Data Center Cooling

Diagram of the Data Center Thermosyphon Loop

Diagram of the thermosyphon loop featuring a heat source (at the bottom) and a counter-flow heat exchanger (at the top). Vapor forms at the bottom and drives the flow due to buoyancy.

Long Title: Dynamic Modeling of a Passively Controlled Thermosyphon Loop for Data Center Cooling


The data centers that power today’s digital era require huge amounts of energy; it is estimated that by 2020, data centers will consume as much energy as 50 power plants running around the clock. While the energy consumption is a problem that is being addressed by electronics engineers, there is additionally the problem of what happens to all this energy? Much of this energy becomes heat and must be dissipated from the data centers to keep all of the electronics operating at a safe temperature. The standard practice is to blow air across the electronics to cool them. However, this method is noisy, requires significant upstream air filtering, and demands additional energy to move the air across the blades. What if we could do better though? What if we could use the heat to work for us?

This is the concept behind an emerging technology called themosyphon loop heat exchangers. The idea is to attach a loop of a low boiling temperature refrigerant onto the heat source; the electronics will boil the fluid in the system and the creation of the bubbles will drive flow in the loop due to buoyancy. The application of thermosyphon loops to data centers is relatively new and there is much to be learned. When I worked with the Laboratory of Heat and Mass Transfer at EPFL, they already had a numeric model of the steady state behavior of a system like this, but no simulation yet for modelling transient behavior. Some important questions that could not be answered with the existing model were: How hot will the electronics become during startup? What is the effect of periodic operation (duty-cycling) of the electronics? How great do parasitic heat load changes have to be to throw the system out of balance?

By the end of this project, I had created a model that could answer these questions and more. Besides aiding the progress of the laboratory, the results were also supplied to a manufacturer in industry where they are being used to design thermosyphon loops for data center cooling.