Heat generation is the only limitation on increasing computer power. That is why new options are needed for cooling server rooms, says Guy Hutchins, sales director of Trox AITCS
MENTION close-control air conditioning systems to most people and they tend to think of computer rooms in which cool air is blown under the floor by down-flow units that then recirculate the air.
These are known as computer room air conditioning (CRAC) units, and they are a popular close-control option for large data centres and in smaller equipment rooms for offices that have PCs connected to a server.
Air has long been the IT technician's cooling medium of choice. But, as computers become ever more powerful and the heat output from servers increases, more and more air is needed to cool these servers. Care must also be taken to ensure units further away from the fan-powered CRAC units do not struggle to get air for cooling. This is particularly true as floor void cabling congestion increases. The airflow can be interrupted by the build-up of cabling. This causes a reduction in floor void static pressure and hotspots develop, which rapidly lead to equipment failure.
The maximum practical limit for air cooling in computer rooms is 5-8kW per cabinet, depending on the layout, space constraints and airflow strategy. This makes it an impractical choice with the heat loads created by today's powerful computers - especially blade servers, which can demand 1,000+ air changes per hour.
A possible solution is water as a cooling medium. Water is certainly a more efficient cooling medium for computers than air. But it conducts electricity, and water damage will have a disastrous effect on the electrical equipment and cabling with which it comes into contact. The risk of water leaks often deters deployment within a data centre environment.
Carbon dioxide, on the other hand, is a perfect cooling medium for IT cooling applications because of its key properties. For example, Trox AITCS says its carbon dioxide-based system:
Saves up to 30% in energy through a combination of its integrated R134a/CO2 chiller and CO2's lower viscosity and pumping duties when compared to chilled water. For example, a 250kW system reduces CO2 emissions by an impressive 290tonnes a year
Have ozone-depleting potential of zero combined with low toxicity
Poses no danger to electrical equipment or cabling because CO2 is electrically benign
Has seven times the cooling capacity of water per kilogram, reducing volume with smaller diameter pipework
And, because CO2 cooling is more efficient than air and water alternatives, the footprint of IT equipment rooms can be reduced by 50-70%, saving valuable space, as equipment densities can be increased.
But it is the energy-saving potential of CO2 that is one of the most compelling arguments in its favour. For example, Trox's award winning CO2OLrac CO2-based blade server cooling system offers substantial savings in power consumption. For a 1MW installation, energy costs can be reduced by up to £155,000 a year.
The system, which is based on circulating CO2, is designed to absorb the heat rejected by blade servers at the rear of the cabinet. CO2OLrac represents a positive use of CO2, a by-product of industrial processes, which could otherwise threaten the environment.
The system has already been successfully installed on a number of projects in the UK totalling 1.7MW, with a further 20MW or more planned for 2008/09 around the world.
Trox believes that all major organisations, particularly those with an environmental agenda, will want to use CO2. This is not only because of its green credentials but because it guarantees high-capacity performance, not only to meet today's demands but also those of the future.
End-users can conduct on-site evaluation of Trox AITCS's CO2 system, with their 80kW CO2OLpac. The package enables data centres to run CO2 cooling linked to their existing chilled-water system, and includes full consultation, site survey, proposal, quotation, installation, commissioning, technician support, thermal and aerodynamic assessment and summary report.