AIR-SITE GROUP White Paper Green Equipment Room Practices www.air-site.com
Common practices to build a green equipment room 1 Introduction Air-Site (www.air-site.com) is a leading international provider of products and solutions for GREEN technology and know-how in reducing power consumption and maximizing the investment benefits. As an example, data-centres can save one million kilowatt hours a year by implementing 11 best practices, according to analyst Gartner. Most of the principles for saving power are the same for computer halls, Telecom shelters, rail track providers equipment sheds and ISPs (Internet Service Providers) cabins, all here shortly called equipment rooms. Gartner says that in a conventional data centre, 35% to 50% of the electricity consumed is for cooling. The figure is 15% in best-practice "GREEN" data-centres. "Virtually all data-centres waste enormous amounts of electricity using inefficient cooling designs and systems," said Paul McGuckin, an analyst at Gartner. "Even in a small data centre, this wasted electricity amounts to more than one million kilowatt hours annually, that could be saved with the implementation of some best practices." The overriding reason for the waste in conventional data centre cooling is the unconstrained mixing of cold supply air with hot exhaust air, said Gartner. "This mixing (of hot and cold air) increases the load on the cooling system and energy used to provide the cooling and reduces the efficiency of the cooling system." said Paul McGuckin. The mixing may be caused by deficiencies in the room/rack structure such as holes in the walls and floors (caused by historical changes in the structure such as hinders for correct air flow) or simply by choice of poor performance cooling systems. 2 Best practices The first 11 practices below are recommended by Gartner, accompanied by the last 3 practices based on experience from efficient green equipment rooms at Mobile Telecom Operators. 1
2.1 Plug holes in the raised floor Most raised-floor environments have cable holes, conduit holes and other breaches that allow cold air to escape and mix with hot air. This single low-tech retrofit can save as much as 10% of the energy used for data centre cooling. 2.2 Install blanking panels Any unused position in a rack needs to be covered with a blanking panel to manage airflow in a rack by preventing the hot air entering the cold-air intake of other equipment in the same rack. When the panels are used effectively, supply air temperatures are lowered by as much as 5.6 C, greatly reducing the electricity consumed by fans in the IT and Telecom equipment, and alleviating hot spots in the data centre. 2.3 Co-ordinate CRAC units Older equipment rooms air-conditioning units (CRACs) operate independently in cooling and dehumidifying the air. These units should be tied together so efforts are co-ordinate. Alternatively, humidification responsibilities can be removed from them altogether and place with a newer piece of technology. Please consult with Air-Site how this can be achieved in a cost efficient way. Air-Site control systems for equipment room climate control. 2
2.4 Improve the under-floor airflow Older equipment rooms typically have constrained space underneath the raised floor that is not only used for the distribution of cold air, but also has served as a place for data cables and power cables. Many old equipment rooms have accumulated such a tangle of these cables that airflow is restricted, so the under-floor should be cleaned out to improve airflow. 2.5 Implement hot aisles and cold aisles In traditional equipment rooms, racks were set up in what is sometimes referred to as a "classroom style," where all the intakes face in a single direction. This arrangement causes the hot air exhausted from one row to mix with the cold air being drawn into the adjacent row, thereby increasing the cold-air-supply temperature in uneven and sometimes unpredictable ways. Please note that when the temperature cannot be predicted, the overall temperature has to be lowered to give the right temperature even in the blind spots. Newer rack layout practices instituted in the past 10 years demonstrate that organizing rows into hot aisles and cold aisles is better at controlling the flow of air in the equipment room. 2.6 Analyse the temperature A small number of sensors can be placed in areas where temperature problems are suspected. Sensors store temperature data that can be transferred into a spreadsheet, where it can be further analysed. This can provide insight into possible temperature problems, as well as a method for analysing the results of improvements made to the cooling. Using Air-Site SiteManager, you can connect many sensors, log the temperature values locally and upload them to your computer automatically or on-demand, locally or remotely via wireless Telecom lines, Internet or your intranet. SiteManager provides the means of analysing the temperature data with powerful built in tools and also export to a spreadsheet or database. 3
2.7 Implement cold-aisle or hot-aisle containment Once a data-centre has been organised around hot aisles and cold aisles, dramatically improved separation of cold air supply and hot exhaust air through containment becomes an option. For most users, hot-aisle containment or cold-aisle containment will have the single largest payback of any of these energy efficiency best practices. 2.8 Raise the temperature in the data centre Many data-centres are run colder than an efficient standard. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) has increased the top end of allowable supply-side air temperatures from 25 C to 26.7 C. Not all equipment rooms should be run at the top end of this temperature range, but a step-by-step increase, even to the 75 F (23.9 C) to 76 F (24.4 C) range, would have a beneficial effect on equipment rooms electrical use. 2.9 Install variable speed fans and pumps Traditional CRAC units contain fans that run at a single speed. Emerging best practice suggests variable speed fans be used whenever possible. A reduction of 10% in fan speed yields a reduction in the fan's electrical use of around 27%. A 20% speed reduction yields electrical savings of around 49%. 4
Air-Site offers a wide range of control systems that can not only connect the cooling equipment together, but also controls each unit at its optimal point. 2.10 Design equipment rooms using modular cooling Traditional raised-floor-perimeter air distribution systems have long been the method used to cool equipment rooms. However, mounting evidence strongly points to the use of modular cooling (in-row or in-rack) as more energy-efficient. 2.11 Exploit "free cooling" "Free cooling" is the general name given to any technique that cools air without the use of chillers or refrigeration units. The two most common forms of free cooling are air-side economisation (Called Free Air Cooling) and water/gas-side economisation. Free Air Cooling is by far more energy efficient as it is works directly to cool the room and not by transfer of the heat/cold to other media. How much the free air can be used to cool the equipment room is depends on two factors: A. The local climate and can be everything between 100 hours per year to complete year around. B. The particular free cooling system efficiency. 2.11.1 Free Cooling System Efficiency By standard, the difference in temperature between 1.5 m above the floor level in the equipment room, and the colder outdoors air is called Delta T. A Free Cooling system efficiency is defined by how low Delta T it can achieve. Lower Delta T maximizes the number of usable hours through the year to utilize the outdoor temperature to cool the indoor temperature. In many climate zones (such as in UK) an efficient free cooling system with the right heat load dimensioning will suffice round the year and an active cooling system is not needed in most cases if a sufficiently efficient Free Cooling system is implemented. In warmer climate zones though, a combination of Free Air Cooling and traditional air conditioners can be used but to maximize the benefit, the two systems must be controlled by a single source of control. 5
Some free air cooling systems use the forced ventilation principle, that is cool air is pumped directly into the equipment room through some kind of filtering mechanism. Forced Ventilation causes the hot and cool air to mix with each other, resulting in an average indoor air temperature. The air that leaves the room is therefore not the hot air but the mixed average temperature air, which would mean a high Delta-T by definition. A Delta T of up to 12 C is not unusual when forced ventilation is used. This would mean that only outdoor temperatures of up to 13 C can be used to achieve 25 C. For example in UK, that would mean only half of the year in hours. The keep 25 degrees in the room, air conditioners have to be utilized the rest of the year. A forced ventilation system has also some other drawbacks. To push out heat from the room, large fans are required at high speed. That could result in unwanted noise levels as well as more dust particles clogging up the filter in a short time period. The efficiency of the system will gradually decrease as the filter clogs up resulting in even higher Delta-T, and hence longer usage of air conditioners and higher power consumption. Research at Air-Site Group has shown that using air pressure instead of Forced Ventilation can provide much better results in terms of Delta-T. This technology called Pressure Cooling utilizes the outside air but to slightly higher pressure in the equipment room. As by the force of nature, heat always raises upwards from the equipment. Pressure Cooling systems works ALONG the natural law of Heat Dissipation and only increases the speed of this process, pressing the hot air up to the ceiling. Adding an exhaust air vent close to the ceiling of the equipment room, will vacate only the hottest air layer. By working alongside the natural process, the technology offers tremendous additional savings in power and achieves a Delta-T of down to 1 C, that is, almost same temperatures as outside can be achieved with this technology. For a set point of 25 C, outdoor temperatures of up to 24 C can be utilized for efficient cooling indoors. For a moderate climate zone, that would be almost all around the year. Beside the uniquely low Delta T, pressure cooling obviously requires considerably less air enabling smaller fan motors which offer: - Lower power consumption. - Lower noise levels. - Less dust in the filters and thus longer time between service Air-Site filters (type F6) comprise of long (1.6 m) bag shaped socks and have in practice shown to be capable of keeping harmful particles from reaching the equipment. The mean time between is up to 5 years requiring minimum system maintenance. Air-Site's wide range of control systems allows use of a combination of free air cooling and up to two sets of air conditioning systems to work together, one as main and the second as backup. Also, many different control scenarios such as emergency cooling, fire, power outage etc is predicted and processed. 6
Please consult with Air-Site about use of free cooling and related control and communication systems. 2.12 Explore racks with top mounted hot air outlet Racks, utilizing the new cooling techniques, force the hot air towards the ceiling. This, in combination with a free air cooling system that builds up a higher pressure in the room than outside, force the hot air out from an air outlet (close to the ceiling of the equipment room) at the same time that the cool air is pressed from below lifting the hot air even more. 2.13 Use automatic control to turn off equipment when not used Equipment rooms are used for different purposes but not all equipment is used all the time. For example, backup servers can be switched off when the backup is finished. At low traffic hours, redundant equipment can be put in to rest etc. Many new servers have this functionality as a built in property that needs to be set up. For others, an automatic switching on and off, may result in longer MTBF (Mean Time between Failures) and power savings, depending on the specifications. 2.14 Consider the service frequency when designing an equipment room. Some operators have a long distance between their equipment rooms making the travel more costly than performing the actual service. Using equipment that have long MTBF (Mean Time Between Failure) is not only essential for keeping a high service level, but is also essential for saving the cost of travel. An air conditioner is traditionally a service requiring equipment. Following simple practices could help extending the life time of the air conditioners: A. Minimize the number of hours air conditioners are on by using a free air cooling system. B. If there is a backup air conditioners, switch between the main and secondary air conditioners, keeping in mind how much time each system has been used. As an example, assume that a Free Air Cooling system can be used instead of the air conditioners ¾ of the year. That would prolong the life of the air conditioners with four times. If the work is then shared between the primary and secondary air conditioner system, the service period will be extended by 8 times. Using free air cooling has a number of other benefits when controlled in an intelligent way. In case of a power failure, a free air cooling system will consume considerably less power than air conditioners. That will load the backup batteries less and gives the equipment room a longer emergency life. Also in case of air conditioner failure, the equipment room can continue its function using the free air cooling system but a temporary higher temperature until the air conditioner system is functioning again. 7
Frequent exchange/cleaning filters for free air cooling systems may be a time demanding and costly factor which has to be calculated in the design of the equipment rooms. The longer between the filter change/cleaning, the less cost and better performance (lower Delta T.) 3 Conclusion Although most users will not be able to immediately implement all 14 best practices, all users will find at least three or four that can be immediately implemented in their current equipment rooms. Savings in electrical costs of 10 to 30% are achievable through these most available techniques. Users committed to aggressively implementing all 14 best practices can save up to 70% of the cooling cost. 8