A Parametric Numerical Study of the Airflow and Thermal Performance in a Real Data Center for Improving Sustainability  
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the world host on their servers organizations with databases, every Internet website, and cloud services. Data centers are consuming more and more electricity worldwide [4; 5; 6]. In 2012, the entire consumption of data centers was assessed to be near 270 TWh [7]. ICT are responsible for roughly 10% of worldwide power consumption and 13-15% of this consumption is due to data centers [8; 9; 10; 11]. It is expected that this consumption will only grow in the near future, thus challenging sustainability goals [12]. In a study where projections up to 2030 are made, data centers could consume, in the best case scenario 3% and in the worst case scenario 13% of the worldwide electricity production [13]. The main factor of such a high level of energy use is the consumption of air conditioning systems, which, given the type of ICT equipment, could account for 24-60% of the entire data center's energy consumption [14]. Data centers are required to follow rigorous technical specifications with the purpose of guaranteeing their optimal operation and security, and engineers need to sure that the ICT equipment should operate without experiencing any loss of performance or interruption. Thus, thermal engineers have a crucial importance in the design of data centers. The reason is that data centers generate a high quantity of heat and need to be refrigerated in order to avert any loss of performance or failures, thus signifying that the power consumption is high [15]. Data center rooms are comprised of racks hosting servers with distinct configurations and distinct capacities. To keep the productivity and operating efficiency of the server racks, the thermal management of the room has to be adequate. Therefore, the highest amount of the consumed energy is for the purpose of cooling the data center rooms with the aid of computer room air conditioning (CRAC) units [16; 17]. However, as a path to move towards sustainability, by managing the cooling properly, as much as 10-15% of energy can be saved. Keeping the surface temperature of the server racks within the admissible limits is a significant challenge for the thermal management of data centers [18]. Two strategic solutions are given by researchers for reducing the cooling system's energy cost: improve the airflow and optimize the refrigeration system. By managing the airflow efficiently, it is possible to cool the server racks of the data center without major investments or having to upgrade the cooling system. In many cases, data center managers invest in additional cooling systems without knowing that the current equipment by being optimized is enough [16]. During the last decade, the trend has been of a constant decrease in size of the server and a constant growth of the power density of the server, thus generating more heat, which requires more and more energy. This represents a challenge for the CRAC engineers since the purpose is designing a cooling system that keeps the operating temperature of the server racks within the specification limits regardless of the power density of the server. However, the challenge is also reducing the overall energy consumption of the CRAC units. More efficient thermal management, cooling, and air distribution are needed to overcome such challenges [15]. According to specialists and researchers, the most effective manner for the CRAC units to cool the air of the server racks is through the use of perforated tiles located under the floor. The purpose is to cool the server racks from beneath. However, this becomes more challenging when a high number of processors are situated in a single server rack, which generates high heating loads. To dissipate such types of loads, a system which distributes the cool air to the racks is utilized [19].