CRACs and CRAHs: A Complete Guide to Cooling Your Data Centers and Computer Rooms

You’re keeping your average data center temperature within 80 to 115 degrees Fahrenheit (26.6 to 46.1 degrees Celsius). That’s great, but are you using the best cooling system for your needs? Read on as I compare 2 common cooling systems, CRAC and CRAH. You’ll get to know how each works along with the main differences. This will help you decide which system best suits your cooling needs.

 Image of server racks in a room.
Chill, you’re in a data center!

First, I’ll start by describing how a CRAC cooling system works.

CRAC: Cooling with Compressors

Computer Room Air Conditioners (CRACs) are advanced cooling systems designed to stabilize a data center’s temperature. They constantly monitor the temperature, humidity, and heat distribution across the entire room. They also decrease your overall power consumption levels. 

A CRAC consists of the following components:

  • Refrigerant
  • Air filters
  • Compressors
  • Evaporator coils

How do these parts work together? Here’s a step-by-step process showcasing a CRAC cooling system’s efficiency.

Step 1

In a CRAC cooling system, you place the computers facing the air intake systems.

Step 2

The CRAC system pumps cold air through perforated tiles to cool the computers. Due to the airflow direction, the cold air pushes the hot air to the hot aisle opposite the computers. 

Step 3

The hot air is then pulled from the hot aisle and cooled via a refrigerator compression cooling cycle. 

Step 4

Finally, the cold air passes through the tiles again to cool your data center. 

This simple process increases your data centers’ cooling efficiency while lowering the process’s cost. 

Next up, we’ll talk about the Computer Room Air Handler (CRAH) cooling system and how it works. 

CRAH: Cooling with a Chiller

The CRAH cooling system also controls a computer room’s temperature like a CRAC. That said, you’ll discover some differences between the two later in this article. 

For now, let’s look at the system’s components and how they work together. A CRAH’s main components include:

  • Air filters
  • EC fans
  • Cooling coils
  • Water chiller system

A CRAH follows this 4-step operational process.

Step 1

The CRAH cooling system takes the hot air in a room and sends it to a cooling coil filled with chilled water

Step 2

Then, a water chiller system circulates the cold air to the cooling coil, which uses a direct expansion mechanism to cool the air. 

Step 3 

The cold air then goes back into the room.

Step 4 

Finally, the EC fans disperse the cool air in the room. The fans serve a dual purpose since you can also use them to maintain static pressure. This allows you to control both the humidity and the temperature.

Now that you know how each system operates, let’s compare CRAC and CRAH.

5 Differences between CRAC and CRAH

I’ll compare both systems based on 5 factors: cooling mechanism, maintenance, granular control, efficiency, and room size. 

1. Cooling Mechanism

How a cooling system works has a bearing on its performance and efficiency. 

CRAC is more of a mechanical refrigeration system. In other words, it’s more like an air-conditioning system you use at home and is often self-contained. This effective system works in any HVAC layout

CRAH, alternatively, uses a water chiller system and fans. It requires under-floor plumbing that feeds water to the system. This system is also effective in any HVAC layout, but you must have the underlying plumbing system in place for it to work. 

Go for CRAH if you already have a good plumbing system in place, or you can easily construct one. Otherwise, CRAC is the better choice.

2. Maintenance

Maintaining the cooling systems must be simple and cost-effective from an operational standpoint. 

CRAC cooling systems contain many parts that work with each other. This equates to more maintenance and a higher possibility of parts failing from time to time. You’ll need a regular maintenance schedule to keep CRAC cooling systems functioning at optimal levels. 

CRAH cooling systems have fewer parts, so they don’t need maintenance as much as CRAC. CRAH requires excellent plumbing systems, though, which could be a downside. Unless the plumbing is efficient, the water flow won’t be consistent. This, in turn, impacts the cooling coil’s temperature

CRAH is a good choice if you have a plumbing system due to its simpler maintenance requirements. If you opt for a CRAC cooling system, you must have a proper maintenance schedule.

Image of a group of miniature workers assembling large mechanical parts.
Maintenance can be expensive for cooling systems.

3. Granular Control

For optimal temperatures, your performance boils down to optimal control. This helps you reach your ideal temperatures while reducing energy costs. Not all cooling systems offer broad granular control, though.

CRAC cooling systems are simpler systems with only one operational mode. Their parts work mechanically, so you have less flexibility to change. This means you also can’t control cooling temperatures easily. 

CRAH cooling systems have simple parts which you can easily move around. In return, you have fine control over the temperature settings

Go for a CRAH cooling system to have more control over your temperature.

4. Efficiency

Your cooling system’s efficiency has a direct impact on the temperatures of your data centers. 

CRAC’s use of refrigerators and compressors makes them less efficient in cooling when compared to CRAH. 

In turn, CRAH cooling systems use a highly efficient cooling cycle. These systems are also more efficient in removing heat and distributing cool air around the room. 

The CRAH cooling system ranks better for efficient cooling. 

5. Room Size

Your computer room’s size affects your cooling system’s efficiency. CRAC cooling systems work well in data centers with less than an average of 200 kW of electrical load per day. CRAH cooling systems work best for computer rooms with more than 200 kW load

Go for CRAH if you’re operating larger data centers and CRAC for smaller data centers.

MechanismSimple and mechanicalHighly flexible
Advanced Plumbing SystemDoesn’t require oneRequires one
Maintenance EffortsMoreLess
Granular ControlNoYes
Room SizeLess than 200 kW electrical loads per dayMore than 200 kW electrical loads per day.
Caption: CRAC vs CRAH, which will it be?

At this point, you should have a clearer idea of which cooling system will work best for your needs. Let’s move on to discuss some factors you should consider when installing CRAC and CRAH.

CRAC and CRAH Cooling Systems: Implementation

Installing CRAC and CRAH systems requires elaborate planning and implementation. Follow this 3-step guide to help you plan your installation. 

Step 1: Evaluate Your Cooling System

Assess your existing cooling system by evaluating its efficiency and performance. Check if you want to replace it for better performance or a decreased energy footprint. 

In particular, take time to understand whether you want to replace certain parts or the entire system. For example, if it’s a faulty thermostat you need to fix, you shouldn’t revamp the entire system. 

This will help save you time and money

Step 2: Get An Expert Opinion

It’s always good to brainstorm ideas with experts. They bring in a lot of experience and can also identify problem areas you might miss

Talk to your HVAC engineers if you want to create or revamp an HVAC configuration. You must also discuss with them how to put a plumbing system in place if you’re going for a CRAH cooling system. 

Experts ultimately help you design and implement the most efficient cooling system for your needs.  This will ensure you have a long-lasting, efficient, and hassle-free system. 

Infographic of an arrow in red depicting hot air points away while a blue arrow depicting cold air pointing in.
Cold air in, hot air out.

Step 3: Build an HVAC System

Once you’ve talked to the experts and planned your HVAC, it’s time to implement it. 

Keep in mind your current and future cooling needs while building it. You should also research and talk to different companies that sell cooling systems. Gather the specifications of each and compare them with your requirements. You’ll then see which system best fits your needs.

You can also consider a few additional aspects to streamline your cooling operations. For example, you can configure your power and plumbing systems to ensure uninterrupted operations. 

This implementation will help you create a scalable system. You can later expand it to meet your growing business needs. In the end, don’t forget to check your backup systems to ensure you have uninterrupted access. 

Following a systematic approach, like the one I mentioned above, will bring you closer to acquiring a high-performance cooling system. In turn, this can reduce your computer’s wear and tear, on top of improved performance and efficiency. As an added value, you also benefit from saving on energy costs

The Bottom Line 

A well-functioning cooling system is crucial to maintaining high levels of efficiency at data centers. CRAC and CRAH offer different operational modes, so you want to choose the system that best suits your cooling needs. One defining factor, though, is room size since CRAC only works for data centers with loads lower than 200kW. 

Have more questions about the CRAC and CRAH cooling systems? Check out the FAQ and Resources sections below!


How does cooling work in an HVAC system?

The cooling system is complex in an HVAC system since the focus is on removing hot air. The two broad types of cooling systems are Computer Room Air Conditioning (CRAC) and Computer Room Air Handler (CRAH) systems. Both dissipate hot air, but in different ways. While the CRAC cooling system uses a refrigerant, the CRAH cooling system uses chilled air.

Is a cooling system necessary for data centers?

Yes, a cooling system is essential in data centers. Today’s computers tend to give out a lot of heat. In turn, this increases their wear and tear. It also reduces their efficiency and performance over time. A good solution for all these problems is having an HVAC cooling system in place.

I have a large data center. Should I go for a CRAC or CRAH cooling system?

If your data center electricity consumption is more than 200 kW per day, go for CRAH. That said, a CRAH cooling system requires advanced plumbing, which isn’t always efficient or feasible. In this case, and if your electricity load is lower than 200 kW per day, go for a CRAC cooling system. 

Is CRAC more energy-efficient than CRAH?

Not necessarily. They may consume more or less the same amount of energy. The main difference is in the way they work. A CRAC cooling system has many components and can require high maintenance. It’s also highly reliable. That said, a CRAH cooling system may not require extensive maintenance, but it does require an efficient plumbing system.

Do CRAC and CRAH cooling systems use humidifiers?

Most CRAC and CRAH cooling systems in the market today don’t have internal humidifiers. Instead, they rely on external standalone humidifiers. This aims to reduce maintenance costs and hassles. 


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