Data centre managers historically have had three main goals when designing and operating the data centre: resiliency, availability and security. However, in a world of ever increasing environmental concerns such as carbon footprints and with the rising cost of energy in UK, a third priority has emerged: the vast amount of energy required to power data centre.
There has been an extraordinary boom in data centre demand as the use of information and communication technologies (ICT) by commerce, industry and the wider population has grown. The demand is determined by global growth of the Internet, electronic transactions in financial servers, eCommerce, high performance scientific computing, and the shift to using electronic medical records for health care, etc. Server and chip vendors packing more computer power into smaller envelopes has caused sharp rises in data center energy densities. Ten years ago, most data centers ran 500 watts to 1 kilowatt (kW) per rack or cabinet. Today densities can get to 20 kW per rack and beyond, and most expect the number to continue to increase. Therefore, every IT manager with a high density data center are considering hot-aisle or cold-aisle containment strategies.
Data centers are burdened with power and cooling challenges. For every 50 kW of power the data center feeds to an aisle, the same facilities typically apply 100-150 kW of cooling to maintain desirable equipment inlet temperatures. Data centers waste more than 60 percent of that cooling energy in the form of bypass air. Consequently, new and growing challenges in the data centre industry concerns computer data centres and the different ways to reduce their energy demand. About half of the data centers have already installed some kind of containment system, and the rest are working out whether or not to pursue containment, figuring out whether to seal the hot or cold aisle, and weighing the other variables of this new data center cooling best practice.
Efforts trying to reduce the power consumption have been seen in data centre companies in recent years in order to improve their energy performance. In a recent data centre industry survey performed by Uptime Institute (2012), the most power saving strategies implemented by the data centre industry were in hot/cold aisle containment (78%) and airflow management of temperatures (75%). According to “Data Center Decisions 2009” around half data centre companies had already implemented these containments or planned to use. Hot/cold aisle is a layout design for server racks and other computing equipment in a data centre, which conserve energy and lower cooling costs by managing air flow. Data centers use a hot aisle/cold aisle arrangement of the IT racks. The fronts of the racks face each other and draw cold air into the rack to cool rack mounted IT devices (i.e. servers, switches, etc.). On the other hand, the rear sides of the rows of racks face one another, distributing the hot air into the hot aisle.
Why containments?
The issue with hot aisle/cold aisle designs is that the air is free to move wherever it will. These hot/cold aisle containment strategies has gained traction because it can better control where hot and cold air goes, then data center’s cooling system running more efficiently. Using containment, the data center makes ever more efficient use of the same or less cooling, cutting the cooling fraction of the total energy bill because of data centers can power down some CRAC units, saving utility and maintenance costs. Containment also allows for lower cooling unit fan speeds, higher chilled water temperatures, decommissioning of extra cooling units increasing the use of free cooling.
Moreover, these containments can reduce fan energy consumption by up to 25-percent and deliver 20-percent energy savings at the cold water chiller, according to the U.S. EPA. They make running racks at high densities more reasonable so that data centers can include new IT equipment such as blade servers. Data center containment brings the power consumption to cooling ratio down almost 1 to 1 match in kW consumed, hence, data centres saving about 30-percent of their annual utility bill (lower OpEx) without additional CapEx. However, there are numerous considerations, and a variety of questions that data center managers should taking into account when implementing this technology, for instance:
- Should you do hot-aisle containment or cold-aisle containment?
- Should you do it yourself or buy vendor products?
- How do you measure whether containment actually worked as hoped?
Hot vs Cold Aisle Containment
Next up for data center managers is deciding whether to implement the hot or the cold aisle. For example, American Power Conversion Corp. (APC) sells a pre-packaged hot -aisle containment product, while, Liebert Corp. sells cold-aisle containment. Not surprisingly, both APC and Liebert argue that their solution is best.
Containing the hot aisle means you can turn the rest of your data center into the cold aisle, as long as there is containment everywhere. The hot aisle is contained so that the precision air conditioning units only receive hot air from the aisles. Therefore, the data center contains the hot aisle to keep the hot air in that aisle and the cold air out. Contrary, containing the cold aisle means you may more easily use containment in certain sections of a data center rather than implementing containment everywhere. However, it needs finding a way to direct the hot air back to the computer room air conditioners (CRACs) or contending with a data center that is hotter than normal.
When comparing hot and cold aisle containment it can be seen that both offer accurately the same level of energy efficiency. The reason aisle containment improves the energy efficiency of data centres is because it increases the temperature of the air returning to the air conditioning units and thus increasing their efficiency. Hot aisle containment frequently reaches a higher level of operational energy efficiency because “most” of the space barring the contained aisle at the back of the server cabinets is kept at the supply air temperature, often around 25°C. This means the return air leaving the servers (within the hot aisle) will rise to 34°C +. With a cold aisle containment system “most” of the space barring the aisle at the front of the servers, would be kept at 34°C +, to gain maximum efficiency. Many data centre operators believe this is too hot for staff to work in, hence, they are not raising the temperature as high as they could. Therefore, it limits the efficiency gained from the containment system. However, cold-aisle advocates say that containing the cold aisle, the control of the flow and volume of cool air entering the front of the servers can be better than containing hot-aisle.
Both Hot Aisle Containment (HACS) and Cold Aisle Containment (CACS) offer superior power density compared with traditional cooling approaches. CACS can offer some improvements in a traditional room-based perimeter cooling layout. However, for most users the additional heating of the uncontained operators is an unacceptable condition which eliminates CACS as a considerable option. Consequently, most high efficiently and high density data centre projects, for new designs and retrofits, incorporate some forms of hot aisle containment the most suitable option.
References
Rath, J. 2011. Data center strategies: simplifying high-stakes, mission critical decisions in a complex industry. Data centre knowledge. Retrieved Aug 2, 2012 from WWW.VANTAGEDATACENTERS.COM/EARTHDAY/PDF/DCK-DATACENTER_STRATEGIES.PD
Stansberry, M & Kudritzki, J. (2012). Data center industry survey. UPTIME INSTITUTE. Retrieved May 15, 2013 from HTTP://UPTIMEINSTITUTE.COM/2012-SURVEY-RESULTS
Daim, T; Justice, J; Krampits, M; Letts, M; Subramanian, G & Thirumalai, M. (2009). Data center metrics: An energy efficiency model for information technology managers. Management of Environmental Quality: An International Journal. 20(6):712 – 731
Schmidt, J. 2008. Optimize data centre energy use: improving cooling processor and server efficiencies to reduce power consumption. Communication new, pp 10.
Normendau, R. (2012). Approaches to Data Center Containment. Retrieved May 14, 2013 from WWW.DATACENTERKNOWLEDGE.COM/ARCHIVES/2012/11/08/APPROACHES-TO-DATA-CENTER-CONTAINMENT/
Fontecchio, M. (2010). Data center hot-aisle/cold-aisle containment how-tos. Retrieved May 15, 2013 from HTTP://SEARCHDATACENTER.TECHTARGET.COM/NEWS/1379116/DATA-CENTER-HOT-AISLE-COLD-AISLE-CONTAINMENT-HOW-TOS
