Merlin: Focus on Cooling

The fully-contained cold aisle inside the data center modules at the Merlin facility operated by Capgemini.

The Capgemini modules use adiabatic cooling, a method of evaporative cooling in which fresh air from outside the data center passes through a filter that is wet, and the air is cooled as it passes through it (as some of the water evaporates). A similar system has been used in modular data centers from SGI and Microsoft.

There are no raised floors or ductwork. Once the fresh air has been cooled, it passes through a wall of 12 variable-speed fans and into a “cool corridor” running the length of the module. The corridor is lined with several rows of equipment rooms, which are enclosed using a cold-aisle containment system. The pressurized air enters the equipment rooms through louvers that can control the flow, pass through the equipment and then into a hot aisle.

The data center is equipped with sensors tracking temperature, humidity and air pressure, which all report back to an intelligent management system. Capgemini’s consultants worked with a global Building Management System (BMS) company to design a new independent BMS for the modules. The BMS can detect changes in conditions within the module and adjust the variable-speed fans that move the air around the modular computer hall.

A three stage cooling system unit is dedicated to each module. The cooling unit uses fresh air cooling for external temperatures up to 24 degrees C (75 degrees F), with secondary evaporative cooling for temperatures between 24 degrees and 34 degrees C (93 degrees F) . Direct Expansion (DX) refrigerant cooling provides final backup for temperatures exceeding 34 degrees C. The system, has been tested up to 48 degrees C (118 degrees F).

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