On demand cooling with real time thermal information

In recent years, the internet services industry has been developing rapidly. Accordingly, the demands for compute and storage capacity continue to increase and internet data centers (IDCs) are consuming more power than ever before to provide this capacity. With large scale power usage comes the large price tag of paying for that power. With growth trends increasing and development expanding, IDC owners realize that small improvements in efficiency, from architecture design to daily operations, will yield large cost reduction benefits over time. One important trend for reducing power consumption is raising the operational temperature of an IDC. Higher ambient temperatures (HTA) have been shown to reduce power consumption based on more efficiently using computer room Air conditioning units. This paper outlines the key architectural details around a customized server and data center design called on-demand cooling. It describes how IDC owners can utilize server real-time thermal data, including inlet/outlet temperatures, power, and server fan speed (airflow demand) as key inputs for improved IDC cooling control and HTA operation. First off, we need to understand current limitations of traditional IDC´s and HTA. In most traditional IDC´s, the operational temperature range continues to be between 18-23C or even lower. Here are three reasons to explain why conservative cooling settings continue to be used. The first reason for conservative cooling settings (over cooling) was needed in the past, was to ensure all IT infrastructure was cooled to within equipment specifications. Because these specifications varied widely between different IT infrastructures, there was the potential to impact the reliability of certain IT equipment with high temperatures. Successful high temperature ambient (HTA) data center operations is accomplished by understanding all equipment temperature thresholds and keeping the ambient temperature within those reliability levels, to still meet SLA- and business application requirements. Fortunately today, modern IT infrastructure (servers and switches) are built to a much higher standard of thermal thresholds. The 2nd reason is that traditional cooling control mechanisms and policies employed in datacenters are based on a limited number of distributed physical sensors on the ceiling of the cold and hot aisles. These sensor measurements cannot reflect the overall picture of a fluctuating temperature field. The non-uniform temperature distribution at server inlets caused by air flow patterns, recirculation or bypass air between hot and cold aisles, etc. won´t be picked up from ceiling sensors. Given the limitation of using just a few sensors to determine ambient temperature over the large and varied physical space of a data center, low temperature traditional air cooling was required. The 3rd reason is the indirect connection between demand (server) and supply (CRAC) in the traditional control policy. Different kinds of servers with different power densities and power distribution always means different cooling requirements (power variation, inlet air temperature, airflow volume). A CRAC unit cannot know and reflect the exact cooling demand directly based on changing server usage. For example, a multi-server application workload increases causing a large power variation and subsequent increased thermal output. The traditional cooling control mechanism will not response until the physical ceiling sensor notices the in-room air temperature rise and reports this to the BMS system. This longer response time causes a larger temperature oscillation range, and therefore a conservative operational temperature setting is needed to ensure the thermal safety of the DC equipment. Higher operational temperatures reduces that thermal headroom for equipment as well as reduces allowable temperature variations in an IDC. IDC operators have less response time to deal with any large power/thermal variation or IDC cooling infrast