Demand for cloud computing exploded in 2020, driving additional expansion of the data center industry. Today, enterprise data center owners are battling hyperscale data center owners for space, as each group needs to ensure they have enough capacity to meet today’s demand and grow in the future.
Adding new facilities to the existing data center inventory raises the question of how these facilities will be cooled. Data centers generate a massive amount of heat, which—if not managed properly—will cause electrical equipment and components to overheat, triggering performance issues (e.g., system shutdowns) and reducing the life of the equipment.
Guidelines for Data Center Cooling
The ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) Technical Committee 9.9 thermal guidelines for air and liquid cooling are considered the industry standard for data center temperature and humidity control. These guidelines define the recommended and allowable temperature and humidity ranges that facilities should target for optimal equipment operations.
As discussed above, high temperatures can damage IT equipment and potentially cause outages. Humidity that is too low or too high can cause other undesirable outcomes. For example, low humidity can enable electrostatic discharges that short out IT components. High humidity can condense on electrical components when the equipment cools down, which is a recipe for disaster.
Types of Data Center Cooling Technologies
Data center cooling systems are essential to the efficiency, performance and reliability of the IT equipment housed in the facility. But cooling isn’t a one-size-fits-all technology.
Let’s look at the different types of data center cooling technologies and how they are best applied in today’s environments.
Air Cooling Technology
Many data centers use air cooling technologies, including room-based and close-coupled cooling systems, to control temperatures within their facilities. These solutions use air cooled by chilled water or refrigerant to remove the heat generated by the IT equipment.
Room Cooling
The most common data center cooling technologies are traditional computer room air conditioners and air handlers.
A computer room air conditioner (CRAC) is similar to a residential air conditioning unit, but the CRAC is designed to handle the heat of a server room. The unit uses a compressor and refrigerant to cool the air supplied to the servers. Compared with other cooling methodologies, CRAC equipment is relatively inexpensive but not the most energy efficient.
Computer room air handlers (CRAH) differ from CRACs in that they use water in place of refrigerant as the cooling medium. CRAH cooling is very efficient, especially in colder climates, but the systems that reject the IT heat to the environment require more space and maintenance.
CRAC and CRAH cooling techniques are most often used in facilities with raised floors and cold aisle/hot aisle layouts. In this layout, IT equipment is mounted in racks on a raised floor. These racks are arranged into “hot aisles” and “cold aisles,” with cold air intakes facing each other and hot air exhausts facing each other in their respective rows.
The cold aisles are equipped with perforated floor tiles that distribute cold air from the pressurized underfloor plenum to the server inlets.
The hot aisles align with return ducts that direct heated air to the cooling units placed around the facility's perimeter.
Partitioning is often used between the aisles to prevent the hot and cold air streams from mixing and affecting server performance and energy efficiency.
The third method of room cooling—free-air cooling—is an eco- and budget-conscious approach that feeds cool outside air into the facility. Although free-air cooling has financial and sustainability benefits, this method introduces air quality and humidity issues that require a filtration system to mitigate. Their ability to adequately cool the data center is driven by the local climate and ambient air temperatures.
Close-Coupled Air Conditioning
Close-coupled air conditioning is an air cooling methodology that works well when IT density makes room cooling less effective. This approach places cooling units closer to the heat source by installing them between racks within the rack rows or directly on IT racks via rear-door heat exchangers.
In higher-density environments, close-coupled air conditioning delivers inlet air more precisely to the source and quickly captures exhaust air. This reduces the power needed to run fans, increasing energy efficiency.
Liquid Cooling Technology
Cloud computing is driving an increase in data center density, and, as a result, owners are adding liquid cooling to their heat-removal strategies.
There are two main approaches to liquid cooling: direct-to-chip and immersion.
Direct-to-Chip Cooling
The direct-to-chip method moves coolant through pipes to a cold plate on the motherboard processors. The cold plate enables the transfer of heat from the chip into a water loop, where it is rejected elsewhere in the facility.
Direct-to-chip is one of the most effective ways to cool high-powered IT devices. However, direct-to-chip cooling mechanisms only capture heat from devices equipped with cold plates, so air cooling via fans in the servers and at the room level is still needed to capture the remainder of the IT heat.
Immersion Cooling
Immersion cooling is different from other cooling technologies in that heat is removed by fully submerging servers and other IT equipment in a dielectric fluid that won’t short out the boards.
There are three types of immersion cooling: single-phase, two-phase and server chassis-level.
Single-phase immersion cooling utilizes hydraulic pumps to push fluid through large tanks where server boards are housed. After the fluid absorbs heat from the boards, it leaves the tank and enters a heat exchanger. There, the heat is rejected, and the cooled fluid is cycled back into the tank.
The two-phase immersion approach submerges heat-generating electronic components into a bath of dielectric heat transfer liquid. When the hot components meet the liquid, the fluid boils and the vapor rises, where it condenses on a heat exchanger, returns to a liquid phase and reenters the bath.
Server chassis-level immersion cooling seals server components inside an aluminum chassis filled with dielectric fluid. The fluid enters the case, circulates around the components then returns to the coolant distribution unit where the heat is rejected from the building or reclaimed for other uses.
Immersion cooling is generally more efficient than other cooling techniques and provides significant energy savings. This is especially crucial for hyperscale cloud data centers like Microsoft's facilities. High performance and therefore high powered workloads like AI are a big driver.
Take a Deeper Dive into Data Center Cooling Techniques
Data center floor space is currently at a premium, due in part to continued supply chain disruptions, skyrocketing real estate prices and rapidly increasing demand for AI and other compute-intensive applications. As a result, data center density is increasing as owners try to optimize space and add capacity.
As data center density increases, so does the need for heat removal. It can be challenging to align cooling technology with the changing needs of your facility, but it is essential. The right combination of cooling methods can prevent downtime, increase efficiency, reduce costs and protect valuable IT equipment from damage.
Download The Complete Guide to Data Center Cooling to learn more about the technologies discussed above and discover how to incorporate the right cooling systems in your new data center design.
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