems work well here and cost less.
The cost comparison between air-cooled and liquid-cooled generators can vary significantly based on specific models and brands, but generally, liquid-cooled generators are more expensive. Here's an approximate cost comparison in percentage differences:
These percentages are general estimates and can vary based on specific circumstances, such as geographic location, brand, and specific model features.
When choosing cooling systems, maintenance should be a key consideration. The simpler the machine is, the more simplistic the maintenance program will be. Air-cooled systems are easier to maintain because they have a rather simple design. They do not create as much of a mess during the cleaning process and can be done by anyone that is handy enough.
Maintenance for liquid-cooled systems is more complex. Most require a specialized kit available to clean the system. And, maintenance is required more frequently with these systems.
The maintenance schedule for generators varies based on whether they are air-cooled or liquid-cooled, as well as on the manufacturer's recommendations and the generator's usage patterns. Here are general guidelines for maintaining each type:
The noise levels for air-cooled and liquid-cooled generators can vary significantly, with liquid-cooled generators generally being quieter. Here's a comparison of the typical noise levels in decibels (dBA) for each type:
The noise level comparison provided earlier generally applies to residential generators in the range of 10 kW to 22 kW. These sizes are common for home backup power systems, and the noise levels can vary within this range depending on the specific design and model.
Choosing the right cooling system depends on the size and use of the generator. Air-cooled systems are suitable for smaller, residential generators, while liquid-cooled systems are necessary for larger, industrial units as well as larger homes. Considerations include cost, maintenance, and noise levels.
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