Comparative study of high ambient inlet temperature effects on the performance of air vs. liquid cooled IT equipment

In response to the growing demand for power and energy across US and world-wide, development of energy efficient solutions has become very important. Considering data center applications, cooling power consumption constitutes a significant part of the overall energy usage of the system. In the process of optimizing the energy consumed per performance unit, liquid cooling has become one of the key solutions. Liquid cooling addresses the critical issues related to typical air cooling in servers because of its better heat transfer characteristics. Water-cooling at the device level can be an efficient solution since water has higher thermal capacitance when compared to traditional heat carrying medium i.e., air. Additionally, moving the cooling source closure to the heat load helps in reducing hot spots at the room level, thereby, improving the effectiveness of the cooling solution. On the other hand, the feasibility to operate liquid cooling at wider temperature range helps in partially or eliminating the room air conditioning units and chiller compressors and reduces the cooling power consumptions substantially. The primary objective of the study is to evaluate air vs. liquid cooled enterprise-class server for the effects of high ambient inlet temperatures. The air-cooled server has five hot swappable fans and two CPU heat sinks to dissipate the total heat in the server. The water-cooled counter-part consists of two-cold plates with integrated pumps to cool the CPUs while the dual in-line memory modules transfer the heat using a heat transfer tape attached to the manifold that is carrying the coolant. The existing practice in the industry is to maximize the use of economizer usage by reducing/eliminating the usage of chiller while taking advantage of outside ambient conditions to cool the data centers. However, higher ambient temperatures would lead to higher operating temperatures of the processors. The operating temperature of the CPU has direct influence on the static power which is known to reduce the performance of the processor. In this study, theair as well as liquid cooled servers will be tested at inlet temperatures ranging from 25°C-45°C (ASHRAE T.C 9.9 A4 and W4 classes) and the corresponding thermal and flow parameters will be compared for both cases. The current work primarily focuses on evaluating the critical inlet temperatures (for air cooled vs. liquid cooled server) at which CPU die temperatures has an influence of the static power. Collectively, a case will be presented as to why l iquid cooling would provide a viable option to operate the data centers at wider inlet temperatures with reduced risk of leakage current and sustain the performance and reliability of the IT equipment.