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HOT AISLE/COLD AISLE

Hot aisle/cold aisle cooling systems are designed to separate hot exhaust from cold intake air.

Hot aisle/cold aisle cooling systems are designed to separate hot exhaust from cold intake air. Cabinets located on both sides of the cold aisle draw cold air through their front intakes, using it to take heat away from the equipment. Hot exhaust exits through cabinet rears and is directed to CRAC/CRAH units, which remove the heat and redistribute air to the cold aisles.

Playing a crucial role in airflow management, hot aisle/cold aisle configurations provide numerous benefits. By separating hot and cold air, the energy required to maintain the optimal data center temperature is minimized—allowing facilities to significantly reduce their utility costs. However, it is important for managers to understand that hot aisle/cold aisle designs are typically only able to accommodate heat dissipations between 3-5 kW. Once rack densities reach 5 kW and above, the system can no longer compensate for the increased heat loads. According to multiple outside studies, most hot aisle/cold aisle solutions only utilize 40 percent of the available cooling capacity, while 10 percent of system racks still experience hot spots—which can result in equipment overheating and system failures.

Processing power and the speed at which crucial networking equipment runs is steadily increasing to keep up with user application demands. Through technology advances, the size of these electronics is shrinking—resulting in greater board population density and higher power consumption. This yields increased heat generation throughout the data center where equipment is housed and operated. High heat levels can damage networking equipment and potentially eliminate a company’s ability to effectively process, communicate and store information. Implementing the proper cooling solution will not only protect data centers from costly damage, but also ensure continuous access to company data and communications in an economically and environmentally responsible way.

Cooling solutions have become more sophisticated—providing new methods for improving cooling while enhancing overall efficiency to adapt to changing networking equipment and data center designs.

Data center managers can select and implement the ideal solution that adequately addresses individual cooling requirements by understanding the evolution of modern cooling solutions, along with their advantages and disadvantages.

Choosing the appropriate cooling strategy consists of more than simply selecting the right design. Applying the appropriate cooling configuration also requires considering the total-cost-of-ownership (TCO) requirements. Cooling TCO costs are not limited to capital expenses associated with purchasing and implementing cooling equipment. Data center managers must also include operational costs and additional design features that can lead to significant savings over the life cycle of equipment.

DIVERSE COOLING CONFIGURATIONSCabinet configurations are available in a variety of options, ranging from simple and inexpensive to costly and complex. The goal of each configuration is the same: help deliver the necessary amount of cool air to each server in the most efficient means possible.

DATA CENTER DESIGN AND DEVELOPMENT CONSIDERATIONS

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Data Center Design and Development ConsiderationsCHIMNEY CABINET COOLINGChimney cabinet cooling solutions consist of a cabinet with top ductwork, which directs hot exhaust air to an above drop ceiling or ductwork that further directs the airflow to the intakes of the CRAC/CRAH unit. Studies have shown that chimney configurations successfully extract heat loads up to 20kW. By providing a direct airflow path for hot air, chimney cabinets perform crucial airflow management—removing heat from the cabinet or aisle and reducing wasted cold air by 99 percent with less than 1 percent of hot air/cold air mingling.

PlenumExtension

CRACUnit

RAISED FLOOR

DROP CEILING

Cool Air from CRAC Unit

Hot Air from Server Cabinets

78° F

55° F

ServerCabinets

Chim

ney

Passive cooling (chimney) cabinets are optimal for containing hot air and directing it back to the CRAC unit.

Numerous outside studies show that the chimney method lowers cooling system costs by at least 25 percent. Additional cost-saving benefits associated with chimney cabinets include: low capital costs, little to no maintenance and fewer CRAC/CRAH units required.

CONTAINMENT SYSTEMSRather than simply separating cold and hot airflow, containment systems erect a barrier to segregated airflows—preventing them from mixing, which reduces energy costs, minimizes hot spots and improves the data center’s carbon footprint. These systems are designed to enclose the hot or cold aisle through the use of aisle-way doors, roof panels and internal sealing within the cabinets. Containment systems offer two cooling options: cold aisle containment or hot aisle containment.

In a cold aisle containment configuration, the cold air is enclosed within an aisle and hot air is prevented from entering the aisle, ensuring that the equipment will only use cold air for cooling.

In a cold aisle containment configuration, the cold air is enclosed within an aisle and hot air is prevented from entering the aisle, ensuring that the equipment will only use cold air for cooling. The cold air can be supplied either by perimeter CRAC/CRAH units—typically through a raised floor—or internally through a cooling source located between or above the racks.

Hot aisle containment solutions are designed to contain hot airflow and direct it back to the cooling units, via overhead ductwork or with in-row cooling for localized air conditioning.

Conversely, hot aisle containment solutions are designed to contain hot airflow and direct it back to the cooling units, via overhead ductwork or with in-row cooling for localized air conditioning. Hot aisle containment systems can significantly increase cooling unit efficiency because the hot air is ducted directly to the CRAC/CRAH unit. This solution is quickly becoming an ideal option for high-density data centers. Ducting the entire hot aisle air above and out the cooling units while using in-row cooling near the heat source improves overall air handling efficiency.

IN-ROW COOLING

In-row cooling units distributed between the cabinets move cold air closer to heat sources to further overall data center efficiency. No raised floor is required.

Dedicated cooling units placed between cabinets allow in-row cooling to capture exhaust air and neutralize it before it mixes with cold air. In-row cooling offers a standalone cooling system for some small rooms that can replace CRAC units, providing

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high-density cooling capacity. Additionally, in-row cooling can be used in conjunction with hot aisle/cold aisle configurations, adding to existing cooling solutions to accommodate growth.

In-row cooling solutions offer a simple way to achieve reliable, high-powered cooling for specific rows. Units provide inherent scalability, allowing users to seamlessly adjust their cooling to fit any data center’s growing networking needs or evolving design requirements.

Designed to deliver cool air only where it is needed most throughout the data center, in-row cooling increases cooling efficiency dramatically. By significantly decreasing the amount of wasted energy, in-row cooling solutions can result in an estimated 82 percent utility savings.

TOTAL COST OF OWNERSHIPData center managers must balance selecting the proper cooling configuration with the total cost of ownership associated with each solution.

Installation vs. OperationUnderstanding the difference between installation cost factors and operational cost factors is important when selecting the appropriate cooling strategy. For example, legacy configurations are simple to install and can be done with very little capital costs; however, the energy needed to run these systems may result in excessive utility expenses. They can also be unreliable, creating hotspots and leading to potential equipment malfunctions—ultimately leading to more labor costs and risk of equipment downtime.

Systems that have high capital costs may still experience lower operation cost, ultimately saving a substantial amount of excess expenses. For instance, containment systems can be expensive to implement, but due to their low to moderate operating costs and their high reliability, can be a cost-effective solution for sophisticated cooling requirements.

Annual SavingsDepending on the company’s cooling strategy, businesses can experience significant annual savings. Characteristics of the cabinets can affect server performance, which ultimately impacts operational costs. Each server manufacturer has specific guidelines concerning the amount of open space required on cabinet front doors. To provide servers with enough cold airflow to

dissipate the heat generated and ensure that the cold air is not restricted from entering the installed equipment, doors must have at least 50 percent open space.

Increasing heat dissipation from a cabinet can also be achieved by the proper placement of fans. Fans on the rear doors can be used in conjunction with the server fans to increase the airflow in specific areas and assist in eliminating hot exhaust air from the cabinet. In random layout data centers, the best way to remove heat from the top of a cabinet is to install a perforated top or a top-mount fan. However, in more efficient hot aisle/cold aisle layouts, the use of top-mount fans can actually impede heat dissipation and overall server thermal performance by drawing cold air away from the server and mixing the cold air with hot exhaust air, wasting the energy that was originally used to create the cold air.

Finally, accessories can be used to assist with cabinet airflow. Companies can implement blanking panels or floor brushes to achieve additional data center efficiency in hot aisle/cold aisle configurations, providing an easy solution with a large fiscal impact. Blanking panels are used to fill empty cabinets and rack space and solid walls are installed to prevent cold air from rushing through cabinets, bypassing equipment and mixing with hot exhaust. Utilizing blanking panels ensures cold air will only pass through equipment to dissipate, providing an easy-to-install and highly effective method for directing cold air, potentially offering tens of thousands in savings annually. Floor brushes, on the other hand, act as both a plenum for distributing cold air to network equipment and provide a path for cable distribution. Rather than using simple cutouts, floor brushes, which act as an airflow block, prevent cold air from leaking through cable entryways into the hot exhaust air.

MOVING FORWARDTo meet the communication needs of any business, technology will continue to evolve by providing networking equipment with capabilities that enable faster data transmissions and greater memory and storage capacities. More powerful data centers require organizations to implement solutions that not only deliver superior protection for their networking equipment, but also remain energy efficient, saving thousands of dollars every year in utility costs. Environmental concerns can also be addressed via a well-designed cooling strategy.

Data Center Design and Development Considerations

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Data Center Design and Development Considerations

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