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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

Steady and Transient Behavior of Data Centers to Variations in Thermal Load

J. Zhang
Mechanical Engineering Department, Rutgers University, Piscataway, NJ 08854

Yogesh Jaluria
Department of Mechanical and Aerospace Engineering Rutgers, The State University of New Jersey Piscataway, NJ 08854, USA

Abstract

The increased demands on data storage make it imperative to investigate the cooling system for data centers since the power required is generally quite substantial. It is also important to study the effect of thermal load changes on the response of the system and possible optimization to reduce the energy usage. This could lead to significant savings in costs and in environmental impact. Thus, both steady and transient operations are of interest. The temperature and flow distribution at both steady state and transient state are studied. The objective of the study is to control the temperature in the data center at an allowable range, as well as reduce the energy and cost for the cooling system. Microchips with high heat dissipation result in significant cooling challenges at the data center facility level. In a typical data center, the power consumption on cooling and thermal management is as much as 45% of the total power consumption. For a 10 MW facility, this would lead to a cost of up to $3.9M annual cost assuming energy price of $0.1 per kWh. Therefore, the thermal management is one of the most importance challenging tasks for data center and computer room managers.

There are two classes of thermal management policies for data centers: those that manage temperature under normal operation and those that manage thermal emergencies. The objective on normal operation thermal management is to reduce cooling cost. On the other side, a large increase in load that causes temperatures to rise quickly can be considered a thermal emergency. The main objective for managing thermal emergencies is to control temperatures while avoiding unnecessary performance degradation. In this work, both thermal management policies have been studied.

The air distribution within a data center has a major impact on the temperature distribution of the equipment located in the rooms. In some data center, the cold air enters the data center from the ceiling through diffusers, and exits the room via vents on the sides of the room. Most of the data centers use hot aisle/cold aisle layout, which is designed to supply cold air through a raise floor. CRACs are used to pump the cooling air into the plenum underneath the data center room. There are perforated tiles on the floor that are used to replace to the solid tiles and allow air to enter the above floor space. The aisles with perforated tiles are cold aisles. The aisles without the cold air delivery are hot aisles. Raised floor data center is popular because of its flexibility. The floor tiles are designed to be removable. If the layout arrangement of the server racks is changed, the corresponding perforated tile locations can be changed so that the cold air can be delivered to where the hot rack is located.

This paper presents the results of a numerical study on the steady and transient operation of data centers under different environmental conditions. Changes in the thermal load are considered. Different scenarios where the cooling system is started before the data center is subjected to a major load increase are considered and the corresponding results presented. The study could be used for optimization of multiple data centers, with respect to load and location, to achieve considerable savings in energy usage.

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