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CRAC and CRAH Cooling Unit HVAC Differences Explained

Large data center

Last Updated on April 6, 2022 by Alterum Data Center Experts

Are you currently designing your data center and trying to determine which cooling system is best for your enterprise? Your air conditioning system is just as critical to your server performance as the servers themselves. 

Data centers need year-round 24/7 cooling in conditions where the high cooling intensity per square foot is a challenging task to tackle. Enterprise servers require perfect temperature, humidity, and airflow conditions to perform. If equipment fails because of overheating, condensation, or other complications, it can cost the enterprise dearly. 

We’ll explain the main differences between CRAC and CRAH cooling HVAC units. We’ll cover the benefits and drawbacks of each system and recommend systems based on the size of your data center. 

Related Link: 10 Best Data Center Migration Practices [2022]

Defining Characteristics of Computer Room Air Conditioner (CRAC) HVAC Units

A CRAC HVAC unit is similar to a home air conditioning unit that utilizes refrigerant and a compressor to cool a room. Designed to cool data centers, CRAC units blow air over a cooling coil while a compressor works to keep the refrigerant within the coil cool. Then the CRAC unit expels the hot exhaust by using water, air, or a glycol mix.

The CRAC unit is usually positioned opposite the hot aisle to cool data centers using a CRAC system. It absorbs the hot air and can cycle it through to blow cool air through the perforations in the raised floor to cool the servers from below. This also helps pressurize the space below the floor. While most CRAC units have an on/off switch, some newer models can vary the airflow. 

Benefits of CRAC HVAC Units

There are several benefits to a CRAC unit:

  • Maintains the air distribution, humidity, and temperature of a data center.
  • Absorbs heat from servers and then blows cool air over the servers to cool them down.
  • Works well in small data centers that don’t need to scale quickly.
  • Can add a unit as demand requires.
  • Space-saving compared to CRAH units because it is a stand-alone unit.
  • Can operate in all outdoor temperature conditions, both cold and hot.

Drawbacks of CRAC HVAC Units

There are a few drawbacks to using a CRAC HVAC system:

  • Consumes a ton of power: CRAC units typically 15% of the energy needed for auxiliary equipment. 
  • Struggles to adjust to fluctuating temperatures: Because most CRAC units have one mode, they struggle to adjust to the temperature fluctuations in the room.
  • Difficult to scale for large data centers: As your server room grows, so does your need for more CRAC units. This limits how many servers you can have in your room. 
  • Wrong sizing of the CRAC unit can cause problems: Condensation and static discharge occur when the CRAC unit is too big. Under-sized CRACs can create thermal over-runs.
  • Installation limitations: Must be configured in specific ways to optimize airflow, limiting how and where components are placed. 
  • Has more parts that can need maintenance: CRAC units have many components that need servicing and monitoring for optimal performance. These components need to be serviced to maintain adequate cooling levels. 

To ensure your data center has the correct size and number of CRAC units, you should consider talking to data center experts. The layout also plays a critical role because of its high density, making CRAC units ineffective in large data centers.

Need help designing your data center? Learn more about our data center design services.

Related Link: Data Center Capacity Planning [Ultimate Guide]

High density data center

Defining Characteristics of Computer Room Air Handler (CRAH) HVAC Units

A CRAH HVAC system blows air over cooling coils, similar to a CRAC system. But the main difference is these cooling coils are filled with chilled water instead of refrigerant. The chilled water is stored in a separate chiller. So when hot air enters the CRAH unit, it transfers the heat to the water, and then the water returns to the chiller. 

CRAH units can also vary their controls and outputs to stabilize fluctuating temperatures and humidity levels in the data center. CRAH can adjust fan speeds to update dynamically as the room’s temperature changes. This creates more stable temperatures and fewer chances of creating condensation or thermal overruns. 

Benefits of CRAH HVAC Units

The CRAH HVAC system has many benefits to consider:

  • Variable controls that adjust to the fluctuating temperatures.
  • Suitable for larger data centers and server farms. 
  • Provide reduced summer demand and longer economizer hours because water is cheaper than refrigerant. 
  • Very reliable compared to a CRAC unit.
  • Can leverage the water storage that is already cold rather than run full time during peak energy rates.

Drawbacks of CRAH HVAC Units

  • More expensive: CRAH systems can cost significantly more, which isn’t cost-effective for smaller data centers. If water is expensive in your area, then the water costs may offset the electricity cost savings. 
  • Limited operating hours: If outdoor temperatures are above 35 degrees F, the system cannot operate efficiently.
  • Space hog: The chiller units are not small and generally require significant space to run efficiently.
  • High maintenance: This could become a fire hazard if not properly installed or maintained.
Smaller data center

When You’ll Want to Install a CRAC vs. CRAH Unit

A CRAH system will be the most ideal in larger data centers or if you foresee substantial growth and need more scalability. But these systems will cost more, and if water is expensive in your area, this might be a costly system to install. 

The CRAC HVAC units are great for smaller data centers, but you’ll want to find units with fan controls similar to a CRAH unit for better temperature and humidity management. 

Layout and maintenance are critical for maintaining performance levels and optimal cooling with both systems. If you need help designing your data center, you should consider hiring data center installation experts that can optimize your HVAC solution for your location. 

Alterum Technologies specializes in designing, planning, and monitoring to maximize the capability of your data center to meet your enterprise’s needs now and in the future. We offer cutting-edge solutions to meet your power needs, no matter its scale.

Want to leverage our expertise when designing your data center for optimal performance and cost savings? Contact Alterum to book an appointment with one of our data center planning experts.

Related Link: Improving Data Center Energy Usage & Efficiency

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