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CRAC design upgrades simplify HVAC maintenance

CRAC/CRAH hardware updates make data center cooling more efficient. And these new systems are easier for admins to maintain and they reduce dust accumulation across infrastructure.

Over the past 10 years, vendors have simplified maintenance for computer room air cooling and heating systems with new motor types, fewer moving parts, reduced humidifier requirements and more sensors for predictive maintenance.

These systems help prevent overheating, regulate temperature and allow facility teams to distribute air and water throughout infrastructure at scale. Computer room air conditioners (CRACs) use compressors for cooling and computer room air handlers (CRAHs) use water from a central chiller, but the hardware and maintenance changes apply to both options.

Motor and fan hardware get an upgrade

The biggest upgrade for computer room air units are newer electronically commutated (EC) motors that use external rotors with concentric direct drive fans. They bring energy efficiency, variable speed and smaller size for cooling and heating operations. These fans are at least 30% more energy efficient than conventional motor and belt drives of the same capacities.

EC-driven fans are smaller, so admins can mount them to optimize air discharge. Admins can even place these fans under the floor, which directly discharges air in a wider pattern. This eliminates the high velocity air plumes that cause uniform cooling challenges.

The motors for EC fans inherently use variable speed. Organizations save energy when all air conditioners, including redundant units, run simultaneously at reduced speed and don't cycle on a schedule. Setups that double fan speed multiply power draw by a factor of eight; halving fan speed reduces power draw by 87%.

EC motors are electronic, but even with built-in protections they are vulnerable to sharp voltage spikes, and low voltage can shut them down. Admins must consider regulation or protective devices where incoming power is poor.

These motors remove belts, pulleys and bearing hardware requirements, which eliminate the belt dirt and grime that causes many CRAC maintenance problems. The motors, cooling coils, air discharge and unit insides are also cleaner, because sealed EC motor bearings don't need lubrication, which eliminates lubricant splatter.

Filter replacement still a necessity

Cleaner CRACs mean less dirt blows into the data center and accumulates under raised floors and in server filters, but replacing filters is still important. Most CRACs have pressure switches to shut down units if dirty filters impede airflow, but variable speed fans change pressure constantly, which makes those switches unreliable.

Some manufacturers now offer optional differential pressure sensors to solve pressure switch issues, and they're standard on many in-row units. It's still best for admins to regularly change filters and keep the data center clean. This means admins should unpack equipment outside the data center, use foot wipe pads to keep shoes clean, mop damp floors and use a data center cleaning service once a year.

Sensors help streamline maintenance and vendor service

Service plans have changed minimally, except vendors don't need to check belts, pulleys and bearings, and cooling coils stay clean longer. Vendors measure motor current because organizations still expect it for reporting, but it's not a particularly useful metric with newer CRAC units. This is because EC motors can run at variable speeds, and certain offerings have sensing circuits to adjust airflow as necessary.

As CRAC sensor counts continue to increase, along with accumulated data, service personnel can find easier ways to troubleshoot issues or perform root cause analysis. Facilities teams can also access some of this data for reporting and general maintenance.

Some data center infrastructure management vendors say AI can predict impending failures from this data, but the sensors in CRACs are general purpose and don't provide enough information to be useful for AI models. Plus, organizations need vibration sensors for AI workflows and the costs and recalibration requirements of near-laboratory quality accelerometers are prohibitive.

New humidity guidelines change infrastructure needs

The updated CRAC and CRAH units and ASHRAE guidelines now make it unnecessary for every CRAC to have a humidifier that directly supports the unit. ASHRAE TC 9.9 currently recommends admins control humidity with dew point measurements, rather than using relative humidity.

Many CRAC and CRAH units on the market do not use internal humidifiers, but rather rely on standalone ultrasonic units in the data center. Regardless of humidifier type -- steam canister, infrared and ultrasonic -- facilities teams should use well-filtered water, preferably deionized, to reduce maintenance, maintain low humidity settings and save energy.

Retrofit options for CRAH and CRAC designs

Vertiv, Stulz and Data Center Resources are a few vendors that offer retrofit kits to replace conventional motors and blowers with EC motors and fans in legacy air conditioners.

The resulting energy savings on CRAHs can yield an ROI of a few years or less. CRACs don't fare as well with retrofit options because most have constant capacity compressors. If admins reduce fan speed but don't change the variable capacity compressor speed, they can cause coil freezing and shutdowns.

Organizations can also add variable frequency drives (VFDs) to most conventional CRAH and CRAC motors at less cost than EC fans to save energy. But VFDs are relatively large, have shorter life expectancies than the motors they support and may require harmonic line filters.

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