Key Takeaways

• CRAC vs CRAH comes down to how each unit generates cooling. A computer room air conditioner uses a direct expansion refrigeration cycle with a built-in compressor, while a computer room air handler relies on chilled water supplied from a central chilled water plant.
• Facility size and existing infrastructure typically decide the winner. CRAC units work well in smaller or standalone facilities without a chilled water plant, while CRAH units are the standard for larger data centers with centralized chilled water infrastructure already in place.
• Energy efficiency favors CRAH units, especially with free cooling. Because CRAH systems don’t rely on compressors, they generally use less energy and can take advantage of economization strategies that use outside air to reduce cooling costs.
• Neither option is universally “better.” The right choice depends on cooling load, facility size, climate, and how much you’re willing to invest upfront versus over the life of the system. Use the decision framework at the end of this guide to match the right unit to your facility.

Introduction

Keeping a data center at a stable temperature is not optional. It is the difference between hardware that runs reliably for years and hardware that fails prematurely, throttles under load, or triggers costly downtime. As server densities climb and IT loads grow more concentrated, the systems responsible for removing that heat have to work harder and smarter than ever before.

In the early days of data center cooling, facility teams could get by with a handful of standard air conditioners. As rooms filled with more equipment, the answer was often just to add more air conditioners and hope the room stayed balanced. That approach breaks down quickly once server densities climb, which is why purpose-built precision cooling equipment became the standard for computer room air management.

Two systems dominate this space: the computer room air conditioner (CRAC) and the computer room air handler (CRAH). Both are designed to remove heat from the computer room and protect sensitive equipment, but they get there through fundamentally different mechanical processes, and that difference has real consequences for energy costs, scalability, and long-term reliability. This guide breaks down how each system works, where each one performs best, and how to decide which technology is the right fit for your facility.

What Is a Computer Room Air Conditioner (CRAC)?

A computer room air conditioner is a precision cooling unit built specifically for data centers and other environments where equipment reliability depends on tight temperature and humidity control. It functions much like a traditional air conditioner, but with the added precision, monitoring, and redundancy that mission-critical spaces require.

CRAC units generate cooling through a direct expansion refrigeration cycle. Refrigerant inside the unit absorbs heat from the warm air pulled in from the computer room, then a compressor keeps that refrigerant in a cool state so it can continue absorbing heat. The excess heat collected in this process is rejected outside the space using ambient air, a glycol mix, or water, depending on the unit’s configuration. Once the air passes over the evaporator coils and gives up its heat, cool air is delivered back into the room to maintain a stable temperature and humidity level.

Because the entire cooling process happens within the unit itself, CRAC systems are considered self-contained. They do not require a separate chilled water plant to operate, which makes them a practical option for facilities that lack that infrastructure.

Core components of a CRAC unit include:

• Compressor: Drives the direct expansion cycle and keeps refrigerant in a cool state
• Evaporator coils: Where warm air gives up its heat before being recirculated
• Refrigerant: The chemical compound responsible for absorbing and releasing heat
• Condenser: Rejects the collected heat using ambient air, glycol, or water
• Air filters: Protect airflow and cooling capacity from dust and debris buildup
• Humidifiers and dehumidifiers: Common in many models to help regulate humidity level alongside temperature

CRAC units tend to work best in these scenarios:

• Smaller or standalone data centers without an existing chilled water plant
• Modular or edge computing facilities that need independent, self-contained cooling
• Sites where a simple, self-contained installation is a priority over long-term energy costs
• Environments requiring precise, localized temperature and humidity control in isolated rooms

Because CRAC systems rely on mechanical refrigeration rather than a shared chilled water plant, they generally offer a lower upfront investment and a more straightforward installation. The tradeoff is that compressors, refrigerant, and the other moving parts inside a self-contained unit require more regular maintenance to keep the system performing optimally over its lifespan.

What Is a Computer Room Air Handler (CRAH)?

A computer room air handler takes a different approach to data center cooling. Rather than generating cooling on its own, a CRAH unit depends on a building’s central chilled water plant to do the heavy lifting. The unit itself is essentially a fan and coil assembly, similar in concept to the chilled water air handling units found in large commercial buildings.

Here is how the process works. Warm air from the data center is drawn into the CRAH unit and passed over chilled water coils. As the air moves across these coils, heat transfers from the air into the chilled water, and that now-warmer water is returned to the central chiller plant to be cooled again before recirculating. The cooled, dehumidified air is then sent back into the computer room to maintain a stable temperature and humidity level.

Because a CRAH unit has no compressor or refrigerant cycle of its own, its main energy draw comes from the fan motors and control valves that regulate fan speed and water flow. This is a big part of why CRAH systems generally use less energy than their CRAC counterparts, particularly at scale.

Core components of a CRAH unit include:

• Chilled water coils: Where warm air transfers its heat into the water circuit
• Fans: Move air across the coils and regulate fan speed to maintain consistent airflow
• Control valves: Manage the flow of chilled water through the coils based on cooling demand
• Filters: Maintain air quality and protect coil performance
• Controls and sensors: Monitor temperature and humidity to keep conditions within a tight range

CRAH units tend to work best in these scenarios:

• Larger data centers with an existing chilled water plant already in place
• Facilities prioritizing energy efficiency and lower long-term operating costs
• Environments with variable or growing cooling loads that benefit from flexible fan-driven airflow
• Operations that plan to integrate advanced building management systems for centralized control

Because CRAH systems rely on chilled water rather than an onboard refrigeration cycle, they generally offer greater heat removal capabilities and improved efficiency at scale, especially in facilities where that chilled water infrastructure already exists. The tradeoff is that a CRAH unit cannot function without a properly maintained chilled water plant, which means its performance is only as reliable as the infrastructure supporting it.

Computer Room Air Conditioning vs. Chilled Water Cooling: The Core Mechanical Difference

At this point, the fundamental split between these two approaches to computer room air conditioning should be clear. CRAC units generate their own cooling using a direct expansion refrigeration cycle and a compressor. CRAH units rely on chilled water supplied from an external source. That single distinction shapes nearly every other difference between the two systems, from infrastructure requirements to energy costs to long-term scalability.

The table below breaks down the core mechanical differences side by side.

Feature	CRAC Units	CRAH Units
Cooling method	Direct expansion refrigeration cycle with refrigerant and a compressor	Chilled water circulated through cooling coils
Heat rejection	Ambient air, glycol mix, or water via a condenser	Returned to a central chilled water plant for re-cooling
Infrastructure required	Self-contained, no chilled water plant needed	Requires a connection to a chilled water plant
Primary energy draw	Compressor and fan motors	Fan motors and control valves only
Airflow control	Often simpler, with limited variability on older models	Regulate fan speed to match cooling demand precisely
Typical maintenance focus	Compressor servicing, refrigerant checks, coil cleaning	Water treatment, chilled water coils, fan inspections

The absence of a compressor is the single biggest factor behind why CRAH systems generally achieve a more efficient cooling cycle than CRAC systems. Removing the refrigeration cycle from the equation means less mechanical work happens inside the unit itself, which translates into lower energy costs, particularly as facilities scale up.

That said, this efficiency advantage only holds when the supporting chilled water plant is already in place and running efficiently. A CRAH unit is only ever as good as the infrastructure feeding it. Unlike CRAC units, which can be installed as a fully self-contained solution, a CRAH unit adds a layer of dependency that needs to be factored into any comparison of upfront cost versus long-term performance.

A few points worth keeping in mind:

• Both systems are capable of delivering stable conditions and precise humidity level control when properly maintained
• CRAC units offer simplicity and independence, at the cost of higher energy use per unit of cooling
• CRAH units offer better efficiency and greater heat removal capabilities, but only where chilled water infrastructure already exists or can be reasonably added
• Neither method is inherently more reliable. Reliability comes down to consistent maintenance, whether that means refrigerant and compressor upkeep or chilled water quality and control valve function

How Computer Room Air Moves Through the Facility

Understanding how CRAC and CRAH units generate cooling is only half the picture. Just as important is how that cooled air actually reaches the equipment that needs it, and how warm air makes its way back to the unit to be cooled again. Airflow management has a direct impact on cooling capacity, energy costs, and how evenly temperature is maintained across a data center.

Most computer room cooling systems, whether CRAC or CRAH, rely on a raised floor design to distribute air. Cool air is pushed into the space beneath the raised floor, then released through perforated floor tiles positioned in front of server racks. As that cool air moves through the equipment, it absorbs heat and is expelled out the back as warm air. That warm air rises into the room, gets pulled back into the CRAC or CRAH unit, and the cycle repeats.

This is where hot aisle and cold aisle containment becomes essential to getting the most out of either system. Without containment, cool air and warm air mix freely in the room, forcing the cooling unit to work harder than necessary to maintain temperature. With proper containment, cold aisles stay dedicated to supply air and hot aisles stay dedicated to return air, which helps optimize air circulation and keeps the unit operating closer to optimal performance.

A few airflow fundamentals that apply regardless of which unit type is installed:

• Raised floor plenum: Acts as a distribution channel for cool air beneath the server racks
• Perforated tiles: Control where and how much cool air enters each aisle
• Hot aisle and cold aisle containment: Physically separates warm air and cool air streams to reduce mixing and improve efficiency
• Return air path: The route warm air takes back to the CRAC or CRAH unit, which should be as direct and unobstructed as possible

As server densities climb, airflow management becomes even more critical. Higher server densities mean more concentrated heat loads within a smaller footprint, and even a well-matched CRAC or CRAH system can underperform if the surrounding airflow strategy has not kept pace with those increases in load. In practice, this means the choice between CRAC and CRAH should never be made in isolation from the facility’s broader airflow and containment strategy.

Where CRAC Units Perform Best

CRAC units are not simply the “smaller facility” option. They are the right fit in specific, well-defined scenarios, and understanding those scenarios helps clarify whether a self-contained cooling approach makes sense for a given facility.

CRAC units tend to be the stronger choice when:

• No chilled water plant exists on site. Without that infrastructure already in place, a self-contained system avoids the added cost and complexity of building out a chilled water loop
• The facility is small to mid-sized. CRAC systems are generally well matched to computer rooms and data centers with lower overall cooling loads
• Speed of deployment matters. Because CRAC units do not depend on external chilled water infrastructure, they can often be installed and brought online faster
• The site is modular or standalone. Edge computing locations, remote facilities, and single-room deployments frequently favor the independence a CRAC system offers
• Redundancy needs are moderate. CRAC units work well in environments that do not require the highest tier availability standards

A rough guideline for cooling load is that CRAC units are typically well suited to facilities with electrical IT loads under roughly 200 kilowatts, though this threshold varies by manufacturer, unit configuration, and room design. Facilities below this range often find that a chilled water plant is not worth the upfront infrastructure investment relative to the load being cooled.

It is also worth noting that CRAC systems, while mechanically simpler in terms of overall operation, contain more individual components susceptible to wear. Compressors, refrigerant, and evaporator coils all require regular attention. When properly maintained, CRAC systems can be highly reliable and deliver stable conditions consistently. When maintenance lapses, the compressor and refrigerant components tend to be the first areas where performance declines.

Typical facility profiles that favor CRAC units:

Facility Type	Why CRAC Fits
Small business server rooms	No chilled water infrastructure needed
Edge computing sites	Fast, independent deployment
Modular or containerized data centers	Self-contained design fits portable footprints
Telecom switching stations	Precise, localized humidity level and temperature control
Facilities without space or budget for a chiller plant	Lower upfront infrastructure investment

Where CRAH Units Perform Best

CRAH units are generally the technology of choice once a facility reaches a certain scale, or once a chilled water plant is already part of the building’s infrastructure. Understanding where CRAH systems earn their keep helps clarify why so many larger data centers standardize around this approach.

CRAH units tend to be the stronger choice when:

• A chilled water plant already exists. If the infrastructure is in place, a CRAH unit lets a facility take full advantage of it rather than duplicating cooling capacity with standalone compressors
• The facility is large or growing. CRAH systems scale efficiently, as additional units can be added to draw from the same central chilled water plant
• Energy efficiency is a priority. Because CRAH systems do not rely on compressors, they typically use less energy per unit of cooling delivered, especially at higher loads
• High availability and redundancy are required. Centralized chilled water infrastructure often supports the kind of tiered redundancy that larger, mission-critical facilities demand
• Free cooling and economization are part of the strategy. CRAH units are far better positioned to take advantage of outside air and waterside economization than CRAC units, which is covered in more detail in the next section

As a rough guideline for cooling load, CRAH units generally become the more cost-effective option once electrical IT loads climb to roughly 200 kilowatts or more. Below that threshold, the cost of building and maintaining a chilled water plant can outweigh the efficiency gains. Above it, the economics tend to favor CRAH systems more clearly as load and facility size increase.

CRAH units also tend to have fewer moving parts within the unit itself compared to CRAC systems, since there is no compressor or refrigeration cycle to maintain on site. That said, this does not mean less maintenance overall. It shifts the maintenance burden toward the chilled water plant, water treatment, and control valve upkeep rather than eliminating it.

Typical facility profiles that favor CRAH units:

Facility Type	Why CRAH Fits
Large enterprise data centers	Chilled water infrastructure already supports scale
Colocation facilities	Efficient cooling across many tenant environments
Facilities with tiered redundancy requirements	Centralized chilled water supports higher availability standards
Data centers pursuing aggressive energy efficiency goals	Lower energy draw per unit of cooling capacity
Campuses with an existing central chiller plant	Cooling capacity can scale without duplicating infrastructure

Energy Efficiency and Free Cooling Considerations

Energy efficiency is often the deciding factor once a facility has ruled out the more obvious constraints like chilled water plant availability or facility size. This is also where the gap between CRAC and CRAH systems becomes most pronounced, largely because of how each technology interacts with outside air.

Why CRAH units generally have the efficiency edge

CRAH systems achieve a more efficient cooling cycle than CRAC systems for one core reason: they eliminate the compressor. A compressor is mechanically demanding and consumes a significant amount of energy to keep refrigerant in a cool state. Because CRAH units skip that step entirely and rely on chilled water instead, their energy draw comes almost entirely from fan motors and control valves, which is a meaningfully smaller load.

This becomes even more significant at scale. In smaller facilities, the efficiency gap between CRAC and CRAH may not justify the cost of chilled water infrastructure. In larger data centers, that same efficiency gap compounds across dozens or hundreds of units, translating into substantial energy cost savings over the life of the system.

How free cooling and economization change the equation

The biggest efficiency advantage CRAH systems offer is their ability to integrate with free cooling, also called economization. Free cooling uses outside air, either directly or indirectly through the chilled water loop, to reduce or eliminate the need for mechanical cooling when ambient conditions allow.

Here is how that works in practice:

• Waterside economization: When outside air temperatures are cool enough, a heat exchanger can cool the chilled water loop directly, reducing or bypassing the need to run the central chiller’s mechanical cooling
• Airside economization: Outside air is filtered and introduced directly into the data center to supplement or replace mechanically cooled air, when climate and air quality conditions allow
• Climate dependency: Facilities in cooler climates or regions with significant seasonal temperature swings see the greatest benefit, since more hours of the year fall within the range where free cooling is viable

CRAC units, by contrast, are built around a self-contained direct expansion refrigeration cycle and generally cannot take advantage of free cooling in the same way. Because the entire cooling process happens within the unit using refrigerant and a compressor, there is no practical pathway to substitute outside air for mechanical cooling. This is one of the clearest examples of why CRAH systems tend to pull ahead on long-term energy costs, even though CRAC systems may still make sense from an upfront cost and simplicity standpoint.

A quick comparison of efficiency factors:

Efficiency Factor	CRAC Units	CRAH Units
Core energy draw	Compressor plus fan motors	Fan motors and control valves only
Free cooling capability	Generally not possible	Can integrate waterside or airside economization
Efficiency at scale	Diminishes as facility grows	Improves as facility grows
Climate sensitivity	Minimal impact on efficiency	Significant impact, cooler climates see greater savings

It is worth noting that energy efficiency should never be evaluated in isolation. A facility with a smaller cooling load, no existing chilled water plant, and no near-term expansion plans may still come out ahead financially with a CRAC system, even with its higher per-unit energy draw, simply because the infrastructure investment required for CRAH does not pencil out at that scale. Efficiency is one input into the decision, not the only one.

Choosing the Right Air Conditioner for Your Facility: A Decision Framework

There is no universal answer to the CRAC vs CRAH question. The right choice depends on how several factors intersect at your specific facility. Use the framework below to work through the decision systematically rather than relying on rules of thumb alone.

Step 1: Assess your existing infrastructure

• Does a chilled water plant already exist on site or nearby?
• If not, what would it cost to install one relative to your facility’s cooling load?
• Is there available space and budget for chiller infrastructure, or does a self-contained solution make more sense?

If a chilled water plant is not already available and unlikely to be justified by your load, a CRAC system is typically the more practical starting point.

Step 2: Calculate your current and projected cooling load

• What is your current electrical IT load, and how does it compare to the rough 200 kilowatt threshold discussed earlier?
• What growth do you expect over the next three to five years?
• Will additional server density push your facility past the point where a self-contained system remains cost-effective?

Facilities expecting significant growth often benefit from planning for CRAH infrastructure early, even if current load could still be handled by a CRAC system.

Step 3: Factor in your climate and free cooling potential

• Does your region see enough cool weather hours annually to make economization worthwhile?
• Would waterside or airside free cooling meaningfully offset energy costs given your climate?
• Are you in a climate where the efficiency gap between CRAC and CRAH is large enough to justify the infrastructure investment?

Step 4: Weigh upfront cost against long-term energy costs

• Can your budget absorb the higher upfront investment a chilled water plant requires?
• Would the long-term energy savings from a more efficient cooling cycle offset that investment within an acceptable timeframe?
• Does your organization prioritize lower capital expenditure now or lower operating costs over time?

Step 5: Consider availability and redundancy requirements

• What tier or availability standard does your facility need to meet?
• Does your redundancy strategy favor the centralized approach that chilled water infrastructure supports, or the independence of self-contained units?

A simplified decision summary:

If your facility has…	Consider…
No chilled water plant and a smaller cooling load	CRAC units
An existing chilled water plant and larger cooling load	CRAH units
Strong energy efficiency and sustainability priorities	CRAH units
A need for fast, independent deployment	CRAC units
Significant projected growth	CRAH units, planned early
A favorable climate for free cooling	CRAH units
Moderate redundancy needs and budget constraints	CRAC units

In many cases, the right answer is not exclusively one system or the other. Some facilities use a hybrid approach, deploying CRAC units in smaller or standalone rooms while relying on CRAH systems for the core data center, balancing redundancy, cost, and efficiency across different parts of the same facility.

Whichever direction fits your infrastructure and goals, the underlying priority stays the same: reliable, well-maintained cooling that keeps your equipment operating at optimal performance and protects your facility from the downtime that comes with unstable conditions.

Ready to Optimize Your Data Center Cooling Strategy?

APA Technologies works with commercial and institutional facility teams across New England to evaluate cooling infrastructure and match the right equipment to your data center’s specific load, budget, and growth plans. Contact our team today to talk through your cooling strategy.