Power & Cooling


assisted devices can be used to improve airflow but this further reduces the efficiency of the overall cooling system by increasing overall power consumption and adding heat to the cold air supply. Density limitations can be avoided if cold aisle containment is used together with row based cooling.


However, the solution can still have limitations when deployed in a row- based approach. For example, since cold aisle containment minimises the overall pool of cold air available to the server, any loss of power and/or cooling supply will result in more rapid temperature increases in the server load. This will shorten the amount of time available to the data centre manager before overheating and thermal shutdown starts to occur. To realise maximum benefits, all cold aisles in the entire data hall should be contained, otherwise mixing of hot and cold air in uncontained areas will occur, diminishing expected energy and cost savings.


An open and shut case for hot aisle containment The Hot Aisle Containment System (HACS) encloses the hot aisle, collecting exhaust air from IT equipment, cooling it and making it available to the air intakes of racked IT equipment.


HACS ensure efficient air distribution by completely separating supply and return of air paths and eliminating the mixing of hot and cold air streams. HACS hold many of the advantages of cold aisle containment whilst avoiding many pitfalls. The efficiency of the HACS will be higher because the hot aisle is capable of maintaining higher temperatures. The net effect of elevated return air to the cooling unit enables better heat exchange across the cooling coil, better utilisation of the cooling


equipment and overall higher efficiency.


Hot aisles typically operate +38?C with high density servers. Consider the practicalities of maintaining the entire data hall at this temperature with cold aisle containment in order to return the same level of efficiency. And whilst it is true that cold aisle containment would enable higher temperatures overall (up to +39?C), it’s unlikely that the average data centre manager would consider this a sensible solution.


Another advantage of hot aisle containment is improved flexibility. HACS create a room neutral cooling zone and does not impact the temperature of the surrounding room. Since HACS do not deliver any hot air to the outside room, they eliminate the mix of hot and cold air that leads to inefficiency. Furthermore, as a row- based cooling approach, a HACS can be easily installed in an existing environment - there


The added bonus is higher availability. Since HACS only ‘contain’ hot air, the rest of the data hall provides a much larger reservoir of cool air which the servers can draw upon to extend runtime.


Conclusion Data centre professionals recognise that legacy solutions have limitations for cooling today’s high-density environments: They can be inefficient, costly and wasteful from a carbon footprint perspective. Row-based cooling and segregation of hot and cold streams can be used to improve upon this situation. Containment offers the benefit of cooling systems that can be set to a higher temperature (saving energy) while still supplying the load with safe operating temperatures and reduction of humidification/ dehumidification costs. In addition, better physical infrastructure utilisation enables right sizing to fit power consumption and cooling needs, it means equipment is running at higher efficiencies and it leads to better PUE.


Both hot aisle and cold aisle


containment offer considerable


advantages over legacy cooling systems in terms of system


is no


need for specialised


duct work and no adjustment required to the existing HVAC systems to manage elevated temperatures. There is, additionally, no requirement for a raised floor with HACS, making the solution suitable for a wide range of installations from small to mega data centres.


32 | DATA CENTRE SOLUTIONS | www.datacentresols.com


efficiency and ability to handle high density


equipment including blade servers. However,


HACS, with its row-based


cooling architecture is more efficient, more flexible, provide better ride through capability, and offer a way to better address the need to manage higher density requirements without making the entire data centre hotter than necessary.


Winter 2010


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