Thermal Performance Of Data Center Research Articles

Improving Thermal Performance in Data Centers Based on Numerical Simulations

Improving Thermal Performance in Data Centers Based on Numerical Simulations

A Novel Multiscale Evaluation Metric for the Thermal Management of Data Centers

Abstract Tremendous burden is compelled on the energy consumption of data centers with the rapid development of information technology, and a healthy thermal environment is critical for improving the cooling efficiency of data centers. Furthermore, the thermal management of the data center is determined by the evaluation of its thermal environment. However, most of the existing evaluation metrics describe the thermal environment through a single scale, which cannot fully reflect the thermal performance of data centers at different scales. To simplify the evaluation of the thermal environment in data centers, a novel multiscale evaluation metric of the recirculation and hot spots index (RHSI) is proposed in this study. The numerical model of an operating data center is established and verified with the experiments on site. Then, the thermal environment of the data center is evaluated based on the RHSI and the existing metrics. Finally, the applicability of the RHSI is further discussed from different scales in detail. The results show that all bypass airflow, hot recirculation, and local hot spots can be derived from the proposed RHSI simultaneously by comparing with the evaluation metrics of supply heat index (SHI) and rack cooling indicator (RCI) at the room scale, β at the rack scale, and index of mixing (IOM) at the row scale. The proposed RHSI can provide a guiding significance for the thermal management of data centers.

Numerical and experimental investigation of thermal performance in data center with different deflectors for cold aisle containment

The rapid development of data center (DC) construction and its high energy consumption problem has caused widespread concern all over the world. Effective airflow management is considered to be a reliable method to improve the utilization of cooling capacity and energy saving of air conditioning system (ACS) in DC. An innovative method of airflow optimization applying deflector in cold aisle containment (CAC) is proposed to improve the uniformity of airflow distribution in this paper. It is found that, in numerical simulation the application of deflector can improve the cooling efficiency of airflow, and the application of convex deflector with height of 1700 mm can obtain the best thermal environment. Meanwhile, the hotspot area of the rack is greatly eliminated and the uniformity of airflow distribution is improved. Furthermore, the thermal performance of DC is compared between the basic and optimal cases under five rack power (1.8 kW, 2.4 kW, 3 kW, 3.6 kW, and 4.2 kW) and three operating parameters (18 °C, 3.5 m3/s; 20 °C, 4.4 m3/s; 22 °C, 5.4 m3/s), and the accuracy of the numerical simulation is verified by field experiments. It is found that the application of the deflectors can reduce the heat accumulation of the rack in different scenarios, avoid the damage to the servers, improve the utilization of cooling capacity, and improve overall thermal environment. Results show that the deflector with optimal structure has wide applicability.

Numerical and experimental investigations on the thermal performance of a data center

Designing an efficient cooling system for a data center can significantly affect its thermal performance. The present paper deals with two kinds of factors that influence the thermal performance of a data center. First the geometry configurations include plenum height (0.4, 0.5, 0.6, and 0.7 m), perforation percentage (10, 20, 30, and 40%) and computer room air conditioning arrangement. Second, the operating parameters include the temperature and volume of air. A total number of 32 configurations have been designed by adjusting the plenum height perforation percentage to investigate the effect of the cooling system arrangement on the overall thermal performance of the data center. The results present a critical range for plenum height (up to 0.6 m) and perforation percentage (higher than 20%) in which the system's thermal performance can be significantly enhanced by adjusting the geometry configurations. Beyond this range, the performance does not change much. Supply air temperature is more related to the thermal performance of the racks near the farther end of the cold aisle. Increasing the supply air volume can effectively improve the air uniformity along the direction of the cold aisle. Plenum with gradient cross-sections created using inclined partitions significantly reduced the inlet and outlet air temperature by 1.7–2.9 °C. By investigating the effects of geometry configurations and operating parameters on the thermal performance of data centers, the optimal geometry parameters and feasible operating strategy of “high temperature, high air volume” are proposed in this article as the reference and guidance for newly built data centers or retrofitted practices.

A new mathematical model for multi-scale thermal management of data centers using entransy theory

Based on entransy theory, this paper proposes a new mathematical model for multi-scale data center thermal management. A comparison of heat transfer optimizing is made first, using exergy/entropy method and entransy dissipation, to verify the fitness of entransy theory. Based on which, a complete model of entransy dissipation for data center heat transfer is built, from CPU level to data center room level, with detailed computational derivation. Specifically, the calculating method of entransy dissipated by undesired air mixing has been derived, which can give quantitative evaluation on air mixing to the entire thermal performance of data center. A case study of a CFD simulation and a CRAC retrofitting engineering have been performed to verify the entransy model. In the case study, the temperature penalty caused by undesired air mixing is calculated using the entransy analysis model and testified by the retrofitting test, which directly reduces the free cooling potential and decrease data center energy performance. This entransy theory based model offers a new method to better optimize the thermal management and gives specific measures to improve the thermal performance of data centers.

Optimizing Thermal Performance of Data Centers with Novel Local Partition Configurations

The indoor environment of data center today has differed from the legacy data centers from the heat density to the air distribution. The energy consumption of cooling system has been taking up a large percent of the total energy of data centers. The reliability problem caused by local overheating and economic problem by undercooling attract the attention. novel local partition configurations are proposed in this paper to optimizing the air distribution and thermal performance of data centers. A basic model and 6 partition models have been simulated to analyze the effectiveness of the novel configurations. The result proves that the configurations with local enclosed partition at tile No.2 show great performance in eliminating the hot spots and undercooling problems.

CFD investigations of data centers’ thermal performance for different configurations of CRACs units and aisles separation

The thermal performance of data centers is numerically studied for different configurations of computer room air conditioning (CRAC) units and physical separations of cold and hot aisles. Temperature distribution, air flow characteristics and thermal management of data centers racks array are predicted and evaluated for the different arrangements. Measureable performance indices: supply/return heat index (SHI/RHI), return temperature index (RTI) and return cooling index (RCI) are used to measure the thermal management effectiveness of data center racks. The results showed that: (i) hot air recirculation, cold air bypass and the measurable performance indices of the racks strongly depend on the racks location in the racks array, (ii) the CRACs units layout affects the thermal managements of the racks array especially the sides and middle racks in the array, and (iii) using cold aisle containments enhances the thermal performance of the data center.

Cross Flow Heat Exchanger Modeling of Transient Temperature Input Conditions

The effectiveness of heat exchangers strongly influences the thermal performance of data center cooling systems. Rear door heat exchangers, in-row and overhead coolers, and fully contained water cooled cabinets are some examples of liquid and hybrid cooling systems used in data centers. Modeling the dynamic behavior of heat exchangers is important for the design of control strategies to improve energy efficiency. In this paper, an existing 2-D model of the transient temperature response of an unmixed-unmixed cross flow heat exchanger, of the type that is widely used in data center cooling equipment, is solved numerically. A detailed analysis of the transient response to a step, ramp, or exponential change in the hot fluid inlet temperature is conducted. The heat capacity rate ratio (E), thermal resistance (R), capacitance ratio (V), and number of transfer units are varied over a wide range to determine their influence on the heat exchanger dynamic thermal performance under different transient input conditions. In addition, the thermal response to the magnitude and time period of the transient input functions are evaluated. The modeling results are used to analyze specific data center cooling scenarios, and provide a means for predicting the transient behavior of heat exchangers used in data center cooling equipment.

Thermal Performance of an Air-Cooled Data Center With Raised-Floor and Non-Raised-Floor Configurations

In this paper, the thermal performances of an air-cooled data center with raised-floor and non-raised-floor configurations are compared with respect to the room and ceiling return strategies. The thermal performance of the data center is evaluated in terms of supply heat index, rack cooling index, total irreversible loss, and the number of racks with at least one server exceeding the maximum recommended and allowable inlet air temperature according to American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) thermal guidelines. The numerical simulations are conducted providing an insight into the flow and temperature distributions, and thus giving a better understanding of the cooling issues. It is found that using a ceiling return strategy for the return of hot exhaust air to the computer room air conditioning units gives a better thermal performance of the data center, for both raised- and non-raised-floor strategy, as compared to the room return. The findings are then extended to a geometrically complex operational data center to improve its cooling effectiveness. The paper also highlights the drawback of using supply heat index alone as a performance metric.