Advances in IBM Z Water Cooling: z13, z14, z15

IBM z15™ continued a broadening of the physical transformation of the mainframe into a new "true 19-inch" frame form-factor. This was done to meet the requirements of a broad range of data centers, including supporting various energy efficiency initiatives. z15 continues to offer a choice of client air cooled (RCU, internal radiator) or client water cooled (WCU) systems for cooling the high-performance processor modules. This paper provides an historical perspective on IBM Z water cooling, focusing on the internal radiator cooling solution, which is a closed loop, preassembled and pretested, enterprise-class cooling solution that, once filled, requires no scheduled maintenance. A review of prior system (z13, z14) thermal design and performance will be put in the context of the thermal challenges introduced by the new form-factor in z15. The paper highlights the thermal design of the cold plates used to cool the processor modules and the performance of various cold plate designs (from 0.30 mm fins to 0.15 mm fins). Overall system thermal performance is described, focusing on improvements in the radiator heat exchanger and transition from system-level air-moving devices to high performance fans. This will be put in the context of supporting the ASHRAE A3 (4th Edition) data center environment without sacrificing processor frequency.