Enhancing rack servers air cooling capability with extra system inlet airflow through air ducts between racks

There is often thermal challenge to keep Central Processing Unit (CPU) temperature within its design specification for rack server systems with air cooling solution, due to the growing demand for higher CPU performance and the ever-increasing CPU thermal design power (TDP). This paper provides an approach to enhancing system air cooling capability of servers mounted on a rack, addressing the challenge of meeting thermal design target. In this paper, extra system inlet airflow is provided to servers from both sides of racks, and the temperature of the extra system inlet airflow is lower than the temperature of an existing rack server system inlet airflow. This means either CPUs temperature can be lowered or the server systems using this approach can support higher CPU TDP and accordingly higher performance. The areas discussed in this paper include: how to design venting holes on both sides of racks, how to avoid the extra system inlet airflow being impacted by the rack's hot exhaust air, how to reduce server system fans inlet airflow temperature, and how to design extra system inlet airflow ducts. Thermal test result with a 2U (1U =1.75-inch ) rack server using the approach shows that at system fans full speed, the server system's overall airflow rate increases by 15.3%, the server system fans inlet airflow temperature decreases by 2.5°C, and CPUs case temperature decreases by 5.6°C as compared to existing air cooling solution. When the approach is applied for thicker rack server systems with larger side vents, a larger system airflow rate can be achieved for the rack servers, CPUs case temperature can be reduced more and higher performance CPU with higher TDP can be supported accordingly.