How Data Center Cooling Is Evolving to Meet the Needs of Slab Floor Data Centers
Top images show how standard perimeter CRAH units create high-velocity airflows that translate into negative pressure at the front of racks at the beginning of the row. Bottom images show how chilled water units for non-raised floor applications help lower airflow velocities to balance pressure across the row.Andrea Moscheni
Product Manager,
VertivSlab, or non-raised floor, data centers have helped cloud and colocation providers meet growing capacity demand by accelerating speed-to-market and reducing capital costs. Those benefits have, however, come with new data center cooling challenges. Cooling solutions not tailored to the needs of slab floor facilities can jeopardize equipment reliability and reduce cooling system efficiency. But with new challenges come new opportunities, and recent developments in control strategies and cooling technologies are enabling high performing cooling in non-raised floor environments.
Data Center Cooling Challenges in Slab Floor Facilities
When slab floor data centers were first gaining traction, the airflow control strategy that had proven effective in raised floor environments was applied to these non-raised floor data centers. But this strategy — which manages airflow and fan speed based on pressure differential, or Delta P — hasn’t been as effective in slab floor data centers as it is in raised floor environments.
Without the duct provided by the space beneath the floor, pressure is more difficult to measure and manage in slab floor data centers. Data center designers also lose the ability to control airflow to racks using properly sized and positioned floor tiles. Instead of cold air being distributed directly to the front of racks through the tiles, air must travel the length of the row. To compensate, many operators drive fan speeds too high, wasting fan energy and resulting in lower return air temperatures that prevent cooling units from operating at their design efficiency.
The need for air to travel down the row also creates airflow patterns that can limit the ability to cool racks closest to the cooling units when standard data center cooling units are used. The velocity of the air at the beginning of the row has to be high enough to ensure adequate airflow at the end of the row. With standard cooling units, that requires velocities so high they create negative pressures in front of racks at the beginning of the row. This increases the potential for temperature-related failures in these racks.
As a result, operators of slab data centers have had to compromise both cooling system efficiency and equipment reliability. But that is no longer necessary, as new strategies and technologies designed specifically for slab floor data centers are now available.
A More Effective Control Strategy for Slab Floor Data Center Cooling
With control based on Delta P proving inefficient in slab floor data centers, Vertiv developed a control strategy based on the temperature differential (Delta T) between the supply air leaving the cooling units and the return air to the cooling units.
Temperature is much easier to measure than pressure, and by setting a temperature control point for return air above the supply air temperature, operators can ensure enough airflow is reaching each rack.
This strategy takes into consideration numerous failure conditions, such as blocked cold aisles, and provides monitoring to ensure air temperatures at the rack are precisely controlled and consistently meet temperature service level agreements (SLAs) — something that isn’t possible with a Delta P control strategy. The need to run fans at higher-than-necessary speeds to compensate for pressure variations across the row is eliminated, and return air temperatures are maintained at the setpoint to optimize cooling unit efficiency. For more on this control strategy, see the Vertiv white paper, Overcoming the Challenges in Cooling Non-Raised Floor Data Centers.
More Effective and Efficient Products for Slab Floor Data Center Cooling
Chilled water cooling systems offer a number of benefits to cloud and colocation provides developing or operating slab floor data centers. One of the most significant
is the ability of chilled water systems to reduce direct and indirect greenhouse
gas emissions compared to other cooling technologies. Reductions in direct emissions are enabled by a chiller’s ability to use low global warming potential (GWP) hydrofluoroolefin (HFO) refrigerants. Indirect emissions are reduced through the overall efficiency of these systems, which can achieve very low power usage effectiveness (PUE) values through the use of intelligent control systems. To learn more, read the Vertiv white paper, How Chilled Water Systems Meet Data Center Availability and Sustainability Goals.
To address the challenge of airflow distribution discussed previously, new chilled water cooling units have been engineered to meet the airflow requirements of slab floor data centers, including perimeter and thermal wall cooling units.
Perimeter units, for example, have been redesigned to relocate the fan at the top of the unit and create a larger surface area for air distribution. This allows these units to distribute more air at lower speeds, improving the ability to move air down the length of the row and reducing the risk of negative pressure at the beginning of the row.
New thermal wall units adapt the air handling unit (AHU) concept to the needs of slab floor data centers. Installed in the service corridor, they blow air horizontally to the server room, providing high volumes of air that move at low speeds. These systems are particularly well suited when high-density cooling units are required.
Both products can be integrated to the chilled water system manager, which optimizes the entire system by coordinating operation of external and internal units.
Optimizing Cooling in Slab Floor Data Centers
Developers and operators of slab floor data centers no longer have to accept compromises in cooling system performance to realize the cost and speed benefits enabled by eliminating the raised floor. By using control strategies and cooling technologies engineered specifically for slab floor data centers, they can leverage the environmental and operating benefits of chilled water cooling while effectively managing airflow and temperature across the facility. For more information on selecting the right cooling system for your data center see the white paper, Chilled Water Data Center Cooling for Non-Raised Floor Applications.Building a sustainable hyperscale facility in South Africa
Understanding Vantage’s advantageDan Swinhoe
News EditorWhile not traditionally a data center hub, digital infrastructure projects are blooming across Africa.
The deployment of new subsea cables, roll-out of 5G, and a global trend towards the cloud means the continent is seeing huge amounts of new data centers. And South Africa – always the biggest hub on the continent – continues to see a number of new projects being developed.
One of those projects was from DigitalBridge’s Vantage Data Centers, which launched a new facility in Johannesburg, South Africa, this year. The company won DCD’s Middle East & Africa Data Center Development Award for its efforts.
In March 2021, Vantage was contacted by one of its strategic customers who “urgently needed significant IT capacity in South Africa.” A few months later in October, after a site was located and secured alongside planning permission and power, Vantage commenced the build of a data center campus in Johannesburg, the company’s first in Africa.
Located in Waterfall City in the Midrand area of Johannesburg, the first data center (JNB11) was completed in July 2022; a two-story, 35,000 square feet, 16MW building. Delivery took place ahead of schedule in just 10 months using prefabricated electrical containers and equipment designed and pre-manufactured by the company’s suppliers, with zero lost-time incidents over 1.5 million working hours.
One challenge was the short delivery timescale required by the customer for the initial facility, exacerbated by the imminent rainy season (December to February).
Once fully developed the campus will consist of three facilities across 30 acres with 650,000 square feet (60,000 square meters) of data center space and 80MW of capacity. Vantage has said it was investing more than $1 billion into the site.
Powered by Eskom, the campus features a dedicated on-site, high-voltage substation. The buildings use a closedloop chilled water system generated through air-cooled chillers alongside an integrated economizer which allows reduced compressor energy based on outside ambient temperature. The facility has an annual PUE of 1.25.
To mitigate power rationing or load shedding – common to the region – a260,000-liter back-up fuel system was installed in the first phase, equal to 48 hours of fuel at full load to serve JNB11. This will be expanded to 1.6 million liters once the campus is fully built-out.
Vantage has also signed a 20-year 87MWp power purchase agreement (PPA) with SolarAfrica to power the facility with renewable energy from a solar farm. Vantage has pledged to reach net zero by 2030.
“The project was a smooth process having thoroughly researched the right location to ascertain available land, power and ease of planning – greatly assisted by the partnership forged with Attacq, a leading Real Estate Investment Trust (REIT) in the region, and the good relationship maintained with Eskom,” the company said.
“We are thrilled to announce that we've won the DCD Middle East & Africa Data Center Development Award in recognition of our Johannesburg campus,” Vantage said after winning the award, sponsored by Meesons. “This award recognizes the hard work and the expertise of our teams who worked diligently to complete our first African data center (JNB11).”
At the event, Abed Jishi, VP of design engineering EMEA, told DCD: “It’s awesome [to win] after all the hard work that we’ve done for the past couple of years to develop that campus.”
“It’s one of the most resilient data centers in the region. One of the biggest achievements for Vantage is to make sure that, building such a big campus in such a developed country, we’re still tapping onto renewable energy sources.”
“One of the big hurdles was the expertise, trying to find the right expertise for the different engineering discipline we go through. I can’t say it was an easy task, but South Africa being so connected to the world, it gave us the leverage to bring expertise to the country in conjunction with local expertise.”
