Publication
As data centers grow exponentially in size and number worldwide, it appears evident that more efficient and reliable cooling solutions are needed to reduce energy consumption and noise level significantly. Thermosyphon-based systems have been proven to respect both these goals, and their inherent natural circulation makes them very attractive for heat rejection of individual servers and entire server racks. In this study, the thermosyphon concept is applied as a retrofit cooling system on an actual server rack. The cooling system is composed of two stages: (i) server-level thermosyphons for the direct cooling of the two Central Processing Units (CPUs) and (ii) a rack-level thermosyphon for the cooling of the condenser side of the server-level thermosyphons. Nearly zero-Global Warming Potential (GWP) refrigerants, R1234ze(E) and R1234yf, are used as the working test fluids for the server-level thermosyphons, while for now R1234ze(E) is the only fluid used for the rack-level thermosyphon. A server-level thermosyphon is first tested when cooled directly by water at 20 degrees C, without a rack-level thermosyphon, to define its thermal performance. Then, the rack-level thermosyphon is installed in such a way that it serves the subcooled liquid at the server-level thermosyphons in a parallel configuration. The condenser of the rack-level thermosyphon is cooled by water entering at 20 degrees C.