Thermodynamics Energy Efficiency Analysis and Thermal Modeling of Data Center Cooling Using Open and Closed-Loop Cooling Systems

摘要

There is a strong need to improve our current capabilities in thermal management and electronic cooling, since estimates indicate that IC power density level could reach 500 W/cm~2 in near future. This paper presents several possible closed and open loop cooling schemes for thermal management of electronic equipment in data centers. To be able to identify the overall energy consumption impact, a thermodynamics coefficient of performance (COP) analysis for a data center under each one of the proposed schemes is presented. A limited condition condition 2nd law of thermodynamics thermal efficiency (η_Ⅱ) analysis of the proposed open-loop schemes is also presented. Using available performance data, the overall data center COP of open and closed-loop cooling schemes is evaluated. Also, the 2nd law efficiency of open-loop schemes is evaluated. To properly design and size the components of a liquid or refrigeration-assisted open or closed-loop cooling scheme requires heat exchanger modeling that need to be incorporated in existing CFD simulation models. For that, analytical modeling of two kinds of direct expansion refrigeration cooling evaporator and a secondary liquid cooling fan coil heat exchanger in conjunction with a computational fluid dynamics (CFD) model to analyze a refrigeration cooled high heat density electronic and computer data center installed on a raised floor is presented. Both models incorporate an accurate tube-by-tube thermal hydraulic modeling of the heat exchanger. The refrigeration coil analysis incorporates a multi region heat exchanger analysis for a more precise modeling of two phase refrigerant flow in the evaporator. The single phase secondary loop fan coil heat exchanger modeling uses an effectiveness method for regional modeling of the spot-cooling coil. Using an iterative method, results of the heat exchanger modeling is simultaneously incorporated in the CFD model and an optimal design of spot cooling heat exchanger is developed. The presented cooling schemes, theoretical thermodynamics analysis along with the detailed thermal-hydraulic heat exchanger simulation in conjunction with the state-of-the-art CFD simulation code should enable data center designers to be able to handle expected increased in heat density of the future data centers. A flow cross sectional area (m~2) ANNUL length fraction of the tube with quality up to 0.85 C_P specific heat at constant pressure (kJ/kg °C) COP coefficient of performance d tube diameter (m) h heat transfer coefficient (W/m~2 °C) K tube thermal conductivity (W/m °C) m mass flow rate (kg/hr) NTU number of transfer units PR power ratio Q heat transfer rate (W) T temperature (°C) t air temperature (°C) U overall heat transfer coefficient (W/m2 °C) W power (W) w tube thickness (m) XDRY length fraction of the tube with quality within the range of 0.85 to 1.0