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

The increasing demand for storage, networking and computation has driven intensification of large complex data centers that run many of today’s Internet, financial, commercial and business applications. Data a centers consume large amounts of electricity, they comprises of many thousands of servers and can use as much energy as small city. The demand for more information and superior analyses of data, along with a gradually rising need to store information, is causing the growth in the number and size of data centers. This growth in turn comes with an augment in the amount of energy consumed, including energy necessary to both power and cool the data centres computer equipment and facility system respectively.

The main problem in data centres is that a significant portion of the energy used is not going to the computers, but to power to the facility and cool the data centre. Data center energy usage can generally be divided into two mainly groups, IT systems (hardware and software) and the required supporting infrastructure (power and cooling systems) of the data center facility itself. Typical data centre energy consumption is attributed by 52% to equipment IT load such as processor, sever power supply , communication equipment and storage, and by 48% to facilities such as HVAC and lighting facilities, which in turn account for 54% of energy total consumption in buildings.
Direct electricity used by information technology (IT) equipment, cooling and power distribution in data centers represented about 1% of total world electricity consumption by 2005. In addition, this sector also is responsible for around 2% of global CO2 emissions approximately the same as the airline industry. Data centres are becoming “electricity guzzlers”, where the server farms alone contribute 200 million tons of CO2 of the total CO2 emissions globally. According to the Lawrence Berkley National Laboratory (LBNL), data centers rank among the most energy-intensive types of Facilities (HVAC and lighting), using as much as 100 times the energy per square foot of a typical building. From 2005 to 2010, server consumption across the world data centres required additional capacity equal to more than 10 additional 1,000 MW power plants. Based on current trends, energy consumed by data centers will continue to grow by 12% per year, due to the growing demand from new services and users, resulting in an increase in GHG emissions. Electricity consumption (as a whole) in Western Europe is estimated to increase from a level of 56 terawatt hours (TWh) per year in 2007 to 104 (TWh) per year by 2020, with data centre power consumption playing a major part in this increase.
Based on current and foreseeable trends, the basic price of energy will continue to rise over time, and may become constrained as global demands rise, making energy use and efficiency a long term business priority. Moreover, Carbon footprint and greenhouse gases are also becoming subject to governmental regulations and taxes. According to The Green Grid report, there are now 28 types of energy policies affecting data centers in 12 EMEA (Europe, Middle East and Africa) countries. Therefore, the rapidly increasing electricity demand for data center operation has motivated efforts to have a better understanding of current data center energy use as well as to identify strategies that reduce the environmental impact of these buildings.

In today’s world, it is almost impossible to discuss any business operation without considering efficiency. The goal for every data center owner or operator is to increase the energy efficiency without impacting on reliability. According to Uptime institute survey over 1,100 data centers around the world in 2012, data centre companies are looking for different energy efficiency strategies related with new cooling solutions that meet the demands of the hardware and the room, while optimizing energy efficiency. Environmental protection agency (EPA) has explored three energy-efficiency scenarios: improved operation, best practices and state-of-the-art, in order to develop a better understanding of energy efficiency, thus, illustrating a significant potential for efficient technologies and practices to improve the energy efficiency of IT equipment and site infrastructure. If state-of-the-art technologies were adopted in data centres, energy efficiency could be improved by as much as 55 % compared to current efficiency trends, representing the maximum technical potential.
Data centre companies are taken different steps in order to go green and to be a more sustainable sector. They notice greater opportunities in data centre cooling, power management and consolidation of servers, followed by facilities management and implementation of standards in order to reduce the energy consumption. Efforts trying to reduce the power consumption have been seen in data centre companies in recent years in order to improve their energy performance. For instance, some companies are implementing more efficient cooling systems and reducing the required power equipment by implementing virtualization and more green IT operations related with servers, memory and networks. In addition, they are implementing power saving strategies such as hot/cold aisle containment, free cooling techniques and CFD (computational fluids dynamics) models, airflow management of temperatures, air side economizer, more efficient processors including 45-nanometer silicon and quad-core processors, and chip cooling technology in order to reduce the energy requirements in data centres.
Consequently, it can be seen that making the operation of data centers “greener” has become the main focus of many research activities recently, looking for an appropriate and more efficient energy management in their operations. Efforts has been made by data centre companies in order to reduce the power in data centres and improve their energy performance, through the implementation of different innovations in the software and hardware, as well as newer installations for cooling data centres. However, data centers have been catalogued as a crucial environmental issue which deserves closer attention, hence, this data centre industry need to be studied in more detail and much deeper.