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Calculated benefits

A university computer research centre provided an opportunity to demonstrate the benefits of rack-based cooling

The Centre for Scientific Computing (CSC) at the University of Warwick is one of the first customers in the UK to benefit from Eaton-Williams Process Cooling’s rack-based cooling technology.

Rapid growth in the use of high performance computing (HPC) resources in the CSC by academics means that the performance of their servers and storage has increased exponentially over the last few years, as has the heat generated by the hardware.

The problem facing the university was to temper the need for expansion with the control of heat and limited floor space.

The University has a number of high-profile research programmes in scientific computing, where vast data sets are processed around the clock, to support research in areas such as molecular dynamics. As the department increased the density of its rack enclosures, so the cooling requirements also increased.

The Centre working with consulting engineer Couch Perry Wilkes Partnership, sought a solution that addressed its environmental sustainability standards whilst providing reliable cooling with capacity for future expansion.

Process Cooling’s approach moved away from traditional Computer Room Air Conditioning (CRAC) units with the recommendation of a more robust, compact and energy efficient solution using its rear door heat exchangers (RDHx) and cooling distribution units (CDUs).

To accommodate Warwick’s existing six cabinets, housing 40 servers in each, Process Cooling installed six of its RDHx units, in conjunction with a downflow CRAC arrangement, to remove up to 15kW of heat from each rack using a chilled water system.

Each RDHx offers condense-free operation, using controlled water from the CDUs. The RDHx’s specifications include refrigeration grade coils, pressure tested to 45-bar, hermetic construction, sealed copper brazed, underfloor manifolds pressure-tested to 20-bar, leak detection and leak-free couplings and hose sets rated to 53-bar. The secondary circuit working pressure, fed by the CDUs in 4-bar, gives an excellent safety margin.

The units reduce the heat output from the servers, which can be in excess of 45deg, by as much as 50 per cent, removing it from the hottest part of the servers (back) and rejecting it into the cooling coils in the rear door, which then cools the rejected air down to close to room temperature (approximately 20degC).

In an adjacent room, as well as two CRAC units there are two Process Cooling CDUs that control the temperature of the water for the RDHx units. Each CDU incorporates full run/standby capability. An externally sited chiller provides chilled water which is delivered to each CDU unit at a temperature of 10degC, increasing free cooling capabilities more effectively than a CRAC-only system.

The RDHx requires no additional fans or electricity and is designed to cool without opening or removing the doors. Because the heat exchangers are in the back of the racks and in the door itself, the actual footprint of the racks and floor space is barely impacted, the firm says.

A major benefit is that as the RDHx cools the air before it leaves the rack there are no hot spots and cooling air at source is very energy efficient. (150kW of heat can be rejected to the primary chilled water system via RDHx and a CDU, consuming only 2.6kW of pump power. A CRAC system would consume around 10-15kW to do the same job and with a much larger footprint, the firm says.)

The under-floor manifolds have been designed to enable up to a maximum of 19 computer racks and RDHx units to be installed without any downtime and minimal M&E work. The room has been designed to accommodate these 19 racks at 15kW per rack, cooled by a conventional air system at up to 7.5kW per rack, combined with Rear Door Heat Exchangers providing the remaining 7.5kW.

Process Cooling’s solution has enabled Warwick to introduce high density equipment with zero thermal impact into its data centre and has set a benchmark which the university plans to implement in its other data centres.