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What Does Precision Air Conditioning Mean Now? And is it Still a Necessity for IT Spaces?

As recently as a couple of years ago, the need to maintain precise temperature and humidity control in an IT space was a top priority for data center managers and a primary motivator behind the purchase of a precision air conditioning system. Over the last several years, however, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has relaxed its recommendations and widened the temperature and humidity ranges deemed acceptable within environments that house sensitive IT equipment, including data centers, server rooms, network closets, technology rooms, or other spaces like medical equipment suites, laboratories, and telecommunications centers. Consequently, precision cooling in its most literal sense is no longer seen as the absolute necessity that it once was.

However, proper IT thermal management most certainly remains a critical priority. Precision air conditioning — or data center-grade cooling systems — are still very much needed, even if precise (within 1 or 2 degrees) temperature and humidity set points are no longer mandatory. In part, this is because even while the spectrum of allowable temperatures in IT space has expanded, so too has the amount of heat generated by the increasingly sophisticated servers needed to support today’s power- and data-intensive applications, including Internet of Things (IoT), artificial intelligence (AI), and others. And properly managing that heat is the key to ensuring IT equipment performs at optimal levels.

Furthermore, the consequences for exceeding recommended heat thresholds are just as serious as they ever were. Excessive heat can take a toll on equipment, leading to component failures or sometimes complete system shutdown, and it can all happen in a matter of minutes. IT equipment failures often snowball into unplanned downtime for a business, which comes at a staggeringly high cost that exceeds the cost of equipment damage and includes lost revenue opportunity, customer service disruption, and reputational damage that can persist long after the equipment is repaired, and the business is back up and running.

To help prevent potentially disastrous threats to business-critical continuity, precision air conditioning — or what Vertiv more commonly refers to as thermal management — is still very much a necessity in data center and IT spaces. 

Can building air conditioning systems cool IT equipment just a well as precision air conditioning systems?

In some IT spaces, such as server or technology rooms located in an administrative building, facilities managers will often rely on the building’s comfort cooling system to maintain the environment in the IT space. It is true that a commercial AC solution can play some role in controlling temperature, humidity, and air quality in these rooms. But the systems are lacking in many ways, starting with the fact that comfort cooling for people spaces and precision cooling for IT spaces are specifically engineered for very different purposes.

Think of it like this: cars and trucks share all the same basic components (engines, steering wheels, brakes, etc.), but you wouldn’t choose a sedan for an off-roading excursion. In other words, the vehicles are intended for very different applications. The same is true for precision air conditioning or thermal management systems.

Specifically, these specialty cooling solutions are built to do the following:

• Handle the unique, concentrated heat load generated by IT equipment. Today’s sophisticated IT equipment generates a significant amount of heat. And when you consider the industry’s continued increase in average rack densities coupled with the growth of smaller, edge sites, it becomes clear that a commercial building’s air conditioning systems is not equipped to accommodate the elevated, concentrated heat loads. Furthermore, many spaces used for IT today were not originally designed for housing critical equipment, creating less-than-ideal environmental conditions that can introduce additional cooling challenges that make comfort cooling solutions even less effective.
  Data center-grade cooling solutions, on the other hand, are specifically engineered to control the heat in these spaces. These thermal management systems are designed to collect up the heat in small, dense spaces and reject it in one of several methods, depending on the type of system selected.
• Run 24 hours a day, 365 days a year, regardless of the outside temperature. When it is cold outside, office buildings do not require AC. But IT spaces still do. Just like a grocer needs specialty equipment to keep the frozen peas frozen even when it is below zero outside, data centers and other IT spaces need a way to remove heat regardless of the outside temperature. But most comfort cooling systems are only designed to run when temperatures are above about 55 degrees Fahrenheit outdoors. Furthermore, regardless of the external temperature, some commercial AC systems shut down after hours or during weekends, leaving always-on computer equipment without protection.
  Data center-grade cooling systems overcome these issues and are specially designed to operate all the time — even when the outdoor temperatures plummet to 30 F or it’s 2 a.m. Sunday morning. This ensures that your equipment is always cooled properly.
• Dedicate most of their capacity to controlling room temperature. With a typical building cooling system, capacity is divided between the tasks of cooling the room and removing moisture (humidity) from the air to keep people comfortable during warmer parts of the year. Up to 40% of the overall capacity of such a system can be channeled to handling moisture. In such a case, the sensible heat ratio is 0.60, meaning that only 60% of the cooling capacity is designated to changing the temperature of the air.
  In IT spaces, that amounts to a lot of waste. IT equipment tends to produce dry, intense heat, so it does not need nearly as much capacity to go toward humidity. Indeed, if a 100 kilowatt (kW) comfort cooling system is purchased to cool 100 kW of IT load, the solution will likely fail since the IT cooling capacity of the system will only be about 60 kW.
  Most of today’s precision cooling systems are designed with a sensible heat ratio of at least 0.90. That’s 90% of the cooling capacity dedicated to cooling the IT equipment and the remaining 10% of capacity dedicated to removing moisture that may infiltrate the room from outside. Many Vertiv™ thermal management systems offer a sensible heat ratio of 0.95.

How does a data center-grade thermal management system work?

While there are several different types of precision air conditioning or thermal management systems designed to meet the unique needs of a variety of applications, all systems generally work in the same manner. The equipment provides optimum air temperature to the inlet fans of the IT equipment using a unit or units installed in the IT space, either at the perimeter of the room, in the row, or in the racks or ceiling if floor space is at a premium.  These interior units use refrigeration or rely on cold water or glycol-based coolant to chill the air. They use fans and airflow to guide the cool air to the right places.

As the same time, the hot air generated by the equipment is collected up and rejected from the IT space. The thermal management system’s heat rejection unit removes the heat in one of several ways:

• By channeling it to a building chilled water plant. Chilled water cooling systems, such as the innovative Vertiv™ Liebert® CW system, are a good choice for large data centers that have access to a chilled water plant. For smaller spaces or spaces in high-rise buildings where it’s not feasible to reject the air outside, a compact perimeter cooling solution, like the Vertiv™ Liebert® PCW, or even a ceiling-mounted precision cooling system, like the chilled water version of the zero-footprint Vertiv™ Liebert® Mini-Mate, can efficiently collect up and send the heat to the building’s chilled water plant by way of a common piping loop.
• By rejecting it outdoors. Air-cooled direct expansion systems pair an indoor computer room air conditioning (CRAC) unit with an outdoor heat rejection unit and use outdoor ambient air to cool the refrigerant. These systems, such as the Vertiv™ Liebert® DS, are extremely reliable because they don’t depend on other building systems to cool the rejected heat. However, each unit requires its own piping and outdoor heat rejection unit, which can take up valuable space.
• By rejecting it to a warm building water loop. Water-cooled direct expansion systems, like the Vertiv™ Liebert® PDX, connect multiple indoor CRAC units to a warm building water loop, usually a cooler tower system where the refrigerant is cooled by the process water. Small and mid-sized rooms in facilities where a building water system exist are good candidates for this solution.
• By connecting to an outdoor fluid cooler such a drycooler. Glycol-cooled direct expansion systems connect multiple indoor CRAC units to a drycooler loop and pumping system, which circulate a warm water glycol antifreeze solution to cool the refrigerant. Small and mid-sized rooms can benefit from these types of systems, but there must be enough roof space to accommodate the drycooler and pumps.
• By using a specialized liquid to directly cool the equipment. Liquid cooling is emerging as yet another option for IT thermal management. If you’ve ever burned a finger badly you know that air (i.e. blowing on it) often isn’t enough to relieve the burn. You need to run your finger under cold water for relief. Breakthrough liquid cooling systems, such as the Vertiv™ Liebert® XDU and Vertiv™ Liebert® XDM, use liquid, rather than air, to cool IT equipment for better results.  A cool liquid is circulated to cold-plate heat exchangers embedded in the IT equipment. This provides extremely efficient cooling, since the cooling medium goes directly to the IT equipment rather than cooling the entire space. However, it requires specialized IT equipment with built-in liquid/fluid heat exchangers. Liquid cooling is most practical for high-density or performance compute applications where the heat is most intense.

Additional Thermal Management System Components

In addition to the indoor units and the heat rejection components, thermal management solutions often include other critical components or can work in conjunction with other pieces of hardware and software to optimize the cooling strategy. These components include:

• Control system: Most thermal management systems come with a basic level of control that allows data center personnel to set and monitor temperature, humidity, and airflow in the IT space. Advanced or intelligent controls can be used to network multiple units together in a space for both redundancy and efficiency purposes. When cooling units are networked, they don’t “fight” or work against each other, meaning some units heating and humidifying while others are cooling and dehumidifying, wasting energy in the process. Instead, networked units work together as a team to optimize cooling and energy performance. The networked units also increase system reliability. Should one unit experience trouble, the others in the team pick up the slack, offering an additional level of protection for IT equipment.
• Sensors: Strategic sensor placements in IT spaces help data center managers keep tabs on the exact temperature of the supply air for IT equipment. This data is used to ensure the thermal management system provides only as much cooling as needed, reducing energy consumption and preventing overprovisioning.
• Centralized and remote monitoring and alerting: The right monitoring hardware and software keeps data center staff up to date on the conditions in IT rooms, which is especially important in the case of remote or distributed facilities or when IT staff is working off-site. With the right solution, IT staff can monitor all of the sites within their network from one central facility. In addition, many solutions include notification and alarm systems that alert team members to component failures or environmental conditions that may be moving out of the specified range of operation, so they can be proactive in addressing situations before a problem occurs.

What are some of the most important features in a data center-grade thermal management solution?

While cooling systems need to work reliably, they are also expected to work as efficiently as possible. IT thermal management systems account for about 38% of total energy consumption in a typical data center. It’s imperative to choose a precision cooling or thermal management system that is built for both reliability and efficiency.   

Some features to look for include:

• Variable capacity fans and compressors. Components that can adjust to actual conditions in the room to provide only as much cooling and airflow as needed are key to controlling energy usage and spend to ensure sustainability. For example, variable speed fan technologies can automatically modulate up and down, from 25-100% depending on the system. By matching airflow output to the load requirements in the space as opposed to operating at peak load 100% of the time, these fans can reduce fan energy consumption by as much as 76%.
• Dual compressors and power supply for redundancy. Precision air conditioning or thermal management systems should be engineered to provide around-the-clock operation and to protect against potential component failure. Look for built-in redundancy for key components. Networking units together as a team can also help ensure 100% availability of the equipment.
• Economization systems. Optional economization systems allow cooling units to take advantage of cooler outside air temperatures to aid in meeting indoor cooling requirement. For example, a pumped-refrigerant economizer can be used on an air-cooled system, whereby a small pump circulates cold refrigerant when outdoor ambient temperatures are low enough. Economization is also an option in water-cooled and glycol-cooled direct expansion systems when the water or glycol temperature drops due to cold outdoor ambient temperatures. Regardless of the type of system, economization reduces the amount of mechanical cooling or refrigeration necessary, thus reducing energy consumption significantly.
• Optional humidifier. To avoid electrostatic discharge that can damage servers or to boost the cooling capacity when using an evaporative cooling system, a humidifier can add needed moisture to a data center or IT space.
• High efficiency air filtration. This promotes air cleanliness in the space and keeps dust and debris from compromising the performance of sensitive IT equipment.

Choosing the right thermal management solution for your application

As this article illustrates, there are many factors to consider when selecting a precision cooling or IT thermal management solution. However, in most applications, the choice boils down to three key factors:

1. Load in the room. The cooling system must be sized to handle the load in the room. The load is the sum of all the IT equipment in the room, plus lights, and any loads caused by the introduction of outside air or heat migration through external walls. Thermal management equipment comes in a range of capacities. Vertiv offers systems ranging from 2.5 to 400 kW to accommodate all types of applications.
2. Space size and logistics. Cooling a large data center is obviously a different challenge than cooling a small network closet, and the space itself will dictate the type of solution you choose. Large, traditional data centers with raised floors can accommodate larger precision air conditioning units that can be installed on the perimeter of the room or in the rows. Smaller IT rooms may need a unit that can be mounted in the rack or on the ceiling.
3. Heat rejection method. How you will remove heat from the space is usually the defining factor in the choice of cooling system. The best option depends on what building systems are available (Can you tie into an existing chilled water plant or cooler tower system?) and the architecture of the facility (Is it possible to reject the heat outdoors?) Floor space and available outdoor and roof space also matter. Finally, if you have a very high-density application, it may be worth looking into emerging liquid cooling solutions that are well suited to these environments. Considering all of these issues, as well as efficiency, operating cost, and environmental concerns, will help dictate what type of precision cooing or IT thermal management system will work best in your space.

The following chart can help you compare the different types of solutions available and provides examples of each for your consideration:

At-a-Glance Comparison of IT Thermal Management Systems

Form Factor Coolant Requirements Advantages Considerations Ideal For Products

Chilled Water

Indoor air handler(s) connected to a building chilled water plant

Chilled water

• Building chilled water plant
• Water source
• Water treatment

• Leverages existing infrastructure
• Reduces investment and space required for heat rejection

• Redundancy strategy to safeguard against chiller failure
• Operational costs and environmental considerations due to water consumption and treatment

• Large data centers
• High-rise building or other spaces where heat can’t be rejected outside

Liebert® CW

Liebert® PCW

Liebert® Mini-Mate

Air-Cooled Direct Expansion

One-to-one indoor CRAC unit with outdoor heat rejection

Outdoor ambient air

None

• Self-contained
• Efficient; low number of heat transfers
• Reliable and easy to maintain
• Optional pumped refrigerant economization 

• One-to-one indoor to outdoor unit ratio
• Long piping lengths (greater than 200-300 feet)
• Requires ample pumping and heat rejection space

Small to mid-size rooms

Liebert® DS

Liebert® DSE

Liebert® PDX

Liebert® Mini-Mate

Water-Cooled Direct Expansion

Indoor CRAC unit connected to a warm building water loop

Process water

• Cooler tower system or other building water system
• Water source
• Water treatment 

• Multiple indoor CRAC units can be connected to a common water loop
• Leverages existing infrastructure
• Reduces investment and space required for heat rejection
• Economization options 

Operational costs and environmental considerations due to water consumption and treatment

• Small to mid-size rooms
• High-rise building or other spaces where heat can’t be rejected outside

Liebert ® DS

Liebert® PDX

Liebert® Mini-Mate

Glycol-Cooled Direct Expansion

Indoor CRAC unit(s) connected to an outdoor fluid cooler

Warm water/ glycol antifreeze solution

• Drycooler loop and pumping system
• Building water system
• Adequate roof space

• No water use
• Minimal water treatment
• Economization options 

Valuable roof space is needed to accommodate multiple heat rejection units

Small to mid-size rooms

Liebert® DS

Liebert® Mini-Mate

Liquid Cooling

Cool liquid is circulated to cold-plate heat exchangers embedded in IT equipment

Specialty liquid

Specialized IT equipment with built-in liquid/fluid heat exchanger

Highly efficient 

Space and cost associated with deploying dedicated liquid cooling infrastructure

• High-density applications
• High-performance computing applications

Liebert® XDU

Take control of your IT environment

Ultimately, a true and comprehensive thermal management system provides more than a way to collect and reject heat in an IT space. While precise temperature control — maintaining the temperature within one to two degrees — is not the issue it once was, thermal management continues to play a critical role in the operation of any data center or IT space. The right thermal management system, comprised of intelligent controls and advanced sensors, efficiency-enhancing features, and a monitoring solution, gives data center staff the ability to efficiently manage the environment and optimize equipment performance around the clock, safeguarding against system failure and costly downtime for the business. 

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